What's the point of 100 watt amps?

[Ch0jin]

Thanks Algonquin, I was hoping that would come up. Yes, it's true, a 100W amp is actually only 23% louder than a 50W amp. Here's the formula, go nuts!

2^log10(100W/50W) = 2^log10(2) = 2^.30102999…. = 1.23. (Just 23%!)

It's fundamentally flawed to apply linear math to guitar amps when you're thinking about power ratings. As the guys here who have used 100W amps have said, it's not necessarily about being a lot louder. Frequently it's about clean headroom (sorry, I don't have a formula for that, but more power amp reserve typically equals more clean headroom, important for all those Jazz gig's we play at metal volume) and/or more low frequency grunt.

It's also been mentioned that bass guitar amps typically run massively higher wattage than comparable guitar rigs, whilst completely true, I'd like to make it clear the same theory applies to Guitar amps.

If you want more perceived volume from the lower frequencies (any 7 string players want to comment?) you'll need more power.

So yeah, if you want stomach churning, pants flapping, brass vibrating, snare rattling, ear rupturing, foundation crumbling bass response in your guitar tone. Keep shopping the 100 Watt amps.

As a personal anecdote though, I jam with another guitarist/bass player and a loud rock drummer and I usually have a 60W all tube Peavey run with the MV wide open and the clean and crunch channel volumes pretty much maxed too. All through a very old (so i'm thinking, inefficient) 4x12 and I usually leave those jams thinking of buying a 100W head. Then I get home and think "H'mm a 5 watt combo would be sweet"

There is a place for both

[Duffy]

My thinking is that low frequency bass wavelengths such as those produced by guitar and bass amps are many feet long for one full wave. How this corresponds to how we perceive the bass sound in a small room or from headphones, I'm not sure. Of course, not being unidirectional, a lot of the waves are not going to have the space to fully form their waves before being reflected and atenuated. They are bouncing all around at high amplitudes reinforcing each other and cancelling each other out.

Here are the frequencies and wavelengths for the strings on a 4 string bass +/-:

String – Frequency - Wavelength
G - 97.9989 Hz - 11.531 ft.
D - 73.4162 Hz - 15.392 ft.
A - 55.000 Hz - 20.545 ft.
E - 41.2035 Hz - 27.425 ft. (329.098 in.)

The above wavelengths will occur in a free space, a space free of obstructions, walls, ceilings, people, etc.

Since our amps are located near walls, have open backs, are in enclosed rooms, etc., there are going to be a lot of powerful high amplitude sound waves bouncing around reinforcing each other and cancelling each other out, as the case may be in any given space. This is what I think Dee is talking about - the situation where you have sound waves bouncing all around and affecting what our ears perceive. Therefore, experimenting with the placement of the amps and speakers, aiming, etc., can have a big effect on how we hear our music. Because of this recording engineers go to great length to try to deal with this problem and the bass frequencies are particularly problematic for them and they go to great length, in some cases, to try to get it right or at least "better" sounding.

Also, it is seemingly confusing why we can hear a 40HZ bass note correctly thru a set of earphones. The amplitude of the sound wave at 40HZ coming to our ear from the headphones is much lower than the amplitude coming out of a bass amp. But the wavelength is still about 27 feet long, so our ears and brains must be processing that E note somehow so that it sounds right, even if the note is very short in duration such as one tenth of a second - it still sounds right.

[NWBasser]

...a lot of the waves are not going to have the space to fully form their waves before being reflected and atenuated.

Actually, the waves are fully formed right at the speaker (electro-mechanical to acoustic energy transfer). For a sound wave to gain amplitude (i.e., fully form) in free space, it would need some sort of energy input.
Sort of like when a bullet exits the barrel of a gun, it's going full velocity at that point and it won't speed up in the air on its own accord.

However, like a bass wave, a bullet can ricochet around and do all manner of odd things. But it certainly won't be going any faster.