Tweeters melting, any fix?

Discussion in 'Speakers' started by Joe Tilley, Jul 16, 2003.

  1. Joe Tilley

    Joe Tilley Supporting Actor

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    This is the second time I have had this problem. I have an all Polk set up using RT55i's for my mains, surrounds,& rear surrounds, & a CS400i for my center. My receiver is a Sony DA 5ES. My speakers are set to small & all crossover points are at 100hz for them.
    So heres the problem the tweeters are getting so hot within a matter of minutes that is is causing them to melt near the voice coil, or more specific the edge of the dome is melting where it joins the coil. I had this happen to my center when I first got them & I had thought it was just defective because this happened at moderate volume. But know I just noticed that my center & both mains are starting to do it again.
    Now I realize the first thing most people are going to respond to is ( turn down the volume ) but it is doing this at pretty mild levels. I have noticed that the tweeters seam to be getting some upper mid bass to them as if you touch them wile you have some music playing they seam to get IMO alot of movement with bass notes.
    I have tried everything I can think of from setting the crossover points different to changing the EQ settings but it either just sounds like crap or I get no real change in how the react.
    So what I'm wondering is there something I can do like modifying the crossover to the tweeter to get less mid frequencies to it, or even if I had to go as far as putting a different style tweeter & crossover in the cabinets. I just wont something that is not going to melt every time I wont to listen to some music, but over all I like the way they sound so I don't wont to go extreme & totally screw up how they sound.
    I realize this is a touchy subject as there can be or are so many variables when getting into crossover points & speaker design so alot comes into play here. But if anyone can give me any ideas that might help to resolve this problem it would be greatly appreciated.
     
  2. Tony Genovese

    Tony Genovese Supporting Actor

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    You might have an oscillation in your receiver. I would have it checked out.
     
  3. Edward J M

    Edward J M Cinematographer

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    E-mail or call Kenneth Swauger at Polk Audio Tech Support.

    This sounds like bad crossovers or a bad receiver. Since you are melting ALL of your tweets, it seems statistically unlikely that the speaks are at fault. The tri-lam tweet in the RT55i and the CS400i is pretty rugged. I have yet to blow one and I crank my system pretty loud (albeit with clean power).

    If your tweets are actually moving, you have a REAL problem, and a bad AVR might have fried all the xo's and you'll need to replace those too.

    Good luck,

    Ed

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  4. Joe Tilley

    Joe Tilley Supporting Actor

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    Thanks guys, I did email Polk & Talked with Kennith. His response was that the receiver was most likely clipping, but I don't see how. If anything I would think it's from over powering them since everything is very smooth & clean at high volume levels, but I could be wrong.
    My thinking is that its something with the crossovers & or the tweeters them self. I did try something a little risky so to speak just to see what would happen. A friend of mine has a pair of RTI70's that he brought over earlier this evening in the trust that if I damaged them I would pay to fix them. So just for process of elimination we hooked them up just as my 55's are & gave them a run.
    Now I do realize that these use a newer style tweeter & most likely a different crossover,but the are close enough the same by my thinking.
    What really surprised me is that at the levels mine were getting warm his were fine. Actually you could play quite a bit louder with no signs of distress at all. They even seamed a little smoother & more detailed than mine. So I don't know if is really a far comparison or not but I figured with being so close to the same design it couldn't hurt to try.
    I do plan on buying a separate amp this fall ( Outlaw 770 ) so if it is in fact something of the receiver clipping I would think that would pretty much solve that problem. But I really wonder if it's just something with the tweeter or crossover design seeing how the 70's played so effortlessly with the same source.
     
  5. Chu Gai

    Chu Gai Lead Actor

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    Joe, I think the evidence points pretty much at the amp as being the root of your problem. Now whether it's clipping and you don't know it or whether its what Tony suggested I don't know. I'm almost willing to bet it's oscillation as Tony suggested that may well be exascerbated by some clipping. Now I could suggest other possibilities like excessive slew rate and improper negative feedback implementation, but there's ways to deal with that.
    What oscillation will do in a general sense is that it'll cause your amp to send over ultrasonic frequencies which of course get pumped over to your tweeter. The tweeter basically gets fried.

    The fix is pretty simple. Get yourself something like an 8 ohm non-inductive resistor that's rated between 5 and 10 watts. Place it in series with a 0.47 uF 400 to 600 volt capacitor. Polypropylene, Teflon, something with a high quality dielectric.dielectric). Can't find a 0.47 then get something as close as you can. A little higher won't hurt. This'll allow your receiver to to see the speakers as basically a resistive load whose value is independent of frequency. It's a cheap fix Joe and essentially sonically innocuous. Kind of like putting a condom on your receiver. You still have fun but you don't have to pay tweeter support.
     
  6. Joe Tilley

    Joe Tilley Supporting Actor

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  7. Lee Bailey

    Lee Bailey Second Unit

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    Joe, take a look at the crossover for the tweeter, is there an inductor in the circuit that is in parallel with the tweeter? Is there also a resistor in series with the capacitor for the tweeter? The answer should be YES to both those questions for all your speakers. It is possible that you have somehow burned out your capacitors and caused them to short, that should be able to be verified with an ohm meter. I know that Polk will respond if you send them an email, or call them.
     
  8. Chu Gai

    Chu Gai Lead Actor

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    It's added external to the speaker and no bypassing of the crossovers is required. You can add it either across the speaker or receiver terminals. Some people are adamant about one approach or the other being superior, but I think with this much debate, it probably doesn't matter from a practical point of view. Myself, I'd add it where I felt it was convenient. MIT cables ring a bell? It's like a zobel network and information about that is everywhere on the web, like here. Click on the figure to get a blow-up.
     
  9. ShaunLB

    ShaunLB Stunt Coordinator

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    I HIGHLY doubt your reciever is pushing too much for your Polks. Mine, particuarly my 55i's can take anything I've thrown at them...very rugged. As far as I can tell from the Polk forums they RTxxi and RTixx tweets are manufactured by different companies, but are very similar in construction and durablity and powerhandling.

    Get that amp checked. I'd recommend taking some of your Polk's to your friends house and see what happens. Hopefully neither your crossover or tweets have been permanatley damaged yet. Good luck.
     
  10. Joe Tilley

    Joe Tilley Supporting Actor

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    Chu, I found the Film & foil capacitors & Resistors on PE's web site Part# 027-458 cap, 004-(value)resistor. They have the values in the Dayton brand & also Audiocap, & Mills. From the searching I have done it looks that the Audiocap & Mills are to be a superior brand to the Dayton brand. So would it be of any benefit to go with them instead of the lesser. The only thing though on the Resistor in the Mills line is a 12watt but are available in values of 1.5 to 82, so I wondered if the 12watt would matter.
    Also my front speakers are bi-wired so should I be placing these in line with just the tweeter or will I need it in line with both the tweeter & woofer section. I would assume it needs to be both from the things I have read so far but I'm not sure.
    I have thought about just going the cheaper route & using the Dayton parts since I really don't know what the outcome will be, but at the same time I don't wont to do the same thing twice if it dose work out & I would have gained something by going with the better quality parts.

    On a side note I didn't think about this before but I took a surge just recently. Chu you may remember me posting in the tweaks about it. Anyway I don't know if it was a cause of it or not but I found out the other day my sub was damaged ( spider ripped ) & when the surge hit everything in my system did make a quick pop, the sub more of a huge twhomp as everything was on. Is it possible that somehow that that could have done the damage to the tweeters? I just started thinking about this because I know my speakers were fine before this happened & I haven't really played them much since the surge.
     

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