HELP: Surround distortion

rlevit

RT35 FRONT
CS275 CENTER
LS F/X SURROUND
ONKYO TX-DS676
ONKYO DV S525
PHILIPS 100Hz TV SET
PHILIPS Hi-Fi VCR

I have bought the above equipment a year and a half ago. It worked fine the first six months but then started to produce highly distorted sound on both surrounds. I have brought the speakers and the receiver to customer service and apparently they are both fine. If I unplug the speakers and plug them back after 24 hrs the problem dissappears momentarily. I am suspicious that the problem might be in the cables (i.e. some interference with power cables or similar, as I installed the cables built-in the walls). The cables are high quality, bought at a HiFi center.

Any hints?

Aaron

Try hooking your main (L&R) speakers up to your rear surround terminals. If they don't produce any distortion, then you know you have a problem with either the wires or the rear speakers. If that's the case, hook your rear speakers up as the main (L&R) speakers using the wires from your main speakers. If there is no distortion here, then you know there is a problem with the wires. Another possibility, as dumb as it may sound, is to check the terminals for your rear speakers on the receiver to make sure you have solid connections and that there are no stray wires creating a short back there. Good luck!

Aaron

TrappedUnder Ice

I wonder if your surround amplifier in your reciever is not the problem. You say if you leave it alone for 24hrs and it goes away for a bit..then comes back- may be the amp warming up and giving you the issue... Just some thought.

I know you took it in for service..but most techs dont take the time... necessary to rule out other things. they probably plugged it in and check and it was fine..not letting it warm up a bit.

One other possiblility...just reaching..is the ohms on your speakers could be less than rated...cuasing issues. I've seen this more with car audio than home..but its another idea.

good luck and let us know what ya find!;)

lbrenner

The fact that BOTH rear speakers act up makes me very suspicious of the dolby decoding in the receiver. I doubt that both speakers or their cables would act up simultaneously!

The suggestion of driving the rear speakers from the front amps is a good one to try. Another idea would be to move some stereo analog source to your 5.1 surround inputs, and play the rears that way. If that sounds normal, the decoding would be very suspect...

rlevit

Let me first thank you all three for providing me your thoughts on the issue. I think I have the answer finally (after a year) and it is somewhat curious.

The fact is that I have the surrounds hang up on the wall, close to the ceiling (say 20 cm below). As it was said in the user manual, if the speakers are close enough to the ceiling they should be installed upside down so that the sound is directed to the ceiling. Well, I installed them that way.

As I said, it worked fine some time and then distortion appeared...

Both speakers were having problems, so I thought the problem was in the receiver. Onkyo service said the receiver was ok.
Then I brought the speakers back to the store where I bought them. They tested them (apparently) thoroughly. The speakers were fine...

That is where I thought the problem was in the wiring. This past weekend I tried many configurations and the cables seemed OK.

I was completely puzzled...

By absolute chance I found out that the only difference between speakers testing conditions and the real ones was that the speakers were upside down in the latter.

Voil

lbrenner

WOW! Nice detective work. At least that could explain why the pair acts up in unison.

I'm concerned about the term "upside down." To me, that would simply mean rotating the speaker 180 degrees (say, clockwise) as you look at it, with the objective of having the tweeter below the woofer as opposed to above the woofer. That shouldn't hurt a speaker.

But if you rotated it so the drivers were firing straight up or straight down (instead of forwards into the room or towards a wall), that might just upset them over time... Just a guess.

Micah Cohen

As it was said in the user manual, if the speakers are close enough to the ceiling they should be installed upside down so that the sound is directed to the ceiling.

Can this be? Did I write this? Has to be before my time. I'm gonna have to search this wacky directive out and figure out what it means.

No surprises at Polk Audio. :rolleyes:

Micah

RuSsMaN

'Voil

joelll

Just a thought, but if the speakers were bare-wire connected, and the wires a little tight, turning them upside down might allow the exposed bits of bare wire ends to touch, or come very close to touching....

Micah Cohen

I'm going home now and turning all my speakers upside down to see if they still work that way.

(What if the sound comes out of them upside down?)

MC

lbrenner

You guys crack me up! But look, I can still type while laughing with my fingers upside down.

The thing about truly upside down speakers that worries me is that the weight of the speaker cone itself may cause the cone to be "at rest" somewhat offset from the expected center of the cone's range of motion, leading to distortion. I don't know that the cone's weight is really enough to do it, but imagine gluing a silver dollar to the center of that upside down speaker. This would push the cone way down compared to where it was designed to be! I think the cone structure itself is stiff enough to keep it centered in a normal position, but the speaker is designed to float fairly freely in its normal plane of motion.

Anyway, that's my speculation for the day... (please be kind!)

[Deleted User]

Hello,
Perhaps I could offer some useful information. Sometimes, in mid-bass drivers one area of the voice coil will blister very slightly. This happens if the temperature of the voice coil gets around 400 degrees for a prolonged period of time. If the blistering is just enough there will be scraping against the inside of the voice coil gap and you'll hear distortion. If you were to take the driver out and rotate it 180 degrees the blistered area would come away from the voice coil side and there wouldn't be any scraping or distortion. Sometimes people will notice that if they lightly touch an area on the driver's surround the distortion will go away, in effect doing the same thing moving the blistered area away from contact. This could be what you are finding, when the speaker is upside down there's distortion, turning it over the damaged area comes away from the gap sides. Eventually the driver will produce distortion no matter what the position. The best thing to do is to replace the driver, please contact me at 1-800-377-7655 extension 891 or email at kswauger@polkaudio.com and I'm sure I can help.
Regards, Ken Swauger

rlevit

Kenneth,

Thanks for your thoughts.

Your explanation seems kind of odd to me as the speakers have never worked in extreme conditions. The only perhaps-strange working condition is being both rotated 180 degrees (tweeter down) for some months. Could this have hurt BOTH speakers? It seems to me that the speakers arrived to me in not very good shape, or simply they are not designed to work upside down.

Anyway, it seems that I will finally have to send the speakers to the US so you can check them (it is not very funny being in Spain...).

I will send you a personal email to organise that.

Regards


Ricardo Levit

raymillr

Just an offhand conjecture, but, if the speaker was facing the ceiling, maybe a little spackling, or bit of popcorn fell off the ceiling into the speaker. The little particles bouncing around on the cone could cause a lot of distortion....Just a wild guess.