Yolk Bookshelf Speakers: print them, build them, stream to them

01 / What you’re building

A two-way speaker with its own amp and Wi-Fi.

Each speaker is a vented 5-inch-woofer-plus-dome-tweeter box. Inside the rear bay sits a small streaming amplifier board: it joins your Wi-Fi, receives the music, splits it into bass and treble with a DSP crossover, and drives the two drivers directly. There is no separate amplifier and no cable between the speakers, only a power brick for each. A subwoofer can join later over the same network.

Figures marked simulated come from a computer model fed with manufacturer datasheet data. Nothing has been measured.

02 / What you need

The parts list for a pair.

Total for the pair: about EUR 360 for the quantities used, or about EUR 415 if you buy the whole packs and spools listed. Prices are snapshots from 16 October 2026 and will move. Items marked ships with your JLC order can go in the same LCSC / JLC order as the Relay boards. Stock changes, so check LCSC before ordering.

03 / Print it

About 98 hours and 4.6 kg for the pair.

Settings below are a Bambu Studio command-line estimate for a Bambu Lab P2S with a 0.4 mm nozzle: the 0.24mm Standard @BBL P2S process, 5 top and 4 bottom layers, no supports. These are slicer estimates, not measured prints. Charcoal PLA for most parts, PETG for the upper body because it holds the warm board.

Download the STL files

All ten files, about 2.6 MB in total, all checked watertight and within the bed. Print the quantities in the table above.

• body_lower.stl
• body_upper.stl
• baffle_lower.stl
• baffle_upper_L.stl
• baffle_upper_R.stl
• rear_plate_lower.stl
• rear_plate_upper.stl
• port_tube.stl
• accent_strip_green.stl
• accent_ring_green.stl

Printing notes

• Test first. Print one port_tube and one baffle_upper to check the driver rebates, insert holes and port socket on your printer before committing about 100 hours.
• No supports. Screw bosses are 45° corbels, the baffles meet on a 45° scarf and the port flares are concave or 45°. Bambu Studio warns of a “floating cantilever” on body_upper: that is the four board standoffs and the finned joint bosses, which should bridge. If they sag, paint supports on just those.
• Walls. The 8 mm cabinet walls print as 4 perimeters with a 25 % gyroid core, a stiff light sandwich that is simulated to push panel resonances up about 20 % versus solid. Do not go below 3 walls or 15 % infill.
• PETG prints best on the textured PEI plate with glue stick.
• Faster: a 0.6 mm nozzle at 0.30 mm layers should cut the time by roughly 40 %.
• Optional, untested: sand-filled side walls for more damping. Do one tub first.

Option / Wooden front (olive)

An olive-wood front, the same box behind it.

This variant replaces the two printed baffles with one solid piece of kiln-dried olive wood, 20 mm thick. The printed body behind it, the 7.9 L volume, the port tuning (57.5 Hz) and the DSP settings stay the same. Like the rest of the speaker it is designed, not built, and the wood figures are estimates.

What changes

	Printed	Olive
Baffle	2 printed plates, 18 mm, 45° scarf	1 piece of olive, 20 mm, 210 × 300 mm, R12 roundover
Neon accent	Strip on the seam, ring round the tweeter	Green strips in a groove round the printed body, 6 mm behind the wood (sides and top). No groove in the wood
Body front	Tongue into the baffle groove	Gasket seat: 5 × 2 mm groove for 5 × 3 mm EPDM closed-cell cord
Drivers	Screws into brass inserts	Wood screws in pilot holes (M4 wood inserts for repeated removal)
Port	Flare printed in the baffle	R12 roundover routed into the Ø40 bore; a 104 mm printed tube glued in from the back
Depth	236 mm	238 mm (the extra 2 mm of wood goes forward)

