Galaxy Audio CORE XP250 - Manual (Page 11)

Ohm’s Law and the CORE X250
The SPEAKER OUTPUT jacks on the front and back of the CORE X250 are designed to power the CORE PA10X or
PA15X and one CORE (or other brand) 8 ohm satellite speaker or two HOT SPOTs. Most professional-type speakers (like
the HOT SPOT) have two jacks which are wired
in parallel (meaning the signal can travel into one jack and out of the oth-
er). Think of each speaker as a “load” added to the amplifier. The greater the number of speakers, the heavier the load.
Adding too many speakers can overload the amplifier, causing it to overheat and distort. If the amplifier begins to distort, or
if it becomes hot to the touch, disconnect any extra speakers. One easy way to determine the load on the amplifier is to
use Ohm’s law, which states: “The total impedance of
N speakers in parallel is equal to the reciprocal of the sum of the re-
ciprocals. In equation form:
Where Z
1
is the impedance (or ohm rating) for the first speaker, Z
2
is the impedance for the second, and so on for every
speaker in the chain. This equation calculates the total impedance of the speaker system, which should NOT be lower than
the minimum impedance rating of the amplifier. The X250 is rated for loads as low as 4 ohms. Therefore, the total imped-
ance of the speaker system must be greater than, or equal to, 4 ohms. Anything less will overload the amplifier.
For one pair of speakers use the short form of the equation: the product of the two speakers divided by the sum of the two
speakers is equal to the total impedance or the equivalent impedance of the speaker system.
This equation may be used to calculate the equivalent impedance for additional speakers in two-speaker increments. De-
termine the impedance of the first two speakers, substitute Z total
for Z , and include the next speaker. Repeat the process
until all speakers have been included. The result should be the same as with the first method.
A word of caution: polarity rules must be observed when connecting multiple speakers. Polarity will not affect the Z, but
can affect the quality and volume of the sound. If you are having problems with any of these applications use Galaxy Au-
dio’s CRICKET Polarity and Continuity Test Set to check the polarity of your cables.
9
Z
1
• Z
2
Z
1
+ Z
2
Z =
1
Z (Total) =
1
Z
1
1
Z
2
+
1
Z
3
1
Z
4
+
1
Z
N
+ +