Car Audio Explained, Part 13: Wiring and Integrating with Factory Systems (Andy Wehmeyer's Lessons)

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This is Part 13 of 19 in the series Andy Wehmeyer on Car Audio, Explained for Beginners. Start here · Download the full guide as a PDF

Unofficial guide. Andy Wehmeyer's points are paraphrased from his public forum posts, blog, tuning guides, videos and podcasts, with a link to each source; the plain-English explanations were written for this guide. Not written, reviewed or endorsed by Andy Wehmeyer or Audiofrog.

4.11 Wiring, fusing, grounding, batteries, caps and the Big 3

What this part is about: How to get power to an amplifier safely and well: where to connect the ground, how to test it, how to join wires, how to fuse, and whether you need thick cable, extra capacitors or electrical upgrades. His general view is that much of the common advice here is overkill.

4.11 #1 · Ground the amp to body sheet metal near it, not the frame; the ground wire can be thinner than the power wire.

The body has more cross-section than any cable and both battery and alternator bond to it; a frame on rubber bushings reduces to its bolts. Scrape paint, use a star washer; doubled 0-gauge battery grounds are pointless, and a shorter ground run allows a smaller gauge. [RARE] Sources: DIYMA 2008-10-17 · DIYMA 2011-08-15 · DIYMA 2021-10-04

In plain English: An amplifier needs two power connections: a positive wire from the battery, and a ground (negative) wire. In a car, the metal body itself carries current back to the battery. His point is that the body's sheet metal has more metal for current to flow through than any cable, and both the battery and the alternator (the engine-driven generator) are connected to it. A frame (the separate steel chassis under some vehicles, such as many trucks), by contrast, sits on rubber bushings, so it connects to the rest of the car only through its bolts. So ground the amp to body metal close to it. Scrape off the paint so bare metal touches, and use a star washer (a toothed washer that bites into the metal). "Gauge" is wire thickness; smaller numbers mean thicker wire, and 0-gauge is very thick. He says doubling up 0-gauge ground cables at the battery is pointless, and because the ground run is usually much shorter than the power run, it can use thinner wire. Many people believe the ground wire must always be at least as thick as the power wire.

4.11 #2 · Check grounds by voltage drop, not resistance.

A DMM can't read resistance in a circuit with current flowing; with the battery connected, measure the voltage drop across the joint. Sources: DIYMA 2021-07-27

In plain English: A DMM (digital multimeter) measures resistance by pushing its own small current through the part it is testing. He explains that it can't do that while the car's own current is already flowing through the circuit. So instead, leave the battery connected, set the meter to volts, and measure the voltage across the joint (one probe on each side of the connection). Any voltage lost across a joint is the sign of resistance there.

4.11 #3 · Crimp, don't solder or tin, wire-to-terminal connections, including the Big 3.

Solder near the battery invites corrosion; screw terminals should clamp bare strands; solder wicks up and stiffens speaker tinsel leads, and a hot iron can melt the plastic terminal boards in Audiofrog GS baskets. Crimp skeptics, he says, "crimp with pliers". [RARE] Sources: DIYMA 2021-07-21 · DIYMA 2021-11-26 · DIYMA 2018-06-24

In plain English: Crimping means squeezing a metal terminal tightly onto a wire with a proper tool. Soldering joins metal with melted alloy, and "tinning" means coating bare wire strands with solder. He prefers crimping, for several reasons. Solder near the battery invites corrosion. A screw terminal should clamp bare strands, so the screw compresses them and increases the contact area. On speakers, solder can creep up the thin, flexible "tinsel" leads (the braided wires that carry the signal to the moving coil) and stiffen them. And on Audiofrog GS speakers, whose baskets (frames) have plastic terminal boards, a hot iron can melt the plastic. The "Big 3" is a common upgrade of the three main charging cables. His jab at people who distrust crimps is that they "crimp with pliers", meaning with the wrong tool. Many people believe solder always makes the best connection.

4.11 #4 · A second battery: ground it to the body, wire it in parallel, and skip the solenoid isolator.

In a truck that killed six MS-8s, the solenoid dropped and reconnected the battery while cranking, and its un-diode'd coil spiked the remote line. Chain turn-on as radio REM → DSP REM-in, DSP REM-out → amps (under 1 A), so amps start after the DSP. [RARE] Sources: DIYMA 2012-01-13 · DIYMA 2012-01-14

In plain English: Some people add a second battery for a big system. His advice: ground it to the body, connect it in parallel with the first battery (positive to positive, negative to negative), and don't use a solenoid isolator, which is a heavy electrical switch that connects and disconnects the second battery. His reason is a real case: a truck killed six MS-8 processors (JBL's MS-8 was a car-audio DSP, a digital sound processor). While the engine was cranking, the solenoid dropped the battery and reconnected it. Its coil had no diode, the small part that normally absorbs the voltage spike a switching coil makes, so the spike went into the "remote" wire, the thin wire that tells audio equipment to switch on. He also gives a turn-on order: radio's remote output to the DSP's remote input, then the DSP's remote output to the amps (keeping the current drawn from that DSP output under 1 amp). That way the amps switch on after the DSP.

4.11 #5 · The amp fuse protects the car, not the amp, and every extra fuse or block is a resistor.

Fit it within 18" (45 cm) of the battery (60 A for the A-series). Customers' added fuses ahead of JBL's A6000GTi dropped enough voltage on ~800 A bass peaks to trip its protection; if the whole car dims and dies, look at the alternator–battery circuit. [RARE] Sources: DIYMA 2013-03-26 · DIYMA 2012-09-12 · A-Series manual

In plain English: A fuse is a deliberate weak link that melts if too much current flows. His point is that the main amp fuse is there to protect the car, not the amp. In the forum post behind this point, he explains that the amp's own output parts fail individually at much lower current than the fuse allows, so the fuse can't save them; what it does is stop one failure from cascading and starting a fire. Fit it within 18 inches (45 cm) of the battery; Audiofrog's A-series amps call for a 60 A fuse. He also warns that every extra fuse or distribution block acts like a resistor and loses some voltage. His example: customers added extra fuses in front of JBL's large A6000GTi amp. On bass peaks of about 800 amps, those fuses lost enough voltage to trip the amp's protection, so it shut down. And if the whole car's lights dim and the car dies, he says the problem is in the alternator–battery circuit, not in the amp.

4.11 #6 · Wire-gauge and charging "requirements" assume sine waves at fuse rating; music draws far less.

Music averages ~1/32 of peak; IASCA judges once docked him for wire that "couldn't work" while hearing it work, and a GB active system in a 2021 Sierra didn't need 0-gauge. Audiofrog lists current draw (0.9 A idle, 60 A max) but no gauge. [RARE] Sources: DIYMA 2012-10-21 · DIYMA 2021-12-22

In plain English: Charts tell you how thick a power cable and how big a charging system you "need" for a given amp. He says those charts assume the amp plays a steady test tone (a sine wave) at the full current its fuse allows. Real music is mostly quiet with short peaks; its average power is only about 1/32 of its peak. So real systems draw far less. Two examples: at an IASCA contest (a sound-quality competition), judges took points off because they said his power wire "couldn't work", while they were listening to it work. And a GB (Audiofrog) active system in a 2021 GMC Sierra truck didn't need 0-gauge (very thick) cable. Audiofrog lists its amps' current draw (0.9 A at idle, 60 A maximum) but not a wire gauge. Many people believe you must size wire straight from the amp's fuse rating.

4.11 #7 · Stiffening caps and electrical upgrades are usually unnecessary.

A 2-farad cap isn't needed at 1,000 W (one kept a member's battery from charging), and he told another member to skip an electrical upgrade. Alternator and battery rules aren't absolute: a Harman trainer's "two 2,500 W amps will shut the car down" demo met an attendee running two on a 40 A alternator. He gives no further view on the Big 3 beyond "crimp it"; silver wire isn't worth trying. [RARE] Sources: DIYMA 2021-08-02 · DIYMA 2011-11-25 · DIYMA 2021-01-13

In plain English: A "stiffening cap" is a large capacitor fitted near the amp to supply quick bursts of current. He says these, and electrical upgrades in general, are usually not needed. A 2-farad cap isn't needed for a 1,000-watt system, and one actually stopped a forum member's battery from charging. He told another member to skip an electrical upgrade. He adds that alternator and battery rules aren't absolute: a Harman trainer told a class that two 2,500-watt amps would shut a car down, and one attendee was running two of them on a 40-amp alternator. On the Big 3 upgrade, the only view he gives is "crimp it". Silver wire, he says, isn't worth trying. Many people believe every big system needs a capacitor and a charging upgrade.

