Car Audio Explained, Part 5: Pods, Tweeter Mounting and Choosing Drivers (Andy Wehmeyer's Lessons)

4 days ago

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This is Part 5 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.

2.4 Pods, back volumes and fabrication

What this part is about: A "pod" is a small custom housing that holds a speaker somewhere the car didn't provide a spot, often on the windshield pillars. This part covers how much air a speaker needs behind it, how to seal and test a pod, practical building methods (grilles, 3D printing, upholstery, cutting holes), and how much custom fabrication is actually worth doing.

2.4 #1 · A pod is an enclosure: size the box to the driver, not the biggest driver to the pillar.

[RARE] An IB-type driver crammed into a pod no bigger than its basket becomes a high-Q mid with no bass and an untamable peak, and a "distortion machine" at its raised resonance, so people cross it low and make it worse. "Put the biggest speaker possible up there" is too simple to be useful. Sources: DIYMA 2013-12-14 · DIYMA 2017-10-01 · DIYMA 2021-11-19

In plain English: Some background first. A speaker's moving part, the cone, has a natural "resonance": a frequency where it vibrates most easily. Air sealed in a small box acts like a spring on the cone and pushes that resonance up. "Q" describes how peaky the response is around resonance; high Q means a sharper hump. An "IB" (infinite baffle) driver is one designed to work with a very large or open air space behind it, such as a door or trunk. His point is that a pod is a box, so it changes the speaker. Squeeze an IB-type driver into a pod barely bigger than its frame and it loses its bass, gains a peak you can't tame, and distorts heavily around its new, higher resonance. People then set the crossover low to get more out of it, which feeds it exactly the frequencies where it is worst. Many people believe "put the biggest speaker possible up there"; he says that advice is too simple to be useful. Pick a driver that suits the box you can actually fit.

2.4 #2 · High-passed at about 200 Hz LR4, a small mid barely cares what box it is in; open-back is often best.

[RARE] Modeled GB25 responses in IB, 0.25 L and the smallest box that covers its back (about 0.162 L) were nearly identical, so venting into the pillar is optional. Its 2015 brief: reach 200 Hz in 0.004 ft³ while taking 100 W RMS / 300 W peak, because "0.5 cubic foot pods look ridiculous on A-pillars". The GB40 wants IB or at least 1 L. A mid crossed above resonance is usually better with no box at all (Fs is always below Fc), given a big enough baffle. Sources: DIYMA 2017-07-02 · DIYMA 2015-05-08 · DIYMA 2021-11-19

In plain English: A high-pass filter lets only frequencies above a set point reach a speaker. "LR4" (Linkwitz-Riley, 4th order) is a common steep filter that cuts 24 dB per octave. The GB25 is Audiofrog's 2.5" (63 mm) midrange; the GB40 is a 4". A liter is roughly a quart, and 0.004 ft³ is about 0.11 liters, which is tiny. His point: once a small mid only plays above about 200 Hz, the box hardly matters. His models of the GB25 with no box (IB), in 0.25 L, and in the smallest box that covers its back (about 0.162 L) came out nearly identical, so letting it breathe into the pillar is optional. Its design brief, as he described it in 2015, was to reach 200 Hz in that tiny space while handling 100 W continuous and 300 W peaks, because pods of 0.5 cubic foot (about 14 liters) look ridiculous on A-pillars. The larger GB40 needs IB or at least 1 liter. The bracket note means: a speaker's resonance with no box (Fs) is always lower than in a sealed box (Fc), so a mid crossed above resonance is usually better with no box at all, as long as the panel it sits in (the baffle) is big enough.

2.4 #3 · Seal and gasket every pod: a small air leak "rattles".

[RARE] A customer's GB25 buzzed only in its pod (bumps, voids, no gasket), and a respected installer blamed the speaker. Kill leaks and openings that let front and back mix, use the supplied foam gasket on a flat baffle, and mount small mids in something sturdy or damped, since they shake at high levels. Sources: DIYMA 2022-03-01 · DIYMA 2022-03-16

In plain English: A gasket is a soft seal, here foam, between a speaker's frame and the surface it mounts on. The front and back of a cone push out opposite sound waves; where they meet through a gap they partly cancel, and air forced through a small gap can buzz. His story: a customer's GB25 buzzed only when it was in its pod. The pod had bumps, voids and no gasket, yet a respected installer blamed the speaker. His point is that a small air leak can sound just like a rattling speaker. So in practice: close every leak or opening that lets front and back sound mix, use the foam gasket supplied with the speaker on a flat mounting surface, and mount small mids in something sturdy or damped, because they shake when played loud.

2.4 #4 · Check a pod with an impedance sweep, and measure the in-pod resonance before choosing a crossover.

[RARE] A leak shows as an extra, port-like resonance ("An enclosure has to actually be an enclosure"); the pod's real volume is Vb = Vas / ((Qtc/Qts)² − 1). Without a DATS, put a multimeter on current in series with the speaker and play a slow, quiet sine sweep: minimum current marks Fs (or Fc in a box). Sources: DIYMA 2022-03-01 · DIYMA 2021-08-26

In plain English: Impedance is how hard a speaker resists the amplifier's signal, and it changes with frequency, peaking at the speaker's resonance. An "impedance sweep" measures it across the frequency range; DATS is a popular tester that does this. His point: a leaky pod shows an extra resonance, like the vent (port) of a ported box. As he puts it, "An enclosure has to actually be an enclosure." The formula lets you work out the pod's real air volume (Vb) from two figures on the speaker's data sheet (Vas and Qts) and the Q you measure in the box (Qtc). Measure the resonance in the pod before you pick a crossover point. With no DATS, set a multimeter to measure current, wire it in series (in line) with the speaker so all the current passes through it, and play a slow, quiet sine sweep, a pure tone gliding through the frequencies. Where the current is lowest is the resonance: Fs for a bare speaker, Fc in a box. That works because impedance is highest at resonance, so the least current flows there.

2.4 #5 · His recipe for a factory-looking recessed grille in a plastic door panel.

