Car Audio Explained, Part 6: Speaker Design, Driver Failures, Tweeter Protection and Wiring (Andy Wehmeyer's Lessons)

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This is Part 6 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.

2.7 Audiofrog product-design rationale

What this part is about: Audiofrog is Andy Wehmeyer's speaker and amplifier company. This part gives his reasons for the way its products are designed, built, tested and sold, and what each choice means for the person installing them.

2.7 #1 · The brief: easy to put in the right places, no aiming needed, smooth directivity, made to work even for people who skip the manual.

His list for a great car speaker: low distortion, smooth flat response, uniform off-axis roll-off, easy mounting, designed with its grille. Performance first, then "wrap something beautiful" around it. Sources: DIYMA 2014-03-04 · DIYMA 2017-07-02 · Absolute Electronix 2023 @16:38

In plain English: This is the design goal Audiofrog set itself. The speakers should be easy to mount in the right places in a car. They should not need to be aimed at the listener. Their "directivity" should be smooth: directivity describes how a speaker's sound spreads out to the sides, and smooth means the sound fades gradually, not in jagged steps, as you move off-axis (off to the side). And they should still work well for installers who never read the manual. His list for a great car speaker is low distortion (little added sound that wasn't in the recording), a smooth, flat response (no notes much louder than others), an even fade off to the side, easy mounting, and a grille designed together with the speaker. Performance comes first. Only then do you "wrap something beautiful" around it.

2.7 #2 · Car drivers must be designed differently from home drivers.

[RARE] Reflections matter more, cars play louder, and the midbass baffle is a corner. Home 6" drivers fake bass with elevated Q ("That higher Q IS distortion"); many car drivers fake it with high inductance. GB uses single-layer flat edge-wound coils, copper pole caps, stiff paper cones and neodymium, which is why a GB60 sounds thin on a display board but full in a car. Sources: DIYMA 2015-12-13 · DIYMA 2016-02-18

In plain English: A "driver" is a single speaker unit: one cone or one dome. Many people believe a good home-audio driver will be just as good in a car. He disagrees. In a car, much of what you hear has bounced off glass and panels, so how a driver sounds off to the side matters more. Cars are also played louder. And the midbass driver usually sits low in a door or kick panel, which acts like a corner and boosts bass (he puts the boost at about 6 dB). Home 6-inch drivers often get extra bass from an elevated "Q", a resonance that makes the bass bump up, and he says "That higher Q IS distortion." Many car drivers fake bass a different way: high inductance (an electrical property of the coil) turns the midrange down so the bass seems louder. Audiofrog's GB drivers use single-layer, flat, edge-wound coils, copper caps on the pole piece, stiff paper cones and neodymium magnets. That is why a GB60 sounds thin on a store display board but full once it is in a car.

2.7 #3 · High-end speakers "are not wedding cakes", and trading down should cost output, not accuracy.

[RARE] GB took its cue from JBL pro arrays that stay clean at concert levels: loud enough (about 450 W) that owners needn't baby them. Low distortion at high level is what costs money, so GS keeps accurate, smooth sound and gives up output: a smaller budget means "not going to play as loud". Sources: CMA Networks 2023 @14:01 · OFCAP Ep. 19 @1:36:02

In plain English: Many people believe high-end speakers are delicate and shouldn't be played loud. He rejects that: high-end speakers "are not wedding cakes," meaning they shouldn't need careful handling like something fragile. Audiofrog's top GB line took its cue from JBL professional speaker arrays, which stay clean at concert volume, and was made to play loud enough (about 450 W) that owners don't have to baby it. Keeping distortion low at high volume is what costs money. So for the cheaper GS line, Audiofrog kept the accurate, smooth sound and gave up loudness instead. A smaller budget means it is "not going to play as loud", not that it sounds less correct.

2.7 #4 · A "work with the factory car" strategy runs through the line.

Shallow drivers for factory depths, low coax tweeters for factory grilles, gaskets and multi-fit adapters, off-axis voicing for factory spots, inline crossovers that avoid door grommets, full-range drop-ins that keep factory processing (GS25) and 3D-printed OE adapters. Sources: CMA Networks 2023 · BusinessWorld 2024

In plain English: "Factory" or "OE" (original equipment) means the parts the car came with. Many Audiofrog products are designed to fit the car's original speaker spots with little cutting. His examples: drivers shallow enough for factory mounting depths; coaxial tweeters (a coaxial speaker has a tweeter mounted in front of the woofer) that sit low enough to fit behind factory grilles; gaskets and adapters that fit many cars; a tonal balance ("voicing") suited to factory spots that don't point at the listener; inline crossovers that avoid door grommets (a grommet is the rubber boot that carries wires between the door and the car body); full-range drop-in speakers such as the GS25 that let you keep the car's own sound processing; and 3D-printed adapters for factory locations.

2.7 #5 · Coaxials are built for low, off-axis door and deck spots.

[RARE] A typical coax crosses its tweeter with one capacitor (6 dB/oct), leaving a hole depending on aim; GS coaxes use a 12 dB/oct tweeter network plus 6 dB/oct woofer low-pass on a PCB in the basket, and a waveguide that lifts the tweeter's middle range, so it crosses lower and handles more power. The G62's top end rises to offset the off-axis loss of door-bottom and package-tray spots. Sources: CMA Networks 2023 @8:06 · DIYMA 2021-09-14 · G62 store listing

In plain English: A coaxial ("coax") speaker has a tweeter mounted in front of the woofer. A crossover is the circuit that sends high notes to the tweeter and lower notes to the woofer. Its slope, such as 6 or 12 dB per octave, says how quickly it cuts sound outside each driver's range. He says a typical coax crosses its tweeter with just one capacitor, a gentle 6 dB/oct cut. That leaves a "hole" (a gap) in the sound whose depth depends on where the speaker is aimed. GS coaxes instead use a 12 dB/oct filter on the tweeter plus a 6 dB/oct filter on the woofer, on a small circuit board in the basket (the speaker's frame). They also have a waveguide, a shaped surround that lifts the tweeter's output in the midrange (the lower end of its range), which smooths the handoff from the woofer. So the tweeter can cross over lower and handle more power. On the G62 the treble rises on purpose. That makes up for the treble lost when it sits low in a door or on the rear shelf (the "package tray"), pointing away from your ears.

2.7 #6 · The G60S puts each crossover at its driver to keep wires out of the door jamb.

Woofer: 6 dB/oct low-pass; tweeter: 12 dB/oct high-pass with protection; pre-terminated one-way plugs; the tweeter strips to the bare element for factory or pillar spots. Wire both crossovers' + inputs together and − together to one amp channel (he conceded the manual should say so). Sources: CMA Networks 2021 @44:02 · DIYMA 2021-06-08 · G60S store listing

In plain English: The G60S is an Audiofrog component set: a separate woofer and tweeter, each with its own crossover. Instead of one crossover box, each driver's crossover sits right at the driver. That keeps wires out of the door jamb (the hinge area between door and body). The woofer gets a 6 dB/oct low-pass (it lets lows through and cuts highs). The tweeter gets a 12 dB/oct high-pass (it lets highs through) with built-in protection. The plugs come pre-attached and fit only one way. The tweeter can be stripped down to the bare element to fit factory or pillar spots. Wiring tip: join both crossovers' + inputs together and both − inputs together, and connect them to one amplifier channel. He conceded the manual should say so.

2.7 #7 · Drivers are matched by voltage sensitivity: GB mids within about 1 dB, tweeters about 6 dB hotter on purpose.

