False wall for IB

[lordpnats]

I'm thinking that mounting my IB in the attic may produce too much noise next door due to the attic vents, so I am considering building a false room inside my theater in which to mount my IB. I thought about building an entire false room inside the room for better sound control, but figured I could get away with just a dividing wall. The wall separating the two 'rooms' would be 2x2 or 2x4 studs with drywall over it and mdf + osb/plywood to mount the drivers in.

The room is 18x11.25x8 ft and I'm thinking of extending the wall out about 4 ft which would make the actual theater 14x11.25. My only installation option besides the attic and the subroom is to flip the theater around and mount the IB in the closet or door of the master bathroom(theater is master bedroom), but that would only leave a gap between the wall and the edge of the screen of 2-3 feet through which you would have to walk to get into the theater, and that seems kind of goofy.

I can't see any inherent problems with this installation, but I'm curious if anyone more experienced/intelligent than myself sees any.

I am also wondering how much sound escapes other people's attics through their vents. It seems like it would be nearly impossible to control the rear wave in an attic.

[ThomasW]

In the history of the forum (5+yrs) two people have had issues with neighbors. Neither person followed up with results after posting their original concerns. No one has posted that they removed their IB due to problems with outside noise.

Insulated attics attenuate a tremendous amount of sound. A minimual amount escapes out any vents (as much will usually go through the listening room walls to the outside). Even without the benefit of insulation, sound that radiates out from anywhere, is attenuated at a rated of 6dB for every doubling of distance from the source.

If you have a large enough access to the attic, I recommend taking a sub up there, then go outside and give a listen. I think you'll be surprised how little sound you'll hear.

Regarding your design there are no inherent problems other than the loss of the space, and having a smaller that optimal space for the rearwave. Though it's significantly more work than a attic mounted IB.

[ryans]

From my experience Thomas is absolutely right. I had the same concerns regarding containing sound in the attic since there's only about 15 feet between my house and my nearest neighbor's house.

I tried a few experiments with my SVS to convince myself that it would be okay:
1) Put the SVS next to a window, played a loud scene and listened in backyard with the window closed. (Pretty quiet)
2) Opened the window and played it again (slightly louder)
3) Put the SVS on my back porch and played it again (Very much louder - similar to the volume I normally get in the living room)

I think the major room boundaries do a lot to contain the bass. Considering the bass would have to escape my attic, travel the distance between houses and then cross another wall boundary into the neighbors house ... there's little chance of having a problem.

I've now got the IB installed and I've checked sound levels in the back yard and they're quite low even with the IB rocking.

If you're still concerned then you could try a similar experiment if you have access to a fairly powerful subwoofer.

[lordpnats]

Cool beans. I'll borrow a sub and stick it in the attic. All I have to borrow is a little 8 inch b&w asw300 , but I reckon it will serve it's purpose. It can probably go loud enough for testing, albiet only down to around 30-35hz. Thanks for the input, guys.

[gottavtr]

I also have concerns about the outside sound. My IB is going to be a bit different. Don't laugh, it is quite ghetto, but I am renting and cannot cut holes in the ceiling. There will be two 15" subs soon sitting in my fireplace. I can mount them there with little modification to the house. I have also planned a way to securely hold the flue open. My concerns come when I think of the chimney as a huge organ pipe. Will this effect the speakers performance? Will it make certain frequencies resonate outside? I know finding the Fs of the chimney is dependant on the diameter and length of the flue. Can anyone respond with the exact equation? Or if I even need to worry?
Thanks,
Zach

[worldleader1]

I assume that would work... maybe you'll end up inventing the next greatest line of IB subwoofers!! chimney style.


I'm lucky that I live in a college neighborhood, so if they piss me off at 3 in the morning with their loud rap music, I just blast them with pure bass at 7 in the morning. Usually they tone their parties down the next week. ;D

[PeterW]

gottavtr said:

I also have concerns about the outside sound. My IB is going to be a bit different. Don't laugh, it is quite ghetto, but I am renting and cannot cut holes in the ceiling. There will be two 15" subs soon sitting in my fireplace. I can mount them there with little modification to the house. I have also planned a way to securely hold the flue open. My concerns come when I think of the chimney as a huge organ pipe. Will this effect the speakers performance? Will it make certain frequencies resonate outside? I know finding the Fs of the chimney is dependant on the diameter and length of the flue. Can anyone respond with the exact equation? Or if I even need to worry?
Thanks,
Zach

You should probably start a new thread in the my projects section..

Im assuming that would give lots of coloration to the sound.
The concept reminds me of a transmission line, it probably would restrict the air movement caused by the subs since there is not lots of space on all sides from the drivers.
If you found drivers with a really low Vas, you might be able to negate this problem to a degree..

As for determining the resonant frequency of your chimeney,
Heres a link to wikipedia,
en.wikipedia.org/wiki/Sympathetic_vibration
go down to "resonance of a tube of air"

I am not sure if your chimeney with drivers at one end and a flue at the other, would act as an open tube or a stopped cylyndrical tube.

Hope this helps you on your quest for awsome bass. ;D

[PeterW]

I just went to have a shower, and i did some quick mental math.
Say your chimney was 14 feet or 4.66 meters long. According to the formula for a tube with one sealed end, the resonant frequencey should be about 28hz. This would affect the IB when the frequency produced by the drivers approached this resonant frequency. I believe that the excursion would go down and the driver's spl levels with it, as the tube began to resonate. The sound level in the room with the fierplace in it would decrease, (assuming that the resonating tube was acoustically discnonected from the room.) The sound level at the top of the chimmeny would be quite loud at resonance. This is not including the variances that must be included in the calculaton to include the flue at the top of the chimeny and the box of the fireplace.

Peter.

[ThomasW]

gottavtr said:

There will be two 15" subs soon sitting in my fireplace. I can mount them there with little modification to the house. I have also planned a way to securely hold the flue open. My concerns come when I think of the chimney as a huge organ pipe. Will this effect the speakers performance? Will it make certain frequencies resonate outside? I know finding the Fs of the chimney is dependant on the diameter and length of the flue. Can anyone respond with the exact equation? Or if I even need to worry?

This question is asked every 6 months or so, as a result I need to put something about it on the FAQ page.

No a fireplace/chimney isn't appropriate for an IB. First off there's not enough space for it to even qualify for the 4 times Vas concept. Second it would in reality be some sort of a mistuned TL (transmission line). Finally the flue mechanism would rattle like mad.

If you need to use the firepit build a sealed box that slides into the opening.

[chrisbee]

The inglenook in my last cottage was 8 feet wide, four feet deep and the rough, iron hard, bog oak beam (still sporting bark after several hundred years of use) was about 5 feet from the floor. The chimney area soared upwards starting from 8ft x 4 feet in a wide inverted funnel shape formed from field stones held together with mud, clay, cow dung and straw. Thomas wouldn't have had much luck convincing me to slide a sealed box into that fireplace. ;D