First Chair — Design Spec

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Status: Design phase, CAD in progress, nothing print-verified. The cup was rebuilt to the locked 54 mm profile on 2026-08-06; the baffle has not been yet. This document is the functional spec the CAD is built against.

The dimensions are settled. The form is not.

This is the beta view — the design as it stands right now, republished on every commit.

The shape in the viewer is a placeholder, and an inherited one. First Chair was forked from the over-ear Daily Driver. The dimensions below were reset to the on-ear numbers and are real; the form was not redesigned, so the model still carries a DT880-family domed cup and a circumaural stance on a 54 mm rim. It reads as a shrunken over-ear because that’s exactly what it is. An industrial-design pass is open to resolve the form properly — a supra-aural is a different object, not a small version of another one.

Everything under the locked geometry and the decisions below is real and settled. One thing is known-unfinished: the baffle is still carrying the Daily Driver’s Ø91 plate diameter and is being rebuilt. All tracked in the repo’s design log.

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Why this is the build to start with

First Chair replaces the Daily Driver as the flagship — not because the Daily Driver is wrong, but because it’s the wrong first build. Makerphones is a learning path, so the flagship should be the first rung, not the last.

The barrier was never the printing. It was the hardware. The Daily Driver’s bill of materials runs roughly $60–70 across eight suppliers, several of them specialty fastener houses, plus heat-set-insert technique before anything can be assembled. Its own BOM notes that one pivot screw sits below the official ISO size sheet, so every supplier brands it “similar to” — which asks a first-timer to judge fastener equivalence on a part that has to fit a printed bore.

That’s a fine BOM for the person the manual creates. It’s a wall for the person the manual is trying to reach.

The target here, stated as a target rather than an absolute: printer, filament, drivers, and one elastic element. Every fastener that survives to the final BOM has to justify itself individually.

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Why on-ear, and what it costs

Three real reasons, not just “smaller”:

• No seal to achieve. Circumaural bass depends on a pad seal, which depends on pad compliance and clamp force — the two hardest properties to hit with printed parts. A supra-aural leaks by design, so its bass is set by geometry you control instead of a seal you can’t.
• Far less bending load on the yoke. Smaller, lighter cups mean less leverage, which is what makes a printed mechanism plausible at all.
• The architecture is genuinely simple. Driver on a ring, pad, open rear, almost no cavity to resonate. Fewer variables to get wrong on a first build.

The cost is bass, and it isn’t small. Grado is the reference here, and Grados are famously bass-light and famously not fussy about placement — those are the same fact. This design leans into that rather than chasing extension the hardware can’t make.

The thing we expected to be worse, and measured better

The obvious worry with a supra-aural is that you trade bass-seal sensitivity for mid and treble alignment sensitivity — the driver sits close to the ear and roughly on-axis with the canal, so small changes in where the pad lands move the tonality. That’s the worse trade, because treble error reads as timbre and listeners don’t adapt to it the way they adapt to a bass shelf.

We had the measurement and hadn’t looked. Six headphones captured on the same rig, 2026-08-03, placement standard deviation in dB:

	20–200 Hz	2–8 kHz	8–20 kHz
SR60x — on-ear, small pads	0.56 / 0.21	0.85	2.72
HD 650 — over-ear	0.40 / 0.59	1.41 / 2.45	3.48 / 5.13
RS1x — on-ear, larger pads	0.71 / 0.53	2.15 / 2.00	4.37 / 5.91

The on-ear was the most repeatable of the three, in exactly the bands the argument predicted it would be worst. The rig’s noise floor was ~0.1 dB and constant, so that spread is physical, not instrument.

The more useful comparison is SR60x vs RS1x, because it holds form factor constant and varies pad size: the smaller-padded one is ~2.5× more repeatable through 2–8 kHz. That points at pad size, not supra- vs circumaural, as the dominant variable — and it’s a direct design input: prefer the smaller pad.

Stated honestly: three different headphones, one unit each, one operator. Directional evidence from the right rig, not a controlled experiment.

The design goal, stated correctly

Not “minimise position sensitivity” — that optimises toward the wrong thing, because sensitivity can be low for two opposite reasons. It can be low because the acoustic design is robust. Or it can be low because the response is already at its floor: a leaky on-ear is insensitive in the bass because there’s no bass left to lose.

So: hold a response you’d actually choose, and be insensitive to placement at that response. As far as we know nobody publishes that as a design goal, and it’s the honest way to compete given the bass trade.

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System architecture

SPRUNG STEEL BOW  (bought — screwed at its end tabs)
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SLIDER × 2  (printed) — height adjustment + the yoke swivel
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YOKE × 2  (printed) — slider to cup, carries the tilt axis
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CUP × 2  (printed) — Ø48 body, Ø54 front lip, integral rear grille
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BAFFLE × 2  (printed, separate) + CLAMP RING × 2 (printed)
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EARPADS  (commodity Grado-pattern — not designed, not shipped)

Three degrees of freedom: swivel and tilt at the cup, plus the slider’s vertical travel.

