If i am not mistaken, it causes a bit more stress on speaker coils to produce a dual tone / multi tone sound rather a single tone.
I'm not sure if this can be done at all, just speaking out of mind. On modulators and other electronic sirens, such as whelen's. Is it possible to set one group of speakers to the higher tone and the other remaining set of speakers to the lower tone? However, would that cause sound cancellation? More or less, if it's possible - has such a thing been done?

For example, lets say we have a Federal Signal Modulator MOD6048 in use. The top three speakers would be producing the higher tone, while the bottom three would be producing the lower tone. Would that cause less stress to an electronic siren when in 'dual tone'?
