Here is a real stupid question,but I got to ask.

[lbwdog]

I guess I've been somewhat blessed most of my career, owning amps that were always plenty powerful for my needs, even in the '70s when I was playin' LOUD.

For example, my first bass amp in 1969 was a solid state, 100watt Coral (by Danelectro) into a sealed 6x12. My band then played some pretty large clubs, not earsplitting loud, but definitely very full. Never left me wanting more volume.
Then, in the early '70s, I'm in a "Deep Purple" style band, so I got a Sunn Concert head (rated 100-125 watts?) into an 18" folded horn. Again, all I needed.

Then in 1988, I got a G-K 800RB and it didn't matter whether I ran it at 200w. into an 8 Ohm 1x15, or 300w. into 4 Ohm 2x15. It was very loud in my six piece band with two guitars, keys, etc.
Bear in mind these were not coffee house bands, but pretty powerful units.

Over the last couple decades, I've played many supplied backline gigs from arenas to outdoor festivals. Therefore I've had occaision to try many other brands with various power ratings in a real world situation. My findings are that G-K's 300w.-500w. amps are considerably more powerful than some other brand's similarly rated units. Most notably SWR, which has always seemed anemic in comparison.

My point is i don't pay much attention to power ratings as such, but use my G-Ks as a benchmark for comparison.
I owned an LM II for a while, and felt like it was close, and recently picked up a Markbass LMTube 800, mainly because I was wanting another superlight head, and my GC didn't have the 500w. LM Tube, which has a couple of features (dual vol control inputs, mute) I was wanting. I figured the 800 watts to be a bonus if I ever needed it.

What all this has to do with RMS vs Peak, I don't know. It's just my take on power ratings. What I don't get is why so many posters here feel they have to have 1000 watts or more, and many don't even gig!

This is all IMHO, etc.

 

[bassclef216]

Geeeeezzz.....
Fred, I was in the same boat and asked the same questions. I think I ended up more confused than when I started. For your purposes (and simplicity's sake) you will want to look at the RMS rating when matching a cab to a head. So, if you buy a 500 watt head and the cab is rated at 250 RMS and 500 peak then it would not be a good match. The head will be too much for your cab. Try to match the head to the cab's RMS rating or go with a cab that has a higher RMS rating than the head to be safe. Make sure you also learn the basics about Ohms also or you could mess up your head unit.

 

[KJung]

I guess I've been somewhat blessed most of my career, owning amps that were always plenty powerful for my needs, even in the '70s when I was playin' LOUD.

For example, my first bass amp in 1969 was a solid state, 100watt Coral (by Danelectro) into a sealed 6x12. My band then played some pretty large clubs, not earsplitting loud, but definitely very full. Never left me wanting more volume.
Then, in the early '70s, I'm in a "Deep Purple" style band, so I got a Sunn Concert head (rated 100-125 watts?) into an 18" folded horn. Again, all I needed.

Then in 1988, I got a G-K 800RB and it didn't matter whether I ran it at 200w. into an 8 Ohm 1x15, or 300w. into 4 Ohm 2x15. It was very loud in my six piece band with two guitars, keys, etc.
Bear in mind these were not coffee house bands, but pretty powerful units.

Over the last couple decades, I've played many supplied backline gigs from arenas to outdoor festivals. Therefore I've had occaision to try many other brands with various power ratings in a real world situation. My findings are that G-K's 300w.-500w. amps are considerably more powerful than some other brand's similarly rated units. Most notably SWR, which has always seemed anemic in comparison.

My point is i don't pay much attention to power ratings as such, but use my G-Ks as a benchmark for comparison.
I owned an LM II for a while, and felt like it was close, and recently picked up a Markbass LMTube 800, mainly because I was wanting another superlight head, and my GC didn't have the 500w. LM Tube, which has a couple of features (dual vol control inputs, mute) I was wanting. I figured the 800 watts to be a bonus if I ever needed it.

What all this has to do with RMS vs Peak, I don't know. It's just my take on power ratings. What I don't get is why so many posters here feel they have to have 1000 watts or more, and many don't even gig!

This is all IMHO, etc.