[RARE] Car amps are voltage sources, so 2.83 V ratings predict relative loudness on one amp (the GB25 has lower impedance to keep up with the GB60). The surplus lets a passive attenuate, or an active system turn the tweeter amp's gain down for less hiss and longer tweeter life; GS tweeters are about 3 dB hotter. Sources: DIYMA 2017-10-01 · DIYMA 2015-11-26 · DIYMA 2021-09-04

In plain English: Sensitivity tells you how loud a speaker plays for a given input. Car amplifiers act as voltage sources: they put out a set voltage, and each speaker draws the current it needs. So the useful rating is loudness at 2.83 volts, the voltage that gives 1 watt into 8 ohms. Ratings at 2.83 V predict which speaker will be louder when both are on the same amp. Audiofrog matched its GB mid drivers to within about 1 dB of each other. The GB25 is given a lower impedance (its electrical resistance to the amp's signal) so it keeps up with the GB60. The GB tweeters are made about 6 dB louder on purpose. That spare loudness lets a passive crossover turn the tweeter down. In an active system it lets you turn the tweeter amp's gain down instead, which means less hiss and a longer tweeter life. GS tweeters are about 3 dB hotter than their mids.

2.7 #8 · Each tweeter is voiced for its own series; don't mix casually.

Poly GS cones have a broad, low-Q top-end bump a simple passive can tame, so the GS10 has a matching lower-Q roll-off; the GB10 plays usefully much lower. A 1.5" GB15 at 1 kHz needs a waveguide about 5" across (fine at home, too big in a car), so use a 3-way. Sources: DIYMA 2016-06-02 · DIYMA 2015-12-21

In plain English: Each Audiofrog tweeter is tuned to blend with the woofers of its own series, so he says don't mix them casually. GS woofers have poly (plastic) cones, which have a broad, gentle bump at the top of their range that a simple passive crossover can tame. The GS10 tweeter has a matching gentle ("lower-Q") roll-off at its low end, so the two blend. The GB10 tweeter plays usefully much lower. He also explains why the 1.5-inch GB15 tweeter can't simply be crossed at 1 kHz (1,000 vibrations per second) in a car. It would need a waveguide about 5 inches (about 127 mm) across, which is fine in a home speaker but too big for a car. So in a car, use a 3-way system: tweeter, midrange and midbass.

2.7 #9 · The GB25 is a true midrange: pair it with a tweeter.

Its top-end peak is meant to be removed by the low-pass; running it tweeterless ("please, God no!") works only by EQing that peak out. Sources: DIYMA 2016-03-03

In plain English: The GB25 is Audiofrog's 2.5-inch (about 64 mm) midrange. Its response has a peak at the top of its range. That peak is meant to be removed by the low-pass filter that hands the highs over to a tweeter. Running it with no tweeter at all (his reaction: "please, God no!") works only if you EQ that peak out. EQ, short for equalization, means turning one band of frequencies up or down. So in practice: pair it with a tweeter.

2.7 #10 · Why Audiofrog makes no 19 mm car tweeter.

[RARE] A smaller dome means a smaller coil and lower power handling, in a market that gives speakers 3× their rating: warranty costs would be massive. Its dispersion gain over a 1" dome is small and falls where music has little content (he made 19 mm tweeters at his previous company). Sources: DIYMA 2022-02-28

In plain English: Some tweeters use a 19 mm (3/4-inch) dome instead of the usual 1-inch (25 mm) one, because a smaller dome spreads sound a little more widely. He explains why Audiofrog makes no 19 mm car tweeter. A smaller dome means a smaller voice coil, which handles less power. And in the car market, people give speakers about three times their power rating, so warranty costs would be massive. The gain in dispersion (how widely sound spreads) over a 1-inch dome is small, and it falls at frequencies where music has little content. He notes that he made 19 mm tweeters at his previous company.

2.7 #11 · Stiff cones push the dust-cap peak above the passband for the crossover to remove.

[RARE] No competent designer builds narrow "car EQ" wiggles into a driver. The GB60 uses the lightest coil/former and stiffest cone so a steep low-pass removes its cap peak (a phase plug would cost sensitivity); the poly GS60 with a 1" coil turns it into a lower, broader hump needing fewer passive parts. Sources: DIYMA 2015-09-30 · DIYMA 2017-07-24 · DIYMA 2021-09-14

In plain English: At high enough frequencies, every cone stops moving as one stiff piece. That causes a peak in its output, often linked to the dust cap (the dome at the cone's center). He says no competent designer builds narrow "car EQ" wiggles into a driver's response. The real design choice is where that peak lands. The GB60 uses the lightest coil and former (the tube the coil is wound on) and the stiffest cone. That pushes its peak high, above the range the driver is meant to play, where a steep low-pass filter removes it. A phase plug (a fixed bullet in place of the dust cap) would cost sensitivity. The poly-cone GS60, with a 1-inch coil, turns the peak into a lower, broader hump that needs fewer passive crossover parts to tame.

2.7 #12 · GB motor and suspension details that matter.

[RARE] Single-layer flat CCA coils shed heat from both sides; nearness of coil to steel decides power handling (the neo motor's back cup is the heatsink); flat spiders cut distortion; the flared pole vent reduces port noise. Shorting rings are self-regulating inductance control, not excursion brakes: GB60 has a pole-top copper cap and a base ring (Klippel: distortion "ridiculously low"), mids and tweeters the cap only, subs no ring. Sources: CMA Networks 2021 @17:00 · DIYMA 2015-06-05 · DIYMA 2017-10-28

In plain English: The "motor" is the magnet, steel parts and voice coil that push the cone. The "suspension" is the spider (a flexible, ridged disc behind the cone) and the surround (the flexible ring at the cone's edge). His points: single-layer flat coils of copper-clad aluminum (CCA) shed heat from both sides. How close the coil sits to the steel decides power handling, and in the neodymium motor the back cup is the heatsink. Flat spiders cut distortion. A flared vent through the pole piece reduces port noise (rushing-air sounds). Shorting rings are copper or aluminum rings in the motor. He says they are self-regulating inductance control (they automatically keep the coil's inductance in check), not brakes on how far the cone moves. The GB60 has a copper cap on the pole top plus a ring at the base, and Klippel testing (a speaker measurement system) showed its distortion was "ridiculously low." GB mids and tweeters have the cap only; GB subs have no ring.

2.7 #13 · Fancy baskets don't change the sound; a custom basket buys fit.

[RARE] Basket "ringing" claims are borderline nonsense; a basket matters only if vents under the spider are too small (mechanical noise). CNC billet is a low-volume cost choice; the real gains are minimal depth, car sizes and room for a flat spider. Sources: DIYMA 2015-09-27

In plain English: The basket is the frame that holds the cone and motor. Many people believe exotic baskets sound better because ordinary ones "ring." He calls basket-ringing claims borderline nonsense. A basket affects the sound only if the vents under the spider are too small, which causes mechanical noise. Baskets machined from solid metal ("CNC billet") are a cost choice for building small quantities, not a sound upgrade. The real gains from a custom basket are fit: minimal depth, sizes that suit car openings, and room for a flat spider.

2.7 #14 · Car speakers need car-grade qualification, so Audiofrog uses a Tier-1 automotive factory.

