Return to quoting peak wattages?

[DukeLeJeune]

Rbonner, note that sine-wave power handling is overly conservative, since as a bass player you aren't trying to reproduce a sine wave wherein 100% of the power is concentrated at one frequency. Instead, the power is spread around, with the two most critical frequencies (from the standpoint of excursion) usually being the fundamental and the first overtone. With a low-E tuning, I estimate about 1/8 of the total power is in the first harmonic, and 1/3 in the first overtone - but I welcome correction on this from anyone who knows these ratios better.

fdeck has written a spreadsheet program that I have found to be quite useful; click on this link and then scroll down to "Excel spreadsheet":

Invalid Link Removed

 

[Jazz Ad]

For the record, most GK amps and Marshall DBS line have a peak power roughly 10 times their nominal power. Would it be fair to advertise their 200 W RMS combo as 2000 W?
The good thing about RMS is that it gives a roughly identical platform of comparison to everyone. It's far from the only factor to consider.

 

[Nick Kay]

For the record, most GK amps and Marshall DBS line have a peak power roughly 10 times their nominal power. Would it be fair to advertise their 200 W RMS combo as 2000 W?

I don't know where you're getting this idea from. An order of magnitude between average and peak? Check these published numbers out.

Max RMS output on the GK 1001RB-II: 700W.
Max consumption on the GK 1001RB-II: 1476W

The laws of physics make it pretty difficult (see: impossible) to have more energy at the output than potential energy at the input. Seeing as we're not burning, performing atomic reactions, or dropping the amplifier from heights in order to produce more energy from the process, we can ignore all forms of potential energy outside of the input from the power mains.

So, assuming 100% efficiency (see: impossible), you have an absolute MAXIMUM output of 1476W, the same as the maximum input. You'd need power consumption above 7000W to reach 10 times the RMS output on peaks.

A much more likely peak spec would be about 1.414 times the RMS spec (ie: 1/0.707, which is how you derive RMS from peak). Some companies may rate their products a bit more conservatively, so you might find a peak spec that's 1.5, maybe even 2 times the RMS rating, but 10 times? That's either an extreme marketing mislabel, or a testing snafu.

 

[Jazz Ad]

For GK, Bob Gallien explains it in detail in the last issue of Bass Gear Magazine (#3), including charges and protections.

For Marshall, it was on all their brochures back then and still Link Removed right now. For this very reason they avertised against using non-DBS cabs with their amps.

I think your post alone justifies the original poster's concerns. You compare peak events to nominal electric consumption, which makes no sense.

 

[Count Bassie]

I just have to say I think it's annoying that most of the time when you go shop for an amp in a store, the 'help' very often doesn't seem to be of any real help at all concerning this subject. I remember the first time I dealt with a Trace Elliot head, it had two volume controls. I needed an explanation of exactly what that meant!

I realize a lack of standardization exists as far as amp construction and specifying; hence application... but it's still true that no matter what part of the world you go to, an egg will break if it hits the ground from high enough up. A speaker will blow if it's abused... overheats from excessive power, gets the crap beat out of it for a long time, etc.

You know, when someone says something that is information, it pays to pay attention and retain it (for the young'uns among us). The simple fact is that if I crank the gain on my PB-1 preamp, EQ'd for a lo-boost, when running it through my Crest FA901 at full crank (for headroom) and into my 115 BW cab, I'm going to lose that speaker in a minute or less. I did a lot of this in my early years, due to blockheadedness and testosterone overload. I did it a year or so ago too! Duh.

So I'm not chiding anyone here as I have no business doing that- I'm just saying that I can't believe this is a complex issue, really...

To finish up here, I have to agree that the way the amp market is managed has little to do with handling correct information and passing it on to the end-user. It has way more to do with profit margins, and that is insured by maintaining a relationship with the mass-market. Cabs are built to a low standard so that you, the end-user, will be back. Like GM...

The only people who respect race-car drivers' interests are their crews (not GM). The only people who respect musicians' interests are the people who work for them (not GC!)!

 

[Mark Reccord]

AM's ego aside, if all other factors are equal, what is going to blow a speaker first, this MuFi amp or a 800w Walter Woods?

The more powerful amp is potentially more likely to damage any given speaker, simply because it can produce more power. The AMS-50 might be slightly more dangerous to speakers than a class AB 50W amp because it will clip asymmetrically which will result in a net DC current through the speaker under clipping. But if we're talking a 500W rated, 8 Ohm speaker, it's extremely unlikely that the AMS-50 could thermally damage it as its maximum output under severe clipping at that impedance would be about 100W. Clearly, if you set the Woods up to be continuously dumping 800W into said speaker, you would most likely damage it. I'd guess the 800W number on the Woods is for 4 Ohms, but this is a purely academic example so I'm not going to worry about it.

 

[billfitzmaurice]

Sorry for the long quote, guys. How exactly do you crunch the numbers like this? I would like to know because I am in the process of designing my own DIY cab. I know the thermal power handling is 500w, more than I need, but I'd like to figure out the mechanical power handling also. I have all of the T-S specs and cab specs.
Do I need a special program? And is it free, or is there a free equivalent?

No offense, but the mere asking of the question says that you are literally years away from having the required skills to design your own cab. First search the FAQ to see the upsides and downsides of DIY, and if you still want to do your own cab build a tested design.