[RARE] Tape the outline; drill a ¼" pilot ¼" inside it; cut from behind with a carbide burr ⅛" inside; file to the line. Clamp matching perforated plastic grille stock between two 12" MDF plates, heat with a heat gun about a foot away (edges more than center) until it sags, press in a rounded MDF plug (hole size minus grille thickness plus 1/16–1/8"), let it cool. Sources: DIYMA 2012-09-08

In plain English: This is his step-by-step method for adding a speaker grille to a plastic door panel so it looks factory-made. MDF is medium-density fiberboard; a carbide burr is a hard cutting bit for a rotary tool; grille stock is plastic sheet full of small holes. Step by step: (1) mark the outline of the opening with tape; (2) drill a ¼" (about 6 mm) starter hole ¼" inside that line; (3) working from the back of the panel, cut out the opening with the burr, staying ⅛" (about 3 mm) inside the line; (4) file the edge out to the line for a clean finish. For the grille itself: (5) clamp perforated plastic that matches the factory grilles between two 12" (about 300 mm) MDF plates, each with a matching hole; (6) warm it with a heat gun held about a foot (30 cm) away, heating the edges more than the middle, until the plastic sags; (7) press in a round-edged MDF plug, sized to the hole minus the grille's thickness plus 1/16–1/8" (about 1.5–3 mm), and let it cool. The plastic sets in a dish shape, giving a recessed grille.

2.4 #6 · 3D-printed parts: design for the process and for cabin heat.

[RARE] If a vinyl-wrapped pod can't be covered, the design is wrong. FDM can't print 1.5 mm holes on 2 mm centers; resin can. Print a grille with its ring (separate thin grilles warp). A part fitted on a 90 °F day warped 1/16–1/8" between bolts: check heat-deflection temperature (about 105 °C for "automotive" resin), blend a flexible resin with brittle high-temp resin, and use glued-in studs, not screws into bosses. PLA's ~88 °C rating is not a 3-lb speaker hanging on four screws. Sources: OFCAP Ep. 38 @15:08 · DIYMA 2021-07-02

In plain English: 3D printers come in two common kinds. FDM printers lay down melted plastic strands; resin printers harden liquid resin with light and can print finer detail. "Heat-deflection temperature" is the point at which a plastic starts to bend under load. PLA is a common, cheap printing plastic. "Bosses" are the raised posts that screws go into. His points: if a pod you plan to wrap in vinyl can't be covered, the design is wrong. FDM can't print 1.5 mm holes spaced 2 mm apart (center to center); resin can. Print a grille in one piece with its ring, because separate thin grilles warp. Car interiors get hot: a part fitted on a 90 °F (32 °C) day warped 1/16–1/8" (about 1.5–3 mm) between its bolts. So check the heat-deflection temperature (about 105 °C for "automotive" resin), blend a flexible resin with a brittle high-temperature one, and use glued-in studs rather than screws into printed posts. PLA's roughly 88 °C rating is for the plastic on its own; a 3 lb (about 1.4 kg) speaker hanging on four screws is a far harder job.

2.4 #7 · Padding under vinyl: stretch and staple, don't glue.

[RARE] For padded vinyl on MDF, pre-stretch foam-backed headliner, tack it with a few staples, then stretch the vinyl over and staple both (around the back, inside the baffle opening). Gluing to foam or carpet makes bumps. Convex shapes can't be done this way: sand smooth and glue vinyl directly. Sources: DIYMA 2021-08-25

In plain English: Upholsterers often put a thin layer of padding under vinyl so a panel feels soft. MDF is medium-density fiberboard; headliner is the fabric used on car ceilings, usually with a thin foam backing. His method: first stretch foam-backed headliner over the MDF and hold it with a few staples, then stretch the vinyl over it and staple both layers together, wrapping them round to the back and inside the speaker opening. Don't glue the vinyl to foam or carpet, because that makes bumps. He adds that convex (curved) shapes can't be done this way: for those, sand the part smooth and glue the vinyl straight onto it.

2.4 #8 · Cut baffle holes with a router and circle jig, not a freehand jigsaw.

"Either the speaker fits or it doesn't fit": he used it as the analogy for objective tuning. Sources: Mobile Electronics column Sep 2017

In plain English: A router is a spinning cutting tool. A circle jig is an arm that pivots on a center point so the router cuts a perfect circle. A jigsaw guided by hand tends to wander. His point is to cut speaker holes with a router and circle jig, because "either the speaker fits or it doesn't fit." In a 2017 magazine column he used this as a comparison for tuning: he argued for objective, measurement-based tuning, where there is a right answer you can check, just as a hole either fits or doesn't.

2.4 #9 · Competent installation is simple: solid mounting, a properly designed sub box, the right locations.

[RARE] Laser aiming and midbass door boxes are "complexity for complexity's sake"; dash rebuilds for symmetry, moved seats, diffusers, foam and carpet come after "everything else in life is done". What makes great systems is installers who know how to install the products. Sources: DIYMA 2010-02-18 · BusinessWorld 2024

In plain English: His point is that a competent installation is not complicated: mount speakers solidly, build a properly designed subwoofer box, and put speakers in the right locations. Things like aiming speakers with lasers or building boxes for the woofers inside the doors he calls "complexity for complexity's sake". Rebuilding a dashboard so both sides match, moving the seats, and adding diffusers, foam or carpet come only after "everything else in life is done," meaning they are last on the list. What makes great systems, he says, is installers who know how to install the products.

2.4 #10 · Fabricate for sound, not for photos; use factory locations that work.

[RARE] He fabricates only to put a speaker in the right spot. Shops show him beautiful four-month builds excused as "not bad for the 20 minutes" of tuning. His mock judging score: 1,000 points for sounding great, 25 for looks. Factory locations were chosen by PhD engineers for a reason: rearranging the car to fit "the thing we've always installed" is a big mistake. Sources: DIYMA 2013-11-24 · CMA Connected Oct 2021 @22:22 · CMA Connected Oct 2021 @37:25

In plain English: He builds custom parts only to get a speaker into the right spot, not to make the car look impressive. Shops show him beautiful builds that took four months, then excuse the sound with "not bad for the 20 minutes" spent tuning. If he were judging, he would give 1,000 points for sounding great and 25 for looks. He also says carmakers' speaker locations were chosen by engineers with PhDs for a reason, so tearing up a car to fit "the thing we've always installed" is a big mistake. So in practice: use factory locations that work, and put the effort into sound.

