the majority of home speakers are 8 ohm the majority of car speakers are 4 ohm

Thanks, Ben, that helps explaining the apparent differences, if the following makes sense:

1) With car speakers at half resistance, amps yield double output (in an ideal world)
2) We're all adding left/right/rear/sub outputs, which is not really meaningful: two speakers (to drive L+R stereo) do not sound twice as loud as a single one. (That may also be the reaon that tanstaafl's friend drives his speakers in mono)
3) We shoud forget about the wattage for subs: they are just to make it all sound richer.

Thus: although my 240.4 delivers suggests that it delivers 240W, the fine print says that this is 2-channel bridged into a 2 ohm load; 30 watts for each of the channels into 4 ohms, max is more meaningful.
To drive 8 ohm home speakers, one would need twice the capacity: 60 watts.
I have no real feel for dB scales, but the 65dB limit (out of 92) on my home system could well be similar to the (theoretical) 60 watts (at 8 ohms) of the car system. QED

Also, car systems are probably significantly more efficient as there's no AC/DC conversion and they probably cut a few corners in cleaning the current; have fewer power supplies; drive lesser loads. Or is this offset by DC inefficiencies??



BTW: going over the manual for my home amp: at a speaker impedance of 2 ohms, the thing is warned to take 25 amps (at 230V). That probably explains why all the lights in the house dim when the bugger is switched on . May be I should get myself a dedicated, high current AC line as the manual suggests . . .

Henno
mk2 6 nr 6