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RF from smartphones causing damage to speaker components


Sailin Rulez

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Hi all,

 

I would appreciate your thoughts on the possibility of RF from people's smartphones causing damage to the components within speakers.

 

A bit about me and my circumstances - I'm the soundie at my local church. I have a few years experience of sound engineering in musical theatre and gigs at uni but my technical knowledge is a bit lacking in places. I know enough to get by and fix most of the problems that come our way within the church but the more technical engineering side of sound tech stuff evades me. My church meets in a school hall with a capacity of around 200 people. We use the best stuff we can find within our rather meagre budget and have a set up with a couple of Mackie SRM350s for FOH and two SRM150s as foldback which just about do.

 

We managed to blow the HF driver in one of our 350s a few weeks ago by short circuiting it (school boy error on the part of one of the team) and someone dropped one of the 150s, causing it to die completely. We sent both back to the supplier for repair and when we got them back, they were accompanied by a warning saying the damage was mostly caused by RF interference from smartphones which has eroded the components within both speakers and that the dropping of the 150 and the shorting of the 350 were only minor factors in their subsequent damage. I was a bit confused by this as it's not damage I've come across of before. I know interference from phones is rather annoying with it's 'bip-bip-biiip' that can sometimes come through (which we've not had come through in our set-up) and is best avoided, I didn't know it could cause actual damage.

 

The report we got said: "the damage to the speakers was most likely from RF from people's mobiles. When they are on, they will transmit RF and the mic leads will act as aerials and pick it up. This RF then goes via the sound desk to the powered, ie amp, speakers and blows components in them. The damage to the SRM350 was from this, albeit at some point the leads may have been mis-connected, and also to the SRM150, which was not damaged other than cosmetically by its being dropped. The HF speaker cone of the large one, which I think you had assumed had been blown, was ok. It was the HF driver that had blown and had to be replaced."

I would appreciate any wisdom/knowledge you have about damage like this you may have seen before and any advice about eliminating this damage (aside from the obvious getting people to completely turn their phones off and not put them onto silent) in the future.

Many thanks. Apologies if there is a thread on this somewhere before. I did search but didn't come up with anything useful.

Hannah

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It sounds like your supplier is taking the wee wee. RF from mobile phones won't damage your speakers. If it did, and your audience of 200 could damage your speakers, imagine how much damage a few tens of thousands of people could do at a major festival! If that's the best reason your supplier can come up with, find another supplier.
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Interesting theory, never heard it before.

 

I'd suggest your supplier is talking out of his hat.

 

Never heard of the "bip" causing damage either, it would have to be some serious RF to cause component failure.

 

The X32 has a nice spot to put a smart phones on, actually designed in, its no more than a bit of antislip plastic, not lead sheiling or anything involved ;)

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I'd also suggest that shorting out an HF driver is likely to annoy the amp, but won't kill the speaker?

 

You can kill a speaker by overexcursioning - where the coil can actually pop out of the space it lives in, which often causes very nasty sounding distortion, or total silence - and I guess square waves from a mobile could cause this - but I have no idea how they come to this conclusion without knowing you did it. Damage of this kind would have been done at the moment the nasty noise happened. I'd tend to agree with gyro - I've never heard of it happening, and to do the damage it would have had to be VERY loud, at the systems maximum.

 

The trouble is, the have determined user damage as the cause, and you have to deal with it. If you have never had mobile interference at massive levels and the failure immediately afterwards, then it cannot be correct. If the speaker just failed, I fail to see how they came to the diagnosis - so ask them what evidence they have this is the cause, because you dispute it. Eroding the components is utter rubbish - they're making it up.

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Hmm, it's highly unlikely that the RF from mobiles would make it from the mic input to the output of the desk (even on a Neve...) or through the amp. Ask the manufacturers for some snake oil to cool and lubricate the speaker coils.

(yes, it's b******s)

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Failed HF amps in the 350 are common - often caused by the 100nF sm caps on the HF amp PCB. In any case, how could you short the amp without opening it up? There are no externally accessible speaker connections!

 

As said elsewhere - time to find yourself a repairer who is a little more honest

 

Dave

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A little bit of audible interference is the worst you'll get from a smart phone. Think of how loud your system can go in normal use. To do damage, the phone would have to be significantly louder than that after passing through the mixer/amp.

 

If RF from a phone could do that much damage, it certainly wouldn't be safe to put up to your ear.

 

If the repair guy offers to sell you a bridge, I suggest you steer clear.

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Time for one of BigClive videos methinks :D

 

Electrically, shorting the physical driver is the best protection it could have! ..yet the worst for the amp. Do you mean actually short circuiting the driver or, accidently connecting say a speak level output to a mic or line level input? THAT could kill a driver.. :(

 

Dropping the other more likely dislogged something, such as a connection to the driver(s) or input(s) or a component on an internal circuit board.

 

Smartphone damage? :** laughs out loud **: :** laughs out loud **: :** laughs out loud **: :** laughs out loud **:

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