Synthesis — Loudspeaker Design

The evolving thesis. Spun out of the hub _inbox loudspeaker-design cluster on 2026-06-28 from three sources arriving together: a T/S parameter explainer (ts-parameters-explained), an enclosure-design calculator (micka-enclosure-calculator), and a fundamentals primer (loudspeaker-primer-hackaday).

Current thesis

Loudspeaker design is predictive, not empirical: a driver’s behavior in a box can be calculated in advance from a small set of measured numbers. The through-line of all three founding sources is the same loop:

1. A moving-coil driver can’t work in open air — its rear wave cancels its front wave (phase cancellation), so it needs a box.
2. The Thiele/Small parameters capture the driver as a small-signal model (resonance Fs, damping Qts, air-compliance Vas, motor Bl, excursion Xmax, …) — themselves measured from a free-air impedance sweep (ts-parameters-wikipedia), and small-signal snapshots that drift with level/temperature/age and vary unit-to-unit, so the predictive loop is only as good as the measured inputs.
3. Those numbers determine the enclosure — sealed vs. vented, the volume, the port tuning — and a calculator turns them into a predicted frequency/impedance/step/group-delay response before any wood is cut.

So the field’s central move is replacing trial-and-error with a datasheet and a simulation. Wattage ratings say nothing about in-box performance; the T/S set is the real spec.

The design tensions (early)

• Sealed vs. vented. Higher-Qts drivers lean sealed (tighter, gentler rolloff); lower-Qts lean vented (more output, steeper rolloff below tuning). The same driver in two boxes is two different speakers.
• Reach vs. resonance. Fs sets a practical low-frequency floor — output falls away below it.
• The cabinet as a second instrument. The box must have mass/rigidity so it doesn’t resonate itself; a perfect alignment in a singing cabinet is undone. The first commercial instance (2026-07-10, chesky-audio-lc2) attacks this by material, not mass: a 3D-printed, double-walled, acoustically-inert composite cabinet + aluminum baffle instead of heavy MDF — a different answer to the same resonance problem.
• Port vs. drone cone. Bass extension has a third route beyond sealed/vented: the passive radiator (a motor-less tuned diaphragm) does a vent’s job with no port to chuff or grow long, which is why it shows up in compact boxes (chesky-audio-lc2: twin 8″ radiators → 40 Hz in a bookshelf). Tuned by moving mass/compliance rather than port geometry.
• Sensitivity, not wattage, sizes the amp. chesky-audio-lc2 (4 Ω, 86 dB/2.83 V·m — “wants power”) makes concrete what the thesis says abstractly: the useful match is sensitivity + impedance vs. amplifier current, not a watt rating.

The numbers have a standard, and the standard expired (research pass)

The predictive loop rests on measured inputs, and this cycle sourced the layer under them for the first time. A datasheet’s T/S figures were produced to IEC 60268-5 — issued 1972, and in its 2003 form the document specifying these parameters, the anechoic chamber, the IEC baffle and the test boxes. It has been withdrawn, replaced by IEC 60268-21, IEC 60268-22 and IEC 63034 (iec-60268-5-replacement, geoff-hill, the spoke’s first T1).

Why it broke is the part that matters here: the standard assumed a loudspeaker was “entirely passive.” The active/DSP speaker this spoke reached from the hobbyist side (camilladsp, the DSP-correction thread) is exactly the device it could not describe. The DSP bridge is not a side-branch off the physics — it is what forced the measurement regime to be rewritten. The new set also adds chirp and multi-tone stimuli, 3D sound-field assessment, and Rub & Buzz defect testing, a fault class the old document had no way to name.

Practical residue for a builder: figures from the old and new regimes are not guaranteed comparable, and nothing here says how you tell which you are holding.

And the unit-to-unit caveat became a measured subject. The thesis above says T/S parameters are small-signal snapshots that vary unit to unit, so a careful builder measures their own driver — carried until now from ts-parameters-wikipedia and builder practice. ts-parameter-manufacturing-variation (AES Convention 125, 2008) measured twenty nominally identical drivers for exactly that spread, and its follow-on phase went further than tolerance: correlating parameter variation with failure mode and lifetime. The figures are behind the AES e-library and are not held here, so what this buys is the standing of the claim, not its magnitude.

