Sda Srs Tweeters Problems

[univera]

I know I read somewhere on this site that there is a problem with tweets cutting out/off on the SDA/SRS. At one time, my tweets went out at loud volume but came back on. The last time I listened, I was playing loud music and everything seemed to be working just fine. When turning my system on yesterday, the left facing speaker tweets are not playing. They definitely aren't blown as I keep protective circuitry on my amp turned on at all times. All the other speakers seem to be operating properly. If there is a way for one to respond directly to my email without my posting that address here, that would be great. Thanks in advance for your help and guidance. Lee

[F1nut]

You most likely fried the polyswitch in that speaker, but you could have fried the tweeters too. If you're tripping polyswitches you have one or more issues that should be looked at. One, the polyswitches are old and need to be replaced. Two, you're playing your system TOO loud and need to turn it down. Three, you need a better amp.

The best place to start, CALL Polk and ask them nicely to send you new polyswitches, which they will do for free.

BTW, the protection circuit in your amp or AVR is for that piece of gear, not the speakers.

[univera]

F1, thanks for the info. The protection circuits are actually NAD soft clipping, which is suppossed to save the speakers from damage at dangerous levels. I am using an amp with a ton of headroom (8db, I believe) and ample power, but who knows. The power is pretty clean and the speakers never seem to struggle. They seem to ask for more.

I know that NAD isn't up there with the Sunfire, etc, but mine is truly a classic 1980's beast and what I can afford at the moment. I do know that I didn't hear them clipping or distorting. I do recall getting the volume a bit over the 12'Oclock spot, so maybe I hurt them. The tweets aren't playing whatsoever. I'm not super handy. Are the switches easy to replace? I have someone who may do a cap/resistor upgrade for me, so perhaps I can do it all at the same time....Any other parts you suggest upgrading strictly based on age? I am aware of the tweet upgrades. By the way, I don't want to turn it down! The SDA's just aren't dynamic unless they are crankin and movin some air! Maybe I just inched the dial a bit too far.

[F1nut]

As a general rule, anything near or beyond 12 noon is into the clipping range, regardless of headroom. In addition, that headroom rating is for like a millisecond, so it doesn't take much for bad things to happen.

Having said that, I still believe your problem is the polyswitch. At volume levels that high the only tweeter playing is the 3rd from the top, so if you're going to fry a tweeter, that'll be the one. Try this, take one or more of the tweeters from the bad speaker and put it/them into the good speaker. If they play, it's not the tweeters.

The poly's are soldered to the crossover board, so if you're going to have them upgraded (an excellent idea considering the age of the stock caps) have the person doing the work change the polyswitches (one per board) along with the caps and resistors.

As a point of reference, 10 o'clock on my volume control makes my 2.3TL's very loud (100-105+dB depending on the recording) and quite dynamic.

[univera]

F1, thanks again. I agree that 10 o'clock is plenty dynamic. Perhaps I am losing my hearing...Thanks for the recommendations. I will give it a shot today. Is the one tweeter only playing at high levels a built in protection or just an issue for sound quality/clarity?

[F1nut]

The tweeter array in the larger SDA's is designed as a progressive point source.

[univera]

which means...Sorry, I like what I hear but don't necessarily understand the science. I appreciate the education. Does that mean that as the levels get higher the need for more tweets is diminished? Essentially saying that one tweet can now do the job of 4 to balance the sound and level of sound since there is more dynamic prescence?

[danger boy]

that's how I understand it.. the tweeters go on and off at different times... they are not always on.. all four of them at the same time.

[F1nut]

This thread should answer all your questions, http://www.polkaudio.com/forums/showthread.php?t=21402&highlight=progressive+point+source

[jcaut]

Jesse has a lot more experience with SDA's than me, but I don't believe that comment about only one tweeter playing at high volumes is correct. I think the crossover is designed so that only one tweeter is playing at the highest frequencies. They should behave the same at all volume levels. The progressive point source concept amounts to a way of controlling the dispersion pattern, based on frequency, not volume level.

I have no personal experience with the original SRS's, but perhaps if the third tweeter from the top is the one that fails most often, it's the "primary" tweeter- the one that doesn't roll off prematurely and therefore would get more signal than the others? I can't say without studying the schematic.

Jason

Edit: I just checked the thread linked above, and I think I'm right.

[F1nut]

Jason is correct, it is frequency, not volume. My mistake. It is the 3rd from the top tweeter that is basically full range and the one that will fry first at loud volumes.

[univera]

Thanks, again, J & J. Interestingly enough, I have noticed once in the past what I believe was the 3rd tweet making a little distorted sound, so it may have been damaged already and would fit the theory. I am calling for the recommended parts as we speak.