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L-Pads, do they cause distortion?

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  • L-Pads, do they cause distortion?

    I recently installed L-Pads on my speakers. Previously, they were very articulate and crisp in the high end, but perhaps a bit too bright at times. I installed L-Pads on the PRV D290P horns. Although they can be tamed down, even at full output they sound different. Cymbals went from a crisp TTsssssSSSTT to dull shshshsh. Any thoughts?

    http://www.parts-express.com/prv-aud...bolt--294-2833

    http://www.parts-express.com/speaker...8-ohm--260-265

  • #2
    Re: L-Pads, do they cause distortion?

    Adding an LPad changed the transfer function of the crossover. Signal shaping is best accomplished with EQ prior to amplification. The result is more precise, and amp headroom is increased as you're reducing the amp voltage swing in the highs.
    www.billfitzmaurice.com
    www.billfitzmaurice.info/forum

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    • #3
      Re: L-Pads, do they cause distortion?

      Originally posted by dalbert02 View Post
      I recently installed L-Pads on my speakers. Previously, they were very articulate and crisp in the high end, but perhaps a bit too bright at times. I installed L-Pads on the PRV D290P horns. Although they can be tamed down, even at full output they sound different. Cymbals went from a crisp TTsssssSSSTT to dull shshshsh. Any thoughts?
      Double check that you have installed them correctly. Where did you tap into the XO? A quick sketch might help us spot a small mistake. One wrong wire connection can significantly alter the filter response.

      Also, try switching back to the pre-Lpad configuration just to confirm that the sound returns to the previous "state" that you remember. Could it be that something else has changed in your system and the differences you're hearing are not due to the L-pad modification???

      Best of luck with your sleuthing.
      ~Marty

      Baby Eidolons
      Sapphos
      Cables (Post #54)
      Other speakers (Post #21)
      Design Thoughts (Posts: 6,10,13,33,35)
      Boundary Augmentation
      Dispersion/Interference

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      • #4
        Re: L-Pads, do they cause distortion?

        I used the two wires that go out of the crossover and into the tweeter. The L-pad has three terminals marked 1, 2, and 3. I wired them like this:

        http://www.pachitalk.com/L-Pad.jpg

        I noticed that some diagrams use amp or crossover positive to pin 1 and then to tweeter positive. Others do the opposite, i.e. amp or crossover negative to pin 1 and then to tweeter. I would not think it should make a difference as it is a rheostat, but I will try wiring the second way to be certain.

        http://i64.photobucket.com/albums/h1...udio/lpad3.gif

        It still sounds good, it just is not as detailed as it was. I was really impressed with how articulate they were, now not so much.

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        • #5
          Re: L-Pads, do they cause distortion?

          The orientation (positive/negative) of the L-pad doesn't matter. But it can always help to try wiring things up in different ways and understand what's happening in each case.

          I would echo Bill's suggestion if a line level filter or EQ is feasible. Horn loaded tweeters can have impedance swings towards the lower end of their range; at the frequency of an impedance peak, the L-pad will not provide as much attenuation, which is probably an undesired effect. If you're able to experiment with a tone control or some other (e.g. software) EQ, how does the sound of that compare to the L-pad?

          An L-pad will work more predictably if you want a *lot* of attenuation, where the shunt resistance is small (so it makes the load fairly resistive), but I'm guessing this is not the case.

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          • #6
            Re: L-Pads, do they cause distortion?

            The typical wiring is
            Click image for larger version

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            Is this how you have it wired up now ??

            Originally posted by dalbert02 View Post
            I used the two wires that go out of the crossover and into the tweeter. The L-pad has three terminals marked 1, 2, and 3. I wired them like this:

            http://www.pachitalk.com/L-Pad.jpg

            I noticed that some diagrams use amp or crossover positive to pin 1 and then to tweeter positive. Others do the opposite, i.e. amp or crossover negative to pin 1 and then to tweeter. I would not think it should make a difference as it is a rheostat, but I will try wiring the second way to be certain.

            http://i64.photobucket.com/albums/h1...udio/lpad3.gif

            It still sounds good, it just is not as detailed as it was. I was really impressed with how articulate they were, now not so much.

            Comment


            • #7
              Re: L-Pads, do they cause distortion?

              I have like this now. Before, according to your diagram, I had pins 1 and 3 swapped. No change in sound quality either way.

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