Differences between voice coils

[slideman82]

I'm a guitar player and I have a friend who builds speakers, mostly woofer and extended bass. I know about their frecuency range and some other characteristics, like voice coil length, conductor used, etc., but is there any notable difference between a guitar speaker voice coil and other like a medium range? We compared a well known guitar speaker (round copper voice coil) and one he reconed with an aluminium voice coil, with a signal generator, and the guitar speaker had great SPL at about 2 kHz and 3.5 kHz, that sure is what it makes its tone. The other one was more linear, reached up to 7 kHz but had no peaks.

[xrk971]

I would guess that the Al coil has lower mass so the resonant frequency is increased - as you observed.

[slideman82]

Not really! That is a 13 or 14 mm long 2" coil for extended bass, and had a 45 Hz resonant frecuency... I think the same coil in copper has about 40-42 Hz. But my point is other: what makes the guitar speaker voice coil have huge SPL peaks at about 2kHz ad 3kHz.

[chris661]

It's not the voice coil, its the cone.

When driven at higher frequencies, the mass of the cone means the outer edge can't keep up with the inner edge, so mechanically disconnects (ie, the cone bends).

The upshot of that is that various resonances occur in the 2kHz+ range, which can produce peaks in the output (if properly damped, the frequency response can remain flat in spite of the resonances - a waterfall plot would, however, show them up as HF ringing).

Chris

[slideman82]

Great! That's was I was looking for! Now I know what to tell my speaker man!

[slideman82]

Thanks!