Can you "bottom" a tower?

Discussion in 'Archived Threads 2001-2004' started by Steve_Ma, Apr 8, 2002.

  1. Steve_Ma

    Steve_Ma Second Unit

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    While measuring my freq response, I was playing various test tones in the 85-90 db range. It seemed loud, but not outrageous. I was surprised when somewhere in the upper range (maybe around 2000-2500hz) I was greeted with a "clack...clack...clack" from my rt tower. Anyone exp this? What's the likelyhood I did some damage? While playing music, movies, and test tones, I don't notice any (perceived or measurable) negative changes as a result. The mains are B&W 603S2s.

    Thanks,

    --Steve
     
  2. Peter Johnson

    Peter Johnson Stunt Coordinator

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    You can definately bottom a tower. Even easier than a sub if you feed it a lot of low frequency stuff.
    However, this wouldnt happen at 2.5kHz...so I have no idea! [​IMG]
    BTW, be careful with test tones. Most tweeters will burn up with as little as 10W of power..maybe a few dB more, but not much.
     
  3. Steve_Ma

    Steve_Ma Second Unit

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    Thanks Peter. Have you ever blown a tweeter? Is it super noticible? Now I'm starting to wonder if I did do some real damage and just didn't notice yet.

    --S
     
  4. SanfordL

    SanfordL Stunt Coordinator

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    Hey Steve, I toasted a tweeter about 4 years ago, and yeah, it's noticible. If you are concerned, hook up 2 speakers that are the same make/model, and feed them a stereo source. Sit right in between, and if one side sounds like broken glass (with my Boston Accoustics, I had a distinct bird seed in the speaker kind of rasping high end,) while the other sounds like a bell, you've killed the tweeter. You might try doing slow frequency sweeps to ensure that it is for certain the tweeter and not a mid-range driver that's damaged. Regardless, the repairs are not going to be radically expensive, more than likely. [​IMG] I never knew you could eat a tweeter with 10 watts of source, but if Peter says it's true, he's probably got a good reason. I suppose the lesson to be learned is, test disks are handy for callibrating, but be careful.
     
  5. Steve_Ma

    Steve_Ma Second Unit

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    Thanks Guys,

    I feel alittle better now. I was doing some 2ch listening the next morning and didn't notice anything. I'll do alittle more tonight, just to make sure, but thanks again.

    --Steve
     
  6. Peter Johnson

    Peter Johnson Stunt Coordinator

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    Usually tweeters dont work at all once they have been damaged. The VC insulation melts and shorts out the VC. The tweeter will either barely work at all, or it wont work at all..

    Most drivers are at less than 1% efficient, ie over 99% of incoming power is converted to heat. Tweeter VC's are very tiny and can dissipate only a tiny amount of power before damage occurs. Obviously it depends on the tweeter on exactly how much it can handle.

    It depends on the crossover frequency, but in a 2-way speaker anywhere from 70-90% of the total system power goes to the midwoofer, and the rest to the tweeter..so you can still put 100W into them, as the tweeter is really only getting 10-30W of this.

    10W is probably a bit of an exxageration...most will probably take 20-30W or so.. still not very much.

    When you clip your amp, more HF info is created, leading to more power to the tweeter...and it goes up in smoke!
     
  7. SanfordL

    SanfordL Stunt Coordinator

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    If you heard it once though, you are probably ultimately going to have to replace the part that's crabbing. I don't know, I'm not a speaker design person by any stretch, but if it clacked once, it more than likely will do it again. [​IMG]
    Have you heard of the self healing plastics that are in development now? How awesome would it be if they came up with a self-healing voice coil, or cone surround?
     
  8. Tom Brennan

    Tom Brennan Screenwriter

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    If you can avoid further clacking you'll probably be all right. I've driven aluminum dome diaphragmed JBL compression drivers into clacking running them down to 500hz with a 1st order crossover, the domes were hitting the phasing plug. Inspection revealed no damage and I changed to a 3rd order crossover, no more problems.
     
  9. Tony Meconiates

    Tony Meconiates Stunt Coordinator

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    When I DJ'd in college, at one point I used Infinity SM255's and powered them with a 2 channel peavey power amp... I think the amp pushed about 225 @ 8 ohms. I cut definitely bottom out the 15 inch woofers and the amp would clip like crazy. Sometimes when I was pushing them hard, the tweeters would just shut off because the speakers had some kind of fail safes... Those speakers got so abused until I replaced them with some gemini cabinets w/ horns.
     
  10. Drew Bethel

    Drew Bethel Screenwriter

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    I have my doubts that you can bottom towers soley from feeding them low info. I would think that once the speaker's lower limit is reached it would simply pass on the lower hzs. If I play test tones for a subwoofer on my tiny computer speakers they wouldn't bottom out either. But I could be wrong.
     
  11. Chris PC

    Chris PC Producer

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    Sure the clacking was not 'clipping'? I doubt it, but just wondering.
    Here is some advice from someone who has been testing their own speakers. Try not to test your speakers at loud volume. You never know what their limit is until you damage them! I have been testing low frequency response and I have gone very low, like 10 hz of bookshelfs and towers, but I also do it very low level to avoid any clipping or overdriving. I don't think I will ever test either of my speakers below 20 hz anymore cause they aren't rated for that anyways [​IMG] Too risky. So far everything is fine, but you never know.
     
  12. Brian Bunge

    Brian Bunge Producer

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    Drew,

    It's not necessarily what frequency you're playing, but at what amplitude. BTW, a ported speaker will bottom more easily below the driver's (woofer's) resonant frequency. For this reason, ported enclosures should be tuned right around this frequency to provide a sharp rolloff below the resonant frequency. This provides added "protection" from damaging the driver.

    Brian
     
  13. Dave Schofield

    Dave Schofield Second Unit

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    Am I correct in assuming that the word "tower" is being misused in place of "tweeter"?
     
  14. Rudy H

    Rudy H Stunt Coordinator

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    You probably were bottoming the tweet. I once hooked up my headphones to a car amp powered from a computer power supply, sounded the same (metallic click/clacking sound).
    Lots of bass from the headphones while they were bottoming though [​IMG]
     
  15. Steve_Ma

    Steve_Ma Second Unit

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    No, I puposely used the word "tower" rather than "tweeter" because I am not positive what freq the test tones was at when it happened. I believe it was probably the tweeter, but since I can't tell you guys the tone's freq for sure....I thought "tower" might be more aproppriate in case it was the midrange driver.

    --Steve
     
  16. Tom Brennan

    Tom Brennan Screenwriter

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    Steve---Well you can bottom-out many drivers: woofs, mids or tweetes. When the driver is fed more power after maximum excursion is reached BANG-CRACK the voice-coil former hits on the plate. This can really sound scary with horn-loaded woofers at 130db! :)
     
  17. Steve_Ma

    Steve_Ma Second Unit

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    Just in the way of a followup, I (more carefully [​IMG] ) ran sine waves through the speakers tonight as well as played some classical music, with my ears right next to the drivers. It appears that all is working fine. I couldn't hear anything unusual with the sine tones or the music. I'll consider it a lesson learned. Thanks all for the feedback.
    --Steve
     

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