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Whoah. I was freaking out a little until I read that last line.
As I understand it, the principle of the bass lens is a little more complex than simply changing the pressure. Any shape in the pathway of sound waves (megaphone, trumpet, reverse trumpet, SE846 low-pass filter, etc) introduces particular resonances in sound and decreases others. Keep in mind that if you put a narrow nozzle on a vacuum hose, not only will the pressure change, but the flow of the air will change and the sound of the suction (which is actually just flow of air anyway) will change.
I don't know if it was ever confirmed that the MA900 uses the XB1000 driver. I doubt that the use of LCP would make a huge difference anyway, given that for instance the EX1000 only exhibit improvements in distortion at high volumes (100db) over the 7550 due to the use of LCP in the EX1000.
Since the XB1000 has earpads that are much thicker than the MA900 and the MDR-R1, swapping pads alone alone would change the sound completely. I do not think that it would be possible to increase bass on the MA900 without decreasing sensitivity and thereby increasing the already quite high distortion at lower frequencies. Now if you combined a stronger low pass filter with the LCP driver you might see some sparks fly!
That's my theory anyway.
Oh yeah, forgot about that (pressure change from lens= sonic change). Although it's a cheap way of tuning the driver, it works, and it's effective.
The reason why I said the MA900 uses a variation of the XB1k driver is because the driver membrane is the same, and the structure looks about the same too. For reference, it's like comparing the AD900 driver to the AD700 driver. It's the same overall structure, but tuned differently, and maybe having a different sized magnet or different magnet design along with the headphone enclosure changes (like the driver angle). I'm sure there's a different magnet behind the MA900, and possibly a different felt material for the ports behind the driver than the xb1k. Since I don't have both headphones, I can't make a legit statement, but it makes sense.
Well, I listen to most of my music at roughly the same loudness a movie theatre is (around 100dB), so I guess I, and any others who listen somewhat loudly, could reap the benefits of a better membrane material. I'm just curious to see what the differences between LCP and the membrane material used in the ma900 is. Is it lighter, thinner, more rigid, etc.? I know that the thinner and lighter the membrane is, the easier the magnet is able to manhandle the voice coil (which is attached to the membrane), which should improve the speed and transparency of the driver, as well as reducing any distortions, like you said.
The earpads won't alter the sound as much as you think. With my AD2000MKIV (a major mod of the AD900s), swapping the earpads improved the headphones in every aspect (improved transparency, greatly improved bass response, soundstage is larger and more transparent, blah blah. The review will give you a more detailed analysis on them). Then again, we're dealing with a different earpad material and thickness, so that could subtly change the characteristics (like absorbing x frequency range, or making x frequency range sound hollow or recessed because of the increased distance). I'm thinking they would make the headphones sound a bit darker and improve the bass quantity. Maybe improve the soundstage width due to the extra distance from your ears from the drivers. I don't know. I just have to get both pairs and take them apart to see what I'm dealing with.
I don't really understand your theory
If you decrease the sensitivity, that basically means that it will take more power to listen at the rated dB level (700mW@ 104dB vs 700mW@ 95dB or 800-ish mW @ 104dB) Well, it really isn't 700mW for the ma900. That's more like the maximum amount of power the driver is able to handle before you start seeing sparks, but it's along the lines of that. It's also the reason why orthos and other hard to drive headphones need a powerful amp in order to get it at the desired volume level (without any distortion). They aren't very sensitive/efficient headphones (the HE-6, for instance has an 84dB sensitivity), so they need a lot of power in order to get the headphones up to a louder volume level. Afaik, a low pass filter attenuates the frequency range past the lower frequencies (it
passes the
low frequencies, and attenuates the rest, wherever x cutoff frequency is at). So, I don't know how that correlates to increasing bass quantity.
The earpads aren't going to make the drivers magically produce more bass. It'll just increase the pressure, given you have a good set of earpads that seal well. You have a bad seal, the bass is going to leak out, which will roll off the lower frequencies (which means little pressure on the low end). You plug in those gaps with earpads that seal well, as well as having a good clamping force, the bass has nowhere to go except to your ears, which will greatly increase the pressure (especially with a 70mm driver), and perceived bass quantity. It's the main reason why many higher end closed headphones have better bass performance than open headphones. They usually clamp more and have better sealing earpads on them, which increases the pressure. None of the lower frequencies are rolled off because of that, and instead of having an attenuated low end, it may/will look closer to many other closed headphones (like a bell-shaped or convex lower frequency range). Well, if you don't cover those holes on either channel on the ma900s, the pressure will still be the same, since the bass has somewhere to escape, but cover those holes with your hands, or rip out some duct tape, and I'm pretty sure the MA900s will have noticeably more bass pressure. The only problem will be how to absorb any resonances or reverberations that the increased pressure will create. The headphone enclosure isn't made to handle that amount of pressure (which will, in turn really vibrate the enclosure), so you probably have to put some kind of dampening material like dynamat in order to help absorb those mechanical vibrations. Then again, the headphones may have a pretty sturdy construction, in spite of their minimalistic looks, so you may have to do nothing to them.
