The usual sensitivity rating of a speaker is 90 dB range, it means the speaker will give a 90 dB of sound in only one watt of power in one meter distance, this is considered as a loud sound. The OSHA, the US government agency for work place safety states that 90 dB is the maximum level a worker can be exposed to over an 8 hour day. For your non-occupational setting, 90 dB setting is just for an a hour in an a 24 hour day.
The loudness you really want, if your trying to break a record maybe you’ll need a lot of power and woofer, but if you want your car audio to give pounding bass notes you maybe only need system with 500 watts max. understand that acoustic power operates on a logarithmic scale. This means after a certain point your sound level will only getting a small increase even after you’re increasing the power input more. Here’s an example, a 100 watts of power will give a sound of 20 dB, a 100 watts of power in a 90 dB sensitive speaker will give you 110 dB level. But if you add another 100 watts or a total 200 watts you only gonna get an increase of 3 dB to a 23 dB sound level, and every time you double the power you’ll only get another 3 dB increase. So with 400 watts of power, if your speaker can endure it, you only get 116 dB output. You’re not getting a big difference in sound level but you certainly going have to pay a lot more for the amp’s price and the current draw from your electrical system. And another risk with 400 watts of power is loosing your hearing if you listen for sometimes at those sound level.
With a mega-watt system you’ll have to think also to upgrades your electrical system. You’ll need to upgrade an alternator which expensive in buying and installing it. You also have to use a larger 0/1 gauge wiring, $6/ft, compare with 4 gauge wiring of $2/ft. You need bigger everything with bigger current draws, not only your amps. The law of diminishing will occur, your mega-watt system will make you pay four times as much but you’ll only get 6 dB more output, you better stick with the more modest system.
So to answer how much power you need, if you want a clear top end and a solid bottom end you can use a 500 watt or less system. You should split 40/60 with the 60% of power for your sub system, 200 watts for the highs and 300 for the lows. This will make a more reasonable alternator’s current draw and still provide the punch and clarity to the system. It’ll also cost you less and safer for your hearing system.
