Audio: Resistance and power

Question

I'm choosing between two USB DACs for a pair 32 Ω headphones and need to choose the one with the greater output, i.e. with the greater loudness. One DAC has a maximum power rating of 18 mW at 16 Ω and the other has a rating of 45 mW at 32 Ω.

I guess it is the second, but which is louder?

How many watts would the first produce if run into 32 Ω?

A bit of nitpicking here: the headphone loading on the amplifier is not a resistance but instead an impedance. This means that the load is at a specific frequency. Most probably, at zero frequency 0Hz the resistance is much much lower. — ghellquist, Nov 19 '22 at 08:18

score 4 · Accepted Answer · edited Nov 18 '22 at 20:03

4

How many watts would the first produce if run into 32ohms?

There are options worth considering: -

The device that produces 18 mW into 16 Ω might provide twice the drive voltage into 32 Ω. This means that twice the power is delivered to the 32 Ω speaker i.e. 36 mW
The device that produces 18 mW into 16 Ω might not increase the output voltage at all and the power into 32 Ω will fall to 9 mW

But, weighing these limit scenarios up means that device 2 (with a power rating of 45 mW at 32 Ω) is likely to be power winner.

edited Nov 18 '22 at 20:03

winny

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answered Nov 18 '22 at 15:28

Andy aka

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second option is more common, I think. – user253751 Nov 18 '22 at 17:20

score 3 · Answer 2 · edited Nov 18 '22 at 20:04

3

Typical USB headphone amplifier will have a fixed output voltage delivered through a few ohms series resistance. Assuming the series resistance is negligible compared to 16 ohms (typically the case for quality devices):

18 mW into 16 Ω is 0.53 Vpp.

45 mW into 32 Ω is 1.2 Vpp.

So the second device has a larger output.

edited Nov 18 '22 at 20:04

winny

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answered Nov 18 '22 at 19:59

user1850479

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Audio: Resistance and power

2 Answers2