Well, after months of cowardice, ocassionally poking around the edges of my HP-50S I finally worked out how to open them and have got the ball rolling. The improvement is astonishing.
My HP-50S, stock, had almost no treble and the bass was pretty clunky, the whole sound was congested and quite muffled to my ear, except in the mid bass and bass.
The first thing I did in line with the guide I found by luddo, was to fill the cavity in the back of the cup with cotton wool. The felt I had was nowhere near as thick as that shown in the guide, but I started with just one layer to start with in each cup. I didn't cut holes for the pegs and still haven't, will get around to that when I've finalised the process. Put the foam back in and closed them up. Instantly the change was immense - the treble and mids were back and the phones, even with this small change were a perfectly respectable and listenable set of phones.
I still felt like the treble could benefit from being bought further forward though so I put another layer of the same felt in each and this seemed about right for me. Still lots of bass but much more of an even sound. It still seemed to be muffled. I opened them up again and tried removing the white filters behind the baffles. That did the trick. Perhaps a bit too much as they were now edging away from the smoothness I quite liked about their sound so far. So I replaced them with circles of j-cloth (kitchen felt) the same size. Much better, now they had clarity with a warm edge.
I liked this balance but still felt it was missing something. Didn't really know what to try but remembered Lecky suggesting micropore on the back on the driver. Others had advised against this for these particular phones but I wanted to give it a try. I covered two thirds of the holes on the back of each driver with the micropore and tried again. Fantastic. It works really well for my personal tastes, seems to bring drums and details at the top of the spectrum further forward.
What next. Well I'd been enjoying a layer of j-cloth/kitchen felt actually in front of the baffle with my MS2i recently so thought I'd give it a go. Liked it. Then tried it behind the baffle as a second layer to the j-cloth filter. Nope. A bit muffled again. Then tried it bare again. Then with the j-cloth up front again... hmmm... still not sure which I prefer. More clarity without it, more smooth without it. No need to make my mind up now. For now I'm going without the cloth but could change my mind again, both are really nice.
With just one session and less than ten opens and closes I've improved these phones immeasurably (to my ear) and am having a great experience listening to Joanna Newsom's Have One On Me as I type. It's not over yet, I'm sure I'm going to change my mind on everything again, and definitely want to have an evening trying different amounts and configurations of micropore to perfect that as I feel a little less might be better, but for a week at least I'm just going to enjoy my new phones.