4.11 #8 · Terminations and passive-network safety.

Crimp ferrules with the proper tool (the terminal screw is not a crimper). Never drive a 2nd-order or steeper passive network without its tweeter connected: with the tweeter open, the shunt coil becomes a near-dead short at the network's resonance. Sources: Audiofrog blog Dec 2020 · DIYMA 2018-01-13

In plain English: A ferrule is a small metal sleeve crimped onto the end of a stranded wire before it goes into a screw terminal. He says to crimp it with the proper tool; tightening the terminal screw does not crimp it. The second warning is about passive crossovers, the networks of coils and capacitors that split the sound between woofer and tweeter. A "2nd-order" network cuts 12 dB per octave, and its tweeter section includes a coil wired across the tweeter (the "shunt coil"). If the tweeter is disconnected or blown, the amp sees that coil instead. At the network's resonant frequency, it then behaves almost like a dead short (a path with almost no resistance). So in practice: never play a 2nd-order or steeper passive network without its tweeter connected.

4.12 Inside factory systems: what factory amps and DSPs actually do

What this part is about: What the factory ("OEM" or "OE", meaning original equipment) audio system in a modern car is really doing behind the scenes. His view is that factory amplifiers and radios do a lot of careful sound processing, and you need to understand it before you replace or bypass anything.

4.12 #1 · A premium factory amp is a powerful DSP tuned by acousticians; swapping it for a big amp with no EQ is a downgrade.

For about ten years he used Harman OE amps as the DSPs in R&D cars, and his 2012 car ran OE Hyundai amps for EQ, crossover, delay and limiting. Bose, Panasonic and Harman engineers (many with PhDs) design these systems; calling them junk for lacking bass, then rearranging the car to install "the thing we've always installed", is "a big mistake". [RARE] Sources: DIYMA 2008-07-09 · DIYMA 2012-04-13 · CMA Connected Oct 2021 @37:25

In plain English: A "premium" factory system is the upgraded, often brand-name sound system (Bose, Harman Kardon and so on). Its amplifier is not just an amplifier: it contains a DSP (digital sound processor) that adjusts the sound, tuned by acousticians (sound engineers). His evidence: for about ten years he used Harman factory amps as the processors in research cars, and the car he ran in 2012 used factory Hyundai amps to do its EQ (tone shaping), crossovers (splitting sound between speakers), delay and limiting. He says engineers at Bose, Panasonic and Harman, many with PhDs, design these systems. Calling them junk because they lack bass, then tearing up the car to install "the thing we've always installed", is in his words "a big mistake". So replacing that amp with a big amp that has no EQ is a step down. Many people believe factory amps are weak junk to rip out first.

4.12 #2 · Almost every factory system with an outboard amp applies EQ, crossovers and delay; head units now add all-pass filters and limiting too.

OEMs often delay the rears for ambience and decorrelation; head units add all-pass filters for the other seat, EQ, and compression to protect small speakers from bass. Identify what's there before assigning a cause. [RARE] Sources: DIYMA 2013-12-17 · DIYMA 2021-02-03

In plain English: An "outboard" amp is a separate amplifier box rather than one built into the radio. He says almost every factory system with one applies EQ (tone shaping), crossovers (splitting frequencies between speakers) and delay (holding some speakers back by a few thousandths of a second). Carmakers often delay the rear speakers to create ambience and decorrelation, which means making the rear sound less identical to the front. Newer radios also add all-pass filters, which shift the timing of sound around a chosen frequency without changing its loudness; these are there for the other front seat. They also add EQ and compression (automatically turning down loud parts) to keep bass from damaging small speakers. So in practice: if something sounds odd, first find out what processing is already there before deciding what caused it.

4.12 #3 · Basic systems process in the head unit's audio-controller chip.

Programmable bass and treble, often a simple 3-band parametric, usually stereo-linked (one set front, one rear). Radios lack real EQ because nobody writes it into the spec: 31 bands instead of 5 is "a few lines of copy/paste" plus UI work. Sources: DIYMA 2013-03-17 · DIYMA 2016-06-03

In plain English: In basic factory systems with no separate amp, the sound adjustments happen inside one chip in the head unit (the radio), the audio-controller chip. He lists what it usually offers: programmable bass and treble, and often a simple 3-band parametric EQ (an equalizer whose bands can be moved to chosen frequencies). It is usually stereo-linked: left and right share settings, with one set for the front and one for the rear. Why don't radios have a proper equalizer? He says it is because nobody writes one into the product specification. Going from 5 bands to 31 is "a few lines of copy/paste" in the code, plus work on the on-screen controls.

4.12 #4 · Most factory EQ corrects the cabin, not cheap speakers.

He estimates only 10–20% compensates for the drivers. Interior designers "own" the cabin, so OEM placement problems get solved with EQ and all-pass filters. [RARE] Sources: CMA 2023 @11:00 · DIYMA 2013-03-16

In plain English: When a factory system applies EQ (boosting or cutting certain frequencies), what is it fixing? Many people believe it mainly covers up cheap speakers. He says most of it corrects the cabin, meaning the car's interior with its glass, seats and odd speaker locations. He estimates only 10–20% of it makes up for the drivers (speakers). His reason: interior designers "own" the cabin and decide where everything goes. So when speakers end up in awkward places, the audio engineers solve that with EQ and all-pass filters (filters that shift the timing of sound without changing its loudness) rather than by moving the speakers.

4.12 #5 · Volume, tone, fader, chimes, Bluetooth and nav prompts often live in the factory amp, not the radio.

Many OE head units send fixed-level audio (OEM JBL Synthesis: under 1 V), with volume and tone applied in the amp on CAN, J1850 or proprietary commands. Some cars also cut volume ~6 dB when they think a door is open, and a miswired door switch can trigger that with the door shut. Sources: DIYMA 2015-05-11 · DIYMA 2013-01-15 · DIYMA 2022-01-30

In plain English: In many cars, the radio is not where volume and tone are controlled. He says many factory head units send audio at a fixed level, whatever the volume knob says; the OEM JBL Synthesis system's output, for example, is under 1 volt. The radio then sends commands to the amplifier over the car's data network (CAN, J1850 or a maker's own system), and the amp applies volume, bass, treble and fader. Warning chimes, Bluetooth phone audio and navigation prompts can also live in the amp. He adds that some cars turn the radio down about 6 dB (a clearly noticeable drop) when they think a door is open, and a wrongly wired door switch can cause that even with the door shut. So in practice: the factory amp may be doing jobs you can't see.

4.12 #6 · Some factory amps shut down with no speaker load, and factory noise cancellation can look like a fault.

No-load protection guards the output filter if a speaker opens (JBL's MS-A5001 "High 2" input adds a thermistor load), so check an OE amp's output with and without a load. Bass that briefly "overwhelms" an integrated system can be the factory ANC at work. [RARE] Sources: DIYMA 2015-04-03 · DIYMA 2015-09-19

In plain English: Two factory behaviors that can fool you into thinking something is broken. First, some factory amps switch off if no speaker is connected. That "no-load protection" guards the amp's output filter if a speaker wire breaks or a speaker dies. JBL's MS-A5001 amplifier has a "High 2" input setting that adds a thermistor (a resistor whose value changes with heat) as a load for exactly this reason. So in practice: test a factory amp's output both with and without a load before deciding it is faulty. Second, if bass seems to briefly "overwhelm" a system tied into the factory audio, he says it can be the factory ANC (active noise cancellation, which plays sound through the speakers to cancel engine and road drone) at work.

4.12 #7 · Step-up factory systems aim for every seat to sound similar, and their drivers are often good.

On average aftermarket systems sound worse than step-up OE (his rental cars vs shop demo cars); factory Harman drivers (e.g. BMW) beat many aftermarket speakers, and owners' complaints are about tuning, bass and Logic 7. Aftermarket listeners judge only bass and loudness and miss the envelopment and two-seat imaging. [RARE] Sources: DIYMA 2008-12-21 · DIYMA 2022-01-10 · Absolute Electronix 2023 @56:27

In plain English: A "step-up" factory system is the optional upgraded audio package. He says these aim to make every seat sound similar, and their speakers are often good. Comparing rental cars he has driven with shop demo cars, he finds that on average aftermarket systems (installed after purchase) sound worse than step-up factory ones. Factory Harman speakers, for example in BMWs, beat many aftermarket speakers; owners' complaints are about the tuning, the bass and Logic 7 (Harman's surround processing). His point is that aftermarket listeners judge only bass and loudness. They miss two things factory systems do well: envelopment (the feeling of being surrounded by sound) and imaging that works from both front seats. Many people believe any aftermarket system beats a factory one.

4.12 #8 · Where factory systems are weak.

