Stephen Dawson
Member
Just to finish off on the matter of headphone output resistance, one last test and some brief listening impressions. I tried out the Audiofly AF140 in-ear monitors. (RRP $AU399) These use three drivers: dynamic for bass, balanced armature for mids and balanced armature for treble. Nominal impedance is 38 ohms, but with that driver arrangement, you'd have to expect some variation across the range. If driven with 470 ohms of in-line resistance, they are presented with a pre-screwed frequency balance:
They also produce sound at a much lower level since more than 90% of the power is being dissipated over the 470 ohm resistor.
Right now I'm listening to some music using these IEMs using the Pro-Ject Pre Box S2 at a nicely loud level. The volume on the Pro-Ject is set at -25dB. When I put the 470ohm load in line (I've measured the Pro-Ject's output resistance at somewhere between 0.24 and 0.37 ohms, so it is insignificant), the volume drops enormously. To get something like the same subjective level I have to wind up the volume control to 0dB. The bass is very prominent with the line resistance in place, the treble very recessed. Anyone using these earphones with a Denon or NAD or Marantz home theatre receiver would probably find them quite unsatisfying.
They also produce sound at a much lower level since more than 90% of the power is being dissipated over the 470 ohm resistor.
Right now I'm listening to some music using these IEMs using the Pro-Ject Pre Box S2 at a nicely loud level. The volume on the Pro-Ject is set at -25dB. When I put the 470ohm load in line (I've measured the Pro-Ject's output resistance at somewhere between 0.24 and 0.37 ohms, so it is insignificant), the volume drops enormously. To get something like the same subjective level I have to wind up the volume control to 0dB. The bass is very prominent with the line resistance in place, the treble very recessed. Anyone using these earphones with a Denon or NAD or Marantz home theatre receiver would probably find them quite unsatisfying.