5.Next, calculate the overall paralleled impedance with the following formulae: ZO = 1 ⎟ [(1⎟Z1) + (1⎟Z2) + (1⎟ZN...etc.)]
ZO = overall paralleled impedance
Z1 = 1st paralleled group after S setting Z2 = 2nd paralleled group after S setting
ZN = additional paralleled groups, when used.
Since only two paralleled groups are used in this example, the calculation is as follows: ZO = 1 ⎟ [(1⎟8) + (1⎟9.12)] = 4.26 Ohms.
Since this yields more than 4 Ohms, the S4 setting for the 4 Ohm group and the S8 setting for the 8 Ohm group are the correct ones to use.
Example 2:
2 pairs of 4 Ohm, 3 pairs of 6 Ohm and 3 pairs of 8 Ohm wall speakers are to be used with eight 760's in an
1. | Calculate the total paralleled impedance of | 4 | Ohm | group | first, | by | dividing | 4 | Ohms | by | 2. | ||
| 4 | ⎟ 2 | = 2 Ohms. |
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2. | Multiply 2 by 4 (for the S4 setting) = 8 Ohms. |
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3. | Calculate the total paralleled impedance of | 6 | Ohm | group | next, | by | dividing | 6 | Ohms | by | 3. | ||
| 6 | ⎟ 3 | = 2 Ohms. |
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4. | Multiply 2 by 8 (for the S8 setting) = 16 Ohms. |
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5. | Calculate the total paralleled impedance of | 8 | Ohm | group | next, | by | dividing | 8 | Ohms | by | 3. | ||
| 8 | ⎟ 3 | = 2.67 Ohms. |
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6.Multiply 2.67 by 8 (S8 setting) = 21.36 Ohms.
7.Next, calculate the overall paralleled impedance ZO. Since three paralleled groups are used, the calculation is as follows:
ZO = 1 ⎟ [(1⎟8) + (1⎟16) + (1⎟21.36)] = 4.27 Ohms.
Since this yields more than 4 Ohms, the S4 setting for the 4 Ohm group, the S8 setting for the 6 Ohm group and the S8 setting for the 8 Ohm group are the correct ones to use.
Impedance Setting Tips
1.You may use the above method to calculate the correct impedance matching condition for practically any combination of speakers and 760s.
2.Use the lowest "S" setting possible consistent with the requirement to keep above the minimum safe operating load impedance for the amplifier. You may have to try 2 or 3 values of "S" for each impedance
group and recalculate the overall paralleled impedance ZO each time, before you arrive at the final correct value.
3.When you test the system, you may find volume differences between the impedance groups when all 760s are set to max. volume. This is normal and is usually not a problem, since the user will be listening at lower levels most of the time. If you feel it necessary to even out the volume levels, move the "S" jumpers to the next higher number on the 760s that feed the loudest group.
NOTE: While speakers of differing impedance can be accommodated using these procedures, it is highly recommended you not do so on a regular basis. The easiest and best performing installation is achieved by using speakers of the same impedance throughout the entire system, referring to the charts for the jumper "S" settings.
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