Vas and diameter of the speaker

[dimitri]

Hello,
there is a nice on-line calculator

http://www.webervst.com/spkrcalc/para.htm

there one can read:

To determine the diameter of the speaker, take the size of the speaker (e.g. 12") times .85

Please can you help me, what is diameter of the speaker?
Is it diameter of the cone itself?
Is it diameter of the cone with rubber surround?
Why .85?

The diameter of the speaker has direct influence on Vas.

Thank you,
Dimitri

 

[SY]

The .85 is a crude attempt to convert the driver nominal diameter to something approximating the radiating diameter.

 

[dimitri]

OK, but which diameter should I measure with trammel?

 

[SY]

Remember, precision here is useless- Vas varies all over the place with changes in temperature, barometric pressure, and use of the driver. If you use the known-box-volume method of Vas determination, you don't even need Sd.

In any case, you can approximate Sd pretty well by dropping the 0.85 factor and using the diameter of the cone plus half the surround.

 

[dimitri]

Thank you, I have heard about assosiating air mass. I use the known-mass instead of the known-box-volume method because I can adjust the mass to be the same order as vibrating system mass. For the same accuracy I will need several boxes with different volumes. I use white noise instead of sweep, it is much faster.