subwoofer phase switch

Discussion in 'Archived Threads 2001-2004' started by Brian Dobbs, Aug 31, 2001.

  1. Brian Dobbs

    Brian Dobbs Ambassador

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    There is a switch on the back of my cerwin vega LW-15 that says , "0-PHASE-180". What does this switch do and what factors should I consider when i choose a setting (room size, system layout, other speakers(2 LS-10s), listening preference)?
     
  2. Dustin B

    Dustin B Producer

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    I'll assume you've seen sine wave graphs in school. So you remember how a full sine wave length was 360 degrees on the x axis. Well the phase switch just shifts the sine wave (or in this case the freqeuncies going to the sub) 180 degrees.
    If you have two identical sine waves and they are in phase or both start at 0 degrees then they will sum and amplitude (or y axis height) will double. If you shift one of the those sine waves 180 degrees though (starts at 180 instead of 0), then the hills of the first sine wave will line up with the valleys of the second sine wave and the amplitude will sum to zero.
    So now lets consider two room options. The first is the sub is at the front of the room and in the same line as your main speakers. Now since the crossover between the mains and sub isn't a brick wall there is some over lap. This overlap can be like the two sine waves above. Since they are in line, they will both be starting a 0 degrees and as such should sum up with each other nicely (since the crossover does attenuate what overlaps between the mains and sub) creating a, hopefully, flat frequency response.
    Now if the sub is at the back of the room it may or may not still be in phase with the mains, if it's not it could be like the above example where the sine waves are 180 out of phase and cancelling each other creating a bad hole in your systems frequency responce around the crossover point. So flipping the phase switch to 180 would bring it back into phase with the mains.
    Now the problem with a 0 or 180 switch is it's not likely that your subs position will have it exactly 180 degrees out of phase with your other speakers. That's why better subs have continously variable phase controls, so you can tune in to a 90, 140, etc degree out of phase position.
    This is quite simplified, and ignores timing issues. In reality it gets way more complicated than my understanding of the subject can handle, but this is how I think of it.
    By the way, how's the DIY subs coming, have you started the boxes yet? Or did we manage to convince you to try taking them back and getting an Adire driver?
     
  3. Brian Dobbs

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    I was asking this for my friend actually. I'm still building my boxes for my "car subs". Sorry if I've dissapointed any of you!
     
  4. Dustin B

    Dustin B Producer

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    Well, although I still think a single Tempest would have been a better choice than the 4 Sony's I'm sure you will be happy with the Sony's (unless you end up with power problems running four 4 ohm drivers off the A and B outputs of a receiver meant for 8 ohms) and that they will provide a chunk of umph in the 40-80hz range for ya.
    Although most of us in the advanced section don't aggree with your choice, we still are all interested in seeing some pics of the construction and final results along with your feelings of their performance, just purely your opinion or with yours and your friends subjective comparison of them to any other sub you can get your hands on. Happy construction [​IMG]
     
  5. Brian Dobbs

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    As soon as they're done, which might be a while, i'll post again. By the way, I'm running the speakers in series only off of the A channel. That's the only safe way.
     

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