Amp power versus wattage

[mbratch]

I read or heard from someone that an amplifier that's 60 Watts (RMS) is about 3dB louder than a 40 Watt (RMS) amp. Can such a general statement be made? Is there some general relationship between wattage and power? I know that this is made more complicated by speaker configuration and whether the amp is class A or AB perhaps (?).

 

[clarkram]

all things being equal (same speakers etc) I think you need to double your wattage for a 3db increase. So an 80w amp would give you 3db more than a 40w.
I may be mistaken, but I think I read somewhere in ancient times that there was a logarithic relationship with watts and decibels.
To literally double the spl of a 40 watt amp you would need 400 watts.

Clark

 

[aleclee]

To paraphrase Nigel Tufnel, "It's 20W louder".

In all seriousness, discussion of relative amp "loudness" has so many variables as to almost be moot. Consider the following:

• Amp power
• Speaker efficiency (a 50W amp with 3dB more sensitive speakers should generate pretty much the same SPL as a 100W amp)
• Cabinet configuration (# speakers, open/closed, etc.)
• Amp voicing--IMHO, one of the most important factors. How many times have you heard someone say one amp has more or less "cut" than another? This is a combination of amp voicing, EQ, power supply and output iron (among other things).
• Clean vs dirty tone. Similar to the voicing issue, some tones are more easily heard than others and will sit differently in a mix.

I'm sure I've missed a bunch of factors but you probably get the idea. IMO the psychoacoustic properties (voicing, tone, etc.) of an amp's output contribute to its apparent loudness as much as its power. If you're not playing in a band, a 60W amp is probably overkill (assuming there are lower-powered alternatives). Depending on the "cut" of an amp, 60W might be too much (think 50W NMV amps) or not enough (some DMAs).

My $0.02, IMHO, FWIW, YMMV, etc.

 

[mbratch]

Actually I have a 40Watt amp that I play in a couple of bands with. Seems to work fine in small club/cafe settings (with just a little break up on the clean), and in bigger scenarios I mic the amp.

I was actually thinking of moving down the wattage ladder to something closer to 30W and wasn't sure if I'd still be happy.

But, overall, I was generically interested in knowing if there was some kind of measureable relationship. I figured there were probably lots of variables.

 

[aleclee]

Originally posted by mbratch
But, overall, I was generically interested in knowing if there was some kind of measureable relationship. I figured there were probably lots of variables.

Assuming equivalent speaker efficiency, the relationship between wattage and SPL is easily calculated. I was just pointing out that even with a twofold difference in power, other variables might render the power difference fairly meaningless.

As far as going from a 40W to 30W amp, the other variables will dominate the perceived loudness. The theoretical SPL change would be only around 1 dB--hardly noticable. Depending on the tones you use, the loss of clean headroom might be quite noticable, though. If your tone is mostly dirty, you might hardly even tell.

 

[ekp]

IMO the psychoacoustic properties (voicing, tone, etc.) of an amp's output contribute to its apparent loudness as much as its power.

You are quite right there are other properties. Since the ears are non-linear, they produce harmonics when the sound is loud. If you provide those harmonics, the sound will sound loud - so it seems.

 

[mbratch]

OK, a related question. I've read that class A watts are louder than class AB watts. I admit, it was in some sales literature. But what's up with that claim?

 

[aleclee]

The same claims are made regarding tube vs SS wattages. My best guess is pschchoacoustics.