Sub thumps sometimes when light switches are used. Normal?

[binister]

Sometimes when I flip a fan or light on in a room adjacent to my computer room I can hear the sub on my Logitech Z-5500s thump. Is this normal and could it be causing any damage?

 

[mikeblas]

It's not normal, no. The transient load caused by switching on the light should not cause your sub's amplifier to be unstable.

 

[The_Engineer]

does this make it a problem with the power system (fuses, wiring etc) in his building? Or is it a problem with the sub? I would think this would be caused by overloading the local circuits, not the sub itself having problems.

 

[Fryguy8]

It's a problem with local circuitry, but it can be very detrimental to the electronics of the amp and the sub itself.

 

[Deleted member 72990]

i thought most modern subwoofers have a muting circuit to prevent this from happening?

 

[Mister X]

What good is a muting circuit gonna do here?
You need some type of mains filtration to deal with these kinds of issues.
You are right when you suggest that most consumer audio gear does have a built in mechanism to deal with micro power surges but when did that ever apply to PC speakers?

 

[mikeblas]

What good is a muting circuit gonna do here?
You need some type of mains filtration to deal with these kinds of issues.
You are right when you suggest that most consumer audio gear does have a built in mechanism to deal with micro power surges but when did that ever apply to PC speakers?

All consumer audio gear, even PC speakers, has a built-in mechanism to deal with micro power surges: the power supply.

A muting circuit turns off the output of the amplifier at start up until the power supply becomes stable. Some circuits will do the same thing at (or after) power off.

 

[Mister X]

All consumer audio gear, even PC speakers, has a built-in mechanism to deal with micro power surges: the power supply..

Lets think about this for a second.
If I add a mains filter to a device what part of that device does it get added to?
Well duh..........The power supply.
But lets imagine for a second that the power supply is not equipped with a mains filter.
What part of the PSU do you think provides this so called built-in mechanism that deals with these micro power surges?

A muting circuit turns off the output of the amplifier at start up until the power supply becomes stable. Some circuits will do the same thing at (or after) power off.

So, what happens to this muting circuit when the power supplies built in mechanism for dealing with micro power surges shunts this micro power surge to ground?

 

[Newbify2]

Do you live in an older building, by any chance? sometimes the ground wiring isn't quite right some older buildings, mainly houses.

 

[mikeblas]

What part of the PSU do you think provides this so called built-in mechanism that deals with these micro power surges?

It depends on the design of the power supply. In a linear supply, it's the voltage regulator. In a switching supply, it's the feedback loop that notices the voltage climbing (compared to the current being drawn) and stops bucking the output capacitor.

The front end of either type of power supply is a step-down transformer. It's dropping the line voltage to something usable by the circuit in question. For a set of PC speakers, maybe it's going down to 18 VAC or 24 VAC. If the line input has a small surge, it might jump 10 or 20 percent. That'll cause the output of the secondary to jump 10 or 20 percent, accordingly.

The regulation provided by the power supply after the output of the secondary is converted to DC inherently absorbs this voltage change. That's why it's called a "regulator".

So, what happens to this muting circuit when the power supplies built in mechanism for dealing with micro power surges shunts this micro power surge to ground?

[/QUOTE]

The muting circuit is intended to prevent the amplifier's output transistors from effectively dumping the energy in the filter capacitors in the power supply straight into the speakers after the amplifier shuts down.

I don't think it would be aware of any surge in the line voltage that the power supply is able to absorb by regulation. A trough in the line voltage that falls through the power supply's cutoff point, on the other hand, might end up activating the muting circuit.

binister's problem probably doesn't have to do with surges, as he's turning other loads on, and not off. I'd expect the problem to because by either noise or a small dip on the mains.

But maybe I'm all wet. I've never heard of "micro power surges", and Googling for the term gives me only two hits. I've just assumed that you've meant short variances of several percent in the line voltage supplied to the equipment; maybe you mean something else.

 

[Max-Powers]

I have the same problem. Like if i turn on my desk fan my logitech z-5500 thumps. maybe its the speakers? or maybe its the power strip its all pluged into?

 

[binister]

House is a newer townhouse (built ~1998).

Strange thing is it doesn't always happen. It seems to happen when the sub has been on for a while and the other device has been on for a while. Then when I turn the other device off (lamp, fan, etc) the sub thumps. Subsequent flipping of the switch causes the sub to thumb again but less each time until the sub no longer thumps.

Ideas?

 

[mikeblas]

What are you trying to do? Fix the problem, or understand why it is happening?

 

[binister]

What are you trying to do? Fix the problem, or understand why it is happening?

Well, it sounds like the consensus is that it is damaging my sub so I would like to know if there is an easy fix. Perhaps get a power strip or backup battery or something like that.

 

[mikeblas]

Yep. Then, try moving the sub to a different branch circuit in your house and see if the problem persists. Maybe re-routing your signal cables can help, too -- are they near any power cables?

 

[binister]

Yep, the signal cables run along side the power cables to all the computer equip. I am going to try a power strip to see if it helps. Thanks for all the responses.