Hi all!

Yesterday I was reading an article about loudness war and how we can improve our dynamic range to avoid squashing the life out of our material, and the author was talking about calibrating the outputs in order to avoid different playback levels with different music (and other psychoacoustics related stuff, bla bla bla...)

Now, to the question:

I'm using an iMac, level is on max (all white squares filled) and the AVG (RMS average) of my music is, say, 0 dBFS on Ableton Live. I'm using a pair of AKG k712pro to monitor the output, and they have a 105 dB SPL/V sensivity, what's the output in dB SPL of my headphones? Does anyone know of any program that can do the math for me at different iMac volume level (e.g. only half of the squares filled, one square filled, all squares, etc...)

Thanks for the help!

 

Hi!
I haven't studied this in-depth, but headphone sensitivity in layman terms means how much power (in miliwatts) is necessary to achieve certain loudness with certain headphones.
105dBV at 62Ohms is rather poor sensitivity, much like K701. 105dBV translates to 93dB/mW e.g. you need 1 mW to achieve 93dB. 110dB needs 51mW (102mW for both drivers)

Basically the calibration cannot be precisely performed without knowledge how much power goes to your headphones. For that you need digital multimeter capable of measuring AC current precisely.
Once you finish measuring mA and mV you can convert them to mW and then calculate (or estimate) the dB level.

 

Hello Sonar Sounds,

As Andrew said, you need to know how your digital level of 0dBFs translates into the electrical power present at the input of the headphones.
Just two corrections with regard to Andrew: 105 dB SPL is a sound pressure level, and this is not to be mixed up with dBV, which is a voltage level. So 105dB SPL is the sound pressure the headphones produce, and 105dBV (which is meaningless for our issue here) would be nearly 503 KVolts (peak to peak).
And for 110dB SPL you need 7.08 mW (not 51mW), given a headphone sensitivity of 93dB SPL/mW.

I think you might do the calculations without a multimeter, if you had the relevant figures of your analogue gear at hand, i.e. the gear that does the D/A conversion and amplifies the audio before going into the AKG cans.
This means: Have a look into the manual of the iMac in the audio card's section. What is the analogue output (in V or dBu or dBV) --at 0dBFs-- of the soundcard and its output resistance (both on the output you are using for the AKG 712)?

If you have that figure, you have the voltage of the iMac output at 0dBFs, and the power delivered to the cans then is the square of the voltage, divided by the sum of output resistance and resistance of the AKG (don't know whether 62 Ohms are correct for the 712, as stated by Andrew). --> P = U²/R .
Do your calculations with the voltage expressed in mV, so you get the output power to the cans in mW. If you have to transfer dBV or dBu figures (from the iMac manual) into Volts, you can use this website: http://www.sengpielaudio.com/Rechner-db-volt.htm .
Then Andrew's figure of 93dB/mW helps you, this figure is approximately correct, if the resistance of the 712 is actually 62 Ohms.

How do you get your SPL output at 0dBFs? Well, you have calculated your output power in mW at 0dBFs as described above, and now you have to translate that in relation to 93dB: Related to 1mW, your mW output from the iMac gives a factor, and this factor has to be applied to the figure of 93dB SPL.
You may use this website for that task: http://www.sengpielaudio.com/Rechner-db.htm

Example: If your output at 0dBFs would be 0.5mW, you'd have to subtract 6dB from the SPL output of 93dB, because subtracting 6dB equals to halving the acoustical "power". Your 712 would produce an SPL of 87dB...

Hope this helps.

 

Thanks guys, I didn't expect to read such a detailed explanation since I know the question is kinda tricky, I really appreciate the time you spent on answering this!!
Is now the output (in volts/mW) the only measure I need to find to solve this problem? I've got a DMM at home, can I use it to measure the voltage (or wattage) at the iMac's audio output? By the way, the measurements Andrew gave are correct, my headphones have a rated impedance of 62 ohms and a sensivity of 105 dB SPL/V (more here: datasheet)

Thanks again!

 

Although slightly off topic, I highly suggest that everybody check out the videos from Mr. Bob Katz on The loudness War. Very interesting information!! The guy is a Sonic Genius


[media]https://www.youtube.com/watch?v=XCd6MHlo_iA[/media]

 

If you own a DMM, I suppose it's easier to use it to measure the voltage at the output (than to go with the soundcard manual). As far as I see, measuring wattage would have to be corrected by the influence of the headphone impedance (which the DMM doesn't "see" at the iMac output).
So I would tend to measure the voltage, and then calculate the wattage at the 712 input: voltage squared, divided by the resistance sum as mentioned.

 

Thanks a lot bellegear! Will do that tomorrow morning since now it's kinda late, and I'll update the results if I manage to do everything correctly

P.S.: @Mykal the issue came up when reading a Bob Katz article on Digital Domain (his website)

 

hahhh... everytime I see "SPL", I always think of Samuel Pool (drum n bass / dubstep prod. "SPL").. man his DnB was* amazing!!!!!! all that Amen stuff I just cannot get sick of it .. and its been 16 years now since I started bein interested in that stuff.






* I say "was" because I haven't been focused on DnB since '09 or so; where I switched focus to Deep Dubstep; but I've been strictly focused on Hard/Dark/Industrial Techno since Nov. 2013... I have a tendency these days to completely do ONE genre at a time

P.S. been listening to some Stars of the Lid lately (specifically, "The Tired Sounds of..." album) at night before bed (not that I can't listen to it at absolutely any time of the day though), for a little reminiscing... my Lord are they just sooooo amazing... all their albums... AND side-projects of course.

 

I sort of figured as much, Bob is such a good guy.I live 15 mins away from him and check out as many of his speakings on Audio as often as possible. So far over the last 15 years I have learned that everything I do is wrong