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How do I stop my surround sound system cutting out?
January 21, 2009 5:26 PM   Subscribe

My surround sound system keeps cutting out at higher volumes. Please help me find a way to stop it happening.

I'm using a Panasonic SC-AK600 receiver; it has 5 speakers and is programmed to receive digital signals. It's plugged into both my DVD player and Xbox 360 through a coaxial cable and optical cable, respectively. When the volume is at higher levels, all but the center speaker cuts out. And it cuts out at a single instance of sound (such as a sudden explosion or noise in the movie/game). I know that this may be some kind of safety feature to keep the speakers from becoming ruined, but I feel that the volume should be able to be higher.

Important point: the volume only cuts out when it is receiving a signal in 5.1 surround sound. If I'm not watching something in that configuration (ie, noise is still coming from all speakers; it's just not in 5.1) I can turn the volume up as high as I want, and nothing happens. So, I know that the fact the volume can't be higher is something to do with it receiving a 5.1 surround signal. The receiver is meant to be able to play this, so I don't know why this keeps happening.

Also, my left surround speaker has some additional speaker wire I had to hook up to it to extend the length, and has a lower volume than the right surround speaker. I don't know if that's a result of the additional speaker wire or not. I know it has nothing to do with settings on the receiver because I've checked that. Anyway, does this lower volume or additional speaker wire on the left surround speaker have anything to do with the speakers cutting out in 5.1 surround sound? I'm no sound expert, but thought I'd throw that out there for anyone who may know.

While I'm at it, there seems to be a slight difference between the audio coming from the TV and from the receiver's speakers (again, only in 5.1) when using the DVD player. I usually just turn down the TV's volume to 0, but feel as I shouldn't have to. There's an HDMI cable running from the DVD player to the TV. And again, the receiver is hooked up directly to the DVD player.

Thanks for reading this whole thing. Please help me with any knowledge/experience you may have.
posted by Beep to Technology (9 answers total)
 
The cutting out is a form of protection to prevent the amplifier from clipping. You can look through the manual and see if there is a way to defeat that but my guess is there is not. Besides, clipping power amplifiers is a good way to destroy speakers. In fact, more speakers have been destroyed by a low powered amplifier driven into clipping than a higher powered amplifier driven too loud (but non-clipping).

If it's not loud enough you may have to purchase a higher powered receiver.

Easiest way to test the lower volume left speaker is to swap it with the right speaker; try switching the cables around, too. Then you'll figure out if it's the left surround channel, the left speaker, or the left cable. If it's the speaker it's probably damaged.

Do you play it at high volume? If you can't carry on a conversation at normal levels then you've probably got the volume too high.
posted by 6550 at 5:41 PM on January 21, 2009


From your description, I am fairly sure that your left surround speaker is shorted. disconnect it from the receiver (please disconnect the right one for symmetry, otherwise my OCD will kick in by proxy) and try again.

If you're technically minded:

You might think a short circuit would be more obvious, but there are two factors:

speakers are VERY non-resistive (4-8 Ohms, same magnitude order as long cheap cables), so a short in the wire going to it wouldn't be much a short, but a lower but comparable load in parallel (say, if your wire adds 1 Ohm resistance, it would be a 1 ohm and an 8 ohm in parallel).

sound volume is logarithmic with power. For most of your tv watching the receiver is outputting in the order of tens of milliVolts. The loud parts are in tens of Volts. So a load 10 times less resistive than normal (the short circuit) won't overload the receiver (say, the current coming out for 100mV with a 1 ohm load will still be 100mA, the cut-off is in the order of ~5A). Once you get to a louder scene (say, 5V output) the protection circuit kicks in. The only symptom during quiet parts would be, as you mentioned, lower volume on the shorted speaker.

The fact that only dolby inputs cause the cut-off might be because dolby digital has a higher dynamic range than PCM.
posted by qvantamon at 7:36 PM on January 21, 2009


While I'm at it, there seems to be a slight difference between the audio coming from the TV and from the receiver's speakers (again, only in 5.1) when using the DVD player. I usually just turn down the TV's volume to 0, but feel as I shouldn't have to. There's an HDMI cable running from the DVD player to the TV. And again, the receiver is hooked up directly to the DVD player.