2.4 #11 · Never invent on the critical path: on a paid job, do only what you already know how to do.

[RARE] His C30 took about six months; quoted from scratch by a shop it would be about $15–17K of gear and $60K of labor (a show report put custom work at $20K of a $35K system). Schedule skill-building days and split a new capability (CAD, printing, design) across staff before selling it. Sources: OFCAP Ep. 38 @24:00 · ecoustics, T.H.E. Show 2023

In plain English: "Critical path" is a project-management term for the chain of tasks that sets the finish date. Here it means a paying customer's job. His point: on a paid job, only do what you already know how to do; never learn a new technique on a customer's car. For scale, his own Volvo C30 build took about six months. If a shop quoted it from scratch, he estimated about $15,000–17,000 of equipment and $60,000 of labor. A show report gave a different split: $20,000 of custom work in a $35,000 system. So in practice: schedule separate days for building skills, and spread a new capability (CAD, which is computer-aided design, 3D printing, design) across several staff before you sell it.

2.5 Tweeter mounting

What this part is about: A tweeter is the small speaker that plays the highest sounds. This part covers how the way a tweeter is mounted changes its sound, whether and how far to aim it, and why certain designs and add-ons (special domes, waveguides, coaxial layouts, mounting hardware) behave as they do.

2.5 #1 · Every dome tweeter has a dip set by dome height above the baffle, and the mounting moves it.

[RARE] Sound travelling from the dome to the baffle and back cancels where that path is half a wavelength (near 12 kHz, depending on dome height); on a flat baffle it shows, in a pillar or sail it moves or vanishes, so baffle-mounted review curves mislead. A ring radiator (dome pinned at its center) lowers the "dome" and pushes the hole higher, with the same dispersion. Sources: Erin's Audio Corner GB15 · DIYMA 2014-06-11 · DIYMA 2021-12-04

In plain English: A dome tweeter's moving part is a small dome that stands up from its faceplate, and the "baffle" is the surface it is mounted in. A wavelength is the length of one sound wave; high notes have short ones (at 12 kHz, about 29 mm or just over an inch). When two copies of a sound arrive half a wavelength apart, they cancel and leave a dip. His point: some sound travels from the dome down to the baffle and back, and where that extra path equals half a wavelength (near 12 kHz, depending on how tall the dome is) it cancels. On a flat test baffle the dip shows up; mounted in a pillar or sail, the dip moves or disappears. So review graphs measured on flat baffles can mislead you about how a tweeter will behave in a car. A "ring radiator" is a design whose dome is held down at its center, so it acts like a lower dome; that pushes the dip higher, and it spreads sound the same way.

2.5 #2 · The GB15 and GB10CF are shaped for car mounting, not a flat test baffle.

[RARE] GB15: a tall, stiff dome in a cup whose ring is a compromise between flush (door top, kick) and unbaffled (sail, pillar). GB10CF: a lens that lengthens the path from the dome center to avoid the half-wave dip, with the stiff dome's 16 kHz peak pushed off axis where the longer in-car path softens it; high-pass 2 kHz or higher, LR4 (COMPANY). Sources: Erin's Audio Corner GB15 · Introducing the GB10CF

In plain English: The GB15 is Audiofrog's 1.5" (38 mm) tweeter and the GB10CF is its 1" carbon-fiber tweeter. "Off axis" means to the side of the direction a speaker points. The point is that both were shaped for how tweeters are really mounted in cars, not for a flat test panel. The GB15 has a tall, stiff dome in a cup, and the ring around it is a compromise between mounting flush in a flat surface (door top, kick panel) and standing free with nothing around it (sail, pillar). The GB10CF has a "lens" in front that lengthens the path from the dome's center, to avoid the half-wavelength dip described in 2.5 #1. Its stiff dome has a peak at 16 kHz, and the design steers that peak off to the side, where the longer path inside a car softens it. Recommended setting: high-pass at 2 kHz or higher, LR4 (a steep 24 dB-per-octave filter). This comes from product material (a GB15 review page and Audiofrog's own GB10CF page, as the Sources show), not from a post signed by him.

2.5 #3 · One 1" tweeter's dispersion is much like another's.

[RARE] Diameter sets the pattern; two 1" domes differ off axis only above about 3 kHz, where stiffness or a center "diffuser" (which can smooth on-axis but hurt off-axis near 15 kHz) matters. Compare data sheets at the same angles; a 15 kHz dip 60° off axis doesn't matter in a car. Sources: DIYMA 2021-11-23

In plain English: "Dispersion" is how widely a speaker spreads its sound, and it depends mostly on the speaker's size compared with the wavelength. Many people believe tweeter brands differ a lot in how widely they spread sound. His point: diameter sets the pattern, so two 1" (25 mm) dome tweeters differ off to the side only above about 3 kHz. Up there, the stiffness of the dome, or a small center "diffuser" placed in front of the dome, can make a difference. A diffuser can smooth the straight-ahead sound but hurt the sound off to the side near 15 kHz. So in practice: when comparing data sheets, compare the graphs at the same angles, and don't worry about a 15 kHz dip measured 60° off axis, because that doesn't matter in a car.

2.5 #4 · Tweeters needn't be flush-mounted; keep both listeners within about ±35° of the axis.

[RARE] Any driver radiates everywhere at wavelengths long for its size, so a baffle is just a simple dispersion control: "The door isn't a perfectly flat baffle, but that's OK." JBL GTi waveguides were designed for use 35° off axis to suit door mounting. Sources: DIYMA 2011-04-15 · DIYMA 2013-03-22

In plain English: "Flush-mounting" means setting a tweeter so its face is level with the surface around it. The "axis" is the line pointing straight out from the tweeter's center. Many people believe tweeters must be flush-mounted. His point: every speaker spreads its sound in all directions at frequencies whose wavelengths are long compared with its size, so a baffle is just a simple way to control where sound goes. As he says, "The door isn't a perfectly flat baffle, but that's OK." His guideline: keep both the driver and the passenger within about 35° either side of the tweeter's axis. He notes that JBL's GTi tweeter waveguides (shaped surrounds that guide the sound) were designed to be used 35° off axis, to suit mounting in doors.

