What the heck is RMS?

Discussion in 'Amps and Cabs [BG]' started by Fetusyolk, Sep 30, 2008.

1. Fetusyolk

Aug 7, 2008
this may be a dumb question, but what is RMS?

i'm looking on sites to buy a new setup, and it keeps mentioning RMS. i understand ohms, and wattage and what not, but what is RMS?

2. LaughingGroove

Jun 19, 2008
Washington State
RMS is the process used to determine the average power output of the speakers over a long period of time. RMS is derived from an equation which produces the most mathematically accurate measure of a speaker's power output. The RMS value is often seen listed as "watts RMS" on product packaging.

The alternative to RMS is PMPO (peak momentary power output) which represents peak output measured in microseconds rather than over a long period of time.

3. kb9wyz

Sep 8, 2008
Bloomingdale,IL
RMS = Root Mean Square

It is a way of expressing what the DC equivalent of an AC signal. So when you talk about wall outlet voltage being 120V, that is the RMS voltage. The peak voltage (or power or current) can be multiplied by 0.707 to get RMS; and RMS can be multiplied by 1.414 to get the peak. (Because we're talking about sine waves)

With audio stuff, the RMS reflects what the amp, speaker, or whatever will handle all the time (unless it overheats). Sometimes they will say "program" instead. The peak value will be the largest signal that the equipment can take for a moment, i.e. a few cycles. Think kick drum hits.

Hope this helps,
Beast

4. Fetusyolk

Aug 7, 2008

Thank you, that actually helps alot,

in regards to the carvin amp i'm looking to get ( https://www.carvinguitars.com/products/single.php?product=SBR410 ) It says RMS at 8 ohms it's 275W/ch, which from what you're telling me means it's putting out 275W per each cabinet.

It also says that by a bridge connection it outputs 800W, but this is only a 600 W Head.

How does this work out?

5. slyjoe

Jun 28, 2008
Valley of the Sun (AZ)

- Power: RMS 8 ohm 275W/ch, 4 ohm 400W/ch, 2ohm 600W/ch, 8 ohms Bridge 800W, 4 ohms Bridge 1200W THD less than .03%

So, the amount of power depends on the load (ohms), and it has 2 channels that can be bridged together.

Remember, these specs are for the amp, NOT the cabinet. You may or may not have one cabinet per channel.

6. Fetusyolk

Aug 7, 2008
The cabinet is 8 ohms. now i'm completely thrown by the bridged thing. sorry these are noobish questions, but i did read the information on amps that's been postd on this site. What do u mean by two channles being bridged? Does that mean i can plug both outputs into the one cab that is in this halfstack, producing 800 watts or something?

7. mjolnirThor's Hammer 2.1.3beta

Jun 15, 2006
Houston, TX
...Looks like a typo. Those specs are exactly the same on the page for the bx600's big brother, the bx1200.

I would imagine the actual 4ohms bridged load is 600W.

8. mjolnirThor's Hammer 2.1.3beta

Jun 15, 2006
Houston, TX
The term "bridged" basically means the amp internally combines the power of both internal amplifiers through one output.

9. Fetusyolk

Aug 7, 2008
so, essentially, even though it's an 8ohm cabinet, since it's only one cab, making it mono and not stereo, it outputs the whole load?

10. mjolnirThor's Hammer 2.1.3beta

Jun 15, 2006
Houston, TX
Something like that.

Each amp is stable down to a certain impedance. This particular one is stable down to four when it's bridged. This means you can plug a single 8ohm cab into it in bridged mode and would take (I guess) around 250W. A 4ohm cab would take 600, or 2 daisy chained 8ohm cabs.

11. Fetusyolk

Aug 7, 2008
so since i'm kind of looking for a half-stack that i don't want to really upgrade any time soon that puts out around 600W, this one may not really be the one for me. Maybe the same head, a diff cab, thanks for all the info, greatly appreciated.

12. mjolnirThor's Hammer 2.1.3beta

Jun 15, 2006
Houston, TX
I hear Avatar puts out some nice cabs for a reasonable price, and if you get a 4ohm 410 cab this head would probably run it quite nicely.

13. Fetusyolk

Aug 7, 2008
thank you i'll look into that right away, i hope you don't mind another stupid question but it would be 8 ohm per cabinet not per speaker in cabinet right? like. it would get 275 W per the whole cab, not speaker correct?

14. mjolnirThor's Hammer 2.1.3beta

Jun 15, 2006
Houston, TX
Yessir, the whole cab. Each speaker does have its own impedance but the way they're wired together determines the entire cab's impedance.

15. Navybass

Mar 12, 2005
Norfolk, Va.
It's not how much the speakers put out, it's the average power the speakers will handle from the amp. Think of the amp as the producer of power and the speakers as the receiver and converter of that power. The speaker accepts the electrical power and converts it into a sound wave. What the speaker puts out is all dependent on what is put into the speaker.

Think of it this way, A speaker may have a 300 watt RMS rating, but if you only have a 100 watt peak amp driving that speaker it will never put out 300 watts rms.

So, a speaker with a rating of 300 watts rms will safely handle 300 watts rms of power applied to it.

16. ebasss

Aug 7, 2006
El Paso
I was wondering if I had an amp that put out 800 wats, would it damage a 400 wat cab?