speaker voltage

what's the story about speaker and amplifier voltage? can a speaker have any voltage put across it? coz ive heard that mains power amps have something like a 100V line, then you've got 12V systems, and even like 40V systems, but do you have to have speakers to suit? coz i've tried a house speaker in my car and it worked and stuff.

Thanks.

Josh.

Josh said:

what's the story about speaker and amplifier voltage? can a speaker have any voltage put across it? coz ive heard that mains power amps have something like a 100V line, then you've got 12V systems, and even like 40V systems, but do you have to have speakers to suit? coz i've tried a house speaker in my car and it worked and stuff.

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'Usually' home speakers are 8 ohms, and car speakers 4 ohms, simply because of the lower supply voltages in a car - a 12V supply will give 4W into a 4 ohm speaker, it will only give 2W into an 8 ohm speaker. Likewise a bridged 'high power' amplifier will give 16W into 4 ohms, or 8W into 8 ohms. Anything higher than this uses an inverter to generate a higher supply rail.

Be VERY aware that car amplifier outputs are greatly exaggerated, the 16W into 4 ohms will usually be rated as 25 or 50W in the specs. Car speakers are similarly exaggerated, so you should never use car speakers on home equipment, or particularly on PA equipment - you will probably blow the speaker quite easily!.

100V line is used for tannoy type PA systems, where you have long runs to the speakers - basically you use transformers to step the impedance upto a high level (this gives about 100V signal level), then at the far end you use another transformer to step it back down to feed the speaker. This reduces losses in the cable, just like they use high voltages for power distribution. It also gives the advantage that you don't need to worry about speaker impedances, you simply add up all the wattage tappings on the speakers connected - if the amplifier is 100W you could have ten 10W taps, or eight 10W and four 5W - and by adjusting the taps on the transformers you can adjust the volume for each individual speaker.