Atlas MA60G Owner's Manual - Page 9

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Owner's Manual

Measuring a Speaker System's Impedance

Note: It is important to only use an Audio Impedance Meter and not a conventional Volt/Ohm meter.

A true audio frequency impedance meter is essential for reliable installation of background music and paging systems in residences,

office buildings and public areas. Avoid costly service calls and amplifier damage by verifying actual speaker system impedance prior

to operation. Unlike conventional volt/ohm meters, which measure DC resistance, an Audio Impedance Meter unit utilizes an internal

frequency oscillator to measure true impedance. It may also be utilized with 70.7V and 100V speaker line transformers, L-pads and

matching Impedance volume controls. There are several Audio Impedance meters on the market, if you need to buy one we suggest

going to MCM Electronics, Parts Express or search the internet for "Audio Impedance Meter".

Measuring 70.7V or 100V Distributed Speaker Systems

Large distributed systems typically utilize 70.7V (North America) or100V (Europe) type system to greatly ease the connection of

multiple speakers and facilitate long cable runs. Shown below are speakers connected in parallel with wattage ratings to calculate

the overall load of the system. Connecting an Audio Impedance Meter to a speaker arrangement such as this will provide the overall

impedance of the system.

Using the following formula you can calculate the load impedance from the speaker selected wattage. The accumulative wattage of

the speaker system must not exceed the maximum wattage output rating of the amplifier or damage may occur. In this example the

measurement for a 70.7V design with three speakers of 15W each, the system impedance would measure close to 111Ω. Formula

70.7V x 70.7V = 4998, 4998 / 45W = 111Ω. The amplifier power requirements would be at least 60W for the system to operate

properly. Note: It is always recommended to use a larger amp than needed with power headroom of at least 25%. Calculate the load

impedance and compare it to the meter's audio impedance reading. Note: They will never be the same due to the additional wire

impedance, but if they are within 10% of the maximum impedance rating or if the impedance is higher than the maximum rating,

proceed connecting the load to the amplifier. If they are not recheck your speaker taps or check for shorts.

MA40G / MA60G

Mixer Amplifier

1601 Jack McKay Blvd. • Ennis, Texas 75119 U.S.A.

Telephone: 800.876.3333 • Fax: 800.765.3435

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Specifications are subject to change without notice.

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