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Discussion Starter · #1 ·
I got my B&K 30 upgraded to the 31 and it has "boundary compensation" that is supposed to help smooth out response on a THX 2 sub "or sub that goes to 20HZ". If you choose it, it defeats the room equalization "notch filter" feature that B&K has (which I have used in the past).


Does anyone know what the boundary compensation actually does? I tried to find it on the THX web site, but couldn't find an explanation. I assume it is some kind of filter(s) but what frequencies?
 

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SBIR operates on the same principle as a comb filter. It is caused by the alignment of bass waves reflecting off front/back, side/side, and floor/ceiling boundaries causing a cancellation in the listening position(s). This cancellation is called a "notch". As the speaker gets closer and closer to a boundary, the notch frequency gets higher. Its effects are worse when the distances between boundaries are equal. One solution is to move the sub(s) closer to the boundary to raise the notch frequency above the 80Hz crossover point and move the L/C/R further from the wall to lower the notch to below the 80 Hz crossover point (see other discussion on bass problems with full range speakers).


I cannot tell you exactly what the B&K/THX is doing to compensate. I can ask John Dahl next I see him.
 

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Discussion Starter · #3 ·
Thanks, Dennis. I am going to play with it this weekend and try to measure the response changes. If you find out from John, let me know.


Thanks,


Randy
 

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Discussion Starter · #5 ·
Dennis,


I have the Sencore 295 but am just getting around to doing more than playing around with it.
 

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The description at TagMcLaren's site states: "Subwoofer Boundary Gain Compensation, dealing with the acoustical side effects when a subwoofer is placed close to a wall..." and they show a response plot of the electrical filter applied to the subwoofer output. Looks like about -3dB @60Hz, and -10 dB at 20 Hz. They used to require this rolloff be built into the sub, but now it is in the processor so it can be used with any sub.


This is my understanding, anyway.
 

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Quote:
Originally posted by Roger Dressler
... Looks like about -3dB @60Hz, and -10 dB at 20 Hz. They used to require this rolloff be built into the sub, but now it is in the processor so it can be used with any sub....
Sounds like Tag reinvented the world's most expensive Rumble Filter.
 

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>>Sounds like Tag reinvented the world's most expensive Rumble Filter.
 
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