[Joe Bloggs]

I'm on a technical streak lately

I know so little about this term that I can't say anything more than posing the question

 

[Xander]

Joe,

Phase distortion isnt really distortion per-se as you understand it, rather then an inaccuracy in loudspeakers due to poor design. When you have atleast a two-way system designed using a complex crossover, phase issues occur when one driver produces sound at a different time then the other. Since at some points, both drivers are re-creating the same frequency near the crossover point, you get the same frequency reproduced twice at different times. Bad.

 

[pedxing]

I am not sure but many other things can produce phase distortion.

Companies that sell expensive cables, like Monster, claim that different frequencies propagate through copper wires at different speeds. The bass and treble will not reach your speak at different times, creating another source of phase problems. This problem in electronics and networking is referred to as signal skewing. Apparently, not only does copper suffers from this problem, but any energy travelling through a medium has this problem including fiber optics.

Also bad encoding or compression can cause phase distortion. Xingtech MP3 encoder was reknown for noticeable phase distortion at higher frequencies.

Another common case of phase distortion is when a audio system is used with a subwoofer. A subwoofer that is not properly placed in the room may cause phase distortion to the audience. Some subwoofers have a switch to reverse the polarity of the phase at certain angles to compensate for such problems. Usually putting it out of phase makes the bass sounds louder and looser to me. It is funny to hear the upper bass of the drum come out of the satellites and then hear the low fequency whump inbetween the drum beats.

 

[Joe Bloggs]

So is there phase distortion in headphones?

Quote:

Quote from Glossary of Headphone Measurements, HeadRoom Using a 1 kHz square wave, hi-frequency losses are shown by loss of steepness on the leading edge of the square wave (called ¡§slew rate limited¡¨), and phase incoherence is shown as ripples in the waveform (usually caused by acoustic and/or mechanical resonances).

 

[Xander]

Phase distortion exists in all speakers. It's not only caused electronically by crossovers, but also by refractions, resonances, etc. Just as that quote from HeadRoom says. Even amplifier and source equipment can cause phase distortion.

 

[Joe Bloggs]

>>phase incoherence is shown as ripples in the waveform (usually caused by acoustic and/or mechanical resonances)

How is this supposed to be phase distortion, though?

I mean how does one read phase distortion off a square wave response graph?

And Bode graphs plot phase in degrees against frequency... what does that mean?

 

[Joe Bloggs]

And what *is* a crossover anyway?

 

[Xander]

Check out this page:

http://www.linkwitzlab.com/phs-dist.htm

I think it'll answer all of your questions.

When HeadRoom speaks about incoherence, I think theyre refering to distortion. As for a crossover, it just filters specific bands of frequencies. For example, if you had a cone tweeter, and a 6" woofer, you might want to cut off low frequencies from that tweeter at 1100hz. You'd use a capacitor to do this. For the woofer, you could simply use a inductor to filter out the high frequencies and cross it over at 1100hz as well. This is a simple example of a crossover. Many are more complex. The more complex the crossover, the more phase incoherence occurs in the circuit. Not only does this contribute, though, but so can resonances with the cabinate, placement of the drivers, etc.

The problem is, most phase distortions normally encountered, arent audible. Or atleast, arguably so, unless the distortion is gross.