TS parameters Vab vs Vb

Kral57

Member
2007-08-08 5:17 am
Vab is defined as the volume of air having the same acoustic compliance as the enclosure.
.
Vb is defined as the Internal Volume of air in an enclosure.
.
Why is Vab different from Vb, and how is it calculated? Does it have something to do with the stuffing?
 

Ron E

Member
2002-06-27 10:41 pm
USA, MN
Vab is defined as the volume of air having the same acoustic compliance as the enclosure.
.
Vb is defined as the Internal Volume of air in an enclosure.
.
Why is Vab different from Vb, and how is it calculated? Does it have something to do with the stuffing?

There's a few theories, with varying degrees of empirical support, but typically you hear that stuffing "adds" 5-20% to volume. I think it more likely that stuffing just damps the airspring and really causes a loss in bass, but I don't have measurements to back that up (yet).
 
Hi,

Its Vas not Vab and it is :
"the volume of air having the same acoustic compliance as the suspension".

Vas is the stiffness of drivers suspension, independent of the box volume.

e.g. a driver with Fs = 30Hz and Qts =0.35 in a box of 1/3xVas will have
Veffective = 1/4xVas, Fbox will double to 60Hz and Qbox will double to 0.7.

rgds, sreten.
 

Kral57

Member
2007-08-08 5:17 am
Small's Paper

soho54 is correct. Section 7 of Small's paper "Closed-Box Loudspeaker Systems Part I: Analysis" has a complete description of the theory of the effects of stuffing on Vab, as well as a (not so easy) method of measuring the effects of stuffing. Thanks.
 
soho54 is correct. Section 7 of Small's paper "Closed-Box Loudspeaker Systems Part I: Analysis" has a complete description of the theory of the effects of stuffing on Vab, as well as a (not so easy) method of measuring the effects of stuffing. Thanks.

Correct, Add this information for a more complete picture of Vab:

b:)
 

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Hi,

My mistake, OK its the effective volume of the box not the actual volume.

Stuffings and linings increase Veff by slowing the speed of sound and as
I understand it the rate of contraction and expansion of the "medium",
whilst also adding some resistive damping to airflow.

I found out the hard way some foams are too dense and can and
does damp airflow too much when used in bulk instead of linings.

If you vary the amount of stuffing in a box Fb will vary, this is
easiest to model by saying the effective box volume is changing.

The effect on damping is more subtle, if Qtc does not vary the
way you would expect it to just by varying Vbox, I think you
would need to manually adjust some damping co-efficient.

I think some simulators do a better job of modelling linings
and stuffings than others, WinISD AFAIK is not good.

rgds, sreten.