or Connect
Head-Fi.org › Forums › Equipment Forums › Sound Science › Calculating 70 dB SPL volume
New Posts  All Forums:Forum Nav:

Calculating 70 dB SPL volume

post #1 of 5
Thread Starter 

So I'm searching to match a 70 db volume.... I have an etymotic er4s with 100 ohm impedance and 100 db per 1 mW. I'm using a fiio e07k with 220 mW@32Ω and, 250 mW@16Ω... I'm using gain of 6 dB (2X) and i'm asuming 2.7 V for the e07k before the gain. So without gain it will 118.62 db max loudness and with gain 124.6434 db...Is this correct? With gain of 6 dB is just multiply 2.7x2=5.4 as new max ouput from the amp? Since the e07k has 60 levels for volume i'm just using proportions to match the desired decibels... but when using equivalents for 70 dB with and without gain it doesn't sound equal... Any help will be apreciated

post #2 of 5

Where'd you get the 2.7V from?

 

What kind of assumption are you making about the volume control steps? Linear in dB across the whole range? Don't count on it. In any case, there seem to be too many assumptions going on, many of which I'm not really convinced on.

 

Anyway, what you want is 0.00316 V rms. So 0.00316^2 V / 100 ohms = 1 * 10^-7 watts = 1 * 10^-4 mW. So 1/10000th of 1 mW, where 1 mW gives you 110 dB SPL. Hence 40 dB less than that, or 70 dB SPL. It's probably easier to just measure that on a multimeter. Note: cheap meters may be very confused by actual music and stuff with high frequencies, not to mention voltages that low. It may be worth using a test tone instead. Also check if the meter even does the low millivolts range.

post #3 of 5
post #4 of 5
Quote:
Originally Posted by LibiSC View Post

So I'm searching to match a 70 db volume.... I have an etymotic er4s with 100 ohm impedance and 100 db per 1 mW. I'm using a fiio e07k with 220 mW@32Ω and, 250 mW@16Ω... I'm using gain of 6 dB (2X) and i'm asuming 2.7 V for the e07k before the gain. So without gain it will 118.62 db max loudness and with gain 124.6434 db...Is this correct? With gain of 6 dB is just multiply 2.7x2=5.4 as new max ouput from the amp? Since the e07k has 60 levels for volume i'm just using proportions to match the desired decibels... but when using equivalents for 70 dB with and without gain it doesn't sound equal... Any help will be apreciated

2.7 volts peak? Peak-to-peak? RMS? Why are you making that assumption?

You want to know how much power for 70dB SPL? 1 mW = 100dB. 70 - 100 = -30dB. 1mW - 30dB = 0.001 mW (10log10(Pi/Po)). Do this without calculator. 30 dB = 3 decimal places, factor of 1000.

Voltage for this? 0.001 = V^V/R. R = 100. V^V = 0.00001. V = 0.00316. RMS. Do this with calculator.

w
post #5 of 5
Thread Starter 
Quote:
Originally Posted by wakibaki View Post


2.7 volts peak? Peak-to-peak? RMS? Why are you making that assumption?

You want to know how much power for 70dB SPL? 1 mW = 100dB. 70 - 100 = -30dB. 1mW - 30dB = 0.001 mW (10log10(Pi/Po)). Do this without calculator. 30 dB = 3 decimal places, factor of 1000.

Voltage for this? 0.001 = V^V/R. R = 100. V^V = 0.00001. V = 0.00316. RMS. Do this with calculator.

w

 

 

Quote:
Originally Posted by mikeaj View Post
 

Where'd you get the 2.7V from?

 

What kind of assumption are you making about the volume control steps? Linear in dB across the whole range? Don't count on it. In any case, there seem to be too many assumptions going on, many of which I'm not really convinced on.

 

Anyway, what you want is 0.00316 V rms. So 0.00316^2 V / 100 ohms = 1 * 10^-7 watts = 1 * 10^-4 mW. So 1/10000th of 1 mW, where 1 mW gives you 110 dB SPL. Hence 40 dB less than that, or 70 dB SPL. It's probably easier to just measure that on a multimeter. Note: cheap meters may be very confused by actual music and stuff with high frequencies, not to mention voltages that low. It may be worth using a test tone instead. Also check if the meter even does the low millivolts range.

 

I'm assuming 2.7 vrms of ouput with 100 ohms of impedance.. I'm guessing the value using 220 mW@32Ω and 36mW@300Ω

 

With that value I'm comparing with 100 dB with 1 mW or 110 with 1 volt....

 

 

So max loudness is 118.62 dBSPL without gain or (not sure) 124.6434 dBSPL  with 6dB gain that is 5.4 vrms ouput at 100 Ω from the e07k

 

The logic is correct?? But I don't feel it when setting the volume... if the volume is not linear then it makes sense....

 

The volume without gain going from "60" equals 118.62 then the volume i want equals 70 dB?

 

 

I don't have a multimeter... was trying to guess it just with the formulas

 

 

 

Also to get 70 dBSPL are needed 0.001 mW or 0.01 V.... but now that I have it I'm trying to set the volumen knowing how much power the amp is giving @ 100 Ω

New Posts  All Forums:Forum Nav:
  Return Home
  Back to Forum: Sound Science
Head-Fi.org › Forums › Equipment Forums › Sound Science › Calculating 70 dB SPL volume