Both sources arrived through the research pass against this spoke’s first-T1 edge, which they close. The floor moves T1 0 → 2, and the shape of what is missing changes with it: the spoke now knows which standards its numbers come from and still holds none of their text.

The environment that cannot be designed

The thesis above works because the acoustic load is known before anything is built: a box you specify, a room that at least holds still. audio-dsp-hardbag-guide brings the first case in this corpus where that fails outright.

On a motorcycle there is no enclosure, and the noise floor is a function of road speed — in-vehicle-audio. Nothing in the predictive loop reaches that. You can still choose the driver by T/S parameters and predict what it does into a known load; you cannot predict wind at 100 km/h, and no calculator here models it.

So audio-dsp arrives in a role the corpus has not had for it. loudspeaker-primer-hackaday calls DSP a shortcut, something that lets you correct rather than get the passive design right, and camilladsp is that shortcut as a tool: active crossovers and EQ replacing soldered networks. Here correction is not an alternative to design — it is the only remaining variable, because the environment half of the problem was never designable in the first place. That does not contradict the thesis; it bounds it. The predictive loop covers the transducer and its load, and stops at the door of the space.

One favourable asymmetry is worth recording, since it cuts the other way from everything else about a vehicle. Speaker placement is dictated by the chassis, so path lengths to the listener differ badly and time alignment becomes necessary rather than optional. But the listener does not move. Sweet-spot correction is a compromise in a room because someone will sit elsewhere; in a vehicle the seat is fixed, which makes per-position alignment worth more here than in any other case this spoke holds.

Evidential standing is poor and the page says so. The source is a store’s blog recommending the category of product the store sells: T4, no author, no measurement, and its specific figures are manufacturer numbers passed through a reseller. One of them fails on arithmetic — 85 ms of delay is about 29 m of path difference, where a vehicle needs under 3 ms. The reasoning above rests on the geometry, not on the vendor. Car and motorcycle audio has its own competitive measurement culture and this spoke holds none of it, which is now a growth edge rather than a gap nobody had noticed.

Open questions

• Measurement. Answered (2026-06-29, ts-parameters-wikipedia). The datasheet numbers come from a free-air impedance sweep around resonance: Re with the cone blocked, Fs at the impedance peak, the Q factors from the curve, and Vas from a second reading that shifts the suspension’s apparent stiffness (added mass or a sealed known box). Three impedance rigs of rising accuracy (constant-current / constant-voltage / small-series-resistor). Key takeaway folded into the thesis: the parameters are small-signal snapshots that drift with level/temperature/age and vary unit-to-unit, so a careful builder measures their own driver. Residual sub-gap: hands-on measurement gear (DATS/REW- class tools) is named but not yet sourced.
• Beyond the box. Drivers materials, horn loading, and room acoustics are named but not yet sourced — candidates if the corpus grows toward general electroacoustics. Crossovers now have their own node (crossover): the first concrete instance was an unconventional low/high split across two drives (2026-06-30, hdd-speakers); the first proper one is active/DSP (camilladsp, 2026-07-09) — Linkwitz-Riley 24 dB/oct done in software rather than a passive LC network. Passive LC crossovers themselves are still unsourced (the traditional path), a remaining gap.
• The transducer alone. hdd-speakers (Niv Singer, via Hackaday) is the first step into the broadening flagged below: a hard-drive voice-coil actuator driven as a speaker. It isolates the spoke’s core physics — the coil-in-a-gap motor is the whole sound-making trick; strip the cone, surround, and box and you still get sound, just badly (limited volume, poor frequency response). The opposite pole from the T/S predictive-design loop: transduction without the engineering.
• The DSP bridge. Cheap drivers + DSP compensation can correct physical flaws digitally (loudspeaker-primer-hackaday) — the one seam toward ../speech-audio-wiki (audio software/ML), vs. this spoke’s hardware/acoustics. Now concrete (2026-07-09): CamillaDSP is an open-source DSP engine that implements exactly this — active crossovers, EQ, and per-driver time alignment in software (an open alternative to miniDSP). It reframes the shortcut as a whole design philosophy: multi-amp + correct in software instead of computing a passive network. Note this DSP is signal-chain filtering/correction of a real transducer — squarely this spoke’s hardware/acoustics seam, not the speech-audio-model neighbor; the bridge stays a cross-link, not a merge.

Growth edges

Ranked; each names the kind of source that would close it (see ../QUALITY.md → Growth edges).