2.5 #5 · Aim only drivers that beam; in a 3-way that's only the tweeter, turned in a little.

[RARE] A 2" mid below about 2.7 kHz radiates everywhere, so aiming it changes nothing; aiming a 1" tweeter changes reflections only above about 10 kHz. A tweeter far off axis needs a top-end boost. A friend who preferred his head "between the tweeters" was just closer to them. Sources: Audiofrog blog Jun 2021 · DIYMA 2013-03-10 · DIYMA 2021-10-29

In plain English: "Beaming" is when a speaker playing high notes sends its sound mostly straight ahead in a narrow beam instead of spreading it around. A 3-way system has a tweeter, a midrange and a midbass woofer. His point: aiming only changes something for a speaker that beams at the frequencies it plays. A 2" (50 mm) mid playing below about 2.7 kHz sends sound everywhere, so aiming it changes nothing. Aiming a 1" tweeter changes the reflections only above about 10 kHz. So in a 3-way only the tweeter needs aiming, and only turned in a little. A tweeter that points far away from you needs a boost in the very top notes to make up for what it loses. And a friend who preferred having his head "between the tweeters"? He explains that the friend was simply closer to them.

2.5 #6 · Sail tweeters: crossfire or aim at the listener is a trade.

There's little difference between 0° and 15°. Crossfiring gives similar levels and a better center for both seats but the image wanders (responses don't match); aiming both at the driver matches responses but adds near-side bias. Sources: DIYMA 2011-11-05

In plain English: A "sail" is the small triangular panel in the front corner of the door window, near the mirror. "Crossfiring" means aiming each tweeter at the opposite seat. The "image" is the illusion of where singers and instruments are; the "center" is a voice that seems to come from straight ahead. His point is that this is a trade-off with no free answer. Turning a tweeter 15° instead of 0° makes little difference anyway. Crossfiring gives similar loudness from both tweeters and a better center for both seats, but the image wanders, because each seat hears one tweeter from a different angle than the other, so their sounds don't match. Aiming both at the driver makes their sound match at the driver's seat, but the nearer tweeter still dominates, pulling the image toward that side ("near-side bias").

2.5 #7 · From swivel hardware to "aim only the tweeter, a little".

[Changed view: at Harman he co-invented Infinity's swivel flush-mount tweeter (US 5,859,917, filed 1997, about 27° of swivel), and a 2015 JBL/Infinity tip sheet (author unnamed, so not certainly his) said to crossfire pillar tweeters; from 2011 on he prefers sails to pillars and treats aiming only as a treble-balance tool.] Sources: Google Patents US5859917A · JBL/Infinity tip sheet · Audiofrog blog Jun 2021

In plain English: This is a changed view. Harman is the company that owned JBL and Infinity, where he worked. While there, he co-invented Infinity's swivel flush-mount tweeter, patented as US 5,859,917 (filed 1997), which let the tweeter turn about 27° so it could be aimed. A 2015 JBL/Infinity tip sheet, which names no author, advised crossfiring tweeters mounted in the pillars (aiming each at the opposite seat). From 2011 on, his own position is different: he prefers sail panels (the small triangles at the front corner of each door window, by the side mirrors) to pillars, and he treats aiming only as a way to adjust how much treble you hear. In short, the swivel hardware and the unsigned tip sheet lean on aiming, while his own teaching since 2011 is to aim only the tweeter, and only a little.

2.5 #8 · A tweeter in front of a woofer cone (coaxial-style) warbles.

[RARE] The moving cone is the tweeter's baffle, so bass excursion modulates the treble (intermodulation, Doppler-like). Fix by moving the tweeter, high-passing the woofer, or listening off axis. A typical coax has no "phase center" (unlike a KEF Uni-Q); its real benefit is treble in the off-axis sound. Sources: DIYMA 2013-11-29 · DIYMA 2018-04-02

In plain English: A coaxial ("coax") speaker has a tweeter mounted in front of the middle of the woofer cone. "Intermodulation" is distortion in which one sound alters another and creates new, unwanted tones. The Doppler effect is the pitch change you hear as a siren drives past. His point: in this layout the woofer cone is the tweeter's baffle, so as the cone moves in and out with the bass, it alters the treble, making a warble similar to a Doppler effect. Fixes: move the tweeter somewhere else, high-pass the woofer (so it moves less), or listen from off to the side. He adds that a typical coax does not make all its sound appear to come from one point (a "phase center"), unlike KEF's Uni-Q design. Its real benefit is putting treble into the sound that goes off to the sides.

2.5 #9 · Waveguides narrow a tweeter's low-end dispersion to match the woofer; what matters is a smooth directivity index.

[RARE] They never widen dispersion (the edge roundover scatters only the highs), and effective ones are big and hard to mount. Narrowing the tweeter's very top to match the woofer makes a power-response hole that "NEVER sounds good"; narrowing its low end is fine if on-axis vs total radiated power stays smooth. Sources: DIYMA 2013-03-22 · DIYMA 2014-04-12

In plain English: A waveguide is a shallow horn shape around a tweeter that controls how widely it spreads sound. A woofer narrows (beams) near the top of its range, while a tweeter spreads very widely at the bottom of its range, so at the handover between them the two can mismatch. "Directivity index" compares the sound straight ahead with the total sound sent out in all directions (the "power response"). His points: waveguides narrow a tweeter's spread at its low end to match the woofer; they never widen it, because the rounded edge only scatters the highest notes. Effective waveguides are big and hard to mount. He separates two cases. Narrowing the tweeter's very top end to match the woofer creates a hole in the power response, which he says "NEVER sounds good". Narrowing its low end is fine, as long as the directivity index stays smooth, changing gradually rather than jumping.

2.5 #10 · Use the supplied mounting hardware instead of shop-made rings.

