RMS Wattage

[sebastian]

Hi everyone,

I'm new to this forum and I was wondering if someone could help me out.
Basicaly, tomorrow I'm planning to purchase a new amp, but I want it to work with my existing cabinet : Carvin RL410T (here's the datasheet of this specific model: http://www.carvinguitars.com/manuals/RL410T_Datasheet.pdf).

The amps I'm planning to test are:

- Ampeg SVT 4 Pro (http://www.ampeg.com/pdf/SVT4PRO.pdf)
- Ampeg SVT 7 Pro (http://www.ampeg.com/products/pro/svt7pro/pdf/sw0787_revb.pdf)
- Gallien Krueger 1001RB (http://www.gallien-krueger.com/manuals/1001RB-II_700RB-II.pdf)

I haven't got a great knowlege in amp sector, even though I was playing bass for many years I'm more of the power switch and volume guy.

The cab has a power handling of 600 watts and nominal impedance of 8 ohms and i just want to make sure that whatever amp I'll choose, will work well with it. Obviously with the time I might consider upgrading the cab, but for the time being that's not on the menu.

What I specifically don't understand is the RMS wattage.
Taking the example of SVT 4 Pro, which has 350W rms @ 8 ohms on the power amp A and B.
Does that mean that I will be able to use it with the Carvin cab and will I only get 350W of power or - is this going to be too much for the cab?

As I said - I'm really new to all this and woud appreciate some help if possible.

Thanks.
Sebastian

[xgsjx]

Try the amps through the cab & get whichever you like the sound of most. Ignore the watts, it means little in respect of what you're looking at.
You've got an 8Ω cab, most amps will run at 8Ω (Some EBS & some valve amps won't run at 8Ω).

There's a lot of good lightweight amps out there from the likes of Markbass, TC Electronic, Genz Benz & also from Ampeg & GK.
The 2nd hand section on this forum is a great place to get an amp & if you don't like it, you can sell it for very little loss & try another.

[EBS_freak]

[quote name='xgsjx' timestamp='1383304481' post='2262819']
You've got an 8Ω cab, most amps will run at 8Ω (Some EBS & some valve amps won't run at 8Ω).
[/quote]

All EBS amps will run at 8 Ohm. You won't get the full beans out of them at 8Ohm though. Fafner, TD and HD want 2 Ohm to deliver their full load, the others want 4.

[chris_b]

How loud are you going to play? Why do you want to choose between these hugely powerful amps? They are overspec'ed for your cab and you could get a better matched amp for a lot less than the cost of these monsters. I would be looking at an amp giving out 500-600 watts at 4 ohms.

The PRO7 has a chequered history of failures.

There are a couple of Mesa Boogie M6 amps in the FS section and Bassgear have Carvin amps. I'd also checkout Genz Benz Streamliner 600/900 amps.

[xgsjx]

[quote name='EBS_freak' timestamp='1383305165' post='2262842']
All EBS amps will run at 8 Ohm. You won't get the full beans out of them at 8Ohm though. Fafner, TD and HD want 2 Ohm to deliver their full load, the others want 4.
[/quote]

I didn't know that. Cheers.

[Bill Fitzmaurice]

[quote name='sebastian' timestamp='1383303923' post='2262811']
Taking the example of SVT 4 Pro, which has 350W rms @ 8 ohms on the power amp A and B.
Does that mean that I will be able to use it with the Carvin cab and will I only get 350W of power or - is this going to be too much for the cab?
[/quote]The cabs power rating is how much it can take before the voice coils melt. In most cases that's well above how much the cab can take before the drivers distort (displacement limited power). Cab companies should tell you what the displacement limited power is, but they won't, since the much lower figure would impact sales. In practice you'll never over-power a cab if you don't push it beyond the point where you hear distortion. That means an amp rated anywhere between one-half and twice the power rating of your cabs is usually appropriate. Less than half probably won't drive your cabs to their displacement limit, more than twice is power you can't make use of anyway.

