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Premium Member
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354 Posts
Discussion Starter · #1 ·
The Stereo Integrity M3 Carbon drivers were on a 50% sale, so I picked up a pair, initially wanting to build an active pair of desktop speakers. That quickly changed as I don't really have the space for desktop speakers, and I've never built a boombox, so I went with the boombox route instead.

The end result is a pretty heavy boombox at 28lbs / ~12.5kg but with insanely sound quality and playback time. The Bluetooth range is extended a lot with the use of an "air-gain" antenna from eBay, although I have to find the best spot to mount it in the box. The USB charging ports are a real nice add-on, you can be sure that your phone won't run out of battery when streaming.

For a while I didn't have a volume control, so the volume had to be set by the source - which works fine over Bluetooth, but not with analog inputs. So, I had to add a volume control and chose the rotary encoder route which seems to work well. As a bonus it also works as a click button allowing me to change between a few different sound modes (various gain levels and effects).

The woofers are crossed quite high so I can get a bit more mid-bass. However, this forced me to run them in mono, as the two woofers share the same port, thus stereo imaging suffers a little bit in the mid-bass range, but it's a sacrifice that's worth it (vs having each woofer have its own chamber and port).

Box:
~10L per Peerless woofer
~2.4" ID port, box tuned to ~45Hz if I remember correctly
Speakers:
  • 1x pair of Stereo Integrity M3 Carbon
  • 1x pair of Peerless 830946 6-1/2" Woofer 4 Ohm
Amplifiers:
  • 1x Dayton Audio KAB-250v3 2x50W Class D Audio Amplifier Board with Bluetooth 4.0
  • 1x Dayton Audio DSPB-250 2x50W Class D Audio Amplifier Board with DSP
Power:
  • 1x Dayton Audio LBB-5 5 x 26650 - 21VDC output to the amp boards
  • 2x External USB for charging mobile phones etc
Inputs:
  • Bluetooth w/ AptX
  • 3.5mm / 1/8" jack
  • RCA jacks
Controls & LEDs:
  • 4 LEDs showing 0-100% battery level when button is pressed
  • BT LED
  • BT reset switch
  • On/off switch (really just standby - no real on/off switch yet)
  • Volume control (rotary encoder). This also acts as a sound mode switch (volume control is also a button that can be pressed), switching between:
    • 0 (default),
    • 1 (6dB gain for low gain sources)
    • 2 (stereo widening effect),
    • 3 (real-time pitch shift to several octaves lower, a fun "trick")
Crossover / DSP programming:


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Premium Member
Joined
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354 Posts
Discussion Starter · #4 ·
Super cool! Also, is that an M3 with Apex ARC-8's?
Good eye! They are Apex EC-7's, 10" in the front, 11" in the rear. Drastically increased the ride quality vs the stock competition 20" wheels, especially considering the state of the roads around here.
 
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