[RARE] Tests simulate 50,000 miles: 200-hour heat/humidity cycling (90 °C to −35 °C), thermal shock, UV, 2 g vibration on two axes, drop and package tests, on passives too. Only two factories interviewed would build to that procedure; the Chinese Tier-1 chosen cost more than any other. The inside of a modern door is drier than the cabin. Sources: DIYMA 2015-07-27 · CMA Networks 2021 @46:02 · DIYMA 2020-12-25

In plain English: Parts for cars have to survive heat, cold, damp and shaking for years. He says Audiofrog's speakers are qualified like car-maker parts, with tests that simulate 50,000 miles (about 80,000 km). That means 200 hours of heat and humidity cycling from 90 °C to −35 °C (about 194 °F to −31 °F), thermal shock, UV light, vibration at 2 g (twice the force of gravity) along two axes, and drop and packaging tests. Even the passive crossovers are tested. Only two of the factories they interviewed would build to that procedure. The Chinese "Tier-1" factory they chose cost more than any other; Tier-1 means a direct supplier to car makers. He also notes that the inside of a modern door is drier than the cabin.

2.7 #15 · Speaker quality is measurable, and line-built beats hand-built.

[RARE] Quality means meeting spec every time: 100% end-of-line tests (parameters, rub and buzz, polarity, response, distortion). 2015 field data: about 0.28% failures against a 2% limit. 2021 fixes: more glue area under the surround, a positioning jig for slapping GS25 leads, leads soldered both sides. Spec-sheet red flags: missing or 1/3-octave-smoothed curves, sub curves flat to the top. Sources: DIYMA 2015-11-15 · DIYMA 2015-05-30 · DIYMA 2021-06-19

In plain English: He says speaker quality means meeting the specification every time, and that this can be measured. Every Audiofrog speaker is tested at the end of the production line. The tests cover its parameters, rub and buzz (scraping or buzzing noises), polarity (whether the cone moves the right way), frequency response and distortion. Many people assume hand-built speakers are better; he says a tested production line beats hand-building. 2015 field data showed about 0.28% failures, against a 2% limit. Fixes made in 2021: more glue area under the surround, a jig that positions the GS25's lead wires so they don't slap, and leads soldered on both sides. Red flags on a spec sheet: missing response curves, curves smoothed to 1/3 octave (which hides peaks and dips), and subwoofer curves that stay flat right to the top of the graph.

2.7 #16 · Passive crossovers are matched to their drivers; don't swap them.

[RARE] The GS610C is for GS10 + GS60/GS690, the GS410C for GS10 + GS40/GS25; GS "4 Ω" speakers measure about 2.3–2.8 Ω for factory and 2 Ω-capable amps. The (now discontinued) GB passives' L-pad kept crossover frequency, slope and Q constant over 12 dB. About 95% of GB installs run active vs 60% of GS. Sources: CMA Networks 2021 @30:06 · GB610C page

In plain English: A passive crossover is a set of coils, capacitors and resistors between the amp and the speakers that splits the sound by frequency. Each one is designed for particular drivers. The GS610C is for the GS10 tweeter with GS60 or GS690 woofers. The GS410C is for the GS10 with the GS40 or GS25. GS speakers labelled "4 Ω" (ohms, the unit of electrical resistance) actually measure about 2.3–2.8 Ω. They are designed for factory amps and for amps rated to drive 2 Ω. The GB passives, now discontinued, had an L-pad (a tweeter level control) that kept the crossover frequency, slope and Q the same across a 12 dB range. So turning the tweeter down didn't change the filter. About 95% of GB installs run active (a processor and separate amp channels instead of a passive), versus 60% of GS installs. So in practice: don't swap passives between driver sets.

2.7 #17 · Components are sold one piece at a time because dealers threw the passives away.

Many buyers go active, and he kept seeing boxes of unused passives in install bays; the G series is the all-in-one-box option for DIYers. Sources: CMA Networks 2023 @7:01 · OFCAP Ep. 19 @1:37:04

In plain English: Component speakers come as separate woofers, tweeters and passive crossovers. Audiofrog sells these one piece at a time, and he explains why. Many buyers go "active", meaning each driver gets its own amp channel and a processor does the crossover. He kept seeing boxes of unused passive crossovers sitting in install bays because dealers threw them away. For do-it-yourselfers who want everything in one box, the G series is the all-in-one option.

2.7 #18 · Audiofrog amp crossovers are 12 dB/oct for a mechanical reason.

[RARE] A 24 dB/oct pot crossover needs an 8-gang pot whose long shaft twists so sections never track; for 24 dB/oct use a DSP and disable the amp's filters (A150.4) or open them out of band (A600.1). Sources: DIYMA 2022-02-28

In plain English: Many amplifiers have a built-in crossover that you adjust with a knob, called a potentiometer or "pot." A steeper filter needs more sections, and each section needs its own layer, or "gang," on the knob. He says a 24 dB/oct crossover would need an 8-gang pot. Its long shaft twists, so the sections never track (stay matched) as you turn it. That is why Audiofrog amps use 12 dB/oct. For 24 dB/oct, use a DSP (a digital sound processor). Then switch off the amp's own filters (on the A150.4) or set them out of band, away from the frequencies in use (on the A600.1).

2.7 #19 · Woofers are designed backwards from the car, so the manual's box is the right box.

[RARE] Audiofrog starts from an in-car target curve (averaged transfer functions from about 30 cars) and a box small enough to keep the trunk, then designs the woofer to hit the target in that box. Manufacturers don't publish deliberately "safe" boxes. Sources: Absolute Electronix 2023 @9:49 · DIYMA 2021-09-04

In plain English: A woofer's box changes how it sounds. Audiofrog works backwards from the car. It starts with a target for how bass should measure inside a car, made by averaging the "transfer functions" of about 30 cars. A transfer function is how a car's cabin changes a speaker's sound, especially the bass. Then it picks a box small enough that you keep your trunk space, and designs the woofer to hit the target in that box. So the box in the manual is the right box. Many people believe a manual's box is a cautious "safe" choice. He says manufacturers don't publish deliberately "safe" boxes.

2.8 Driver engineering, ratings and failure diagnosis

What this part is about: This part covers how speaker drivers are engineered and rated, what the numbers on a spec sheet really mean, and how to work out why a speaker is misbehaving or seems to have failed.

2.8 #1 · Choose drivers by measurements, not cone material or marketing.

[RARE] He judges on- and off-axis response (0–60°), 2nd/3rd-harmonic distortion at small and large signal, and Thiele/Small parameters; buying by material is choosing shoes "based on what the cow ate". A deep cone has no more effective area (Sd) than a flat one; Sd is the cone plus about 1/3–1/2 of the surround. DSP fixes response, not a poor driver's distortion. Sources: DIYMA 2015-09-29 · DIYMA 2021-09-17 · DIYMA 2021-09-15

In plain English: Many people choose speakers by cone material (paper, plastic, metal) or by marketing. He judges them by measurements instead. He looks at frequency response straight on and off to the side (0–60 degrees). He looks at 2nd- and 3rd-harmonic distortion, which means extra tones at two and three times the note being played, at both low and high volume. And he looks at Thiele/Small parameters, a standard set of numbers describing how a driver behaves at low frequencies. Buying by material, he says, is like choosing shoes "based on what the cow ate." A deep cone pushes no more air than a flat one of the same diameter: its effective area (Sd) is no larger. Sd is the cone plus about 1/3–1/2 of the surround. A DSP (digital sound processor) can fix a driver's frequency response, but it can't fix a poor driver's distortion.

2.8 #2 · Compare Xmax only within one method.