1. First T1 — CLOSED 2026-08-08 by the research pass: iec-60268-5-replacement (a standards-committee account of the measurement regime) and ts-parameter-manufacturing-variation (AES Convention 125). T1 0 → 2.
2. The standards’ own text. The spoke now knows its numbers come from IEC 60268-21/-22 and 63034 and holds none of them. — needs: the standard itself, or a committee/working-group document specifying a measurement procedure · hunted 2026-08-08 — paywalled, nothing ingested. IEC standards are sold, not published: iTeh, BSI, the ANSI webstore and GlobalSpec all return a catalogue page with the scope paragraph and none of the procedure. The scope alone is informative and is recorded here rather than paged — IEC 60268-21:2018 covers physical measurement of transfer behaviour between an arbitrary input and the acoustical output at any point in the near and far field, in both small and large signal domains, across transducers, TVs, portable audio, automotive and professional systems, and can account for the target application’s acoustic boundary conditions. It explicitly “does not assess the perception and cognitive evaluation of the reproduced sound” — so the standard that replaced IEC 60268-5 draws the same physics/perception line this spoke keeps running into. No cooldown set: this failed on access, not on scarcity, and fourteen days changes nothing. The edge now needs a working-group document, an AES paper describing the procedure, or a library copy — not another search.
3. No measured data, still. T/S parameters and alignments are explained and now documented as measured elsewhere; no measurement set lives here. ts-parameter-manufacturing-variation‘s figures are behind the AES e-library. — needs: an open driver test set, or a paper citing that study’s numbers.
4. Broaden toward general electroacoustics (microphones, amplifiers, room acoustics) rather than fragmenting. — needs: T1/T2 on any of the three.

Coverage edges (added 2026-08-08, at the curator’s request for a wider backlog). These widen what the spoke covers instead of answering an open question above; one ordinary solid source closes any.

5. How measurement is actually done. The spoke keeps failing to buy the standards’ text and has no page on the instruments people measure with — REW, Klippel, a calibrated microphone and a gate. — needs: an AES paper on method, or the software’s own documentation.

6. The room. In-room response departs from anechoic by more than any driver choice, and room modes, boundary reinforcement and treatment appear nowhere. — needs: an acoustics text or an AES paper.

7. Horns and waveguides. Directivity control is the third enclosure family beside loudspeaker-enclosure and passive-radiator, and it has no page. — needs: a design text or an AES paper with polar data.

8. Listening tests as a discipline. IEC 60268-21 explicitly excludes perception, which leaves the preference research (Toole, Olive) as the only thing that connects a measurement to a listener. — needs: an AES paper on preference and its correlation with anechoic data.

9. Vehicle audio, measured. New 2026-08-10. in-vehicle-audio entered on a single T4 retailer page plus geometry, and car audio has a large competitive measurement culture this spoke holds none of. — needs: an in-car response measurement or an AES paper on automotive acoustics, not another installer guide.

10. What DSP correction costs. New 2026-08-10. audio-dsp is now paged as the correction layer and the corpus cannot say what it gives up: fixed vs floating point, cumulative filter error, or the excursion ceiling that bounds any EQ boost. — needs: a DSP text or an AES paper; music-tech-wiki’s digital-filter-audibility is the nearest thing anywhere in the hub.

Bass costs time, and the market doesn’t pay for either (research pass, 2026-08-10)

A directed research pass on hi-fi bass reproduction — no source handed in, two fetched — added the timing axis the spoke had been gesturing at and one adjacency it had never touched.

The bass bargain, stated. Every mechanism that buys low-frequency extension or output is resonant, and resonance returns energy late. Ports, passive radiators, high-pass filters and EQ boosts all pay in group-delay, and milliseconds cost more at 30 Hz than anywhere else because a cycle is 33 ms long. This sharpens the founding sealed-vs-vented tension from a preference into a currency: extension and output are bought with time, and the tuning frequency sets the price.