Tweeters: a coil-spring flush mount (even force all round, unlike leg clips) into a 1" or 1-1/2" hole, a back strap for behind-panel spots, a bendable "tweeter cannon" for pillars. Mids: multi-fit adapter, cast-aluminum ring to machine or bond into panels and upholster, chrome trim ring with room for vinyl, mesh on a damping rubber U-channel. GB60 into wood: plate behind the ring, gasket over the threaded holes, screw speaker and grille through. Sources: DIYMA 2014-10-30 · CMA Networks 2021 @23:03 · DIYMA 2021-12-15

In plain English: His point is to use the mounting parts that come with the speakers rather than having the shop make its own rings. For tweeters, that means: a flush mount held by a coil spring, which presses evenly all the way round (unlike small spring "leg" clips), fitting a 1" (25 mm) or 1-1/2" (38 mm) hole; a strap for mounting behind a panel; and a bendable "tweeter cannon" for pillars. For mids: a multi-fit adapter; a cast-aluminum ring you can machine or glue into a panel and then upholster; a chrome trim ring with room for vinyl; and a mesh grille that sits in a rubber U-channel that damps vibration. For the GB60 (Audiofrog's 6" woofer) going into wood: put a plate behind the ring, put the gasket over the threaded holes, and screw the speaker and grille through.

2.5 #11 · Direct-fit OE tweeters: check the critical dimensions first.

3D-printed housings put a GB10 or GS10 behind factory grilles (BMW, Audi, Porsche, VW, GM/Bose, Toyota, Tesla and more); GB10OE high-pass 2.5 kHz and GS10OE 3.5 kHz, both 24 dB/oct. Removal tips include reusing BMW's foam cover and unhooking GM Bose tweeters without breaking grille tabs. (COMPANY.) Sources: Direct Fit Tweeters and Adapters · GB10OE-0006 sheet

In plain English: "OE" means original equipment: the parts the car came with. "Direct-fit" means made to drop into the factory location. This comes from Audiofrog's own company material. Its 3D-printed housings let a GB10 or GS10 tweeter sit behind the factory grilles in many cars (BMW, Audi, Porsche, VW, GM/Bose, Toyota, Tesla and more). So in practice: check the listed critical dimensions for your car first. The recommended filters are a high-pass at 2.5 kHz for the GB10OE and 3.5 kHz for the GS10OE, both 24 dB per octave (a steep slope). The removal tips include reusing BMW's foam cover, and unhooking GM Bose tweeters without breaking the grille's tabs.

2.6 Choosing drivers and system topology

What this part is about: Choosing speakers and arranging them into a system. A crossover splits the music into frequency bands and sends each band to the speaker suited to it: a "2-way" uses a woofer and a tweeter, a "3-way" adds a midrange between them. It covers where to split, active versus passive crossovers, and how to handle factory systems and processors.

2.6 #1 · The key upgrade is a small midrange high in the door, making a 3-way.

[RARE] A 2.5" "in just the right spot (high in the door)" may beat a 4" in the wrong one, and with a small mid neither midbass nor mid needs aiming; even cheap OEM 3" mids used only from 900 Hz to 4 kHz bridged a 6" and a tweeter well. Sources: DIYMA 2014-03-04 · DIYMA 2014-04-08

In plain English: His point: the most important upgrade is adding a small midrange high in the door, which turns a 2-way into a 3-way. A 2.5" (63 mm) mid "in just the right spot (high in the door)" may beat a 4" (100 mm) mid in the wrong spot. With a small mid, neither the midbass woofer nor the mid needs aiming, because, as 2.5 #5 explains, neither beams (narrows its sound) in the range it plays. Even cheap factory (OEM) 3" (75 mm) mids, used only from 900 Hz to 4 kHz, bridged the gap between a 6" (150 mm) woofer and a tweeter well. Many people believe a bigger midrange is always better; his point is that the right spot can matter more than size.

2.6 #2 · The 6" + 1" door 2-way has a built-in off-axis hole that no EQ fixes.

[RARE] A 6" is badly attenuated off axis around 3.5 kHz while most 1" tweeters can't play low enough to meet it; in a car you hear power response (all directions), so the hole is audible even when on-axis is flat, and EQing it makes the direct sound bright. Aiming only moves the hole between direct and reflected sound. Studio monitors get away with 2-ways because the mixer hears mostly direct sound: "The difference is the listening space, not the speakers." Sources: DIYMA 2013-03-10 · DIYMA 2021-11-30 · DIYMA 2022-01-05

In plain English: "Off axis" means to the side of where a speaker points. "Power response" is the total sound a speaker sends out in all directions. EQ (equalization) means boosting or cutting particular frequencies. His point: a 6" (150 mm) woofer sends much less sound to the sides around 3.5 kHz, while most 1" tweeters can't play low enough to take over below that. So off to the sides there is a gap, a "hole", around the handover. In a car you hear the sound from all directions, because so much of it bounces off glass and panels, so the hole is audible even when the straight-ahead measurement looks flat. Boost it with EQ and the direct sound turns bright. Aiming only moves the hole between the direct and the reflected sound. Studio monitors (the speakers used to mix music) get away with being 2-ways because the person mixing hears mostly direct sound: "The difference is the listening space, not the speakers."

2.6 #3 · Fixes for a 2-way's hole: add a small mid, or use a big tweeter.

"Big tweeter for a 2-way, small tweeter for a 3-way": a tweeter with Fs below about 1 kHz crossed at 1.5–2 kHz (GB15 1.5" + GB60), or a waveguide that narrows the tweeter to match; "in a 3-way any tweeter is fine". No 6" "dispersion widening technology" avoids it: "physically impossible". Sources: DIYMA 2013-03-20 · DIYMA 2014-10-30

In plain English: This follows from 2.6 #2. He gives two fixes for the hole in a 6" plus 1" door 2-way: add a small mid (make it a 3-way), or use a big tweeter. His rule: "Big tweeter for a 2-way, small tweeter for a 3-way". A tweeter whose resonance (Fs) is below about 1 kHz can be crossed at 1.5–2 kHz, low enough to take over before the woofer narrows; his example is Audiofrog's GB15, a 1.5" tweeter, with the GB60, a 6" woofer. Another option is a waveguide that narrows the tweeter's spread to match the woofer. "In a 3-way any tweeter is fine". He says no 6" with "dispersion widening technology" avoids the problem, because that is "physically impossible".

