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Welcome to our Technical page. This section gives you a
few simple answers to FAQ. We hope that this information will be of help to
you.
Wireless microphones & In-Ear monitors.
When choosing a wireless microphone or In-Ear system, keep
in mind that as a general rule, the more expensive a system is, the more
durable it will be. This is especially important in live music where movement
and sweat create a real tough environment for any microphone and r.f
transmission system .
UHF vs. VHF Wireless Microphone & In-Ear Systems transmit sound
using VHF (Very High Frequency 169-215 MHz) or UHF (Ultra High Frequency
600-900 MHz) radio & TV frequencies. The VHF band of frequencies is more
crowded and therefore make VHF wireless microphone systems more susceptible
to interference. Also, more susceptible to electrical noise.
A UHF wireless microphone or In-Ear system, although slightly more expensive,
will give you more reliable performance well into the future. The good news
is that UHF prices are being driven down as new technology arrives.
Remember, if you run more than one wireless microphone system at the same
time in the same room, they each need to be on different frequencies.
Frequency Planning
When using two or more Radio Microphones or In-ear systems in one place it is
important to consider planning the radio frequencies you plan to use. We can
calculate the best set of frequencies to use for the venue and we can take
into account local TV and Radio transmitters as well as any other
transmitting devices that are likely to be used in the same venue. These can
also affect the performance of multi-channel radio systems even if they are
working on an entirely different frequency. We offer this service free of
charge when systems are sold or rented through us and we can guarantee that
systems from Wireless Mics and Ears will operate to the best possible
standard.
In-Ear Monitors
What are the advantages in using In-Ear Monitors
There are several advantages and here are a few
Improved Sound
- bring monitors closer to the performer
- front of house sound improved with no loudspeaker monitors
More Mobility
- performer is not “tied” to a monitor loudspeaker
- monitor mix can be consistent regardless of new venue acoustics
Reduces Feedback
- loudspeaker monitors present more feedback potential
Hearing Protection
- overall stage volume is reduced, allowing the user to perform
with lower sound pressure levels at the ear
Who can use In-Ears Monitors
Pro & semi-pro musicians, Broadcasters, Classical Concerts performers,
Studio monitoring, Theatre Religious facility, Anyone else that needs to
monitor audio
Where can I buy systems from ?
Wireless Mics & Ears 01621 843200
info@wirelessmics.co.uk
An Audio
Frequency Induction Loop System (AFILS) comprises a cable in the form of a
loop connected via an amplifier to one or more sources of sound signals. In
simple terms an AFILS can be compared to a transformer with the loop cable as
the primary and the hearing aid as the secondary.
The amplifiers manufactured by SigNET are
constant current drive and specifically designed for AFILS, they produce an
audio frequency electric current in the induction loop cable, causing a magnetic
field to be produced. This magnetic field is a reproduction of the signal
feeding the amplifier and can be picked up by suitable receivers, such as the
SigNET RXTI or hearing aids equipped with a 'telecoil' and an 'M-T' or
'M-MT-T' switch.
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Micro-buds
E1
Shure e2
Using a guitar on a belt-pack
wireless system.
Tips for you to remember.
Avoid overloading the body-pack transmitter.
Adjust volume of receiver identical to the original
output level of the guitar.
If the signal out of the receiver is exactly like the original guitar signal,
you will get a similar or a close characteristic in sound and performance as
with a guitar cable.
In some cases, the input signal of the body- pack transmitter must be
drastically attenuated to avoid clipping of the audio signal.
Choose a crystal controlled wireless body-pack rather than a
Synthesised control type, for the following reason:
A PLL system (synthesised controlled system) checks the carrier frequency the
whole time. If there is a drift, the synthesiser will try to correct it by
sending out a control voltage to the VCO.
Very low audio frequencies can be misunderstood as a drift in the
carrier. Therefore the control circuit tries to fight against it.
In the background of the audio signal you will hear another sound together
with the audio signal alternating oscillation. The old Shure EC1 together
with a bass guitar was a typical example for that occurrence.
To protect PLL systems against this risk, low pass filters are required.
The roll off for PLL systems has typically to start at higher frequencies
than for a crystal controlled system. That is for example the reason why the
Shure crystal controlled UT Series has a much better low end performance than
their PPL U and Premier Series.
Another reason for the bass roll off is to protect the compressor circuit,
which needs some protection against sub-audible signals.
The disadvantage of a crystal controlled design is that you
normally only get one or maybe two channels. Never the less, the crystal
system should sound better, particularly on bass guitar.
Typical Noise Levels
Sound Source Level (dB SPL)
Heavy Street Traffic (5 feet)
90
Cabin of Jet Aircraft at Cruise 80
Vacuum Cleaner (6 feet)
70
Car (60 mph, 90 feet)
65
Average Suburban Home (night)
50
Quiet Auditorium
40
Quiet Whisper (6 feet)
35
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The
inverse square law (PAG)
For those of you who read our mailing
on Microphone Conference Mixing, below we give the PAG equation.
