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Discussion Starter · #1 ·
...my question is about subwoofers.


First of all, my needs are small - I'm not trying to bend any walls. And although I've HEARD of T/S parameters, we're not acquainted well enough to share a pizza yet (i.e. my design skills are nil). I've been looking at car subs for my small home theater application because I can go to the manufacturer's websites and they'll give me box building recommendations that take the guesswork out of box design. For instance, I know that as long as I keep internal volume in a well-sealed box to about .375 cu ft, that a JL Audio 8w0-8 should happily reside in the 45hz neighborhood.


Problem is, I've heard that SOME car speakers don't work well in home environments because they're optimized to take 'cabin gain' into account. Assuming I know what all that means, is there a way to similarly (and quickly, without a lot of calculations) evaluate true home theater subs and ascertain their effectiveness and ultimately box dimensions that would work?


If these particular JL Audio speakers will work well, I'm happy to use them since I have a source at a good price. But if you know of any similar 8" drivers that would be better (assuming a sealed box size of .375 cu ft or smaller), I'd be most happy to hear your recommendations.


Equipment: JVC 7.1 receiver (7x100w), Carver TS series speakers (L-C-R), Fluance dipole surrounds.


I've salvaged a 120w plate amp from an old Optimus 12" sub of mine and have my eye on a second identical amp. I am building a 'home' for my 56" DLP TV and it will be sitting between two existing columned bookshelves. These bookshelves have enough room under the bottom shelf to house an 8" sub each, and I'd like to snuggle one in there and dedicate an amp to each one.


Any help, advice, jeers, raspberries, or leftover pizza will be gratefully accepted...
 

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You should think, even if abstractly for now, of some of the differences in car audio and home audio;


Cabin gain is the increase (gain) due to the room inside a vehicle (cabin).


Room gain is that increase within the boundaries that define the room in which your sub plays within your home.


There are two major reasons you will see smaller sub enclosure sizes recommended for cars while larger sizes dominate the home market, and several less major reasons. One is the difference in room, or cabin, gain. The second reason is the engineering of the driver itself for the different sizes and types of environments. A minor factor, for example, is that sizing recommendations for a car are given to accomodate the fact that space is at a premium in most vehicles. Combine this with the cabin space factor and you find very small box size recommendations on some car audio subs.


Disregard what you see in car audio when you are working on a home audio project. Select from drivers made for home use and look to other sources than those geared toward car audio.


It will make things simpler.


Inasmuch as you have already planned the installation locations of these subs, you are planning to deny yourself the benefit of finding at least these two important things: the size and type of sub(s) that will sub bass that will make you proud, and the optimal placement of said sub(s) so that best response can be experienced in your room. A good design has incorporated the best components for the situation and has incorporated them into the best possible places. Leave yourself some openings for options in all categories you described...size, number and type of woofer, and placement in the room.
 

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Discussion Starter · #3 ·
Stev, thanks for your thoughtful comments - I can and do appreciate the nuances, but as with most things in life, this, too, is a compromise. I started out by saying that my needs are small. I have no illusions that I will be putting together any kind of system that would make an audiophile proud - I doubt very much that most who inhabit this board would even consider a project like mine 'worth doing'.


But this is my first foray into speaker DIY and I expect that this will be a learning experience for me. There is a huge 'sliding scale' of what's acceptable and what isn't. For example, I remember at age ten, almost 40 years ago now, being inordinately proud of my first 'stereo' project - a homebuilt Graymark transistor radio, onto which I cobbled two 5x7 speakers built into cigar boxes. It wasn't 'stereo', but I didn't know that - to me, it sounded *great*.


This project is simply a way for me to get something a notch or two above whatever's on sale at Best Buy (where the vast majority of the listening public get their gear), that's also acceptable to my wife. I picked the sub locations because there are very few places in this particular 100 year old, arts and crafts, mission style house where *any* sort of high end gear wouldn't appear as anachronistic as a caveman with a Timex. I am constrained by these small spaces because that's literally *all* I have to work with. And besides, my building skills are esthetically best suited for places out of sight... :)


As I said, I only considered the JL sub because their website gave me box dimensions (that I don't have to calculate) that might work in this particular room - that I could hide from view. So I'm guessing, based on your explanation, that there is *no* DIY home sub that would lend itself to a space that small... ? I hear great things about Sunfire subs, for example, and others that make great bass from a small box. Are there no DIY projects that lean in that direction?


Remember, in my situation, *anything* is better than nothing - but I'd still like to do the best job possible with the constraints I have. So if there's a home sub that will do a measurably better job in a box size offered by the JL, I'd like to go with that...


For those interested, here are the T/S parameters for the JL 8w0-8:


(Fs): 32.2 Hz

(Qes): 0.579

(Qms): 9.029

(Qts): 0.544

(Vas): 1.02 cu. ft. / 28.9 liters

(Xmax): 7.4 mm

Efficiency (1W/1m): 84.0 dB SPL

Effective Piston Area (Sd): 33.8 sq. in. / 0.0218 sq. m.

DC Resistance (Re): 6.40 ohm

Nominal Impedance (Znom): 8 ohm

Thermal Power Handling (Pt): 75W

Driver Displacement: 0.023 cu. ft. / 0.6 liters


A sealed box (easy for me to make and fit in my cabinet) of volume .375 cu ft will produce an F3 of 45Hz with a Qtc of 1.003... in a car.


I get that it won't sound as good in my living room, but will it sound *bad* (keeping in mind that that's a subjective term)?


What else is out there that I might consider? I've heard good things about the Tang Band subs available at Parts Express - are there any box plans that might work for me?
 

