Re: How to test speaker resistance

Jerry Gaffke

Interesting, though raises more questions than it gives answers to.

The graphs show different speaker responses, mostly for no particular reason.

At the start he defines resistance and impedance as two different things (probably should read resistance and reactance),
then in the graphs it properly shows complex impedance as ohms of impedance with a phase angle,
which is the combination of resistance and reactance.

More puzzling to me, he shows a self resonance at 130 hz or so in the first graph,
and the phase angle flips there from positive to negative just like an LC circuit.
But "impedance rise due to voice coil inductance" in the second graph doesn't take over till 1khz and beyond.
What exactly is going on at self resonance?   That's a central concept here, and left unexplained.
And seems a resonance at 150 hz would be extremely disruptive to the sound spectrum we hear. 

He shows a base-reflex speaker's impedance to have two peaks (at two different frequencies),
then claims that if they are the same height (same max impedance on both peaks)
then the "resonant frequency of the speaker matches the resonant frequency of the box".
But the frequencies certainly don't match.

Not sure I trust anything in the writeup now, but that second graph is interesting.
Shows his nominally 4 ohm speaker to have a dc resistance of 3.2 ohms
and a resonance at 30hz of about 31 ohms.  At resonance, it's far from 4 ohms.

Conclusion:  A 4 ohm speaker can have drastic variations in impedance 
over the audio frequency range.

Jerry, KE7ER

On Thu, Mar 22, 2018 at 06:03 am, Raj vu2zap wrote:
Worth reading this page.

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