How might one measure the dB of sound output by the headphone?
You can calculate the dB SPL output of the headphone by using it's base sensitivity figure and then adding (or subtracting) based on how much power you give it. You need to know how dB adds based on the power. Here are a couple of rules that will help with that:
1. Doubling input power adds 3 dB.
2. Multiplying the power by 10 adds 10 dB.
Let's do a few examples. We will pretend that the headphones we are talking about produce 102 dB SPL with 1 mW of input power.
1. What's the SPL if we give it 2 mW?
2. What is the dB SPL for 10 mW?
3. How about 20 mW ?
4. ...and what about 4 mW ?
Scroll down for answers....
1. The base for these calculations is 102 dB with 1 mW. 2 mW is double of 1 mW. We know that doubling the power adds 3 dB, so we will get 102 + 3 = 105 dB SPL from 2 mW.
2. 10 mW is 10 times 1 mW, so we know we can add 10 dB. 102 + 10 = 112 dB SPL.
3. 20 mW... hmmm... Now we have to combine some rules. We can get from 1 mW to 20 in two steps. 1 x 10 = 10. 10 x 2 = 20. So we use the 10 x rule first and then the 2 x rule. 1 -> 10 gives us +10 dB. 10 -> 20 gives us +3 dB. So: 102 + 10 + 3 = 115 dB SPL.
4. We can get from 1 mW to 4 mW by doubling twice. So we get to add 3 dB twice. 102 + 3 + 3 = 108 dB SPL.
I hope that helps you understand dB calculations a little better.
Brian.