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Discussion Starter · #1 ·
My new HT room is *very small*, only about 12' square. By the time I get my furniture and HT equipment in there, it's pretty cramped.


I have a pair of 10" powered subs (Radio Shack specials...yet another reason to *change*... :) that sit out like two bumps on a log.


My idea is to incorporate a pair of powered subs into the fairly shallow bookcases (9" shelves I used to hold media) that I have flanking my corner screen. Here's my idea:


I've been dabbling in speaker design for a few years - have never embarked on a serious project (but hope to get stated on a Vifa-based HT system next year), but I have a pair of JL Audio 8" subs that were left over from a car audio project I never finished.


I was thinking about taking the lower portion of each bookcase and enclosing a 1cuft volume to match the sealed box parameters of these subs - and powering each of them with their own Parapix-like 100w amp from Apex Jr.


Question: any one else ever intermixed car and home audio components with anything other than good results? Will these JL Audio subs be up to the task or am I missing something?
 

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I think you're going to have several problems with this idea. First of all a sub built into caswork will probably rattle anything right off the shelves. Secondly, most car audio drivers are not well suited to HT.

Any way to do an IB? That would be the ultimate space saving option.

How about a coffee table sub? Several people have built them when space is the priority.

You can see my idea for a space saver, even tho it's 16 cu.ft., it'll be hidden by the ent. ctr. I'm going to build.

http://members.home.net/bcwwkg/image...ll%20Thing.JPG


Pete
 

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Discussion Starter · #3 ·
PMazz: First of all a sub built into caswork will probably rattle anything right off the shelves.


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I thought about that - and wondered if a layer or two of dynamat or neoprene between the subbox and the rest of the bookcase would help alleviate that problem... ?




PMazz: Secondly, most car audio drivers are not well suited to HT.


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Why? What's inherently different about a 'car sub' vs. a 'home sub'? Do they 'sound' different once they're sealed in their T/S parameter defined box?
 

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Discussion Starter · #5 ·
Mr Hookup: There are a number of In Wall or In Ceiling Subwoofers. Car subs are mostly 4 ohm, home subs are usually 8 ohm.


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I know - I've seen them for sale. But inpedance notwithstanding, if the dedicated sub amp can handle the load, what's the difference?


The point is, I already have the JL Audio subs - I'd have to buy any others.


I'm still looking for a reason as to why it *can't* or *shouldn't* be done. What is it about car audio equipment (some of which is very high quality - JL Audio most notably) that precludes it's use in a Home Theater environment?


Nothig personal, but I'm looking for a reason, not a bias...
 

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It looks like most of the JL 8" drivers have an Fs of ~35 Hz. This is pretty typical of car audio subs. HT drivers have Fs of ~20 Hz. With the car audio stuff, cabin gain makes up for the lack of real LF power, but in a typical HT room, it takes quite a bit more raw driver power to "fill" a room.

WRT llining the sub/casework with sound deadening material, it will help. Try to isolate one from the other. Foam may be better for this than neoprene, but you'll probably have to experiment. My sub can rattle things off of shelves across the room, if driven hard enough and long enough.

The only way to know for sure is to give it a try. I like to slap a quick box together, forgoing bracing and appearance and terminal cups, etc.


Pete
 

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Hi Jim,


First, let's clear up this car audio driver confusion. A driver is a driver. It has parameters which allow for a certain range of alignments (box size, type, and resulting response curves). What we have to realize is that a sub which is designed to have flat response in a car will typically have low end extension to only 50-70Hz. A car subwoofer takes advantage of the very small cabin volume which can be predicted with reasonable reliability. So, obviously each 8" driver in a sealed box won't be doing much "sub-bass" in your room.


That said, there are many cases where a car audio sub's parameters lend well to ported alignments. Since we are talking about only an 8" woofer here, you need to be concerned with having enough output as we get lower in frequency. An 8" ported sub could roughly equal what most 10" sealed subwoofers can do, and in the small space you have, a pair might be enough for now, depending somewhat on your main speakers and how loud you like to listen.


For a plate amplifier, you might want to also check out the plate amps on sale at Parts Express. Since you likely won't need a ton of power, you might be able to save money with one amp to drive both subs in series. Stryke Audio and Apex Jr. both offer the same 350W/4 Ohm amp which would probably be enough even driving both subs. This also allows 1 set of controls for both subs.


Now for the box. Most of the JL subs come with Thiel/Small parameters in the manual. These are reasonably accurate from drivers I've checked. Which 8" do you have and what are the specs? Give us the specs, and we can give you some suggestions. Fortunately, the small room you have will help with the low end extension where you will see gain in output starting around 30Hz from the same mechanism which boosts the bass output in a car where this gain typically starts kicking in between 50-85Hz (larger space, lower frequency where gain begins). This means you could get away with an f3 point somewhere in the 30Hz range.


One thing to also consider is the dimension of your room and placement of your sub or subs. The 12' dimension will cause peaks at ~47Hz. Fortunately, the 2nd mode will be above the sub's crossover, and the mode due to the cieling which I presume to be ~7.5' is around 75Hz. You may be able to tame this peak by just moving the crossover on the plate amp you use down below this. For the other peak, see if you can get the sub at 1/4 or 1/2 points on a front or side wall.


I threw a lot of info out here, but it does show that a little thought and experimentation could make for a great little sub and good performance without dumping a ton of cash.


Now the work is back in your court. ;)
 

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Discussion Starter · #9 ·
Mark: exactly the type of information I was looking for - thanks!


Here's the information on the JL insert with the driver:

Model Nr: 8W1-4

Fs: 33.2Hz

Qts: .345

Qes: .355

Qms: 11.5

Vas: .90ft3 or 25.5 liters

Xmax: 7.2mm

Efficiency: 86.2 dB

Impedance: 4ohms

power handling: 100w (continuous)


Having given more thought to the building of the sub in the bookcase (and the advice given herein, that I may not be able to isolate the vibration from the rest of the bookcase), I'll probably modify the design - though it might be a nice effect for the books to come tumbling down when the T-Rex stomps into my living room, it's hell on the books... :)


I'm now thinking of maybe an isobaric, possibly a 4th order dual ported design that can sit behind the framing of my screen - with ports opening into the room.


If I wire these puppies in series, I get my 8 ohm impedance and I can power them with a single 250w amp, giving me a single set of controls as you suggested.


You're right! Got more research to do! And more room designing to consider!


Any further advice you can provide will be welcome!
 
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