[RARE] Audiofrog rates it as (coil height − gap height)/2 plus 15%: GB60 (20.45 − 5)/2 = 7.75, +15% ≈ "9 mm"; a reviewer's Klippel 10%-distortion method gave about 4.7 mm. Sources: Erin's Audio Corner GB60

In plain English: Xmax is how far a cone can move in one direction while still behaving cleanly. Companies measure it in different ways, so he says compare Xmax figures only when they were measured the same way. Audiofrog's rating takes the voice-coil height minus the magnetic-gap height, halves it, and adds 15%. For the GB60 that is (20.45 − 5) ÷ 2 = 7.75 mm, plus 15%, which gives about "9 mm." A reviewer who used a Klippel method (the distance at which distortion reaches 10%) got about 4.7 mm for the same driver. The difference comes from the method, not the driver.

2.8 #3 · How power ratings work: a rating is not a requirement.

[RARE] "RMS power" should be continuous average power. Audiofrog tests RMS and peak together for 100 hours with shaped noise (average = RMS rating, peaks = peak rating; GB25 at 100 W/300 W down to 200 Hz), so peak isn't invented as 2–3× RMS. A mid or tweeter rating depends on its high-pass; "3× RMS for headroom" is nonsense, and 300 W into a 100 W mid is laughable. Sources: DIYMA 2021-09-20 · CMA Networks 2021 @46:02 · DIYMA 2014-10-30

In plain English: A power rating tells you what a speaker can take, not what it needs. He says "RMS power" should really mean continuous average power. Audiofrog tests the RMS rating and the peak rating together for 100 hours, using shaped noise (a random test signal). Its average level equals the RMS rating, and its peaks reach the peak rating. For example, the GB25 is tested at 100 W average and 300 W peaks, with the signal going down to 200 Hz. So the peak figure is tested, not invented as 2–3 times the RMS figure. A midrange's or tweeter's rating depends on the high-pass filter (which keeps low notes out) used in the test. He calls the advice to buy an amp with 3× the speaker's RMS rating "for headroom" nonsense. Putting 300 W into a 100 W mid, he says, is laughable.

2.8 #4 · Phase plug or dust cap: pick by how the driver is used.

[RARE] A plug's main job is filling the hole left by removing the cap (which would resonate like a bottle); it doesn't raise the beaming frequency. Removing the cap removes its peak but costs area and sensitivity, so behind a low-pass a cap is better. Sources: DIYMA 2015-10-09

In plain English: The dust cap is the dome in the middle of a cone. A phase plug is a fixed, bullet-shaped piece that sits there instead. Many people believe a phase plug helps a driver spread high notes more widely. He says its main job is to fill the hole left when the cap is removed, because an open hole would resonate like blowing across a bottle. It doesn't raise the frequency at which the driver starts to "beam" (send its sound in a narrow forward beam). Removing the cap gets rid of the cap's peak, but it costs cone area and sensitivity. So for a driver that plays behind a low-pass filter, which cuts off the top of its range, a dust cap is the better choice.

2.8 #5 · Where driver distortion comes from, by order.

[RARE] Even-order (2nd) comes from asymmetry: a spider pushing unequally, or fringe fields differing above and below the gap. Odd-order comes from symmetric limits, mostly the coil leaving the gap. The spider dominates at and below resonance; motor distortion grows with excursion (inductance change, falling BL). Odd sounds mechanical, even masks detail; 0.2% ≈ −54 dB. Sources: DIYMA 2022-03-16 · DIYMA 2021-12-14

In plain English: Here distortion means extra tones a speaker adds that weren't in the signal. Even-order (2nd) distortion adds a tone at twice the note's frequency; odd-order (3rd and so on) adds tones at three times and other odd multiples. He traces where each comes from. Even-order comes from asymmetry, when something acts differently pushing out than pulling in. Examples are a spider that pushes unequally, or a magnetic field that differs above and below the gap (the narrow slot in the magnet where the coil sits). Odd-order comes from limits that are the same both ways, mostly the coil moving out of the gap. The spider dominates at and below the driver's resonance. Motor distortion grows as the cone moves further, because the coil's inductance changes and BL (the motor's strength) falls. To the ear, odd-order sounds mechanical and even-order masks detail. For scale, 0.2% distortion is about −54 dB: the added tones are 54 dB quieter than the music.

2.8 #6 · Break-in is the spider's resin cracking, so it matters for subs, not for correctly crossed mids and tweeters.

[RARE] The spider works mainly at and below resonance; heavy resin doping to hit Vas and Q targets is a shortcut that makes parameters drift. Big shifts mean a problem; tweeters have no spider. [Changed view (nuance): 2015 "no break-in needed" → 2017 "real, but it is the spider" → 2021 "real only for subs".] Sources: DIYMA 2015-05-30 · DIYMA 2017-07-28 · DIYMA 2021-11-01

In plain English: Many people believe new speakers must be "broken in" by playing them for hours before they sound right. His view is that what changes is the spider's resin (its stiffening coating) cracking. The spider works mainly at and below the driver's resonance (its natural low frequency). So break-in matters for subwoofers, but not for mids and tweeters crossed over correctly, which never play that low. Some makers dope spiders heavily with resin to hit target Vas and Q numbers (two of the standard low-frequency figures). He calls that a shortcut that makes the numbers drift. Big shifts mean a problem, and tweeters have no spider at all. His view shifted in nuance over time. In 2015 he said no break-in was needed. In 2017 he said it is real, but it is the spider. In 2021 he said it is real only for subs.

2.8 #7 · Dual voice coils: series or parallel changes only the load; CCA is fine in coils.

[RARE] Motor force, Q, Vas and Fs stay put because (BL)²/Re scales together; the real cost of dual coils is a wider gap (a DVC can't be single-layer). Spread tinsel leads around, don't bunch them. Coil designers want resistance, so copper-clad aluminum suits coils, unlike power wire. Sources: DIYMA 2022-03-23 · DIYMA 2015-06-16

In plain English: A dual-voice-coil (DVC) woofer has two coils. You can wire them in series (one after the other, giving twice one coil's ohms) or in parallel (side by side, giving half). He says this changes only the load the amplifier sees. The motor force, Q, Vas and Fs (the driver's main low-frequency numbers) stay the same, because the quantity that sets them, (BL)²/Re, scales together either way. BL is the motor's strength and Re is the coil's resistance. The real cost of dual coils is a wider magnetic gap, because a DVC can't be wound in a single layer. Spread the tinsel leads (the flexible wires to the coil) around; don't bunch them. Copper-clad aluminum (CCA) is fine in coils because coil designers want resistance. Power wire is different: there you want as little resistance as possible.

2.8 #8 · A narrow dip near 600 Hz that lines up with an impedance wiggle is an "edge hole", a driver flaw.

[RARE] It is the surround-to-cone joint resonating; only design changes fix it, so check for it before buying. Sources: DIYMA 2015-07-23

In plain English: On a frequency-response graph, look for a narrow dip near 600 Hz that lines up with a small wiggle on the impedance graph. He calls this an "edge hole," a flaw in the driver itself. It is caused by the joint where the surround meets the cone resonating. Only changing the driver's design fixes it, so check the published graphs for it before you buy.

2.8 #9 · Painting cones: check the solvent; cone "treatments" don't help.

Make sure the paint won't soften the adhesives; EnABL-type treatments measured worse in everything he saw. Sources: DIYMA 2015-10-27

In plain English: If you paint speaker cones, first make sure the paint's solvent won't soften the glues that hold the speaker together. Cone "treatments" such as EnABL-type patterns, applied to a cone in the hope of better sound, measured worse in every case he saw. So he says they don't help.

2.8 #10 · Diagnose pops by their sound.

