I want to buy a pair of headphones with these stats: Sound pressure level (SPL) 97 dB (SPL) at 1 mW, 300 ohms

And I have this audio interface but I can't tell by the specs if it can power these headphones. http://us.focusrite.com/firewire-audio-interfaces/saffire-pro-24-dsp/specifications

Basically, are audio interfaces equipped with a high output so they can power any headphones or is an amplifier a must-buy element for high impedance headphones?


  • Personally I'd avoid them. There's going to be a time when you need to plug them into something else and listen. Versatility is pretty important in a pair of headphones, unless you will really never remove them from your desk. Commented Dec 17, 2014 at 8:33
  • Actually I wont. These would be my desk headphones only. Commented Dec 17, 2014 at 9:58

1 Answer 1


"Power" isn't really the issue. Certainly, most interfaces can offer enough wattage to cause ear damage, theoretically.

However, the actual power is not determined by the HP-output alone, but by the headphones' own impedance as well: if it's substantially larger than the output impedance, then

P = U2 / Z

where U is the (RMS) output voltage of the interface; this is really the relevant parameter of a headphone-out's performance. Now, 300 Ω is a pretty fat impedance, so this means you need a higher voltage to get the same power than you would with lower-impedance headphones. You should definitely not expect very loud volume range when connecting these phones to an ordinary interface; in particular USB-powered models have a tendency to not offer very impressive voltage. For a FireWire model like the Saffire-Pro however, you can expect more generous output.

Definitely the headphones will work, the only question is whether they'll be loud enough for you. High-impedance phones aren't really meant to be driven very loud anyway, so if you need it loud another pair might be more suitable.

  • Can you please update the answer with where can I find headphone RMS for an interface? I don't need to crank it up, just in order to hear everything well and in enough of a quality to mix. Commented Dec 17, 2014 at 9:33
  • 1
    @IvanIvković: no, headphones output voltage is generally not specified. As a rough estimate, it'll typically be something like 1/4 of the voltage the device operates at, i.e. in case of the Saffire 3 V, which should be quite sufficient (9 V² / 300 Ω = 30 mW, so the phones would produce an SPL of 97 + (log₂ 30 * 3) ≈ 112 dB. Commented Dec 17, 2014 at 9:46

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