Evidence of Headphone Break-In?
The nice folks over at AKG decided to send me a bunch of Quincy Jones headphones, including three Q701s! That's good news for both you and me. For me, because it will allow me to do some experiments I've been wanting to do for a long time. The AKG K701, now reborn as the Quincy Jones Q701, is notorious for needing hundreds of hours of break-in before they sound right. I want to see if that can be measured, and in this article I'll show you the first sets of measurements.
It's good news for you, because when all is said and done, I'll give away two pairs of the Q701 headphones to some lucky reader.
So, let's talk about break-in, shall we...
What is Break-In All About?
Separating voodoo from science in the audio world isn't easy. The human hearing system is exquisite, but it also has the annoying habit of learning and changing, so what we hear one day may not be what we hear in the same circumstances the next day. The placebo effect is strong in listening experiences. Was there really a change when you swapped cables? Or were you fooling yourself? It's not easy to tell.
One area where voodoo and science struggle mightily is over the idea that audio products in general, and headphones in this particular case, "break-in" and change over time. This idea seems logical enough for headphones: the new driver in the headphone needs to wiggle around some and exercise its flexures to settle into its norm. Problem is, if you're trying to hear it you only get one shot; once something has hours on it, you can't take them back off to compare. Headphone enthusiasts get one try to listen for changes during break-in of brand new cans, and over-attentive listening is one very likely path to fooling yourself.
I rarely hear break-in. I reckon the diaphragm does change a bit, but by the time it's got a couple of hours on it, it's done settling in. There is one exception in my mind, however, the AKG K701 is notorious for needing long break-in, and I've heard it a number of times. It's got me convinced that there is such a thing as a break-in period for headphones, and some need it more than the others.
I decided to see if it could be measured.
I took a brand spanking new pair of AKG Quincy Jones Q701 headphones; put them on the dummy head; and measured the frequency response over time, playing pink noise in between measurements. I measured the cans fresh out of the box; immediately after the first test (so it had about 5 minutes on them); then after 25; then 1 hour; 2 hours; 5 hours; 10 hours; 20 hours; 40 hours; 65 hours; and finally after 90 hours of break-in.
Once all the data was gathered, I really couldn't tell what the differences where by eye, so I plotted the data as differences. I used the 90 hour data as the reference, and plotted how the data in each set was different than the 90 hour data. My assumption was that the first measurement out of the box would be most problematic, and that the data should settle in the direction of the longest burn-in time.
Any good mathematician will tell you that this method is a recipe for making the data look like it's settling toward the reference set. Just because the line in these graphs is getting less wiggly over time, doesn't mean that the frequency response is getting smoother. It just means that the frequency response is changing over time and moving in the direction of the 90 hour data. That's fine, because all I'm looking for here is a clear trend where the data changes smoothly from the start to the end reference, which might indicate a change in the sound over time possibly due to break-in. Whether it is break-in or not is another story. I just want to see if I could see trend in the data.
Let's take a look shall we?