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Old 6th May 2013, 10:25 AM   #11
gk7 is offline gk7
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Although anything Ken Rockwell writes should be taken with a grain of salt to say the
least, he has the B&W Bass Alignment Filter user manual online:
B&W Bass Alignment Filter

The manual has some errors, but I think they are obvious.

For the Matrix 805 the filter frequency appears to be 36Hz.
A resulting f3 of 42Hz for the whole system as indicated by abraxalito sounds reasonable.

Last edited by gk7; 6th May 2013 at 10:29 AM.
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Old 6th May 2013, 10:42 AM   #12
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To me this is confusing but perhaps I'm missing a vital piece. To get a new f3 of 42Hz the peak boost would have to be above this frequency no?

I suggest suck it and see - to extend the original 50Hz boost freq down to ~35Hz, put a 220nF in parallel with the existing 470nF in both positions.
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Old 6th May 2013, 11:26 AM   #13
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In the case of an exact B6 (Butterworth) Alignment there would be f3=fb=ff, without the filter the response would be down to -9dB at fb. If I remember correctly this would
require a driver Qts of 0.39. Other Alignments (QB6 "quasi" Butterworth) are possible
and were described by Thiele & Small. Those with the filter frequency above f3 do not
provide a boost, they actually lower the reponse of a high Q speaker to a flat B6 like
response. These type of alignment is not commonly used. Any alignment for a speaker with
a Qts lower than 0.39 would have a ff below f3.

A more practical approach is described in a paper by D.B. Keele (attached).
In his case ff is always fb (which is good because at fb almost all output comes from
the port, so there is no added speaker excursion at the boost frequency) and the applied
boost is always limited to 6 dB.
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Old 6th May 2013, 07:21 PM   #14
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What if I use 2 of the 470 nF caps and replace the resistors with a 15k resistor and a 10k potentiometer? That way I could adjust the frequency with the pot and see what yields the best results.
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Old 6th May 2013, 08:16 PM   #15
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Is this what the circuit would look like using discrete components, in place of the op amp?
Click the image to open in full size.
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Old 23rd July 2013, 11:28 AM   #16
gk7 is offline gk7
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Quote:
Originally Posted by gk7 View Post
... If I remember correctly this would
require a driver Qts of 0.39...
Should be "0.29"
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Old 1st November 2013, 06:43 PM   #17
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Default Emulating using software EQ

Hi, I've got hold of a pair of 805 Matrix speakers and I'm really pleased with them. They could do with a bass boost and I've been looking at Windows software alternatives of doing this. The is a program called Equalizer APO which enables you to create what seem to me to be really complex filter arrangements. I had a basic idea about gain and frequency before but Q and different filter types were a mystery until a couple of hours ago. I've been playing around with editing an existing bass boost function in the program and it's made a difference already. Currently I've got a 'PK' filter giving a 6dB boost at 50Hz with a Q of 0.5. I need to read up on low pass filters but I imagine using one of them would improve things?

If you understand this all better than I do it would be interesting to see the results others get!

Last edited by will9895; 1st November 2013 at 07:03 PM.
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Old 2nd November 2013, 02:59 PM   #18
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The Q of 0.5 confuses me. This would be -6dB not +.
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Old 3rd November 2013, 04:54 AM   #19
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All very interesting. I haven't done Butterworth Filters in years.

So what B&W did with their add-on box of tricks is to add a second order electrical filter to a fourth order bass reflex to make a 6th order bass filter.

Bit of a job to deconstruct this:

Click the image to open in full size.

Vishay Precision Group - Foil Resistors - Case Study: Upgrading High-Pass Alignment Filter for Audio Systems

Then you can find B&W's resistor settings here for the Matrix series:
B&W Group North America Service & Support - B&W Archive Manuals & CAD Drawings

Presumably you could fiddle with the box alignment for different 4th order results too. As noted, you could build your own 2nd order electrical filter based on Don Keele's work too.

I'm not sure it's really worth the effort. If you think that closed box is second order, reflex generally 4th order at whatever steepness you fancy, then even steeper 6th order is pretty small beer in the overall scheme of things.
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Old 4th November 2013, 06:29 PM   #20
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Quote:
Originally Posted by gk7 View Post
The Q of 0.5 confuses me. This would be -6dB not +.
I don't fully understand the relationship of the Q to the gain. I thought it only altered the range the gain was spread over? I'm taking an experimental approach and +6dB gain definitely ups the bass, while -6dB gain decreases it...
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