Read post 11 Most of the variances you are describing have to do with the voicing of the head and the SPL of the cabinets.

Again, to the OP, the RMS ratings across amps are a reasonably good indication of performance 'in a vacuum'. Depending on the cab SPL, the voicing of the heads low end, and your EQ choices, absolute volume will vary a bit. The discussion of 'how many watts you need' is completely unanswerable as a simple question without taking cab SPL, absolute volume needs, playing technique, and tone profile into account.

 

[lbwdog]

Read post 11 Most of the variances you are describing have to do with the voicing of the head and the SPL of the cabinets.

Again, to the OP, the RMS ratings across amps are a reasonably good indication of performance 'in a vacuum'. Depending on the cab SPL, the voicing of the heads low end, and your EQ choices, absolute volume will vary a bit. The discussion of 'how many watts you need' is completely unanswerable as a simple question without taking cab SPL, absolute volume needs, playing technique, and tone profile into account.

Well....yeah, I agree with most of that. Maybe my real point was that power ratings in and of themselves don't tell a whole lot. Perhaps too, I've been blessed with pretty efficient speakers most of the time, therefore not requiring megawatts to drive them to high volume.

I do stand by my comparisons from one brand to another. Many times I've played different 300w amps into the same cabs and realized much different SPL, even taking into consideration gain structure, voicing, etc.

I just don't put much stock in ratings till I use a unit on a real gig. Does that make a little more sense?

Oh and forget about speaker cab ratings. A cab will either take what I dish out, or it won't. I know a $300, "1000 watt" 410 ain't gonna come close!

 

[KJung]

Well....yeah, I agree with most of that. Maybe my real point was that power ratings in and of themselves don't tell a whole lot. Perhaps too, I've been blessed with pretty efficient speakers most of the time, therefore not requiring megawatts to drive them to high volume.

I do stand by my comparisons from one brand to another. Many times I've played different 300w amps into the same cabs and realized much different SPL, even taking into consideration gain structure, voicing, etc.

I just don't put much stock in ratings till I use a unit on a real gig. Does that make a little more sense?

Oh and forget about speaker cab ratings. A cab will either take what I dish out, or it won't. I know a $300, "1000 watt" 410 ain't gonna come close!

+1 The early SWR amps were a classic case of putting out SO much deep low end (below 30hz I believe), that their published wattage seemed way overstated. However, as soon as you put a hi pass filter in the signal chain, set to around 30hz, the output really jumped.

So, +1, published wattage specs are only part of the equation in determine the performance of an amp head. That being said, again, my experience is that the correlation between published wattage and absolute output (speaker cab and general EQing kept relatively constant), is probably around .75.... i.e., a pretty good linear relationship with some variance along the way due to either extreme voicing of some units, or flat out lying by manufacturers, etc.

IMO!

 

[lbwdog]

+1 The early SWR amps were a classic case of putting out SO much deep low end (below 30hz I believe), that their published wattage seemed way overstated. However, as soon as you put a hi pass filter in the signal chain, set to around 30hz, the output really jumped.

Well that makes sense! My experience with them has basically been as backline supplied, so never got into any deep tweaking.
Just last fall, I used an SM 900 on an outdoor festival and literally had to open the thing almost all the way up to match stage volume with the band. Any of my G-Ks or MarkBass could have done it at idle!

 

[greenboy]

Also people think knob position actually means something. One of my guitar players had a Fender combo that took the manufacturer's often sneaky ploy to an extreme. He'd say, "Lookie here: I'm blowing away Scott's (the other guitarist) amp and I'm only on two! My amp is teh bestest ever"

I'd say, "BFD. Scott's amp actually can be turned up near the top and has smooth control over the entire range for its ouput. And when it's up there higher, your amp can't touch it no matter where your knob is".

 

[KJung]

Also people think knob position actually means something. One of my guitar players had a Fender combo that took the manufacturer's often sneaky ploy to an extreme. He'd say, "Lookie here: I'm blowing away Scott's (the other guitarist) amp and I'm only on two! My amp is teh bestest ever"

I'd say, "BFD. Scott's amp actually can be turned up near the top and has smooth control over the entire range for its ouput. And when it's up there higher, your amp can't touch it no matter where your knob is".

