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Discussion Starter #1
Guys - I came across this product and was wondering if you think it has merit: http://www.spatialcomputer.com/page9/page10/page10.html

I am going to be sitting right in the middle (length-wise) of a 28' room I plan to build and know I will have challenges a 20hz, 60hz, 80hz etc due to room modes. I do not think such a product is a subsitute for good room treatments and base traps, which I certainly plan to use. However it seems this product may be able to eliminate or reduce the ringing and 20hz void and other such issues I may have.

The following are some graphs from the manufacturer as posted in this discussion thread from 2012: http://www.audiocircle.com/index.php?topic=103187.40


Above: Results Without Black Hole product, according to what the manufacturer apparently posted in that thread


Above: Results WITH Black Hole product, according to what the manufacturer apparently posted in that thread

I spent a few hours googling it and didn't find much about it. There was a fair amount of discussion on some audio forums in 2012, but not much since. I would think that if this product could help a lot that by now it would be talked about more around AVS and other places. Yet it doesn't seem to have much traction just based on the lack of much posted about it in the past few years.

The website shows the price as $1,295 with a 30 day return, assuming this is current. If this product can potentially work as the manufacturer claims it could be worth trying for me - once I see exactly what base slow decay issues I have after room treatments.

What do you guys think?
 

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Using a second sub to radiate a reverse polarity wave to tame a response peak can work. But it will only work well in one place in the room: where the mic is placed. For the money you'd be far better off with additional subs, placed and integrated correctly they'll smooth response throughout the room.
BTW, you're aware that sitting in the middle of the room is problematic. Don't.
 

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I'm with Bill, avoid the middle of the room since you know it has issues (it certainly does in mine)! I would also lean toward additional subs over the product you link, but then again I have never used it so who knows. I do know multiple subs was the only way I could get the response I wanted in my room.
 

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Discussion Starter #5
Thanks guys. I agree. However I really cannot avoid having the MLP in the middle of the room. Well, technically the MLP is at 54% of the room length so maybe that's a bit better than exactly at 50%? One thing that may help is that in the height dimension I will only be at about 33%. And in the width dimension about 40% (10% off center). Also the front half of the room is 3.5 feet wider than the back half - so I'm hoping this "unevenness" instead of a perfect rectangle will changes the modes just enough to help mitigate the issue. Attached is a model of the room for your quick reference.

I mean I COULD avoid sitting in the middle, but it would be too big of a compromise. For example, I could make the back of the room, say, 4 feet smaller. But then I would not have any room behind the back row for a bar/counter-top area and a few stools that I want to use for food/drink/casual hanging out and overflow seating. Or I could move all the seating backward, but then I will lose the immersive experience as I want about 1.1x screen widths at 2.35 and about 1.5x with 16:9 (and also the rear row will be way to far in that case). Or I could move all the seating forward, but then the front row would be way to close for comfort with like a 60+ degree viewing angle . Therefore, I'd rather sit in the middle and go into it knowing I'll have acoustic issues along with a plan to hopefully largely mitigate them. Also while I want the bass to not be obnoxious in the second row, I really only care about optimizing for the front row.

Indeed I do plan to have multiple subwoofers to help with this issue. See the discussion here http://www.avsforum.com/forum/113-s...ucers/1905233-improving-20hz-middle-room.html which includes an REW model which shows that I should, hopefully, be able to resolve or largely diminish the issues - I think...

Now that I understand that the back wall is a big factor in these modes, I'm interested in this idea off offsetting the back walls effect by potentially using this Black Hole - likely in conjunction with another sub. I am planning on treating the back wall with bass traps and likely 6-8" of absorbers but with limiters so that targets mostly the lows only, leaving the mids and highs to still reflect. I will start there and see how the room measures. If the ringing is still an issue I may try the Black Hole and see how much it helps. If it can take a few hundred ms off the ringing in the low end (assuming the room treatments are not sufficient) than it would be worth it - assuming I can place it in the needed location without it being in the way.

Love to hear your thoughts on this - thanks guys!
 

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The main issue you'll have isn't response peaks caused by room modes, it's response dips caused by the wave reflections off any and all room boundaries meeting the original wave 180 degrees out of phase at the LP. The best way to fix that is multiple subs, so that any dip sourced by any one sub and the reflections of its output is offset by the other subs.
 

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The null at the midpoint of the room is an issue with any room; the only difference is at what frequencies it happens.

It takes a LOT of treatment to counter anything at 20 Hz. Look up the absorption curves and see how they become less effective at very low frequencies.

Realistically the only practical solutions are to move the MLP and/or add subs to counter the null.

That said, in theory a resonant device, active or passive, can counter a null by eliminating reflections. I did not look up the Black Hole so no idea if it works that way. There are active and passive solutions available but I've no experience with consumer versions; the ones I have used or seen are effective but costly and typically custom-designed for the application. Nor have I kept up so have no idea the availability, cost, or efficacy of today's solutions.
 

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Discussion Starter #8
The main issue you'll have isn't response peaks caused by room modes, it's response dips caused by the wave reflections off any and all room boundaries meeting the original wave 180 degrees out of phase at the LP. The best way to fix that is multiple subs, so that any dip sourced by any one sub and the reflections of its output is offset by the other subs.
Thanks Bill. Can you please take a look at this post http://www.avsforum.com/forum/113-s...-improving-20hz-middle-room.html#post32043921 and specifically the second graph in there showing the predicted FR response with 2 subs to see if that seems reasonable? Thanks!
 

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