The Siren Board

If the amplifiers are the Class-D type, using a switch-mode output stage, they contain an output filter to remove the PWM carrier frequency (which would otherwise overheat the drivers with the superimposed but inaudible carrier frequency)

a lot of the modern integrated Class-D ICs (e.g. TriPath-based) use a switching frequency of around 400 kHz, and the impedance of any reasonable loudspeaker is going to be so high at that point that it doesn't matter. The filtering on the outputs is partly (or mostly) there to squash emitted RF noise. This is especially critical in automotive audio since the harmonics from the switching can utterly destroy radio reception.

not that I'm bitter or anything, I only spent one weekend in 90° heat re-working cars which were stop-shipped because of this.

I have a hunch Federal wasn't using Class D amps in their sirens. ATI holds the patent on using Class Ds in high power warning applications. It only seems like the Class D only became suitable for outdoor warning use in the late 90s/early 2000s.

See my write-up here: https://airraidsirens.com/forums/viewto ... nt#p136312

uncommonsense wrote:I have a hunch Federal wasn't using Class D amps in their sirens. ATI holds the patent on using Class Ds in high power warning applications. It only seems like the Class D only became suitable for outdoor warning use in the late 90s/early 2000s.

See my write-up here: https://airraidsirens.com/forums/viewto ... nt#p136312

wow, talk about a garbage patent. Has that ever been challenged? I can't see how it would hold up to either a prior art claim, or be vacated based on how obvious it is.