+1 all the way. I mentioned in my post # 11 that this also contributed to the 'old amps are louder than the newer stuff' myth, since the early GK's, Edens, Acoustics, etc. seemed to reach full volume with the input gain set optimally and the master at 10 o'clock!

 

[agedhorse]

Whoa, there's some interesting descriptions of these terms being used here, most of them completely inaccurate. There are very sound and technically accepted definitions of "RMS" and "peak" power, based on the following information:

1. "RMS" power it the term commonly accepted to be the true delivered power to a resistive load based on measured RMS voltage. The reason why RMS is important is because it represents the true power (heating effect) of any AC signal no matter what the shape of the waveform and is integrated over many cycles. When measuring a the output of any power amp, a true RMS meter that's designed for arbitrary (non-sunusoidal) waveforms must be used otherwise generally the meter will read low. RMS meters that take the peak AC voltage and do a mathamatical calculation to determine the RMS value are only accurate for pure undistorted sine waves. Many bass preamp/amp circuits intentionally generate (hopefully pleasing) distortion components which will cause inaccurate readings on "typical" meters. "RMS" power = RMS voltage squared divided by the load resistance.

2. The peak power is the power based on the measured peak voltage. The peak voltage of a sine wave is exactly 1.414 times the RMS voltage. When you do the math, 1.414 squared = 2 which is where the doubling of the RMS power to peak power conversion occurs. Peak power of 1000 watts is exactly the same thing as the RMS power of 500 watts and both represent EXACTLY the same waveform IF the wave is purely sinusoidal.

3. Sometimes marketing folks take the peak power number and advertise it because it looks better. IF you know what the two numbers actually mean, then it makes no difference. If you don't know the difference, you should IMO learn so that you become an educated consumer.

4. There are also terms like dynamic power, burst power and dynamc headroom. All of these have a very viable place in describing the dynamic nature of a non-regulated power source. Generally, though not always, these measurements are based on the short term RMS voltage. The problem is that different dynamics time constants mean different things to different users. For example, a 20mSec burst rating is really the ONLY meaningful measurement for an amp that is driving the HF section of a PA horn because that's the type of waveform that is being reproduced. This number is, however, meaningless for low frequency amplification where something on the order of 100-200mSec is more appropriate. There is no difference between these time constants and the time constants applied to multi-band limiting because both are based on the appropriate parameters for each corresponding waveform.

5. None of this applies to a real speaker load because the above measurements are based on driving a resistive load where the voltage and current are in phase. Add inductance and capacitance and power will vary with frequency and will always be less than the DC resistance of the speaker. The real power equation is Voltage x Current x power factor, where power factor is the cosine of the phase angle between voltage and current.

6. The phase angle between voltage and current on a real load is the "gorilla in the room", since an amp (a good one anyway) must be designed to handle a wide range of currents and voltages with a phase shift between them. Therefore, when limiting excessive current by clamping or limiting the drive voltage there MUST be adequate design headroom otherwise instead of traditional clipping of the top of the waveform, the clipping will occur as bites out of the side of the waveform (the position based on the amount of phase shift) and this is one of the nastiest forms of distortion.

7. Properly designed class D amps can take all of this in stride since non-linear amps do not care about voltage and current phase relationships (within reason) and rather than dissipating this difference (stored energy in the electro-magnetic field of the speaker versus cone position) as wasteful heat, it is recovered and re-used. This is a difficult concept for linear guys to get their heads around, but it's the way of the future.

 

[greenboy]

+1 all the way. I mentioned in my post # 11 that this also contributed to the 'old amps are louder than the newer stuff' myth, since the early GK's, Edens, Acoustics, etc. seemed to reach full volume with the input gain set optimally and the master at 10 o'clock!

Yep. I hate that. All the con games some of these companies have plied. Some of them have the baked-in voicings that play mainly to their own cabs' weaknesses and make things seem louder. Sometimes that backfires horribly because those hidden default voicings are clumsy with most other cabs. Or were poorly engineered and didn't take into account what happens at higher volume.

Nowdays, voicing a preamp/head needs to be a lot more subtle to really win, because speaker cabs are moving on into the 20th century. Ahem.

