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Old 23rd October 2011, 09:19 AM   #1
spot is offline spot  Australia
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Default Adjustable Linkwitz Transform filter

Do they exist (in analog form)?
I would like to be able to have two adjustments to fine tune the speaker to the filter as the speakers are new, and as they age the parameters may change.
Looking at the spreadsheet though it seems that to change the Q or the F3 of the speakers response in the filter requires changing all component values.
I would really like a filter which just flattens the response, not adding another Q and f3 lower down - and then have a separate filter to provide the low freq rolloff. Dont know how or if its possible though.
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Old 23rd October 2011, 09:42 AM   #2
GTHICM is offline GTHICM  United States
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Default Marchand Bassis

What about the Marchand Bassis? It would seem to fit the bill. Have a kit on hand but have not gotten around to building it and trying it.
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Old 23rd October 2011, 11:48 AM   #3
spot is offline spot  Australia
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Originally Posted by GTHICM View Post
What about the Marchand Bassis? ...
Thats exactly what I was looking for, thanks.
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Old 23rd October 2011, 01:12 PM   #4
AndrewT is offline AndrewT  Scotland
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Which filter do you want to adjust? or both?

The low pass that feeds the bass only speaker or the high pass that feeds the upper bass, mid & treble speakers?
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Old 23rd October 2011, 02:17 PM   #5
tb46 is offline tb46  United States
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Hi,

I think spot is talking about a low cut in front of the Linkwitz transform circuit to reduce subwoofer excursion at the very low end - subsonic filter, and the Marchand WM8 Bassis fits the bill.

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Last edited by tb46; 23rd October 2011 at 02:20 PM.
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Old 23rd October 2011, 02:41 PM   #6
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by spot View Post

I would really like a filter which just flattens the response, not adding another
Q and f3 lower down - and then have a separate filter to provide the low freq
rolloff. Dont know how or if its possible though.
Hi,


Your complicating matters, a peaking high pass filter does both and is simpler.
Its fairly easy to arrange the peaking (flattening) Q to be adjustable, but it
needs an initially overdamped response.

A LT unlike the above flattens an already peaking response, its quite complicated.

What functions you need depend on the driver and the box.

rgds, sreten.
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Last edited by sreten; 23rd October 2011 at 02:44 PM.
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Old 24th October 2011, 02:09 AM   #7
spot is offline spot  Australia
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Quote:
Originally Posted by AndrewT View Post
Which filter do you want to adjust? or both?

The low pass that feeds the bass only speaker or the high pass that feeds the upper bass, mid & treble speakers?
Im thinking of the LW transform - not a LW crossover filter. The transform (filter) cancells out the speakers Q and f3 and replaces them with new ones, lower and better - at least for a theroretically pure speaker.
I'm not wanting to use fixed value components in the LW Transform design as the speakers are new and may change over time with use, so I would like to be able to adjust for this - so I would want to adjust the Q and F3 that the transform cancells out. The new Q and F3 of the system does not need to be adjusted (unless I change my mind).

.
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Old 24th October 2011, 07:03 AM   #8
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The pure Euclidean logic which underlies LT is really only the roughest guide to producing a good sounding installation (a) in your room and (b) in relation to Fletcher-Munson stuff. Such corrections, however compelling their logic are for connoisseurs of beautiful theoretical sound or as just general guidance for builders.

With the best theory, satisfying bass will still elude you until you do mic testing. So just have a flexible parametric EQ box on hand - even a single band, and old-time tone controls or loudness circuitry on your pre-amp will be very helpful.

We all love beautiful theories, no denying that.

Ben
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Old 24th October 2011, 09:54 AM   #9
forr is offline forr  France
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Adjustable Linkwitz Transform filter Do they exist (in analog form)?

B.J. Sokol proposed an adjustable transform, in "Practical subwoofer design"Wireless World December 1993. pp 41-43. Ian Hegglun slightly modified it in Electronics World, May 1996.
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Old 24th October 2011, 10:06 AM   #10
spot is offline spot  Australia
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Quote:
Originally Posted by bentoronto View Post
... With the best theory, satisfying bass will still elude you until you do mic testing. So just have a flexible parametric EQ box on hand ...
Years ago (about 20 - I must be getting old) equalisation was all very expensive but now I'm amazed at what is available in the DSP realm. $99 for minidsp and $150 for beriger feedback destroyer (can be programmed as a multiple parametric eq).
I'm going to use the minidsp in my car system and will probably get something like that for my HTPC - maybe just software. There's my adjustability problem solved.
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