2
\$\begingroup\$

When playing sound on a MP3 player to headphones, does the volume level affect how much power is used? Intuitively I think that high volume = high power consumption, and low volume = low power consumption, but that's just an assumption.

I know this is a very general question, as it will probably always depend (at some level) on the specific device.

Would the answer change depending on what was plugged into the MP3 Player? (Nothing/Earplugs/Large headphones/AC powered stereo through AUX)

\$\endgroup\$
4
\$\begingroup\$

Yes, most likely higher volume means higher power. This is particularly true for devices with limited power so that were therefore designed to conserve power to a reasonable extent. A portable MP3 player running on batteries would be such a device.

Most likely, the MP3 player has a class D audio amp chip in it to drive the headphones. This is the most efficient way available to produce a power audio output signal. These things can be quite efficient. For a perfect class D amp, all the input power would go to drive the output. The output power is the square of the output voltage divided by the load impedance. If the output voltage doubles, the output power goes up by a factor of 4.

In reality you won't see a factor of 4 power draw increase from the batteries when the output voltage is doubled because there are losses in the system and some fixed bias currents for various circuits. However, there should still be a significant effect.

\$\endgroup\$
  • \$\begingroup\$ Any idea about the relative power needs of a microcontroller(?) doing MP3 decoding, vs. the audio output circuit? \$\endgroup\$ – The Photon Nov 4 '12 at 16:55
  • \$\begingroup\$ @Olin could you please address the last part of my question as well? (what's plugged into the MP3 Player) Won't the losses mean that more power is required to achieve the same thing? So that the factor in power draw should be greater than 4? \$\endgroup\$ – RasmusWL Nov 4 '12 at 20:48
  • \$\begingroup\$ @Rasm: As I already said in my answer, the output power is inversely proportional to the impedance (assuming the amp can maintain the desired output voltage). Nothing is obvious high impedance and therefore should be the lowest power draw. AC powered stereo provides its own power, so probably presents a higher impedance than headphones. Check the impedance of your devices. \$\endgroup\$ – Olin Lathrop Nov 4 '12 at 21:01

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.