He never heard a Harman OE center that didn't "suck"; HK/Mercedes 3" metal cones lose dust caps (fix with thick super glue; dealer parts ~$180); old Bose ran 4" drivers at ½ Ω with no tweeters; factory Logic 7 lacks power and bass. Factory high-level outputs clip near maximum volume. Sources: DIYMA 2016-01-18 · DIYMA 2015-07-30 · DIYMA 2018-05-22

In plain English: His list of weak spots. He never heard a center channel (a speaker in the middle of the dash) in a Harman factory system that didn't "suck". In Harman Kardon systems in Mercedes cars, the 3-inch (about 75 mm) metal-cone speakers lose their dust caps (the small dome in the middle of the cone); he says thick super glue fixes them, while dealer parts cost about $180. Old Bose systems ran 4-inch (about 100 mm) speakers at ½ ohm (a very low electrical load) with no tweeters (small treble speakers). Factory Logic 7 systems lack power and bass. And factory high-level outputs (the speaker-wire signals) clip, which means they distort because they run out of voltage, near maximum volume.

4.12 #9 · Factory dash "middlers" aimed at the windshield work for two reasons.

The narrowing HF beam reflects off the glass to everyone (a "poor man's tweeter"), and boundary gain (+6 dB per halving of space) lets a 2.5" dash speaker play to 200–250 Hz on the 15–20 W an OEM amp gives it. [RARE] Sources: CMA Connected Oct 2021 @32:43 · CMA Connected Oct 2021 @34:22

In plain English: "Middlers" are small midrange speakers in the top of the dashboard, often pointed up at the windshield. Many people assume that's just a cheap compromise. He says it works for two reasons. First, as the pitch rises, a speaker's sound narrows into a beam; that beam bounces off the glass and reaches everyone, which he calls a "poor man's tweeter". Second, boundary gain: a speaker tucked against surfaces gets louder, +6 dB each time the space it plays into is halved. That lets a 2.5-inch (65 mm) dash speaker play down to 200–250 Hz on just the 15–20 watts a factory amp gives it. Hz (hertz) measures pitch: the lower the number, the deeper the sound.

4.13 Getting the factory signal: where to tap and what to measure first

What this part is about: If you keep the factory radio and add your own amps or processor, you must take ("tap") the sound signal from somewhere in the factory system. This part covers what kind of signal you'll find, where to tap it, and how to measure it first without damaging anything.

4.13 #1 · First learn what kind of output you have: its voltage, and whether it is single-ended or floating (balanced, BTL).

Speaker outputs are almost always ~8 V and look identical; "low level through a LOC is a terrible waste of output", and BMW "voltage problems" are usually an installer's LOC or a removed amp. Voltmeter test: each lead ~6 V DC to chassis means balanced; into a balanced input, + to hot, − to cold, ground left open. [RARE] Sources: DIYMA 2009-08-24 · DIYMA 2009-01-21

In plain English: Before connecting anything, find out what kind of output the factory system gives you. A "single-ended" output has one signal wire measured against ground (the car's metal), like an RCA plug. A "floating" output, also called balanced or BTL (bridge-tied load), uses two wires carrying opposite copies of the signal, and neither is tied to ground. He says factory speaker outputs are almost always about 8 volts, and you can't tell what kind you have just by looking at the wires. A LOC (line output converter) turns that speaker signal down to the low RCA level, and he calls doing so "a terrible waste of output". He adds that BMW "voltage problems" are usually caused by an installer's LOC or a factory amp that was removed. His test: with a voltmeter on DC volts, measure each speaker lead to the chassis (car body). About 6 V DC on each means the output is balanced. To connect it to a balanced input: + to hot, − to cold, and leave ground unconnected.

4.13 #2 · Balanced speaker-level signals beat RCA pre-outs.

They sit ~6 V off ground, are higher in voltage and lower in impedance, and reject noise just by twisting the pair; many factory systems already use them ("silly" that aftermarket radios don't). The catch is a head unit that clips at the top of its volume range; Helix high-level inputs take 7.1 V RMS. [RARE] Sources: DIYMA 2013-01-15 · DIYMA 2021-09-25 · DIYMA 2022-02-27

In plain English: "Pre-outs" are the low-voltage RCA outputs on an aftermarket radio, meant for feeding an amp. Many people believe these are always cleaner than speaker-level signals. He says balanced speaker-level signals (two wires carrying opposite copies of the signal) are better. They sit about 6 volts away from ground, carry a higher voltage, and have a lower impedance (roughly, they are "stiffer" and harder for noise to disturb). Simply twisting the two wires together makes them reject noise. (That works because noise picked up lands on both wires equally, and a balanced input cancels whatever the two wires share.) Many factory systems already use them, and he calls it "silly" that aftermarket radios don't. The catch: some head units clip (distort) at the top of their volume range. Helix processors' high-level inputs take 7.1 volts RMS (a kind of average voltage).

4.13 #3 · Where to tap: after the factory amp to keep chimes and controls; before it only when its processing can't be undone.

MS-8 recipe: keep the factory amp, feed its outputs to speaker-level inputs, radio REM → DSP REM-in, DSP REM-out → factory amp. Toyota JBL Synthesis's fixed-level balanced head-unit output lets you drop the factory amp if the DSP has volume control. [Conflict: a secondhand ClubLexus report says he found MS-8 worked in a Lexus GS only when tapped before the amp.] Sources: DIYMA 2012-12-25 · DIYMA 2016-03-14 · ClubLexus (secondhand)

In plain English: Where should your new processor get its signal? He says take it after the factory amp, so you keep the chimes and controls the amp handles. Take it before the amp only when the amp's processing can't be undone. His recipe for the MS-8 (a JBL processor) is to keep the factory amp and feed its outputs into the MS-8's speaker-level inputs. For switching on, the radio's remote (turn-on) output goes to the DSP's remote input, and the DSP's remote output goes to the factory amp. One exception: Toyota's JBL Synthesis head unit puts out a fixed-level balanced signal, so you can remove the factory amp if your DSP has its own volume control. The [Conflict] tag: a secondhand report on the ClubLexus forum, written by someone else, says he found the MS-8 worked in a Lexus GS only when connected before the factory amp. So his general recipe and that car-specific report point different ways.

4.13 #4 · Bypassing the factory amp so it won't "touch" the music is an arbitrary goal with costs.

A box can't tell music voltage from phone voltage. With a fixed-level radio you lose volume control (add a DSP with volume or a pot) and possibly chimes, Bluetooth and nav prompts. Sources: DIYMA 2013-04-23 · DIYMA 2012-09-11

In plain English: Some installers want to bypass the factory amp so that it won't "touch" their music. He calls that an arbitrary goal, and one with costs. His point is that a box can't tell music voltage from phone voltage; to the electronics, a signal is just a voltage. If the radio sends a fixed-level signal (the same level whatever the volume knob says), bypassing the amp loses your volume control. You would then need a DSP with its own volume control, or a pot (a volume knob). You may also lose warning chimes, Bluetooth phone audio and navigation prompts, since those can live in the factory amp.

4.13 #5 · Adding a sub: tap the factory amp's sub channel so the sub tracks the volume knob.

Use an amp with speaker-level differential inputs or a passive LOC; a powered LOC with its own level control means re-balancing the sub at every volume change. Sources: DIYMA 2009-07-06

In plain English: To add a subwoofer (a big speaker for deep bass) to a factory system, he says to take the signal from the factory amp's own sub channel. That way the new sub gets louder and quieter with the volume knob, in step with the rest of the system. Connect it with an amp that has speaker-level differential inputs, or with a passive LOC (a line output converter with no power supply of its own). He warns that a powered LOC with its own level control means re-balancing the sub against the other speakers every time you change the volume.

4.13 #6 · Measure every factory output first for response, delay and polarity; a rough measurement beats none.

Response: test tones on CD, a multimeter and his Excel sheet, or a sound card and REW. Delay: an impulse via Aux, or a CD with a pulse every ~15 s and a 2-channel scope program. Polarity: an Audacity DC-offset track and a voltmeter; compare each output with unaltered pink noise, not channel with channel. [RARE] Sources: DIYMA 2016-02-08 · DIYMA 2015-06-30 · DIYMA 2021-05-20

In plain English: Before tuning, he says to measure every factory output for three things. Frequency response is how loud each pitch comes out. Delay is whether some outputs are held back in time. Polarity is whether the signal pushes the speaker out or pulls it in. Even a rough measurement beats none. For response, play test tones from a CD and read the voltage with a multimeter into his Excel sheet, or use a computer sound card and REW (Room EQ Wizard, free measuring software). For delay, play an impulse (a sharp click) through the Aux input, or a CD with a pulse every ~15 seconds, and view it with a 2-channel oscilloscope program. For polarity, make a DC-offset track (a steady one-direction push) in Audacity (a free audio editor) and check the voltage's sign with a voltmeter. Compare each output with the original, unaltered pink noise (a test hiss containing all pitches). Comparing one channel with the other, he says, can't show which one carries the filter.

