Silent Speakers, Dummy Loads, Thiele-Small Parameters...

[schnoops]

Hi again,

I'm sure your all know about reactive loads and silent recording (THD hot plate, Marshall Power Soak, Weber Mass, etc.)

I'm sure you've also heard of master Randall Aiken (www.aikenamps.com) and his reactive load design (there are actually two design proposals on his web site: http://www.aikenamps.com/spkrload.html )


I'm willing to build a reactive load to match the eminence speaker that's in my fender blues deluxe combo. Randall explains you need to tweak the components values to match the impedance curve of the reactive load to the impedance curve of the real speaker you're trying to simulate.

The problem is that it seems difficult to newbies to maesure the impedance curve of a real speaker (you need special gear and analysis software to do that).
However you can easily find the Thiele-Small parameters of your speaker on the manufacturers web sites (www.eminence.com, www.celestion.com).
If you don't know what TS parameters are about, have a search on google of read this:
http://editweb.iglou.com/eminence/em...s02/params.htm

They give you nominal impedance at DC (Re) the frequency (fs) and height (Zmax) of the resonant peak, as well as a nominal inductance (Le) and two quality factors (Qms and Qes) that describe how peaky is the resonnant peak and of steep the impedance raises at higher frequencies (I guess).

Would anyone familiar with electronics have the guts to correlate those physical TS parameters the resistors, capacitors and inductance values of Randall's designs?

I figured out the obvious myself (considering the second design of randall's web site):

fs<--------->1/(2*pi*sqrt(L3*C1))
Zmax<--------->R1+R2+R4
Re<--------->R1+R2

but the quality factors Qem and Qes are too much for me. I think they'll be used to set the widht of the resonant peak and the steepness of the last part of the impedance curve, but.... how?

Thank you guys, its in your hands now!

[bgavin]

The published Zmax peak is for free air. This changes drastically in a sealed or vented box.

There is a single impedance peak in a vented box at the resonant frequency. A vented box has two: one peak on either side of the box tuning frequency.