What the speakers can handle

ExiLeZX · Sep 10th, 2005, 12:43 AM

My speakers can handle about 55W RMS. My head unit is a 50x4, so it can put out somewhere around 15-30W RMS. Does this mean they are safe from blowing even at max volume? I had a friend in the car with me today and he cranked the volume to 25 and it goes to 30 max I believe...and it scared me, lol. But he told me what I just said at the top of this post, is that true?

Also on a side note, does anyone know or have a guess what a '97 Sentra's stock subwoofer and amp wattage ratings are?

Thanks.

sr20dem0n · Sep 10th, 2005, 02:24 AM

There are two ways you can blow a speaker, thermally and mechanically. The power rating you see on the speaker is the thermal rating, which means it should be able to take somewhere around 55rms consistantly without the voice coil melting down and siezing. Now, your headunit is capable of around 20rms of clean output, but if you drive it into clipping things change. Audio signals are a composition of sine waves, if you play a solid tone it just looks like a single sine wave. When you increase the volume, the size of this sine wave increases. If you increase the volume too much you get what's known as clipping, basically the headunit chops off the top and bottom of the sine wave because it's not capable of outputting as much voltage as is required for those peaks. While the peak voltage doesn't increase when this happens, the rms voltage (think of it as the area under the curve) does, which means the rms power does. When the clipping is bad enough, that sine wave basically turns into a square wave which contains a LOT more thermal energy (a lot more area under the curve) than a sine wave. Your 20rms amp will be able to supply up to 40rms if it's pushed into full clipping. Mixed with the fact that a clipped signal doesn't have as high of a peak voltage as a clean signal of the same power, which means the speaker won't be moving as far, so your speaker won't have as much cooling as with a clean 40rms signal....you're getting near the edge. It is possible to thermal those speakers if you clip the headunit bad enough, but chances are you won't.

The second way to blow a speaker is mechanically, which simply means the cone is moving too far and the speaker starts slamming into itself, bending and possibly breaking the moving parts. This happens when you give the speaker too much power at too low of a frequency. At say 40hz, you'd easily be able to reach the mechanical limits of those speakers with that amp, even though it's only rated at less than half of the speakers' power rating. The mechanical limits are what you really have to worry about, without a highpass filter (cuts the power at low frequencies to prevent mechanical problems like this) you'd easily be able to destroy those speakers with your headunit. Just listen to the speakers, if you hear any distortion, I mean any at all, then turn down the volume. If you don't there's a good chance you'll blow the speakers.