Why Are Church Sound Systems & Church Acoustics So Confusing?

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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!

 

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I

I

    Symbol used to indicate amps. (amps=current/wattage)


IEM (in ear monitor)


impedance

    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.


impedance balancing


inductance

    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.


infra-red

    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 IR.


inline


input

    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.


input attenuator

    Term used for gain control.
    see gain, def. 4


insert

    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.


insertion gain/loss

    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.


instrument (lighting)


instrument level

    Term to describe audio signal levels which fall between -20 and -10 dBU.


intelligibility


interference

    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 signal.
    3. Audio Signals: addition of electromagnetic signals into the audio signal such as hum or buzz.


intermodulation

    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.


IR

    see infra-red


isobar

    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.


isolation

    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.


isolation transformer

    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.


 

Sources

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 and acoustics.

Glen Ballou, Handbook for Sound Engineers–The 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 11/9/98
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, Stephen!