I would like to keep listening levels with my headphones at safe levels.
This means that the rms of the sound should be in general below 85 dBSPL.
(There are various formulae for upper bounds on safe durations at higher dBSPL exposure per week,
but for simplicity I only consider the 85 dBSPL limit.)
In particular Stax listeners claim that the "clean" sound seduces people to turn up the volume beyond safe levels.
So, high volumes seem to be reasonable concern.
Let us consider the case that no fully equipped headphone measurement device is around to measure dbSPL at ear level.
For simplicity I consider a digital setup with integrated DAC and amp with a single volume control:
digital sound file -> amp -> headphone.
The following steps are required:
Here is my first question. If 2. can be achieved but the amp has no -dB display: What are you doing to keep dBSPL at safe levels?
Painting some small dots in -5 dB intervals next to the volume control knob are one option.
It seems that the more expensive an amp the more restrained its design.
In particular amps for Stax headphones have the least amount of information around the volume control knob.
[Side note: I do not consider here controlling the volume via the media player when listening to music. This would be directly reducing the dynamic range of the audio. Controlling the volume via amp/DAC offers at least the chance that DR is not reduced if the amp has a reasonable quality. On the other hand, controlling via mediaplayer might be useful during analysis of the amp volume control.]
My second question is: How can 2. be achieved for Stax?
Here is what I have done for 2. for a dynamic headphone and an amp with -dB display:
I measured with a multimeter the unloaded voltage of the amp at max setting of the volume control for a full scale sine signal.
Then I looked up the output impedance of the amp. (Actually, I also calculated the output impedance with a multimeter and a shunt.)
I looked up the resistance of the headphone.
Then it was straightforward to determine the voltage over the headphone at max volume.
Now: How can I determine 2. for, say, an amplifier for a Stax headphone? (Ok, here amp and DAC have to separate except for the SRM-D10.)
Things get complicated because of the capacitive reactance of the headphone.
Output impedance of an amp is not specified by Stax and I would rather not connect a shunt at those high voltages to make measurements on my own.
Furthermore, even if the output impedance of the amp was known, the impedance of Stax headphones is specified as a real value in Ohm. I am not sure about the complex (real + imaginary) calculations required in analogy to the dynamic headphone case since I have only a very rudimentary understanding of electrophysics.
The maximum output voltage as specified by Stax might be helpful in this calculation. But then again I wonder if the specified amp gain of, say, 60 dB applies to the unloaded output voltage of the amp. Or if the unloaded voltage of the DAC output is multiplied by the amp by 1000 into the output voltage with the headphone as the load connected.
I posted this here in the science forum because my guess is that in the Stax thread in the high-end audio subforum people would stop reading after my proposal to paint small dots next to the amp volume control knob.
This means that the rms of the sound should be in general below 85 dBSPL.
(There are various formulae for upper bounds on safe durations at higher dBSPL exposure per week,
but for simplicity I only consider the 85 dBSPL limit.)
In particular Stax listeners claim that the "clean" sound seduces people to turn up the volume beyond safe levels.
So, high volumes seem to be reasonable concern.
Let us consider the case that no fully equipped headphone measurement device is around to measure dbSPL at ear level.
For simplicity I consider a digital setup with integrated DAC and amp with a single volume control:
digital sound file -> amp -> headphone.
The following steps are required:
- Determine the rms of the digital soundfile. (Easy: several free tools available).
- Determine the voltage that is fed into the headphone for a full scale sine signal at maximum volume of the amp.
- Find out the sensitivity of the headphone. (dBSPL @ 1 Vrms @ 1 kHz. Should be easy: check product sheet.)
Here is my first question. If 2. can be achieved but the amp has no -dB display: What are you doing to keep dBSPL at safe levels?
Painting some small dots in -5 dB intervals next to the volume control knob are one option.
It seems that the more expensive an amp the more restrained its design.
In particular amps for Stax headphones have the least amount of information around the volume control knob.
[Side note: I do not consider here controlling the volume via the media player when listening to music. This would be directly reducing the dynamic range of the audio. Controlling the volume via amp/DAC offers at least the chance that DR is not reduced if the amp has a reasonable quality. On the other hand, controlling via mediaplayer might be useful during analysis of the amp volume control.]
My second question is: How can 2. be achieved for Stax?
Here is what I have done for 2. for a dynamic headphone and an amp with -dB display:
I measured with a multimeter the unloaded voltage of the amp at max setting of the volume control for a full scale sine signal.
Then I looked up the output impedance of the amp. (Actually, I also calculated the output impedance with a multimeter and a shunt.)
I looked up the resistance of the headphone.
Then it was straightforward to determine the voltage over the headphone at max volume.
Now: How can I determine 2. for, say, an amplifier for a Stax headphone? (Ok, here amp and DAC have to separate except for the SRM-D10.)
Things get complicated because of the capacitive reactance of the headphone.
Output impedance of an amp is not specified by Stax and I would rather not connect a shunt at those high voltages to make measurements on my own.
Furthermore, even if the output impedance of the amp was known, the impedance of Stax headphones is specified as a real value in Ohm. I am not sure about the complex (real + imaginary) calculations required in analogy to the dynamic headphone case since I have only a very rudimentary understanding of electrophysics.
The maximum output voltage as specified by Stax might be helpful in this calculation. But then again I wonder if the specified amp gain of, say, 60 dB applies to the unloaded output voltage of the amp. Or if the unloaded voltage of the DAC output is multiplied by the amp by 1000 into the output voltage with the headphone as the load connected.
I posted this here in the science forum because my guess is that in the Stax thread in the high-end audio subforum people would stop reading after my proposal to paint small dots next to the amp volume control knob.