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Not a huge surprise that the impedance varies that much
Fang has already stated they've had many problems with their QA and they have been working to improve it. Didn't they just hire some new QA manager? Anyway with all the cable variations and broken cables as well to be had, not the biggest surprise that the drivers are not well matched. As long as they own up to it when they make the mistake I guess it's alright. At least they are trying to improve. It is unfortunate for the price of the HE-500 all the inconsistencies it's been through.
I am sorry but I disagree on this. Do HifiMan accept returns based on measured impedance? I haven’t realise that!
But let us look in QA issues. QA issues are emerging when controlling something that needs to be qualified by a human, e.g. how well the cable is soldered to the connectors. Of course, a simple pass/fail test should be performed for every cable, and all the cables should work OK when leave the factory. But if QA is not good enough then some soldered joints that are not robust would pass the human QA test and will eventually fail. This was a problem in some HE-500 cables and, also, in some early HE-400 wire connections inside the headphone (please, correct me if I am wrong here, I do not really follow HE-400 threads).
But the big impedance variation problem is not a human controlling problem. It is, firstly, a manufacturing deviation problem (high tolerances in a procedure) AND absence of a simple test verification method. The manufacturer should have include a simple pass/fail test to control the impedance variation. But he didn’t. Why he didn’t?
As I said earlier, big impedance variations means big variations in an important manufacturing process which, I believe, is affecting SQ. But, this SQ variation cannot be easily spotted from his customers, because it is not as huge as a broken cable. One must compare his HE-500 with other’s HE-500 to spot the difference. So, probably, the manufacturer has
chosen to
keep every headphone driver membrane, even if it’s impedance varied considerably, to
save some money.
But this is not a cheap headphone, isn’t it?
Of course, it is common that manufacturers tolerate ‘flaws’ as long as their customers do not realize them. Look all the fuzz about the ‘veiled’ LCD-3s. Hey, probably even Sennheiser do this. But that’s what the power of internet gives to the average Joe: knowledge and comparison.
Maybe I am just too harsh on HifiMan. I really enjoy my HE-500, I think it is one of the best headphones around. But I am disappointed that such an expensive headphone has such big impedance deviation. I do not think it would be too expensive to correct it (but I am not an expert here, so if someone knows better, please correct me if I am wrong).
Some will say that impedance variation does not affect SQ much. I do not think so. It does affect it, and probably way more than a cable change