2.6 #4 · A crossover's first job is keeping the smaller driver safe: cross every driver except the sub above its resonance.

[RARE] Each octave lower costs about 2× power and 4× excursion, and at and below resonance the spider ("parking brake") is the main distortion source; crossed above it, driver distortion is "a nothingburger". Tweeters go at about 1.5–2× Fs. Don't cross a tweeter impossibly low to stop a 6" beaming: build a 3-way. Sources: OFCAP Ep. 19 @1:41:04 · DIYMA 2022-03-13 · DIYMA 2021-08-21

In plain English: Resonance (Fs) is the frequency where a speaker's cone vibrates most easily. An octave is a halving or doubling of frequency, such as 1 kHz down to 500 Hz. "Excursion" is how far the cone moves in and out. The "spider" is the ribbed fabric ring behind the cone that centers it and pulls it back; he calls it the "parking brake". His point: the first job of a crossover is to keep the smaller speaker safe. Each octave lower costs about 2× the power and 4× the excursion. At and below resonance, the spider becomes the main source of distortion; crossed above resonance, the speaker's own distortion is "a nothingburger", meaning negligible. So in practice: cross every speaker except the subwoofer above its resonance, and tweeters at about 1.5–2 times their Fs. Don't cross a tweeter impossibly low to stop a 6" from beaming; build a 3-way instead.

2.6 #5 · Its second job: hand over where the low-passed driver still disperses widely.

[RARE] Using drivers only where they beam would need about 15" midbass, 10" mids and 4" tweeters. Home-speaker rules still apply in a car because dispersion doesn't change there: matched directivity at each crossover makes off-axis sound resemble on-axis, which makes EQ work (the mic can't separate direct from reflected). He published a chart of dispersion by driver size for picking low-pass points. Sources: DIYMA 2013-03-14 · DIYMA 2021-09-02 · DIYMA 2020-12-23

In plain English: The "low-passed driver" at a crossover is the speaker playing the band below it, such as the woofer under the tweeter. His point: a crossover's second job is to hand over while that lower speaker still spreads its sound widely. He notes that the other approach, using each speaker only where it beams, would need about 15" (380 mm) midbass, 10" (250 mm) mids and 4" (100 mm) tweeters. The rules for home speakers still apply in a car, because a speaker spreads sound the same way there. If both speakers spread sound alike at each crossover, the sound to the sides resembles the sound straight ahead, and that makes EQ work, because the measuring microphone can't tell direct sound from reflected sound. He published a chart of dispersion (how widely sound spreads) by speaker size to help pick these low-pass points.

2.6 #6 · His full door recipe.

[RARE] Tweeters in the sails, a small mid at the top of the door, the 6" crossed at 400 Hz–1 kHz, everything but the tweeter in its piston range, only the tweeter aimed (a little). It minimizes windshield reflections and maximizes width; add a center that plays to 200 Hz plus steering for two seats. "I can make almost any car sound similar." His MS-8 development Mini took 2nd at IASCA finals this way. Sources: OFCAP Ep. 38 @35:03 · DIYMA 2014-03-30

In plain English: This is his complete front-speaker layout. A "sail" is the small panel in the front corner of the door window. A speaker's "piston range" is the frequencies where its cone moves as one solid piece and spreads sound widely. A "center" is a speaker in the middle of the dash, and "steering" is processing that sends shared, centered sound to it. His recipe: tweeters in the sails, a small mid at the top of the door, the 6" crossed somewhere from 400 Hz to 1 kHz, every speaker except the tweeter kept in its piston range, and only the tweeter aimed, a little. This minimizes reflections off the windshield and makes the stage as wide as possible. For two good seats, add a center that plays down to 200 Hz, plus steering. "I can make almost any car sound similar." His Mini, the development car for the MS-8 (a JBL processor from his Harman years), took 2nd at the IASCA finals, a sound-quality competition, with this layout.

2.6 #7 · His crossover points for an Audiofrog 3-way, and why the mid needn't play low.

Sub 60 Hz; GB60 80–300 Hz; GB25 300 Hz–3 kHz (200 Hz OK, 250 Hz safer; reaching Xmax in IB at 375 Hz LR4 would take about 2,445 W); tweeter above 3 kHz (amp-crossover version: 3.5 kHz). A 4" mid brings no real advantage and needs more box; a big 4" dash mid crossed at 100 Hz only makes sense with no midbass. Raising the GB60/GB25 point usually hides DSP clipping or a leaky pod. Sources: DIYMA 2022-03-10 · CMA Networks 2022 @57:02 · DIYMA 2017-12-19

In plain English: The GB60 is Audiofrog's 6" woofer and the GB25 its 2.5" mid. "Xmax" is how far a cone can travel before it starts to distort badly; "IB" means no box. His suggested split: subwoofer up to 60 Hz; GB60 80–300 Hz; GB25 300 Hz–3 kHz (200 Hz is OK, 250 Hz is safer); tweeter above 3 kHz, or 3.5 kHz when using an amplifier's built-in crossover. He also worked out that pushing the GB25 to its Xmax with no box, crossed at 375 Hz with an LR4 filter, would take about 2,445 W, far beyond its 100 W rating (see 2.4 #2). A 4" mid brings no real advantage and needs a bigger box. A big 4" dash mid crossed at 100 Hz only makes sense when there is no midbass. People who raise the GB60/GB25 crossover point are usually hiding DSP clipping (distortion from overloading the processor) or a leaky pod.

2.6 #8 · Use a tweeter: he can't find "a credible argument for not using a tweeter in a car".

