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These HD 438s don't sound bad, that's for sure. They are clearer and have a more expansive and accurate sound stage than my HD 201s. The only problem is I bought them for increased bass over my HD 201s, and in that regard I feel disappointed. 
 
According to this graph: http://graphs.headphone.com/graphCompare.php?graphType=0&graphID[]=473&graphID[]=1223
 
I should be hearing over twice the amount of bass in ratio with the treble, but I'm not. In fact, the bass increase is so small I would say there is no more than 3db increase in bass. 
 
I know burn in is supposed to help a little, but a headphone should sound 90% like it will forever in the first few hours. They have been played for around 30 hours. What's even funnier is that my HD 201 has horrible isolation because the pleather pads have been worn thinner so my ear is touching the driver, and the pad barely holds to my skin. So with a worse seal the HD 201 STILL produces similar bass to the HD 438.
 
Is headroom wrong with their charts, or what?

 

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Bump 
 
I did some testing and found the charts are close to the right ratio. In a slow 1hz-100hz sweep I found the HD 438 to play deeper audible bass. The HD 201 could play audible bass from 25hz and up while the HD 438 could play around 8Hz and up. I don't understand how i was able to even hear 8hz though, but I was using audacity which is trusted. I used a linear sweep which was divided into 6 sections, and with the HD 438 I could hear actual bass around half way through the first section, while the HD 201 would be audible at around the 1.5 section.
 
Burn in still implementing at around 40 hours. The sound is much warmer in the HD 438 now with a huge mid range emphasis, and it will take a bit of time to get used to. The bass is a bit more dominant now, but according to headroom it should increase a bit more. The chart shows the bass should fall between the HD 201 and CX300-II, while for now the bass is still a little less than in the middle, but getting there. I hope with more burn in I can squeeze out more bass dominance.