# Decible calculatin'?

Discussion in 'Amps and Cabs [BG]' started by Nomadic Herder, Oct 8, 2001.

Aug 20, 2000
Worcester, MA
Is there any kind of formula with which one can calculate how many decibles an amp is capable of?

And can anyone tell me how many decibles my Ampeg B3158 (100 watts to a 15 and 50 to an 8) can put out? And how many of those are before it distorts?

2. ### JMXVorsprung durch Technik

Sep 4, 2000
Cologne, Germany
It's not calculated from the amp specs, but the speaker specs - the SPL rating.

Let's say a cab has SPL of 100 dB 1W/1m and a power handling of 100 W RMS.

That's means if you put 1 W into it you get roughly 100 dB.

10 times the power give you + 10dB.

So you get 120 dB with 100 W power.

Another way of calculating it:
Twice the power gives you +3 dB

1W = 100dB
2W = 103dB
4W = 106dB
8W = 109dB
16W = 112dB
32W = 115dB
64W = 118dB
128W = 121dB

This also shows the logarithmic relationship quite clearly.

3. ### Joris

Conclusion: you need to know the speaker's sensitivity first (the "dB-at-1W-at-1m" figure)

The maximum SPL is always the "power-at-the-verge-of-clipping".

4. ### HeavyDutySupporting CurmudgeonStaff MemberGold Supporting Member

Jun 26, 2000
Suburban Chicago, IL
Then, if you're like me and suck at advanced math, go here .

5. ### Steven Green

Jul 25, 2001
Pacific NW
What if you have two cabs that have a different dB/SPL rating?

I have a Eden 410XLT which is 106 @1w/1m

&

118XL which is 100 dB @1w/1m

and 625 W rms driving them?

What would my total SPL be?

6. ### Steven Green

Jul 25, 2001
Pacific NW
Also, is that MAX or not? If not, what is MAX?

Thanks!