ALMOST impossible... Please dont mis-quote me.
The statement I made is with the intention that your not going to get 60Hz out of it (extreme example).
The Sony ECR-500 is a Walt Brand device. Its also from 1970, and is reported to have a low efficency... However I am unable to pull up pics for this device, so I have no Idea if its a clam shell design or not... I have to do more research on this. It is a very good pair of headphones, though allot more money at the time then the gredo's Im talking about right now
MDR-V6 use more of a cup design, and nice pads... though I fear cup designs because they tend to echo a bit.
Thoose Beyer's look like the ones I would want to try, though look at the reveiw...
http://www.headphonereviews.org/headphone.php?action=view&headphoneId=17
Headphones can produce sub level sounds (bellow 100hz). Your ears just cant hear these tones, and you certainly wont FEEL them... maybe if they physically move a bit... then again, lets just put vibrators in our headphones.
Try getting a sub 150hz out of the bookshelf speakers bose makes... then tell me that the 1/2" driver in these will produce this low sub sound.
Mike