View Full Version : RMS wattage
12-24-2008, 03:38 PM
This is probebly an old question but....
I have a Marshall 4X10 cabinet. On the back it says "140 Watts RMS" Does this mean it is safe for use with any amp up to that power output? In other words, just about any guitar amp out there.?
12-24-2008, 03:49 PM
RMS is one way to rate power handling capabilities. Those cabinets can handle most amps up to 100 watts.
12-25-2008, 10:41 AM
RMS (root mean square) is a method of calculating power.. Here is some info if you're interested:
Old Tele man
12-25-2008, 03:55 PM
"RMS" refers to the root-mean-square values of the VOLTAGE and CURRENT levels across a common load (resistive or reactive) only, not to the resulting power. RMS is the DC-equivalent "heating" values of sinusoid voltage and current levels...a mathematical conversion from peak sinusoid to equivalent DC-value.
...the resulting power is AVERAGE power, not RMS power. There is no such thing as RMS power.
...when you see something like 100W(rms), it simply means the 100 watts average power value was calculated using the RMS values of either a sinusoid VOLTAGE (P = (V^2)/R), a sinusoid CURRENT (P = (I^2)*R), or both (P = V*I).
12-25-2008, 05:34 PM
Or it was just taken from the speaker literature and means how much power a cabinet can take, using an RMS rating system as most amps from that company are rated by.
12-25-2008, 10:01 PM
An amp driven into heavy overdrive can put out upwards of twice its clean RMS power. So if you have a 50W, have fun. If you have a 100W, be careful. (In either case you'll likely be way too loud for the venue:phones)
12-26-2008, 09:16 PM
Another way I figured to rate the power handling capability, is to pull the back off the cab and see what/if the speakers have a watt rating printed on them. Then I figure the power rating for the whole cab is the sum of all the speakers added together. Such as four 25 watt speakers make a 100 watt cab. Its been a while since I've read the book.
On a side note, I remember about 5-6 years back I think, Carvin was selling there newest coolest 100 watt tube amp in a 1x12 combo that had only a 70 watt Celestion in it. I'm no expert but man, that just don't seem right.
12-26-2008, 11:12 PM
Carvin used to halve the rated wattage of speakers they used, even the Celestions and Emminence's.
12-27-2008, 03:25 PM
In live sound, power amps are scaled at 1.8-2.2 times the average power of a load. So, a speaker with a 1000w average rating would be powered by an amp 1800w-2200w.
12-27-2008, 04:21 PM
Celestion under rates their speakers. Carvin also use to put out a 100 watt Legacy combo amp with two Celestion Greenback 25 watt rated speakers. Never knew of one to blow the speakers. They eventually changed to Vintage 30 speakers, that are rated at 60 watts per, but the changes was due not to a problem with the Greenbacks failing but with Steve Vai preferring the V30's.
12-27-2008, 08:52 PM
I always thought that RMS expressed as a (rough) percentage was 70% of peak value...
vBulletin® v3.8.5, Copyright ©2000-2013, Jelsoft Enterprises Ltd.