Electro-mechanical formulas ( Thiele / Small )

Posted by Wayne Parham [ 70.128.110.173 ] on January 04, 2009 at 19:31:33:

In Reply to: Re: Vad calculator posted by hitsware on January 04, 2009 at 11:03:26:

I stopped maintaining the VadCalc applet. It was written in a weird little language called CA Realizer (Computer Associates), which I also used to write tubing movement programs for the oil and gas industry. I do most of my programming in C++, but that language was easier to use for some things, so I gave it a go for a while.

I assume you want to use it because you don't want to build a box to find Vas with the sealed box method. If that's the case, I suggest the added mass method. Then again, I understand the desire to have a method that works without two impedance sweeps. The VadCalc process was simple to do, and provided a pretty good estimate of Vas.

Here's a formula that you can use to calculate Vas, knowing efficiency n₀, Q_es and f_s:

More woofers specs list the SPL output at 1W/1M than reference efficiency, so here's a converter:

These days, I use Keith Larson's Woofer Tester and Speaker Tester products. They really make life easier. It has evolved a long way since the original Woofer Tester that he used to sell through Parts Express. You can use it to do acoustic measurements and make a digital crossover using Spice models to simulate passive crossovers. It's a great tool. And it still does the T/S measurements.

Smith & Larson Audio

If you want to find T/S specs making measurements manually, or if you want to calculate values from other known values, here's a list of formulas that can be used to solve pretty much whatever you want to find:

Speaker system total Q at f_c