Quote from he stickied thread "an interview with John Grado" http://www.head-fi.org/forums/showthread.php?t=129877
"As an aside, is anyone interested in knowing how to tell HP-2’s and HP-3’s apart? No? Okay, I won’t spill the beans on that. Oh what’s that I hear? Some threats of castration? Heh, no need to get all uppity and everything! The answer is…..on the underside of the pads, just like we tell the production number of the Reference series and the Pro series! On each HP-3, it was clearly marked HP-3. This HP-3 is easily rubbed off though. Ah crap then…how can we really know if someone can just rub it off? Well, for one thing, only 50 HP-3’s were ever made! Yep, that is a fact! The number is 50 max, likely less. The first batch of drivers were not as closely matched as possible (where the matching of the drivers was less than the .05 db) and so the decision was made to sell them at a cut below the HP-2’s. These would be paired up and shipped out as HP-3’s. However, on the later runs, the drivers were all able to be matched to .05 db. Therefore what was sold as HP-3’s were usually HP-2’s. That means, of the 50, the majority are up to HP-2 spec anyway, or in a word, HP-2’s rebadged. For those of you with definitive HP-3’s, John said he could not tell the difference in most trials between any of the models. The HP-3’s are so close or dead on exactly like the HP-1’s or 2’s. Another thing, the HP-1’s and 2’s, sound identical to him as well. There should be no difference in the sound at all. The only difference in sound should be equated with the cables if at all. Regarding cables, and this is interesting…only TWO cables were ever produced for the Signature series. The first is the Standard Joseph Grado Signature Cable, and then the second generation or the Joseph Grado Ultra-Wide Bandwidth Signature Reference Cable. But waittaminute…what about those HP-1000’s that came with a cable without any writing on it? Those, folks, are equipped with the RS-1 cable. Some of the phones had to be recabled and those that were, were recabled using the newest cable. I find it very very interesting that those who have heard all three cables have nearly unanimously agreed that the unmarked cable is the best. How many times have I read that Joe was the master and that much was lost on his apprentice John? Could it be that in fact, John does know what he is doing and that as I already stated, the priorities and/or goals are simply distinct? What is also important is that John was working full-time at Grado during the development of the HP-1000’s. Having assembled each and every one, he is keenly aware of their build quality, the production costs and most importantly, their sound. Above all, it was during the production of these HP-1000’s that John took over the company. I think I’m back on track now, aside finished."