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OK - Questions:


What's the maximum size (volume) you can use for each sub? Is it only .375 ft^3? If it's big enough for an 8" driver, the face must be about 10" x 10" or more. Any bigger than that? What's the depth? Can this stick out at all, out further than the face of the bookshelf?


What size are these speakers? If they are small, a sub that doesn't go very low would still be very valuable to you. So I would encourage you to proceed. In fact, I say go for it no matter what, though there are 'probably' better 8" home subwoofers to use.


What size room is this? Low frequences get reinforced by the room and disapear in larger rooms. The bigger the room, the more volumen and lower frequencies you will need (ok, want) to produce.


What's your budget? Can you afford a big amp? There's a saying that's something like... Small Size - Small Amp - Low Frequencies: pick any two. A small sub in a small box with a lot of power can still do a reasonable job.


And also, before anyone else beats me to it... you could consider an "IB" application. That's easy to build, would free you for a bigger sub and better performance, but would require a hole to be made in the floor/wall/or ceiling. The idea is to use your attic, basement, etc.. as a very, very big 'box'. Plenty to read on here if you search.
 

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Discussion Starter · #5 ·
Thanks, Andy, for your comments...


I did some measuring (and negotiating with the wife :) this morning and determined that the area I have to work with is approximately 20" x 10" x 10" - something more than I originally thought - a little over a full cu ft (1.16?). I assume this gets me closer to a true 'home sub' rather than having to deal with the car JL's...?


But I'm still in the same predicament... unless the manufacturer gives me specific box dimensions optimized for that sub, I wouldn't have any idea how to calculate it... Sealed or ported, doesn't matter much to me. Just 'easy to build' since I'm just cutting my teeth... :)


Who knows? Once I get this project finished, the 'bug' may bite and I'll have to do another... :)


In cruising around the Web, I came across a design from DECware called 'The Wicked One'. If I can HIDE a high quality sub... or better yet, have it serve dual duty as a coffee table, I think I'd have a much easier time convincing the wife that it should go in our living room... But as much as I liked the design of that box, I know it's WAY beyond my skill as a woodworker... for now, anyway... :)


*****


OK, so with the added volume, what drivers would you recommend? Still looks like I have to stay with an 8" (a pair actually, since there are TWO identical bookcases...), but hoping that two 8's...at 120w each, will give me enough bass to make the project worthwhile...


Thanks again for your help...
 

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Discussion Starter · #6 ·
Me and my big mouth... :)


In discussing the design of the new entertainment center with my wife, we've now decided to scrap the whole project, and move the 100 year old oak cabinets upstairs to our bedroom and use them as an entryway into the adjoining room, creating a master suite...


The bad news: my construction project is now encompassing multiple floors of the house and as such, has grown 3-4 fold...


The GOOD news is that the huge 8'x10' opening between the living and dining room is now a blank slate.. I can design as I see fit... PROVIDED, I stay with a Mission/Arts and Crafts style AND I HIDE the home theater/audio equipment as much as possible. That means that any subwoofer(s) will STILL have to be integrated into the unit, BUT I'm now relatively wide open as far as drivers, and box size.


Now before you all go crazy on suggestions for IB subs and huge 18" 15Hz monsters, the actual Home Theater is STILL to remain fairly modest by audiophile standards. I still want to keep the sub project to a pair of 8" (...or 10" :) drivers, each powered by their own 125w plate amp.


So NOW I'm looking for ideas and suggestions on a good *home quality* 8-10" sub - and, if you please, box dimensions for said sub. I think I can go as much as 2 cu ft for each driver box, if that helps in the component selection.


Can you point me to any plans?
 

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Typically in the past car subs were much much more $ than comparible performance from a DIY indoor sub. Consider as well that most car enthusists have differing prioirities when it comes to subs.

1. Status (why else crank it so the neighbours wake up)

2. Volume

3. How cool it looks with neon lights


Somewhere down the list is sound quality and even farther is musicality.


Whats going for you is that if you get any quality woofer that's recommended here and slap it in any solidly built box, you'll best anything Best Buy offers.
 

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1st, I'd go with at least 10" subs simply b/c there are more & better choices.

2nd, it would generally be better to go with one bigger sub rather than 2 smaller subs. There are many more choices for 12" then 10", more 10" than 8". Bigger subs can (generally) go lower in frequency than smaller ones. Adding a 2nd duplicate increases volume, but doesn't give you lower frequencies.

3rd, look at what's available at www.PartsExpress (which sometimes include box designs).

4th, There are many people here that can and will help you design an appropriate box for any driver, given the driver's specs. This can range from teaching/helping you learn how to design yourself with free software tools, up to and including just telling you exactly what size box to build. (and you are right that a sealed sub is easy and fairly fool-proof)

4th, I'd either change the title of this or start a new thread, because people tend to ignore the many 'I want to use a car sub' or 'why not use a car sub' - they come up often.

5th, do a search on here (or just scan through the history) to find previous discussions about 10" or larger (see point 2) subs.

6th - budget?
 

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Agreed on all points I had that idea for using car subs and scrapped it too going another way pretty soon just getting all the stuff together for the project. As a matter of fact I heard those same subs I was planning to use in a bit of a similar application and it made me say .."Damn I am glad I didn't waste my money!". And those were cheaper than what you were looking at. Do alot of research around here and you would be very surprised at how helpful an informative the members of this blessed forum can be. This is a God sent gift so lets use it. Good luck with your project. I am all too familiar with the "Wife Approved Budget" as well.
 
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