[RandomBass]

As a slight aside, I have never fully understood the term of RMS watts. RMS voltage, yes. RMS current, yes. And using RMS voltage into a purely resistive load of 8 Ohm would surely give average power, not RMS power. RMS and average are not the same thing.

Or am I just being dim? And sorry for the hijack....

[sebastian]

[quote name='Bill Fitzmaurice' timestamp='1383308808' post='2262914']
The cabs power rating is how much it can take before the voice coils melt. In most cases that's well above how much the cab can take before the drivers distort (displacement limited power). Cab companies should tell you what the displacement limited power is, but they won't, since the much lower figure would impact sales. In practice you'll never over-power a cab if you don't push it beyond the point where you hear distortion. That means an amp rated anywhere between one-half and twice the power rating of your cabs is usually appropriate. Less than half probably won't drive your cabs to their displacement limit, more than twice is power you can't make use of anyway.
[/quote]

Does it mean that when we're talking about the cab of 600 Watts - the amp of 900 Watts is appropriate or the other way around - the amp of around 300 Watts? I'm sorry - I'm really bad with it as you can see.

[sebastian]

[quote name='chris_b' timestamp='1383305786' post='2262851']
How loud are you going to play? Why do you want to choose between these hugely powerful amps? They are overspec'ed for your cab and you could get a better matched amp for a lot less than the cost of these monsters. I would be looking at an amp giving out 500-600 watts at 4 ohms.

The PRO7 has a chequered history of failures.

There are a couple of Mesa Boogie M6 amps in the FS section and Bassgear have Carvin amps. I'd also checkout Genz Benz Streamliner 600/900 amps.
[/quote]

I'm going to be potentially pretty loud - it's for rather heavy klunky sound with low D etc. but also for funk and R&B - hence the amp should be pretty versatile. I've heard about Ampegs and its failures - that's why I'm still not 100% on with my decision apart from the fact that I obviously need to try them first. Looking at SVT 4 Pro and 350W @ 8 ohms vs Carvin 600W @ 8 ohms - should these two work together ok?

Also - I had Carving R1000 and it was a fantastic amp, but unfortunately something wen't wrong with it and no-one around could repair it so I had to sell it for parts. Now I'm looking for a bit more agressive sound hence my choice of the amps.

[Guest bassman7755]

[quote name='RandomBass' timestamp='1383309931' post='2262943']
As a slight aside, I have never fully understood the term of RMS watts. RMS voltage, yes. RMS current, yes. And using RMS voltage into a purely resistive load of 8 Ohm would surely give average power, not RMS power. RMS and average are not the same thing.

Or am I just being dim? And sorry for the hijack....
[/quote]

Well since P = V * (V / R) given a constant resistance the relationship between RMS voltage and RMS power will be a linear one i.e. twice the RMS voltage will give twice the RMS power.

[Bill Fitzmaurice]

[quote name='sebastian' timestamp='1383310250' post='2262948']
Does it mean that when we're talking about the cab of 600 Watts - the amp of 900 Watts is appropriate or the other way around - the amp of around 300 Watts?
[/quote]Both of the above and anywhere in between.
[quote]As a slight aside, I have never fully understood the term of RMS watts.[/quote]Measure the amp's maximum output RMS voltage swing into the rated load at the rated THD and that's 'RMS' watts. The watts aren't RMS, the voltage swing is.

[dincz]

[quote name='bassman7755' timestamp='1383315166' post='2263063']
Well since P = V * (V / R) given a constant resistance the relationship between RMS voltage and RMS power will be a linear one i.e. twice the RMS voltage will give twice the RMS power.
[/quote]

Actually power is proportional to the square of the voltage - P = V² / R, so doubling the voltage quadruples the power.

[pby]

[quote name='Bill Fitzmaurice' timestamp='1383315729' post='2263071']
Both of the above and anywhere in between.
Measure the amp's maximum output RMS voltage swing into the rated load at the rated THD and that's 'RMS' watts. The watts aren't RMS, the voltage swing is.
[/quote]
I think RandomBass was confused about specs from ampeg manual, the units used are confusing.

