Description: 

This design is maxing out what a standard 3D printer with 250mm square build volume can handle to create a large subwoofer with high sound pressure level, without ending up with a 3D printed parts puzzle with 20 pieces.  

The port is tuned for 35 Hz, F3 (-3dB) 30 Hz. The plate amp has an effective 12dB low pass filter, so it will fade out at around 120Hz on standard settings, but of course this can be adjusted higher with the crossover potentiometer. 

The sub is rather large - stands around 70cm tall. Instead of standing up on feet down-firing, it can be positioned on the side, for this I have included a grille for protection which can attached to the threads for the feet. The grille is not needed when upright. 

Cost of the components is moderate, at the time the speaker is US $ 40, the plate amp $ 50, PLA around $ 50, heat inserts and bolts $10. 

You will need satellites which can go as low as at least 100 Hz, from there the subwoofer will take over. I combined it with my 4" full range speakers (see 4th picture) which was quite impressive with broad sound stage and clarity, although the subwoofer had to be turned down a lot by decreasing the volume on the amplifier to match the low efficiency of the full range speakers. Currently I run the setup on the Onoorus D4 Pro Amplifier, which  amongst things like HDMI and optical input has a low pass filter for the subwoofer and also a high pass filter for the satellites - the satellite speakers are hardly moving at high levels and can be played a lot louder before mechanically exceeding their Xmax amplitude and start distorting or getting destroyed. 

Compared to the previous subwoofer design with 2x 4" long throw chassis, this uses a single 6.5" woofer which equally can go down to an F3 of 30 Hz, but is much more efficient and hence louder - 89 dBA at 1 Watt, vs 83 dBA for the soft suspension speakers. See attached near field measurement graph from REW.  The Peerless speaker is also quite reasonably priced, compared to the two long throw 4" woofers from Dayton Audio, or one 5" Tang Band. 

The plate amplifier is 100W @ 8Ohm Class AB, which sounds better and warmer than the usual Class D amps in previous designs. It also does not need a power brick (I hate these things lying around), it plugs straight into mains with a kettle cable. It gets mildly warm on the cooling fins as you would expect for a Class A/B with MOSFET transistors, but never hot. The plate amplifier slightly leaks air through various holes for switches and potentiometers despite the manufacturers attempts to seal it, so it gets its own sealed enclosure with just the speaker cable passing through.

Alternative: Class D 2.1 amplifier with or without Bluetooth (see fifth photo).  This has the advantage that is it a bit cheaper, the satellites can be powered as well, and no external amplifier is needed. As I did not want to redesign the whole thing for this, there is an adapter plate which fits into the Class D amplifier case, no other changes needed. Disadvantage would be a little less power, and an external power supply is needed. However, that is a neat and powerful sound system for around $ 200 which can be used for computer or TV via RCA input, or phone/laptop with Bluetooth connection.  

The internal size of the cabinet of 655mm creates a standing wave of around 260 Hz which is well noticeable despite the low pass filter kicking in at 100 Hz. To eliminate the standing wave, there is a Helmholtz resonator build in the top section, just in case you are wondering about the the weird internal structure. That took a lot of tuning to get it right, but it avoids spending $ 200 on passive components for a notch filter or enormous amounts of damping material. 

Printing:

Core XY printer required - I don't know if a bed slinger can handle a 2 kg heavy object without slowing down. One could try, I guess. 

It will take at least a week of printing time, so make sure your printer is in good shape. I used PLA matte, the cheap 5kg spools from Sunlu/Jayo on eBay or AliExpress. If you have an AMS which loads new spools, I guess 1kg spools would work. PLA-CF or PETG-GF would be looking a bit more classy, but is 2x the price and not available in large spools. Suggest TPU for the feet.

A well cleaned PEI print plate provides enough bed adhesion. Auxiliary cooling turned off to prevent warping. Some of my prints warped a tiny bit, maybe 1 millimetre, but pulled the PEI plate up from the magnetic base rather than coming off the build plate. 

Suggest a 0.6mm nozzle, with 0.24 mm layer height. I have not tested this with a 0.4mm nozzle, however it should work but takes 30% longer print time. 25% gyroid infill to prevent warping.

When oriented correctly on the build plate, no support for any of the parts is needed - all support structures are designed in with breakaway fins, walls and rings.

The orientation of the parts on the build plate:

Assembly:

After printing, break away all the inbuilt supports, in the amplifier enclosure, around the outside of the base and mid section, the port.  The baffle and three sections have to be glued together, start with the baffle.  I used JB Weld PlasticBonder as its starts curing around 20 minutes, but any Epoxy glue or construction adhesive will do, with some longer curing time. Clamp for 1 hour with JB Weld, or a 24h with Epoxy. Avoid Superglue - it's too viscous and will create leaks. Some glue around the loudspeaker cable where it enters the amplifier enclosure. Several M5 and M4 bolts for the loudspeaker and amplifier. The speaker chassis has a foam gasket attached, so none additional needed. 

Damping material:

Not needed, most conventional damping materials would be not doing anything at low frequencies < 200Hz. If your are worried about cabinet resonance, sound proofing material like Alubutyl (as used in cars) can be applied to the internal walls. For standing wave suppression , see above, the Helmholtz resonator takes care of this. 

Bill of materials:

8kg of 3D filament like PLA matte

6.5 " Speaker Peerless HDS-P830990, or alternative same size with paper membrane and even better efficiency Peerless HDS-P830875

Class A/B Amplifier 

Class D Amplifier 2.1 Aiyima 

Class D Amplifier 2.1 with Bluetooth 

Heat inserts 10x M4 8.1mm long for the amplifier, 6x M5 9.5mm long for the speaker  - like the ones from CNC Kitchen

30cm of 14G loudspeaker cable from amp to speaker

PLA compatible glue like JB Weld PlasticBonder (small tubes, expensive) or any Epoxy/construction glue of choice

10x M4 hex bolts 10mm and 6x M5 hex bolts 12mm, stainless steel or blackened mild steel