Originally Posted by mikeaj
I checked FiiO's website, and that says only 220 mW into 32 ohms for the E17.
Even at that level, it's around 2.65 V rms into 32 ohms, so it should at least be that much for ~62 ohms and not really have performance issues for those. So more than 115 mW or so max. Depends.
Wait, I should have just checked the X3 page. 540 mW into 16 ohms, so 3 V no problem. So say 145 mW into 62 ohms, very similar to ~115 mW though anyway. If it can handle 16 ohms like that, it has plenty of current and probably won't mind 62 ohms.
On the other hand, InnerFidelity measurements show lower sensitivity than AKG's specs, more like 100 dB SPL / 1 V (88 dB SPL / 1 mW). Crazily enough, that means that 145 mW is not quite enough for 110 dB SPL peaks, which I think are realistic if you want to listen at a high volume to certain classical recordings with very low average volume. It may realistically be enough. Depends on tastes.
Or actually, their second sample, was slightly more sensitive and would be driven to just over 110 dB SPL when maxed out there. So let's just say that it's in that range.
I don't quite understand how to calculate the required power/voltage/current for a headphone.
I can't post a link to his blog but NwAvGuy posted in his power article:
120 dB SPL is also the level at which even short term exposure can cause permanent hearing impairment. Studies have shown even sustained average levels above 85 dB SPL can cause hearing damage. For more on these thresholds see Sound Pressure Levels. The research indicates the average maximum level should be at least 85 dB, and with classical music, that puts the peak level up to 30 dB higher at a worst case 115 dB). For more typical music peak levels of 110 dB SPL are more reasonable.
That makes sense since he also stated earlier:
Wide Dynamic Range Classical: –18 dB to –30 dB
(85 dB SPL + 30 dB SPL = 115 dB SPL)
So for someone who has hearing damage, 85 dB SPL might not be enough. So maybe 90 dB SPL is adequate, and that's what Tyll measures at Innerfidelity, the K 701 (sample B from the downloads) requires 0.238 Vrms to reach that SPL with a measured impedance of 67 Ω at 1 kHz, or 1.20 mW of power.
With 90 dB SPL, or a theoretical maximum of 120 dB SPL with classical for the quietest parts of a song, 1.20 mW * 2^10 = 1228.8 mW or 1.2288 W of power is needed.
If Power = (Vrms^2) / impedance
Then sqrt(1.2288 * 67) = 9.07 Vrms at 67 Ω is needed
First of all, are these calculations and assumptions correct? XD
On the X3's specification page it says:
MAX output voltage > 8 Vp-p
From my understanding, 1 Vrms = 1 * 2 * sqrt(2) = 2.8284 Vp-p
So 8 Vp-p / 2.8284 Vp-p = 2.8284 Vrms
2.828 Vrms < 9.07 Vrms
Second of all, are these calculations correct?
Now this is where I'm having a hard time interpreting things. Based on this, the X3 shouldn't provide enough voltage to reach 120 dB SPL. Does this mean the X3 won't supply enough volume to reach the desired level?
A JDS Labs C5 portable headphone amplifier has a specification of:
From JDS Labs's C5 blog post:
Is power supply the same as the maximum output voltage? If so:
So 14 Vp-p / 2.8284 Vp-p = 4.9498 Vrms
4.9498 Vrms < 9.07 Vrms
So this headphone amplifier still doesn't provide enough voltage to reach 120 dB SPL either.
Here is the setup I have:
iPhone playing some V0 LAME MP3 classical music --> FiiO L9 line out dock -> JDS Labs C5 maximum volume -> AKG K 701 (newer 8-bump headband) -> my ears
Of course I would never listen to music this loud even with classical, but this setup was pretty dang loud. I don't completely know what clipping sounds like, apart from clipping due to poor mastering, but the music sounded just fine. I have no idea what 120 dB SPL sounds like but it was loud, for me.