Safe listening levels?

[mepds9]

Hi! I'm currently trying to find out how loud is it safe to listen to music, knowing headphone impedance, sensitivity, and knowing the output specs of my computer (I listen mostly from my iMac). I really don't know much about these subjects of resistance and sensitivity, and was hoping for someone to enlighten me.
 
I currently use my Shure srh840 with my iMac (no amps or dacs as of yet). They are low impedance (44ohm) and have a sensitivity of 102dB/mw.
 
My iMac has an output impedance of 65ohm and a "maximum level: 1.4 V nominal (root mean square), 4.0 V peak-to-peak", which I don't understand.
 
Can I with this calculate how much dB are produced at maximum volume? How many dB is the safe listening level? I think this is really important, cause I want to preserve my hearing and enjoy better headphones in the future. Sometimes I get headaches after listening for too long; and I don't know if it's because I'm listening too loud, or I'm still getting used to the clamping force.
Thanks!

 

[mepds9]

Here is the link where I got my iMac information http://support.apple.com/kb/TA26045?viewlocale=en_US&locale=en_US

 

[stv014]

Quote:

Here is the link where I got my iMac information http://support.apple.com/kb/TA26045?viewlocale=en_US&locale=en_US

 
If the specs are correct (they are often not), then the maximum level is 110.6 dB, which is rather loud and can indeed be damaging over longer periods of time. Note that the headphone output has a maximum voltage of only 1 Vrms, so that is actually 3 dB lower. The SRH840 may also be less sensitive than advertised by a couple of dB. However, with those taken into account, more than 105 dB is still possible. Of course, you do not have to listen at the maximum volume.

 

[mepds9]

How did you make these calculations? That's the part I don't understand. By no means i listen to maximum volume... My head would explode. I actually listen to about slightly more that a quarter of the volume... How loud would that be? How loud is "safe listening" considered?

 

[stv014]

Quote:

How did you make these calculations? That's the part I don't understand.

 
Maximum voltage on the headphone:
 
1.4 * 44 / (44 + 65) = 0.565 Vrms
 
Maximum power:
 
0.565 * 0.565 / 44 = 0.00726 W = 7.26 mW
 
Maximum SPL:
 
102 + 10 * log10(7.26) = 110.61 dB
 
The numbers in bold were taken from the first post.

 

[mepds9]

Thanks!!! Now with this info I think I can determine more or less how loud do I actually listen, and if it's ok. Assuming that volume increase in my computer is directly proportional and not exponential, max volume (16 volume points-mac) is 110.61dB on MY heaphones. The maximum I've ever gotten to hear music is 7 volume points.
 
http://www.sciencedaily.com/videos/2008/0304-dangerous_decibels.htm
 
This nice article (with video) tells about hearing loss at young age and states that scientists recommend no more than 85dB for music listening.
 
14tics------------aprox.110.6dB
7tics--------------x?
 
If x is  aproximately 55dB (tops), I guess I'm way from having listening problems. I only go higher than that with classical. I find Science Daily to be quite trustable. However, there's still a chance the initial specs weren't perfect right? That's the only detail... I guess it doesn't care much since there's a large margin between what I listen and the top safe loudness.
Thanks again! Learned a bit today!

 

[joeyjojo]

Converting "tics" to voltage is your unknown and you don't have enough information to have a guess.
 
The only thing you can really do is get a multimeter, set the laptop to the volume you listen at, pull the headphones out and measure the voltage (probably would need to slice up a mini jack cable to get at the wires) then calculate how loud the headphones theoretically go at that voltage. You'll need a sensitive meter though to get < 1V AC, they're usually for measuring tens or hundreds of volts AC.
 
I've been wondering the same thing recently so this is how I'd do it. Otherwise if they're big headphones a normal sound level meter might work - I'm hunting for a good value one atm.

 

[mepds9]

hmmm... I guess you could be right, probably the representation of "tics" isn't directly proportional to the output voltage. In the end what I care about is the loudness the headphones get to at a certain voltage. Could some kind of metering microphone work? If I use a microphone, the tiniest leak could alter the results though...

 

[joeyjojo]

Quote:

hmmm... I guess you could be right, probably the representation of "tics" isn't directly proportional to the output voltage. In the end what I care about is the loudness the headphones get to at a certain voltage. Could some kind of metering microphone work? If I use a microphone, the tiniest leak could alter the results though...

 
This is exactly the sensitivity of the headphones which you know already (102dB/mW). A microphone probably wouldn't be much use - as I said about a SPL meter is what you need. Or measure the voltage as I suggested and it's an easy calculation to get the power, and thus the loudness of the headphones.

 

[mepds9]

Maybe, though it's really complicated to find a sensible voltage meter under 1V, that has a 3.5mm jack (I don't live in the US)... The other day I wondered if some kind of application exists that provides constant info on the audio jack output... I'll try searching for that.

 

[iZMXi]

RMS voltage is what directly correlates to SPL (Sound Pressure Level).

All loudness is derived from SPL.
 
Terms like "peak power" and "peak to peak voltage" only exist to impress laypersons with irrelevant information.
 
If you want to measure the part-volume voltage:
1. Get a digital multimeter and a cheap male-to-male audio cable.
2. Chop off one of the cable ends and strip its wires.
3. Use the multimeter to measure voltage in AC Mode (Alternating Current).
4. Play a pure sine wave (test tone) of any frequency.

It is important to play a sine wave, as playing music will increase the power consumption, but not the SPL.