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welcome to the mysterous world of raw drivers

155.218.169.247

Posted by Mart on November 2, 1999 at 06:36:11

In Reply to: then another question on zobels posted by klaus on November 2, 1999 at 04:08:13:

at least you don't seem to have a short circuiting ring which temporarily flattens the impedence from 1.kHz to 2.kHz or are trying to zobel a tweeter where skin effect is increasing the impedence rather than the voice-coil inductance making the usual driver model obsolete. These non-linear effects are tedious & cumbersome to overcome.

The ideal Zobel frequency occurs @ Sqrt[2] times the minimum impedence (the lowest impedence during operation which reads from the graph as 6.ohms which doubles as your Zobel resistor as well), not the 2*Rdc that you were considering (you forgot about phase). The simplistic Le/(2*Pi*Rdc) which is a good approximation when no other available data is available, but you have the graph.

1.4142 * 6.ohms = 8.5ohms

So, we interpolate from the graph that a proper Zobel frequency should be about 3.65kHz. Thus, you should use a 7.3uF Zobel cap.

What frequency low-pass were you planning on implementing on this driver in order to cross-over to the tweeter? Let's assume for sake of example you used 3.kHz because off-axis response is starting to become poor there.

Your Zobel will be [6. - j*7.26735]ohms but your speaker will roughly be a magnitude of 7.8ohms. Using 6.ohms as the real value we get a reactionary component of 4.983975.13907ohms. Putting the two in parallel we get:

 [6 - j*7.26735]*[6 + j*4.98397]        
--------------------------------- == [6.01771 + j*0.00337049]
[6 - j*7.26735] + [6 + j*4.98397]       

Is it any clearer now?

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