[aNomad]

Hey fellow subwoofer geeks,

I recently had a plumbing issue which caused me to have to cut my drywall end to end across my theater room *GASP*. Also, I recently acquired a long throw 15" woofer from TC sounds. *Cool coincidence!*

I had a flash of genius tonight: I'd love to use the wall as a huge speaker box! Here's my idea:

I will use the largest stud spacing as the actual box, floor to ceiling. I will use the smallest adjacent stud area as the port, ceiling to floor. I will make a small "cabinet" into the room which will be about 2-3" thick, which is (obviously) attached to the wall, to hold the extra woofer depth and the port opening, and to hold the grille. It only needs to be about 17" tall by about 28" wide.

I figure the (in wall) box to be about 16" wide by 6" deep by 10' tall (I have high ceilings). The port will likely be just as long by just as deep by 9" wide (the narrowest adjacent stud spacing).

First question: Do any of you think that port dimension will be a problem (the port being so large; it will be 10' long), second issue, do you think having it so big will reduce the amplitude? I know port noise won't be an issue.

I am not worried about the drywall or 2x4's being a problem, nor small leaks, since the box will be so big (low pressures). Any hints?

Hey buds, any input would be appreciated. I'll post photos soon. Thanks!

Bill

P.S. My girlfriend is impressed by my knowledge about plumbing, electrical wiring etc. I don't want to let her down now LOL! :rofl:

 

[michael hurd]

You could google and download *BOXNOTES* a freeware program off of the net and input the proposed size and see where the resonances stack up. I have a feeling that the 10' dimention will give you a wicked top to bottom resonance in the intended pass band.

If it was me, I would simply build a conventional box or a sonotube. Which TC Sounds 15" driver did you acquire, and can you tell us your goals?

 

[Mike P.]

Which 15" sub did you get? Modeling will show which size cabinet and tuning frequency will get the most performance from the sub.

 

[aNomad]

I'm not sure what the model number is because it was custom made for me a long time ago (I'm friends with Thilo). I have L.E.A.P. and will model this and adjust the port dimensions accordingly, but my goal is to tune it around 20-21Hz. I have had large woofers before and am tired of small sealed box woofers with EQ. I just can't get that stomach shaking bass I crave, but I don't want to lose a lot of space in my room.

I have examined the drywall (which is 5/8") and it seems pretty dense and rugged, so I'm not expecting much trouble from it. Also, since it's so tall / narrow, I don't think I'll need much bracing.

I'll measure the T/S parameters today and post them. I'm not expecting the existing stud dimensions to magically work out, but it would be nice. :bigsmile: I do know from experience that a bigger cabinet is usually better though, and since the pressures should be pretty low, leaks shouldn't be much of an issue (I hope). :whistling:

 

[Mike P.]

I figure the (in wall) box to be about 16" wide...

Are you sure? Most studs are on 16 inch centers, the inside measurement between the studs would be 14.5 inches.

 

[Mike P.]

IF the width is 14.5 inches by 6 inches deep and 120 inches high, you'll have a volume of 6 cu.ft. Assuming the port is 9 inches wide and 6 inches deep, it will take a length of 54 inches to tune it to 20 hz.

 

[aNomad]

Thanks Mike!

I haven't played with LEAP yet, but I did get the T/S parameters yesterday. They are:

Fs= 38.2Hz
Qt= 0.679
Qe= 0.765
Qm= 6.041
Vas= 79L
Mms= 193g
Cms= 0.0897mm/N
Spl= 89.4db
Bl= 20.2T-m
Dia(eff)= 31.7cm (12.5")

I tried to take a photo of it, but my camera seems to have died. Basically it's a long throw 15" woofer with decent efficiency. I'll post photos soon.

If a port length of 54" will do it, that would be great! That's roughly the height of my new pex hot water pipe. I can just put a cross member in to block the top of the stud space and duct the "enclosure" into it. One thing I'm a big fan of is HUGE bass ports. My old homemade speakers were 15 cu' and had a bass port that was about 2' wide by 6" tall, and they put out beautiful bass! I hope this works out as well.

I'll let you know. :jiggy:

 

[Mike P.]

There aren't enough parameters to properly model this sub. I did a model and assumed a Re of 3.8 ohms, 20 mm Xmax and 500 watts power handling. This is definitely a custom car audio sub with a Fs of 38 hz. 400 watts input brings the sub to Xmax with a high pass filter at 19 hz.

