Sub woofer in back of room

[tom31415926]

Greetings,

Please forgive me if this post is a repeat. I have done some reading in this forum and recently joined it. I'll be happy with links to any information if my questions are old ones.

We are close to embarking on a remodel project to remove a large double chimney that separates a family room from a living room. the resulting great room will be about 29 feet by 15 feet. The floors are wood, but the hole left by removing the chimney will make possible some holes for IB sub woofers.

The problem is that the holes will be _behind_ the primary seating area for home theater applications. If I understand correctly, this orientation is not recommended, as the main left, center, right channels will be about 16 feet away from the sub, with the seating area in-between.

What, if any, low-frequency crossover would make this situation tolerable? I'm afraid that the sub has to be in this location, or it cannot be IB. Is there a technological solution to the location problem (adding delays on mains?)

I'm guessing that if the room is smaller than a wavelength, then it doesn't much matter where the sound enters the room.

There is really interesting information here, and I hope I can "join the club" by building and posting an IB sub woofer.

BTW. my browser or computer seems to be very busy doing something when I'm on this forum. The cursor is blinking fast and irregularly, and the windows scroll sluggishly. Is there a fix for this?

Tom

[tom31415926]

I'm sorry, I didn't get this thread started in the right section.

This thread would better have been placed in the "my project" section.

I'd be happy if the moderator moved it to the appropriate place.

I'd try to move it myself, but my computer is still bery sluggish when I'm looking at this forum and I can't manage a complicated task right now.

Tom

[ThomasW]

You're the only person to report any issues with the forum. Could be the scrolling pictures or the map loading, those are Macro-Media Flash based things.

Forum software doesn't allow anyone to move threads or posts.

Personally I can't stand having a sub behind me, it drives me nuts. Perhaps it won't bother you. This is something you should test out before committing to an IB.

[chrisbee]

I'm afraid I also get very slow scrolling on this forum. I just haven't mentioned it until now.

I'm forever hitting the wrong link or thread as the scroll continues for several seconds after a wheel scroll.
Editing my posts prior to posting is good fun.

That said, I'm quite happy to continue enjoying the forum as it stands.

[ryans]

You can certainly use delay settings, phase adjustments and/or reversing the amp wiring to try to match phase between the front mains and the subwoofer. Its really only important for the phase to match at the crossover frequency. But with the sub in the back of the room, you'll only be able to match phase perfectly for 1 listening location (at a time). The others will be somewhat off. Probably not a big deal.

So cancellations can be minimized by the above methods. But the bigger question may be whether you'll be able hear any directional queues and whether this will be ackward for you. A lower crossover will help. But you'd also want to limit harmonic resonances. This might mean choosing a very low distortion woofer and over-building your manifold (or array) to eliminate any rattles or resonances. The first step - like Thomas suggested - is to try putting a standard subwoofer behind your seating position and see how it sounds.

[ThomasW]

chrisbee said:

I'm afraid I also get very slow scrolling on this forum. I just haven't mentioned it until now.That said, I'm quite happy to continue enjoying the forum as it stands.

What's your standard connection speed to the 'net'.

If the Flash based graphics are slowing down the forum itself, I can just eliminate the scripts.

With my cable connection everything loads including the map in less than 5sec.

I'll pull out the script for the map. Let me know if that helps.....

[jagman]

I have a DSL connection and no problems whatsoever. Everything happens very quickly.

[titch]

Everything is running fine here to.

[ken]

l only run dial up atm and np at all

Ken

[tom31415926]

thanks for the information.

I was thinking of a crossover around 80 Hz. My guess is that that is a bit high for most of the IB sub woofers. But it is probably a lot higher than most would tolerate in a sub woofer that is behind them.

I'm no expert on room acoustics, so I'd be interested to hear thoughts on the following. I can't recall where I go this idea, must have read it somewhere. For a given size room, at frequencies that are low enough, the sound energy is not in waves that are propagating, but in regions of rising and falling air pressure. Sort of analogous to a Jello mold vibrating in various modes. At such low frequencies, does it really matter where the energy enters the room?

Clearly, however, folks on this board can tell if the sub is behind them and do not like the result. I'll see if I can listen to some sub woofers (probably not IB, though) and get some idea of how the sound is affected.

80 Hz is about as low as I wanted to crossover, to keep power handling in the main speakers down. Is that crossover feasible at all, even if I can get the IB sub woofer in the front of the room?

thanks again.

Tom

P.S. sorry to be the one to start the sluggish scrolling thing. . .

[ThomasW]

80Hz is the standard XO for a sub mounted in the front. That's way too high for one in the back of the room. It will smear the stereo image. For a rear firing sub I'd use a XO point no higher than 40Hz.

[chrisbee]

Thomas

I have 512/128 ADSL running Firefox.

My ISP's own speed test software shows (average of 3 tests) 200KByte/sec download but only 13KByte/sec upload speeds. Perhaps my firewall and antivirus software are slowing things down? Since others seem not to be troubled by the forum setup I'd forget about changing anything.

Let's get back on topic.

[tom31415926]

Thanks for the info, Thomas!

I was pretty sure that 80 Hz was too high for a sub in the read of the room. Going with a 4-way system seems to be one solution that would let me use a sub crossed over very low. Quite a bit more complex, however.

I'll just read some more of the forum articles for a while as I ponder different solutions. The enthusiasm of the folks here does make me want to use an IB if it is feasible.

Tom

[norpus]

If you can use 40-60Hz you will not likely notice the directionality
I am planning a second IB sub at the back to help the first in the front. Will let you know how the project goes

[tom31415926]

Thanks,

I would like to hear how the second sub works out.

Tom