Quote:
Originally Posted by
jaddie 
You have to understand that when you say there's a 20dB difference after burn-in, and nobody else is showing that, there's going to be a little disbelief. Did you, for example,have a "control" pair that were tested at the same time as the burned-in pair to show there was not change in the test setup? Or was there some other way used to verify the test setup had not changed? Any way to post the graphs?
Perfectly understandable. 20 dB is an enormous difference - but then again one has to know what signal can achieve true burn in.
No, the intent was to show exactly the same pair of JVC HA-S770 hps "before" and "after" the 48 hour burn in regime - using the very same measuring setup, documented down to serial # of artificial ear, analyzer , etc, etc. I will translate the whole thing proper and post graph for the right channel that survived - there is no way the software used can identify as "before burn in" and "after burn in", so they are labeled Left and Right in the graph - for actual measurements for the surviving right channel - before and after burn in.
I went to the trouble of having made these measurements by no less than Bruel & Kjaer because I really had it with people who do not believe in burn in and insist on precise measurements to verify it. But I will describe how this change can be heard - with the exact tracks and comments what is wrong with hps out of box and how they behave once properly burnt in. It can be heard ( and FELT on ears ) - and the difference is dramatic indeed. I limit myself to "before" and "after" - there is any degree "in between" , so when you read that a certain hp "sounds after so and so many hours of playing so and so" - do not dismiss this as BS, the guy who wrote that just might be honestly trying his best to describe the sounds he is actually hearing.
That failure of the left channel was an unfortunate fluke - every hp listed in my profile went through the 48 regime and all but this pair sing happily ( and better... ) ever after.
Remember - factories can not afford to burn in hps ( save for exceptions, for example Stax - see the report on the visit of head-fi in Stax Japan ) - nor it is performed when third party measures them. First the knowledge to do it is needed, second time is needed for that, probably less than 48 hours regime I use, but I do not believe it can be done in say 8 hours - and 2 measurements have to be made - all this combined is costly indeed. Were it not for the fact that the owner of the company that measured these phones was not an enthusiast himself and partially turned blind eye regarding actual time used for making measurements, all the extra and at first not agreed upon measurements would have costed me a small fortune. Normal bussines practice can not afford such luxury.
Burn in is thus left for the consumer to do. Depending on hp type and listener sensibilities, it can range from "no difference" to "dramatic" - be it due to pads getting slightly different shape with use, be it to driver change ( like I would like to prove ) , be it to listener's changed appreciation. It is much like new shoes - some really "fit like a glove", some will give you a blister or two before becoming really comfortable. I hope no one will dispute this last claim. It is the same with new car - for certain period or mileage, you are not advised to push it to the max, after certain mileage there is mandatory first service check up - to verify everything is as it should have been.
The only audio manufacturer I am aware of that readily offers and encourages such check up after initial burn in is Van den Hul - because every phono cartridge will change its mechanical parameters a little and final adjustments can only be made after burn in of say 50-100 hours of playing. Every other serious cartridge manufacturer will do the same if the cart is returned - I can speak for Benz first hand, because I used to work there.
