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Volume vs. watts


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12/13/1997 8:30 PM
LP
Volume vs. watts
How much can be inferred about the volume an amp will produce from its power rating in watts (through the same speaker cabinet)? I've heard statments like 'this is the loudest 50 watt amp I've ever heard, way louder than so-and-so's 50 watter'.
 
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12/14/1997 12:08 AM
Bill Bolton

> How much can be inferred about the  
> volume an amp will produce from its  
> power rating in watts (through the  
> same speaker cabinet)?  
 
Even with speaker efficency taken out of the equation, it depends on the distortion level at which the power rating specification was set.  
 
Honesty in power rating figures seems never to have been particularly high on agenda for most guitar amp manufacturers.  
 
Cheers,  
 
Bill
 
12/16/1997 5:33 AM
Mook

Wattage is logrithmic. This means that  
at a certain wattage, say 30 watts, you  
get a certain volume. If you increase  
the wattage to, say 80 or 100 watts, you  
WILL NOT increase the volume all that  
much. In fact, the difference in volume  
is probly unnoticable, given the same  
speaker configuration. A lower watt amp  
will breakup a little sooner, that's all.  
This for me is GOOD -- so when shopping  
for an amp, I go for lower wattage amps.  
 
 
I don't know about anyone else, but  
my small Fender Pro Jr. at 15 watts is  
TOO goddamm loud!!  
 
 
Here's the formula:  
 
increasing the wattage by 10 will give  
you ONLY double the volume.  
 
 
 
So, by practical means, 50 watts is just  
as loud as 100 watts, given the same  
cabinet/speakers.  
 
I really laugh at people who say they  
need 100 watts of power. I say just  
buy a 40-50 watter and save $$ on NOT  
having to replace two extra tubes every  
year.
 
12/17/1997 11:17 AM
dave

Volume (i.e. loudness) is measured in decibels, which i believe is also a logrithmic scale. Also perceived human hearing I have read increases in a logrithmic fashion.  
 
 
I must respectfully disagree with the statement that the difference in loudness between a 30 watt amp and a compable 100 watt amp is not noticeable. Not to say that 30 watt amps aren't 'loud'; They defintely can fill a room with volume and compete with the volume of bass and drums. But a 100 watt amp can fill a larger room with volume and be heard over a louder background noise.  
 
I do agree that the perceived difference in loudness between a 50 and 100 watt amp is not very noticeable when you're playing in a small room with no backgroud noise. They're both ear-shattering. But put into a larger room and with lots of competeing noise... IMHO it makes a noticeable difference.  
 
Of course this is a moot point anyway, because PA miking can boost anybody's 15 watt amp to a desired loudness.  
 
Also, if you increase an amp by ten watts and it only 'doubles' the volume, it sounds like the you're saying that volume increases logrithmically to power - in other words, a 40 watt amp is 100% louder than a 30 watt amp?. I guess you meant 10 times the wattage will double the volume.  
 
I wonder if anyone (I assume someone with a lot of free time) has performed decibel measurements on amps of difference power ratings in a controlled setting? That would give you the answer.
 
12/17/1997 11:47 AM
R.G.

The problem with doing cross-amplifier meausements is that speaker efficiency varies all over the map. The range os SPL out at 1W/1M (commonly quoted measure for speakers) for common guitar speakers may show a 10 or 12 db range. This represents up to a four to one input power range for getting the least efficient speaker and the most efficient speaker to sound equally loud.  
 
You'd have to test every amp with the same speakers.  
 
Worse yet, the "perceived power" illusion comes into play for smaller amps. Tube amps have the earliest stages of distortion such that the distortion is mistaken by the human ear for more loudness, not distortion. You have to use an SPL meter.
 
12/17/1997 10:34 PM
John Kos

Yeah, the "perceived power" does have a lot to do with it. I remember reading an article in Home and Studio Recording a few years ago in which they did an experiment with different amps in a mixing room.  
They measured the preferred volume and distortion level (albeit very low) of a few engineers with the stock amp and then replaced the amp with a more powerful one. Guess what, the engineers turned it up until it hit about the same distortion level, not the same volume.  
So, smaller amps will seem to sound louder than they may measure because of the earlier distortion.  
 
John Kos
 
12/18/1997 1:08 PM
Jim S.

Also, I read somewhere (Dave Funk column?) about studies that were done to find out why a tube amp often sounds louder than a solid state amp of the same power rating. Supposedly, it had to do with the proportion of odd and even harmonic overtones added by the output circuits when the amps are near or at full output power.  
 
The theory is that a balanced mix of even harmonics along with a not excessive amount of odd harmonics tend to make the amp sound fuller and louder while a preponderance of odd harmonics will tend to make the sound seem "flatter" and not as loud.  
 
I don't really know if this is true, but it is an interesting idea and certainly would explain my own experience with tube vs. ss amps..
 

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