Baffle wall used for IB

[hifijeepster]

I have the opportunity to do a baffle/false wall for a IB and a I have some questions.

1. I have a window that will be behind the false wall. With the window closed, the area would be approximately 180 cubic feet. Using 8 FI IB3's could I open the window and make it IB? Open window area is 44x21.

2. To make the false wall, I could make it 2 or 3 feet deep. Obviously I would like to keep it 2 feet, if 2 foot=180 cf, if 3 foot=250 cf. If the window idea won't work would it be better to use the FI in 250cf or Dayton Ultimax 18 in 180cf

Edit: I think posted in the wrong section. Can you move me to the correct one?

[pitviper33]

The window is tricky. I doubt anybody's done any real analysis on such a situation, so I doubt you'll find anyone with solid answers. My gut says the area outside the window won't really "count" as IB backspace. the area of that window is less than half of the area of the drivers. That suggests to me that it's a significant restriction. Besides, if the window is behind the baffle wall, how are you going to open it? And what if you want to watch a movie while it's raining? That's usually when I MOST want to watch a movie.

But besides all that, I have another question for you. If you're going to have 8 drivers to play with, why do you want to put them all at one end of the room? are you hoping to create a planar wave? What's your plan to keep that wave from reflecting off the back wall?

[hifijeepster]

It would be a double bass array. Still debating do a foot thick absorber on the back wall or also doing shallow subs on the back wall delayed in time or doing a combination of the two with less subs. Probably will do door #3.

[pitviper33]

Interesting. The planar wave approach is really intriguing to me. But a foot thick absorber sounds pretty thin...

I've never heard of the combination approach before. So you'd use time and phase delayed drivers for the back of the room, but they'd have substantially less displacement than the front array? And this is enabled by also having an absorber back there to supplement? My first thought on that is that the back array will eventually run out of steam as you decrease frequency. But as you decrease frequency, building an effective absorber to compensate becomes more challenging. Or looked at another way, an absorber that's thick enough to be effective at the bottom end will also be quite effective up higher in frequency, thereby making the back array entirely redundant. So what's the benefit of the combination? Either means of counteracting the reflection has to be sized for the bottom end to be effective.

I hope these comments/questions aren't viewed as too much of a derailment. You've piqued my interest.

[hifijeepster]

I learned about the double bass array (DBA) on the AVSforum. You can also do a single bass array (SBA) with serious absorption on the back wall. Basically the DBA is an array of woofers on the 1/4 points on the front wall. This is supposedly really efficient in creating a uniform bass wave with minimal interactions. The rear wall array is supposed to be identical to the front. The timing is such that front wall wave is cancelled by the rear wave.

I don't think I can fully fit a complete system in the rear but I could probably do a half system with lots of absorption.

Ideal result is super clean bass across all seats with minimal reverberation!

[pitviper33]

I'm pretty familiar with the DBA approach to planar wave bass. But I've never heard of this combination method for the sink side. You haven't given a detailed explanation of the theory behind your dual-mode sink, but I'll caution you that the most challenging frequencies to capture back there are the bottom end of the spectrum. Neither the relatively thin absorber you describe or a marginal capacity array of drivers is going to excel at that.

You should share the details of your idea on the thread over there. The other contributors to that thread and I would love to explore a new variation on the concept, and more discussion on the physics should help us all learn.