[PTheD]

I dare to disagree, the iPod is 30mW per channel and around 1.10v across both channels.

 

[AdamWill]

the systems of the major search engines actually encourage it. they basically work like this - your page is ranked based on how many other pages link to your site. so big sites always score high. ever wondered why useful niche sites like this one never score high on google, but cnet, amazon, cnn, msn yadda yadda does? that's why.

 

[PTheD]

Correction, this site, head-fi.org, scores very high on google. Head-fi discusions are some of the first results in many of my searches for headphone related equipment and services.

 

[PTheD]

This thread is offtopic, end of off topicness ends now, either thread ends or continues on original track..

 

[AnonymousGuy]

Yeah it's a monster old thread but the first result on google.

The voltage I measured out of my desktop computer with onboard/integrated sound card was 1.1 V_rms at full volume. I used a 400 Hz Sine Wave tone to test it. Seems like it must be a standard that my computer and an ipod have the same max voltage.

 

[owendelong]

I have a little trouble reconciling the claims in this thread...
 
1. Apple specs claim 30mW per channel headphone out on virtually all of their audio devices (iPad, iPods, iPhones).
    (verified with Apple specs)
 
2. Measured rms output voltage 1.1V (peak V = around 1.556 based on that).
 
3. Most headphones have a 1Khz impedance between 8Ω and 32Ω. (http://www.soundonsound.com/sos/jan03/articles/impedanceworkshop.asp) and most small-jack headphones come in the 16-32Ω range (based on observation, experience, and reading a fair number of spec. sheets)
 
So... Getting to the reconciliation issues...
 
Ohm's law sates that P=EI and V=IR (where P is power in Watts, E is pressure in Volts, I is Current in Amps, and R is Resistance in Ohms).
 
The whole point of having a characteristic impedance of a device is so that we can treat it as resistance for calculations and assume that the effective impedance is roughly the same across the intended frequency range. (The difference between resistance and impedance is that resistance is DC resistance, so no frequency or phasing effects need to be considered. Impedance is the effective resistance at a given frequency. For audio devices, usually 1Khz.)
 
So, if we have 1.1V and let's take a middle of the road 24Ω (half-way between 16Ω and 32Ω) headphones, we get the following results:
 
I=E/R = I=1.1v/24Ω = I=0.04583333=45.8mA
P=IE = P=0.0458333 * 1.1 = 0.05041666 which is a little more than 50mW/channel.
 
OTOH, if we assume 30mW per channel and work backwards from there:
 
P=IE = 0.03W =I * 1.1v = 0.0272727A = I
I=E/R = 0.0272727A=1.1V/R = 0.0272727A*R=1.1V = R=40.3333737Ω
 
So it seems either the devices are able to deliver 50mW/channel, or, they are expecting 40Ω headphones, both of which seem extraordinary.
 
I'm perfectly willing to accept that I may well have gotten something wrong here and I would appreciate it if anyone can show me what.

 

[randomdude87]

I know this thread is 8 years old but I had the same question and couldn't get a real answer from reading what you all posted. Most of you went on a tangent about headphone impedance and power ratings which isn't relevant to the OP's question. You don't need math or any knowledge of headphones to answer this, you just need an oscilloscope or voltmeter. I just did some measuring so for anyone else who's interested here you go:
 
 
The pk-pk voltage coming out of the headphone jack on my Samsung Galaxy S2 phone at max volume is 2.26V
 
The pk-pk voltage coming out of the headphone jack on my Dell Precision T3500 desktop computer is 3.42V at max volume
 
 
As an additional test I kept my speakers (Altec Lansing) at a fixed volume and plugged them in to a variety of other headphone jacks (all devices set to max volume playing the same song) to see how different the outputs are. The Galaxy S2 is the quietest, the next loudest is the iPhone 3G followed by an iPod Nano and then my computer's sound card. That means that all of these devices have a pk-pk output of between 2.26V and 3.42V at max volume with the Galaxy S2 being the weakest and the computer being the strongest. The Galaxy S2 battery was charged to 85% and the iPhone 3G was charged to 97% for this test, although it doesn't make a difference in audio volume.
 
I also measured the output voltage as a function of volume level and it does not scale linearly. For example, at 50% volume the desktop computer output 1.3V even though its 100% volume voltage is 3.42V. This is done intentionally because humans perceive pressure waves (audio signals) on a logarithmic scale.
 
 
 
Enjoy!