 

[aNomad]

Sorry about that Mike, The impedance is 8 ohms (Re= 6.72 ohms). The xmax is about 30mm (TC specializes in long throw woofers; the flex wires are even woven into the spider). Your model looks good. I remember the low end sag from when I originally designed this woofer into a speaker box with passive radiators. It needed lots of EQ, but it sure sounded sweet once that was done.

I'm going to put about a kilowatt into it. That said, I'm going for quality more than quantity. I want sweet sounding bass, but I probably won't push it to the full kilowatt often; if ever.

I don't know what it is, but though my sealed box speakers have EQ and are technically flat down to 20, they just have never sounded as nice as my old vented speakers (with a very similar response). I suspect it's the low frequency resonance. I even added a filter with low frequency resonance to my current woofers, but they just don't have it.

IMO, there's no substitute for a large sub!

 

[Mike P.]

Parameters corrected. 1000 watts input with a high pass filter at 18 hz.

 

[SteveCallas]

You'd better hope that that single spot in the room will yield a decent FR at your seat. otherwise the time and effort could be disappointing. With a discrete enclosure, you can at least move things around a little bit.

As to the design itself, if possible, go a little larger on the enclosure so you can go shorter on the port length.

 

[aNomad]

Thanks Mike and Steve,

Yes Steve, that does worry me. I am planning on having the port and woofer side by side in the bottom of the studs, so maybe I can test the location with a discrete woofer. Thanks for mentioning that! Fortunately, there are many studs visible.:teeth:

 

[cixelsid]

6" isn't deep enough, you'll run into back EMF issues.

Modeling this as a regular box doesn't take the long thin shape into account. You'll end up with something closer to a grossly mistuned TL than ported box.

In addition when there are distances of 5'+ between the driver and the port they don't load properly.

Lastly you should worry about the drywall flexing.

 

[aNomad]

Hi Cixelsid, good points, thanks!

I am going to have to space the driver out from the wall anyhoo, because it's too deep. I'm thinking that will help a lot. I understand what you're saying because form factor does matter, but one of my best experiences with a woofer design was in a tall thin box. Also, I'm planning on ducting the port section out fairly low. Mike said 54" I think, that's pretty low, so there won't be a huge path to traverse. Most of the enclosure will be volume.

I also get your drywall flexing point, and I would have said the same thing last month, but after working with the stuff for awhile now, I feel it's pretty dense and stiff; I think every bit as good as plywood, and the span being only 16" wide, is supported pretty well.

I was going to play around with models and external subs, but now I'm thinking go for it; I'm doing drywall anyway, if it doesn't work, patching another rectangle is no big deal! I'm just gonna go for it. Please wish me luck! :-D

BTW, I got a photo of the driver finally, I just need to upload it at work. I'll try to do that tomorrow. Night all, and rock on!:yay:

 

[Mike P.]

Build pics would be nice too! It would be great to have it added to the "Subwoofer Database". :yes:

 

[cixelsid]

Bill,

Having a 10' long enclosure with a 14.5" X 6" cross-section, means you're not building a ported box, your building a LT. And the rules for TLs are a bit different than those for simple ported boxes.
http://www.t-linespeakers.org/design/classic.html

 

[CZ Eddie]

IF the width is 14.5 inches by 6 inches deep and 120 inches high, you'll have a volume of 6 cu.ft. Assuming the port is 9 inches wide and 6 inches deep, it will take a length of 54 inches to tune it to 20 hz.

How are you getting 6 cu.ft? I'm coming up with somewhere between 2 & 3 cu.ft.?
He would have to build an MDF enclosure within the wall cavity. Because the 1/2" drywall (most common) would flex too much.

This enclosure would have some wicked resonance which would prevent it from sounding top notch.

 

[Mike P.]

14.5" x 6" x 120" = 10440 cu. inches. Divide by 1728 = 6.04 cu.ft.

 

[CZ Eddie]

14.5" x 6" x 120" = 10440 cu. inches. Divide by 1728 = 6.04 cu.ft.

But that is external volume and useless. You still need to account for 3/4" on all sides + all the bracing that would be required to prevent a 10' tall enclosure from flexing.

 

[Mike P.]

I'm under the impression he is mounting the sub between the studs and covering it with drywall as stated in the second paragraph of post 14.