Shielded speakers recommendation

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Level 4

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Shielded speakers recommendation

I have a pair of JBL Duets (original version) plugged in to the headphone socket, on either side of my MBP. They pickup my iPhone searching and produce the classic mobile phone interference noises.

Can anyone recommend any well shielded small speakers which will not do this?

Are USB speakers less prone to interference?

Thanks

MacPro 2.66(1,1), 8 Gb, X25-M + 4x1Tb, HD3870. MBP 2.2, 4 Gb, 128Gb SSD + 500 Gb, Mac OS X (10.6.2), 30" ACD, E4P eSATA, XP in Parallels, Vista Win 7 in Boot Camp, iPhone 3Gs

Posted on Dec 16, 2009 10:57 PM

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Answer 1

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louie

Level 4

2,950 points

Dec 17, 2009 1:54 PM in response to Mike Boreham

Interesting - usually it is the high gain (microphone) inputs that are susceptible to the GSM cell phone signals. Are you sure it it solely the speakers, not the Mac? For example, play an iPod through the speakers instead of the Mac and see if there is still interference.

You could try ferrite inductors on the input cable, too.
http://www.maplin.co.uk/Module.aspx?ModuleNo=32799

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Answer 2

Dec 18, 2009 2:16 AM in response to Mike Boreham

I haven't been able to solve this problem no matter what speakers I use, USB or otherwise.

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Answer 3

Mike Boreham Author

Level 4

2,096 points

Dec 18, 2009 2:40 AM in response to DaddyPaycheck

Oh well, thanks. At least should save me some effort/money.

Have you tried the ferrite inductor suggestion?

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Answer 4

louie

Level 4

2,950 points

Dec 18, 2009 8:46 AM in response to Mike Boreham

If interference is heard with USB speakers, too, I would suspect the source is the Mac and not the speakers. If so, the ferrite on the speaker cable wouldn't help, since the signal incursion is probably not at the speaker input cable. I don't seem to have the problem, although I seldom have my GSM phone closer than about 12 feet from my computer.

What sound input is selected on the Mac? Do you have another sound source to try with the speakers while running the phone? Tried booting the phone (to instigate a cell search) and moving it around in the vicinity of the speakers, cable and Mac? I may try this myself this weekend. It's a terrible problem in professional audio.

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Answer 5

Dec 18, 2009 3:49 PM in response to Mike Boreham

Nope. I use "airplane mode" a lot.

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Answer 6

Mike Boreham Author

Level 4

2,096 points

Dec 18, 2009 9:06 PM in response to Mike Boreham

Good tip about instigating searching (I actually did it by switching airplane mode on and off). It enabled me to do some proper testing, although still quite a random element. Doesn't happen every time.

What I found is:-

1. It happens even if the speaker lead is disconnected from the computer.

2. It only happens when the iPhone is set to 2G only (3G off ...as my wife's always is).

So one solution is to put her phone on 3G all the time.

I marked this solved because at one point in testing I convinced myself it didn't happen if the phone was more than eighteen inches from the right speaker (with the power input and amp), but after several tests which confirmed this, there was a loud interference with it four feet away...as if not all interference events are equal strength. So I am re-marking unanswered for now, although I have one solution.

Does this new info suggest any other options?

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Answer 7

Mike Boreham Author

Level 4

2,096 points

Dec 18, 2009 9:19 PM in response to louie

Message deleted....duplicate. The process of changing of "solved" to "unsolved" confused me. At first I thought the "comment" I wrote when changing status wasn't going to get posted, but it did.

Message was edited by: Mike Boreham

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Answer 8

louie

Level 4

2,950 points

Dec 18, 2009 10:02 PM in response to Mike Boreham

Mike Boreham wrote:

1. It happens even if the speaker lead is disconnected from the computer.
2. It only happens when the iPhone is set to 2G only (3G off ...as my wife's always is).

OK, now we know more - based on 1), it is the speaker alone. A wiser person would know the frequencies for 3G and perhaps be able to design a filter to install inside the speaker at the input cable, or experiment with shielding. Without doing that, the only practical thing I can see is the snap-on ferrite inductor. At least they are inexpensive, but the results are unpredictable.

My understanding is that cell phones vary their transmit power depending on tower signal strength. You may have to just do as you've described to minimize this interference.

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Answer 9

Mike Boreham Author

Level 4

2,096 points

Dec 20, 2009 9:22 AM in response to louie

Ferrite clip on doesn't make any difference.

Thanks for all the input. I am putting my wife's phone on 3G for now....see if she notices any adverse effects (battery, "no service", etc). She doesn't do anything with the phone where 3G benefits.

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