 

[gary mitchell]

I can't argue with that. I am not that smart. YET

 

[lowendfriend]

Folks, not lots of mystery around RMS and why it's used. Musical tones are usually described as sinusoidal waveforms. The peak power of a sinusoidal waveform is not the best indicator of "average electrical power" produced by a varying waveform. The trouble with averaging a sinusoidal waveform is that the positive peaks cancel out the negative peaks in a mathematical average thus the average is zero...even less representative of the power than peak. Root Mean Squared is a mathematical attempt to get to a meaningful "average" power number for a sinusoidal waveform. It is .707 X the peak value.

But the real confusion in all this amp stuff comes from converting the electrical power pumped out by the amp into mechanical displacement of the speakers and then on into the acoustic sound power (SPL) from within a specific cabinet design for specific frequency bands. It's complicated and frankly beyond what most people really want to know. What bass players want to know is "Is it loud enough?"

RMS watts out give you a parameter to compare across similarly used equipment.

RMS is a reasonable way to compare amp heads in very gross terms.

 

[agedhorse]

Note that for average power, when the calculation is made there is an implied "absolute value" term involved. Otherwise the average voltage of any symmetrical AC waveform is always zero.

 

[Calaverasgrande]

I'd like to thank the gentleman from Genz Benz for dropping some facts into the mix. I would also like to point out that more than one amp company quotes peak power that is way more than double the RMS.

It is all good to say that amps will sound different through different cabs/loads etc but the truth is that you cant really try an amp out at a music store short of bringing your whole band in and running down the set list. Instead you try and find an amp that seems like it sounds good at music store levels and then check the power rating printed next to the jacks to get a ballpark idea if it will be usable in a band.

 

[KJung]

I'd like to thank the gentleman from Genz Benz for dropping some facts into the mix. I woudl liek to point out that more than one amp company quotes peak power that is way more than double the RMS.

It is all good to say that amps will sound different through different cabs/loads etc but the truth is that you cant really try an amp out at a music store short of bringing your whoel band in and running down the set list. Instead you try and find an amp that seems like it sounds good at music store levels and then check the power rating printed next to the jacks to get a ballpark idea if it will be usable in a band.

+1 As most have been saying, the standard RMS power rating is a pretty good indication 'in a vacuum' of the performance of an amp. Peak rating should pretty much be ignored.

 

[agedhorse]

I would also like to point out that more than one amp company quotes peak power that is way more than double the RMS.

Yeah, there is peak to peak power of course, which is 4 times greater, but it should be mentioned in the same sentance that this value really does have no value in our physical world since those peaks are offset by 180 degrees in time, and no work can be done by these numbers once the polarity is included. This is purely a bottom of the barrel marketing ploy only.

 

[dpbass613]

i don't get it never will...i have never had an amp or a cab burn out on me, typically running 700 watt cabs, swr or aguilar, with a 500 watt head...never had problems, pretty happy with the tone...i am sure there is a better way to run it, but if its quality gear it will hold up. I tried to understand that and i got flamed on it. Do what sounds good, if you happen to blow something up, don't do it again hahah!!!

 

[dincz]

It's a mess. There's no such thing as "RMS" power. RMS is only applicable to voltage and current - which may have positive or negative polarity. Negative power doesn't exist in my limited universe.

"RMS" power is a misnomer arbitrarily taken to mean continuous sine wave power into a resistive load. Continuous power is a useful indication of what a power amp is capable of - or it would be if there was an agreed standard of distortion.

"Peak power" could mean (depending on who's using the term) power calculated from the peak voltage of a sine wave - in which case by definition it's always going to be twice the continuous power and so doesn't need to be stated anyway. Or it's sometimes used to show the short-term burst capability, which would also be useful to know, except that it's also meaningless unless the burst duration is specified.

The whole subject seems to be badly understood by those who should know better, and further complicated by marketing departments.

 

[agedhorse]

"RMS" power has for 20 years or more been taken to mean power based on RMS voltage. "RMS" power can be continuous, or burst depending on the need of the application.

 

[greenboy]

Hey, lets all talk about typical duty cycles and crest factor now ; }