How can this happen??

[nat8808]

The other night I was laying on the sofa when I could hear a mains-like buzz coming and going.

I thought it was coming from my amp and speakers but nothing...

Then I sat and listened around a bit, followed the sound.

It was coming from the midrange of an UNPLUGGED pair of speakers! They've not been plugged in for many months yet the midrange was buzzing on and off with a mains-type hum.

How can this happen?

My guess is that a capacitor was charging and discharging itself somehow? They are a pair of old B&W 802s and they have some kind of speaker protection. I think this is passive though, not requiring a battery of any kind (which would long since have expired).

It's not disimilar to buzz I do sometimes get in my main system - could there be some kind of electromagnetic inductance going on?

[Roy S]

Audio Poltergeist?

[Macca]

Tempting though it is to blame the supernatural I would guess that you have some really strong RFI coming from somewhere. Is there a cab firm nearby?

[nat8808]

More like a spirit getting inside .

I'm in a big block of flats so who knows what's around me.. no cab firms though. Could it be my own wireless? Or my laptop giving out crazy RFI?

I've heard the sound before but it only happens now and again as far as I'm aware anyway.

[walpurgis]

I'm with Martin on this. RFI from somewhere nearby, probably the internal speaker wiring acting as an aerial and feeding the voicecoil to produce the buzzing.

[alan47]

Could be the thermostat on your water bed......

[Macca]

A block of flats in London. Anything could be going on. I'd look at turning your entire flat into a Faraday cage. Only way to be sure ;)

[sq225917]

If there's an active circuit in there, where capacitors are used for power storage then it could happen that they could discharge. But you'd need to be talking about large power caps with multi thousand uF ratings not 10uF poly caps from Ansar or whoever. 802 don't have any active components in them and the driver protection is passive, basically fuse wire.

Unless you happen to live in the firing line of some special unknown 'alien space gun' or the exhaust ports at CERN, there's no reasonable way RFI could be responsible for making your drive units move on an unplugged pair of speakers.

I'd rule out the likely before you start making up 'new science' to fit what you heard. Mice, or a draught would be the most likely culprits-or drink.

[bobbasrah]

The other night I was laying on the sofa when I could hear a mains-like buzz coming and going.
.......

It's not disimilar to buzz I do sometimes get in my main system - could there be some kind of electromagnetic inductance going on?

I'm with Martin on this one as have had previous similar experience with RF on some small speakers....

Cities tend to be awash with RF and spuriae. Short of borrowing a GDO you might never narrow down the offending frequency before trying to identify the potential source....

IMHO if they are surplus, move them somewhere else or sell them.

[Audioman]

Block of flats in london ! - probably picking up interference from the generators of a neighbouring cannabis farm. :)

[nat8808]

I'm with Martin on this one as have had previous similar experience with RF on some small speakers....

Cities tend to be awash with RF and spuriae. Short of borrowing a GDO you might never narrow down the offending frequency before trying to identify the potential source....

IMHO if they are surplus, move them somewhere else or sell them.

That's why I've got them out - a reminder to do them up a bit to move on.

As with all things hifi though, you think "I wonder what they'll sound like with my new set-up..." and so they wait for another audition.

[nat8808]

If there's an active circuit in there, where capacitors are used for power storage then it could happen that they could discharge. But you'd need to be talking about large power caps with multi thousand uF ratings not 10uF poly caps from Ansar or whoever. 802 don't have any active components in them and the driver protection is passive, basically fuse wire.

Unless you happen to live in the firing line of some special unknown 'alien space gun' or the exhaust ports at CERN, there's no reasonable way RFI could be responsible for making your drive units move on an unplugged pair of speakers.

I'd rule out the likely before you start making up 'new science' to fit what you heard. Mice, or a draught would be the most likely culprits-or drink.

Mice and draught are the unlikely ones - unless a mouse has invented an analogue synth and was jamming out to a saw-tooth wave. I had my ear to the mid driver (not the tweeter) and it was pulsing a very quiet buzz, on for say 5 seconds then off for 3 or so.

I've heard it before but not bothered tracing it before, thinking it was from my system. I have had the same pulse and buzz from my system before too and had assumed it was some equipment introducing interference into the mains.

In science, sometimes what you think is unlikely and that which you have dismissed turns out to be the answer. It's the self-belief that you already know how the world works that hinders the finding of the real truth. I'm wouldnt personally dismiss RFI as I don't know the specifics of the possibilities.

If AM radio stations can be picked up by crystal radio sets without amplification then I'd quess that there are possible ways that similar electromagnetic waves can be picked up by the 802s with their many metres of internal wire (inductors etc).

I suppose the most interesting part for me is the science behind the cause.

[NRG]

Do you have any mobile phone masts close by? My phone induces a buzz into my unpowered desktop PC 'speakers when a call is incoming...the speakers and PC are off but they still buzz.