Thanks! Yes, thinking of going as large as 8 or 10 inches. Of course those will probably require a thin plywood panel over the foam to support the weight of the drivers which will be pushing 6-8 lbs ea at that point.
Those are actually grey colored open cell foam blocks. I initially put them in there to reduce the Q of the cabinet but found that I was losing too much bass due to the volume they take up so I ended up pulling them out. The sub achieved deeper bass (by about 5 Hz) and the flex on the foam enclosure provides adequate de-Q'ing damping I think. Currently they are running empty - no stuffing, no foam, no felt or fiberglass lining.
Thank you for sharing your project, xjk. You are now #2 on my list of amazing tinkerers (after Patrick Bateman). I will probably try your 1" foam idea on my next iteration of Bateman's "sound bar". Also perhaps combine with my ever-growing collection of "free" coroplast (harvested road sid signs). 
If you are interested in using XPS foam for speakers, let me introduce you to the "Light as Air BLH" it was reverse engineered by me and executed by Bcmbob (the master of water cooled Nelson Pass amps), that you can make a nice compact BLH fullrange speaker that reaches 30Hz with the DNA horn implemented in pink foam.
http://www.diyaudio.com/forums/full-range/235457-decware-dna-horn.html
http://www.diyaudio.com/forums/full-range/235457-decware-dna-horn.html
What is your question? Can we build a DIY version of the mp3 speaker in your photo? You can take the driver and amp out and put it into a larger enclosure and it will sound better. A Cornu would work. But that thing is already small. So don't understand your question of how to build it so it is not huge?
I heard this gizmo (belongs to a relative) and I'm impressed by the sound a tiny Bluetooth speaker can deliver. Rather than dissect the unit as some others have done in this thread I would like to build some thing for portable use that is a little more upscale. I am still working my way through the foam core thread (up to April 2013!) This would make a wonderful project for me. I probably won't do a spiral type. I don't have any precise design but I envision something that would fit under a standard laptop and/or giant Android pad (12.5 " screen). Portable is required, battery power is not. I think I'm drifting off topic of this thread; perhaps you can direct me to others? Thanks!
Sent from my NV570P using Tapatalk
Sent from my NV570P using Tapatalk
I agree fiberglass or carbon fiber would be great. But a 1/8 in layer of plywood glued on with liquid nails or contact cement would help a lot too. Heck, a burlap bag and PVA would be great
but the charm is how simple and clean it is to make and I don't think the sound vibrations through the foam are detracting from its function as a sub.
Get two of these they are only $10 more ea but pack a wallop with 8mm xmax and lower fs. I can build a sim of this one as a SLPP sub if you want. You can wire in series for 8ohms or in parallel for 2ohms if you have a 2ohm amp.
MCM Audio Select 8'' High Excursion Woofer - 120W RMS 4ohm | 55-2421 (552421) | MCM Audio Select
This could be a very powerful and compact sub with these drivers. Hope you give it a try.
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SLBP Sub with MCM 55-2924 drivers
Design is with dual MCM 55-2924 drivers wired in series each driver has a 25 liter chamber behind it (approx 11 in long x 14 in deep x 10 in tall ea) with central 4.75 in wide slot x 10 in tall x 15 in deep slot fitted with push-pull drivers. Each chamber has a 0.5 in wide x 10 in tall x 15 in long slot vent feeding into the central slot port. Rough exterior dimensions of box is 25 in tall x 16.5 in deep x 11.5 in tall if using 0.75 in thick ply. If using 1 in XPS foam, size will be about +1 in all exterior dimensions. Use two layers of 1/8 in ply sandwiched (contact cement of liquid nails) with 1/2 in XPS for the driver cutout panels for wood screws to bite into. This sub has the ability to reach a true 30 Hz at almost 120 dB at 1m when drivern to xmax at 43 volts. I am using a 25.5 Hz -24dB/oct HPF to prevent cone over excursion. I know, it is not a perfectly flat response but this is preliminary and I can tweak some more. However, room gain and room modes will really mess with it and not care how flat it is now.
SPL vs Freq at 1 m in 2pi (no back wall):
Cone excursion at xmax:
SPL vs Freq at 1m in 2pi at xmax:
SPL vs Freq at 1m in 2pi at xmax with 100 Hz -48dB/oct LPF:
Design is with dual MCM 55-2924 drivers wired in series each driver has a 25 liter chamber behind it (approx 11 in long x 14 in deep x 10 in tall ea) with central 4.75 in wide slot x 10 in tall x 15 in deep slot fitted with push-pull drivers. Each chamber has a 0.5 in wide x 10 in tall x 15 in long slot vent feeding into the central slot port. Rough exterior dimensions of box is 25 in tall x 16.5 in deep x 11.5 in tall if using 0.75 in thick ply. If using 1 in XPS foam, size will be about +1 in all exterior dimensions. Use two layers of 1/8 in ply sandwiched (contact cement of liquid nails) with 1/2 in XPS for the driver cutout panels for wood screws to bite into. This sub has the ability to reach a true 30 Hz at almost 120 dB at 1m when drivern to xmax at 43 volts. I am using a 25.5 Hz -24dB/oct HPF to prevent cone over excursion. I know, it is not a perfectly flat response but this is preliminary and I can tweak some more. However, room gain and room modes will really mess with it and not care how flat it is now.
