Bose Ohms & Yamaha DSP-AX757SE


Well-known Member

I'm in the middle of setting up my Yamaha DSP-AX757SE, and it says in the manual under CAUTION - if you are using 4 or 6 ohm speakers set the impedance to 4 or 6 ohms, from what I can find out my Bose cubes are rated between 4-8 ohms, this might seem like a silly question, but should I alter this setting to 4-6 ohms, or is it ok to leave, if it is left and the wrong ohms are selected what would happen?



Standard Member
Normally the DCR (DC Resistance) of a speaker is close to it's impedance rating (99% of the times)...get a multimeter and put the positive on the positive terminal of the speaker and the negative on the negative terminal of the speaker. Then set the impedance as required on the Receiver.

Also the amplifier might go into "protect mode" or will work and then shut off due to overheating at loud listening volumes for extended period of times.


Well-known Member
The impedance switch is a current limiter (of sorts), designed to prevent the amp from toasting itself/distorting badly when driving low impedance loads, such as 4Ohm speakers.

In actuality, there's really no such thing as a 4 Ohm speaker - when they rate them, the rating is nominal in nature, as the true impedance will vary according to the input frequency of the signal - hence some makers refer to them as 4-8 Ohm speakers.
Some makers use a nominal rating (such as 8 Ohms nominal), and other use a minimum rating (such as 6 Ohms minimum) - some even give you both, such as "8 Ohms nominal, 5.6 Ohms min"

There are differing ways of doing it, but a common way for these impedance selector switches to work is:
In the lowest impedance setting it reduces the voltage on the internal power amps, so that the output power is restricted when driving low impedance speakers.

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