Car Stereos: how many amplifiers do i need and what type?

Question
I am planning on updating my car's audio system. My car currently has 4 stock speakers. I want to replace the two front speakers and add a subwoofer. I have two speakers with 160W RMS, and a subwoofer with a 500W RMS for a total of 660 RMS.

I heard that car amplifiers are not 100% efficient and some of them only have about a 60-70% efficiency. Does this mean that I will need a 1000W RMS amplifier for my speakers and subwoofer because the actual power will be 600-700W RMS?

Would It be better and/or cheaper to get two Amplifiers? One for the speakers and one for the sub? Also, how many channels will I need?
Thanks

Answer
Hi Adam,

Sorry about the delay in answering this question.   

You don't have to account for the amplifier's efficiency when you're looking at a power rating.  The efficiency of an amp refers to the difference in output power and input power--in other words, how much of the power that the amplifier takes from the vehicle's charging system is wasted as heat, and how much is actually sent to the speakers?  An amplifier that is 60% efficient needs to draw 1000 watts of power from the vehicle's alternator and/or battery in order to send 600 watts of power to a speaker.  This information is useful when you're trying to decide what gauge power wire and fuse size to use, but it doesn't affect the amplifier power rating.

As for the type of amplifier to use:  the most flexible setup is to use one amplifier for the subwoofer, and another amp for the speakers.  The best option for a subwoofer amp is usually a mono design; mono amps are generally made just for subs, and they can work with a wide variety of subwoofer systems.  The amp for the full-range speakers will usually be a multi-channel amp, either 2-channel or 4-channel.

Another option is to use a single 4-channel amplifier, with two channels driving two (or four) full-range speakers and the other two channels bridged to drive a single subwoofer.  This is usually the least expensive option, but this type of setup is limited in the types of subwoofers that can be used with it.

A 5-channel amp is another option.  This is a combination of a 4-channel amplifier with a mono amplifier in one package.   This allows more flexibility than a 4-channel amplifier, but there aren't a lot of 5-channel amps on the market, so it might be more difficult to find one that's a good match for your speaker system.

If you'd like to follow up with the brand and model numbers of your speakers and your sub, I can give you a better idea of some amplifiers that might work well for you.

Hope this helps!

Brian