Anyone reverse eng. 801 bass alignment filter? - diyAudio
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Old 8th June 2004, 02:23 PM   #1
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Default Anyone reverse eng. 801 bass alignment filter?

Looking to build a discrete, balanced bass alignment filter for 801's

Thanks for looking

Mike
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Old 8th June 2004, 03:21 PM   #2
sreten is offline sreten  United Kingdom
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The 801's use a Bessel 4th order alignment, basically
overdamped, but well suited to typical room gain.

The classic way of re-aligning is a 2nd order high pass filter
set at the port frequency with Q adjustable between 1 and 2.

For a non-vinyl system with no subsonic rubbish, its also
possible to use a low bass shelving circuit, which has
better transient response, this can be entirely passive
at line level, as maximum loss would be 6dB.

Design of either approach is fairly straighforward.

sreten.
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Old 8th June 2004, 07:28 PM   #3
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Thanks for the excellent info!
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Old 8th June 2004, 10:41 PM   #4
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do you mean to say "all pass" filter for time alignment? Here's the design which Ballard used in his 1982 Speaker Builder Article with "virtual instruments" thrown in -- the output of the filter lags the input by 50uS.
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Old 9th June 2004, 12:03 AM   #5
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I used this for several years. Same target as B&W's box.
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Old 7th June 2013, 11:10 AM   #6
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I've just got a pair of 805 Matrix speakers and power them with my LM3886 gainclone. How much benefit does a BAF give? The bass on these is not quite as punchy as I would like, although the sound qualtiy is far better overall than my old Tannoy MX4 floorstanders. I use a PC as my exclusive source for music. Would a software EQ do much the same thing?
Thanks!
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Old 7th June 2013, 12:12 PM   #7
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A software EQ will do exactly the same, and is much easier to use.
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Old 7th June 2013, 01:09 PM   #8
PB2 is offline PB2  United States
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The vented 801 with the auxiliary filter is a real world implementation of Thiele's 6th order Butterworth (B6) alignment 15 where you'll see an alpha of 2.73 versus 1.414 for alignment 5, a B4 without the filter:
http://www.readresearch.co.uk/thiele..._article_1.pdf

Thiele assumed zero box losses whereas in real life we usually see a Ql of 5 to 10 which shifts the parameters to roughly an alpha of 1 for a B4 and 2 for a B6. All have Fb = Fs and also = Fboost for the aux filter.

The B6 alignment allows for about half the box size as compared to a B4 with roughly 6 dB loss at Fb due to the smaller box. The boost filter provides 6dB of boost, complimenting the curve so that it is again maximally flat and -3dB at Fb.

Some have noted that if you look at the 4th order speaker-box section of a B6 without the filter that it is roughly a Bessel alignment.
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Old 7th June 2013, 01:43 PM   #9
PB2 is offline PB2  United States
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T&S Papers online:
Read Research - Articles

Links to more online papers:
Links to Online Technical Papers (AES))
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Old 9th June 2013, 03:27 PM   #10
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Quote:
Originally Posted by StigErik View Post
A software EQ will do exactly the same, and is much easier to use.
Ok thank you, it's good to know the solution is simple and free!
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