well, the jury is in on the playback quality of these things...
Two or three things are apparent. Firstly there is a general bathroom-mid-frequency-early-reflections kind of component to the sound.
The bakelite earpieces themselves were of considerable thickness; more than 7mm (for whatever design purpose I can't imagine) and each hole, which matches to a corresponding gap in the donor headphone grille, is acting like a little reverberant tunnel for the sound to pass down. Bakelite is I suppose halfway to being a ceramic compound and the effect is very much like a micro-bathroom sound with a muddling of the mid-frequency information. Because of the small distances involved between driver surface and ear the reflective influence is slight.
I've got to say; I've never listened so critically to anything before and have been establishing all sorts of shortfalls in material I have been testing with! The sound is not unpleasant and entirely within the expectations of many domestic ear phones but it is apparent that the earpieces are having an effect.
Secondly, these cans are really efficient and have great bottom/low mid response!! I have not even approached 70% of their ability but the DLR driver housings are very sturdy "cabinets" for the donor drivers to fire from. The considerably sized "port" which I added to each rear piece (hidden under the strain-relief) acts as a small sound O/P itself and plays back a much attenuated version of the content within!
And finally, thanks to the dozen 5.5mm holes drilled in each earpiece- they are quite uncomfortable!! The centre-in concave bevel of the earpieces themselves is not enough to remove the drilled surfaces from the ear cartilage and as such parts of my ears touch these drilled surfaces. Although not sharp, these holes have an edge and I expect if worn for long perios my ears whould bare octopus-style marks afterwards!!
Analysis responses and final pictures to follow.
JimP