"2 x 900 watts rms @ 2 ohms (600 watts continuous), 3% THD"

I don't know how they got the 900 watts rms value but pretty sure it's electrically irrelevant as the real/apparent power of the amp is way less than that. I'm guessing the continuous power IS the average power.

Edited November 1, 2013 by pby

[Guest bassman7755]

[quote name='dincz' timestamp='1383317485' post='2263103']
Actually power is proportional to the square of the voltage - P = V² / R, so doubling the voltage quadruples the power.
[/quote]

Yes your right thanks for the correction.

[RandomBass]

[quote name='Bill Fitzmaurice' timestamp='1383315729' post='2263071']

Measure the amp's maximum output RMS voltage swing into the rated load at the rated THD and that's 'RMS' watts. The watts aren't RMS, the voltage swing is.
[/quote]

Yeah that's the point. The result is not RMS Watts, but is denoted as such. It's just a way of saying 'this power calculation was derived using V RMS'. It's a misnomer.

[Bill Fitzmaurice]

[quote name='pby' timestamp='1383323290' post='2263222']
I think RandomBass was confused about specs from ampeg manual, the units used are confusing.

"2 x 900 watts rms @ 2 ohms (600 watts continuous), 3% THD"

I don't know how they got the 900 watts rms value but pretty sure it's electrically irrelevant as the real/apparent power of the amp is way less than that. I'm guessing the continuous power IS the average power.
[/quote]Looks like specsmanship to me. Traditionally RMS was assumed to mean continous, anything other than continuous was called peak, or music power, or any of a half dozen other marketing euphemisms created for the sole purpose of inflating the actual power output.

[brensabre79]

Simple Answer...
Your Cab should be OK with any amp that will output less than 600 Watts at 8 Ohms.
OK As in it won't catch fire or damage the speakers even at full volume.

BUT... If you crank the Low Frequencies up high enough, you can still do damage.

[xgsjx]

[quote name='brensabre79' timestamp='1383326474' post='2263278']
Simple Answer...
Your Cab should be OK with any amp that will output less than 600 Watts at 8 Ohms.
OK As in it won't catch fire or damage the speakers even at full volume.

BUT... If you crank the Low Frequencies up high enough, you can still do damage.
[/quote]

It should also be ok with an amp that outputs more than 600 watts at 8 ohm as long as you use your ears.
Though whereas you say it should be ok at full volume in theory, in reality an amp rated with a much lower wattage could damage the speakers.

[RandomBass]

Even RMS Watts is a marketing ploy. It makes no sense.

[Bill Fitzmaurice]

[quote name='RandomBass' timestamp='1383332605' post='2263342']
Even RMS Watts is a marketing ploy. It makes no sense.
[/quote]It makes as much sense as using the wattage rating of a lightbulb to gauge its brightness, which is to say, none. But the powers that be decided long ago not to provide the consumer with the specs that really matter.

[RandomBass]

Disagree on that one - different light bulb wattage has a definite difference in its brightness. Sticking the letters RMS after the word Watts doesnt.

[Mr. Foxen]

[quote name='RandomBass' timestamp='1383341471' post='2263507']
Disagree on that one - different light bulb wattage has a definite difference in its brightness. Sticking the letters RMS after the word Watts doesnt.
[/quote]

Compact fluorescent at 11w, and about same brightness as 60w incandescent. So no.

[RandomBass]

[quote name='Mr. Foxen' timestamp='1383341716' post='2263513']


Compact fluorescent at 11w, and about same brightness as 60w incandescent. So no.
[/quote]
Yawn. And increase the wattage and they get brighter? Or not?

[chris_b]

.... and you guys are helping the OP, how?

[Mr. Foxen]

[quote name='RandomBass' timestamp='1383342499' post='2263520']
Yawn. And increase the wattage and they get brighter? Or not?
[/quote]

Increase from the 11w one to the 60w one, same brightness. Because watts isn't the determining factor of brightness. Same way that it isn't the determining factor for loudness.