4.13 #7 · Never connect both radio channels to one computer input.

Headset-adapter leads tie one side of each speaker output to computer ground, so joining both channels ties their negatives and can trip the radio's output protection. Measure one channel at a time, put a LOC in front, or use a USB interface with balanced XLR inputs (hot and cold, ground open) plus an attenuator. [RARE] Sources: DIYMA 2021-11-01 · DIYMA 2021-11-01

In plain English: A common cheap way to measure a radio's output is a headset adapter that plugs into a computer. He warns that these adapters connect one side of each speaker output to the computer's ground. If you connect both the left and right radio channels this way, their negative wires get joined, and that can trip the radio's output protection so it shuts off. His safe options: measure one channel at a time; put a LOC (line output converter) in front of the adapter; or use a USB audio interface with balanced XLR inputs (a three-pin professional connector). Wire your test leads to its "hot" and "cold" pins, leave ground unconnected, and add an attenuator, a part that lowers the voltage so the interface isn't overloaded.

4.13 #8 · Audiofrog amps take factory outputs directly (product-specific).

Speaker-level inputs to 30 V peak at 1.2 kΩ; line level 0.5–10 V peak; turn-on by signal sense, 6 V BTL offset detection or remote wire. The A600.1D sums its two inputs, and the A150.4D's 3-channel mode feeds outputs 3–4 the sum of inputs 1–2. Sources: Audiofrog amplifiers · A-Series manual

In plain English: This point is specific to Audiofrog's own amplifiers (the company he co-founded). They can take factory outputs directly. Their speaker-level inputs accept up to 30 volts peak and present 1.2 kΩ (1,200 ohms, a light load) to the factory system. Their line-level (RCA) inputs accept 0.5 to 10 volts peak. They can switch on three ways: by sensing a signal, by detecting the 6-volt DC offset that a balanced (BTL) factory output sits at, or by a remote (turn-on) wire. The A600.1D, a one-channel amp, combines ("sums") its two inputs. In 3-channel mode, the A150.4D feeds outputs 3–4 the combined signal of inputs 1–2.

4.14 Factory all-pass filters, summing, de-EQ and factory delay

What this part is about: Factory systems often contain hidden timing tricks: all-pass filters and delays. This part explains what they are, how to detect them, what happens when you try to undo them or combine ("sum") factory channels, and how his own approach to this changed over the years.

4.14 #1 · Factory all-pass filters let both front seats image, because delay works for only one seat.

A 1st-order all-pass is 90° at its frequency (0° above, 180° below); a 2nd-order is 180° (≈360° below). Typical layouts: one channel polarity-reversed plus a 1st-order all-pass restoring bass phase, centering vocals around 250 Hz; or two 1st-order all-passes near 250 and 500 Hz; Bose often stacks several on fronts and rears. [RARE] Sources: DIYMA 2021-05-13 · DIYMA 2021-05-16 · DIYMA 2021-05-19

In plain English: In a car you sit closer to one side's speakers, so their sound arrives first and pulls the stereo "image" (where the singer seems to stand) toward that side. Aftermarket tuners fix this with delay, holding back the nearer speakers a few thousandths of a second. He points out that delay works for only one seat. Factory systems instead use all-pass filters so both front seats get a usable image. An all-pass filter leaves loudness alone and changes only phase, the timing of a wave measured in degrees (360° is one full cycle). A 1st-order all-pass shifts phase by 90° at its chosen frequency, about 0° well above it and 180° well below. A 2nd-order one shifts 180° at its frequency (about 360° below). The typical factory layouts he describes: one channel's polarity reversed, plus a 1st-order all-pass that brings the bass back in step, centering vocals around 250 Hz; or two 1st-order all-passes near 250 and 500 Hz. Bose often stacks several on front and rear speakers. Many people believe delay is the only way to fix imaging in a car.

4.14 #2 · Two tests to tell factory all-pass filters from factory delay.

By ear: with all-pass filters a centered vocal is centered (not pinpoint) from the driver's seat and both sides are audible from the passenger seat; with delay, everything collapses into the passenger door. On an analyzer: mono pink noise, view L+R; one big dip at 200–500 Hz means all-pass, a dip followed by evenly spaced dips (a comb) means delay. [RARE] Sources: DIYMA 2021-10-26

In plain English: How can you tell which trick a factory system uses? His listening test: play a song with a centered vocal. With all-pass filters, from the driver's seat the vocal sounds centered, though not pinpoint sharp, and from the passenger seat you can still hear both sides. With delay, from the passenger seat everything collapses into the passenger door. His analyzer test: play mono pink noise (a test hiss with the same signal in both channels) and view the left-plus-right sum on an analyzer, a screen that shows loudness at each pitch. One big dip between 200 and 500 Hz means all-pass filters. A dip followed by evenly spaced dips, a pattern called a "comb", means delay. (A comb appears when a sound is mixed with a time-shifted copy of itself.)

4.14 #3 · "Reversed" OEM polarity is usually deliberate, so test empirically.

Factory harnesses built thousands of times can't be miswired; if it sounds better as connected, it was designed around the phase EQ. [Conflict: 2015, a 1st-order all-pass flips polarity below its corner; 2021, pulse checkers read all-passes like crossovers, so they don't show a reversal.] [RARE] Sources: DIYMA 2021-05-20 · DIYMA 2015-12-07 · DIYMA 2021-05-16

In plain English: Polarity is whether a speaker pushes out or pulls in for the same signal. When people find a factory speaker that seems wired "backwards", they often assume it's a mistake. He says it's usually deliberate: factory wiring harnesses are built thousands of times and can't be miswired. If it sounds better as connected, it was designed to work with the factory's phase EQ (its all-pass filters). So in practice: judge by testing and listening, not by assuming an error. The [Conflict] tag notes two statements of his. In 2015 he said a 1st-order all-pass flips polarity below its corner frequency (the frequency it is set to). In 2021 he said the pulse-type polarity checkers people use read all-pass filters the same way they read crossovers, so they don't show an all-pass as a reversal.

4.14 #4 · With factory all-pass filters in place, don't add delays.

They are a different fix for the same problem and take the place of delay; delay on top makes them work poorly, and the passenger is spared a driver-seat tune's "nightmare". An all-pass can't be inverted: match it with the same filter on the other channel, or use FIR at the cost of latency (hands-free calls suffer). Factory Subaru case: leave polarity alone, no front time alignment. [RARE] Sources: DIYMA 2021-05-27 · DIYMA 2021-03-26 · DIYMA 2021-05-11

In plain English: If the factory system already has all-pass filters, he says don't add delays. Both are fixes for the same problem (imaging in a car where you sit off-center), and the all-pass filters take the place of delay. Adding delay on top makes them work poorly. The upside is that the passenger is spared the "nightmare" a driver's-seat-only tune sounds like from the other seat. You also can't simply undo an all-pass filter, because no filter exactly reverses it. Instead, put the same filter on the other channel so the two match. Or use FIR, a type of digital filter that can reshape timing, at the cost of latency (extra delay through the system), which makes hands-free phone calls suffer. In a factory Subaru case, he advised leaving polarity as it was and adding no front time alignment (delay).

4.14 #5 · Finding all-pass filters.

In REW they're easy to see with flat response and the initial delay removed (T=0). Or record the radio's L and R outputs and mix them to mono in a DAW: phase differences show up as response differences; DSSF3 (ymec.com) shows correlation directly. Sources: DIYMA 2021-05-16 · DIYMA 2021-05-16

In plain English: Two ways to spot all-pass filters, according to him. In REW (Room EQ Wizard, free measuring software), they're easy to see when the response is flat and the starting delay is removed, by setting T=0 so the time it takes the signal to arrive doesn't hide the phase pattern. Or record the radio's left and right outputs on a computer and mix them to mono in a DAW (digital audio workstation, recording software). Wherever the two channels' timing differs, the mono mix shows a change in loudness. He also mentions DSSF3 software (from ymec.com), which shows correlation (how alike the two channels are) directly.

4.14 #6 · All-pass filters were the one thing MS-8 handled badly.

