Humming sub woofer

[JoeJoe]

Hi guys/gals.

Humming is annoying at the best of times, but when your sub starts to do it, it ain't funny.

I'm not sure when it started, recently I think.
There's a low pitched humming coming from the sub when it is active. Let me give you the scenario -

1/ All equipment is powered off. No problem.
2/ Everything is powered on, sub on standby, no problem.
3/ As soon as the sub becomes active ( green light comes on ), the humming starts.
4/ Doesn't matter what cables I remove, or if I switch off the amp, the humming continues. The only time it stops is if I power off the sub ( and as it's powering off, it greets me with a whopping thump ).

As I said, it only seems to have started recently.
Currrently, the sub is connected to a cheapo 6 gang connector which all the other AV equipment is connected to.
I moved the sub plug to the other, double socket, socket so it is now on it's own. No improvement. Moved the plug to another socket the other side of the room, still no good. Nothing that I know of has changed in my AV setup, before or after the problem started.

Any ideas? Is this a fault my sub has developed?

The spec is Kef Egg speaker package and Denon 2802 amp. All cables are Profigold.

Many thanks.

 

[Sinzer]

Not sure about the sub front, I am not an expert. Sounds like something is going though.

On the electrical front, you should really buy some surgemaster protection. I learnt the hardway and have since spent 40 squid on an 8 way Belkin Surgeprotector and it does make a lot of difference.

If you have £1000+ of equipment on that 6 way, then that is a lot of damage if there is an electrical problem.

 

[JoeJoe]

Thanks Sinzer, I'll do that.

Further update. I moved the phase wheel all the way to the right ( I guess fully on? ) and this just about got rid of all the humming but you can just here it still. I suspect I'd not have noticed before but now I'm listening out for it!
Someone had been fiddling with it I think as it's always been in that position. Do you think I still have a problem? Although I'm not really concerned about the minimal hum any longer, the following does seem concerning .

However, with Monsters Inc. ( not tried any other dvds yet ), when the sub outputs a loud longest sound, there seems to be some residual sound coming from the sub after the effect seems to have finished which lasts a few seconds.

How can I explain it, a bit like reverb maybe?

 

[JoeJoe]

I have further info after a little fiddle.

Firstly, I've now noticed the sub has no where near the umph it had a few weeks ago.
When the sub would have been shaking the room, it would no longer, and when the sound effect was gone, the sub hums for a few seconds before settling down again.

So, I went into the Denon speaker test menu, set it to manual on the Sub and got what seems a perfectly good rumble from the sub.
However, I then turn up the volume on the sub slightly and there is occasional popping sounds. I turn it up further and the popping sounds increase, the rumble disappears and then the sub just outputs a steady load noise, similar to the hum but louder.
Turn the volume down again quickly and the humming hangs around for a second or two before returning to the rumble.

Does this sound like my sub has gone tits up? All speakers are set to small, cross over set to 120.

 

[Jase]

Originally posted by JoeJoe


Does this sound like my sub has gone tits up?

I would think so. Trip back to the dealer is needed or alternatively email Kef directly. Here´s their site www.kef.com

 

[JoeJoe]

I was wondering that. I'm no expert on audio which is why I posted the symptoms. Ho hum.
Which bit of my description led you to believe the sub could be goosed?

It shouldn't make any odds for the sub to be on a heavy pile carpet should it? Nothing in the manual about it.

Well, at least the beast is only 6 months old, so there shouldn't be any arguments.

Thanks for the advice.

 

[Jase]

Subs shouldn´t hum, that´s the first thing, though that could be down to cabling etc.

You shouldn´t get any after bass like you describe or any popping noises at all. You might get a tiny pop as the sub is switched on after being off for a while but not like you´re describing.

Placing the sub on carpet, spikes, floor etc will change it´s bass, make it tighter, looser etc but should´nt make it pop!

If it´s under guarantee then it should be replaced, Kef are normally pretty good when it comes to things like this .

 

[JoeJoe]

Your help is much appreciated.
As always, when I have a problem, this forum is always friendly and helpful.