[RARE] Widebanders were made for desks 18" away: aimed at you they sound "clinical", off axis dull, and only aimed at the windshield do they work. A 3" loses off-axis treble about 1.5 octaves lower than a 1" tweeter; tweeterless systems give tiny images, and "High frequency reflections are pleasant". Pairing "dash widebanders" with a midbass removes the job they were designed for. Sources: DIYMA 2014-04-13 · DIYMA 2015-08-23 · DIYMA 2021-12-02

In plain English: A "widebander" (full-range speaker) is a small speaker, often 2–3", meant to play almost everything with no tweeter. Some enthusiasts prefer a widebander in the dash with no tweeter. His point: he can't find "a credible argument for not using a tweeter in a car". Widebanders were made for desks about 18" (45 cm) from the listener. Aimed at you in a car they sound "clinical", off to the side they sound dull, and they only work when aimed at the windshield. A 3" speaker loses its treble to the sides about 1.5 octaves lower than a 1" tweeter does (1.5 octaves is almost a factor of three in frequency). Systems with no tweeter give tiny images, while "High frequency reflections are pleasant". And pairing "dash widebanders" with a midbass woofer takes away the very job they were designed for: playing the full range alone.

2.6 #9 · Put cone breakup and dust-cap peaks out of band.

A breakup peak comes from a small part of the cone, so it doesn't fall off axis; the dust cap decouples high up with wide dispersion. Diameter sets where off-axis roll-off begins; cone profile matters only via stiffness. Tweeters reach "40 kHz" mainly to push breakup out of the audible band. Sources: DIYMA 2012-09-06

In plain English: "Cone breakup" happens at high frequencies, when a cone stops moving as one piece and parts of it flex, causing peaks. The "dust cap" is the small dome in the middle of a woofer's cone. "Out of band" means outside the range the crossover lets that speaker play. His points: a breakup peak comes from a small part of the cone, so it spreads widely and doesn't fade to the sides. Up high, the dust cap moves separately from the cone and also spreads its sound widely. A cone's diameter sets where its sound starts fading to the sides; the cone's shape matters only through how stiff it is. Tweeters are built to reach "40 kHz" mainly to push their breakup above what we can hear. So in practice: set crossovers so these peaks fall outside each speaker's band.

2.6 #10 · Cross midbass-to-mid actively; a passive belongs only between mid and tweeter.

[RARE] Audiofrog made no midbass/mid passive ("You should really run an active crossover there"); its hybrid 3-ways pair a mid/tweeter passive with an active midbass split. When the tweeter sits close to the mid, a passive set is where to save money: a 1.5 in offset is half a wavelength at 4.5 kHz, so if the RTA shows a deep narrow dip there, reverse the tweeter. Sources: DIYMA 2014-09-26 · DIYMA 2021-09-26

In plain English: An "active" crossover splits the signal before the amplifiers, usually in a processor (DSP), so each speaker gets its own amp channel. A "passive" crossover is a box of coils and capacitors between one amp channel and the speakers. An RTA (real-time analyzer) uses a microphone to show the level at each frequency. His point: Audiofrog made no passive crossover for the midbass-to-mid split ("You should really run an active crossover there"). Its hybrid 3-ways use a passive between mid and tweeter and an active split between midbass and mid. When the tweeter sits close to the mid, a passive mid/tweeter set is where to save money. A 1.5" (38 mm) offset between the two is half a wavelength at 4.5 kHz, so if the RTA shows a deep, narrow dip there, reverse the tweeter (swap its + and − wires).

2.6 #11 · Car speakers are "NEVER mounted on a flat baffle", so use steep slopes (LR4), not home-style 6 dB/oct overlaps.

[RARE] A 6 dB/oct filter's only advantage is phase and it barely protects; cars use more power and compromised placement, so keep the overlap band small. And the "crossover point" is where the measured acoustic curves cross in the car, not the DSP dial. Sources: DIYMA 2014-10-30 · DIYMA 2021-09-27 · DIYMA 2014-08-06

In plain English: A filter's "slope" is how quickly it cuts sound outside its band. 6 dB per octave is gentle and common in home speakers; LR4 is steep (24 dB per octave). The "overlap band" is the range where both speakers play at once, and "phase" describes how their sound waves line up in time. Many people use home-style gentle 6 dB/oct overlaps. His point: car speakers are "NEVER mounted on a flat baffle". A 6 dB/oct filter's only advantage is its phase behavior, and it barely protects the speaker. Cars use more power and compromised placement, so keep the overlap small with steep slopes. Also, the real "crossover point" is where the two speakers' measured curves cross inside the car, not the number set on the DSP.

2.6 #12 · Never run a passive network with a section unloaded or split.

[RARE] Using only a passive's tweeter side is safe only if the woofer section is a single series inductor; a shunt part can short the amplifier at the network's resonance, and an open tweeter on a 2nd-order network does the same. Splitting a 2-way passive (tweeter side used, mid on its own channel) makes the system cut out at volume. Ohm the tweeter (an Audiofrog one reads 2–3 Ω). Sources: DIYMA 2015-08-27 · DIYMA 2018-01-13 · OFCAP Ep. 19 @2:00:03

In plain English: A passive crossover ("network") is built from coils (inductors) and capacitors. A "series" part sits in line with a speaker; a "shunt" part is wired across the speaker's terminals. "Unloaded" means no speaker connected; "2nd order" means a 12 dB-per-octave filter that uses both a coil and a capacitor. His point: using only the tweeter half of a passive is safe only if the woofer half is a single series coil. If it has a shunt part, at the network's resonance it can short the amplifier. A disconnected (open) tweeter on a 2nd-order network does the same. Splitting a 2-way passive (using its tweeter side while the mid runs on its own channel) makes the system cut out at high volume. So in practice: check the tweeter's resistance with a meter ("ohm" it); an Audiofrog tweeter reads 2–3 Ω (ohms).

2.6 #13 · In a series passive crossover the parts swap roles.

The filter sits in parallel with the driver, so the tweeter's high-pass is a shunt inductor where a parallel network would use a series capacitor. Sources: DIYMA 2022-01-13

In plain English: Most passive crossovers are "parallel": each speaker's filter is wired separately to the amplifier. A "series" crossover chains the speakers instead. A capacitor passes highs and blocks lows; a coil (inductor) passes lows and blocks highs. His point: in a series network, the filter sits in parallel with (across) the speaker, so the parts swap roles. The tweeter's high-pass becomes a coil wired across it, which drains the low notes away from it. In a parallel network, the same job is done by a capacitor in line with the tweeter.

