OT: WiFi interference

[Mike Barnes]

Not DIY but I'm hoping to tap into the electronics expertise here.

In our home cinema setup there's an active sub-woofer that's picking up interference (a constant burbling noise) from a WiFi router which is a couple of feet away.

When I speak to the manufacturers of the sub-woofer they say that it's not their problem because WiFi routers must be placed "well away" from other electronic equipment.

I explain that there are several other boxes (AV receiver, DVD player, DAC, media server PC) closer to the WiFi router that don't pick up any interference. So it seems like there's something wrong with the sub- woofer.

No, they say, the sub-woofer is special because it contains a "low frequency amplifier".

I think I'm being fobbed off, but before I get more persistent I'd like a second opinion or two. What do you think?

[Peter Crosland]

It is not unusual for radio interference to get into equipment in this way. Not all equipment is as good at rejecting it. The solution is to try moving the router further way. Another possibility is to put some ferrite rings on the signal cable feeding the sub woofer.

[Dave Liquorice]

Presumably confirmed by turning off the router? Though that isn't conclusive that it's purely the router that is the problem, it could be the router and something else (video sender, Bluetooth, ...)

Well that makes a change to what is normally in the written CE approvals. Namely "switch it off", either the kit itself or the interfering source.

Is this a well known brand? A couple of feet should be enough seperation, IMHO, for decent quality kit. Does the burble go away or alter if you change/remove any connections? Is this a pure sub or does it also drive the L, R, C lr/Rr speakers? Do they burble?

[Martin Brown]

Active in the sense of mains powered or with wireless data transmission as well? I can well imagine that having a wireless router that close to another type of wireless interconnect might well interfere with it.

I find it harder to understand if the thing is fed an analogue signal. (in which case try putting a magnetic choke clip on filter on the line)

That is good advice.

Not necessarily - it is just a bit more sensitive to interference than the other boxes. Back in the old days of turntables and magnetic pickups it wasn't uncommon to get nearby taxis breaking through.

You might be being fobbed off a bit, but it is unreasonable to put two units competing for bandwidth in the same spectrum so close together. You might be able to cure or minimise it by changing Wifi channels.

[jrwalliker]

You are being fobbed off. There is nothing special about a "low frequency amplifier" which would make it sensitive at 2.4GHz or 5GHz if competently designed.

Good advice, but it should not be needed. Ask to see the test lab report which backs up their CE marking. If they refuse, suggest that perhaps Trading Standards could look at it on your behalf.

They may have used the technical construction file route and self-certified. In that case, ask to see how they justify CE compliance and whether they have done ANY testing.

Perhaps they need some EMC consultancy. Several people here would be able to help.

John

[The Natural Philosopher]

i think they are talking bollocks

[Mike Barnes]

About six feet away makes the interference almost inaudible. But that's inconvenient for a number of reasons.

I should have mentioned that I'd tried disconnecting the signal lead and it made no difference.

[Brian Gaff]

I have one of those, the amp inside the speaker picks up. radio china international, Mobile phones, fridge thermostats etc, and the is quite frankly due to the internal psu being crap. Its wide open, no filtering at all anywhere ab part from the low pass input. Does the manufacturers name begin with a vowel by eny chance. The only partial fix i've found is a mains filter lead on the mains supply, It still picks up the mobile phone though if its within 10 foot and thermostats can just be heard. However, no chinamen any more. Brian

[Brian Gaff]

If it is the same one I have, the pcb is completely unscreened inside the wooden box and the filtering on the mains cable is only a partial fix. The earth leads to the amp or wherever its fed from also can pick stuff up as does the actual pcb. I suspect that the length of wire or circuit inside the unit could well tune it to the high frequencies and as this bypasses the low pass filter for the audio it can be quite loud as I have found. It really de[pends on how pro active and invasive you want to get. Putting capacitors all over the place inside the amp might bhelp of course but if its under warranty you would invalidate it by doing so. Brian

[Mike Barnes]

[e-mail]:

Thanks, that's something to bear in mind if things get difficult.

My main concern at this stage is to back up my request for a return and refund, and reassurance that I'm not likely to get the same problem with whatever I replace it with.

[Mike Barnes]

Exactly. Disconnecting power from the router makes the noise stop instantly.

True. But there are no video senders in the house, and I'm not sure how Bluetooth is relevant. FWIW the broadband router is yards away.

Dunno, but definitely not downmarket.

Only if I remove the mains lead. :-)

It persists if I remove the signal lead.

It's a pure sub. The other five speakers are driven directly by the AV receiver (Onkyo). There's no extraneous sound from them.

[Mike Barnes]

Mains powered, the only other connection being a phono lead from the SUBWOOFER PRE OUT socket on the receiver. And the sound persists if I remove the signal lead completely.

I didn't know that there was such a thing as a wireless sub, otherwise I'd have mentioned the fact that this isn't one.

[Peter Crosland]

All good in theory but complete over reaction to what is in all probablity a minor problem that can easily be solved. In any case the CE standards don't offer complete immunity just a reasonable level of effectiveness.

[tony sayer]

Me too..

This just should not happen these days what with EMC compliance regs. Alluding to an earlier post the CE makings are just that markings.

If they want to argue then fitness of use should see them taking it back and giving a refund..

A router that close and power they don't emit shouldn't be a problem..

[The Natural Philosopher]

well I dont thnk its a complete overreaction and although it can be easily solved at the design stage, bitter expereince shows that its a bitch to discover in any given case what the solution is, and it always makes it cost more.

And if the amplifier design is plain bad, it may not be soluble at all by 'adding stuff on'..

[AnthonyL]

Whilst the advice on here can be very good there are some real and practical experts on alt.internet.wireless and whilst not necessarily UK based you may get some valuable help there.

I could cross-post but I'll leave it to you.

[tony sayer]

In article , AnthonyL scribeth thus

Whilst they might be good at 2.4 and 5.8 Ghz odd I shouldn't think they'll know that much about what's really going on here with this situation;!..

From the sound of what's happening this is a poorly designed non EMC complaint piece of tat..

Most any semiconductor junction works at much higher frequencies than what its needed to for audio usage. Circuit design techniques exist to overcome things like this example of unintentional demodulation and have done so for years but they add to the cost of manufacture.

It is quite probable that the router you have apart from radiating in the 2.4 GHz ISM band as intended if its a wi-fi one, will radiate a small amount of electronic RF "noise" which will be very small. Now putting what amounts to an open channel receiver close to that will result in some bother!.

Its just poor design which we see very little of these days apart from such as cheapo computer speakers, you might have a pair of these which make that odd noise if your mobile rings when its close to them etc.

The fault is simply a poorly designed piece of audio equipment, its as simple as that!...

[Dave Liquorice]

Bluetooth is yet another thing in 2.4 GHz could be intermodulation between it and the router. Not particularly likely though.

£800 / 5.1 set... ought to perform better than it is regarding susceptabilty to RF interference. Though reading the website does start to make my snake oil alarm quietly jingle, countered a bit by the "best buy" awards etc

connections?

Can you short circuit the input? Does it go if you do?

[Graham.]

Could be, but the OP has not given us enough to say for sure.

This is an active speaker, so is the low level audio feed to it ballanced or un-ballenced? How long is the cable? Is it screened? if unballenced is *well* screened? Is the interference still present with the cable disconnected?

[fred]

In article , Graham. writes

"Mains powered, the only other connection being a phono lead from the SUBWOOFER PRE OUT socket on the receiver. And the sound persists if I remove the signal lead completely."