 

[Family Guy]

This could actually be an earth problem. If the sub and the amp are earthed, this may cause the sub to hum or other speakers for that fact. Disconnect the sub from the amp. If the hum stops, it's an earth problem. If the hum stays, your sub is knacked. Could be you have the sub plugged into the same ring as the amp. If this is the case, the answer is to cut the earth on the sub. It will still be earthed via the outer braid on the cable connecting it to the amp.

 

[JoeJoe]

Originally posted by Army Bloke
This could actually be an earth problem. If the sub and the amp are earthed, this may cause the sub to hum or other speakers for that fact. Disconnect the sub from the amp. If the hum stops, it's an earth problem. If the hum stays, your sub is knacked. Could be you have the sub plugged into the same ring as the amp. If this is the case, the answer is to cut the earth on the sub. It will still be earthed via the outer braid on the cable connecting it to the amp.

Hi.

I take it you mean remove the phono cable ( apologies for my wrong terminology ) from the sub which goes to the amp ( must be as that's the only one ). Yes, tried that and the hum remains.

Sub and amp are plugged into the same ring. I could try the one up stairs I think. I'll give it a go.

The AV shop I bought it from advised that all subs hum/buz to a certain extent as they have an amp in. I'm not sure if he's talking about the very low buzz or the fact that some amps can buzz quite loudly?
They advised I bring it back and they'll hook it up to have a look.

Any recommendations regards ensuring that if the amp is goosed, I get the message across to the AV shop properly. IE: I explain it clearly. I don't want them to start waffling me back home cos I'm fairly certain there is a problem.

 

[Member 14718]

I think what you have explained already is a clear indication that there is a problem with the sub. You say its worked fine but now buzzes, makes crackling noises and thumps when it switched off and that you never noticed this before. You have obviously heard it operating far better than it does now so dont let the sales guy's bulls**t you as you have payed good money for it, you deserve fair treatment.

Most manufacturers of powered subs take great care to reduce hum to a minimum and you should not hear it, say for a mechanical hum from the transformer or if the sub is up full volume. A typical S/N (Signal to Noise) figure being better than 100dB I dont know what the spec is for your sub but if they qoute around these figures then you should not hear any hum

 

[JoeJoe]

Thanks for the info Dan. I'm sure I won't have any problems, but ya never know.

 

[JoeJoe]

Just a courtesy update as you guys were so helpful.

Returned the sub to Sound and Vision in Bolton.
"What do you mean you're not buying anything, get away unclean person, we're too busy" was my initial impression, even though I was the only one in the shop with 4 shop assistants.

Anyway. Symptoms explained -
Popping
Lower power
Sub hanging onto sound after it had finished
Humming sound

After a little fiddling, the crossover switch was moved from the far right to the middle "There you go sir, shouldn't have it set full on".

What???. That's solved everything?? I was not driving all the way home to find I still had a problem. I requested they do a white noise test.
Sorry, we don't have any remotes for the 40 TV/amps we have on display!!! We'll send it to customer services to be checked.

So it was. 1 Week later, I phoned to find out what is going on.

Shop can't help, need to speak to customer services. Only 1 person on it at the mo. ( check out their website and I quote "National call centre" !! ).
3 Days and no contact. I phone the shop back up and insist they find out what's going on. Within 2 seconds, I had a response from the shop. They can find out on their computer it seems.

The sub was knackered ( told you so ) and it's gone to KEF.

Another week passes. Customer services now have two people working again, and contact is no longer an issue.
So... cutting to the chase... my sub woofer is lost!! Kef haven't go it.
5 days and Sound & Vision can't seem to get hold of the carrier or KEF repairs. I asked for both phone numbers and the consignment number. It takes me 20 minutes to contact the courier, KEF and find out that my sub has now been found trying to escape the KEF dungeons.

The amp relays had gone fubar, amp replaced, sub returned. Ahh, my baby is home.

All's well that ends well, as long as you do the spade work and don't rely on anyone else.

 

[JoeJoe]

Thanks for all your help.

 

[Sinzer]

Sounds like a nightmare!!!!!

At least it ended well!

 

[Member 14718]

Dear me Joe Joe, its that old saying what can go wrong will go wrong.

Thanks for letting us know the outcome.