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Discussion in 'Amps and Cabs [BG]' started by dfreeman, Oct 17, 2002.
I have a 4x10 that is 8 ohms, what if I get a 1x15 that is 4 ohms? How many ohms will I have total?
I'll save you the multiple "do a search, this has been done before" replies.
Total Ohms will be approximately 2.67
1/Ohm1 + 1/Ohm2 + .... = 1/OhmTotal
=>1/8 + 1/4 = 3/8
=> 8/3 = 2.67 Ohms
2.67 ohms isn't a safe load for most amps. Your best bet would be to get an 8 ohm 1x15, making your total load 4 ohms, when used with the 4x10.
To calculate the impedance seen by the amp (or presented by the cabinets) use:
A * B / (A + B)
Where 'A" is the impedance of one cabinet and 'B' is the impedance of the other.
So, for your situation:
A = 8
B = 4
4*8 / (4+8) = 2.6
This is why some amps (SWR for example) provide a power rating at 2.6 ohms.
You best advice to avoid limiting what amps you can use is to go with another 8 Ohm cabinet.