Has anyone had luck with EMI abatement, specifically with regards to
room shielding? I am involved with a situation where, depending on
microphone location within an iso booth, noise will come and go
according to position. We are using all high quality components.
There are no influences originating from within the building. There
is, however, a direct line of sight to the Empire State Building.
I've been researching the use of grounded copper wire meshes to shield
an entire room and drain any EMI to ground. Can anyone recommend a
contractor, installer, or source for shielding materials? Much
thanks!

Randall Merrill wrote:
Has anyone had luck with EMI abatement, specifically with regards to
room shielding? I am involved with a situation where, depending on
microphone location within an iso booth, noise will come and go
according to position. We are using all high quality components.
There are no influences originating from within the building. There
is, however, a direct line of sight to the Empire State Building.
I've been researching the use of grounded copper wire meshes to shield
an entire room and drain any EMI to ground. Can anyone recommend a
contractor, installer, or source for shielding materials? Much
thanks!

Just thinking about how much it will cost you to construct an RF screen
room in your studio.

Are you sure it's RF? Do you have access to field strength meter or
someone you know with an RF spectrum analyzer to narrow it down?

And are you sure it's Empire State building and not somebody's wireless
thing one floor down? If it were, you could just talk them into moving
it across the room. Even buying them an alternate setup might be less
expensive in time and money.

Have you tried replacing the microphone, cable, and preamp with ones of
different brands, at least just to troubleshoot? Be sure to try a
different length of microphone cable.

Is your preamp and other gear properly grounded, and have you tried
additional grounding to chassis, besides the a.c. power cord?

Have you tried getting one or two of those ferrite filters that just
clamp on a cable, like what you see on the video cable for your computer
monitor, to clamp on the microphone cable? Do you know someone handy
with a soldering iron that could make you a little XLR-M to XLR-F
adapter with some additional RF filters in it to treat that one
microphone cable right where it goes into the preamp, or just open up
the existing XLR end that plugs into the preamp, and solder in some
components?

Randall Merrill wrote:
Has anyone had luck with EMI abatement, specifically with regards to
room shielding? I am involved with a situation where, depending on
microphone location within an iso booth, noise will come and go
according to position. We are using all high quality components.
There are no influences originating from within the building. There
is, however, a direct line of sight to the Empire State Building.
I've been researching the use of grounded copper wire meshes to shield
an entire room and drain any EMI to ground. Can anyone recommend a
contractor, installer, or source for shielding materials? Much
thanks!

There are some studios that use a full-room Faraday cage. You can get the
things constructed either with copper mesh or copper sheeting depending
on how low you need to go.

I'd make sure you don't have power line problems before doing anything
else. But check your noise and see if it's 29.97 Hz stuff... if so, it's
almost certainly residual frame trash from TV broadcasts rather than power
line junk at 60 Hz.

You might start here for information on shielded rooms and facilities:
http://www.eskimo.com/~joelm/tempestsource.html
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Try this. Build a short f-xlr to m-xlr jumper

In the female end wire a 82pf/100v ceramic disc cap between the case lug
and pin 2.

Wire another 82pf/100v cap between the case lug and pin 3.

Split the shield and wire one leg to the case lug and the other leg to
pin 1.

Connect the leads from the male side as normal. Solder the case lug
wires after all connections are made.

Eric

"RAMPS @ NAB: 4/20/04: Napoleons Bar, Paris Hotel"

Randall Merrill wrote:

Has anyone had luck with EMI abatement, specifically with regards to
room shielding? I am involved with a situation where, depending on
microphone location within an iso booth, noise will come and go
according to position. We are using all high quality components.
There are no influences originating from within the building. There
is, however, a direct line of sight to the Empire State Building.
I've been researching the use of grounded copper wire meshes to shield
an entire room and drain any EMI to ground. Can anyone recommend a
contractor, installer, or source for shielding materials? Much
thanks!

Paging Rick Ruskin...

You might see if you can Google-up some of his comments about dealing
with an environment full of RFI, EMI, and probably extra stuff.

http://www.google.com/advanced_group_search?hl=en

--
ha

(Randall Merrill) wrote in message . com...
Has anyone had luck with EMI abatement, specifically with regards to
room shielding? I am involved with a situation where, depending on
microphone location within an iso booth, noise will come and go
according to position. We are using all high quality components.
There are no influences originating from within the building. There
is, however, a direct line of sight to the Empire State Building.
I've been researching the use of grounded copper wire meshes to shield
an entire room and drain any EMI to ground. Can anyone recommend a
contractor, installer, or source for shielding materials? Much
thanks!


