sub hum normal?

[madshi]

If one turns an active subwoofer on and to full volume, while the only cable connected to the subwoofer is the power cable (but no audio cable!!), should the subwoofer be totally perfectly silent in this situation? Or is it normal, that it is somewhat audible?

My subwoofer in this situation hums a bit (the hum level increases with the sub's volume control), and I'm trying to figure out whether there's something wrong with the subwoofer or whether a little bit of humming is normal.

It can't be a ground loop, AFAIK, because no audio cable is connected.

Thanks!

[Italo Tettoni]

Depends on the brand of the sub, its price band and its construction. A low hum on a low-to-mid price subwoofer is considered 'normal' since it's probably a noise introduced by the internal amplifier.

If you have an expensive sub and the hum is quite loud I'd be getting the service people to have a look at it.

[madshi]

It's a Sunfire True Subwoofer Signature, which is quite expensive. The problem for me is that "quite loud" is very subjective. E.g. I had the Panasonic service here to check out my "loud" plasma display and they said it's totally normal. Then I've had my brother here and he laughed about me complaining about the plasma "noise" (which he barely heard). I've not had the sub when my brother was here, so I don't have his opinion on the hum. So all in all I'm simply unsure whether my sub's hum is "quite loud" or rather "acceptably loud".

Thanks for your help!

[sanejo]

Try earthing the sub to your amp.

[madshi]

How can I do that? And what purpose does that have? I mean there's no connection at all between the receiver and the sub right now.

Thanks!

[eviljohn2]

It sounds fairly normal to me. Presumably the hum is only barely audible when the volume is below about 2/3 maximum.

[AngelEyes]

Originally Posted by eviljohn2

It sounds fairly normal to me. Presumably the hum is only barely audible when the volume is below about 2/3 maximum.

agreed, having your sub at full volume (gain?) is not a realistic setting for normal use so you shouldn't have it set there anyway.

[Italo Tettoni]

You did write that you had the sub at full volume so hearing a hum in that unlikely circumnstance is 'normal'', ever tried turning your amp/receiver at max volume with no input?

Do you hear the hum when the sub is set at an appropriate listening level? If not (or it's at a very low level) I'd consider that 'normal'. You would have to pay a good deal of money for a sub with extensive shielding to the internal amp to hear no hum whatsoever. All the best for the season!

[madshi]

Thanks guys.

There is a little but of hum at normal levels, too, but it's really low and from my normal hearing position I have to concentrate on it to hear it at all. It's just that my older much cheaper sub was totally silent (as far as I can tell), and so I wanted to have confirmation about whether a sub may hum at all or not.

[Nick_UK]

The problem with sub woofers is that they are tuned to the exact frequency range that produces mains hum. So even a small amount of hum will come through where it might not be so noticeable on bookshelf speakers.