Phase cancellation issues between subs and tops.

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Phase cancellation issues between subs and tops.

#1 Post by Bill Fitzmaurice » Mon Dec 04, 2006 8:57 am

David Perry posed this question:
My DR290's need the 12" polarity adjusting or I get a noticable drop at the crossover freq. I ended up adjusting the phase to get best results using my Ultradrive, but certainly the polarity swap showed it as being obvious. I am just trying to check if this is a standard requirement of the DR folded geometry and it just has not been picked up before or is just an oddity of my set up?

In any set-up a combination of factors is at work. For instance, the pathway of the DR290 woofer is a quarter-wavelength at about 90Hz, giving 90 degrees of phase lag at 90 Hz. That won't manifest as out of phase with a 90 Hz crossover. But it has a 180 degree lag where the pathway is 1/2 wavelength long, at 180 Hz, so the closer the crossover is to 180 Hz the greater the potential for the main and sub to be out of phase at the crossover. This possibility is exacerbated if it's a direct radiator sub and if the two sources share radiating planes. This is but another reason why system integration is aided by using as low a crossover as your tops will permit and by separating the subs from the tops by at least a wavelength at the crossover frequency.