I'm still trying to wrap my brain around this concept.
How would more power help the sound exactly? If you take an amplifier with two gain settings (say the HA-2 since it's relevant to this thread : p), are you implying that the LCD-2 will sound better out of high gain ("More power tightens up the bass, making it less muddy, and improves dynamics") compared to low gain (less power) if they're matched at the same volume?
From Innerfidelity's measurements of the LCD-2, the least efficient measurement was 0.87 mW to reach 90 dB SPL, which is quite loud (about the same SPL as a busy freeway) and the HA-2 should happily provide more than 10 times that amount.
http://www.innerfidelity.com/images/AudezeLCD2Rev2.pdf
[Update: Please read this as "85 dB rms" not "85 dB peak"] 85 dB is about as loud as I like to listen, and many headphones have sensitivity specs in excess of 85 dB with only 1 mW.
The OPPO PM-2 specifications, for example, state:
| Sensitivity | 102 dB in 1 mW |
The dimunitive Sansa Clip+ has been measured to produce an output of only 7.5 mW into 32-Ohms, which is 7.5 times more power than that needed to achieve 102 dB with the PM-2, but try to find someone who will argue that the PM-2 doesn't sound better with more power than what the Sansa Clip+ can deliver, all the while listening at a SPL of only 85 dB. Not only is the PM-2 bass a little bit sloppy (uncontrolled) with 7.5 times more power than that necessary to achieve 102 dB, even the mids are woolly, along with suffering flattened dynamics - a lack of punch whenever the signal calls for a momentary spike in SPL.
The less efficient LCD-2 sounds much worse than the PM-2 when powered by the Sansa Clip+, even though Tyll Hertsens has no doubt accurately determined that only 0.87 mW is needed to reach 90 dB.
So, how do we reconcile this difference between measured sensitivity and what we hear?
For the matter of bass being tighter (more controlled) when there's more power, let's try an analogy: If you grab the knob of a door and then try to fan the door quickly to push some air, by opening and closing it rapidly, you'll find that the heavier the door, the more inertia it has, and the harder it will be to decelerate then accelerate then decelerate, over and over again. Once you've got it moving, it will want to keep moving, but you've got to overcome that inertia to change its direction repeatedly. If you're having a hard time controlling the door - to make it move as precisely as you want, you could replace the door with one made of a lighter material (get a more sensitive headphone) -or- you could get someone stronger to fan the door (get a more powerful amp). Either way, you'll get tighter control of the moving parts - even though the amount of air you're pushing, by fanning the door, is the same.
For the matter of better dynamics when there's more power, I can't think of a good analogy, but when we listen to music reproduced with speakers or headphones there can be momentary demands for
a lot more power than that necessary to maintain the
average SPL we desire. If the amp is already operating at or near its peak output to obtain our desired average
SPL, it will not have the
headroom necessary to respond to signals that call for instantaneous, short-duration peaks in power output. Even if the amp is not clipping (where the signal is flat-lined against a ceiling to create audible distortion), the lack of sufficient power to meet those momentary demands will be heard as a lack of punch or slam - dynamics that are lifeless compared to driving the transducers with a lot more power.
How much more power is necessary? I doubt there's any way to calculate that, but I can say from empirical observation (which I admit has a subjective component) that when I move the fairly efficient OPPO PM-1 from the OPPO HA-1's TRS jack to its 4-Pin XLR jack, I hear very little improvement in bass control or dynamics. In fact, people have mistakenly said that the OPPO PM-1 doesn't "scale" to more power. (More on that in a moment.)
The HA-1 supplies the PM-1 with 500 mW rms per channel into 32-Ohms from the TRS jack (a
lot more than the 1mW needed for 102 dB SPL), but the 4-Pin XLR jack can output 2000 mW rms per channel into 32-Ohms - four times as much power as the TRS jack - but again, I cannot hear a difference when moving the OPPO PM-1 from the TRS to the XLR jack - apparently because 500 mW is more than enough power to maximize the performance of the PM-1 in terms bass control and dynamics. 2000 mW is overkill for the PM-1.
My four-year-old 50-Ohm LCD-2 rev.1, on the other hand, for which I do not have sensitivity specs, but which can surely do better than 80 dB with 1 mW (plenty loud on 1 mW), "scales" noticeably when moving from the HA-1's TRS jack (455 mW rms per channel) to the 4-Pin XLR jack (1817 mW rms per channel).
I must conclude that the lower sensitivity of the LCD-2 rev.1 leaves it wanting more than 455 mW into its 50-Ohm load. Indeed, Audeze support recommended a minimum of 1000 mW for the LCD-2 rev.1, which is more than satisfied with the 1817 mW available at the HA-1's XLR jack. I've had the CEntrance DACmini CX for about three years now, and find that its roughly 600mW output into 50-Ohms actually does the job very nicely with the LCD-2, in terms of bass control and dynamics (not to mention other traits), but my experience has established a pretty firm line in the sand that says 500 mW into 50-Ohms isn't enough power to bring out the LCD-2's best possible performance.
Head-Fi member "Gary in MD" runs about 8,000 mW (8 Watts!) into his 110-Ohm Audeze LCD-3, which has a sensitivity of 102 dB at 1 mW. He has his LCD-3 directly connected to an Odyssey Audio Cyclops Extreme - a very highly regarded speaker amp that's rated at 110 Watts into 8-Ohms. If this sounds crazy, consider that Audeze rates their LCD-3 as having a maximum power handling capacity of 15W for durations up to 200ms - not continuous, but rather momentary. Gary is only supplying it with 8W rms into 110-Ohms, which translates to peaks that can hit about 11W into 110-Ohms. He's operating his LCD-3 completely within Audeze specifications - at 8,000 mW rms into 110-Ohms. Can he really hear any improvements with 8,000 mW rms vs. the HA-1's roughly 1500 mW rms into his 110-Ohm LCD-3? I don't know, but he isn't leaving anything on the table.
Revisiting my having said that some people feel the PM-1 doesn't scale well to additional power, I have to laugh, because if they want to hear it scaling to more power, all they have to do is start out listening to it on a Sansa Clip+ for a while, then try it on the HA-2. It scales just as readily as any other headphone, but the scale starts lower, due to the PM-1's high efficiency.
Mike
