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Discussion Starter · #1 ·
I've been working on the next gen of my home subwoofer, figured I'd post it to add to the collection.

Driver:

Image Dynamics IDQ15 D4 v2
Fs = 21.5
Qes = .309
Qms = 6.1
Qts = .280
Vas = 258 liters
Xmax = 13.5mm (linear excursion)
Xlim = 25mm (spider's very non-linear, so not easily getting to this without excessive power)
Sd = 840cm^2
Spl = 94.7 dB
Power = 800 watts program

Amp:

Behringer A500
bridged mono, 500w into 8 Ohms

The old cabinet was 6cu ft, 3/4" MDF, and not well braced. It was not a great result, although it did have a Q = .56 or so, and sounded very nice at lower powers, but it just was not clean as the power went up, and the cabinet vibrated heavily.

The new cabinet is a 20" cube, netting about 81 liters after the driver, the bracing, and walls. The internal bracing is probably excessive, but its pretty effective. The sub is stuffed with fiberglass, about twice the density of R16 in the back half, and normal in the front half, with the immediate vicinity of the sub left clear for airflow.

The results aren't exactly flat, but then with the inductance of this driver's VC, and the 46Hz Fc and Q of .6, it's going to be a long taper.

My next steps are to build an active EQ that can do a linkwitz transform to flatten out the response (on both ends).

It sounds pretty great, though. Nice full sound, very fast response, and it goes deep. Haven't tested with home theater yet, but a fair bit of music.
 

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Discussion Starter · #2 ·
The rear panel is held in with t-nuts and bolts so that I can easily remove and adjust stuffing, wiring, etc.

I'm using a 4 pole Speakon connector, wired per Neutrik's specs to allow for amps using standard or bridged wiring. I greatly perfer the speakon over bananas, especially as this can't be shorted externally - or shock a kid if they mess around with it. The output voltage for a 500W amp is certainly enough to shock if touched. Granted, at 500W the kid's going be deaf, too (120dB territory).

***

I'm planning on sacrificing a lot of that peak SPL to flatten the response out using a linkwitz transform. I can be 100dB spl at 20Hz with 500w, so I can flatten out the rest using the linkwitz transform. Makes it more or less a "50w" system to pick up that 10dB of gain, but from eyeballing the amp's output meters, I'm never near -12dB on the output, anyway, let alone at that low of a frequency. Even during movies with heavy bass rumbling. We live in a quiet area, so we just keep the gains pretty low.

I'd love to move up to a >800w amp, and pick up that extra headroom, though.

****

After doing the EQ, and a couple other projects around the house, I'll get around to veneering the cabinet (probably oak with a dark cherry-red stain and satin finish).
 

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I think this is the first time I have seen an Image Dynamics sub used for the home. I came very close a couple of times in buying these for my vehicles. At the time I was unable to get a good deal and did not want to pay the price.

It will be interesting to see the response with the LT.
 

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Nice build. Thanks for the close mic raw response. Not enough people do measurements like this. Little bit of an inductance hump in there. Added to the archives.
 

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Discussion Starter · #6 ·
I think this is the first time I have seen an Image Dynamics sub used for the home. I came very close a couple of times in buying these for my vehicles. At the time I was unable to get a good deal and did not want to pay the price.

It will be interesting to see the response with the LT.
I paid about $250 for this driver. At the time, I wasn't really aware of any of the HT oriented drivers, and was looking at car audio drivers (JL Audio 12w6, Shiva, etc). My previous sub build was based around a JL Audio 10w3, which was a pretty decent little sub, and sounded great in a pickup truck cab, but wasn't enough for our house (main living area is 7-8000 cubic feet).

I still think that for the money, it was a good buy. Although if I ever try to do stereo subs, finding another driver's going to be hard.
 

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Discussion Starter · #7 ·
It's definitely got enough bracing, vibration won't be an issue. Looking forward to the response with the LT.
Thanks! bracing was an important part of my design, after the issues I had with the previous cabinet. Putting spikes on it to get the bottom of the cabinet off the floor, and get it well-anchored to the floor, helped an astonishing amount.

Floor is hardwood, and I'm using Parts Express' spikes with the metal disks to protect the floor. The foam rubber pads for the disks have a rather surprising amount of grip on the floor. I can't slide the sub without worry of pushing it off the disks, and it's rather uninclined to move, and transmits very little vibration into the floor.

Which had the effect of not driving the room modes nearly so strongly. A bunch of nulls/peaks are now missing (or heavily evened out).
 

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Discussion Starter · #8 ·
Nice build. Thanks for the close mic raw response. Not enough people do measurements like this. Little bit of an inductance hump in there. Added to the archives.
With Room EQ wizard, the nearfield is so easy to take, I don't see why people don't do it. Modeling responses can totally miss the effects of VC inductance (if you don't have the right values for Bl and Le). The modeled response is pretty off in WinISD Pro for that hump, too. It's either off by half an octave and too small, or on the right frequency and WAY too large. Playing with Qa to try to simulate the stuffing sorta gets it close, but not nearly close enough.

However, with that info, I know that the crossover from the mains (80Hz in my system) is pretty f'd up, with a 5th order low-pass and 4th order highpass (summation of the acoustic and crossover responses).

Hence why my project to do an LT on the low end will also include LT of the low-pass (to some degree, probably just push the response flat out to 400 hz, and then let it fall off a cliff where it won't be heard, anyway). Then the low-pass at 80Hz (4th order will have everything down at -50dB or so anyway by then).

There's an audible hole in the 80-120Hz range, and I'm sure that the hump masks the low end of the crossover area, and then the -6dB slope of the inductive falloff is adding to that hump. But 80Hz is as low as the Marantz will do a crossover, and the Polk mains have for bass below 60Hz, anyway.
 
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