[leichnitz]

I think my Grado SR125 are too bright and my Denon D5000s just right.  But when I A/B them to my friends, they inevitably pick the Grados, sometimes using words like "clear" and "transparent."  Personally, I think it is just because people associate loud with good, and I notice the Grados are much louder at the same volume, amplification than the Denons.  I assume this has something to do with efficiency, but not sure.  I find it frustrating that I cannot get my friends to hear past the loudness difference to appreciate the brightness point.  What gives?

 

[bugeyed]

You're correct in assuming that people usually pick the louder sounding product. That's why every effort is made, in controlled testing, to equalize the volume. Not that easy, but some effort must be made or the test is completely invalid.  
 
Cheers,
kev

 

[Saren]

All it comes down to is efficiency and the impedance as well. As the Impedance (ohms) rises the power (mw/W) going into a headphone decreases and they tend to become harder to drive by weaker amps.
 
I'll give you an example from my set up. My amp on high gain delivers 2 watts to the 50 ohm Hifimans, whereas my 600 ohm beyers receive 166 miliwatts. Mind you the Hifiman's have a far lower efficiency so that rounds out, but if the efficiencies were similar the high ohm rating does affect volume a fair bit on lower amps.
 
The sensitivity is how much power it takes to get a headphone louder, for example a 600 ohm headphone with 96 dB/mW efficiency will be quieter than the same 600 ohms on a sensitivity of 104 dB/mW. The 104 dB/mW headphone is more efficient.
 
I'd be guessing the Grado's are a fair bit more efficient than the Denon, despite the marginally higher impedance. I've never seen grado's efficiency stats myself however.
 
Also the grado does have a hard tilted upper midrange/lower treble and it might be possible that coupled with the on ear design could plausibly seem louded than a denon as well. I found myself listening to my Grado SR60i back in the day at a lower level than the DT770 perceiving it to be louder, when it may have been that it was just very aggressive in its sound.
 
It may seem clearer to your friends because of the tilted treble, I've heard many suggest titled treble increases detail, but I've never adheared that strictly to that.

 

[TMRaven]

Grados are popular for having that type of coloration that comes off as crystal clear sounding.