Headphone voltage levels?

[Agnivesh]

I wanted to know the voltage levels driving the headphones n laptops/mp4 players etc.. On wikipedia, i found some info bout the maximum limits, but i wanted to know the average/nominal levels. I probed the one on my laptop at full volume with some heavy metal and just got a max of about 16mV. It would be very nice if someone could probe and let me know the results.

[FenderBender]

What did you probe with?

[Psi]

If you want to measure it with a DMM play a 50Hz sine wave and measure the AC volts.
Then multiply by 1.4 and you will get the peak voltage.


Here, i made you a 50Hz wav file.
http://psi.abcom.co.nz/50Hz.wav

[FenderBender]

That's what I was suggesting. It's going to be hard to measure a heavy metal song with high frequency transients on a DMM accurately.

Scope would work.

I like PSI's suggestion though.

[Agnivesh]

What did you probe with?

Using a fluke multimeter in the min-max mode...

If you want to measure it with a DMM play a 50Hz sine wave and measure the AC volts.
Then multiply by 1.4 and you will get the peak voltage.


Here, i made you a 50Hz wav file.
http://psi.abcom.co.nz/50Hz.wav

Yeah, ill try that. Thank you very much.

[T4P]

Either use a actual scope or use PEAK mode available on some DMMs, that way you get actual pk-pk voltage

[ivan747]

That's what I was suggesting. It's going to be hard to measure a heavy metal song with high frequency transients on a DMM accurately.

Scope would work.

I like PSI's suggestion though.

Yeah, that metal distortion creates some high harmonics

A scope would be useful to see of the signal degrades for any reason.

[amyk]

Make sure you use AC mode. 16mV is around the order of magnitude of acceptable DC offset on the output.

The voltage depends on the impedance and power output.

[Agnivesh]

If you want to measure it with a DMM play a 50Hz sine wave and measure the AC volts.
Then multiply by 1.4 and you will get the peak voltage.


Here, i made you a 50Hz wav file.
http://psi.abcom.co.nz/50Hz.wav

I just probed while playing your 50Hz file.
 
With the diaphragm coil(i don't know if that's the correct term) attached, I got 55.6mV RMS voltage. That's around 156mV pk-pk. Probably the impedance was 16 ohms, but I'm not sure.

When i cut the coil, I got around 1.575V RMS.

Waiting to hear what you all have to say.

[Psi]

If you want to measure it with a DMM play a 50Hz sine wave and measure the AC volts.
Then multiply by 1.4 and you will get the peak voltage.


Here, i made you a 50Hz wav file.
http://psi.abcom.co.nz/50Hz.wav

I just probed while playing your 50Hz file.
 
With the diaphragm coil(i don't know if that's the correct term) attached, I got 55.6mV RMS voltage. That's around 156mV pk-pk. Probably the impedance was 16 ohms, but I'm not sure.

When i cut the coil, I got around 1.575V RMS.

Waiting to hear what you all have to say.

With computer soundcards there can be some trickery behind the scenes.
Some soundcards auto detect what the load is (speakers vs headphones vs powered device expecting line level)
and they will change their output to match.

EDIT: There was a big math mistake here before (fixed)
A typical soundcard might be able to supply 2W and typical headphones might be 32ohms.
So that's around 8V peak and about 230mA 
 
Your reading of 1.57V seems pretty normal for a soundcard in default line-level mode.
Line level is 0.5 -> 2V

[Agnivesh]

Okay, thank you everyone!

I've got a small question: if I'm not wrong, the headphones are inductive loads. The impedance is therefore due to inductive reactance, which is dependent on frequency, so how do manufacturers label their headphones as 16 ohm/ 32 ohm. Do they take any standard frequency?

[olsenn]

It greatly depends on what you intend on driving. An ipod for instance outputs a voltage of 0.5V RMS when at max volume; a typical sound card on the other hand outputs 2V RMS. Some headpone amplifiers output 10+ volts. Usually headphones are marked with an impedance and sensitivity rating, which can be used to get an idea of how much voltage you need get get a certain volume. Just make sure you can output lots of current as well!

[T4P]

Headphone amplifiers can do 10VPP because some audiophiles insist 32ohm cans sound bad and 600 ohms sounds fantastic
Computer sound cards does 2VPP into a 1K ohm load on the Line-out, but on the outputs meant for headphones or 1k ohm line output (They do auto switching nowadays) while on the headphone output is unknown