SPL vs Freq at 1 m in 2pi (no back wall):
Cone excursion at xmax:
SPL vs Freq at 1m in 2pi at xmax:
SPL vs Freq at 1m in 2pi at xmax with 100 Hz -48dB/oct LPF:
Attachments
Drivers from the grave
Love the XPS sub!
xrk, can you sim one made with these drivers (attached)? I've had them sitting idle for ages... I even refoamed them 13 years ago!
If not those, how about these: JAMO 20395 8" Treated Paper Cone Woofer
*Power handling: 50 watts RMS/100 watts max
*VCdia: 1"
*Le: 1.40 mH
*Impedance: 8 ohms
*Re: 5.02 ohms
*Frequency response: 40-2,000 Hz
*Fs: 44 Hz
*SPL: 90 dB 1W/1m
*Vas: 1.7 cu. ft.
*Qms: 5.08
*Qes: 0.61
*Qts: 0.55
*Xmax: 2 mm
*Dimensions: A: 8-1/16", B: 7-1/4", C: 3-1/4"
You are a wonderful asset to this forum, my man. Cheers.
Love the XPS sub!
xrk, can you sim one made with these drivers (attached)? I've had them sitting idle for ages... I even refoamed them 13 years ago!
If not those, how about these: JAMO 20395 8" Treated Paper Cone Woofer
*Power handling: 50 watts RMS/100 watts max
*VCdia: 1"
*Le: 1.40 mH
*Impedance: 8 ohms
*Re: 5.02 ohms
*Frequency response: 40-2,000 Hz
*Fs: 44 Hz
*SPL: 90 dB 1W/1m
*Vas: 1.7 cu. ft.
*Qms: 5.08
*Qes: 0.61
*Qts: 0.55
*Xmax: 2 mm
*Dimensions: A: 8-1/16", B: 7-1/4", C: 3-1/4"
You are a wonderful asset to this forum, my man. Cheers.
Attachments
Love the XPS sub!
xrk, can you sim one made with these drivers (attached)? I've had them sitting idle for ages... I even refoamed them 13 years ago!
If not those, how about these: JAMO 20395 8" Treated Paper Cone Woofer
*Power handling: 50 watts RMS/100 watts max
*VCdia: 1"
*Le: 1.40 mH
*Impedance: 8 ohms
*Re: 5.02 ohms
*Frequency response: 40-2,000 Hz
*Fs: 44 Hz
*SPL: 90 dB 1W/1m
*Vas: 1.7 cu. ft.
*Qms: 5.08
*Qes: 0.61
*Qts: 0.55
*Xmax: 2 mm
*Dimensions: A: 8-1/16", B: 7-1/4", C: 3-1/4"
You are a wonderful asset to this forum, my man. Cheers.
Thanks for the kind words.
Qts is kind if large so cabinet will be big if you want to go low. What are your goals in terms of bass extension and max cabinet size, etc.
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Tweaked MCM 55-2421 PPSL Sub
I tweaked the design some more to flatten it and to set the bass extension at 30 Hz (-3dB) while trying to minimize the volume to keep it small. To do this, I am using a corner room placement typical of how a sub like this will be used (in my experience) to give the added bass gain that enables a smaller box. The design ended up at 18.5 liters per chamber with 0.75 in deep x 10 in tall x 24 in long slot vents leading to a central push-pull slot-loaded vent that is 4.75 in wide (to fit drivers in push-pull) x 10 in tall x 10 in deep. A 27 Hz -24dB/oct HPF is used to prevent over-excursion and it has wide bandwidth up to nearly 200 Hz if you wanted to use it that far. I have opted for a 120 Hz -48dB/oct LPF that should let this integrate well with many systems (or set it lower if you want). Here is the predicted response at max drive voltage of 46 volts.
I tweaked the design some more to flatten it and to set the bass extension at 30 Hz (-3dB) while trying to minimize the volume to keep it small. To do this, I am using a corner room placement typical of how a sub like this will be used (in my experience) to give the added bass gain that enables a smaller box. The design ended up at 18.5 liters per chamber with 0.75 in deep x 10 in tall x 24 in long slot vents leading to a central push-pull slot-loaded vent that is 4.75 in wide (to fit drivers in push-pull) x 10 in tall x 10 in deep. A 27 Hz -24dB/oct HPF is used to prevent over-excursion and it has wide bandwidth up to nearly 200 Hz if you wanted to use it that far. I have opted for a 120 Hz -48dB/oct LPF that should let this integrate well with many systems (or set it lower if you want). Here is the predicted response at max drive voltage of 46 volts.
