Tuning at or below Fs - Page 3

gafhenderson · 2nd February 2012, 08:55 PM

all i've got are these.

Fs 37.4
qts 0.76
qes 0.88
qms 5.28

PeteMcK · 3rd February 2012, 12:48 AM

brand/model?

GM · 3rd February 2012, 06:17 AM

Quote:

Originally Posted by PeteMcK

with Qts that high, it's probably more suited to a closed box or OB

Or TL.

GM

speaker dave · 3rd February 2012, 02:06 PM

What you find with all vented box allignments is that they are relativly insensitive to changes in woofer compliance. Imagine that a manufacturer may make a production lot of woofers and every one has the same BL and mass, yet the compliances (or Vas) are all over the place. If you designed the ideal vented box for a woofer dead center in the tolerance band, you would find that the final system performance varied very little when trying any of the other woofers of differing stiffness.

This can explain the Peerless observation.

It also means that "Q of .383 and tune to fs" may work fine but isn't a requirement. In the hypothetical batch of productions woofers, if mass and BL didn't vary (these are the crucial parameters) you would find that each woofer had a different fs and different Qt. Interestingly, you would also find that the ratio of fs/Qt would be fairly constant. We already said that performance in the final enclosure would be relativley constant. That means that some would be tuned to the free air resonance of the woofer and others would not (box tuning would be constant, woofer resonance would vary).

There was a good paper years ago called "Loudspeaker Athletics" (by R.J. Newman, I think) where he showed how you could take advantage of the insensitivity to woofer compliance. If you took a woofer of the "wrong" Q and calculated what parameters it would have if it had the "right" Q (purely by shifting the compliance) then you could use the hypothetical woofer's parameters to design the ideal enclosure, which would work just fine for the "wrong" woofer you have. (Hard to explain in a paragraph, but worth reading the paper).

Regards,
David S.

3rd February 2012, 12:48 AM	#22
PeteMcK diyAudio Member Join Date: Feb 2002 Location: Western Sydney	brand/model? __________________ Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency

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2nd February 2012, 08:55 PM	#21
gafhenderson diyAudio Member Join Date: Jan 2012	all i've got are these. Fs 37.4 qts 0.76 qes 0.88 qms 5.28

3rd February 2012, 02:06 PM	#24
speaker dave diyAudio Member Join Date: Nov 2009 Location: Toronto	What you find with all vented box allignments is that they are relativly insensitive to changes in woofer compliance. Imagine that a manufacturer may make a production lot of woofers and every one has the same BL and mass, yet the compliances (or Vas) are all over the place. If you designed the ideal vented box for a woofer dead center in the tolerance band, you would find that the final system performance varied very little when trying any of the other woofers of differing stiffness. This can explain the Peerless observation. It also means that "Q of .383 and tune to fs" may work fine but isn't a requirement. In the hypothetical batch of productions woofers, if mass and BL didn't vary (these are the crucial parameters) you would find that each woofer had a different fs and different Qt. Interestingly, you would also find that the ratio of fs/Qt would be fairly constant. We already said that performance in the final enclosure would be relativley constant. That means that some would be tuned to the free air resonance of the woofer and others would not (box tuning would be constant, woofer resonance would vary). There was a good paper years ago called "Loudspeaker Athletics" (by R.J. Newman, I think) where he showed how you could take advantage of the insensitivity to woofer compliance. If you took a woofer of the "wrong" Q and calculated what parameters it would have if it had the "right" Q (purely by shifting the compliance) then you could use the hypothetical woofer's parameters to design the ideal enclosure, which would work just fine for the "wrong" woofer you have. (Hard to explain in a paragraph, but worth reading the paper). Regards, David S.