Open Speaker V0.2 — short-M3 modular prototype

Fasteners

• Front basket ↔ motor/spider plate: 3 × M3 × 16 mm
• Rear magnet carrier ↔ motor/spider plate: 3 × M3 × 12 mm
• 6 × M3 hex nuts
• Optional M3 washers under exposed screw heads

The two screw patterns are staggered, so each joint is completely independent.

What to print

PLA / PETG

• front_basket.stl — 1
• motor_spider_plate.stl — 1
• rear_magnet_carrier.stl — 1
• coil_mandrel.stl — 1 (tool only)
• diaphragm_template.stl — optional tool
• coil_sizing_gauge.stl — optional tool

TPU

• surround_TPU.stl — 1
• spider_TPU.stl — 1

All structural pieces are intended to print in the supplied orientation without supports.

How the rigid stack bolts together

Front joint — M3 × 16

1. Print the front basket with its large annular face on the bed and the three standoffs upward.
2. Press one M3 hex nut into the pocket at the free end of each standoff.
3. The motor/spider plate sits against those three standoffs.
4. From the rear side of the motor plate, install three M3 × 16 screws into those captive nuts.
5. The motor plate has recessed screw-head pockets so the heads sit essentially flush with its rear face.

This leaves the rear face clear for the magnet carrier.

Rear joint — M3 × 12

1. Press three M3 nuts into the three front-side pockets on the motor/spider plate. These are on a smaller, 60°-staggered bolt circle.
2. Place the rear magnet carrier against the rear face of the motor plate.
3. Install three M3 × 12 screws from the back of the rear carrier into those captive nuts.

The rear carrier can therefore be removed without loosening the front basket or disturbing the diaphragm/surround.

Magnet

Built around these magnets:

https://www.amazon.ca/Neosmuk-Neodymium-Mounting-Magnetic-Strength/dp/B0FVR9PQDJ/ref=sr_1_26

The carrier is based on the measured magnet size:

• ~30.0 mm OD
• ~6.35 mm thick
• centre mounting-hole clearance defaults to 5.5 mm; edit magnet_mount_hole_d after measuring the actual supplied screw

You only need one magnet. Keep the other three well away during assembly.

Voice-coil former

The final former is not printed.

1. Print coil_mandrel.stl.
2. Wrap thin PET or paper around the mandrel.
3. Glue only the seam.
4. Remove the tube after the seam cures.

Voice coil

Use your 30 AWG enamelled copper wire.

1. Put the lightweight former back onto the winding mandrel.
2. Leave ~100 mm as the first lead.
3. Wind tightly and evenly over roughly 8 mm height.
4. Start around 80–120 turns.
5. Use the minimum adhesive needed to stabilize the winding.
6. Leave ~100 mm as the second lead.
7. Measure DC resistance before connecting an amplifier.
8. Remove enamel only at the two electrical ends.

coil_mean_d = 24.0 remains an experimental starting point because your pot magnet does not have the same engineered radial air gap as a commercial loudspeaker motor.

Moving assembly

The moving object is:

diaphragm + former + copper voice coil

The stationary object is:

front basket + motor plate + rear magnet carrier + magnet

The TPU surround and TPU spider connect the two while allowing axial motion.

Spider

1. Slip the TPU spider over the former.
2. Glue the spider inner ring to the former.
3. Pass the moving assembly through the motor plate.
4. Center the former carefully.
5. Glue the spider outer ring to the raised spider land on the motor plate.
6. Verify free axial motion with no rubbing.

Surround

1. Glue the surround inner lip to the diaphragm perimeter.
2. Glue the outer lip to the front basket flange.
3. Gently press the diaphragm. It should move axially and return to neutral without scraping.

Recommended build order

1. Print only the three rigid parts first.
2. Insert the six captive M3 nuts.
3. Assemble the front joint with M3 × 16 screws.
4. Assemble the rear joint with M3 × 12 screws.
5. Test-fit one magnet.
6. If all rigid geometry fits, print TPU pieces and make the voice coil.
7. Assemble the spider, moving assembly and surround.
8. Route very flexible coil leads to stationary terminals.
9. Test at low amplifier level first.

Why V0.2 is better than the (unpublished) V0.1

• Uses your existing M3 × 12 and M3 × 16 hardware.
• No long through-bolts.
• Rear carrier is independently removable.
• Front diaphragm structure can remain assembled while experimenting with the magnet/motor.
• Captive nuts avoid heat-set inserts.
• Screw patterns are staggered to avoid collisions.
• Structural pieces remain support-free FDM parts.