[RARE] A sharp pop is probably the former hitting the backplate: stop, repeated hits destroy it. A dull thud is spider or surround bottoming: harmless, just bad-sounding. Also check the surround against the grille (2.1 #19). Sources: DIYMA 2016-05-07

In plain English: He says you can tell what is wrong from the sound of the pop. A sharp pop is probably the former (the tube the voice coil is wound on) hitting the backplate at the rear of the motor. Stop, because repeated hits destroy the speaker. A dull thud is the spider or surround reaching the end of its travel ("bottoming"). That is harmless, but it sounds bad. Also check that the surround isn't hitting the grille (see point 2.1 #19).

2.8 #11 · Most "blown" mids and "crackling" tweeters are DSP clipping: check the signal chain first.

[RARE] About 70% of GB25 warranty claims were DSP input clipping, 25% broken terminal screws; returned "crackling" units measure perfect. Tweeter crackle when the sub is turned up is digital clipping. If distortion persists with the volume down, check the source (streams and phone levelers clip). Compare two tweeters' DC resistance with a meter. Sources: DIYMA 2022-03-13 · DIYMA 2021-11-14 · Absolute Electronix 2023 @36:46

In plain English: He says most midranges returned as "blown" and tweeters reported as "crackling" are fine. The real cause is usually clipping in the DSP. Clipping happens when a signal is pushed past the most a device can handle, so its peaks get chopped off and it sounds harsh. About 70% of GB25 warranty claims were DSP input clipping, and 25% were broken terminal screws. Returned "crackling" units measure perfect. If the tweeters crackle when you turn the sub up, that is digital clipping. If the distortion stays even with the volume turned down, check the source: streaming services and phone volume "levelers" clip. Use a meter to compare the two tweeters' DC resistance (the basic resistance a multimeter reads). So in practice: check the signal chain before blaming the speakers.

2.8 #12 · Fix the car before tuning it, and hunt the one real fault.

[RARE] Untunable cars he sees: tweeters left in the dash behind new on-axis mid pods, a midbass wired out of phase "on advice", a split passive. Messy wiring usually isn't the problem; one thing is (a full-rewire bet ended with a broken terminal found in five minutes). GB passives have no polyfuse, so cut-outs mean amp protection or a loose connection. Sources: OFCAP Ep. 19 @1:56:02 · OFCAP Ep. 19 @1:58:00 · DIYMA 2017-07-12

In plain English: "Tuning" means adjusting the processor's settings. He says fix the installation before you tune. Cars he has seen that couldn't be tuned had tweeters left in the dash behind new mid pods aimed at the listener ("on-axis"), a midbass wired out of phase (backwards) "on advice," or a split passive crossover (the notes don't spell out exactly what was done to it). Messy wiring is usually not the problem; one specific fault is. He once made installers a bet over whether a full rewire would fix a car. It ended when a broken speaker terminal was found in five minutes. GB passive crossovers have no polyfuse (a self-resetting fuse that cuts the sound when overloaded). So if a GB system cuts out, suspect the amp's protection circuit or a loose connection.

2.8 #13 · A customer who keeps blowing speakers may be boosting bass at the head unit.

[RARE] His case: a disco fan (bass-light 1970s mixes) with no sub-level control boosted bass about 12 dB past clipping, burning tweeters and effectively cancelling the midbass high-pass. Fix: raise the crossover, set it up like pro sound, give up front bass he didn't care about. Sources: CMA Connected Oct 2021 @43:34

In plain English: His case is a disco fan whose 1970s recordings are light on bass. His system had no control to raise the sub level, so he boosted bass at the head unit (the car's radio or source unit) by about 12 dB, past the point of clipping. That burned out tweeters and, in effect, cancelled the high-pass filter that was keeping deep bass out of the midbass speakers. The fix was to raise the crossover point and set the system up the way pro sound systems are set up. That meant giving up "front bass" (bass that seems to come from in front of you), which this customer didn't care about.

2.8 #14 · Don't buy used drivers online; Audiofrog speakers can't be reconed.

A stripped terminal screw may be fixable; "maybe you can have it fixed" means walk away. Sources: DIYMA 2020-07-01

In plain English: He advises against buying used drivers online, and Audiofrog speakers can't be reconed (rebuilt with a replacement cone and coil kit). A stripped terminal screw may be fixable. But if a seller says "maybe you can have it fixed," walk away.

2.9 Tweeter protection

What this part is about: Tweeters are the small speakers that play the highest notes, and they are the easiest to damage. This part covers how he says to protect them: protection capacitors, safe crossover settings, and the real reasons tweeters fail.

2.9 #1 · Put a series capacitor on tweeters even in active systems: a "parking brake".

[RARE] Turn-on pops, a cratering amp, engine noise or a wrong DSP entry can send bass straight to a tweeter, whose coil is about 1/32" long. Example: 68 µF for a 4 Ω tweeter; a $1.75 non-polar electrolytic is fine, since the cap acts below the passband (a 24 dB/oct 2.5 kHz filter is already −48 dB near 600 Hz). Sources: Audiofrog blog Dec 2020 · DIYMA 2015-10-04 · DIYMA 2018-05-04

In plain English: In an "active" system, each driver has its own amp channel and a processor does the crossover, so many people put nothing between the amp and the tweeter. He recommends a capacitor in series with the tweeter anyway, as a "parking brake." A capacitor in series blocks low frequencies and lets highs through. Several things can send bass straight to a tweeter: turn-on pops, an amp that fails ("cratering"), engine noise, or a wrong number typed into the DSP. A tweeter's voice coil is only about 1/32 inch (under 1 mm) long. His example is 68 µF (microfarads, the unit of capacitor size) for a 4 Ω tweeter. A $1.75 non-polar electrolytic capacitor is fine, because the cap acts only below the tweeter's working range, where the crossover has already turned the signal far down. A 24 dB/oct filter at 2.5 kHz is already 48 dB down near 600 Hz.

2.9 #2 · How big a protection cap: the documents differ.

[Conflict: Tuning PDF v1 (~2018) puts −3 dB about an octave below the tweeter's Fs; the amp manual (c. 2022, COMPANY) says 50 µF plus a resistor, about an octave below the crossover; Tuning PDF v2 (2023) drops the step and relies on LR4.] Sources: Tuning PDF v1 (~2018) · A-Series amplifier manual · Tuning PDF v2 (2023)

In plain English: This point carries a [Conflict] tag: Audiofrog's documents give different rules for sizing the protection cap. Tuning PDF v1 (about 2018) says to choose a cap whose −3 dB point is about one octave (half the frequency) below the tweeter's Fs. The −3 dB point is where the signal has been turned down by 3 dB, and Fs is the tweeter's resonance frequency. The amplifier manual (around 2022, a company document) says 50 µF plus a resistor, about an octave below the crossover. Tuning PDF v2 (2023) drops the step altogether and relies on the LR4 crossover filter. LR4 is a common 24 dB/oct filter type (Linkwitz-Riley, 4th order). The point simply records the three versions without settling which is right.

2.9 #3 · Turn-on pops through a protection cap: add a resistor across it.

[RARE] Amps built on the IR2092 class-D driver chip have a small, unremovable DC offset at turn-on/off; a 10 Ω resistor in parallel with the cap cures the pop (Audiofrog added one to its protectors). Sources: DIYMA 2022-03-16 · DIYMA 2021-07-06

In plain English: Some amplifiers "pop" when switched on or off, and the pop can come through a tweeter even with a protection cap. He says amps built on the IR2092 class-D driver chip have a small DC offset at turn-on and turn-off that can't be removed. Class-D is an efficient amplifier design, and a DC offset is a small steady voltage. A 10 Ω resistor wired in parallel with the cap (across its two ends) cures the pop. Audiofrog added such a resistor to its own tweeter protectors.

