Question about matching speaker and amplifier RMS ratings
 

I'm in the planning stage of replacing my cars Bose system and will installing a set of 6.5 inch components in the front door. I have an amp from a previous car install that is rated at 110 watts RMS per channel, the components are rated at 90 watts RMS; will I hurt the components by using them with this amp? Should I look for a new amp with lower RMS rating?

TIA

An amp does not output at RMS power at all times. I tend to think of RMS as the maximum amount of power I expect to get out of the amp when turned up to full blast at the loudest part of a song.

Since most people don't drive around with their amps at full blast, having a speaker with a lower RMS is not going to cause problems. Your ears will probably suffer damage before the speakers will if you drive around with your system at full blast all day.

As long as the RMS's are reasonably close together, don't worry about one being higher then the other. Chances are you'll never drive the amp hard enough to go past the speakers RMS, and if you do, it will be for short periods of time, which the speaker is designed to handle (It's Peak rating).

I've heard a saying somewhere that says your amp should be running around 30% of it's maximum output at your normal listening volume for best quality sound. YMMV, but it gives you an idea about how much power you need for normal listening VS impressing your friends by cranking it all the way up.

Protecting your speakers or amp from damage is more related to making sure your system is tuned properly and won't clip or distort then it is matching up all the RMS ratings of the equipment. If your amp is putting out to much power for a speaker to handle, it's the operators job to bring the gain on the amp down to where it won't put out enough current to fry the speaker.

you're thinking wrong then. The RMS is basically the average power you should expect from you amp. The RMS rating is less than the max power you'll be seeing during balls out music playing. That's why some manufacturers include max and RMS ratings. Keep in mind though, max ratings are normally bullshit unless you're seeing them from a few of the reliable companies.

This is true. I tend to go higher on the amp side. Proper gain settings and tuning after the install will leave your amps and drivers safe.

Indeed. The best way to do it is to set all of your EQ and bass boost settings flat. Turn your amp's gain all the way down and your deck's volume up to 1 or 2 numbers/ticks/whatever from being maxed out. Turn your gain up to the loudest you'll want to listen to it w/o driving the speakers into distortion and leave it alone. Now tune your eq settings so that your music sounds right to your ears, again w/o driving the speakers into distortion

I see no reason to push an amp past RMS in the first place. I want average to be as loud as I'll ever need, like the loudest part of the loudest song I own. if average isn't loud enough, I'll add a bigger amp, not push the amp till it smokes. Case in point, I don't even think my system currently gets anywhere near the RMS of my amp, and I'm pushing 115DB. Louder if I tune for SPL instead of SQ. If I was consistently hitting RMS, I'd need a bigger alternator and an optima battery.

RMS stands for Root Mean Square. Mean is another word for average, so this is power levels you can expect most of the time. Max is the MAXimum amount of power an amp can put out, but the way most manufacturers rate their amps this would only be at max volume while being struck by lightning and is not usually a reliable number. If you have a good clean signal, meaning that you are not turning the volume up to the point of distortion, too much power will not usually hurt your speakers. It is a good practice to have more power than you can use. This is called headroom. For example, I used to compete in SQ competitions with my truck, which has a true 600 watts RMS going to a single pair of 6.5" components. The effect is very clean sound at almost any volume, and they have been going strong for over 5 years now. This includes at least a year of competition use, which can be quite hard on components. The number you should be more worried about is the pre-amp voltage coming from the source(usually the head unit). Anything less than 2 volts is not acceptable for a higher end system, and up to about 6 volts is prefered. Anything more is just overkill. This will get the cleanest signal to your amplifier (because you don't have to turn it up as high for the same volume levels) and be the safest for your equipment. Keep in mind that some amplifiers have a limit to the amount of pre-amp voltage they can handle, but most can do at least 6 volts. The best advice I can give you is to avoid knock off brands and stick with the tried and true brands. This usually results in a more accurate power rating, as well as better quality (read: safer and more reliable)components within the equipment. The old saying, "you get what you pay for" was never more true than in the mobile electronics field. As noted by other posters, the single largest contributor to whether you are going to blow something up or not is tuning. I have seen $10,000+ systems sound like complete garbage and blow up components left and right, and I have seen $500 systems that sound absolutely beautiful and operate trouble free for years.

Thank you everyone, I appreciate all the info and I learned something too.

one of these days i'll be kidnapping socket for a full speaker replacement in my car.