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Amp power verses cab power?

E

eno50

Jan 31, 2009
566
23
North of Memphis
#1
Hello everyone,
I'am a little confused about Amp power and matching a cab to the amp
For years I have used a GK 800rb with an Ampeg 810 cab with no problems,but about ten years ago I sold that gear and down sized to a smaller rig.
Now the GK was an 300 watt amp (400 watt bi-amped)
and the ampeg cab I think was rated at 800 watts and that combo worked well,and I'am now in the market for another rig ,I may go back to that rig I don't know but I'am still shopping around and looking whats out there.
Now having said that,There is a whole new market out there with the class D light wieght amps to look at and
some of the ones I'am looking at are in the 500 watt
@4 ohms range,which I think is plenty for me,but matching it up to a 810 cab ? well I have been told by salesman of different cab companys that a class D 500
watt amps is underpowerd for there 810 cabs,and this threw me off a little becaused I used the GK /ampeg rig for years and never thought I was underpowerd.
So someone inlighten me on this amp power to cab power,and I know headroom is important to a Bass player and I never had an issue with my old rig,it was plenty loud for clubs and outdoor gigs,I just miss that tone of an 810 and you can't get it with anything else.
Upond trying to research this here on the fourm I came across a post where someone was saying that Class D amp power ratings were misleading and were not true RMS ratings(can't find that post again to tag it) but is there any truth to this?

Eno
 
#2
Speaker cabinet power rating is mostly fictional, and useless. It tells you essentially how much power the speakers can handle before the wire in the voice coil melts. The cones will be destroyed way before that happens so it's a useless figure. And the idea that "underpowering" a speaker will hurt has been pretty well debunked over the years too.

The only thing that might have a bit of a glimmer of truth in what the salesman said is that if the specific cabinet you're looking at is inefficient, 500 WRMS might not be enough to get the speaker cabinet loud enough to do the job. That's all pretty highly subjective and depends on you, how you play, how you EQ the rig, and the specific speaker cabinet.

As for power ratings for different amps, I don't know anything there.

John
 
#3
Greenboy has said something similar to the part about class D having misleading ratings, but it's not that they have misleading ratings...the ratings are by and large accurate (except for TC amps where they blatantly lie about it then add compression and high pass filtering and claim it's twice as much wattage), but once you get to the higher end of the volume they put out, they do kind of run out of juice. With most micros I've seen, once they hit their RMS wattage ratings, they don't have anything left in the tank, unlike lead sled amps, which have plenty of peak wattage in reserve. That peak wattage is highly distorted, but it does help those amps not run out of juice if you get close to the top end of the RMS wattage. I'm not a tech or an amp expert or anything, but when bench tests get run on micros in Bass gear Magazine, this generally seems to be the case. This is not a bad thing...it's just the way it is.

As for underpowering, the salesman who told you that is a dunce. Only overpowering blows speakers, not underpowering.
 
#4
JimmyM said:
Greenboy has said something similar to the part about class D having misleading ratings, but it's not that they have misleading ratings...the ratings are by and large accurate (except for TC amps where they blatantly lie about it then add compression and high pass filtering and claim it's twice as much wattage), but once you get to the higher end of the volume they put out, they do kind of run out of juice. With most micros I've seen, once they hit their RMS wattage ratings, they don't have anything left in the tank, unlike lead sled amps, which have plenty of peak wattage in reserve. That peak wattage is highly distorted, but it does help those amps not run out of juice if you get close to the top end of the RMS wattage. I'm not a tech or an amp expert or anything, but when bench tests get run on micros in Bass gear Magazine, this generally seems to be the case. This is not a bad thing...it's just the way it is.

As for underpowering, the salesman who told you that is a dunce. Only overpowering blows speakers, not underpowering.
Click to expand...
All this is stark reality obtained from JimmyM's many years of practical experience.
:bassist:
 
#5
Hey Jimmy,

Actually the distinction I was trying to impart is that once you get into the group of pro power amps that are capable of producing more output than an AC receptacle is capable of continuously delivering (let's say that's around 2000 watts and up), you begin to have to talk about musical signal duty cycles and AC power consumption, and not just RMS.

But none of that is directly tied to amp CLASS, and it's not relevant to what we are seeing in bass micro/mini heads anyway, since they are all within the range that can be properly described with an RMS continuous rating.

There is no reason other than marketing BS for any company making micro-heads to invent any non-referenced quasi rating, since their products' outputs can be expressed in RMS.
 
#6
greenboy said:
Hey Jimmy,

Actually the distinction I was trying to impart is that once you get into the group of pro power amps that are capable of producing more output than an AC receptacle is capable of continuously delivering (let's say that's around 2000 watts and up), you begin to have to talk about musical signal duty cycles and AC power consumption, and not just RMS.

But none of that is directly tied to amp CLASS, and it's not relevant to what we are seeing in bass micro/mini heads anyway, since they are all within the range that can be properly described with an RMS continuous rating.

There is no reason other than marketing BS for any company making micro-heads to invent any non-referenced quasi rating, since their products' outputs can be expressed in RMS.
Click to expand...
Thanks for the more detailed explanation, Greenie. I had a feeling I only got it partially right...but to be fair, I was only partially awake when I wrote that ;)
 
#7
more to the OP point, a new class D bass head rated at 500 watts at 4 ohms will most likely have less volume potential with that 810 than the 800RB 300 watt amp. The scientists here will tell you otherwise but I'll bet $1,000 that the real results will be as I previously stated. Let's set 'em up, I'll play and we'll hear for ourselves, any takers? :-)
 
#8
Yeah, because scientists are just losers who don't know anything.
:rolleyes:

That anti-science argument is so lame and pathetic that it really puts everything you say into the dumpster, really. Your years of experience become meaningless if you seriously think you know how the gear works better than the people who invented the gear.