Do a search for "screen room"

How far away is the Empire State Building

Unless you are really close to it 1 mile) , I would say a screen room
is overkill.

Try some clamp on ferrite filters from Radio Shack that clamp over the
outside of the mic cables and will have NO effecct on the audio.
Place them near the mic pre input. More drastic measures require RF
filtering at the mic inputs. Anybody know of any commercially
avaialbe RF low pass filters designed for mics with XLR connectors.

If your problem is really RF from the ESB it would be VHF or UHF or
higher. EMI from AM modulated VHF and UHF TV stations would sound
like a 60 Hz buzz. (its actually 59.94Hz) EMI from FM radio stations
is a bit more obscure but you can usually hear the music as you move
the cables around a bit.

Mark

In Article ,
(Randall Merrill) wrote:
Has anyone had luck with EMI abatement, specifically with regards to
room shielding? I am involved with a situation where, depending on
microphone location within an iso booth, noise will come and go
according to position. We are using all high quality components.
There are no influences originating from within the building. There
is, however, a direct line of sight to the Empire State Building.
I've been researching the use of grounded copper wire meshes to shield
an entire room and drain any EMI to ground. Can anyone recommend a
contractor, installer, or source for shielding materials? Much
thanks!

EMI can come in through the air or through the ground.

Before you create a Faraday Shield, check out the grounds on your AC plugs
and look around for ANYTHING metal that can be removed.

I de-spooked a studio in DC once by finding the metal orchestral music stand
they were using as a copy stand was also an RF re-radiator.

All their gear was sort of plugged into different AC plugs which didn't help.

Do that and if you need more try using mic cables on which the shields are
connected at each end to the XLR shells.

The internet is a wonderful place. I just gave away at least $100 of
information.

Regards,

Ty Ford



For Ty Ford V/O demos, audio services and equipment reviews,
click on http://www.jagunet.com/~tford

Thanks very much for the reply!

Are you sure it's RF?
At this point I'm guessing it's not RF becauseI don't hear any radio
in the audio. It's buzz, though I haven't measured the periodicity.

Do you have access to field strength meter or
someone you know with an RF spectrum analyzer to narrow it down?
No, but I can borrow an oscilloscope.

And are you sure it's Empire State building and not somebody's wireless
thing one floor down?
I was told there aren't any wireless devices, motor rooms, etc. either
above or below, though I haven't seen for myself.

Have you tried replacing the microphone, cable, and preamp with ones of
different brands, at least just to troubleshoot?
I tried a different mic cable, two different U87s, and two different
Avalon mic pres.

Is your preamp and other gear properly grounded
Yes
and have you tried
additional grounding to chassis, besides the a.c. power cord?
No, but what should I ground it to? This installation doesn't have a
technical grounding scheme. Would a building structure or conduit be
sufficient?

Have you tried getting one or two of those ferrite filters that just
clamp on a cable
I will definitely try this

Do you know someone handy
with a soldering iron that could make you a little XLR-M to XLR-F
adapter with some additional RF filters in it to treat that one
microphone cable right where it goes into the preamp, or just open up
the existing XLR end that plugs into the preamp, and solder in some
components?
Yes, what should I use?

Thanks very much!
Randy

Thanks for the reply,

Do that and if you need more try using mic cables on which the shields are
connected at each end to the XLR shells.

Do you know offhand if a U87's body is grounded to pin 1 of the XLR or
not? I will definitely try this. Thanks,
Randy

Eric,
Thanks for the suggestion. I'll get a chance to test it tomorrow.
I'm just curious, why 82pF?
Thanks,
Randy

Randall Merrill wrote:

Are you sure it's RF?
At this point I'm guessing it's not RF becauseI don't hear any radio
in the audio. It's buzz, though I haven't measured the periodicity.

That is probably RF and not a magnetic field. You should measure the
period, though, so you know if it is RF from the power line or from
a TV transmitter.

Do you have access to field strength meter or
someone you know with an RF spectrum analyzer to narrow it down?
No, but I can borrow an oscilloscope.

That does not help. Ask your local frequency coordinator to come out
with a spectrum analyzer. In Manhattan it may be so filled with trash
that it won't be all that useful, but it's a good start.

And are you sure it's Empire State building and not somebody's wireless
thing one floor down?
I was told there aren't any wireless devices, motor rooms, etc. either
above or below, though I haven't seen for myself.