2.9 #4 · Remove the protection cap when the tweeter goes back on a passive crossover.

[RARE] It sits in series with the network's capacitor (series caps combine as 1/(1/C1 + 1/C2)), changing order, slope and Q: it "wacks out" the crossover. Sources: DIYMA 2021-09-22

In plain English: If you switch from active back to a passive crossover, take the protection cap out. The passive network already has its own capacitor in the tweeter's path. Two capacitors in series combine into a smaller value, given by 1/(1/C1 + 1/C2). That changes the crossover's order, slope and Q (how sharply it bends), so it "wacks out" the crossover.

2.9 #5 · A protector (TP-50) guards against faults below the crossover, not too much power above it.

About 15 dB of low-frequency attenuation with no effect in band; it can't stop bad gain setting, an oversized amp or clipping's extra treble, and isn't needed with passives. Wire amp → protector → tweeter. (COMPANY.) Sources: TP-50V2 page

In plain English: The TP-50 is Audiofrog's tweeter protector, and this point comes from the company's product page. It cuts low frequencies by about 15 dB, which guards against faults below the crossover point, and has no effect within the tweeter's working range. It can't protect against badly set gains, an oversized amp, or the extra treble that clipping creates. It isn't needed with passive crossovers. Wire it amp → protector → tweeter.

2.9 #6 · Playing at or below Fs is dangerous only for tweeters.

Their only suspension is the surround, so excess excursion destroys them; other drivers just distort. Sources: DIYMA 2015-06-05

In plain English: Fs is a driver's resonance frequency, where it vibrates most easily. He says playing at or below Fs is dangerous only for tweeters. A tweeter's only suspension is its surround, so too much movement destroys it. Other drivers just distort.

2.9 #7 · Tweeter high-pass: about 2× Fs, steep, never lower "because the slope is steep".

GB10: 2.2 kHz or higher at 24 dB/oct, or 2.5 kHz at 12 dB/oct or more; GB tweeters without the passive: 2.5 kHz LR4 or about 3 kHz with shallower slopes; GB10OE 2.5 kHz and GS10OE 3.5 kHz LR4; GB10CF 2 kHz LR4. Sources: OFCAP Ep. 19 @1:44:09 · DIYMA 2017-10-29 · DIYMA 2021-12-15

In plain English: The high-pass filter decides how low a tweeter is asked to play (kHz means thousands of vibrations per second). His rule: about twice the tweeter's Fs, with a steep slope. Never set it lower just because the slope is steep. His settings: GB10 at 2.2 kHz or higher at 24 dB/oct, or 2.5 kHz at 12 dB/oct or steeper. GB tweeters without their passive: 2.5 kHz LR4 (a standard 24 dB/oct filter), or about 3 kHz with shallower slopes. GB10OE at 2.5 kHz and GS10OE at 3.5 kHz, both LR4. GB10CF at 2 kHz LR4.

2.9 #8 · Do steeper slopes protect better?

[Conflict: his Oct 2021 blog says steeper slopes don't protect better and crossing lower because the slope is steeper is "a BIG mistake"; his DIYMA posts (2020–21) say LR4 gives high-passed drivers the most protection, "greater even than" 48 dB/oct, without derivation.] Practical reading: use LR4 at a safe frequency. Sources: Audiofrog blog Oct 2021 · DIYMA 2020-10-03 · DIYMA 2021-09-27

In plain English: This point records a [Conflict] between two things he wrote. In an October 2021 blog post, he said steeper slopes don't protect better, and that crossing lower because the slope is steeper is "a BIG mistake." In forum posts from 2020–21, he said LR4 (a 24 dB/oct filter type) gives high-passed drivers the most protection, "greater even than" a 48 dB/oct filter, without explaining why. A high-passed driver is one with a filter keeping low notes out. The point's own practical reading is: use LR4, set at a safe frequency.

2.9 #9 · Tweeters die from excess high-frequency power, not from "too little power".

[RARE] A tweeter gets about a watt; with pink-noise-shaped music, a "20 W" setting gives about 0.16 W at 2.5 kHz and 0.02 W at 20 kHz, so a 200 W amp at full output can kill a passive's tweeter without clipping. Clipping toward a square wave doubles average power, all added as treble; class-D sub amps' output filters spare subs, nothing spares tweeters. Sources: DIYMA 2020-10-14 · DIYMA 2021-07-01 · OFCAP Ep. 19 @27:00

In plain English: Many people believe tweeters are killed by "too little power," meaning a small amp that clips. He says tweeters die from too much high-frequency power. A tweeter gets about a watt. Music has far less energy in the treble than in the bass, and he models this with pink noise, a standard test signal that gets weaker as pitch rises. On his numbers, if an amp is set to "20 W," the tweeter's range gets about 0.16 W at 2.5 kHz and 0.02 W at 20 kHz. So a 200 W amp at full output can kill the tweeter of a passive set without clipping at all. When an amp clips, its output flattens toward a square wave. That doubles the average power, and all of the extra is treble. Output filters in class-D sub amps spare subwoofers from this, but nothing spares tweeters.

2.9 #10 · Disconnect tweeters and small mids before setting gains with sine waves: "Never, under any circumstances."

[RARE] A "100 W" tweeter is rated for its share of a spectrum calibrated at 100 W at 20 Hz, not 100 W continuous; a 0 dB or −10 dB sine track with tweeters connected is the classic killer. Sources: A-Series amplifier manual · DIYMA 2020-12-23

In plain English: A sine wave is a pure, steady test tone, and installers often use one to set amp gains (the amp's input level control). He says to disconnect tweeters and small mids first: "Never, under any circumstances" leave them connected. A tweeter labelled "100 W" is rated for its share of a music-like spectrum calibrated to 100 W at 20 Hz. That share is far less than 100 W, and it is not 100 W of continuous tone. Playing a 0 dB or −10 dB sine track (a full-level or near-full-level tone) with tweeters connected is the classic way to kill them.

2.10 Wiring, termination, polarity and noise

What this part is about: This part covers the wiring side of a system. It explains how to join wires to speakers so the joints last, how to size and fuse power wiring, how to check that every speaker is wired the right way round, and how to track down noise such as engine whine and hiss.

2.10 #1 · Crimp, don't solder, wire-to-terminal joints, and crimp ferrules with the proper die.

[RARE] Solder can wick up and stiffen tinsel leads, and on GS speakers heat melts the plastic and flows the terminal's joint off the internal PCB (not covered by warranty). Solder terminal to board, crimp wire to terminal; spade lugs last decades. "Cinch terminals are not crimpers": don't let a screw crush a heat-shrunk ferrule. Sources: DIYMA 2021-07-21 · Audiofrog blog Dec 2020 · CMA Networks 2021 @42:00

In plain English: Crimping means squeezing a metal connector tightly onto a wire with a special tool. Many people believe solder always makes the best joint. For wire-to-terminal joints, he says crimp instead. Solder can wick (soak) up the strands and stiffen the tinsel leads (the flexible wires that run to the coil). On GS speakers, soldering heat melts the plastic and makes the terminal's joint flow off the circuit board inside, which the warranty doesn't cover. His rule: solder the terminal to the board, and crimp the wire to the terminal. Spade lugs (flat crimp connectors) last decades. Crimp ferrules (metal sleeves over a wire end) with the proper die, which is the shaped jaw of the crimping tool. "Cinch terminals are not crimpers": don't let a terminal's clamping screw crush a heat-shrunk ferrule into place.

2.10 #2 · GB terminal recipe: 16 AWG, strip about 1/4 in, don't tin, push the wire in while backing the screw out, then snug.