See the olive version in 3D

Buying the wood

• Kiln-dried olive, 8–10 % moisture. Ask for a meter reading. Fresh or air-dried olive moves and cracks badly.
• Size per baffle: finished 210 × 300 × 20 mm, so rough stock of at least 230 × 330 × 25–27 mm. Two baffles, plus a spare blank if the board has defects.
• One quartersawn board is best. Wide clear olive is rare, so 3–4 edge-glued staves are fine. Grain vertical (along the 300 mm), growth rings alternating between staves, joints away from the narrow bridges between the cut-outs.
• Reject checks (cracks), pith, bark inclusions or loose knots near the woofer, tweeter or port cut-outs, or near the screw positions 14 mm from the edges. Small tight knots in the middle are decoration.
• Acclimatise the wood for 1–2 weeks in the room where the speakers will live, stickered with air on both faces, then plane both faces equally to 20 mm.
• Finish: sand to P180–240, wipe with alcohol (olive is oily), two thin coats of hard-wax oil on the front and edges, and seal the back face and every cut-out too so the board stays flat.

A CNC shop works straight from the DXF or STEP. With a hand router, stick the 1:1 template on the front, centre-punch every cross and cut the rebates and cut-outs with a circle jig. Test the rebate depths on scrap so the driver flanges sit flush. Print the body halves, rear plates, port and green strips from the repository’s speakers/stl/olive folder: those body halves have the gasket seat and the accent groove.

Cutting drawings

04 / Assemble it

Solder-free, one speaker at a time.

Nothing has been built yet, so treat the steps as a plan that the first prototype will correct. Do every step twice, once per speaker. The 3D model below walks through the same eleven steps on the real CAD parts; switch it to the olive front, explode it, or cut it open to see the port, the damping and the board bay.

1. Press in the heat-set inserts

   Use a soldering iron with an insert tip, about 220 °C for PLA and 240 °C for PETG. No solder is involved.

   Baffle lower: 4 × M4. Baffle upper: 4 × M3. Body lower: 4 × M4 in the front corbels, 4 × M4 in the column tops at the split, 8 × M3 in the rear face. Body upper: 4 × M4 in the front corbels, 6 × M3 in the rear face, 4 × M2.5 in the board standoffs.

   No iron at all? The CAD has a self-tapping option for thread-forming plastic screws, fine for a few reassemblies.

2. Test-fit before gluing

   Check the woofer and tweeter sit flush in their rebates, the port tube fits its socket snugly, and the tongue of one body half slides into the groove of the other with light pressure.

3. Join the body halves

   Run a bead of sealant in the groove of the upper body, stack it on the lower body and fit the four M4 × 20 bolts: two at the front inside the chamber, reached through the open front, and two in the rear bay. Wipe off squeeze-out inside.

4. Glue the port

   Epoxy (or CA glue for PLA) the port tube into the socket on the back of the upper baffle, flare towards the inside. Check it is square.

5. Fit the baffles

   Dry-fit both baffles. Then add sealant in the baffle grooves, glue the 45° scarf faces together with epoxy, and fix each plate with four countersunk M4 × 16 screws. Let it cure.

6. Add the neon inlays

   Glue the green strip into the seam groove and the ring around the tweeter, a drop of CA glue every 2 cm. The strip covers the scarf seam.

7. Damping, before the drivers

   Line the divider (both sides), the top and the bottom of the chamber with 15–20 mm wadding, about 0.18 m² per speaker, using spray adhesive or hot glue. Keep 30 mm clear in front of the port’s inner end, and add a light loose layer behind the woofer.

8. Wire through the divider

   Pass two pairs of 0.75 mm² wire, one for the woofer and one for the tweeter, about 40 cm each, through the Ø10 hole in the upper divider. Fit the grommet and seal around the wires with silicone. The box must be airtight. Mark the plus wires.

9. Connect and mount the drivers

   Crimp insulated female fastons on the wire ends. Measure the tab widths first. If a tab will not take a faston, use a WAGO 221 lever connector on a short tail. Push them on with red (+) to the marked wire.

