Fun stuff indeed! It's interesting that moderate temperature changes would be that significant. It's also interesting that, "the active noise reduction will really only be effective in the low frequencies (
which works out ok, because it's the lows that don't get sealed out well by the earcup and ear cushion)."
GARTHWILSON wrote:
In car stereos, they've gone for 4Ω and apparently even 2Ω speakers, plus bridged outputs, because the power supply voltage is so limited.
Yeah, those are two approaches that've been used: lower-impedance loudspeakers, and/or two amplifiers per loudspeaker.
Another approach I've seen doesn't use the car's 12 Volts directly. Instead, the power amplifier chassis also incorporates an inverter -- a switch-mode power oscillator and a toroidal step-up transformer, followed by rectifiers and filter cap's. Of course this arrangement can supply DC to the power amp's at pretty well any voltage you choose; you're no longer stuck with 12 volts.
I don't do a lot of mucking about with this sort of gear, so I'm not sure how widely adopted this approach is. But I've heard some
ridiculously loud car stereos, and I expect that, at such high power levels, the inverter approach becomes the only reasonable option.
Cheers,
Jeff
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) is short, fat cables terminated with absolutely pristine connections. After all, you'll be carrying scores or even hundreds of amperes of 12V power to the amplifier assembly. 
At those current levels, it doesn't take many milliohms of resistance to seriously degrade performance -- and/or start a fire.
