DIY subwoofer project thoughts please?

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This post may end up being a bit long, and for that, I thank you for your patience. I'm considering the undertaking of building my own sub for my living room to replace my current dated and not overly-impressive Energy e:XL-S12.
My current system looks like this:
16'x20' Living room, carpeted
Samsung PN63C8000 63" Plasma TV
Onkyo NR5008 AV receiver (9.2 chanel, HDMI, Audissey, etc)
DirecTV HR23-700 HD DVR
(Panasonic DMP-55K) Blu Ray DVD player
Adcom GFA-555II (mains)
Adcom GFA-545II (center channel, bi-amplified)
Adcom GFA-545II (surround)
mains: KEF Reference 104/2 Raymond Cooke S.E. loudspeakers
(KEF Kube 104/2 EQ)
Center: KEF Reference Model 90
Surround: Polk Audio FXi3 bi-pole
Sub (presently) Energy e:XL-S12 12" powered sub

This system is used for both music and home theater, so the sub I'm looking to build will be as musical as I can make it. I'd like any input on issues with my idea, suggestions, criticisms if you feel the need. Whatever. I appreciate any input. I've worked in the car audio industry as a master installer for 20+ years, and have worked in cabinetry as well, so I have the tools to undertake this task, and I hope, the skills as well.

double-layer (1.5") of 0.75" Baltic Birch plywood, sealed down-firing cube enclosure of around 1.4' per side for an internal volume of about 2.5 cubic feet after displacement of driver, bracing, and reinforcement. I'll be putting a layer of acoustic foam on each of the interior panels (top, sides)
The enclosure will be elevated about 4-6" off the floor. The use of floor spikes is still up in the air, depending on how I design the box and feet.
My first issue here is if I need to go larger for a home environment for this box. I considered going to 3 cubic feet, but I'm looking at the recommended (car) volume for this driver, as well as knowing I want to keep the sub snappy and responsive (detailed) so a smaller box within recommended specs is favorable. The box will, after construction, be veneered in Waterfall Bubinga 20 mill BFV veneer, and finished with 4 coats of oil and poly, with sandings between.
Link to veneer
I can get the Baltic birch plywood in packs of 12 3/4"x20"x30" sheets for about $200.

I'm trying to keep cost reasonable, so I'm looking at using the Dayton Audio SPA1000 plate amplifier. It's rated @ 950 watts RMS @ 4 ohms @ 0.92% THD @ 1/3 duty cycle. (I'm a strong believer in having a lot of reserve power. Especially for a sub.)
plate amplifier link

The sub I chose is a hand built sub, made by a company I've used in my car systems with great success. I want to go with an Fi Q15, 15" DVC sub, with the following specs:
Fs: 32.1 Hz
Re: 1.4 Ohms/coil
Qms: 8.61
Qes: .44
Qts: .42
Mms: 299g
Cms: 0.82mm/N
Sd: 810cm^2
Vas: 75.6 l
Spl:89.4dB 1W/1m
Bl: 19.65 N/A
Xmax: 28mm
Rms: 1000W
Sealed box: 2-2.6 cuft
Ported box: 2.8-4 cuft @ 28-33Hz
Sub OD: 15.625”
Cut ID: 14.125”
Mounting depth: 8.500”
Displacement: 0.19cuft

Those are the specs for the stardard driver, but I'll be having it modified by the builder with a few options:

Cooling: The 2010 Q now features a solid pole piece that allows the addition of the Helicool cooling system that will allow an additional 200-500 watts of power handling depending upon install and scenario. Bottom line this option increases thermal power handling capacity over a “Stock” Q. 

High QTS: This option is for users who intend on using the new Q series woofers in only a sealed enclosure.

Spider: This option adds an additional spider to the spider pack to help with mechanical power handling and keeping the moving assembly under control.

 I Heat Ring: This option is a machined aluminum ring in the gap that lowers the inductance of the voice coil which allows it to play up a little higher in the frequency range and have better overall transient response.

Link to subwoofer website

This is a description of the driver (Q series)

"The Q Series of subwoofers is our sound quality reference line. Featuring a hefty high strength single magnet motor structure with a heavily bumped t-yoke, the 27mm of Xmax allows for incredibly detailed, tight, and powerful bass. Triple progressive spiders keep the incredible linear excursion of this sub under control, while the extra heavy lead wire feeds the giant voice coil. With technology pulled from the larger BTL line the new Q has more options than ever before. Hyper chamfer, full cooling, high or low Qts topologies, as well as the ability to add an inductance ring in the high Qts design, there is now even more flexibility within the Q platform. Working well in both small ported and sealed enclosures, you do not have to give up your trunk to have strong bottom octave foundation for the rest of your system. "

So this is pretty much what I'm looking to do. I'd love to hear any thoughts on improvements or issues with the concept. I haven't done much work in custom building things for home audio before, and I'm sure people here have a much firmer grasp of possible issues.

Thanks for any input you can offer. I'm tempted to re-veneer the KEFs to match the sub enclosure if it works out well.
I generally don't like replying to threads by most Car Audio guys due to the fact that what works in a car isn't necessarily going to work very well in a listening room. However you seem to have been doing this sort of thing for awhile so this probably isn't a problem.

I suspect that your choice of driver for your sub is partly because you're familiar with their products and seem to have established a good relationship with them.

My recommedation is based on my experience with subs used in a domestic listening space. Having said that, you may want to consider some of the Exodus Audio drivers.

