Stereo fails at high volume
July 15, 2010 7:50 AM   Subscribe

Why does my stereo shut itself off at higher volumes?

(Initial disclaimer: I know as much about practical electronics and audio setups as your average Rhesus monkey.)

I recently came into custody of a pair of these Polk tower speakers. They seemed, to my untrained eye, to be in great condition for their twenty years, so after making sure that they had the same impedance rating (6 Ω) as the speakers that had come with my own stereo, I swapped them in, wiring the speakers directly to the stereo. (I have a receiver too, but I couldn't figure out how to put it in the loop.)

The sound is great, but if the volume gets past a certain point (which seems to vary from track to track), the stereo shuts itself off. What sort of mistake am I likely to be making? Could it be a problem with my wiring job? Is the stereo not appropriate for the speakers after all? Do I need the receiver or any other additional equipment?

Stereo specs: AC 120V; 60HZ; 80W
Speaker specs: 6 Ohms; recommended power 20-250 watts per channel; efficiency 89.5 dB
posted by Iridic to Technology (16 answers total) 1 user marked this as a favorite
Probably the power supply is crowbarring. Switching supplies in these kinds of devices are often designed to protect themselves from over-current conditions by shutting down.
posted by Chocolate Pickle at 7:56 AM on July 15, 2010

Some stereos have protection from high loads they can't handle and have heat sensors to shut down when they get too hot. I'm guessing that little stereo can't handle it. I'd try to get that receiver plugged in.
posted by damn dirty ape at 7:57 AM on July 15, 2010

What do you mean by 'shuts itself off' does the whole stereo power off or do just the speakers turn off but the display and such on the stereo keep working? What do you have to do to make it all work again? Unplug the stereo? Push the power button? Wait a few minutes?
posted by Confess, Fletch at 7:58 AM on July 15, 2010

Do they get hot? They could be overheating. Is it particularly warm where you are?

Alternatively, are there any loose connections you can see? Are the wires to your system loose? It could be vibrations are shaking things away from where they normally go. If this is the case, you might be able to fix it with some simple soldering.

Do the speakers just go caput, or is there static?

Admittedly, these are all pretty low tech. Someone with more experience in audio electronics might have some better suggestions.
posted by wayland at 8:00 AM on July 15, 2010

Your stereo receiver probably doesn't have enough power to speakers at the volumes you want. You could get a more powerful unit or get an amplifier.
posted by wongcorgi at 8:00 AM on July 15, 2010

While I don't have a definitive answer, I do have an anecdote.

When I was in college, I used to DJ a party using my house's regular stereo equipment. It would get hot enough that it was someone's job to keep surrounding the amp with bags of ice, otherwise it would cut out. 300 bodies in a tight room will generate a lot of heat, apparently.

While this isn't quite your problem, I would check with overheating first. There's a chance (I'm not sure how good) that this could be causing your problem.
posted by SNWidget at 8:13 AM on July 15, 2010

Your little stereo simply doesn't have the muscle to drive those Polks. Those things are pretty power-hungry speakers. Your little stereo can do ok at moderate levels, but simply cannot drive the speakers at louder or more dynamic intervals.
posted by Thorzdad at 8:16 AM on July 15, 2010

Those are 6 ohm speakers and your amp is almost certainly not designed to drive them; 8 ohm is the standard for consumer gear. You are straining the power transistors in your amp and if you keep this up it is going to burn out. Even if the volume levels are low. Buy a proper high powered amp (something that is labeled for 4 or 6 ohms), or sell the speakers and get something more appropriate.
posted by seanmpuckett at 8:32 AM on July 15, 2010

Yeah, the speakers should be plugged into your receiver. Does the mini-stereo have a line out? That can go into one of the receiver's inputs via RCA cables if you don't want to get new components (i.e., a CD player).

In short, your stereo's line out ---RCA---> receiver -> speakers.
posted by supercres at 8:33 AM on July 15, 2010

Do you get anything normal levels of audio? Do you get anything approaching LOUD before things cut off?

That stereo has a vanity power rating... even on a very good day it's not going to deliver 150 watts into anything.
posted by MikeWarot at 8:38 AM on July 15, 2010

In my experience this happens when there's a short in the speaker wires. If it's minor they'll muddle on but at higher output it's enough to short and shut down some sort of protector circuit.

Speaker wire can be cheap. I'd suggest buying an unspoiled roll and trying it w/o any funny business (routing it prettily, etc etc) and if you can get a friend with a soldering iron to tin the tips so there's no chance of stray wires, all the better.
posted by phearlez at 8:40 AM on July 15, 2010

This happened to me a few months ago and became very frustrating. After inspecting my receiver and every speaker in our living room, I found the culprit: one of our dogs had bumped into a front speaker causing the banana plugs to touch each other, causing a short.

At low volumes, the shorting apparently wasn't an issue. However, whenever a movie got really loud, the receiver would just turn off. Simply separating the banana speaker plugs fixed this issue.

Since then, it's happened a couple more times (hyper dogs!), and separating the plugs always fixes it. I suppose I should just wrap those plugs in electrical tape or something . . .
posted by siclik at 8:57 AM on July 15, 2010

Wow, I just noticed the little mini system you're hooking up to those towers. I would stick to the stock speakers on little system, I doubt it would even standard bookshelf speakers very well.
posted by wongcorgi at 9:10 AM on July 15, 2010

What do you mean by 'shuts itself off'...What do you have to do to make it all work again?

The whole stereo goes dark in an instant, as though the plug had been pulled out. It turns on again without any delay or need for adjustments.

Does the mini-stereo have a line out?


In my experience this happens when there's a short in the speaker wires.

I hadn't thought about that. I just used the old wires which came with the speakers. On inspection, a couple of the ends are pretty frayed.

I'll try a two stage solution. I'll get a new roll of wire, perhaps with pin connectors, and see if that does the trick.

If it doesn't, I'll invest in a decent stereo. If it does, I'll probably invest in a decent stereo anyway.

Thanks, guys!
posted by Iridic at 11:38 AM on July 15, 2010

It does sound like underpowered amplifier driving low efficiency (but hifi) speaker, causing what is probably an intended shutdown to keep from overheating and failure.

If the speaker impedances are matched, you should have no significant problem at low volumes. Regardless, if the Polks are significantly less efficient than the old speakers, you may have to crank up the volume to compensate, overworking the amp at high volumes. The 150 Watt amp rating is probably a peak rather than continuous rating, and likely optimistic at that.
posted by 2N2222 at 11:48 AM on July 15, 2010

When they say "6 Ω", they mean "as eyeballed by the manufacturer": a speaker's impedence changes with frequency. Some manufacturers will include a curve on their spec sheet, like this [pdf]. It's possible that the Polks are a little harder to drive than the original Sharp speakers. The 80 W figure might also be a bit optimistic (not by much, but still).

If you buy a new receiver or amplifier, you might want to check that it can drive a 4 Ω load, just to be sure that your Polks will be ok.
posted by Monday, stony Monday at 5:43 PM on July 15, 2010

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