The reframe comes from svs-sealed-vs-ported (T3, and a port vendor): the timing penalty tracks where a box is tuned, not the presence of a port — tune below 20 Hz and the phase rotation falls under the music band. Unverified, and exactly the claim that seller benefits from, but it is a testable statement rather than a slogan, and it recasts “sealed for music” as a shorthand for “most ported subs are tuned too high.”

room-gain is the second place the loop stops. The spoke already knew the room isn’t designable (in-vehicle-audio was the extreme case). Room gain names the specific bass consequence: below the lowest wavelength that fits, the speaker pressurizes a volume and output rises, so the simulated curve and the heard curve diverge exactly where the design work was hardest. A sealed box’s gentle fall can be spent against that rise — a designer choosing an alignment for a room they will never measure.

And then the market ignores all of it. hifi-value-guide-potteries prices used hi-fi by brand, condition, completeness and scarcity. Not one measured quantity appears — no T/S figure, no response curve, no group-delay plot. Speakers span £30 to £3,000+ a pair on badge and box condition. Recorded as loudspeaker-resale-value, an adjacency (economics, not electroacoustics) that is kept because it is the only place a design decision gets priced by someone other than the designer. It doesn’t contradict the predictive thesis — it bounds its reach: the loop predicts quality, and quality is not what clears the used market.

One live sub-thread: passive boxes hold value because they cannot obsolete, while audio-dsp-carrying active speakers have an end-of-support date. The spoke’s DSP thread therefore has a resale cost attached to it that nothing in the corpus has measured.

Growth edges added: #11 a neutral, measured sealed-vs-ported group-delay comparison (the figures in circulation are content-farm numbers; Audioholics’ myth piece 403’d); #12 does measured performance predict resale value, controlling for brand — answerable with a used-market scrape plus a measurement database; the Headphonesty depreciation dataset (Feb 2026) also 403’d and should be retried.

Contradictions / tensions

• Measured vs. heard (2026-07-10). The spoke’s thesis is that loudspeaker quality is predicted from measurement (T/S numbers → simulated response). The first commercial-product source, chesky-audio-lc2 (a Future Audiophile review), asserts quality the other way — subjective listening plus a knuckle “knock test,” with no gated/anechoic measurements. Not a factual contradiction (the two describe different stages — design vs. evaluation), but a real epistemic tension: enthusiast reviews are how most buyers judge speakers, and they sit orthogonal to the measure-first ethos. Held as a T3 data point, not evidence for the predictive loop. Watch for a measurement-based review/spinorama to bridge them.

Cross-spoke adjacency

• ../speech-audio-wiki — owns speech & audio AI models (TTS/STT/audio-gen). This spoke owns the physical transducer + acoustics. The bridge is DSP correction of physical speakers; cross-link, don’t merge.

Index — Loudspeaker Design Wiki

Catalog of every page, grouped by schema.org @type. Spine: synthesis (thesis), log.md (history), this file (catalog). Spun out of the hub _inbox loudspeaker-design cluster on 2026-06-28 (3 sources).

DefinedTerm (concepts / components)

• thiele-small-parameters — the driver’s electromechanical spec set (Fs, Qts, Vas, Bl, Xmax…); the calculation basis of the field · concept
• loudspeaker-driver — the moving-coil transducer: cone, voice coil, magnet, surround; woofer/mid/tweeter · component
• loudspeaker-enclosure — the box: sealed vs. vented/bass-reflex, infinite-baffle ideal, Qtc, cabinet construction · concept
• crossover — the frequency-splitting network (woofer/mid/tweeter): passive LC vs active/DSP, slopes & Linkwitz-Riley; the integrate-the-drivers layer · concept
• audio-dsp — the correction layer: EQ, time alignment, active crossovers, compression, acoustic correction; what it replaces (the passive network, some of the box) and what it can’t (excursion and output) · concept
• in-vehicle-audio — car and motorcycle reproduction; the first case where the acoustic load cannot be designed, so correction stops being optional — offset by a listener who never moves · environment
• group-delay — how late each frequency arrives (ms vs. Hz); why extension and output are bought with time, and what “tight bass” names · concept
• room-gain — the room’s own rise below its lowest fitting wavelength; where the predictive loop stops and correction starts · environment
• loudspeaker-resale-value — adjacency: what a used speaker fetches (brand/condition/completeness), and why it tracks the measurements so poorly · market
• passive-radiator — motor-less tuned diaphragm (“drone cone”): a vented box’s bass extension with no port; the fourth alignment, tuned by mass/compliance · concept

Product (loudspeakers)

