# Calculating RMS

Discussion in 'OT Technology' started by Biomechanoid, Jan 8, 2004.

1. ### BiomechanoidNew Member

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how would I calculate the RMS wattage of a particular sub? Prefferably some kind of equation.

2. ### 04Guest

You really can't

RMS doesnt mean a whole lot anyways. It simply states a certain power level at a "snapshot" in time.

There are two different kinds of power handling for a speaker.

The first is thermal. Thermal is simply how much electrical power the driver can handle before it burns out.

The second is mechanical. A speaker can only move a certain distance before the strength of the motor drops significantly and distortion gets pretty bad. The size of the enclosure you are using as well if it is ported will determine the amount of cone movement you have at a given frequency. As you go up in frequency, the power handling of a speaker becomes more and more dependent on the thermal characteristics of the driver than the mechanical ones. Obviously, this means that at lower frequencies, the speaker's power handling is more based on the amount of movement the driver has. A speaker may be rated at 1000 watts, but in a large sealed box it may only take 200 watts mechanically for it to reach its maximum movement (called excursion) at a low frequency like 30hz. Consequently on the other end of the spectrum at say 100hz, the speaker may be able to handle 2000 watts mechanically, but as you can see, at this point the driver is limited by thermal power handling, NOT mechanical handling.

IMO most reputable speaker manufacturers rate their products pretty fairly. If you hook a speaker rated at 1000 wattts up to a 1000 watt amplifier and keep the volume to the point where you don't hear distortion, you will probably be fine thermally speaking.

One way to determine the maximum mechanical power handling is to download winISD PRO and set a specific maximum power input and click the excursion graph. You can see how far the driver will move with a certain amount of power. Be warned though that the figures will be a bit liberal, because they dont take into account motor strength and suspension non-linearities.

3. ### BiomechanoidNew Member

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I was thinking of getting a different amp for my system after I had to return my JBL due to a manufacturing error. I hooked it up for a test run on my current box and it wouldn't turn on. tripple and quadruple checked everything (power wires, accesory wire, fuses, speakers, ground wire. hell I even hooked it straight up to the battery at one point I was so frustrated), so I sent it back.

I was asking about RMS, because the subs I ordered don't list an RMS value, but include shiloads of other stats.

4. ### 04Guest

What subwoofer do you have? A lot of people don't list the power rating as RMS because RMS by itself doesnt mean much.

5. ### BiomechanoidNew Member

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those stryke AV12MKIIs that I ordered based offa your reccomendatios

6. ### 04Guest

Well those 3 should have no problems taking 1000 watts, and even 1500 should be fine, unless your box is really large.