A 50 watt amp attenuated at -12db would be 3.125 watts, right? Is there a formula for calculating the decibel level for that?

The big question is if the amp is really pushing 50 watts. The whole double your wattage you get 3 dbs thing is supposedly the correct formula

Too many other variables to be able to say that 50w = X decibels. Different speakers will give different decibels with the same amp.

Awe yes my bad. Your speaker sensitivity is rated for one watt one meter a way. So, a greenback is 98dbs at one watt, x2 is 101dbs at 2 watt. 2 watt x2 would be 4 watts at 104dbs and so on.. According to the formula.

That's what I'm looking for DrainBamage! Now, I *think* I should be able to calculate what I was at for about 30 minutes earlier. Yes, an SPL meter would be simpler, but I don't have one.

p.s. The only variable I'm not sure about is how many actual watts I was running. The amp volume was on 8 so I'm going to assume it was at, or close to, max power (50 watts).

What's the amp? I've heard amps are rated as to their clean power... if you are at 8 and it's already crunching, you're probably way past 50 at this point.

With a single GB @ 1 watt it should put out 98dB so at 3 watts it should put out ~102dB...I think the estimate is that you add 3 dB everytime you double the amount of speakers. So you could be looking at 108dB or thereabouts with a 4x12.

If you are running it 'clean' it will put out ~ 50 watts. If it's in rude health and cranked right up it might put about 85 watts. So I'd calculate at around 70 watts or so for a rough estimate and then minus the 12 db for the attenuation. So very roughly you could be putting out 116db from the amp, adding 6 db for the extra speakers and then pulling off 12db which will put you at about 110db. This is naturally pretty rough but prob not that far off.

That is only correct if the power PER SPEAKER stays the same. However, if an amp is pushing 1 watt into 4 speakers, then per speaker the power is 0.25 Watt. Next to that, there will be interference effects between the sound waves coming from the speakers that will have more or less noticeable effects, depending on the frequency of the sound. Without interference, and a fixed power from the amp, the number of speakers should have no effect on the SPL when you double the amount of speakers.

Ah huh...more reading to do...cheers mate! So now we have a rough idea of the rig, (rough wattage potential, speakers, efficiency etc), what would you think it could put out?

If you have an iPhone, JL Audio has an app that includes SPL, RTA and for checking absolute phase. If not, Radio Chack has SPL meters for a reasonable price. The problem with estimating the SPL is that the room has an affect and, if you don't consider this, hte result won't be accurate. As the speaker gets closer the speaker gets to the corner, the three surfaces add to the level, especially in the low end.

http://www.youtube.com/watch?v=PMh0tUDGbck&feature=player_detailpage Frank you might enjoy this Slash VS Yngwie - How Loud? Its pretty interesting. Im assuming greenbacks are in the cabs. And you also have to figure that their conclusion isnt based off of the speakers being measured one meter away like how speakers are measured on the the specs sheet. If I remember correctly every meter away is another deduction of 3 dbs.

I wouldn't want to be that poor sap sitting in front of those things holding the meter. Unless they changed speakers, the cabs have G12T-75s. I'm surprised he switched guitars for the test. The LP's pups are likely hotter than the Strat.