Re: Ribbon Mic picking up Radio Frequency Interference

On Sep 13, 2:39 pm, Eeyore <rabbitsfriendsandrelati...@xxxxxxxxxxx>
wrote:
Truth wrote:
Eeyore <rabbitsfriendsandrelati...@xxxxxxxxxxx> wrote:

It sounds like they've been pumping you full of nonsense.

No they are correct. When my LCD monitor is on I can hear a definite
hum or buzz. When I turn it off it goes away, so I turn it off while
recording.

That proves the sum total of nothing other than poor product design. I know, I'm a
pro-audio designer and pretty expert in RF interference matters actually.

Because the microphones use magnetism to function they are
prone to these problems.

Rubbish. The fact the mics have a magnet inside is totally and completely irrelevant to
RF pickup. Where the hell do you get this crap from ? What is especially relevant by the
way is inductance and 'loop area'.

They sound good when they work,

As some badly designed equipment (especially esoteric hi-fi) often does.

Graham

I got it from here:

http://svconline.com/mag/avinstall_understanding_controlling_rf/

And also reading on Royers site the documentation for the mics.

Snip from Royer:

"All ribbon microphones employ magnetic components as a basis for
their operation. All microphones that utilize magnets are somewhat
susceptible to induced magnetic radiation, especially from alternating
magnetic fields such as those found in motors, transformers and video
monitors. These fields can be strong enough to induce an alternating
electric current in microphones that in turn gets amplified by the
preamplifier. This is the same effect that plagues electric guitars,
especially those with single coil pick-ups. If you experience this
phenomenon, locate the source of the radiated field and move it away,
shut it off, or simply move the mic away from the offending device."

I'll be the first to admit I don't understand entirely how this all
works exactly, I'm not an electrical engineer, but the mics do have
problems with things such as those I mentioned. It's not rubbish as
you suggest, I've experienced the video monitor problem first hand.
It seems the RF and magnetism is all connected actually, though this
particular problem is different from the usual hum and buzz... here's
a snip from the article:

"Unintentional RF sources are most commonly devices that produce an
electrical spark. Sparks are potent RF generators-before vacuum tubes,
they were the heart of radio transmitters-that splatter energy over a
wide frequency spectrum. Any wiring connected to the spark source not
only conducts the RF but also acts as a transmitting antenna to
radiate it. Common sparking sources include electric welders, brush-
type motors, relays and switches of all kinds. Less obvious sources
include arcing or corona discharge in power line insulators (common in
seashore areas or under humid conditions), malfunctioning fluorescent
or neon lighting and automobile spark plugs. Lightning is the ultimate
spark and a well known producer of momentary interference to virtually
anything electronic.

Other unintentional RF generators are devices that abruptly interrupt
current flow using some form of electronic switching. The most common
examples are light dimmers, fluorescent lights, TV or computer CRT
displays and any piece of equipment using a switching power supply or
"clock" oscillator (computers and other digital devices). The RFI
source may be in the same room as your system or, worse yet, it may be
a part of your system.

RFI symptoms The tolerance of equipment to RFI depends largely on how
well it is designed. Generally, symptoms will appear when sufficient
RF energy reaches an active device-IC, transistor, tube-inside the
equipment. The energy can arrive in two ways: radiation or conduction.
As it travels through the air, internal equipment wiring can act as a
receiving antenna and deliver RF voltages directly to an active
device. This is most common in equipment with plastic or wood
enclosures that have no RF shielding ability. Because any wire can
become a receiving antenna, RF energy can also be conducted into the
equipment's active devices via any wire leaving or entering the
equipment. Interference can also arrive via any wire coming into the
building. Because power, telephone, CATV and even driveway intercom,
landscape lighting, or outdoor loudspeaker lines also behave as
outdoor antennas, they are often teeming with AM radio signals and
other interference. The most troublesome sources, however, are
frequently inside the building where the interference is distributed
via the power wiring. At high frequencies, a building's power wiring
behaves like a system of misterminated transmission lines gone
berserk, reflecting RF energy back and forth throughout the power
wiring until it is eventually absorbed or radiated. The RF does not
just follow the green ground wire back to the earth ground rod and
magically disappear.

RF power line noise is coupled through equipment power supplies into
system ground conductors. Therefore, significant noise voltage will
inevitably exist between the chassis grounds of any two devices in AC-
powered systems, whether safety grounded or not. This is the dominant
noise source in most systems, not noise picked up by cables as is so
widely believed. When this noise flows in the shield of unbalanced
signal cables, the voltage drop directly adds to the signal as shown
in Figure 1."

.

Relevant Pages

  • Re: Mains filters
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  • Re: Power Line Noise
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  • Re: Power Line Noise
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    (rec.radio.cb)
  • Re: Power Line Noise
    ... It's nice to have that noise gone out of your ears no doubt. ... Its a add on goof ball scheme, that getting more attention then BPL has done good. ... A power grid system has a number of maintenance crew who keep it running. ... What are the equipment, installation, training, test equipment, maintenance costs? ...
    (rec.radio.cb)
  • Re: Power Conditioners?
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    (rec.music.classical.recordings)