Topic: Cell phone interference: how can I shield against it / what's wrong with my rig?

[Church-Audio]

This is where I get my mesh screen from http://www.ksmetals.com/Craft/Tooling_Foil_&_Mesh.asp

The screen does not need to be earthed if it is 100% around the mic it will still act as a shield. And it will not change the sound of your mics I use the same screen on my mic capsules to sheild them for this very reason Another trick of the trade.

Hey I just thought of another solution that "MIGHT" work create what is called a faraday shield by going to a hobby store and pickup some fine brass screen and make little mic pockets surround the mics in this fine brass screen I bet that will solve the problem.

I was initially looking at faraday cages when I thought the problem was with the iriver.  Didn't think about using it on the mics. I wonder if I can do this without screwing the sound?

Would I need to ground the cage somehow?  Otherwise wouldn't it act like an antenna?

Edit: hrmm...I wonder where I can source the mesh.  The local hobby shops don't seem to have it.

I may need to order from these guys: https://www.twpinc.com/twp/jsp/product.jsp?type=11# (some interesting info about RFI there too).

edit2: gah...just noticed the fine print...minimum order is $75. :-/

[it-goes-to-eleven]

GOOD hardware stores will sell 'hardware cloth' of various mesh sizes.  I'd suggest sandwiching the shield in shrink wrap. That may also allow you to avoid soldering or sewing the seam, etc. Any contact with the mesh with fingers/etc could cause handling noise by changing the inductance and capacitance of the ground plane. So having it covered isn't such a bad idea. I'd think you'd want to ground it but I'm not sure if you'd need to for these frequencies.

[Church-Audio]

Good ideas doe’s hardware cloth come in a very fine mesh? I have never seen it I would like to check it out if you know where I can get some. I think if the shield can be 100% or almost 100% now that I think of it it’s not a bad idea to attach it to ground somehow. I would try it with or without and see what happens. How would you heat shrink it with out interfering with the mics performance? Hey maybe it’s not a bad idea to use a windscreen under the brass screen or hardware cloth? I know lots of companies use this brass screen like Neumann and AT to name a few. It does work hardware cloth would be good too I think if you can find a very fine mesh the stuff I am talking about is finer then the permanent mesh coffee filters. Its looks like silk the holes can not really even be seen with the naked eye.

Chris Church

GOOD hardware stores will sell 'hardware cloth' of various mesh sizes.  I'd suggest sandwiching the shield in shrink wrap. That may also allow you to avoid soldering or sewing the seam, etc. Any contact with the mesh with fingers/etc could cause handling noise by changing the inductance and capacitance of the ground plane. So having it covered isn't such a bad idea. I'd think you'd want to ground it but I'm not sure if you'd need to for these frequencies.

[whatboutbob]

Its looks like silk the holes can not really even be seen with the naked eye.

Hrmm...by the photo that's what the stuff in the link I posted above looks like.  I'm having a hard time finding anything suitable.  By the looks of it there's nothing called 'hardware cloth' down here.

Does the mesh have to be brass or copper?  Could it be another metal?

If I can find something I was thinking I'd put a layer of it over a very thin pair of windscreens I've got.

[Church-Audio]

As long as the metal in question is a conductor, it should be fine. I would make sure you get the finest mesh you can find. Go to a cooking store and see if they have any strainers that are fine mesh they should. Buy one and cut out the mesh.

Its looks like silk the holes can not really even be seen with the naked eye.

Hrmm...by the photo that's what the stuff in the link I posted above looks like.  I'm having a hard time finding anything suitable.  By the looks of it there's nothing called 'hardware cloth' down here.

Does the mesh have to be brass or copper?  Could it be another metal?

If I can find something I was thinking I'd put a layer of it over a very thin pair of windscreens I've got.

[whatboutbob]

I would make sure you get the finest mesh you can find. Go to a cooking store and see if they have any strainers that are fine mesh they should. Buy one and cut out the mesh.

Mwaha...I'll leave that as a last resort.

edit: ok...so I got impatient and was getting bored with the enthralling England v Paraguay match, so my kitchen is now minus one strainer but my mics have two fabulous-looking RFI shields.

...but do they work, you ask?

Initial tests show a small decrease in interference while using the rf-doms (tm).

It gives me some hope if I can just find some finer mesh.

[whatboutbob]

grrr...ok...i found some finer mesh (2 x $1 tea strainers later).

