Phase Correction: How do it work?


Silver Member
Username: Fishy

Tamarac, FL USA

Post Number: 368
Registered: Sep-04
I understand the relationship between phase and unlike path links, but what I don't understand is how a processor in a head unit would actually correct this.

A simple time delay just won't work because phase differences between two separate drivers with different path links from the listener also depends on frequency(wavelength). Shorter wavelengths(higher frequency) are generally more "susceptible" to this type of phase interference than longer ones.

In other words a succesfull phase correction processor would have to adjust the separate signals by using varying time delays for individual and adequately narrow bands of frequency, i.e. each frequency has to be delayed a different amount.

How would this work? and exactly how hard is it to set one of these things. Is it simply a matter of entering the pathlink difference between the two drivers? Seems like that would be enough info to get the job done.

Just curious. :P Jonathan?


Gold Member
Username: Jonathan_f


Post Number: 2106
Registered: May-04
Naw, it works differently than that. Remember that even when the drivers are in perfect acoustic phase (pathlengths are equal) the wavelengths will still vary according to frequency, yet the drivers are always in acoustic phase. The phase inverter doesn't adjust for every frequency. Absoolute(acoustic) phase is related solely to driver location(as long as they're in electrical phase, anyway). If you had perfect acoustic phase ,such as in a home, and then flipped polarity to one of the cabinets, the speakers would be 180 degrees out of phase. In a car, there is also a set degree that the speakers are out of phase due to location and timing. All a phase inverter does is allow you to adjust the phase of that driver, so say your right speaker is 30 degrees out of phase with the left, you can adjust the phase inverter (they go from 0 to -180) to bring it back into place. Remember that the wavelength will change with frequency, but the driver will ALWAYS be 30 degrees (according to our example). Just as that home system with the speaker were wired out of phase, it would be 180 degrees out of phase at all times.. Look at this diagram:Upload
They're playing different frequencies, but on the lower speaker, when it plays a 5 wave tone, and the other plays a 6.5 wave tone, sound will cancel. Since those speakers are exactly 180 degrees out of phase, if you set the phase inverter to -180, you would effectively "flip" the bottom waveform, resulting in being constructive instead of destructive. Same with any other frequency. Of course, your speakers won't be exactly 180 degrees out of phase, so you'd have to play around with it a little and find what works best (or use test equipment). Basically a phase inverter helps the speakers to acoustically be in phase by making the waveforms equal. I really can't tell you the electronics used in a phase inverter, but I can tell you they do their job, just ask Alma Gates :-).
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