A printed or MS Word (via E-Mail) full version of the PAG equation is available
upon request at : info@wirelessmics.co.uk
Note. This equation describes what happens in so-called “free field” and does
not take into account interference from things like reflected sounds or room
acoustics. Nether the less, it will give you a good understanding of what to
expect.
Remember this:
If the calculated results are good and the room acoustics are also good, then
your sound system should work just fine.
If the results are poor, room acoustics are bad, then your sound system will
not work very well.
PAG= 20 log D1 - 20 log D2 + 20 log Do - 20 log Ds
D1 = distance from microphone to loudspeaker.
Do = distance between the talker and the farthest listener.
D2 = distance between the loudspeaker and the farthest listener.
Ds = is the distance between the talker and the microphone.
Get your LOG calculators out and have a go.
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Predicting
speech to background noise ratio
A microphone is the first component
in any speech recording or transmission system. Its function is to convert
acoustic sound waves into an equivalent electrical signal. This signal can
then be recorded, transmitted, amplified, or modified. However, a microphone
cannot effectively sort out desired "noise" (speech) from undesired
background noise. Also, a microphone cannot improve the acoustic environment
in which it is placed.
What are acceptable speech to noise ratios?
Fundamental psycho-acoustic research states that intelligibility is a
function of speech to background noise ratio.
· If speech level is 0dB to 10dB above background
noise level, intelligibility will be unacceptable to poor.
· If speech level is 10dB to 20dB above background
noise level, intelligibility will be poor to fair.
· If speech level is 20dB to 30dB above background
noise level, intelligibility will be fair to good.
· If speech level is 30dB to 50dB above background
noise level, intelligibility will be good to excellent.
How to predict if speech will be intelligible at the microphone location.
1. At the desired mic location, measure the Sound
Pressure Level (SPL) A weighted. Make certain all background noise sources
are operating, e.g. air conditioning, fluorescent lights, equipment cooling
fans.
Example: Background noise measures 46dB SPL A weighted
2. Measure the distance (in feet) from the farthest
talker location to the mic location. Assuming that the talker produces 68dB
SPL at 1 foot, use this formula: 68 - [(Distance in feet) log x 20] This
provides the SPL of the talker at the mic location.
Example: Farthest talker is 8 feet from microphone. Working out the formula
gives:
log of 8 = 0.9
0.9 x 20 = 18
68 - 18 = 50dB SPL
3. Subtract the background noise SPL from the talker
SPL at the mic location. Compare the result with the speech to noise ratios
listed above.
Example: 50dB SPL(talker) - 46dB SPL (room noise) = 4dB This is unacceptable
to poor intelligibility.
What to do if the predicted intelligibility needs to be improved?
1. Move the microphone closer to the talker
2. Make the room quieter via acoustical solutions
3. Both of the above
4. Accept the predicted level of intelligibility
THERE ARE NO OTHER SOLUTIONS!
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Microphone Sensitivity Rating
What is microphone sensitivity?
A microphone sensitivity specification tells how much electrical output (in
thousandths of a volt or "millivolts") a microphone produces for a
certain sound pressure input (in dB SPL). If two microphones are
subject to the same sound pressure level and one puts out a stronger signal
(higher voltage), that microphone is said to have higher sensitivity.
However, keep in mind that a higher sensitivity rating does not
necessarily make a microphone better than another microphone with a lower
sensitivity rating.
What is "dB SPL"?
The term "dB SPL " is a measurement of Sound Pressure Level (SPL)
which is the force that acoustical sound waves apply to air particles.
As a person talks or sings, SPL is strongest near the mouth and weakens
as the acoustical waves move away from the person. As reference levels,
0 dB SPL is the quietest sound a human can normally hear and 1 dB is the
smallest change in level that the human ear can detect. For comparison,
at three feet, speech conversation level is about 60 dB SPL and a jackhammer's
level is about 120 dB SPL.
 
Wireless Mics. & Ears
A division of Teleconference Business
Systems Limited, Unit 2, Heybridge Unit 19C, Bentalls
Shopping Centre,
Heybridge, Maldon, Essex CM9 4GD United Kingdom
Tel. (44)
01621-843200. Mobile 07802-363292.
E. Mail info@wirelessmics.co.uk
www.wirelessmics.co.uk
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Phantom power
Phantom power is a DC voltage (usually 12-48 volts) used to power
the electronics of a condenser microphone. For some (non-electret) condensers
it may also be used to provide the polarizing voltage for the element itself.
This voltage is supplied through the microphone cable by a mixer equipped
with phantom power or by some type of in-line external source. The voltage is
equal on Pin 2 and Pin 3 of a typical balanced, XLR-type connector. For a 48
volt phantom source, for example, Pin 2 is 48 VDC and Pin 3 is 48 VDC, both
with respect to Pin 1 which is ground (shield).
Because the voltage is exactly the same on Pin 2 and Pin 3, phantom power
will have no effect on balanced dynamic microphones: no current will flow
since there is no voltage difference across the output. In fact, phantom
power supplies have current limiting which will prevent damage to a dynamic
microphone even if it is shorted or miss wired. In general, balanced dynamic
microphones can be connected to phantom powered mixer inputs with no problem.
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