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The decisions, and why

Spring steel, not a printed spring. Printed plastics creep under sustained strain and a headband is a sustained-strain application. PLA is worst and will visibly lose clamp force in weeks; PETG is better, nylon better still, but no FDM plastic is a good spring. A printed headband that works on day one and is loose by month three is the single most likely way this build disappoints someone. Forming our own bow was tried with printed jigs and failed — the steel springs back and the jig deflects before the stock does.

Screws at the bow joint. The fastener-free through-post sandwich is dropped. The bow has end-tab holes and is designed to be screwed; we use them. That spends a small number of M3s at the one joint carrying sustained spring load, which is the right place to spend them.

Commodity Grado-pattern pads. We design a rim the foam stretches over and ship no pad at all. This is the one interface where we deliberately don’t innovate, because diverging costs the builder the entire aftermarket. It also means bass tuning is a $10 purchase rather than a reprint — swapping flats for bowls is the main tonal lever you have.

Clamp ring for driver retention, and the framing that comes with it is the build’s standing tie-breaker: not ideal for a manufactured model, but for a tweaker it’s great. When serviceability and manufacturability conflict, serviceability wins, because the user is a tweaker.

Separate baffle — and for a better reason than print flatness: manufacturing, tweaking and repair. The baffle is the part a builder iterates on.

Clamp target: the HD 600 / DT 770 class. Explicitly not Grado — a Grado’s light clamp isn’t the goal. Watch item: both references are circumaural, so their clamp spreads around the ear onto the skull. The same force on a supra-aural concentrates on the ear itself, so the pressure is much higher. Expect the first wear test to be the arbiter.

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The locked geometry

The cup profile came off a Grado on the bench, then off a dimensioned reference solid. The key insight is that the “lip” is not a feature on the cup — it’s the front plate overhanging the body, and that single reading explains pad retention for free:

front plate / pad rim    Ø 54.0    LOCKED
steps in 3.0 per side
cup body                 Ø 48.0    LOCKED
interior                 Ø 42.0    → 3.0 mm wall
overall depth            27.6      LOCKED

The foam stretches over the Ø54 rim and grips the Ø48 body behind it. Retention is axial — the lip stops it climbing forward — and only lightly radial: it rotates freely on the cup, so the grip is locating, not clamping. That means lip depth matters more than rim-diameter precision, and the interface is forgiving: the same pads fit cups across a Ø54–56.7 family.

Driver: 40 mm, confirmed. It’s the standard and the design doesn’t chase a non-standard part.

Where we diverge from Grado on purpose

Copying a Grado would be the least interesting version of this project.

Grado does	We do	Why
Ø39.2 register smaller than the driver, so it seats behind a restricted aperture	Treat the aperture as a free acoustic variable, decoupled from the mount	With a clamp ring the aperture doesn’t have to double as the register
Screen as a separate Ø45 × 2 mm disc	Integral printed grille	One fewer part, one fewer thing to source
Barrel profile from wood turning	Whatever prints well	A barrel is a lathe form; inheriting it would be copying a manufacturing process we don’t use
Glued / pressed assembly	Clamp ring, serviceable	The tie-breaker above

The one place we don’t diverge is the pad interface, for the reason given above.

Prior-art boundary

Reference CAD from a forum thread was used to understand the architecture and to take the pad-mounting diameter as an interoperability dimension — the same class of act as matching a screw thread. No third-party geometry is imported, traced, or re-derived into our parts. This repo ships CAD publicly under MIT.

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What’s still open

• The form itself. The dimensions above are locked; the shape is not. The build was forked from an over-ear and the industrial-design brief was renamed rather than rewritten, so the CAD faithfully built a shrunken DT880. A form pass is open to resolve what a supra-aural in this family should actually look like — Grado is the right architectural reference (small cup, minimal band, everything visible) and the wrong styling target.
• The printed friction slider is the mechanism’s real unknown, and the part with the least precedent — printed detents that still hold after a few hundred adjustments are not a solved problem in the maker literature. A physical test coupon (one rail, five sleeves at graduated leaf thickness) settles it by feel rather than by analysis.
• The baffle is still on the Daily Driver’s Ø91 numbers and needs the same 54 mm rebuild the cup just had.
• Cable entry — fixed or detachable — is undecided.
• Clamp force as a number. The HD 600 / DT 770 target is a feel, not a spec. Converting it is cheap: spread the headphone across two blocks at a known separation, rest one arm on a kitchen scale, read the force, repeat with the references.

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Source: The CAD, STLs, and the running design log are developed in the open at github.com/makerphones/first-chair, the canonical home for the design files. The model is fully parametric — change the driver, the pad, or the head size and the parts regenerate to match.