Maybe if you understood what the scientific people were talking about then you wouldn't have that attitude... but obviously you don't understand.
 
#10
Seriously--that's one example of understanding how and why an amp can seem to be louder. Hard and soft clipping are other common factors, that absolutely do come into play with the old GK head. It's not the amp class, it's what you do with it.

Just look at the threads about the TC Electronic heads--they are all about maximizing perceived loudness using everything that makes the GK head loud, with a class D engine.
 
#11
vail_bass said:
more to the OP point, a new class D bass head rated at 500 watts at 4 ohms will most likely have less volume potential with that 810 than the 800RB 300 watt amp. The scientists here will tell you otherwise but I'll bet $1,000 that the real results will be as I previously stated. Let's set 'em up, I'll play and we'll hear for ourselves, any takers? :-)
Click to expand...

It probably depends upon the head used, don't you think?

It probably would be an informative experiment for all parties involved. We should all know that output wattage is a moving target when it comes to volume, and while some people want to write it off as ‘class D’ watts vs. ‘tube watts’ or ‘class AB’ watts we know that that doesn’t hold water. What does hold water is knowing HOW that wattage is applied. Things like harmonic distortion, compression and limiting, frequency response range and default voicing are all important to perceived volume. Once people suss that out, and really understand how and why it creates the perception of volume it falls into place.



It explains why companies like TC Electronic got away with calling an amp that's output limited at 236w a 450w amp for quite a while before someone figured out what and how they were doing it.


Or we can just keep thumpin’ away without trying to understand how our gear works…
 
#12
If you were happy with the 300W GK then the 500W Class-D amp will be just fine. RMS power is RMS power, industry measurement criteria and measurement standards do not change for different amplifier classes, A, AB, B, D, etc, they are all measured the same way. Do pay attention to steady-state RMS Vs peak when comparing amps. Steady-state RMS is what you usually want to compare.
 
#13
That's fine advice, but the inconsistent, and ambiguous way that MI manufacturers rate their power amps make it tough, and sometimes impossible to discern what's going on.

What percentage THD are we talking about? Is there a limiter involved? Ive heard that Mesa and GK use RMS. SWR uses peak. TCE uses alchemy. It's all so varied that apples to apples comparisons can be quite tricky, if not impossible.
 
#15
bongomania said:
Yeah, because scientists are just losers who don't know anything.
:rolleyes:

That anti-science argument is so lame and pathetic that it really puts everything you say into the dumpster, really. Your years of experience become meaningless if you seriously think you know how the gear works better than the people who invented the gear.

Maybe if you understood what the scientific people were talking about then you wouldn't have that attitude... but obviously you don't understand.
Click to expand...

Wow, calm down now, no need for such anger. :-)
You can think anything you want .....and so can I.:-)
Your response is quite emotional. Let's all take a breath...now I know you have some sort of dislike for me, that's odd since we've never met. Back to the topic, I have my opinion and I back it up with my personal experience. You can have your opinion and back it up with whatever you like. The OP can decide for him/ herself based on their own ideas. Personal attacks serve no constructive purpose and only make some people feel bad. Words like lame/ pathetic and such have no place in a civilized dialogue and I hope that this approach will cease and we can get back to talking about music. :-)
 
#17
vail_bass said:
...now I know you have some sort of dislike for me, that's odd since we've never met.
Click to expand...
It's entirely because you regularly make comments like the one I responded to: "scientists may say one thing, but I know better." If scientists don't know what they are talking about, then how did they design all the PA gear you use? You think maybe they just threw some stuff together, and left it to the bass players to figure out how it all really works?
vail_bass said:
I have my opinion and I back it up with my personal experience. You can have your opinion and back it up with whatever you like.
Click to expand...
What you're missing is that this is not about opinions, it's about measurable, verifiable facts. Ones that are well-known to people who actually know how amps work. Your experience is limited to (a) the specific equipment you've used, and (b) how you used it. So if you didn't know how to get the best results from a piece of gear, that left you with a negative experience of it. The problem is not with the gear.
vail_bass said:
Personal attacks serve no constructive purpose and only make some people feel bad.
Click to expand...
Think about that the next time you are about to blow off everyone who designed the equipment that helps you make a living.
 
#18
bongomania said:
It's entirely because you regularly make comments like the one I responded to: "scientists may say one thing, but I know better." If scientists don't know what they are talking about, then how did they design all the PA gear you use? You think maybe they just threw some stuff together, and left it to the bass players to figure out how it all really works?

What you're missing is that this is not about opinions, it's about measurable, verifiable facts. Ones that are well-known to people who actually know how amps work. Your experience is limited to (a) the specific equipment you've used, and (b) how you used it. So if you didn't know how to get the best results from a piece of gear, that left you with a negative experience of it. The problem is not with the gear.

Think about that the next time you are about to blow off everyone who designed the equipment that helps you make a living.
Click to expand...

double wow, take another 20 minutes, you're still very angry.;)
 
#20
gnjpowell said:
If you were happy with the 300W GK then the 500W Class-D amp will be just fine. RMS power is RMS power, industry measurement criteria and measurement standards do not change for different amplifier classes, A, AB, B, D, etc, they are all measured the same way. Do pay attention to steady-state RMS Vs peak when comparing amps. Steady-state RMS is what you usually want to compare.
Click to expand...

I played in Concord last night, Capitol Theatre. We should have hooked up for a coffee or something.
 

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