A phase-inverting midrange all-pass in a Lexus factory amp (2010) and Bose's phase-reversing all-passes in center-less systems (2016) defeated its summing; the upside, a 2012 Fiat 500 Bose system images in both front seats with no center. Sources: DIYMA 2010-08-05 · DIYMA 2016-05-11

In plain English: This point is about the MS-8, a JBL processor from a specific period, built to take in factory signals and combine ("sum") them back into plain stereo. He says all-pass filters were the one thing it handled badly. Two examples: in 2010, a Lexus factory amp with an all-pass filter on the midrange that inverted its phase; and in 2016, Bose systems without a center speaker that used phase-reversing all-pass filters. Both defeated the MS-8's summing. The upside of those filters: a 2012 Fiat 500 with a Bose system images (gives a clear stereo picture) in both front seats without any center speaker.

4.14 #7 · Summing factory outputs through LOCs is "the worst way", because factory crossovers were designed to sum acoustically.

Summed electrically, their phase shifts turn asymmetrical and leave holes (e.g. a midbass hole when factory sub and front channels are summed). His "correct" method: processor 1 (e.g. a PS8) EQs and delays each factory channel to sum through symmetrical resistors, processor 2 tunes; ~$2,000, or one speaker-level-input DSP if there is only a factory radio. [RARE] Sources: DIYMA 2015-06-13

In plain English: "Summing" means combining several factory outputs (for example tweeter, midrange and sub channels) back into one full-range signal for your own processor. He calls doing this with LOCs (line output converters) "the worst way". Factory crossovers were designed to blend acoustically, in the air, from speakers in their places. Wired together electrically, their phase shifts turn asymmetrical, as he puts it, and leave holes in the sound. One example is a midbass hole when the factory sub and front channels are summed. His "correct" method uses two processors. Processor 1 (for example a PS8) applies EQ and delay to each factory channel so they combine properly through symmetrical resistors (a simple resistor network that mixes them), and processor 2 does the tuning. That costs about $2,000, or a single DSP with speaker-level inputs if the car has only a factory radio. Point 11 below explains how his approach later shifted.

4.14 #8 · Uncorrected factory delay is "an imaging nightmare", and few integration DSPs remove it.

It comb-filters and makes your own time alignment wrong. In 2013 almost no de-EQ DSPs undid delay and in 2015 only the discontinued MS-8 did; AudioControl's 2016 DSP could delay inputs before summing. Choose an integration DSP by its input-correction tools. [RARE] Sources: DIYMA 2013-12-17 · DIYMA 2015-05-10 · DIYMA 2016-05-01

In plain English: Some factory systems delay certain speakers. If that delay is left in when you take the signal for your own processor, he calls it "an imaging nightmare": it causes comb filtering (evenly spaced cancellations in the sound), and it makes your own time alignment (delay settings) wrong. An "integration DSP" is a processor made to take factory signals. He says few remove factory delay. In 2013 almost none of the "de-EQ" processors (ones that undo the factory's tone shaping) undid delay, and in 2015 only the MS-8, by then discontinued, did. AudioControl's 2016 DSP could delay its inputs before summing them. So in practice: choose an integration DSP by the tools it has for correcting its inputs.

4.14 #9 · Reading a bad summed measurement (Audi/Bose case).

A hole near 200 Hz = asymmetrical factory crossovers plus front delay vs the sub; ~5 kHz 20 dB hot = DSP level mismatch; narrow notches near 4.5 and 9 kHz = comb filtering from uncorrected tweeter/mid delay. Sources: DIYMA 2015-06-13

In plain English: Here he diagnoses a bad measurement from an Audi with a Bose system, where the factory channels had been summed. A measurement graph shows loudness at each pitch. He reads three problems from it. A hole near 200 Hz comes from asymmetrical factory crossovers, plus the front speakers' delay relative to the sub. A region around 5 kHz that is 20 dB too loud (a large difference) comes from a level mismatch in the DSP. Narrow notches near 4.5 and 9 kHz are comb filtering, evenly spaced cancellations, caused by the tweeter-to-midrange delay that hadn't been corrected.

4.14 #10 · Leave factory rear outputs out of the sum; double processing is fine.

Rears are often out of phase or delayed, so summing them cuts highs and the input EQ lifts treble and hiss. A factory DSP feeding an aftermarket DSP breaks no rule; his own car ran several A/D/A conversions. [RARE] Sources: DIYMA 2014-03-02 · DIYMA 2013-10-08

In plain English: He says to leave the factory rear-speaker outputs out when summing the factory signal. Rears are often out of phase (timing reversed) or delayed, so adding them in cancels some of the treble. The processor's input EQ then boosts the treble back up, and with it the hiss. His second point: running one processor after another is fine. A factory DSP feeding an aftermarket DSP breaks no rule, and his own car ran several A/D/A conversions (analog to digital and back again). Many people believe processing a signal twice, or converting it back and forth, ruins the sound.

4.14 #11 · "Get back to zero" first, or work with the factory processing?

In upmixing factory systems he now wires each factory output one-to-one to an amp channel, adds speakers and power, and just retunes EQ and levels: the factory already holds the delays and crossovers. Taught this way, installers call it the best thing they've built. [RARE] [Changed view: 2013–2016 his correct method was de-summing, de-EQ and delay removal (points 7–8); 2021–2023 says all-pass filters serve a purpose, are very hard to delete, and "back to zero" isn't always efficient.] Sources: DIYMA 2015-06-13 · CMA Connected Oct 2021 @38:54 · Absolute Electronix 2023 @58:34

In plain English: "Back to zero" means undoing all factory processing to get a plain, flat stereo signal before tuning. An "upmixing" factory system creates extra channels, such as center, sides and rears, from stereo. In these, he now wires each factory output one-to-one to its own amp channel, adds speakers and power, and simply retunes the EQ and levels. His reasoning is that the factory processing already holds the delays and crossovers. He says installers taught this way call it the best thing they've built. The [Changed view] tag describes two positions. In 2013–2016 his "correct" method was to un-sum, undo the EQ and remove the delay (points 7 and 8). In 2021–2023 he says the factory all-pass filters serve a purpose and are very hard to delete, and that getting "back to zero" isn't always efficient.

4.15 Keeping factory features, and OEM upmixers (QLS, Logic 7) and digital links

What this part is about: Many premium factory systems use an "upmixer", a processor that spreads ordinary stereo music across more speakers. This part covers why they exist, how to keep or remove them, their quirks, how to test them, and why aftermarket gear rarely has one. It ends with digital audio links.

4.15 #1 · Factory upmixers exist to make stereo better, not for movies.

Logic 7-type processors steer ambience to the sides and rear and plant a center image for each passenger; in Pro Logic II, Logic 7 and DTS Neural the rears carry only ambience, hence "the rears don't play". Every car he has owned for 20+ years ran an upmixer, including his ~2004 Mini Cooper competition car (18 speakers, Logic 7). [RARE] Sources: DIYMA 2015-12-29 · DIYMA 2021-09-08 · OFCAP 19 @1:18:00

In plain English: An upmixer takes a normal two-channel stereo recording and creates extra channels from it, such as center, sides and rears. Many people believe surround processing is only for movies. He says factory upmixers exist to make stereo music better. Logic 7-type processors steer ambience (the room echo and reverb in a recording) to the side and rear speakers, and they place a center image (where the singer seems to be) in front of each passenger. In Pro Logic II, Logic 7 and DTS Neural (three upmixer types), the rear speakers carry only ambience. That's why owners complain "the rears don't play". Every car he has owned for over 20 years used an upmixer, including his roughly 2004 Mini Cooper competition car (18 speakers, Logic 7).

4.15 #2 · OE systems are deliberately tuned for both front seats, so build on that.

Carmakers chose good sound in both seats over a driver-only delay tune; better passenger sound costs nothing if the driver isn't compromised. Some cars image well but won't play loud: keep the imaging and add level, starting from what can't be removed (the radio, often the amp). [RARE] Sources: DIYMA 2021-09-09 · OFCAP 19 @3:15:06 · OFCAP 19 @1:04:03

In plain English: He says carmakers deliberately tune their systems for both front seats. Aftermarket tuners usually use delay to optimize the sound for the driver's seat alone, and carmakers chose good sound in both seats over that. His view: better sound for the passenger costs nothing, as long as the driver's sound isn't compromised. Some factory cars image well (give a clear stereo picture) but can't play loud. So in practice: keep the imaging and add level (the ability to play louder), starting from the parts you can't remove, which are the radio and often the factory amp.

4.15 #3 · Harman QLS 3-D: use it properly or remove it entirely.

