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Weird results with different amp placements.

Discussion in 'Amps, Mics & Pickups [DB]' started by bobbykokinos, Jun 23, 2005.


  1. Hey guys, I've got a question.

    Last Saturday I had a gig with a big band using my DB and my Eden 2x8 combo. We were on a portable stage. I had my amp set ontop of the dummers low tom case positioned behind me to the right. I was able to get good volume without feedback.

    Well, Tuesday I had another gig with the same band and same equiptment. Due do space restraints, I had the amp on a chair about 2 feet immediately to the right of me. I couldnt get the volume I wanted without feedback. Plus, I couldnt arco at all without MAJOR feed back. This was on a concrete floor..

    The results are exact opposite of what I wouldve thought. I thought the stage would be more resonate and the amp behind me promote more feed back. But, I got feedback on a concrete floor and the sound from the amp going straight out instead towards me..

    Any help or suggestions??
     
  2. Yup - you're learning that stages are different, rooms are different, and if you move the speaker w.r.t. the bass, or even point the bass in a different direction weird things can happen. The trick is to be flexible, and experiment until you find something which works - stick with it until you have a problem, and then change things until you fix the problem. Bear in mind that your bass will sound different at the playing position, to how it sounds out in the audience. I've found that getting the speaker off the ground usually helps - you might try angling the speaker away from the bass. Is the cab you're using open at the back or infinite-baffle (sealed back)? Hey, part of the fun is experimenting¬Ö

    Good luck -

    - Wil
     
  3. Sealed back.. Its a Eden Silver Series 2x8.. I bought a keyboard amp stand I'm going to try out. I gets it high enough and angled back so it fires at my face rather than the body of the bass.. I'm hoping i can hear it better that way and eliminate some of the feedback..
     
  4. Marcus Johnson

    Marcus Johnson

    Nov 28, 2001
    Maui
    Hey Bobby..in your original post, you mentioned the "dummer"'....wonder what Freud would think of that...
     
  5. mje

    mje

    Aug 1, 2002
    Southeast Michigan
    Real rooms are complicated things, acoustically speaking. They're full of hot spots, where certain frequencies get emphasized, dead spots where reflections cancel out frequencies (sort of like wolf tones) and so forth. You always have to experiement to see what works best.

    Incidentally, talking about the direction a cabinet "fires" really only applies to high frequencies. Any speaker is omnidirectional at frequencies whose wavelength is larger than the radiator. An 8" speaker radiates omnidirectionally below 1.7KHz. Harmonics will tend to be directional, and that's what you tend to use to localize the sound.
     
  6. winston

    winston Supporting Member

    May 2, 2000
    Berkeley, CA
    I'm not an expert in physics, or the properties of speakers and wave propagation or whatever you call it, or the psychoacoustics of human hearing (nor do I play such an expert on TV). However, I thought that at least as far as the human ear is concerned, you can't really place where a fundamental tone is originating if you are less than a full wavelength away from the source. I didn't know that the size of the speaker had anything to with the perception of directionality, and I'm wondering how this theory translates to things like the column of air in an organ pipe, or the human voice, or a vibrating timpani or double bass.

    I'm not trying to flame or say I have the correct answer; I'm genuinely curious and would like to know more. I also understand there's a difference between the physics of vibrating bodies and the nature of human perception of such vibrations. Time to dig out Benade's book on musical acoustics and Helmholtz's "On the Sensations of Tone".
     
  7. Umm, yeaahhh. I just play bass and am not a scientist.. :)

    I guess what Im asking, am I taking the correct first step for speaker placement experimentation by trying an amp stand?
     
  8. winston

    winston Supporting Member

    May 2, 2000
    Berkeley, CA
    In your original post you mentioned that you got widely different results in two different situations where the amp was elevated, so it seems like just raising the amp on the stand will not completely solve the problem, although it's a good start for fighting feedback.

    A number of people on TB have had great feedback-reducing results by weaving a piece of rubber tubing or leather through the afterlength of the strings, and by wedging a piece of foam between the tailpiece and the top of the bass. Of course this will inhibit the natural acoustic projection of your bass, but it should reduce feedback.

    I've also foundthe Fishman Pro Platinum Bass EQ to be very handy for fighting feedback. It has an adjustable low-cut filter for dialing out rumble, a phase switch, an adjustable compressor, and a 5-band EQ.
     
  9. Well tonight I had another big band gig.. I did put the amp up on an amp stand that tilts back. It was about waist high and facing towards my face. It was place to the right of me facing me directly (which works out good because I'm on the right of the back so the rest can hear it). Results, no feed back at all. Good clean arco sound with no feedback. Atually, that amp stand was the best $40 I have spent.. I world of difference. I can actually hear myself ALOT better and my intonation, if I do say so myself, was right on all night..
     
  10. As you can see here I use a similar stand. And indeed, IME it helps tremendously in being heard, hearing yourself, get a clean sound, and reduce the risk of feedback.

    Cheers,

    Vincent
     
  11. mje

    mje

    Aug 1, 2002
    Southeast Michigan
    That's not really a factor. You can't localize the fundamental, or any pure tone whose wavelength exceeds the distence between your ears. You localize based on the harmonics, via a variety of clues, including phase difference between the ears.

    My point had more to do with the difference in on and off-axis reponse for fundamentals and harmonics.