Home -> Church
Audio & Acoustics Glossary -> I
Church Audio & Acoustics Glossary
This glossary is being put online to help with unfamiliar
words when visiting this site. Since this is a web site devoted
to church audio and acoustics, the glossary will cover common
words used when talking about church audio and acoustics.
This is only one step beyond typical glossary listings, since
it's specific to churches. New words will be added as they come
up; if you have any suggestions, please
let us know!
There are a number of words that relate to churches in general,
as well as video and lighting terms. You usually need to know
a little of everything...
Many words don't have definitions yet, we're working on it.
This is a project in motion; it will be updated as time permits.
If you would like to contribute a definition for any words listed
here, just let
us know, thanks!
JUMP < - A -
B - C - D
- E - F - G
- H - I
- J - K - L
- M - N - O
- P - Q - R
- S - T - U
- V - W - X
- Y - Z - > JUMP
IEM (in ear monitor)
Resistance to AC (alternating current) flow through a wire
or circuit. Different from resistance which is used for simple
DC (direct current) circuits. Impedance is frequency dependant.
Abbreviated "Z" and measured in ohms.
Typical speaker impedance is 4 to 8 ohms, professional microphone
impedance is 200-250 ohms, consumer high-impedance microphones
are 600+ohms. Typical line-level inputs & outputs are
10,000 ohms (10K ohms). Video cable is 75 ohms per mile, common
computer coax cable is 50 ohms per mile.
A wire carrying an electrical current creates a magnetic
field around it. When that magnetic field penetrates into
another wire, it causes an electric current in the second
wire with the same waveform as the current in the first wire.
This magnetic transfer is called inductance.
This is particularly bad in audio when AC power lines or amplifier
speaker lines are run next to (parallel) other low-current
carrying lines (microphone/line level). The same effect occurs
if the lines are coiled and on top of each other. The best
defense against this type of interference is to keep different
current carrying cables away from each other; run them in
different conduits. If they need to cross each other, do so
at 90-degree angles.
Elecromagnetic waves (light) that can't be seen by humans
because they're of a much higher frequency than we can see.
Litterally, beyond red. Often used for wireless devices such
as remote controls and hearing impaired systems. Such systems
can be interfered with by outdoor light, candle light, and
objects in the path of the transmitter to reciever. Abbreviated
The point where a signal is put into a given component or
circuit. A microphone is connected to the input of a mixer.
Outputs always go to inputs. One must be careful to make sure
the output of one device can be handled by the input of another.
There are different signal levels available, and even if the
connector is the same, the signal level may not be. Proper
adapters that change the physical connector and the electrical
signal characteristics must be used.
Term used for gain control.
see gain, def. 4
A point in the signal path that allows connection of an external
device. Typical connections are via a single 1/4" TRS
jack which function as output AND input connections. The connector
carries both the signal being sent from the mixer as well
as the signal returning into the mixer. For example, on a
mixer there may be an insert jack on each input channel. You
might use the insert jack on a particularly hot (loud, explosive)
vocal to connect a compressor. Other devices that are commonly
used with insert jacks are reverb processors and equalizers.
The amount of extra gain or loss a device will incur to an
audio signal. How much a device will affect the signal by
just being in the signal path.
1. Acoustics: the disruption of normally smooth sound waves.
Comb filtering is an example.
2. Radio Frequency: reception of secondary or unintentionaly
radio signals on the same frequency as the intended primary
3. Audio Signals: addition of electromagnetic signals into
the audio signal such as hum or buzz.
When two or more radio frequency (RF) signal mix. The mixing
can produce a summed, difference, or harmonic multiple frequency.
The more wireless systems being used in an area, the higher
the chance is that there will be IM trouble.
Inverse Square Law
The name given to a law of physics which states "for
each doubling of distance a sound wave travels along a path,
the level of sound will drop to 1/4th (the inverse of the
square of the distance)". Doubling the distance reduces
the sound pressure level (SPL) by 6dB.
The lines on a plot (map) showing continuous level. In a
speaker plot, it shows the pattern where the sound is a given
level lower than the direct center (on-axis) at a given frequency.
For microphones, the isobars on the plot show the relative
sensitivity at different angles off axis (based on frequency).
Usually isobars are given in increments of 3 or 10dB.
Keeping two (or more) items apart from each other. This can
include cables, chassis, etc. Keeping an audio signal in an
mixer's channel strip out of adjacent channel strips. Also
can mean keeping sound out of a certain area.
A transformer with a 1:1 (one-to-one) power ratio. That is,
the signal level going in equals the signal level coming out.
Commonly seen used in direct boxes or microphone line splitters.
This allows the same signal to drive different inputs such
that they two inputs don't interfere with each other, but
are isolated from each other.
No, we didn't write all of these definitions ourselves. What
we did was take a word, read several definitions from books
and listings on the internet, then write our own version. In
some cases we used phrases word-for-word, but usually we reworded
the definition to be more clear and applicable to church audio
Glen Ballou, Handbook for Sound EngineersThe New Audio
Cyclopedia. Howard W. Sams & Co., MacMillan, Inc. 1991
Don & Carolyn Davis, Sound System Engineering. Howard W.
Sams & Co., MacMillan, Inc. 1997
Glossary of Wireless Microphone Terms. Lectrosonics, http://www.lectro.com/wg/wgglos.htm
John Eiche, Guide to Sound Systems for Worship. Hal Leonard
Publishing Corp, 1990
Tim Vear, Microphone Selection and Application for Church Sound
Systems. Shure Brothers, 1996
Tim Vear, Selection and Operation of Wireless Microphone Systems.
Shure Brothers, 1994
Microphone Techniques for Music, Shure Brothers, 1994
Joe De Buglio, Why Are Church Sound Systems & Church Acoustics
So Confusing?, 1998
various handbooks and users manuals for specific equipment especially
by Mackie, Spirit, Shure, and Rane.
EXTREME thanks to Stephen Lund of LaRue Electrical Specialties,
who began writing a glossary of terms, never fully completed
it, but has passed his words and definitions on to us for use
in this glossary. There are many definitions he had written
that were so simple to understand, we took them as-is without
any editing. We finally finished it! (...almost) Thanks a million,