silence the static on my imac's external speakers

March 7, 2007 4:01 PM

Audiophile-ter: I recently purchased a 20" dual core iMac. My EVENT TR6 monitors sit very close to the computer, input through a Firewire interface. I get noisy static from the Right speaker when the iMac is "thinking". What causes this, and how to remedy?

A few troubleshooting tests performed:
-unplugged firewire unit, problem persists
-unplugged speakers from any input with power on, problem persists
-moved iMac away from speakers, problem fades with distance
-switched cables, bought balanced speaker cables... doesn't fix it.
-while moving my firewire unit (Focusrite Saffire LE), I moved it inbetween the DVD slot on the right side and the monitor, and the static went away!

The simplest solutions, while disregarding budget, are to either:
- get a new, wider desk that provides more space between the computer and the monitors, or
- get speaker stands for upwards of $80 for them to sit farther away from the computer

But what the hell else can I do that doesn't require new furniture? Why does the iMac emit interference through the DVD opening of the case that produces noise in grounded studio monitors?

posted by blastrid to technology (5 comments total)

Can't necessarily fix it, but I can tell you the likely mechanism behind it. You say your monitor input is Firewire. That means that your monitors are not just speakers, but have at least a D to A and some amplification inside. Physically separating the speakers and the Mac reduces the noise, which means it's nothing to do with cables or grounding - the electronics in your speakers are picking up electromagnetic (radio) interference radiated directly by the Mac.

When you moved your Firewire unit in between the DVD slot and the monitor and the noise went away, that's an indication that the radio interference is escaping the Mac case through the DVD slot, and that physically interposing something or other with a grounded metal case was enough to reduce it to non-detectable levels.

So try putting a grounded sheet of metal between the noisy speaker and the Mac; maybe try sticking a layer of foil down that side of the speaker and wiring it to the shield on the Firewire plug.
posted by flabdablet at 4:17 PM on March 7, 2007 [1 favorite has favorites]

It would seem that your speakers may not have shielding or sufficient shielding. Without shielding they can pick up noise from the monitors and other closely positioned electronic equipment. You can move them further away. You can also wrap them in tin foil. This will have the added benefit of shielding them from alien/government listening, but it will be butt ugly. Usually the interference goes the other way, but these are powered speakers so more subject to picking up low level intereference and amplifying it. You could also try shielding the computer. Really, tin foil jokes aside, anything conductive which surrounds either the computer or speaker to make a Faraday cage should do, that or just move the speaker further away. A little extra stereo separation might sound good.
posted by caddis at 7:45 PM on March 7, 2007 [1 favorite has favorites]

Looking at the specs on the Event TR6's, I think it's worth pointing out that they DO NOT have a direct FireWire input. If I'm understanding you correctly, you're feeding them (using their XLR or TRS inputs) from the Focusrite, and furthermore, that you still get interference in them when the Focusrite is disconnected. Those monitors have amps in them, but no A/D circuitry---the DAC is in the Focusrite. (You, I'm sure, already understand this, but I'm putting here for the benefit of everyone else.)

So it's obvious you're getting some sort of EM interference from the Mac. I could think of a few solutions; the most elegant is probably to just buy some monitor stands and move the speakers further away from the Mac, and then route all the analog cables far from it as well. (So, you determine what the "minimum safe distance" is from the Mac in order to not get intereference, and you put the Focusrite and the speaker cables and the speakers themselves outside of that. There are decent monitor stands for about $90 on Zzsounds & Sweetwater.

The other thing, would be to try and create some shielding between the speakers and the Mac. This could take any number of forms. You could try grounded pieces of sheet metal between the Mac and the monitors, or maybe even some metal window-screen (if you can find any real metal stuff, and figure out a way to ground it). Optimally, you're going to want to build a Faraday cage of sorts around the Mac (with an open front), to contain its spurious emissions.

There is one other option that I could think of. You said that getting a bigger desk was an option, so I assume that you have the space to spread out, just not a desk that's big enough. If you only need to move the monitors out a few feet on either side, maybe you want to consider either wall-mounting them, or, just getting a big piece of plywood or MDF, or even just a big pine board (like a 1x12 or something), and laying it across the desk to create "wings" sticking out on either side, on which you can put your monitors. As long as you keep them balanced (and if you don't mind damaging the desk, I'd bolt it down), that might give you some extra space for cheap.
posted by Kadin2048 at 7:48 PM on March 7, 2007 [1 favorite has favorites]

Tin foil, Brilliant!

My long-term solution is definitely to get a larger desk to remove the noise, widen my stereo separation, and shit--just to have more working space on the surface.

The solution meantime, tin foil. After marriage (fall) we move out! Then, new desk...

Thanks for your responses, people. Very helpful in understanding the problem.
posted by blastrid at 9:29 PM on March 7, 2007

Or... perhaps contact Event and ask them about this? I've had powered Event "20/20 bas"s for 7? 8? years now, and they are not shielded. The Event guys told me in some support correspondence a while ago that I could purchase some new shielded drivers from them to replace the ones that came with mine for something like $200, but I didn't bother, since I seem to do ok even with the speakers about 3 inches away from my CRT's, on either side. Closer than that causes the CRT's to discolor. ;)

'Course if the solution is something like that, and you don't wanna spend any money (if you should even HAVE to, but that's another discussion), maybe you just wanna stick with the tinfoil.
posted by bitterkitten at 10:57 PM on March 7, 2007