He found it in Hyundai/Kia, Maserati and Lincoln; about seven filters split center, side and in-between content, with "In the audience" and "On the stage" setting the wrap. Its outputs may not sum back to stereo, so tapping one output won't do; removing it in a Genesis may need a MOST adapter. [RARE] Sources: EDUCAR tech tip · OFCAP 19 @1:19:00

In plain English: QLS 3-D is a Harman upmixer. He found it in Hyundai/Kia, Maserati and Lincoln cars. It uses about seven filters to split the music into center content, side content and the in-between. Two settings, "In the audience" and "On the stage", control how much the sound wraps around you. His advice: either use it as intended, or remove it entirely. Its outputs may not add back up to normal stereo, so taking the signal from just one output won't give you the whole music. Removing it in a Hyundai Genesis may need a MOST adapter; MOST is a fiber-optic digital network some cars use to carry audio.

4.15 #4 · Mercedes HK Logic 7 has no full-range stereo signal to tap, and on Mark Levinson/Logic 7 cars "DO NOT TRY TO SUM this car back together".

Options: a Mobridge DA1 into the DSP; remove the Logic 7 amp and have the dealer recode the radio as no-amp; a DSP with its own volume control fed before the factory amp; or one replacing fronts, center and sub while sides and rears stay factory. [RARE] Sources: DIYMA 2015-12-28 · DIYMA 2021-09-26

In plain English: In Mercedes cars with Harman Kardon Logic 7, he says no output carries a full-range stereo signal; every output is an already-processed piece. For Mark Levinson cars with Logic 7 (Mark Levinson is Lexus's premium system), he wrote in capitals: "DO NOT TRY TO SUM this car back together". In other words, don't try to recombine the pieces into stereo. The options he gives: a Mobridge DA1 interface feeding your DSP; removing the Logic 7 amp and having the dealer recode (reprogram) the radio as a no-amp system; a DSP with its own volume control, fed from before the factory amp; or a DSP that replaces the front speakers, center and sub while the side and rear speakers stay factory. Many people believe any factory system can be summed back to stereo.

4.15 #5 · Matrix upmixers mis-steer some music and magnify source clipping.

Logic 7 and PL2 compare channels thousands of times a second (in-phase content forward, out-of-phase rearward), so producers' out-of-phase width tricks go rearward and sides and rears switch on and off. A clipping source sounds terrible through Logic 7: turn the head unit down and the processor up. At CES, EMMA judges needed an hour to find a track that "broke" Logic 7. [RARE] Sources: EDUCAR tech tip · DIYMA 2015-07-17 · DIYMA 2018-04-06

In plain English: A "matrix" upmixer like Logic 7 or Pro Logic II (PL2) works out where to send sound by comparing the left and right channels thousands of times a second. Sound that is the same in both ("in phase") goes forward; sound that is opposite in the two channels ("out of phase") goes to the rear. Recording producers sometimes use out-of-phase tricks to make sounds seem wider, so the upmixer wrongly sends them rearward, and the side and rear speakers switch on and off. He also says a clipping (distorting) source sounds terrible through Logic 7. His fix is to turn the head unit down and the processor up. He also notes that at CES (a big electronics show), EMMA competition judges needed an hour to find a track that "broke" Logic 7.

4.15 #6 · Test signals for upmixers.

Use uncorrelated pink noise only to tune a matrix upmixer, correlated (mono) noise for everything else. Mono noise through Logic 7/PL2 comes mostly from the center with L/R ~6 dB down; invert one channel and it comes from the rears. [RARE] Sources: DIYMA 2021-10-08 · DIYMA 2017-08-05

In plain English: Pink noise is a test hiss containing all pitches. "Correlated" (mono) pink noise is identical in left and right; "uncorrelated" noise is different random hiss in each. He says to use uncorrelated noise only when tuning a matrix upmixer, and correlated (mono) noise for everything else. He describes how mono noise behaves through Logic 7 or PL2: it comes mostly from the center speaker, with the left and right speakers about 6 dB quieter. If you invert one channel (flip its polarity), it comes from the rear speakers instead.

4.15 #7 · Why aftermarket DSPs lack upmixers: product managers, not cost.

Upmixer licenses are cheap (discrete surround isn't); someone must understand it, fight for it past finance, and explain it to users. Sources: DIYMA 2021-08-01 · DIYMA 2017-07-07

In plain English: Why don't aftermarket processors include upmixers? He says it isn't the cost: upmixer licenses are cheap, though licenses for discrete surround (true multichannel formats like movie soundtracks) aren't. The obstacle is product managers. Someone inside the company must understand upmixing, argue for it past the finance people, and then explain to customers how it works and how to use it.

4.15 #8 · Digital links and phone audio.

Optical never became standard because a digital feed bypasses the radio's volume, so every amp needs its own volume or a bus; floating outputs into differential inputs nearly match its noise immunity. A cheap decoder can be tapped at its I2S bus with leads a few inches long. Through a processor, "a 100% reliable solution is more important than a completely transparent one". No Andy statement on A2B was found. Sources: DIYMA 2013-11-22 · DIYMA 2015-08-11 · DIYMA 2010-06-13

In plain English: Optical links carry audio as light, in digital form. He says they never became standard in cars because a digital feed bypasses the radio's volume control. Every amp would then need its own volume control, or a data bus to receive volume commands. He adds that floating (balanced) outputs feeding differential inputs come close to matching optical's immunity to noise. For a cheap decoder box with poor analog outputs, you can take the signal from its I2S bus, the internal digital link between its chips, but only with leads a few inches long. On phone audio, a 2010 case of Bluetooth calls through the MS-8 processor involved processing delay. There his principle was "a 100% reliable solution is more important than a completely transparent one". The researchers found no statement from him about A2B (a newer automotive digital audio bus).

4.16 Staged upgrades and factory-fit products

What this part is about: How he suggests upgrading a factory system one step at a time, keeping the factory processing as long as it helps. Several points describe Audiofrog products (his company) designed to fit factory locations; those are product-specific.

4.16 #1 · New speakers alone are a real upgrade on a factory-EQ'd system, and a DSP fixes most "voicing" complaints.

In Bose and other premium systems that already EQ out the car, similar speakers in the same places keep the factory EQ doing useful work. Before swapping speakers for their sound, add a DSP. [RARE] Sources: CMA 2023 @11:00 · DIYMA 2022-01-14

In plain English: Many people believe new speakers can't help a factory system until you replace or bypass its processing. He disagrees. In Bose and other premium systems, the factory EQ (tone shaping) already corrects for the car's interior. If you fit similar speakers in the same places, that factory EQ keeps doing useful work, so new speakers alone are a real upgrade. "Voicing" is a speaker's built-in tonal character, and people often switch brands because they dislike it. His advice is that a DSP (digital sound processor) fixes most of those complaints. So in practice: before swapping speakers because of how they sound, add a DSP.

4.16 #2 · His staged path keeps the factory EQ and crossover until the last step.

(1) Better speakers on the factory amp and EQ; (2) more power; (3) sub, rears, amps and a DSP. On a 2023 Chevy truck with Bose the tiers ran about $2,000/$3,500/$4,500/$7,500; demo each stage with binaural recordings on headphones. Gary Biggs's IASCA BMW kept every factory driver and added amps, an MS-8 and a sub. [RARE] Sources: CMA 2023 @12:05 · OFCAP 19 @49:01 · DIYMA 2022-01-10

In plain English: His recommended upgrade order keeps the factory EQ and crossover (the circuit that splits sound between speakers) until the last step. Step 1: better speakers, still on the factory amp and EQ. Step 2: more power (amplifiers). Step 3: a subwoofer, rear speakers, amps and a DSP. On a 2023 Chevy truck with Bose, he priced the tiers at about $2,000, $3,500, $4,500 and $7,500; the sources list these as speakers, then amps, then a subwoofer, then a DSP tuned for a center image. To let customers hear each stage, demo it with binaural recordings (recordings made with microphones in a dummy head's ears) played on headphones. He also cites Gary Biggs's competition BMW in IASCA (a sound-quality contest), which kept every factory speaker and added amps, an MS-8 processor and a subwoofer.

4.16 #3 · GS25: for factory systems whose active crossover and EQ make passive component sets "a big problem".

Common in GM, Toyota and Mercedes systems; the GS25 is a 2.5" full-range (200 Hz–20 kHz) with no crossover and break-off tabs for factory dash spots, taking the 50–75 W factory dash speakers can't. Pair it with GS60/GS690 doors or add a GS10 for an active 3-way. [RARE] Sources: GS25 listing · CMA 2023 @9:01 · CMA Connected Oct 2021 @36:43

In plain English: In many GM, Toyota and Mercedes factory systems, the factory amp itself splits the sound between the dash and door speakers (an "active" crossover) and applies EQ. A typical aftermarket "component set" comes with its own passive crossover box, and in these systems he calls that "a big problem". The GS25 is Audiofrog's answer. It's a 2.5-inch (65 mm) full-range speaker covering 200 Hz to 20 kHz, with no crossover, and break-off tabs so it fits factory dash locations. It handles 50–75 watts, which factory dash speakers can't. Pair it with GS60 or GS690 door speakers, or add a GS10 tweeter to make an active 3-way system.

