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Subsonic frequencies

Discussion in 'Amps, Mics & Pickups [DB]' started by heymrbassman, Apr 3, 2003.


  1. I am interested to know whether certain peizo pickups can produce sub bass frequencies that can potentially damage speakers. If so, would these frequencies be reduced if a preamp is used?

    I use a shadow pu without a preamp into an EAiamp 350 combo. I tried it recently through an active DI and the bottom end was reduced slightly. (I haven't gigged with it yet.)

    Is that due to the impedance being better matched?
    Are there any products/preamps/amps that actively cut sub bass frequencies coming from the pickup?
    Do some amps simply not reproduce low frequencies well enough and so solve the problem?
    If it is a problem at all.

    H
     
  2. Touch

    Touch

    Aug 7, 2002
    Boulder, CO
    I use a Rane AP-13 preamp. It is a 2-channel unit, one side for a piezo and the other for a mic.

    Both channels on the preamp have a sub-sonic filter which I find can really tighten up the sound and eliminate stage rumble.

    Touch


    http://www.rane.com/ap13.html
     
  3. erik II

    erik II

    Jul 11, 2000
    Oslo, Norway
    I observed violent speaker cone movement when running my DB (either with a Shadow or the K&K Bass Max) directly into my Clarus. When I added a preamp, the speaker movement was barely visible. The sound got maybe a bit cleaner, but with no significant loss of bottom - I believe most of these sub-harmonics are inaudible.

    So according to AI, whom I e-mailed about this, the Clarus reproduces the deep frequencies that the pickup obviously delivers, while the preamp filters them out. They recommended use of a preamp, or to use a sealed cabinet, where the speakers won't move so much.

    So if your combo is a sealed cabinet construction you may not actually see this, as I did with my ported cab. I didn't want to risk pushing the speakers like that anymore, so now I use a preamp.
     
  4. Bob Gollihur

    Bob Gollihur GollihurMusic.com

    Mar 22, 2000
    New Joisey Shore
    Big Cheese Emeritus: Gollihur Music
    The Series II (latest models) of the Acoustic Image Clarus, Contra, and Coda has a switchable high pass filter, -12 dB/octave sweepable from 30 to 700 Hz, so you can attenuate frequencies that add mud and don't enhance your bass sound.

    That said, I have never found it necessary to use it or use any special subsonic filters or other devices to eliminate lower frequencies aside from the usual on-board equalization controls. While I am no sound expert, and quite willing to be contradicted by someone more knowledgeable, it seems to me that bass notes generate overtones, not frequencies beneath the fundamental. However, I suspect that ambient low frequency sounds, drums, etc., rumble could be picked up by the bass body and passed on through the pickup, as would any other sound.
     
  5. mje

    mje

    Aug 1, 2002
    Southeast Michigan
    What happens is not that the bass generates subsonic frequencies- although it probably does- but it picks up and feeds back subsonic frequencies just because it's a large surface that's free to vibrate.

    You can often hear this if you're too close to the amp as a muddiness or a metallic sort of ringing that results from the subsonics mixing with the desired frequencies. I've found the high-pass filter on my Clarus to be useful in limiting this. Great amp, the Clarus. Mine came from Bob indirectly through a friend whom I think misses it ;-)
     
  6. I had a look through the newbies links for preamps but couldn't find a recommended match for my shadow pickup. I am now thinking that it would improve the sound by using a preamp.

    The Rane looks great but a bit overkill for what I need. How much is it anyway?

    I think I would like to get a small preamp that can clip to the bass or belt then use the EQ on my iamp to cut the real low end out.
    I have an old Shadow preamp used for a peizo replacement bridge for an electric bass. It has a tone and volume controls.

    Would this do the job just as well as any other?
     
  7. I have not seen or read about any evidence that a doublebass generates subsonic frequencies. I can't see how that would be possible. However, it certainly is possible that the bass (and the pickup) could act as a microphone to amplify sympathetic vibration of external subsonic frequecies.