Bass Alignment filter for B&W Matrix 805 - diyAudio
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Old 3rd May 2013, 09:13 PM   #1
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Default Bass Alignment filter for B&W Matrix 805

I've been trying to find a Bass Alignment filter for my B&W Matrix 805s, but have been unsuccessful. While searching I came across this thread Anyone reverse eng. 801 bass alignment filter?. That got me thinking maybe I could build one. I'm not too savy in the engineer department (though I would love to learn), but I can read a schematic and operate a soldering iron, multimeter, and scope. I wanted to see if someone here could help me out on the design of a BAF for my speakers. From what I understand, the BAF is a high pass filter with a bump at the speakers port frequency. I'm thinking a bump around 40 Hz, with a rolloff of the low side, would do the trick Anybody want to help me out with this?
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Old 4th May 2013, 02:21 AM   #2
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Why do you need "" a bump around 40 Hz""?!
A baffle step comes to mind...
Do you mind to elaborate.
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Old 4th May 2013, 02:43 AM   #3
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What you want is 6dB boost around 50Hz or so, like this (ignore the opamp type) -
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Old 4th May 2013, 04:25 AM   #4
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Quote:
Originally Posted by abraxalito View Post
What you want is 6dB boost around 50Hz or so, like this (ignore the opamp type) -
What type of Op amp should I use, and what +/- voltages do I need to supply to the op amp?
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Old 4th May 2013, 10:10 AM   #5
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Itīs a Sallen and Key high pass filter with a Q of about 1.94.
In combination with the 4th order alignment of the speaker you
get an approximate B6 alignment. (lower bass & subsonic protection).
Use of an (unity gain stable) opamp is ok, but a good discrete buffer
would be possible also.
The 50 Hz mentioned are way to high, itīs more around 35Hz, have a look at
these measurements (Fig.2):
B&W Matrix 805 loudspeaker Measurements | Stereophile.com
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Old 4th May 2013, 05:38 PM   #6
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So Georg, would the circuit that Abraxalito posted work if I adjust the cap & resistor values to make the center frequency 35hz, and replace the op amp with a descrete amp circuit?
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Old 5th May 2013, 11:41 PM   #7
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For some reason the notification email that you'd replied didn't arrive - hence tardy reply.

Quote:
Originally Posted by Bluethunder View Post
What type of Op amp should I use, and what +/- voltages do I need to supply to the op amp?
The opamp chosen depends on what quality level your system is. A decent mid-range choice would be NE5534 (or NE5532 for stereo). If you choose 5534 don't forget the 22pF comp capacitor. Power supplies depend on what its feeding - into a poweramp then +/- 5V should be sufficient as poweramps have nominal 1VRMS sensitivity normally.

As regards the cut-off frequency, I was going from memory of the original alignment, not measurements. If you look at the original Matrix 805 owner's manual you'll see it states 'Sixth order Butterworth alignment 42Hz cut off'. Since the speaker alone has 4th order alignment I take it the 42Hz figure is with the BAF in-circuit.

http://akdatabase.org/AKview/albums/...s%20Manual.pdf
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Last edited by abraxalito; 5th May 2013 at 11:52 PM.
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Old 6th May 2013, 01:49 AM   #8
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I've read that krell made a BAF for the matrix speakers that was even better than B&W version. Any idea what they did different?
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Old 6th May 2013, 01:55 AM   #9
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Also, if it helps, the BAF will feed into a Hafler DH500 and then into the 805's.
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Old 6th May 2013, 07:43 AM   #10
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Krell being Krell probably put it in a fancy thick-fronted box with a much stiffer PSU. The original B&W BAF used discrete transistors (an emitter follower I think) as the unity gain element. That would probably sound better than an opamp.
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