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Should I hear voices from my subwoofer? PE 70W amp

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  • Should I hear voices from my subwoofer? PE 70W amp

    I just finished an Exodus Anarchy tapped horn subwoofer. It's being powered by ae PE #300-784 70 watt subwoofer amplifier.

    Connecting a full range signal to the line-in on the amp, I hear vocals and it all sounds like poop. Using a dedicated subwoofer line out from a receiver, I hear no voices and it sounds great.

    The literature that came with the amp claims a 12db slope on the internal variable crossover. The vocals are loud and clear with the knob set at the 40hz indicator.

    Is there something wrong with my particular amp, or are they all this bad?
    www.timkulincabinetry.com

  • #2
    Re: Should I hear voices from my subwoofer? PE 70W amp

    Originally posted by timk View Post
    I just finished an Exodus Anarchy tapped horn subwoofer. It's being powered by ae PE #300-784 70 watt subwoofer amplifier.

    Connecting a full range signal to the line-in on the amp, I hear vocals and it all sounds like poop. Using a dedicated subwoofer line out from a receiver, I hear no voices and it sounds great.

    The literature that came with the amp claims a 12db slope on the internal variable crossover. The vocals are loud and clear with the knob set at the 40hz indicator.

    Is there something wrong with my particular amp, or are they all this bad?
    Sounds good!

    I hear voices from my subwoofer with no signal applied.

    I'm gonna need an exorcist or a shrink (both?)

    A 12db slope is not very steep when you consider how low in level (relative to the midband) and how much less audible (fletcher munson) sub-bass frequencies are.

    The problem is that you are listening to it by itself.

    It's the same as folks listening to tweeters by themselves to determine which is best (usually ends up being the one with the best low frequency performance).

    The fact that it sounds good when connected to the reciever indicates it's probably operating properly.
    Last edited by daryl; 03-11-2012, 05:01 AM.

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    • #3
      Re: Should I hear voices from my subwoofer? PE 70W amp

      My description was not clear.

      I can listen to it with the mains running when I hear the voices using a separate amp for the mains. It sounds terrible.

      The only time it sounds good is when the signal to the sub is already a low pass signal from a subwoofer line output.

      Can I add some additional low pass filtering to the output of the subwoofer amp?
      www.timkulincabinetry.com

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      • #4
        Re: Should I hear voices from my subwoofer? PE 70W amp

        From what I've read about this amp, it has always had this problem. I don't know what the true crossover frequency is, but it definitely doesn't crossover at the indicated 40Hz, which you discovered when you hooked it up to your receiver. I don't know why the problem has never been fixed. If you read through the reviews of the amp, you'll see that several customers have had to come up with their own methods of getting a true low-pass signal out of the amp. It seems it's just a design flaw.
        Eric L.

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        • #5
          Re: Should I hear voices from my subwoofer? PE 70W amp

          Originally posted by timk View Post
          The only time it sounds good is when the signal to the sub is already a low pass signal from a subwoofer line output.
          You have answered your own question . . . a 2nd order (12dB/octave) lowpass is not sufficient for a subwoofer which is not co-located with the main speaker, and the "crossover" in your plate amp may have other problems as well. The solution is as you have indicated, use an appropriate crossover before the sub amp . . . as is provided in almost any HT receiver.

          Crossing correctly to a subwoofer is every bit as difficult (and all the same considerations apply) as any other crossover, and the problems are compounded by the crossover frequency typically being in the area of some of the worst room modes, so it's often hard to isolate what's going wrong, and why the sub doesn't integrate well with the rest of the system (although in your case at least part of what's wrong is clear). My guess would be that the little "sub-amp" is intended for use in relatively small systems (like computer speakers) where the sub will be located close to the sats, and where the sats themselves are too small, and need all the "help" they can get well up into the "low bass" region . . . where what's coming from the "sub", however poor it is, sounds better than nothing at all.

          Another guess would be that your tapped horn rolls off pretty hard on the low end, and needs all the boost it can get "on the bottom" . . . the result being that its rising efficiency as signal moves up into the bass region accentuates the problem (the 12 dB rolloff in the amp may do little more than flatten the overall response). You need a 4th order crossover (while possibly leaving the 12 dB rolloff set in the sub amp as well). Since you already have one in your receiver . . . well . . . use it.
          "It suggests that there is something that is happening in the real system that is not quite captured in the models."

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          • #6
            Re: Should I hear voices from my subwoofer? PE 70W amp

            Originally posted by Deward Hastings View Post
            You have answered your own question . . . a 2nd order (12dB/octave) lowpass is not sufficient for a subwoofer which is not co-located with the main speaker, and the "crossover" in your plate amp may have other problems as well. The solution is as you have indicated, use an appropriate crossover before the sub amp . . . as is provided in almost any HT receiver.

            Crossing correctly to a subwoofer is every bit as difficult (and all the same considerations apply) as any other crossover, and the problems are compounded by the crossover frequency typically being in the area of some of the worst room modes, so it's often hard to isolate what's going wrong, and why the sub doesn't integrate well with the rest of the system (although in your case at least part of what's wrong is clear). My guess would be that the little "sub-amp" is intended for use in relatively small systems (like computer speakers) where the sub will be located close to the sats, and where the sats themselves are too small, and need all the "help" they can get well up into the "low bass" region . . . where what's coming from the "sub", however poor it is, sounds better than nothing at all.

            Another guess would be that your tapped horn rolls off pretty hard on the low end, and needs all the boost it can get "on the bottom" . . . the result being that its rising efficiency as signal moves up into the bass region accentuates the problem (the 12 dB rolloff in the amp may do little more than flatten the overall response). You need a 4th order crossover (while possibly leaving the 12 dB rolloff set in the sub amp as well). Since you already have one in your receiver . . . well . . . use it.
            Great answer and good advice. Thank you. Due to considerations I won't detail now because they are irrelevant, it's nearly impossible for me to use a receiver with a sub out.

            I'll check the reviews, but I think I need to figure out how to add some low pass filtering either to the input or output of that amp.
            www.timkulincabinetry.com

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