Impedance Enclosure/Driver Prediction

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schmeet

schmeet

Member
Joined 2008
#1
Ok so I'm trying to look at the physics behind enclosure design.

I am happy with calculating the input acoustic impedance of the enclosure which you then convert to a mechanical impedance with Sd^2.

I think you then add this complex impedance, in series, with the complex mechanical impedance of the driver to get a system impedance.

My two problems are a) calculating the driver mechanical impedance as I am sure you need to know the stifness which I can't seem to find for any drivers.

And secondly, and probably more importantly, I have no real idea how to use the impedance to calculate the SPL output from the speaker.

I have read the thiele/small papers on closed and ported systems but I am struggling to get very far. Can any help me out with this please?!?

Cheers,
Pete
 
#3
Thanks for the quick response bjorno. I should now be able to get a decent idea of system impedance. Assuming I am correct in adding the two impedances together in series is the right thing to do.

Do you have any suggestions, (or know of any good resources I should read), to go from here towards getting the SPL (or Volume Velocity) output from the system..

Thanks again,
Pete
 
#4
schmeet said:
Ok so I'm trying to look at the physics behind enclosure design.

I am happy with calculating the input acoustic impedance of the enclosure which you then convert to a mechanical impedance with Sd^2.

I think you then add this complex impedance, in series, with the complex mechanical impedance of the driver to get a system impedance.

My two problems are a) calculating the driver mechanical impedance as I am sure you need to know the stifness which I can't seem to find for any drivers.

And secondly, and probably more importantly, I have no real idea how to use the impedance to calculate the SPL output from the speaker.

I have read the thiele/small papers on closed and ported systems but I am struggling to get very far. Can any help me out with this please?!?

Cheers,
Pete
Click to expand...

Hi,

Just download a free simulator, WinISD or WinISDpro or BoxSim.

If you want theory download the free version of Basta! and its manual.

rgds, sreten.
 
#6
schmeet said:
Thanks for your response sreten but I can't seem to see any theory in
the user manuals. I am not interested in the simulation programs, just
the theory behind what is going on.

Pete
Click to expand...

Hi,

The Basta! manual details the full electrical equivalent circuit used,
which is then basically plugged into a SPICE circuit emulator to
get to the mechanical results predicted by the electrical model.

Theory wise there is no problem switching between electrical
and mechanical domains - see your control system theory -
a lot of the parameters of a speaker are simply derived from
the others, e.g. moving mass and suspension stiffness define
Fs. Mms and BL and cone area define SPL etc.
The driver editor in WinISDpro with "autocalculate" on can be
played with and is a way to see how parameters interact.

You can derive certain aspects of the frequency response
from an impedance curve, but its unnecessary hard work.
Especially if the impedance is free air into half space, you
don't really care, what you want are the parameters that
really matter, basically Qts, Vas, Fs and sensitivity.

Those 4 are all you need most of the time.

rgds, sreten.
 
#7
I'm not even trying to design a speaker, I am just interested in the theory. My main interest lies with transmission lines and resonant pipes. I am happy with the theory of the quarter-wave and I understand the formula to get the impedance curve of the pipe. I would just like to be able to apply that to the output of the driver.
 
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