Hi all. I'm surprised no one has made any comments to expand this thread, but anyway, now for my opinions on several headphones, including what this thread is really all about - the burn in characteristics of the Sennheiser PX100 and the Koss portaPro as well as PX100 vs portaPro.
I've been doing many comparisons with many different types of music as well as leaving the portaPro just playing music while I go off and do things I need to do so as to burn them in more quickly. The first thing I found is that the portPro burns in a lot quicker than the PX100s did. I would say that the PX100s take at least 50 hours to start sounding even close to their full potential, but to my ears sounded just perceptively better closer to 100 hours. They probably have something close to 200 hours on the clock now.
I liked the sound of the portaPros straight out of the box, however there was a little edginess which bordered on harshness here and there, but the thing that kept me listening to them and not just throwing them in the draw, was a relatively linear frequency response and best of all, the transient attack. Anyway, they would probably have about 150 hours on the clock now, but for the last few days I haven't noticed any sound improvement. I would say that the portaPros are definitely burnt in and reach their best in about 50 hours. So the portaPros will start giving their best in roughly half the time when compared to the PX100s.
To recap, straight out of the box, the PX100s appear laid back with a prominent bass and not a whole lot of top end, almost as if there was a dip in the frequency response around the 8K area and then an over exaggerated airiness in the top end with some music. The conclusion is that the top end does come back to be more linear after the 8K or so dip. I've already mentioned my thoughts of the portaPros straight out of the box, so will not repeat it again here.
So which is best? I guess here I had better explain how each headphone has changed since new. The PX100s got MUCH more linear with its frequency response, so in effect completely lost the "boom box" sound it had from new, and to my ears ended up sounding slightly warm and very smooth sounding with very good extension at both ends of the frequency range. The portaPros on the other hand lost its occasional harshness over time. It already had a well extended bass and good high end, but like the PX100s, everything smoothed out with time.
My summary. The portaPros definitely offer the better sound. Great transient attack, well extended at both ends, a midrange which can "bite" when it should, although with the top end I would say the PX100s extend just that little bit further, but the PX100s with their slightly warm sound may not suit everyone's taste. Put simply, you can play anything through the portaPros and they will excite and impress everytime. The PX100s offer great sound too especially if you wish to listen to orchestral music. This is because they present the warmer sound. The portaPros on the other hand give a nice edge to brass instruments.
I guess the final word is this ... if you listen to orchestral or easy listening music most of the time ... buy the PX100s. Their warmer presentation and generally sweet sound make for a great listen. For those who listen to all other types of music the winner is definitely the portaPros - they get you tapping you toes and very involved in what you are listening to.
I suppose that I haven't really helped you if you listen to ALL types of music as I do. For me, I'll still be listening to the portaPros though ... they are the better all rounder.
Remember this though - whichever of these cheap headphones you do buy - they both have their virtues and good and not so good points. For the price, which in Australia is about the same for either headphone they are the only two which give you total value for money.
Since writing this I've had a listen to several Grado headphones and again, in Australia, the Grado SR60 is probably the better sounding - read more accurate - headphone, but it's slightly more expensive and lacks the deep bass, although what is there is just as accurate. This is where the SR80 comes in to its own - bass extension. Ok, it's more expensive than the PX100s, portaPros and it's younger brother, but as I've also listened to the 125s, 225s RS-1s and even had a go with the GS-1000s, the SR80s offer almost everything these other much more expensive headphones offer, but at a fraction of the price. So it really boils down to your pocket and the equipment you own.
MY FINAL WORD - For an inexpensive headphone, buy the portaPro, but also remember my comments about the PX100s. If you have reasonable equipment and can afford it, buy the SR80 - best value bar none. If you have audiofile grade equipment buy the GS-1000s - if you can afford them!. If you have equipment anywhere in between, try the Grado that suits your pocket - SR80 through to the RS models. Now I say this because I did read somewhere that each Grado is incrementally better than its cheaper brother, and by God, they're not far from 100% correct!!! Admittedly I haven't tried Grado's full range, but believe I took a more than reasonable sampling of their range. I should point that the Grado models I listened to were the "i" models, ie, SR60i, SR80i, etc... AND FINALLY, I did listen to other models from Koss, AKG and Audio Technica and while they all sounded great in their own way, I must admit that I was the most impressed with Grado's consistency between models, and since this thread has nothing to do with headphone reviews of every headphone I've had the pleasure or displeasure of listening to, I only make honourable mention of Grado. What I really mean here, is that if you are in the market for really good headphones, start with Grado as a benchmark and then listen to the other brands in that particular price category.