[RARE] Tinning makes the wire solid so the clamp grips less; under-stripping tempts overtightening. Done right you can swing the speaker by its wires. Don't drill a stripped set screw (shavings reach the gap). Sources: DIYMA 2021-12-18 · DIYMA 2018-06-24

In plain English: GB speakers have screw-clamp terminals, and this is his method for them. Use 16 AWG wire. AWG is the wire-size scale, where smaller numbers mean thicker wire; 16 AWG is about 1.3 mm across. Strip about 1/4 inch (about 6 mm) of insulation. Don't tin it, which means coating the bare strands with solder. Push the wire in while backing the screw out, then snug the screw. Tinning makes the wire solid, so the clamp grips it less, and stripping too little tempts you to overtighten. Done right, you can swing the speaker by its wires. If a set screw strips, don't drill it out, because shavings reach the gap (the slot in the magnet where the coil moves).

2.10 #3 · Power wiring: size it from real music power, fuse near the battery, test grounds by voltage drop.

[RARE] Music's average power is a small fraction of peak, so gauge "requirements" from fuse ratings overstate it (a GB active system didn't need 0-gauge), and a short ground run can be thinner. Scrape to bare metal; 60 A fuse within 18" of the battery (COMPANY manual). Check grounds with the battery connected by measuring voltage drop; an ohmmeter can't read a live circuit. Sources: DIYMA 2021-12-22 · A-Series amplifier manual · DIYMA 2021-07-27

In plain English: Power wire runs from the battery to the amplifier. He says size it from the power music really uses. Music's average power is a small fraction of its peaks, so wire "requirements" worked out from fuse ratings overstate what you need. A GB active system he discussed didn't need 0-gauge wire, which is very thick cable, and a short ground wire can be thinner. Scrape the ground point to bare metal. The company's amp manual says to fit a 60 A fuse within 18 inches (about 46 cm) of the battery. Check grounds with the battery connected, by measuring voltage drop: the voltage lost across a connection while current flows. An ohmmeter (a resistance meter) can't read a live circuit.

2.10 #4 · Big 3 and stiffening caps: crimp, don't solder, and skip the farad cap.

Solder near the battery invites corrosion, so crimp Big 3 joints with the right tool; a 2-farad capacitor is unnecessary at 1,000 W. He never said whether a Big 3 upgrade itself is needed. Sources: DIYMA 2021-11-26 · DIYMA 2021-08-02

In plain English: The "Big 3" is a common upgrade to the car's three main charging-system cables. He says crimp Big 3 joints with the right tool rather than soldering them, because solder near the battery invites corrosion. A stiffening capacitor is a large capacitor wired near the amp, here 2 farads. He says one is unnecessary at 1,000 W. He never said whether the Big 3 upgrade itself is needed.

2.10 #5 · Verify every driver's polarity, but don't trust a pulse checker on midbass.

Pulses are too short for low-passed drivers and can't flag an all-pass-filtered factory channel. Mute the others and use band-limited tracks, or play a DC-offset track and read the voltage at the leads with a meter. Sub polarity markings are almost never wrong (3 of ~4,000 on reversible terminals). Sources: DIYMA 2015-06-30 · Audiofrog blog Aug 2021 · DIYMA 2018-04-07

In plain English: Polarity means a speaker's + and − are connected the right way round, so its cone moves out when it should. He says to check every driver's polarity, but not to trust a pulse-type polarity checker on midbass. The pulses are too short for drivers behind a low-pass filter. They also can't flag a factory channel that has an all-pass filter, which shifts the timing of the sound without changing its tone. Instead, mute the other speakers and use band-limited test tracks (tracks covering only that driver's range). Or play a DC-offset track and read the voltage at the speaker leads with a meter. Subwoofer polarity markings are almost never wrong: 3 out of about 4,000 on reversible terminals.

2.10 #6 · Some "reversed" mids are correct: baffle placement and crossover order can require it.

[RARE] 1st-, 2nd- and 3rd-order slopes shift phase 90°, 180° and 270°, so a passive that inverts a mid "isn't a mistake"; check the summed response before "fixing" it (unlike flipping one side to center vocals, which he forbids). Sources: Audiofrog blog Aug 2021

In plain English: Crossover filters shift phase, which is the timing of a wave within its cycle. He says 1st-, 2nd- and 3rd-order slopes (6, 12 and 18 dB/oct) shift phase by 90°, 180° and 270°. So a passive crossover that connects a mid reversed "isn't a mistake," and where the drivers sit on the baffle can require it too. Measure how the drivers add up together (the summed response) before you "fix" it. That is different from flipping one side's polarity to pull the vocals into the center, which he forbids.

2.10 #7 · Match signal cable to the amp's input: ohm the RCA shield to power ground first.

[RARE] Near 0 Ω means single-ended (use coax or an LOC); hundreds of ohms or more means differential (use twisted pair, or the head unit's balanced speaker outputs). Twisted pair into single-ended, or coax into differential, lets noise through. Heavy-gauge RCAs are useless; the old "power and signal on opposite sides" rule predates module-filled cars. Sources: DIYMA 2021-09-17 · CMA Networks 2022 @49:00 · DIYMA 2021-07-10

In plain English: Amp inputs come in two kinds. "Single-ended" is the classic RCA input, where one signal wire sits inside a shield that is also the ground. "Differential" uses two signal wires, and the amp responds only to the difference between them, which rejects noise. To tell which your amp has, use an ohmmeter between its RCA shield and its power ground. Near 0 Ω means single-ended: use coaxial RCA cable, or an LOC (line-output converter, which turns speaker-level signals into RCA-level ones). Hundreds of ohms or more means differential: use twisted pair, or the head unit's balanced speaker outputs. Twisted pair into a single-ended input, or coax into a differential one, lets noise through. Heavy-gauge RCAs are useless. The old rule of running power and signal wires down opposite sides of the car predates modern cars full of electronic modules.

2.10 #8 · Engine noise: regrounding rarely fixes it now; inputs do.

[RARE] Ohm the head unit's RCA shields to each other and chassis, then the amp's to its power ground; if all are grounded the system is built to loop, and only an isolator (or removing the single-ended unit) fixes it. Star grounding dates from all-single-ended days. Avoid single-ended-input amps whatever their heatsinks. Sources: DIYMA 2015-04-18 · DIYMA 2021-11-03

In plain English: Engine noise is a whine that rises and falls with engine speed. Many people believe the cure is regrounding, for example "star grounding," where all grounds meet at one point. He says regrounding rarely fixes it now; the inputs do. Use an ohmmeter to check the head unit's RCA shields against each other and against the chassis, then the amp's RCA shields against its power ground. If they are all grounded, the system is built to form a ground loop, a noise path created by grounds at several points. Then only an isolator (a device that breaks the loop) fixes it, or removing the single-ended unit. Star grounding dates from the days when everything was single-ended. He says to avoid amps with single-ended inputs, whatever their heatsinks look like.

2.10 #9 · Hiss is not a ground loop (loops whine); find the source before buying fixes.

[RARE] Unplug the inputs: hiss that remains and drops with gain is the amp (DSP amps are inherently hissier); hiss rising with head-unit volume is the head unit. Cure tweeter hiss by lowering that amp's gain and boosting in the DSP, not with series resistors. Sources: DIYMA 2015-09-16 · DIYMA 2021-10-14

In plain English: Hiss is a steady "shhh"; a ground loop makes a whine. He says hiss is not a ground loop, so find where it comes from before buying fixes. Unplug the amp's inputs. If the hiss remains and drops when you turn the amp's gain down, it comes from the amp, and amps with built-in DSP are inherently hissier. If the hiss rises as you turn up the head unit's volume, it comes from the head unit. To cure tweeter hiss, lower that amp's gain and boost the level in the DSP, rather than adding series resistors.