   Mount the woofer with four M4 × 12 screws and the tweeter with four M3 × 10, tightening in a cross pattern only until the flange seats. Over-tightening cracks PLA.

10. Mount the amp board in its vented bay

    The board lives in the rear bay, outside the sealed chamber. Screw it onto the four standoffs with M2.5 × 6 screws, components facing out through the window. Crimp fork spades on the wires and connect the woofer to output A and the tweeter to output B. Check the silkscreen for which terminal is which. Leave the bay vents uncovered.

11. Rear plates, feet, power brick

    Fit the lower rear plate (slots at the bottom) and the upper rear plate (the window) with M3 × 8 countersunk screws, and stick four rubber feet underneath. Plug the 24 V brick’s lead into the board’s barrel jack through the window. The brick connects to the wall with a normal C13 mains cord and stays outside the speaker.

Wiring, per speaker

Simplified wiring. Confirm the terminal labelling on your board’s silkscreen.

Sealing check, before any music

With the drivers in and the rear plates off, cover the port mouth with tape. Push the woofer cone in gently with flat fingers: it should spring back slowly. A quick return or a hiss means a leak, so check the body split, the scarf, the baffle edges and the grommet, and fix it with sealant. Remove the tape afterwards.

05 / Set up the sound

Flash, tune, pair.

1. Flash the board

   Use the browser installer for the airplay-esp32 project in Chrome or Edge, pick the louder-esp32-s3-plus target, connect the board by USB-C and flash. The web interface files are included in the web install.

2. Join Wi-Fi and name the boards

   Join your network through the board’s setup access point, then name one “Yolk L” and the other “Yolk R” on their web pages.

3. Before connecting the brick for real

   In the board’s web interface, mute output B (the tweeter) and set the maximum volume to about 50 %. The factory signal chain sends full-range audio to both outputs, and bass would damage the tweeter until the crossover is in.

4. Load the crossover

   Open the board’s /bq equaliser page at its IP address. Set routing to “one channel to both outputs”: Left on Yolk L and Right on Yolk R, outputs not ganged. Use “Build crossover” with “both bands on one amplifier”, 2000 Hz, Linkwitz-Riley 24 dB/oct, then add the three extra filters from the table below by hand. Apply, then unmute B at low volume, listen, and “Commit to flash” once it sounds right.

5. Check polarity

   Temporarily tick Inv on B. The sum should get clearly worse, with a deep dip around 2 kHz. If it gets better, a driver is wired backwards: fix the wiring, not the tick box.

6. Pair left and right

   Group “Yolk L” and “Yolk R” in your AirPlay controller (for example Control Center or a Music Assistant group). Play a mono click track and sit at the listening position: you should hear one sharp, centred click, not two.

DSP values (starting point, simulated)

Levels: A (woofer) 0 dB, B (tweeter) −4.5 dB. Inv: none. These are a simulated starting point and should be refined by measurement.

The board’s equaliser also accepts raw biquad coefficients; the repository’s DSP file lists them at 48 kHz.

First power-on checks

• Drivers wired plus to plus (red tab), woofer on A and tweeter on B, no stray strands at the screw terminals.
• Output B muted and max volume about 50 % before the first stream.
• Power the brick. The board LED comes up, with no smell or noise. After 10 minutes the board should be warm, not too hot to hold.
• Stream quietly and check the woofer alone. Then enter the crossover, unmute B and check the tweeter alone (mute A). Then both together.
• The sealing check passed, and there are no buzzes on a slow 20–200 Hz sine sweep at moderate volume.
• After an hour of loud playback, the board and standoffs stay below about 60 °C. Keep the bay vents uncovered and don’t push the speaker against a wall that closes the window.

06 / How it sounds on paper

Simulation only. Nothing measured.

07 / Known risks

What could go wrong.

A design that has never been built has open questions. These are the ones to know about before you spend 100 hours of printer time.