keithe@tekgvs.UUCP (Keith Ericson) (10/16/86)
In article <1366@uwmcsd1.UUCP> shop@uwmcsd1.UUCP (Thomas Krueger) writes: >> ...I noticed that the ones that seemed to have the best imaging (Polk) >> use 24db/octave crossovers as opposed to 12db, 18db, etc. >> >As I recall, odd order filters used for crossovers have 180 degrees of >phase shift at the crossover frequency. Even order filters do not have this >pronounced phase shift, but take many more expensive components than odd >order filters. Lessee - as I recall it's 45 degrees per pole at the 3db point. But that's plus 45 degrees for one filter, and minus 45 degrees for the other (minor handwaving: without looking it up I'm not sure which network exhibits the lead, which the lag)*. So you end up with a total of 90 degrees per pole. Therefore with 2 pole networks ->180 degrees (the bad one); 3 pole networks -> 270 degrees; 4 pole networks -> 360=0 degrees; 5 pole networks -> 450=90 degrees; 6 pole networks -> 540=180 degrees, etc, etc. But note that the angular reduction (angle >= 360) can be fallacious since this really represents time delay. For a 500 Hz crossover point, 500 Hz=2ms and 360 degrees is equal to a 2ms delay. Audible? Maybe, maybe not... But then, what do I know? keith * Let me try to figure this one out. For a woofer, a simple crossover is a series inductor. I get noise out of the speaker by putting a voltage out of the amplifier, causing a current to flow in the speaker coil. With an inductive load (remember I put an inductor in series) I'll get - ELI the ICE man - the voltage leading the current -> the current lags the voltage. For a tweeter a simple crossover is a series capacitor. Same reasoning as above, I get the current leading the voltage. So It looks like the phase is "plus" for the high-pass network and will be "minus" for the low-pass. But then, what do I know?