I'm sad to report that the rfi is still there...marginally lessened...but still there.

I've had enough.  I'm looking at new mics (audix m1290c's seem to fit the bill).

I just have to cross my fingers that I don't get the same problems. 

Thanks again to those who've chipped in their advice on this thread.

[Digital Quality]

New mics are always a good idea anyway

I had another thought whilst driving to Wakarusa. I'm not sure if it's GSM but there used to be a protocol where the tower would commuinicate with the phone even when it was switched "off". The power only put it in a sleepy state and turned off the screen and such. The phone still woke up every now and then to check in with the tower. The only way to get it turned off completely was to take out the battery. Maybe just another thing to try at the next show.

Good luck with the new mics!!

[whatboutbob]

New mics are always a good idea anyway

Hehe...yeah...there is a small chance that all of this is actually an elaborate plot to psychologically justify that I must have new mics. To quote a fine 'made in australia' film..."there is no spoon"... 

I'm not sure if it's GSM but there used to be a protocol where the tower would commuinicate with the phone even when it was switched "off".

Thanks for the thought...I've read the same thing somewhere, but I'm 99% sure that's not the case with the aussie phone network and is not the source of at least the rfi i get on my recordins.  My reasoning:

a) I've never had speakers suffer from rfi while our phones are off (while its a fairly common occurence when phones are on)
b) usually when my recordings have rfi i hear it over my monitors and can place it to some wook within a few meters of me clicking ''send' to make a call or send a txt msg

[whatboutbob]

>Thank you for your inquiry and sorry to take so long getting back to you. Your message was routed to me while I was out of the office.   The GSM >interference issue has been a huge problem for the audio industry.  We addressed (and resolved) this in our revamp of the UniPoint line with the >UniGuard technology.  You may need to upgrade to the new UniPoint line to resolve your issues.
>Please let me know if you need additional information.
 
>Rick Jxxxxx
>Manager, Audio Solutions
 
>Audio-Technica U.S., Inc.

[whatboutbob]

Alas, but upon receipt of my new (to me) audix m1290 mics today I confirmed that cell phone interference is not an issue just with audio technica mics.

I think I'll just live with it until it kills an otherwise awesome recording again and then snap and buy some u853's or other supposedly rfi-protected mics.

Man this is frustrating (/expensive).

edit: fat fingers

[rokpunk]

Buy some Neumanns and see if that fixes the problem. It won't help with the cell phone interference, but at least you'll have some good mics.

[Church-Audio]

Send your stuff to me I am try and see if I can fix the problem.

 My offer still stands

Chris Church

Alas, but upon receipt of my new (to me) audix m1290 mics today I confirmed that cell phone interference is not an issue just with audio technica mics.

I think I'll just live with it until it kills an otherwise awesome gig again and then snap and buy some u853's or other supposedly rfi-protected mics.

Man this is frustrating (/expensive).

[jeromejello]

Alas, but upon receipt of my new (to me) audix m1290 mics today I confirmed that cell phone interference is not an issue just with audio technica mics.

I think I'll just live with it until it kills an otherwise awesome gig again and then snap and buy some u853's or other supposedly rfi-protected mics.

Man this is frustrating (/expensive).

that sure does suck... have you thought about using those rf shields that clip on to cables (i really dont know what i am talking about)
the ua-5 i have came with a plastic shield that clicks over a headphone cord when plugged into the unit.  

let it be known that:
a) i am not sure if this for the same thing
b) if it would have any other adverse effects on the mics
c) where to get them

+t for your crappy cellphones in oz

[whatboutbob]

that sure does suck... have you thought about using those rf shields that clip on to cables (i really dont know what i am talking about)
the ua-5 i have came with a plastic shield that clicks over a headphone cord when plugged into the unit. 

Funny you should mention that.  I got a ua-5 in the mail today too...saw the doohickey and thought I'd give it a shot on the mic cables.  It made no impact.

Send your stuff to me I am try and see if I can fix the problem.

My offer still stands

Chris: Thanks once again.  I didn't want to put you out, but it seems I've exhausted all other avenues apart from buying mics that I'll have to sell a body-part to fund, so I think I'll take you up on that very generous offer now.  Could you pls pm me your mailing address?

Right...I'm off to watch (on tv) Australia play in the second round of the world cup (who woulda thunk it?!).