Will a Linkwitz transform...transform the driver?

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Thanks, Ed., but may I also ask the question another way... Can I take a high Q driver, measure and transform it to a (effectively) low Q driver, then design a box for such a low Q driver (ie, smaller) and will the box then do as I expect it to as if the driver were truly low Q?


I can see that I would probably choose your point of view for some situations but with a horn I'd like to reduce the box size a little if possible.
 
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Thanks, Ed., but may I also ask the question another way... Can I take a high Q driver, measure and transform it to a (effectively) low Q driver, then design a box for such a low Q driver (ie, smaller) and will the box then do as I expect it to as if the driver were truly low Q?

I can see that I would probably choose your point of view for some situations but with a horn I'd like to reduce the box size a little if possible.

You should probably do it the other way around. Design the box, based on the T/S parameters of the high Qts driver, which will give you a lower system Q (than the driver on its own). Applying a Linkwitz transform will extend the lower end response and, within the pass band, give you a lower system Q (you would need the in-box transfer function in order to do LT. But the LT on its own will result in a shelved boost of all LF signals; It should be implemented with a High-pass filter to reduce over-excursion or overdriving the amp.

And then: LT was intended for use with sealed enclosures. However, it is possible still to apply equalisation (generically speaking) to obtain the Q and final transfer function of your choice.
 
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I have SPL to spare, no worries there.

I think I get the whole issue now. The transform alters the response level and phase, but doesn't touch the acoustics.

For example, I could appreciate someone taking a high Q woofer, closed boxing it to Chebyshev, then transforming it back to Bessel.... this will give you a smaller box than you otherwise need, but I don't think the transform will fix the Chebyshev ringing.

I could produce a horn that's intentionally smaller than it need to be and transform the resultant response, but then I'd know that issues like reactance nulling were fudged, and mouth response was abused, etc.

Just wanted my cake and to eat it too :p

I did take a dipole rolloff once and reverse it up to flat with a Linkwitz transform. Now that was the right way to go ;)
 
For example, I could appreciate someone taking a high Q woofer, closed boxing it to Chebyshev, then transforming it back to Bessel.... this will give you a smaller box than you otherwise need, but I don't think the transform will fix the Chebyshev ringing.

No. It is the final system response that matters. If you end up with Chebyshev, yes, you'll have ringing. But if the end result is Bessel, then you have the characteristics of Bessel, etc.
 
LT is not for modifying the driver

The LT is not a "driver parameter modifier" circuit. It modifies the behavior of a driver mounted in a closed box (a second order system). It does this by creating two electrical functions, one that "cancels" the existing response of the driver+CB, and one that generated a "new" response.

Because a horn loaded speaker has a 3rd or 4th order response, and that is not what the LT circuit is designed for, this will not work.

The LT is also not just a magnitude "boost" like the knob labeled "bass" on your preamp or receiver. It also has particular phase characteristics that a tone control or parametric equalizer does not.

If you want to modify Qts of a driver, you can do that with feedback or series resistance. Qts can be increased or decreased.

-Charlie
 
Sorry that is not quite correct and you can do exactly what you want with an LT.

The driver Qts and Fs are your "unequalised" Q and F, and your target Q and F are what you want the parameters to change to. Vas will remain the same. There may be a problem though that just changing those parameters a small order of magnitude results in un-realisable component values or rule violation of the LT.

However, in a box design as has been pointed out already, you would not do it this way but instead correct the resulting box response back to what you want. Because the horn is not a 2nd-order system you can't work it that way. I was under the impression that parameters are of much less importance than the horn design anyway, so you are probably going to waste time and money trying to compensate the basic driver.
 
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Horn parameters more significant than driver parameters....that may be the salient point.

Could the LT be used to allow a smaller vented box to be used? Noting that the vented box is 4th order, could I take a transfer curve of the desired and actual responses and shave this off, retaining the desired transient response or better?
 
I think you should not restrict yourself to "Linkwitz Transform", as this describes a very specific application. "Equalisation" is probably more suitable, as it is more generic, not being limited to a specific filter type.

Keep in mind that below the port resonance the driver quickly runs out of excursion, so any boost applied here must be chosen judiciously.

Check out this article. Active Equalization of Loudspeakers. It uses SoundEasy loudspeaker design programme but the discussion is, I believe, relevant to what you seem to be contemplating.
 
ESP - The Linkwitz Transform Circuit

it's just an EQ curve which is the inverse of a closed box speakers roll off so allows the speaker to operate with flat frequancy response at lower frequancys. It does nothing to the actual speaker just changes the input to the speaker.

This was the right answer to the original question. the Linkwitz circuit (or the KEF Kube) does nothing to change the parameters of the woofer, it is just a precise method of "undoing" the combined (woofer and box) response you have, and replacing it with a desired response. You haven't changed the parameters of the woofer and placing that woofer in a new box will get you a different response that the EQ will no longer suit.

If I recall correctly, horn drivers need to be low mass for bandwidth and high Bl. You can still use a "wrong" woofer and equalize the result, but the needed EQ won't have anything to do with what EQ worked for the sealed box.

Here is a question for the real experts out there: lets say we use negative output impedance to lower the effective Q of the woofer. Would that transfer from box to box? Can we add external network components to simulate higher mass? Will that transfer from box to box?

David
 
..Here is a question for the real experts out there: lets say we use negative output impedance to lower the effective Q of the woofer. Would that transfer from box to box?..


Hi David,

Yes it would.

Can we add external network components to simulate higher mass? Will that transfer from box to box?

Yes but how effective depends on the driver in use among other aspects. See:

http://www.diyaudio.com/forums/subwoofers/104447-ace-bass-amplifier-design.html

and

http://www.diyaudio.com/forums/multi-way/83982-enclosure-high-q-driver-4.html#post976317

b
 

Ah, yes, ACE Bass. I had forgotten about that. A clever way to "transform" the woofer.

Note that at the woofer terminals, the acoustical response of a woofer to an electrical input doesn't change. Still, the amplifier/woofer combinations do make the woofer appear to have different parameters and react accordingly when placed in different cabinets.

Regards,
David
 
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