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Markbass combo - tweeter problem? (RESOLVED - no problem)

Discussion in 'Amps and Cabs [BG]' started by BassyBill, Sep 28, 2008.

  1. BassyBill

    BassyBill The smooth moderator... Gold Supporting Member

    Mar 12, 2005
    West Midlands UK
    On a gig the other night, I was troubled by the occasional high pitch feedback type squeal. Managed to get through okay.

    Just testing at home to investigate the problem, and it's weird. It seems to happen when I get close to the amp (as you might expect with feedback), and some basses seem slightly worse than others in this respect. The highs from the amp are way attenuated, which leads me to suspect the tweeter is shot. But he squeal is still there, and I think it's coming from the tweeter. I've eliminated the leads and the bass as the problem as it still happens when I switch these for something else and it doesn't happen with my other rig.

    So, questions:

    1) Why should it start squealing when it hasn't done so before with the same rig (and even in the same venue)? Is squealing a symptom of dead or dying piezo tweeters?

    2) Do you think the squealing was CAUSED BY a problem with the piezo tweeter? Or could the squeal initially have been due to something else and the tweeter then got blown because of excess HF energy?

    Opinions welcome, especially from piezo experts.
  2. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    It wouldn't. Something has changed.
  3. Sounds to me like there is an unstable area in your amp that the signal from your bass, at close quarters, is nudging into high frequency oscillation. This high frequency is being reproduced by all of your speakers but most efficiently by the tweeter. I would suggest a trip to a tech.

  4. I get a high pitch feedback out of my Markbass combo sometimes also. Usually when I get close to the tweeter with the pickups, and the amp is up loud. It doesn't happen all the time either. I'ts just feedback so I don't worry.
  5. Bassflute


    Jun 24, 2006
    Endorsing Artist: MTD basses and strings; Bergantino Amps & Cabs
    They feedback when you get close. There is probably nothing wrong, you just haven't noticed it before. Do they still sound alright?

    That's why I'm somewhat skeptical about Bill Fitzmaurice's multi-piezo tweeter arrays; his cabinet designs look fascinating, and I still am going to try one, but I think I would replace all the piezos with a nice smooth horn of some kind - maybe the lovely bullet tweeter from my Bergantino cabs. Also, piezo feedback is particularly nasty, and comes upon one very suddenly and is uncontrollable - it's not like that nice low end feedback us bass players are used to. It ramps up really fast, before you can get a handle on it.

  6. JazznFunk


    Mar 26, 2000
    Asheville, NC
    Lakland Basses Artist
    I had the same thing happen to me occasionally with my SWR cabs and my Eden or SWR heads. My problem stemmed from some interference from electrical equipment, and from a grounding issue in my apartment. It was very intermittent and short-lived, but when that squeal would happen it was very unnerving. I noticed it more with my SWR heads because they are so treble-heavy... the highs are attenuated a bit more on the Eden, even with the same cab settings for the tweeter and such. It could be some sort of random interference setting off the upper end of things on your amp? Just a thought.
  7. BassyBill

    BassyBill The smooth moderator... Gold Supporting Member

    Mar 12, 2005
    West Midlands UK
    Thanks guys, I will contact Markbass today and ask their opinion. But I'm pretty sure the tweeter is dead - the amp sounds as if the VLE is turned up about halfway when it's not dialled in at all.

    Could the squealing have blown the tweeter?
  8. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Sure, if it was out of the tweeter's safe handling range. And since the VLE at halfway sounds identical to pulling the tweeter out of the circuit (not that I've ever done it because that would void the warranty ;) ), I'd say that's what happened.

    But I'll tell you, if you can find one that size, I think you're better off with a better tweeter. As you well know, the one thing I have never been thrilled with on my combo is the tweeter. On the other hand, I don't know a lot about tweeters, so it could be possible that it's as good as it gets with that small size. But I have to think there's something better because it's pretty harsh. Once the warranty runs out on mine, I'm going to look for a better tweeter. Don't have much use for anything past 5k, but I like it for practice so I can hear if I'm being too noisy.
  9. BassyBill

    BassyBill The smooth moderator... Gold Supporting Member

    Mar 12, 2005
    West Midlands UK
    I might ask a tech to look at swapping the piezo for something else, maybe. Only problem with that is a crossover would be needed (unlike a piezo which rejects LF without the need for one).
  10. barrybass33

    barrybass33 Supporting Member

    Jan 7, 2008
    westchester new york.
    I had a similar prolbem last week with a epifani cab I took back the cab to nick and he changed the diaphram behind the tweeter and 5 min. later i was done.
    He said it was caused by feedback. I'm also have a markbass head. that has no mute
    switch he also told when your hands aren't on the bass shut off the volume via. the
    bass or the master vol.... I hope this helps you out. Barry.
  11. BassyBill

    BassyBill The smooth moderator... Gold Supporting Member

    Mar 12, 2005
    West Midlands UK
    Well, I still haven't worked out why I was troubled with feedback on the gig. Maybe we were playing louder that night than we had before at the place. The stage is pretty cramped and I was more or less standing right next to my amp.

    Anyway, the tweeter seems okay, as it turns out. My bad - because I hadn't had anything like this happen with this rig before, I guess I panicked when I did my quick test the other day and managed to convince myself that the highs weren't as present as before. Now I've calmed down and checked things out properly I think I was mistaken. Thanks for the comments, though. Live and learn, as they say.

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