AtlasSound.com
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Specifications are subject to change without notice.
Owner’s Manual
AA240 Mixer Amplifier
1601 Jack McKay Blvd. • Ennis, Texas 75119 U.S.A.
Telephone: 800.876.3333 • Fax: 800.765.3435
Measuring Speaker Loads
Below is an ipedance load chart for the AA240. When measuring the load impedance prior to connecting the load to the amplifier, the
enclosed load chart will provide you the information to determine if the load or speaker system impedance is too low for the amplifier's
rating. In every install it is always recommended to measure the load first to be sure the system was installed correctly.
Measuring a Speaker System's Impedance.
Note: It is important to only use an Audio Impedance Meter and not a conventional volt/
Ω
meter.
A true audio frequency impedance meter is essential for reliable installation of background music and paging systems in residences,
offices buildings, and public areas. Avoid costly service calls and amplifier damage by verifying actual speaker system impedance prior
to operation. Unlike conventional volt/
Ω
meters, which measure DC resistance, an Audio Impedance Meter unit utilizes an internal fre-
quency oscillator to measure true impedance. It may also be utilized with 25V/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 or search the internet for Audio Impedance Meter.
Measuring 25V/70.7V Distributed Speaker Systems
Large distributed systems typically utilize 25.2V or 70.7V transformers (50V and 100V in Europe), to greatly ease the connection of
multiple speakers and facilitate long cable runs. These speakers are connected in parallel, as shown below, with total wattage ratings
added to calculate the overall rating of the system. Connecting this meter to a speaker arrangement such as this will provide the overall
impedance of the system. Using the following formula you can calculate the wattage. Simply put, when connected to a distributed sys-
tem, take the voltage of the system (normally 70.7V or 25.2V), squared, divided by the impedance displayed on the meter. Your answer
will be the total system wattage. This total wattage must not exceed the wattage output rating of the amplifier or damage may occur.
In this example the measurement for a 70.7V design with speakers of 10W, 30W and 60W, the system impedance would measure
close to 50
Ω
. Formula 70.7V x 70.7V = 4998, 4998 / 100W = 49.9
Ω
. If this speaker system load is connected to at least a 120W amp @
70.7V, the system will operate properly.
Note: It is always recommended to use a larger amp than needed with output power headroom of at least 25%.
AA240 Max Load Chart
Speaker Tap
AA240
4
Ω
4
Ω
25V
2.6
Ω
70.7V
20
Ω
100V
41
Ω
(10 W)
(30 W)
(60 W)