4.16 #4 · G62 coax is voiced for off-axis factory locations; G60S is packaged for factory doors (product-specific).

The G62's treble rises to offset off-axis loss in lower doors and decks, and its tweeter sits low for factory grilles (~85% go behind one). G60S: inline crossovers by each driver, a tweeter kit that comes apart for factory spots, a shallow basket. Sources: G62 page · CMA 2023 @5:05 · G60S listing

In plain English: These are Audiofrog products. A coaxial (coax) speaker has its tweeter mounted in front of the woofer, as one unit. Factory speakers often sit low in the doors or on the rear deck, pointed away from your ears ("off-axis"), and treble fades off-axis. So the G62's treble is made to rise, offsetting that loss. Its tweeter also sits low so it fits behind factory grilles; about 85% of installs go behind one. The G60S component set is built for factory doors. Its crossovers sit inline, right by each speaker. Its tweeter mounting kit comes apart to fit factory spots, and it has a shallow basket (frame).

4.16 #5 · Direct-fit tweeters and adapters (product-specific).

GB10/GS10 in 3D-printed housings for BMW, Tesla, Audi, Porsche, Range Rover, F-150, Golf, Silverado/Sierra Bose and several Toyotas; GB10OE high-pass 2.5 kHz and GS10OE 3.5 kHz, both 24 dB/oct; GB25OE/GB40OE adapters for factory dash mids. Check housing dimensions first. Sources: Direct Fit Tweeters and Adapters · OE Tweeters collection

In plain English: These Audiofrog products replace factory tweeters (small treble speakers) without custom work. The GB10 and GS10 tweeters come in 3D-printed housings shaped for specific cars: BMW, Tesla, Audi, Porsche, Range Rover, Ford F-150, VW Golf, Chevy Silverado/GMC Sierra with Bose, and several Toyotas. The GB10OE has a built-in high-pass filter (it blocks lower sounds) at 2.5 kHz, and the GS10OE at 3.5 kHz, both cutting 24 dB per octave (a steep cut). GB25OE and GB40OE adapters fit factory dash midrange locations. So in practice: check the housing dimensions for your car first.

4.16 #6 · Volvo S60 (c. 2001–2009): keep the factory Dynaudio speakers and add amp, EQ and sub.

Replacing them is "a waste of money"; feed a real amp from the radio's sub-1 V DIN preamp signal (which carries remote turn-on) and flatten the head unit's hidden EQ. "How do I know this? I have one." [RARE] Sources: DIYMA 2012-03-25

In plain English: This is his advice for a Volvo S60 from about 2001–2009. Keep the factory Dynaudio speakers; replacing them, he says, is "a waste of money". Instead add an amplifier, EQ and a subwoofer. Feed the new amp from the radio's DIN preamp output, a low-level signal of under 1 volt on a DIN-type connector, which also carries the remote turn-on signal. Then flatten the radio's hidden EQ, the tone shaping the radio applies without showing it. His credential: "How do I know this? I have one."

4.16 #7 · Bass is still the aftermarket's way in.

OEM suppliers can't get a 40 lb sub box and a 60 A amp approved, so the core upgrade stays a better front plus added bass. Sources: OFCAP 19 @58:06

In plain English: Why is there still a market for aftermarket car audio? He says it's bass. Carmakers' audio suppliers can't get a 40-pound (18 kg) subwoofer box and an amplifier drawing 60 amps approved for a production car. So the core aftermarket upgrade remains a better front stage (the front speakers) plus added bass.

4.17 MS-8-era integration tips (JBL MS-8, 2010–2016; posts to 2022)

What this part is about: Tips for one specific product, the JBL MS-8, a car sound processor with automatic tuning that he helped bring to market. These tips come mainly from 2010–2016, and he kept answering questions about it in posts up to 2022. They apply to that unit and its era.

4.17 #1 · MS-8 was designed first for factory integration: put the factory sub on input 7 or 8.

It covers 48 speaker configurations by rule; its de-EQ must see a HF channel before a LF one. With an aftermarket radio, feed fronts to inputs 1–2 and skip input calibration; if it's too quiet on low-level inputs, check whether it's tapped at the radio or the factory amp. [Era: MS-8] Sources: DIYMA 2011-06-09 · DIYMA 2011-10-18 · DIYMA 2021-12-28

In plain English: This is about the JBL MS-8 (an era-specific product). He says it was designed first of all to work with factory systems. When connecting a factory system, put the factory subwoofer's signal on MS-8 input 7 or 8. It supports 48 speaker layouts and works by built-in rules. Its "de-EQ", the step that undoes the factory's tone shaping, must see a high-frequency (treble) channel before a low-frequency (bass) one; the point doesn't spell out the details of that rule. With an aftermarket radio, connect its front outputs to inputs 1 and 2 and skip the input calibration step. If the MS-8 is too quiet on its low-level (RCA) inputs, check whether it is connected to the radio's output or the factory amp's output.

4.17 #2 · "Signal None" vs "Signal Low".

None = no signal, or one altered beyond frequency and delay (e.g. a sample-rate error); Low = too little voltage; chimes during calibration also trigger "none" (he cites Ford). Sources: DIYMA 2010-07-09 · DIYMA 2014-11-10

In plain English: These are two messages the MS-8 (an era-specific product) shows while checking its inputs against its setup disc. He explains them. "Signal None" means either there is no signal, or the signal has been changed in some way beyond its frequency balance and timing. One example is a sample-rate error, where digital audio plays at a slightly wrong rate. "Signal Low" just means too little voltage. He adds that warning chimes playing during calibration also trigger "none", citing Ford cars.

4.17 #3 · Hiss after integration usually means an EQ is boosting treble.

MS-8's input de-EQ, output EQ and 31-band can each lift highs; if hiss drops with processing off, raise the tweeter amp gain and recalibrate. With a radio that adds heavy bass boost and treble cut (2013 Ford Fusion), raise its treble, set MS-8 ~−6 and calibrate at the highest volume still reading "OK OK OK". [RARE] Sources: DIYMA 2015-07-10 · DIYMA 2013-12-05

In plain English: This is MS-8-specific (an era-specific product). Hiss is a steady background "shhh". He says that hiss after connecting to a factory system usually means an equalizer is boosting the treble. The MS-8 has three stages that can each raise the highs: its input de-EQ, its output EQ and its 31-band user EQ. If the hiss drops when processing is switched off, raise the gain on the tweeter amplifier and run the calibration again. A 2013 Ford Fusion radio, for example, adds heavy bass boost and cuts treble. There, he says to raise the radio's treble, set the MS-8 volume around −6, and calibrate at the highest radio volume that still reads "OK OK OK" on the MS-8 display.

4.17 #4 · Why MS-8 results go bad: clipped sweeps, one reversed midbass, running out of boost.

Sweep with MS-8 around −20 and the sub amp near 2 V (if you can feel the sub sweep, its gain is too high); "MS-8 absolutely hates one midbass out of phase". Expect lower level after auto-EQ, since it prefers cuts: "Boosting all the holes is a bad way to EQ." Sources: DIYMA 2010-08-05 · DIYMA 2013-01-23

In plain English: This is MS-8-specific (an era-specific product). The MS-8 tunes itself by playing test sweeps (tones gliding from low to high) and measuring them. He names three reasons results go bad. One is sweeps so loud they clip (distort). Another is one midbass speaker with reversed polarity; in his words, "MS-8 absolutely hates one midbass out of phase". The third is the EQ running out of boost. His settings: run the sweeps with the MS-8 volume around −20 and the sub amp's gain near the 2-volt setting. If you can feel the sub sweep, not just hear it, the sub gain is too high. Expect the system to play a bit quieter after auto-EQ, because the MS-8 prefers cutting peaks to boosting dips: "Boosting all the holes is a bad way to EQ."

4.17 #5 · First-time settings, and the sub-level workaround.