You mean time difference? If it's an HDTV, it has a video lag of anything between 10 and 200ms. The sound the TV outputs is delayed to match the video (so it's also lagged by the same amount). The DVD sends the HDMI A+V and the Optical Audio at the same time, so if the receiver has no internal lag, it will play earlier than the TV. Most receivers have a hidden setting to adjust the A-V delay (it's generally a per-source setting). Find it and tweak it until it's sync'ed with your TV (not because of the TV sound, you'll want to leave that off anyway - but to get better lipsync b/w tv and receiver).

You can also discover your TV's lag with a guitar hero or rock band game - it should save you some time in trying to find out the optimal value for the receiver's delay setting.
posted by qvantamon at 7:45 PM on January 21, 2009


[sorry for the rapid-fire comments]

If it's NOT an HDTV, new receivers come factory-adjusted to 40ms delay on the assumption that they'll be used with HDTVs. So if you have a CRT (which generally has no delay) and a new-ish receiver the audio on the receiver might be _late_ by 40ms. Again, find the A-V delay setting and tweak it.
posted by qvantamon at 7:52 PM on January 21, 2009


I'm with qvantamon with the theory that the left surround may be shorting. Do you have a splice in the cable? If so, recheck the splice and make sure no strands are loose and touching the other polarity of the cable. In any case, make sure both ends of the cable (receiver and speaker) are secure with no stray copper strands.

Also, what's the total length of the run, and if you know it, what's the cable's gauge?
posted by pmbuko at 7:53 PM on January 21, 2009


Agree with qvantamon,
You need to find the A-V delay setting and tweak it.
posted by closebeauty at 1:12 AM on January 22, 2009


I absolutely agree with qvantamon re: the short to the left speaker. I had the same issue with my 5.1 receiver. My sound would completely cut out at high volumes and the receiver would display something along the lines of "PROTECTION". My right rear speaker wires were twisted together (red to red, black to black) but the red and the black bare wires were touching each other. Once I seperated the colors out and ran some electrical tape over each wire, the problem went away.
posted by Brettus at 7:07 AM on January 22, 2009


The two polarities of the cable were touching each other. I fixed it. Now, my left surround speaker is as loud as the other one, and I can also turn the volume up higher with no problem. Thanks guys. To clarify the delay problem: there is no delay between the audio and visual when I'm watching something on the TV. What I mean is, there is a slight time difference between the audio from the TV's speakers and the receiver's speakers. It's only noticeable when there is dialogue, and it's very slight, but enough to be annoying. That is why I just turn down the TV's speakers to 0 and listen to things from the receiver. Is that what I'm supposed to do? Thanks again.
posted by Beep at 5:32 PM on January 22, 2009


You're never supposed to use the TV and receiver speakers together. Otherwise: your sound placement will be all wrong (too front/center heavy), you can never make them have absolute zero time difference, you'll get weird interference artifacts, and finally, your speakers and the tv have a different timbre (how the sound "sounds", like more plasticky, more woody, etc), and mixing speakers of different timbres sounds weird.

There should be an optical/coaxial _output_ from the TV, so you can use the receiver for OTA tv. If you watch over the air tv, I suggest you connect that to the receiver, and ALWAYS use the receiver, and NEVER the TV speakers. Unless you live in an apartment with thin walls, in which case you might want to use the TV speakers at night.

what I said about the delay is exactly your symptom. a 40ms lipsync error is not perceptible by itself (that is, unless you're very trained you can't notice that the sound is coming 40ms later or earlier than the video). But it's quite obvious if you're playing the same sound in two different speakers with a 40ms time difference.

Again, find the AV delay setting on the receiver, and adjust it until there's no perceptible sound difference between the TV's speakers and the receiver. Then turn off the TV audio and never turn it back on again

Alternately, if you have access to rock band 2, it can measure the video and audio lag separately. run the calibration (while using the surround system), and adjust the A-V delay on the receiver until the audio lag is the same as the video lag. It's more work, but might be more exact if even your TV's audio isn't perfectly in sync.

Even though you can't "consciously" detect the lipsync lag, I find that stuff just "feels better" after a couple hours in a correctly lipsynced system (especially when gaming).
posted by qvantamon at 12:08 PM on January 23, 2009


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