Most of the time it will be very young people that were"suckered" into purchasing huge powerful, filled with distortion amps. Most amp manufacturers lie through their teeth regarding distortion and power characteristics. However to answer your question. Yes. You probably need a 100A alternator if you will be running a powerful stereo system, car electronics, battery that the alternator must charge continuously, etc. Dual batteries and a battery isolator also are great if you really have a seriously powerful system.

However, (here is my lecture). I am an electronic/electrical engineer and have extensive knowledge and experience with car and home audio systems. Especially "high end" stuff.

The rule is that you typically get what you pay for. A super clean/distortion less system with speakers mounted and designed such that they operate within their design characteristics will be perfect. Unfortunately, most installers haven't a real clue.

Proper, clean installation and wiring are a must. Fused at the battery and at the device you are running power wires to. The fuse on the amp, protects the amp only. The fuse at the battery protect the wiring from the device and the battery (and your electrical system). Energy storage is necessary (1 farad caps at the amp) if you have serious power amps. Low level signal wires run down one side of the car. Power wires down another and speaker wires down the middle (or switch either). However, never near each other and when you have to cross them, do so at right angles only. The most frustrating thing is to install your gear and wiring only to have alternator whine, not because of the equipment, but because of a bad wiring job.

A speaker rated at say, 90 db/1W/1M gives a sensititive of 90 db loudness at 1 watt output of the amp at a distance of 1 meter (three feet). 90 db will run anyone out of the room. And that is at 1 watt. Think about this. So, great power is absolutely not needed. Sensitive and clean equipment and wiring is. Get the best you can afford. Or upgrade equipment one piece at a time until you get there.

Remember, you will never reach full output and stay alive anyway. on a clean system, 20 watts will drive you out of the car. So, remember that. The only reasons that you need serious power is if the a) speakers are so inefficient that they require much more power to drive them. Therefore, get new speakers. b) The speakers are so large and need to move large amounts of air, so serious amps are needed.

But, a good design will give great audio contest winner results with small amps, serious electronics and great speakers and installation.

My system, and I do this routinely for people and friends:

1. Nakamichi MB100 CD/Tuner two chasis system.
2. Nakamichi Tape deck
3. Nakamichi EC200 and EC200h active crossovers.
4. Morel 6.25" speakers in the front doors
5. Boston Acoustics tweeters in the front.
6. Great 6x9s in the rear for rear fill only.
7. Nakamichi Sp80 (8 inch) subwoofers mounted in custom, correctly sized and ported box in my trunk. Enough base to get the lowest needed.
8. Namakichi PA300II 75wpc amp for subwoofers (all I need)
9. Two ADS four channel amps (25wpc) for the front and rear fill speakers.
10. Canare signal wiring and connectors.
11. Mogami 10 gauge speaker wires.
12. Power wires run directly to battery and fused at battery.
13. Sound insulation on doors inside door panels, and on floor and kick panel areas.

6.9s mounted on the box firing up through the rear deck. SP80s mounted in separate ported areas in the box firing through the rear seats, Amps, relays, etc monted in box with hinged area in box for easy access. Entire box takes up less than a third of the trunk area in my 244T.

I use a 70 amp alternator and listen at less than 10 watts of power to the speakers. Typically, 5 watts will do.

enjoy