I see that several of their drivers are on sale right now, so you might want to look at them. I believe that the Tempest and the Shiva are marked down.
If you really want it all, although at a higher cost, there's the new Maelstrom 21 inch subwoofer!
(Edit: Exodus has a pretty good price on a sub amp as well.) : Intro » Home » Exodus Subwoofers

Best Regards,
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I'll definitely take a look. Thanks. I'd gone with the Fi Q sub due to it's specs. Great Xmas and Xmag, low Fs, great BL curve and fairly efficient. I could also customize the sub for high Qts for a sealed box, add an extra spider, and cooling options which help, too. It was really as you noted, a matter of knowing the product and the person (Scott) who designed and builds them. I'm not as familiar with component drivers for a lot of home applications, although I have worked with a lot of smaller drivers that work in both settings, like Seas, DLS, DynAudio, and so forth. I wanted to stick to a 12" or 15" sub due to the smaller room size, and trying to keep the cabinet inconspicuous, and more integral to the room instead of being a focal point.
Yeah as I noted, I've been in the car audio world more, as I worked as a master installer for a long time, but I'm an electrical engineer as well, so I'm not your typical bass-head car stereo kid. Thanks for the reply. I appreciate it. I wondered why I wasn't getting very many responses to any of my threads here or on AVS. haha

I'll take a look at both their subs and amps. I wasn't sure who else had some decent plate amps out. I'm hoping to keep this project in the $1000 and under range if I can. I'm considering going from the Birch to standard MDF for the enclosure, as the cabinet is going to get vaneered anyway, so the only place the MDF would ever be seen is inside the cube.

Now it's mosly planning out the internal bracing, and the enclosure volume.
Having taken a look at that page, If I go to MDF, use the Tempest X2 15" (great looking sub, by the way. I've used XBL^2 motor subs before and love them), and go from the plate amp to the Dayton SA1000 rack mount, My total cost for this drops from about $1100 to about $800. I can't complain there. The specs between the Fi Q and the Tempest in this case don't really seem to be enough to warrant staying with the more expensive of the two. It might be different if we weren't talking bottom octave only from the driver. I just want something with good linearity, control, and detail. XBL^2 with adequate power achieves that.
You might consider using a different amp. For these power levels, a pro amp is often a better choice. The Behringer EP4000 (essentially the same as the EP2500) is nearly $100 cheaper than the Dayton, and testing of the 2500 suggests that it will deliver twice the power (1300 watts into 8R, 2000 into 4R) of the Dayton. You may need to swap the fan, but that is not a big deal, and you'd still be money ahead. I'd recommend the Peavey IPR 1600 too, as it is even cheaper than the EP but still delivers plenty of power (>450 W 4R stereo), but it is a bit difficult to bridge.
5 cubic feet seems exceptionally large for a sealed 15" sub. I was thinking closer to 3 cubic feet.
I looked at the Behringer EP4000. Decent looking amp, but it lacks any sort of LPF network like the Dayton offers, and mainly, it appears to be for the EU market, and I'm in the US. Thanks for the suggestion, though.
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5 cubic feet seems exceptionally large for a sealed 15" sub. I was thinking closer to 3 cubic feet.
I looked at the Behringer EP4000. Decent looking amp, but it lacks any sort of LPF network like the Dayton offers, and mainly, it appears to be for the EU market, and I'm in the US. Thanks for the suggestion, though.

Hmmm, the EP's are in use all over in the US. I have a 2500, a friend uses a 4000. The EP2500/4000 is arguably the cheapest sub amp as far as dollars per watt delivered of anything I am aware of. I paid $249 for mine, shipped....:cool: Chuck's testing at AVS suggests that it delivers 1300 watts into a 8R load when bridged, that is serious bang for the buck. When I tried for a kilowatt plus, I popped the circuit breaker....time for a re-wire. :(

Best? No, not even close, but I don't play in that league...:D
Cheapest? Without a doubt, I like the most for the least...:D

Cheapest price I could find from a reliable source is Amazon...

Having a HPF is an issue for some. The Dayton rolls off a little high in my opinion , the EP is even higher at 30 Hz (when switched on). Adding a HPF may not even be necessary, it all depends on the driver and the enclosure. If I use one with mine, it will likely be combined with a DSP to handle sub EQ duties.
I said LPF. There's no active crossover network to allow for phase shift, low-pass crossover point and Q (slope), etc.. The only LPF I'd have is the LFE feed preset from the AVR, which is lacking severely in settings. That EP4K is designed as a full range amplifier, which would lead me to require a separate crossover network which puts the price right back in the range of the Dayton, but yeah it is a lot of power for cheap, and that's nice. I'm still leaning toward using a plate amp though, and not a stand alone. I'm as yet undecided on that front.

You are correct, I do not need an infrasonic filter (HPF) with a sealed box.
Not too bad, but most shoot for a Q of around 0.5, as the shallower roll-off integrates with the room better. A=0.84 on it's own (no room gain) would sound okay, but the gain provided may well accenuate the slight rise into a more boomy, one-note sound. Might be an idea to kill it off with some eq.

And an infrasonic filter should be used. Even if it won't kill the driver, you won't reproduce 5Hz, but it will certainly eat up headroom.
Oh that's great, I really appreciate it. I was just noting why it wouldn't work in my given application. It does look like a good amp. I just need a sub-specific one, and the Dayton seems to have some good features. (I'm looking at the newer version of it, as listed on parts-express.)
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