Calculate Acoustic Speaker Models

Goodday,

I was wondering how a response in a (for starting) a sealed cabinet is calculated.
I use WinISD a lot to help me building my speakers so when i checked the helpfile I found the following:

Voltage source, Uad, is so called "constant pressure generator". Resistance models acoustic resistance, capacitor models compliance (volumes) and inductor models mass. There are several ways to determine component values. One, which is used in WinISD pro, is where we start on driver Vas to determine Ccas:

Ccas = Vas/(roo·c²)

Then, we'll use fs to determine Lmas:

Lmas = 1/((2·pi·fs)²·Ccas)

Then, Qes and Qms is used to determine Rae and Ram:

Rae = 1/(2·pi·fs·Qes·Ccas)
Ram = 1/(2·pi·fs·Qms·Ccas)

Now, we'll calculate box volume modelling capacitor Ccab just like Ccas. If we have closed box, we'll have only determine the leak and absorption modelling resistors. These are determined by so called Q-factors. For lack of better models, these are determined at resonance frequency of boxed driver.

Ik looks pretty clear to me.
But i don't know where the 'roo' and 'c' value comes from, anyone here knows ?

Or another formule to calculate the response of a speaker in a sealed box.

Thanks in advance,
 
rho = density of air

c = speed of sound

If you want a good reference for the type of lumped parameter modeling used in these types of computer programs I would highly recommend the textbook Acoustics by Leo Beranek. It is without a doubt the best text I have ever found for deriving and explaining the fundamental relationships required for understanding and using the Thiele and Small speaker modeling techniques.
 

Thawach

Member
2007-12-13 9:48 pm
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