So, assuming 100% efficiency (see: impossible), you have an absolute MAXIMUM output of 1476W, the same as the maximum input. You'd need power consumption above 7000W to reach 10 times the RMS output on peaks.

The short term peak output power of an amp isn't limited by the power available from the wall, because the amp power supply capacitors store power. Large enough capacitors can store a hundred or even a thousand times the power available out of the wall, the catch is that they can only deliver that power for very short periods before being drained. Unfortunately a few milliseconds is all it takes to toast a voice coil.

 

[SpamBot]

I think you may have misinterpreted my question. The cab is designed in WinISD. What I want to know is how to derive the mechanical power handling of the cab, already designed, at certain frequencies.

 

[billfitzmaurice]

I think you may have misinterpreted my question. The cab is designed in WinISD. What I want to know is how to derive the mechanical power handling of the cab, already designed, at certain frequencies.

That information is in WinISD Alpha Pro, as it is with all full function box programs. My point is that someone with the requisite audio engineering skills to design his own cabs would know this. WinISD doesn't design cabs, it's a tool which a cabinet designer uses to make fast calculations that otherwise are very time consuming to perform.

 

[fdeck]

For the record, most GK amps and Marshall DBS line have a peak power roughly 10 times their nominal power. Would it be fair to advertise their 200 W RMS combo as 2000 W?
The good thing about RMS is that it gives a roughly identical platform of comparison to everyone. It's far from the only factor to consider.

No. See posts 97-100. An amp rated at 200 W RMS cannot deliver 2000 W to its rated load because of the series resistance of the speaker.

 

[Jazz Ad]

Take a look at post 127 for an explanation.

 

[tombowlus]

I caught the HINT by Tom Bowlus. I mentioned this a couple weeks ago in another thread Tom, what needs to happen is a few of the Techno Heads need to get together and actually WRITE a method of testing that allows TOOB and SS amplifiers to equally be compared.

I think we have a good method worked out - and it's not super complicated. However, before we start testing with this method, we're going to get some peer-review feedback from Andy Field, Bob Gallien, and a few others.

 

[B-string]

Just to clarify; Bob Gallien (G-K) over builds his power supplies to provide 5 times the current needed for his amps rated outputs. Does not employ limiters but instead uses a protection circuit for amp shutdown if extended (like a short circuit) happens to the output. This allows a Bass players to enjoy all the dynamics they and their bass guitar is capable of (unless you hang a compressor/limiter in your signal chain).
JIMO this allows a more tube like response to the dynamic player {subjective: punch and powerful response}.

 

[Jazz Ad]

I find strange to associate this with tube response, since tubes do exactly the opposite by slightly distorting and compressing the signal on attacks.

 

[JimmyM]

The more powerful amp is potentially more likely to damage any given speaker, simply because it can produce more power. The AMS-50 might be slightly more dangerous to speakers than a class AB 50W amp because it will clip asymmetrically which will result in a net DC current through the speaker under clipping.

It's been explained to me by many amp techs that if an amp ever sends DC to the speakers, it's broken.

 

[B-string]

I find strange to associate this with tube response, since tubes do exactly the opposite by slightly distorting and compressing the signal on attacks.

Would that be dependant on how much of the avalible gain you are nominally using? I am not speaking of full output, instead nominal playing conditions. The reserve of a well designed tube amp provides massive reserves at 1/4 gain to 1/3 gain unless you are building in a "crunch" stage.

 

[fdeck]

Take a look at post 127 for an explanation.

Explain to me in your own words how an amplifier with a given output voltage limit V (i.e., typically the hard clipping limit of the power amp) driving a speaker with series resistance R can deliver more current than V/R.

Use for your explanation any waveform that a musical instrument is likely to produce.

 

[RickenBoogie]

That's obviously impossible, and I'm certainly no EE. But any fool with a basic knowledge of Ohm's Law can see the impossiblity of that business.

 

[Mark Reccord]

It's been explained to me by many amp techs that if an amp ever sends DC to the speakers, it's broken.

In the sense that they are talking about it, that's true.

What I'm talking about is different and is the result of an asymmetrically-shaped waveform, which results when an amp's output stage is not biased to the exact center of the power supply, which is very common in true class-A amps. This leads to one side of the output waveform clipping before the other, which gives a net DC current through the speaker. Any time an AC waveform is not symmetrical about the 0 axis, there's a DC component. I can prove that mathematically if you like.

It's not much of an issue with class AB amps because they're inherently biased to the center of a split power supply (i.e 0 VDC), so the clip points are X volts positive above 0 and X volts negative below 0 as opposed to X volts positive and Y volts negative in a typical class A circuit.

 

[Jazz Ad]

Explain to me in your own words how an amplifier with a given output voltage limit V (i.e., typically the hard clipping limit of the power amp) driving a speaker with series resistance R can deliver more current than V/R.

Use for your explanation any waveform that a musical instrument is likely to produce.

I once again refer you to post #127 and Bass Gear Mag. Mrs FitzMaurice and Gallien obviously explain it better than I could.
As for waveforms, they're almost irrelevant here. We're talking about attack/sustain ratio so an ADSR representation of a bass note would be much more useful and accurate.