Starting Qtc for Speaker used for Linkwitz Transform

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This makes little sense to me. :) Do you mean you plan to use a Linkwitz-Riley filter, or that you want to make an open baffle speaker?

Best,

E
The Linkwitz Transform (same guy, different filter, assuming you are referring to a crossover) is an approach that undoes a speaker's Qtc (and Fs) and allows the designer to substitute figures that better suit his or her purposes. It is typically used to extend low end response, though it could be used to make F3 higher.

I am trying to find out the constraints on the starting Qtc from someone who has a deeper practical understanding of the implementation of the approach.
 
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Mentioned filter works most effectively when starting Qtc and desired Qp are equal. It will behave like normal low shelf filter. This combination will always give best power conversion efficiency regardless of driver or volume used. No more knowledge needed.
 
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Mentioned filter works most effectively when starting Qtc and desired Qp are equal. It will behave like normal low shelf filter. This combination will always give best power conversion efficiency regardless of driver or volume used. No more knowledge needed.
How would you characterize the results, for example, when starting Qtc > Qp.

For example:

A. Qtc = 1.2, Qp = 0.7
B. Qtc = 1, Qp = 0.7

Thanks so much.
 
It is good to have a reasonably low starting Qtc. Due to tolerances and long-term drift the zeros of the Linkwitz transform circuit will never exactly cover the poles of the loudspeaker box. That could result in a long (but low-level) ringing when the poles of the loudspeaker are very poorly damped, like when you use current drive and/or a very small box. I'd try to keep Qtc well below 2.
 
The difference between Qp 1.0 and 0.7 corner frequency level is 3 dB so output after normalization to equal maximum voltage will be 3dB less. It means less efficiency for given input wattage. I don't know how to explain it properly in English. It is good to use larger box or to damp it with dense open-cell material. Qp of 0.8-0.9 isn't that bad when fp is carefully tuned to in-room modal resonances and room gain.
 
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The difference between Qp 1.0 and 0.7 corner frequency level is 3 dB so output after normalization to equal maximum voltage will be 3dB less for given input wattage. I don't know how to explain it properly in English. It is good to use larger box or to damp it with dense open-cell material.
I should have been clearer.

Assuming I have, for practical purposes, unlimited power and power handling, and understanding that the filter becomes more difficult to implement, what is the effect on sound quality as [starting Qtc - Qp] gets larger. Please assume that the circuit is perfect.
 
In theory there is no sq degradation but in reality highly undamped mechanically system will generate high level of harmonics which frequencies are around tuning frequency.
Thank you so much.

Would you say that starting Qtc = 1.2 is still okay, or would you recommend 1.0, 0.9?

I am just wondering where the sweet spot is for the smaller box, poorer sound compromise.
 
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So, I'm not sure why Qtc even comes in here. It looks like it takes a sealed sub, and extends the bass electronically? Based on this graph, I see a normal sealed woofer, to which rather simple EQ is applied, reminds me of basic tone controls back when they were done right.

What am I missing?

An externally hosted image should be here but it was not working when we last tested it.
The line "Original" is defined, in part, by the speaker's Qtc.

The filter must reverse the curve of the Original line, and reset the system frequency. Note that the Original line has slight rise before it rolls off, which would seem to indicate a Qtc in perhaps the 0.8 - 0.9 range. The X'form curve has an offsetting dip, before it adds a 12 dB/octave equalization.

This is much more complicated than a simple tone control.
 
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The Linkwitz transform is more than just a shelving filter like the ones used in tone controls. It is a little more refined shelving filter (a biquadratic filter to be exact) because it is able to correct fc and Qtc.
In its original form it is restricted in terms of the achievable Qtc and fc ratios. With more complicated topologies one could go a little further. it is not restricted to the use of frequency Extension - it can also be used for the reduction of frequency response in order to achieve a target acoustic transfer function of a crossover/driver combination.

I wouldn't use it for the correction of very high Qtc values either (like over 2). But corrections like EQing a closed box with a Qtc of 1.0 to a Qtc of 0.5 one octave lower is easily doable.


Regards

Charles
 
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