Alpair 5.2 mini array for rear 4 channel per side

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I've completed 2 channels in PVC for the Alpair 5 Gen.2. I took great care in order to have them flush mounted to the enclosures. Also, they are individually amplified with Tom Christiansen's LM3886DR 68W Class AB amplifiers inside each enclosure. The goal was to keep the wires from the amp to the drivers as short as possible. 4.5" in this case. I bought the 2 bare boards from Tom and assembled them myself.

The +-30V power come from a 500W external SMPS and the audio signal from the output of a miniDSP 2x4 and go thru a DIN type connector mounted to the enclosure. A miniDIGI mounted together with the miniDSP allows optical input and pass-thru to the other channel. This 500W power supply and miniDSP/miniDIGI combo are capable of powering 4 channels per side.

So far, I have been able to listen to them and experiment with volume levels. 50% is way too loud. I only did this for a split second as I realize these as all MA drivers need a break in period.

Credit to Tom Christiansen and miniDSP for excellent documentation.
 
You asked for it!
First a picture of my front channel speakers using the Pluvia 7's and a size comparison. The Pluvia 7 enclosure is about .1cuft with a rolloff of about 150Hz. The Alpair 5.2 enclosure is about .05cuft with a rolloff of about 200Hz.
I chose the Alpair 5.2 because of it's unique single suspension. It has no spider.
 

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Here are the beginning stages where I'm seeing if the board will fit inside. Also I have pictured the 2 variable hole saws I purchased from eBay to drill the flanges with the drill press.
EDIT: I actually wound up using one standoff and screw to mount the board. No reason for 4, it's not going anywhere!
 

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Back to the LM3886DR internal board mount and the heatsink I chose. The heatsink needed mod so it doesn't hit the capacitors. You'll see this mod in future pics. But it's plenty big for driving these little 20Watt Full rangers! (I hope).
EDIT: Because I really wanted to make these little units to be taken apart, it was at this point I decided to use a single screw and standoff for the amp board. Otherwise I would've had to remove the heatsink then screw/unscrew the board on that side (under the heatsink). I made a judgment call that all that effort would be a waste.
EDIT: You can also see the reliefs or slots I cut into the PVC for easier disassembly. Those other 'ribbed' endcaps I wound up not using.
 

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Here's the final flange mounting after painting the endcaps. I had to have the driver mounted to the flange then 'eye' it so the driver looked flush, then I hot PVC glued the flange to the enclosure. It worked pretty well, but I needed another gasket to make the Alpair flush, which you can see those orange ones I had to manually cut with an exacto knife and scissors.
A side note: I originally wanted to press fit in the Alpairs, but then some little voice in my head said 'no', isolate the driver from the enclosure, so I went abit wider on the final holes for driver placement.
 

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This was the difficult part since I wanted to make these enclosures able to be taken apart easily. How to wire? How long, etc.
In the second pic you can see how short the wires are from the amp to the drivers. Also how I had to mod the heatsink to clear the cap's on the amp board.
EDIT: Also, the lovely miniDIGI/miniDSP combo on the left. ;)

We're getting there. Almost done!
 

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In this pic The +-30VDC power/GND is wired and also RCA in/GND. 5 pins. So in order to disassemble, driver removed first. then slip off front endcap. Then you have to desolder the power in and RCA in and then the rear encap can be removed. Abit convoluted but I dare anyone to come up with something better.
 

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Left pic: Final prewiring and staging. My 2 little babies completed with the miniDIGI/miniDSP combo's and the 2 +-30VDC SMPS's.

Right pic: Final setup for the left channel. Power for the miniDSP combo comes from a 15VDC 1A separate output from the SMPS. No spdif in yet...
 

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Left pic: Getting ready to program the miniDSP's with the plug-in from the laptop.
Right pic: Success! All wired up and running. All smoke intact and not let out. Whew! Actually had to rearrange some jumpers on the miniDSP to get it working (been through that b4).

Thanks for watching!
 

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Nice project. How does the Alpair 5.2's sound compared to the Pluvia 7 (sonically)?
It's difficult to say offhand because it's been awhile since I've listened to just 1 Pluvia 7 per side.
I can say it sounded crisp and clear, with no thought of adding a tweeter. Definitely needs low end help obviously, especially with an enclosure this small.

Tom's amplifier @68W was way more than I needed, which is a good thing as I want to keep away from distortion, clipping or anything even close to maxing anything. Even at half volume they were plenty loud. But I only did a split second test because there's no HP filter yet and the drivers aren't broken in yet.

What I was planning to do soon was get a FR plot using REW and a mic on the Alpair 5.2. It shouldn't be too difficult to dismount 1 P7 and do a comparison, although the P7 will be powered by an external amplifier with a programmable crossover @200Hz (not sure how many dB/oct). For the Alpair 5.2's I'll first program the miniDSP's for a high pass filter at 48dB/oct @200Hz then do the fequency sweeps and measure.
 
I'm no expert with REW, but I setup the speakers again like in Post#13, except pointed forward. I have a Dayton external mic, pointed at the right speaker, hooked up to a Behringer UM2 which has phantom power to the mic and outputs the signal to the computer thru USB that REW is seeing. On the left channel is another Dayton mic plugged into a tablet at the same distance from the left channel to approximate SPL. Got it up to 80dB. I didn't want to damage the drivers as they aren't broken in yet, only a few hours. So this is why not at their rated 84dB, but close..

What I've noticed is:
1) Even in this ultra small .054cuft enclosure bass started to come in @60Hz from the sine wave log sweep.
2) Tons of low frequency noise below that, like my fridge and 19in rack mount fans.
This is the plot without any DSP programming. Hopefully a decent reference? Any tips or hints to more accuracy? I intend to have a very steep high pass @200Hz as I've mentioned.
 

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Looks fantastic!...
The FR plot or the speakers?

...Can I ask why you chose to put an amp in each box rather than wiring them into one single amp?
3 primary reasons in order of importance:

1) Eliminate the inductance and resistance associated with long wires between the amp and drivers.
2) A DSP per driver to experiment with frequency shading the mini arrays.
3) See if a really good 68W amp could successfully drive a driver rated @15W without hurting it.

Sometime soon I should have a chance to do a FR plot on the Pluvia 7 .1cuft enclosures for comparison. These have been fully burnt in, believe me!
 
This project continues.
Over the past month I've been ordering stuff here and there. Not quite enough to complete 6 more channels for a total of 8 per side, but getting there. I was impressed with what I had heard from the original 2 single suspension Alpair 5.2 drivers.
Last night, I just put together 6 more PVC enclosures, just bare endcaps and tubes to join the endcaps.
6 more heat sinks for LM3886 Done Right Amps.
6 more LM3886 IC's.
And today just ordered 6 LM3886 Done Right bare boards.
 
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