2.10 #10 · Noise in one door or only at high excursion: check leads touching metal, then move the passive.

Tinsel or tweeter leads, or a metal frame, touching body metal cause noise; passive crossovers near noisy electronics pick up radiated noise at low volume. Sources: DIYMA 2015-12-27 · DIYMA 2022-01-02 · DIYMA 2021-08-26

In plain English: If you hear noise in only one door, or only when the speaker moves a lot, he says first check for wires touching metal. Tinsel leads or tweeter wires, or a speaker's metal frame, touching the car's body metal can cause noise. A passive crossover mounted near noisy electronics can pick up radiated noise (interference through the air), heard at low volume. Moving the passive away cures that.

2.10 #11 · Class-D amps: shield them from the FM tuner, and know the output filter reacts to the load.

[RARE] A class-D output filter is designed for one load, so a 2 Ω load rolls off the top and a rising-impedance tweeter can peak near 20 kHz; Audiofrog's A-series moves it to 40 kHz, matched to its tweeters (flat to almost 30 kHz). Its case and one PCB layer are ground shields, and quiet layout keeps transformer fields from the preamp. Sources: CMA Networks 2022 @35:07 · Absolute Electronix 2023 @29:58 · Audiofrog amplifiers page

In plain English: Class-D amplifiers are efficient amps that switch on and off very fast, and they need an output filter to remove that switching. He makes two points. First, they need shielding from the FM radio tuner. Second, the output filter is designed for one load, so a 2 Ω load rolls off the top end. A tweeter, whose impedance rises at high frequencies, can show a peak near 20 kHz. Audiofrog's A-series amps move that filter up to 40 kHz, matched to its tweeters, which play flat to almost 30 kHz. The amp's case and one layer of its circuit board act as ground shields. A quiet circuit layout keeps the transformer's magnetic fields away from the preamp (the low-level input stage).

2.10 #12 · Some factory amps need a load: check before condemning one.

[RARE] Many OE amps shut down without a speaker load (to protect their output filter); A-series speaker inputs take up to 30 V peak with no built-in load resistor, so some cars need one. Measure the OE output with and without a load first. Sources: DIYMA 2015-04-03 · CMA Networks 2022 @16:01

In plain English: Many factory (OE) amplifiers shut down when no speaker is connected, to protect their output filter. Audiofrog's A-series amps can take the factory speaker wires directly, up to 30 V peak. But they have no built-in load resistor, a resistor that stands in for a speaker, so some cars need one added. Before you decide a factory amp is faulty, measure its output with and without a load.

2.10 #13 · Feed a mono sub amp from one left and one right DSP channel.

[RARE] Then you can tune the whole right side including the sub, then the whole left, which makes bass and midbass much easier to get right. Sources: DIYMA 2021-08-22

In plain English: A mono sub amp has a single channel. He says to feed it from two DSP channels, one left and one right, rather than from one. Then you can tune the whole right side including the sub, then the whole left side. That makes bass and midbass much easier to get right.

2.11 Top rarely-discussed points in this section

With any high-pass, a door midbass needs a sealed baffle, not a door box; tiny sealed boxes are "bass prevention" (2.1 #1, #2).
Pull out foam cup baffles; foam rings belong on the bracket and only stop rattles (2.1 #6, #7).
The door-plus-corner gain is why a car midbass should be flat and low-Q (2.1 #8, #9).
Cross door midbass near 80 Hz and the sub near 60 Hz; 40 Hz midbass wears out the spider and makes a car untunable (2.1 #10).
Midbass "punch" lives at 1–4 kHz, not in a bigger woofer (2.1 #13).
Leave clearance beyond Xmax: the cone travels through the top-plate thickness too (keep grilles about 1.25 in off a woofer) (2.1 #19).
A flat +6 dB with the door trim off is the car's door-switch volume cut, not the panel (2.1 #22).
Absorbing a 200 Hz reflection takes about 1.5 ft of material; a 250 Hz peak is usually a reflection, so test with a tone before deadening (2.2 #2, #3).
Quiet tires were his best midbass upgrade, and rattles pull the bass image backward (2.2 #4, #7).
Measure the distance to the nearest surface before building: it sets the reflection null (6" ≈ 500 Hz; a pod a foot off the pillar corner ≈ a 250 Hz hole) (2.3 #1, #3).
A small dash mid aimed at a raked windshield is a "poor man's tweeter"; cut the dash's free low-end gain instead of boosting the top (2.3 #8, #9).
Choose locations by acoustic reciprocity: speaker at the driver's head, mic at each candidate spot (2.3 #13).
A leaky pod "rattles"; an impedance sweep shows the leak, and at 200 Hz LR4 a small mid barely cares how small its box is (2.4 #2–#4).
The 6" + 1" door 2-way has an off-axis hole no EQ fixes; studio monitors get away with 2-ways only because of the room (2.6 #2).
In actively crossed factory systems, keep the factory processing and go one-to-one rather than "flattening" the signal (2.6 #15).
Most "blown" mids and "crackling" tweeters are DSP clipping, not bad drivers (2.8 #11).
Tweeters die from excess treble power (clipping, big amps, sine-wave gain setting), never from "too little power" (2.9 #9, #10).
Ohm the RCA shield to pick the right cable; regrounding rarely cures modern engine noise (2.10 #7, #8).

Changed views and conflicts in this section

8" door woofers (2.1 #15): in 2016 Audiofrog would make no 8" and offered the GS690 6×9; the shallow GS8ND2 followed in 2020, framed as a woofer crossed at about 300 Hz, not a midrange.
Dash-top center (2.3 #11): a "frequency response nightmare" in 2010 that still raised the stage, and already his preferred center in the MS-8 FAQ (2011 or earlier; 1.10 #5); by 2021 he advised mounting it as close to the windshield–dash junction as possible, calling its 2 kHz dip helpful. A softening, not a full reversal.
Windshield reflections (2.3 #9): the GS25 deliberately uses the windshield as its tweeter, while his custom door 3-way (2.6 #6) minimizes windshield reflections. An apparent conflict only: one is a factory-location strategy, the other a custom build.
Tweeter aiming (2.5 #7): Harman-era swivel tweeter patent (filed 1997) and a JBL/Infinity tip sheet favouring crossfired pillar tweeters, versus his 2011–2021 advice to use sails and aim only the tweeter, a little.
Protection-cap size (2.9 #2): an octave below the tweeter's Fs (Tuning PDF v1), 50 µF plus a resistor about an octave below the crossover (amp manual), then no cap step at all (Tuning PDF v2).
Do steeper slopes protect? (2.9 #8): his 2021 blog says no; his 2020–21 DIYMA posts say LR4 protects most, even more than 48 dB/oct. Unresolved in his own material.
Tweeter high-pass numbers (2.9 #7): 1.5–2× Fs, about 2× Fs, 2.2 kHz, 2.5 kHz and 3–3.5 kHz appear in different documents; all are well above Fs with steep slopes.
Break-in (2.8 #6): 2015 "no break-in needed" → 2017 "real, but it is the spider, below resonance" → 2021 "real only for subs". A refinement rather than a reversal.
Door boxes (2.1 #1): consistent from 2008 to 2016 (no box with a high-pass; if you build one, size it like a sub box and expect only rattle control).
Era notes: the GB passive crossovers are now listed as discontinued (2.7 #16); MS-8 settings (2.6 #14) are Harman-era.

The full series

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