There always are. Somebody has a touch lamp or a light with a dimmer.
Somebody has a heater at their desk with a bad thermostat that is arcing.
Tracking these down usually turns out to be a matter of popping breakers
one at a time until you find the source.

additional grounding to chassis, besides the a.c. power cord?
No, but what should I ground it to? This installation doesn't have a
technical grounding scheme. Would a building structure or conduit be
sufficient?

Technical grounding is ALWAYS a good idea.

Have you tried getting one or two of those ferrite filters that just
clamp on a cable
I will definitely try this

If turning the guitar changes it, it's almost certainly coming in the
pickups and this will not help. But it's ALWAYS worth trying.

Do you know someone handy
with a soldering iron that could make you a little XLR-M to XLR-F
adapter with some additional RF filters in it to treat that one
microphone cable right where it goes into the preamp, or just open up
the existing XLR end that plugs into the preamp, and solder in some
components?
Yes, what should I use?

Shure will sell you the things.
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Randall Merrill wrote:
Thanks for the reply,

Do that and if you need more try using mic cables on which the shields are
connected at each end to the XLR shells.

Do you know offhand if a U87's body is grounded to pin 1 of the XLR or
not? I will definitely try this. Thanks,

It is not. Tying to the chassis is essential. You may consider using
a three conductor mike cable also, so the ground return is not carried
on the shield. Neumann recommends this.
--scott


--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Randall Merrill wrote:
Eric,
Thanks for the suggestion. I'll get a chance to test it tomorrow.
I'm just curious, why 82pF?
Thanks,
Randy

Well, everyone will have a different opinion, but I would have started
at 1000 pF (Radio Shack #272-126), tRC is still a couple orders of
magnitude away from audio. Why not yank it down?

If you want to go with the "82 pF" suggestion, Radio Shack 100 pF is
#272-123.

I would have said throw in a couple of ferrite beads in series before
the caps as well. Maybe 1K Ohm @100 MHz, DCR single digit Ohms, but I
don't see any at Radio Shack website. I'm used to my selection of
surface mount components. Someone else in here suggest a radial/axial
component. Or a common mode choke.

While I've got the Radio Shack site up on the browser, the snap-together
ferrite choke is #273-105. Get a couple. Cable end nearest preamp is
most important place.

Always, always walk into a Radio Shack with catalog number ready to
recite. Radio Shack sales people are clueless, but can look up a number
on the computer and b-line to the merchandise extremely quickly without
wasting your time, and you pre-empt any useless discussion by doing so.

Someone mentioned Shure. I see their A15RF, but it is only rated to 70
MHz and "$41.67". I suppose you could try it and return if it didn't
work. Obviously has a common mode filter in it, from the graphs.

All this assumes it comes down to "it's RF" and "the mic/cable" is the
pickup and you've done all the grounding things people suggested.

Scott Dorsey wrote:

You may consider using
a three conductor mike cable also, so the ground return is not carried
on the shield. Neumann recommends this.

Like those skinny brown things EV used to include in their mic boxes? I think I still have a couple of those out back...

Garth D. Wiebe wrote:

Someone mentioned Shure. I see their A15RF, but it is only rated to 70
MHz and "$41.67". I suppose you could try it and return if it didn't
work. Obviously has a common mode filter in it, from the graphs.

Shure will send you the schematic. It's a common mode choke and a couple
of bypass capacitors. You can find it for less than list price, too.
Considering what barrel connectors cost these days that's not so bad.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

In article writes:

You may consider using
a three conductor mike cable also, so the ground return is not carried
on the shield. Neumann recommends this.

Like those skinny brown things EV used to include in their mic boxes? I think
I still have a couple of those out back...

Did EV ever supply mic cables wired that way? I don't recall that, but
it would be nice.


--
I'm really Mike Rivers - )
However, until the spam goes away or Hell freezes over,
lots of IP addresses are blocked from this system. If
you e-mail me and it bounces, use your secret decoder ring
and reach me he double-m-eleven-double-zero at yahoo

Mike Rivers wrote:

In article writes:


You may consider using
a three conductor mike cable also, so the ground return is not carried
on the shield. Neumann recommends this.


Like those skinny brown things EV used to include in their mic boxes? I think
I still have a couple of those out back...


Did EV ever supply mic cables wired that way? I don't recall that, but
it would be nice.


Pretty sure they came with both my RE-15s and my RE-50 (mid-'80s purchases.)