Amps ~2 V; MS-8 −30 for sweeps; sub/front 80 Hz 24 dB/oct, tweeter 3.5 kHz, sides 100 Hz, subsonic 20 Hz 12 dB/oct; JBL MS amps "Low", pot fully CCW, amp filters off. MS-8 sets sub level from the 50–80 Hz sweep before EQ and can over-boost lows (e.g. small sealed boxes): reverse the sub's polarity and set the sub amp's crossover highest, or run the front as a 3-way with front-low at 70 Hz. Sources: DIYMA 2012-12-29 · DIYMA 2018-04-08 · DIYMA 2015-07-28

In plain English: This is MS-8-specific (an era-specific product): his starting settings for a first-time setup. Set amp gains around 2 volts and the MS-8 volume at −30 for the test sweeps. Cross the sub and front at 80 Hz with a 24 dB-per-octave slope (a steep cutoff). Set the tweeter at 3.5 kHz, the side speakers at 100 Hz, and a subsonic filter (which removes rumble too low to hear) at 20 Hz, 12 dB per octave. On JBL MS amps, set the input switch to "Low", turn the gain pot (knob) fully counter-clockwise, and switch the amp's own filters off. He also explains a quirk. The MS-8 sets the sub's level from the 50–80 Hz part of the sweep before it applies EQ, and that can over-boost the low bass, for example with small sealed boxes. His workarounds: reverse the sub's polarity and set the sub amp's crossover to its highest setting, or run the front as a 3-way with the front-low crossover at 70 Hz.

4.17 #6 · What MS-8's correction does in OEM-style multichannel systems.

EQ corrects speaker locations (e.g. "front right"), not individual crossover channels; delays exist so one-seat tuning works through the upmixer and are barely used in "Front" mode. Check it with a multi-mic average; outside correction of sides/rears fails; no real custom firmware exists (encrypted binary, one display update). [RARE] Sources: DIYMA 2022-02-03 · DIYMA 2021-09-28 · DIYMA 2018-04-08

In plain English: This is about how the MS-8 (an era-specific product) works in factory-style systems with many speakers. Its EQ corrects each speaker location, such as "front right", not each separate crossover channel, such as that location's tweeter and woofer on their own. Its delays are there so tuning for one seat still works through the upmixer (the processor that spreads stereo across more speakers), and they are barely used in its "Front" mode. To check its work, he says use an average of several microphone positions, not a single mic. Trying to correct its side and rear outputs with another processor fails. And there's no real custom firmware for it: its software is encrypted, and only one display update was ever released.

4.17 #7 · Factory layouts with MS-8: bi-amp the front before adding discrete rears.

For a 10-speaker OEM JBL 4Runner, parallel the D-pillar speakers with the sides and run 5.1 with the front bi-amped; with BMW under-seat systems he asked owners to try feeding the factory amp's sub output. Sources: DIYMA 2012-09-03 · DIYMA 2011-11-08

In plain English: This is MS-8-specific (an era-specific product). "Bi-amping" means giving each front speaker in a pair, the woofer and the tweeter, its own amplifier channel. "Discrete" rears are rear speakers with their own separate channels. His priority: bi-amp the front before adding discrete rears. For a Toyota 4Runner with the 10-speaker factory JBL system, he suggests wiring the D-pillar speakers (in the rearmost pillars) together with the side speakers, and running the MS-8 in 5.1 mode with the front bi-amped. In his words, "There's a bigger benefit to biamping the front than in discrete rear channels." For BMWs with woofers under the seats, he asked owners to try feeding the factory amp's sub output to the MS-8.

4.17 #8 · MS-8 hardware quirks.

It won't boot in the cold because it waits for the slow LCD (disconnect the display), yet it can't run without its own display, which holds its own processor; random balance shifts usually mean an intermittent input. Sources: DIYMA 2022-01-05 · DIYMA 2019-01-13 · DIYMA 2018-12-15

In plain English: These are quirks of the MS-8 (an era-specific product). In cold weather it may not start, because on start-up it waits for its screen, and LCD screens respond very slowly when cold. Disconnecting the display gets around this. Yet the MS-8 can't run without its own display, because that display holds its own processor and software, so another screen can't stand in for it. The sources don't say more about how the cold-start workaround fits with this. If the sound randomly shifts to one side, he says that usually means an intermittent input, a connection that is cutting in and out.

4.18 Top rarely-discussed points in this section

Cabin gain belongs to the car and every box type gets it, so build the most efficient box you can fit and EQ the peak (4.1 #1, #2, #6).
Open windows turn the cabin into a vented box; convertibles get little cabin gain and want a bandpass box firing into the cabin (4.1 #9, #10).
Bass gives away its location through distortion and rattles, not arrival time (4.2 #2).
Cross the sub at 60 Hz and the midbass at 80 Hz (LR4), and lower the sub low-pass half an octave per 12 dB of sub boost (4.2 #6).
"Half a wavelength of delay plus a polarity flip" fixes phase at one frequency only, and impulse auto-delay fails on subs: use a tape measure (4.2 #11–#13).
Vented boxes tuned for minimum excursion beat small sealed boxes on huge amps, and box Q is immaterial when the sub is crossed below Fc (4.3 #1, #6, #7).
A down-firing sub box is an accidental bandpass enclosure (4.3 #17).
Behind the rear seat is the worst sub location; confirm a cross-car mode with a ~7 ft tape-measure path difference (4.5 #2, #3).
Never port a door box into the door; with a sub, a high-passed free-air midbass is enough (4.6 #5).
Music averages ~1/32 of its peak power, and a tweeter sees ~0.16 W of a "20 W" calibration (4.7 #1, #2).
About 70% of GB25 warranty claims are DSP input clipping; set the DSP input for maximum volume at the source's loudest frequency (4.7 #6, 4.8 #1–#2).
His 8-step gain method uses a sine wave on the sub amp only (4.8 #4).
DSP amplifiers can't recover output lost to EQ cuts; high-end systems need amps with analog gain (4.8 #9).
Hiss is not a ground loop, and differential inputs ended the ground-loop era; use twisted pair, not coax, into them (4.10 #1, #2, #5).
Crimp, don't solder (Big 3 included); the ground wire may be thinner than the power wire; every added fuse is a resistor (4.11 #1, #3, #5).
Never connect both factory radio channels to one computer input when measuring (4.13 #7).
Tell factory all-pass filters from delay by ear or by mono-noise L+R, and don't stack delays on them (4.14 #2, #4).
In upmixing factory systems, wire factory outputs one-to-one to new amps and keep the factory processing (4.14 #11).

Changed views and conflicts in this section

Changed views

Sub/midbass crossover: ~80 Hz LR4 on both sides (2010–2015) → sub 60 Hz / midbass 80 Hz stagger because the sub gets boosted (2020–2022) (4.2 #6).
Sub delay: "don't time-align subs" (2009–2010) → delay everything to the sub (2015) → tape-measure the sub like any speaker (2018–2023 PDFs, 2021) (4.2 #12).
All-pass filters on sub/midbass: never made them work (2010–2013) → used them in his own car (2015–16) → fix the crossover instead, and use the high-pass side if you must (2021) (4.2 #15).
Gain overlap: clip on a −10 dB tone, ~9–10 dB overlap (2009–2015) → "never appropriate" at the DSP input; −10 dB tones license tweeter-killing clipping (2021) (4.8 #5).
Gain-setting method: scope and −10 dB sine (2008) → by ear (2014–2016) → DSP-era method with a sine on the sub only, the rest by pink noise and RTA (2018–2022) (4.8 #4).
Midbass Q (partial): car midbass should be low-Q (2015; 2021 blog) → crossed above resonance its Q "is not really important" (2021 DIYMA) (4.6 #3).
Factory integration: sum, de-EQ and remove factory delay with two processors (2013–2016) → keep the factory all-pass filters and processing, go one-to-one (2021–2023) (4.14 #11).

Conflicts

Impact: midrange/3 kHz (2009, 2021 DIYMA) vs midbass–sub phase for club-style impact (CMA Connected Oct 2021) (4.2 #3).
Efficiency vs power: "efficiency matters more" (2021) vs "Efficiency is overrated. Power is cheap." (2013, in a level-matching context) (4.7 #11).
Class-D blind demo: ~800 demos/3 listeners (2022) vs ~1,500 demos/4 listeners (2023) (4.9 #3).
Xmax method: one-way overhang, no fudge (2008) vs (coil − gap)/2 + 15% (2020) (4.3 #21).
1st-order all-pass and polarity: flips polarity below its corner (2015) vs pulse checkers see no reversal (2021) (4.14 #3).
Lexus tap point: secondhand ClubLexus report (tap before the amp) vs his general advice to tap after it (4.13 #3).
DSP starting level: −12 dB in the title-attributed DIYMA guide vs −6 dB in the 2022 eight-step post (4.8 #4).

Gaps: no statement from Andy on A2B was found. On the Big 3 he only says to crimp it, not solder it, and lists it among noise "fixes" that don't help (4.10 #2, 4.11 #3). On stiffening caps he says only that a 2-farad cap is unnecessary at 1,000 W (4.11 #7).

The full series

Download the complete guide as one PDF (351 pages, every point with its explanation).