Crossover Frequency Shift?

[Klewless]

Crossover experts,

If you put an 8 ohm speaker on a crossover designed for 4 ohms, which way would the electrical crossover point go. Up or Down? Not asking about the acoustic effects, only the theoretical electrical. Thanks

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John P

St Paul, MN

[Andy W]

For a low-pass filter the crossover frequency doubles when you go from 4 to 8 Ohms. For a high-pass filter the crossover frequency is halved going from 4 to 8 Ohms.

So, for a first order crossover, a 4 Ohm driver allows you to use an inductor half the size, but requires a capacitor twice the size.

The math goes like this:

Xl=j*2*pi*f*L and

Xc=-j*2*pi*f*C

The j refers to phase and you can ignore it in magnitude calculations, and if you use the half power point as the crossover frequency you can substitute Z (driver impedence) for Xl and Xc:

Z=2*pi*f*L (solving for L gives inductor value for low-pass)and,

Z=1/(2*pi*f*C) (solving for C gives capacitor value for high-pass)

Of course, to be more accurate, you need to use the driver impedence at the desired crossover frequency.

Hope this helps,

-Andy W

[Klewless]

Andy,

Thank you.

A buddy of mine is connecting a 16 ohm woofer to an 8 ohm xover.

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John P

St Paul, MN