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  • What would cause this?

    I have a Peerless 850488 5.5" HDS sandwich cone midbass that is very flat according to factory spec sheet, and previous measurements that I've made. I removed the Peerless GFC midbass that I was using as a mid on my 3-way, and installed the 850488. I was hoping to have less breakup at 5k to filter out, and that I could simplify the x-over. When I made measurements, the midrange between 1k and 2k was like a roller coaster. There was a peak at 1.5k followed by a dip at 1.8k. The GFC cone did not react similarly, so I assume that it isn't diffraction. The mid chamber is about 5 or 6 inches deep, and most of the volume is filled with rigid fiberglass. I may remove some of the fiberglass to see if anything changes, but I'm not expecting it too change. Any ideas as to what would cause this?

  • #2
    Re: What would cause this?

    Originally posted by rpb View Post
    I have a Peerless 850488 5.5" HDS sandwich cone midbass that is very flat according to factory spec sheet, and previous measurements that I've made. I removed the Peerless GFC midbass that I was using as a mid on my 3-way, and installed the 850488. I was hoping to have less breakup at 5k to filter out, and that I could simplify the x-over. When I made measurements, the midrange between 1k and 2k was like a roller coaster. There was a peak at 1.5k followed by a dip at 1.8k. The GFC cone did not react similarly, so I assume that it isn't diffraction. The mid chamber is about 5 or 6 inches deep, and most of the volume is filled with rigid fiberglass. I may remove some of the fiberglass to see if anything changes, but I'm not expecting it too change. Any ideas as to what would cause this?
    1.5K is 1/4 wave of 6K or about 2.25", 1.8K is 1/4 wave of 7.2K, or about 1.8" Do not rule out diffraction, different materials radiate differently. Also, if the motor is different, it could be some sort of rare wave reflection you are seeing. Espically since 6K is somewhat close to the 5K you are seeing breakup begin. Just some thoughts around the wavelengths you are dealing with.
    .

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    • #3
      Re: What would cause this?

      Originally posted by rpb View Post
      When I made measurements, the midrange between 1k and 2k was like a roller coaster. There was a peak at 1.5k followed by a dip at 1.8k.
      How big are the peaks and dips? (1dB? 10dB?)

      Can you grab a screen-shot for us?

      Are the cone profiles similar or drastically different?

      Out of curiosity, what are the baffle dimensions? (I saw the part about swapping out the drivers... but I'm still curious about the speaker's dimensions.)
      ~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: What would cause this?

        The baffle is 9 x 19. The mid is centered horizontally, and 6" down from the top.

        Driver is high passed with a cap.

        The cone profiles look the same to me. Here's the GFC that is working well.
        http://www.parts-express.com/pdf/264-1074s.pdf

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