555 IC Project - 'Red Alert' Siren query.

[Nick]

PS: "Watts RMS". Tsk Tsk

This drops the power dissipated in the speaker to about 5W RMS

Still, 5W isn't far off. The peak voltage might be 6V, depending on the rail, and depending on the losses in the transistors. The EF configuration will drop a minimum of 0.6 to 0.7V, and a bipolar 555 isn't quite "rail to rail".

But of course, the exact power will depend on the duty cycle of the second 555, with a maximum at 50% (which they obviously don't achieve in the default astable configuration). And I suppose that this should be multiplied by the duty cycle of the first so that we can derive a "continuous average power" rating.

The RMS reading was calculated over a 5 second window, taking into account the duty cycles of both 555s and losses in the output stage (2N3055) for both the original and corrected versions - it wasn't a straight V=IR calculation - it is indeed a "continuous average power" rating...