DIY EMI Shielding for soundcards?

[Raptor550]

I have noticed newer sound cards having an "EMI" shield. They look like a little pieces of tin or something around the case. I do not know how much these shields add to the product, but several cards have a SNR over 117! http://dodevice.com/asus-xonar-d2-sound-card/

I was wondering , what stuff could be used to make an EMI sheild? I mean, I doubt that wrapping my soundcard in tin foil would be helpful. don't computer electronics come in little plastic bags made to shield from static, could those be used?

I know next to nothing about this, just looking for ideas.

[ThomasW]

Google for 'Mu metal'

[Amphiprion]

Actually, wrapping your sound card in tinfoil could be helpful. But it's likely you would just short out something on the card. Seriously, don't do this. How would you test the results?

[JonP]

Actually, wrapping your sound card in tinfoil could be helpful. But it's likely you would just short out something on the card. Seriously, don't do this. How would you test the results?

Yeah, it's effectively what you want to do, just practically not a very good idea.

Mu metal would be best, since it magnetically shields, besides just electically.
But a pure electric shield (like aluminum) would probably keep most noise out.

You would want to make a "can" of some thin metal that covers all the circiutry, and tie it to the ground of the circuit board at several places around the edge. Wouldn't be a bad idea to cover the back side of the board, too. Shorting would be deadly to the card, so you'ld want to cover the inner sides with something to insulate them.

Very custom work, with the need to ground it in several places that weren't designed into the board... Possibly tough...

Sound difficult enough, yet? :W

[Amphiprion]

Is Mu Metal effective at RF or does it just have real high permeability to DC fields?

A simple improvement method is just to move the card away from anything that is expected to have high frequency, high current switching going on (i.e. the power supply).

[Operandi]

I think most of the "noise" comes from the system bus, not RF interference so I don't think a shield is going to accomplish much if anything.

Besides if it was effective you'd see on pro level cards first not a consumer level card the like the Asus.

[Florian]

The 'EMI-shield' on the Asus sound card is just marketing BS :. To get an effective EMI-shield over a wide frequency range you would need:

- A closed metal box
- EMI filters on all cables running in or out of the box
- A circuit without onboard EMI problems

Not easy to realize for a sound card .

[Wilk]

Saying that it is just marketing BS is a little ruff. Where I doubt it is a completly effective sheilding system. If it is even reasonably executed it will make a measureable diffence to the noise floor of the card.

Most high end test and measurement equipment is built off of a computer based sytem any longer. That sheilding method is used alot. I have vector sig gens built on a computer base that have noise floors in the -140dbc range.

There also will be much more "noise" in the air inside a computer than on the "Bus". I would be willing to bet that 10-20% of the regular smt componets on a current motherboard are there for filtering. I thas been like that since the early P4 chips, and the introduction of DDR ram. The rise times of pulses generated by current computers requires a very noise free transmission path, or they just flat out won't be registered.

[Hank]

I work at a company that has been doing electronic component and PCB shielding for many years, principally via the "static bags" that protect populated PCB's. A static bag encompassing a sound card MAY help. Operandi has a point, but Wilk is correct in that modern motherboards filter the HECK out of bus noise - as he implies, they HAVE to. Try a static bag over the card - cheap test. Not here to sell, just to learn from the gurus.

[JonP]

I work at a company that has been doing electronic component and PCB shielding for many years, principally via the "static bags" that protect populated PCB's. A static bag encompassing a sound card MAY help. Operandi has a point, but Wilk is correct in that modern motherboards filter the HECK out of bus noise - as he implies, they HAVE to. Try a static bag over the card - cheap test. Not here to sell, just to learn from the gurus.

Static bags have a conductive layer inside... but it is very thin, and of a pretty high resistance. (generalizing here) Just to dissipate static charges you can get by with very high resistances, tens or hundreds of Meghohms. This would make them less efficient as a RF shield. Not to say it wasn't a good idea. Just I'd think that the bag material would not make the tightest Faraday Cage due to it's properties. Hmmm, maybe one of those aluminized Mylar balloons might be better... Whatever it is, you'd need to make a good connection to the ground. Otherwise, it's just a big antenna , maybe picking up more noise and transferring it to your circuits then they had before.

OTOH, there are sound cards out there that approach or pass -120dB noise floor, WITHOUT needing a shield around them... so maybe we're trying to solve a problem that dosen't exist... Now, high end test equipment with a -140dB floor... yeah, it probably NEEDS shielding to get there. But with good bypassing and filtering of power, good board design... I'd think about as good as you could expect from audio DAC/ADC chips could be had without shields in a PC. I'm seeing nearly that good on my Delta 410 right now...

[Florian]

Saying that it is just marketing BS is a little ruff. Where I doubt it is a completly effective sheilding system. If it is even reasonably executed it will make a measureable diffence to the noise floor of the card.

Yes, calling the shield BS was a little ruff. But looking at the pictures in the review on bit-tech.net, I think the the ground connection of the shield is not very well executed. I really don't think it makes a measurable difference.

[joecarrow]

Have you considered an off-board USB or firewire sound card? If we were talking about acoustic noise, it would make more sense when someone says "Hey, this backup generator in my living room is killing me! Any advice on mufflers?" to suggest that they just move the noise source away from where it will cause problems.

[dwk]

Okay, maybe I'm missing something but wouldn't you think the shield would be more effective if placed *towards* the source of noise, rather than facing the side of the case? In a typical configuation, the backside of the board would be facing the PS, cpu, vid card (as in review photos) etc, and the backside is unshielded. Makes little sense.

Leaving aside the wierd asymmetries in some of the tests, the performance isn't bad. However, it's no better than the Emu 1212 which is simply a well executed conventional card - no external shielding. So, I certainly don't see any compelling reason to think it's more than cosmetics (unless it's there to reduce *emitted* noise, which would be ironic)

I have wondered whether something like putting a grounded blank PCI proto board in the slot(s) surrounding the soundcard might have some sort of shielding effect, but I've never tried it and haven't really thought through the idea. My 1820M is currently performing well enough that this sort of idea isn't climbing too far up the todo list.

[Wilk]

The sheild is in the right place. It needs to be as close as possible to what would be the most likey reciever to any noise. In this case it would be the componet side of the board. I will agree after taking a better look of the pictures in that link that this paticular sheild is not a great design. Not nearly enough ground connections, and fairly large gaps in the enclousure for the amount of frequencies involved in EMI sheilding inside a computer. I am sure it is making a positve impact on the noise floor, but I am just as sure that someone could do a much better job. Keep in mind though this is a sound card marketed for Gamers so it is probably going to preform quite well in that task.

I would have to agree with the idea of a usb or firewire being the best possible solution for a better noise floor. If you need to improve on that still. Take the case to the external setup, and line the inside of it with conductive adheasive copper tape. Make a few connections to ground, and put it back together. That'll buy you another couple of db for the floor at most frequencies.