2.6 #14 · Don't band-pass a door woofer as the "mid" of a 3-way from 75 Hz.

[RARE] The overlap with the sub kills punchy bass; run the front as a 2-way whose high-pass matches the sub's low-pass. His MS-8 settings: subsonic 20 Hz 12 dB/oct, sub low-pass 80 Hz 24 dB/oct, woofer/tweeter 3.5 kHz 24 dB/oct. Sources: DIYMA 2015-04-21

In plain English: A "band-pass" limits a speaker at both ends, so it only plays a middle band. A "subsonic" filter cuts very deep bass the subwoofer can't use. His point: don't set up a door woofer as the "mid" of a 3-way playing from 75 Hz. Its overlap with the subwoofer kills punchy bass. Instead, run the front as a 2-way (woofer plus tweeter) whose high-pass matches the subwoofer's low-pass. His settings for the MS-8, a JBL processor from his Harman years: subsonic 20 Hz at 12 dB/oct, sub low-pass 80 Hz at 24 dB/oct, and woofer/tweeter split at 3.5 kHz, 24 dB/oct.

2.6 #15 · When the factory system is actively crossed, keep its processing and go one-to-one.

[RARE] Factory EQ is only about 10–20% speaker correction; Bose/Harman all-pass filters can't be "un-EQ'd", so summing back leaves an unfixable midrange hole. Replace each factory driver with one suited to its channel (GS25 dash, GS60/GS690 door), then add an amp on each factory channel and just retune EQ and levels: no new delays or crossovers. Sources: CMA Networks 2021 @35:00 · Absolute Electronix 2023 @58:34

In plain English: Many factory systems are "actively crossed": the factory amplifier splits the music and sends each speaker its own band, with its own EQ and timing. "All-pass" filters change timing (phase) without changing level. "Summing" means combining the factory channels back into one full-range signal, which many add-on processors do. His point: only about 10–20% of factory EQ is correcting the speakers. Bose and Harman systems use all-pass filters that can't be "un-EQ'd", so summing the channels back together leaves a midrange hole you can't fix. So in practice: keep the factory processing and go one-to-one. Replace each factory speaker with one suited to its channel (for example a GS25 in the dash, a GS60 or GS690 in the door), add an amplifier on each factory channel, and just retune EQ and levels, with no new delays or crossovers.

2.6 #16 · For a high-end system, use a separate DSP and amps with analog gain controls.

[RARE] A DSP amp's input must squeeze every signal down to its converter's ceiling (about 1–4 V), and after the DAC there is only digital gain, which can't exceed 0 dBFS: after tuning cuts a "1,000 W" amp may deliver about 10 W, with no way back. Sources: Absolute Electronix 2023 @33:35

In plain English: A DSP (digital signal processor) handles EQ, crossovers and timing; a "DSP amp" has one built in. Its input converter turns the music into numbers, and a DAC turns it back into a signal. "0 dBFS" is the highest level a digital system can carry; above it, the sound clips. His point: a DSP amp's input must squeeze every source down to fit its converter's ceiling (about 1–4 V). After the DAC there is only digital gain, which can't go above 0 dBFS. So once tuning has cut the levels, a "1,000 W" amp may deliver about 10 W, with no way to get the rest back. That is why, for a high-end system, he recommends a separate DSP and amplifiers with analog gain controls.

2.6 #17 · There is no perfect speaker, and "point source" is not a shortcut.

[RARE] The rules are a century old (enough power handling, flat response across its band, low distortion); change one parameter and "a thousand other things" change, so a speaker is only right for an application. The only practical point source is a headphone; aligning mid and tweeter acoustic centers exactly is "garbage" in a car where heads move. Sources: CMA Networks 2022 @7:02

In plain English: A "point source" is a speaker whose sound all seems to come from a single point. A speaker's "acoustic center" is the spot its sound effectively comes from. Many people treat a point source, or exactly aligning the mid's and tweeter's acoustic centers, as a shortcut to great sound. His point: the rules for a good speaker are a century old: enough power handling, flat response across its band, and low distortion. Change one design parameter and "a thousand other things" change, so a speaker is only right for a particular use; none is perfect. The only practical point source is a headphone. And exact acoustic-center alignment is "garbage" in a car, where listeners' heads move.

2.6 #18 · A 3-way he endorsed with big doors and kick mids.

A user's layout of 9" door woofers at 70–600 Hz, 3.5" kick-panel mids at 600 Hz–2.7 kHz and tweeters above 2.7 kHz got "You're doing it right". Sources: DIYMA 2014-04-02

In plain English: This is a layout a forum user proposed, which he approved with "You're doing it right". It uses 9" (230 mm) woofers in the doors playing 70–600 Hz, 3.5" (90 mm) mids in the kick panels (the side panels by the front footwells) playing 600 Hz–2.7 kHz, and tweeters above 2.7 kHz. It is an example he endorsed, not his own standard recipe.

2.6 #19 · A center speaker must play down to at least 200 Hz, and should be able to play loud.

Use small drivers that reach 200 Hz (a GB25 crossed there works; two 4" drivers let his CES center take a 100 Hz high-pass). His C30 center is a GB60 + GB10, not for bass but because the GB60's 2" coil (vs about 1" on smaller drivers) lets it play loud. Sources: DIYMA 2016-01-18 · DIYMA 2018-03-28 · OFCAP Ep. 38 @1:10:05

In plain English: A center speaker sits in the middle of the dash. The "voice coil" is the coil of wire that drives a speaker's cone; a bigger coil can take more power. His point: a center must play down to at least 200 Hz and should be able to play loud. Use small speakers that reach 200 Hz; a GB25 crossed there works. Two 4" (100 mm) speakers let his CES show car's center use a 100 Hz high-pass. In his Volvo C30, the center is a GB60 (6") plus a GB10 (1" tweeter). That isn't for bass: it is because the GB60's 2" (50 mm) voice coil, versus about 1" on smaller speakers, lets it play loud.

The full series

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