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-   -   BSC for near wall speakers (http://www.diyaudio.com/forums/multi-way/201310-bsc-near-wall-speakers.html)

Doug76 27th November 2011 05:52 PM

BSC for near wall speakers
 
I've been giving this a lot of thought. The general idea is the roll off occurs due to baffle width allowing frequencies to go around the speaker. This assumes a free standing speaker, away from boundaries such as walls.
However, with a speaker mounted on the wall, or standing on the floor with it's back against the wall, at some point the wall again comes into play, and you should see the response rise again at frequency wavelengths longer than the combined baffle width/cabinet depth distance, creating more of a broad shallow notch in the response vs a shelving of the response.
What do you think? And if this is true, how does one create a circuit to compensate for this?

speakerdoctor 27th November 2011 06:46 PM

The BS should be less with the speaker next to a wall. All you need do is adjust a standard BSC circuit to have LESS compensation.

Doug76 28th November 2011 12:29 AM

And that I have done for my newest, going with 3db instead of 6db compensation.
Still, it seems to me that because of the wall's proximity, one would likely see a broad and shallow notch rather than the shelving response.

sreten 28th November 2011 01:09 AM

Hi,

Yes you need less overall BSC and yes you will get a severe discontinuity,
unless you build a relatively very wide and shallow box for wall placement.

The problem with most boxes is a severe wall dip, right where you don't want it.
Easy to confirm will any decent box speaker, they sound poor near any wall.

The dip drops in frequency and magnitude the further away from a wall it is.

rgds, sreten.

Worst is a box about the size of your head against a wall, grim stuff.

speaker dave 28th November 2011 10:55 AM

http://www.diyaudio.com/forums/multi...ml#post2767942

Here are some curves of a speaker mounted on wall and an EQ network that corrects for it.

David S.

speakerdoctor 28th November 2011 11:54 AM

Quote:

Originally Posted by speaker dave (Post 2797889)
http://www.diyaudio.com/forums/multi...ml#post2767942

Here are some curves of a speaker mounted on wall and an EQ network that corrects for it.

David S.

Couldn't find the EQ network at your link. :(

speaker dave 28th November 2011 01:55 PM

The network is not a "network" but the resultant filter response shown in the center graphs. The left curves show an on-wall speaker against the wall and in free space. The curve with accentualted bass and the lower midrange dip is the one against the wall. The cure was to have 2 different switchable networks for the "lower" woofer of a 2 1/2 way design. For free space the usual 1st order rolloff of the lower woofer. For the boundary condition a bumped 2nd order network with the bump very carefully placed at the dip frequency.

2nd group of curves show the resultant 2 pi corrected curve vs. the free space curve. Good correction for a passive network. You could do a little better with an active correction.

Note that these types of corrections must be precisely done for the exact boundary conditions that you are under.

David S.


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