• chesky-audio-lc2 — Chesky Audio: ~$1,995/pr reference bookshelf; 3D-printed acoustically-inert cabinet, aperiodic tweeter, twin 8″ passive radiators → 40 Hz; 4 Ω / 86 dB; the first finished-product instance · source · T3 · futureaudiophile.com

TechArticle / WebApplication (sources)

• ts-parameters-explained — AudioJudgement: the T/S parameter set explained with DIY cases (sub selection, sealed vs reflex, Fs floor) · source · T3 · audiojudgement.com
• loudspeaker-primer-hackaday — Hackaday “Know Audio”: how a driver works, crossovers, why enclosures exist, MDF cabinets, the DSP shortcut · source · T2 · hackaday.com
• micka-enclosure-calculator — Micka: online enclosure calculator (vented/sealed/custom; driver DB; FR/impedance/step/group-delay) · source · T2 · micka.de
• ts-parameters-wikipedia — Wikipedia: the T/S reference; how the parameters are measured (impedance sweep, Vas via added-mass/sealed-box), small-signal caveat — closes the measurement open-Q · source · T2 · en.wikipedia.org
• hdd-speakers — Hackaday: Niv Singer drives hard-drive head actuators as speakers (voice-coil = the whole transducer; a low/high crossover across 4 drives; plays Future Crew’s “Second Reality”) · source · T2 · hackaday.com
• iec-60268-5-replacement — Geoff Hill (chair, AES SC-04-03; member, IEC PT 60268-22) on why IEC 60268-5 was withdrawn — written for an “entirely passive” device in 1972, no chirp/multi-tone, no 3D sound field, QC and R&D procedures incompatible — and the three standards replacing it (60268-21 / 60268-22 / 63034, adding Rub & Buzz defect testing). The spoke’s first T1, and its first source about the measurement regime rather than a measurement · source · T1 · audioxpress.com
• ts-parameter-manufacturing-variation — Laurin & Reichard (Penn State), AES Convention 125, 2008: T/S parameters measured across twenty nominally identical drivers, with a follow-on phase correlating the spread with failure mode and lifetime. Turns this wiki’s measure-your-own-driver advice from folklore into a measured subject — figures behind the e-library, listing only · source · T1 · aes.org
• audio-dsp-hardbag-guide — American Hard Bag (Harley audio retailer): a five-function taxonomy of audio-dsp (EQ / time alignment / crossover / compression / acoustic correction), the ADC→maths→DAC chain, fixed vs floating point, RP2040-RP2350 as capable silicon, and vendor specs (11 channels, 110 filter bands, 85 ms delay). Brings in-vehicle-audio into the spoke. Store blog selling the category it recommends; the 85 ms figure is ~29 m of path difference, two orders past any vehicle use · source · T4 · americanhardbag.com
• svs-sealed-vs-ported — SVS (subwoofer maker): sealed vs. ported tradeoffs; sealed + room-gain in small rooms, ported for 2–4× deep output; the reframe worth keeping — the group-delay penalty tracks the tuning frequency, curves said to converge above 30 Hz. No measurements shown · source · T3 · svsound.com
• hifi-value-guide-potteries — Dave Spence / Potteries Auctions (2026-04-23): used hi-fi price brackets (speakers £30–£3,000+/pr; Naim/Linn/Rega £500–£5,000+); value driven by brand, condition, completeness — no acoustic measurement appears in the list · source · T3 · potteriesauctions.com
• camilladsp — RASPIAUDIO: open-source DSP engine (Rust) as a Raspberry Pi 5 appliance — active crossovers (LR 24 dB/oct), PEQ, time alignment; 8xOUT board; an open miniDSP alternative for active speaker builders · source · T2 · github.com

Person / Organization (entities)

• geoff-hill — loudspeaker measurement engineer; chairs AES SC-04-03, sits on IEC PT 60268-22, invented the Tetrahedral Test Chamber · author
• audio-engineering-society — Organization: the professional society behind both of this spoke’s T1 sources — the venue its growth edge named · publisher
• iec — Consortium: the standards body whose 60268-5 defined how every T/S datasheet figure was measured, and whose committees withdrew it · standards body

Synthesis

• synthesis — the thesis: loudspeaker design is predictive — datasheet numbers → simulated box → response, before any wood is cut

Notes

• Publisher/maker entity nodes (Hackaday, AudioJudgement, Micka, and the driver brands) are deferred — thin at founding; page them when one recurs or a query needs it.