Monday, August 16, 2010

What does the corner frequency for a speaker crossover network represent, and how do you calculate it?

I built a simple crossover network using just an inductor as a lowpass filter an just a capacitor as a high-pass filter for an electronics class. (Then hooked up to a woofer and a tweeter) I have all the data pertaining to the circuit, including graphs of the transfer function versus frequency, but now I need to calculate the corner frequency observed in the network we built, then calculate the values of the capacitor and inductor needed to make a crossover network with a corner frequency of 1 kHz for both speakers. Problem is, I have absolutely no idea what a ';corner frequency'; is, so any help would be appreciated.What does the corner frequency for a speaker crossover network represent, and how do you calculate it?
On a low pass filter, the corner frequency is the frequency at which the output power drops 3dB from the dc point. This corresponds to the point where the output voltage decreases by 30% (or, more accurately, where it drops to 1/sqrt(2) of the dc value). So, if you already have measured the output voltage over frequency (with a constant amplitude input voltage), then just find the frequency at which the output voltage drops 30%.


Do the same for your high pass, only this time find the point at which the voltage is 30% less than the high frequency 'flat' portion.


If you designed your speaker network correctly, both the low pass and high pass would have the same crossover frequency.

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