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Am I Ever Using All of My Watts?

dexplosion

dexplosion

Jun 17, 2008
103
2
South Louisiana
#1
I have an Aguilar AG500SC that puts out 500 watts into 4 ohms. I also have a GS212 4 ohm cabinet to be able to receive all 500 watts.

But I was wondering, are all of those 500 watts ever being used?
For example, if the master volume is maxed, am I getting them then?
Or, what about when I adjust the gain? Does that control the wattage?
Would both master volume and gain have to be cranked in order to have full wattage?

If someone could put that in perspective, I would be ever so thankful. :smug:
 
#3
probably not ever getting all 500, and not for any length of time.

The volume of your preamp being maxed does not mean that you would be providing all your watts to your speakers.It means that the preamp is boosting as high as it can. If you were to say, run a sine wave sweep between 500 and 20hz at full volume with a very strong input signal, barring any filters, you could get all (or More and all) your watts. This would more than likely blow your speakers though.

You don't have a control on your preamp that controls power amp wattage. You have several that effect gain levels in the signal controlling your amplifier.
 
#4
The engineers here can answer it in more detail but no, you're not always using all your watts unless you're cranked up to full input and full output.

Amps are rated at a certain wattage at a certain percent of distortion, they can put out more than their rated power with higher distortion levels.
 
#5
You dont have to have volume control cranked to put out full power. Normally you would be using about 50 to 100 watts but bass is very dynamic and full power peaks can happen alot just by hitting a note hard even when your volume isnt cranked. Most solid state amps have a peak limiter built in so that it wont distort on loud passages. Without it an amp could distort even at relativly lower volumes because the dynamics of bass.
 
#8
Probably only in extremely short bursts if ever during normal playing, regardless of your settings.
As long as it's getting the job done, who cares? IMO watt ratings on amps are just a frame of reference rather than a truly significant spec.
 
#10
If you are playing loud there are peaks in signal that will reach 500 watts. These peaks can be reached with the volume not cranked all the way up. The actual AVERAGE POWER the amplifier is producing is much less. The peak power capability in your amplifier is put there to provide the magic term : HEADROOM. Headroom is there to handle the peaks without clipping and destruction of the amplifier.

I have rendered a much longer description now pasted in the first sticky under the section about tube and SS watts arguement. HAVE FUN. BOB
 
#12
Watts don't mean a lot unless you consider the acoustic energy you can get out of them.
The sensitivity/efficiency of the cabinet to take a watt and turn it into acoustic sound.
If you went for a high efficiency design cabinet like Bill Fitzmarice cabinet - you're 500w would be acoustically much much louder.
 
#15
I am responding here on "gut" feeling based on too many years as a journeyman bassist rather than any empirical theory, but while others may be right that you seldom if ever use all your 500 watts I am sure that even at low volume you can hear the difference. That is, if you play a fifty or 100 transistor watt head softly then your 500 transistor watt head at the same volume through the same cab I would expect your head to send "better" - that is, tighter and punchier. This to me is the benefit of headroom. I know that there are other variables to consider such as components but, all things beiong equal, this is what my gut tells me to expect.
So yes, in my roundabout intuitive way you are using all those watts.
I am now waiting to be shot down.
 
#16
username1 said:
You dont have to have volume control cranked to put out full power. Normally you would be using about 50 to 100 watts but bass is very dynamic and full power peaks can happen alot just by hitting a note hard even when your volume isnt cranked. Most solid state amps have a peak limiter built in so that it wont distort on loud passages. Without it an amp could distort even at relativly lower volumes because the dynamics of bass.
Click to expand...

However, most cabinets rated at 500W rms will handle peaks up to 1,000W, so there's some built-in headroom for those loud transients.
 
#17
dexplosion said:
But I was wondering, are all of those 500 watts ever being used?
For example, if the master volume is maxed, am I getting them then?
Or, what about when I adjust the gain? Does that control the wattage?
Would both master volume and gain have to be cranked in order to have full wattage?
Click to expand...

Actually it depends on (at least) four factors: The output voltage delivered to the speaker is given by

Vout = (Gpreamp * Gmaster * Gpwramp) * Vin

where

Vin: preamp input voltage, i.e. bass output voltage
Gpreamp: preamp voltage gain; depends on gain knob setting
Gmaster: master volume voltage "gain"; varies between 0 (off) and 1 (cranked)
Gpwramp: power amp voltage gain; normally a fixed factor

Assuming RMS voltages, the power is then (for the sake of discussion into a resistive load)

P = Vout^2 / R

where

R: speaker resistance (think nominal impedance for simplicity)

Hence, how much of the power on tap you're using, depends on how "hot" signal the pickups deliver (and of course the volume setting on the bass itself), how much gain you put to use in the preamp input stage, to what degree the preamp output signal is attenuated by the master volume, and finally the voltage gain of the power amp.
 
#18
Munjibunga said:
However, most cabinets rated at 500W rms will handle peaks up to 1,000W, so there's some built-in headroom for those loud transients.
Click to expand...
True, but most 500w cabs will also fart out at 250 watts or less. In use the average output of most amps is usually no more than 1/4 what the user thinks it is.
 
#19
Normally you set up the preamp gain such that the preamp operates internally (EQ, compressor if present, FX loop etc) at a "convenient" voltage; not too high, so you don't risk running into clipping in the preamp itself, not too low, in which case the thermal noise inherent to the amp would get disturbing. Next you set the master volume to arrive at the desired volume (SPL).

With the gain structure setup as above, you're not using the full output power until the power amp is at the onset of clipping. Unless you have a cabinet with unusually low sensitivity (SPL at a given power (or rather voltage)), and/or play very loud, I'd say you're on average only using a fraction of the available power:

A typical cabinet yields 95 - 100 dB @ 1 W, 1 m. 10 W corresponds to 10 dB more, 100 W gives you 20 dB more, and 1000 W 30 dB more. If you have a simple SPL meter you can check the ballpark SPL level you're outputting, and do the math to see roughly in what power bracket you're running. As you can see from this example 10 - 100 W is already plenty.

HTH,
Fredrik
 

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