I've been building a test capability so I can quantify my designs.
Here is the frequency response of the Rastapants with the O2 pads (IMPORTANT NOTE: The RP2 tested here has two mods from what I published: about 6-7 cotton balls/wool in each cup and the vent 50% closed. These mods make a nice and easy upgrade, and work for the 840 pads, as well. The 840 testing with the same RP2 setup indicates that 75-85% closed works pretty well, though I'm not done). I validated the above results through multiple tests, which were actually quite consistent, and averaged 10 plots to generate these charts.
Here is the frequency response of the LCD 2:
A few notes:
1) These tests are on a flat baffle, which is not going to give the same curves as a "ear" or "head" measurement system. In other words, they will look different from the test Tyll publishes, and they'll also be different what Purrin measures because his rig is somewhat different, as is his software. The key thing to understand with headphone testing is that one testers charts can really only meaningfully be compared to more charts BY THAT TESTER. And they should be seen as RELATIVE but not ABSOLUTE, as there are so many variables that affect results. Tyll has written a ton of great stuff on why that is (and knows more than I do on this) so I won't repeat it...
2) The bass measurement is more accurate than mids/highs due to wavelengths so take high frequency results as a general indicator of response curve SHAPE, but not exactly what you'll hear (again, see Tylls blogs). For example, my suspicion is that the deep notch at 4.5K on the LCD2 is probably a standing wave rather than a real hole in their frequency response, so don't go dissin' those cans because of it.
The LCD2 has deeper extension below 30Hz. The bump of the RP2 gives it a bit more bass slam and weight, sort of like the JH16 sound, which actually really is fun to listen to, and does not sound "boomy," but not as "absolutely accurate" as I'd like. I'd like to flatten the bass out a bit more and get a few more Hz out at the bottom. It's not "too much of a good thing." The sound, as you'd probably expect from the spectral tilt, is a bit warmer than the LCD2, though and the highs feel brighter. I'd characterize the RP2 as sounding "bigger" than the LCD2, with a better defined top-end, but a bit less extension and linearity at the bottom.
The RP2 has a notch from 3-5KHz that pulls the upper mids back a bit. It's not objectionably obvious like a big spike in frequency response, but it will liven up the sound even further to address this, so I'll be giving it my best shot.
I did do some waterfall plots but won't publish until I'm more confident in my testing skills. I will say they validated one area that made me prefer the Rastapants 2; it has SUPER fast decay above 1.5K and less ringing than the LCD2 I tested. And the LCD2 decay is excellent.
Again, I wouldn't say this is absolute, I'm still learning my test rig setup, but it did validate one of the things I really like about the RP2. It's possible the difference is how I tested vs. what I tested, if you follow, so for this reason, I don't want to publish the waterfalls until I am more confident I'm testing accurately.
Thanks to Tyll and Purrin for some inspiration, ideas and direct input on testing. My next post on mods will either be doing a fully reversible design or further optimizations on the Rastapants 2 to smooth those to areas of interest out.
Edited by mrspeakers - 10/24/11 at 6:06pm