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Tuesday, April 17, 2012

The effect of break-in: Sennheiser HD650

Introduction

It is generally known that a new pair of headphones must go through a "warming up(aka break-in)" phase for certain period of time before it opens up its true sonic potential.

According to AKG:

"...we cannot confirm that there is a burn in effect of the transducers taking place. Normally the sound of headphones changes only over many years and then mainly caused by the ear pads (less low end since the ear pads get more densely by sweat etc.).  However, during the first hours of use of headphones, the ear pads -  in the beginning a little stiff – start to accommodate to the users ears and head and the sealing becomes better, as a result the bass can be increased a little, on the other hand the distance between the headphones and the ear may become closer..."
from http://www.akg.com/forum/index.php/topic,1736.msg5270.html#msg5270



In contrast, here's what Grado has to say in regards to the headphone break-in:
"..As any mechanical device, the headphones will improve in performance with use.."

And according to Ultrasone, their recommended break-in period is about 100 hours:


Previously, both electroacoustic and psychoacoustic aspects of a 100 hours-long headphone break-in have been presented with SONY MDR-EX1000, a headphone with a 16mm dynamic transducer: The physical transformation is evident, yet its degree is not of a night and day difference, as audiophiles normally describe it.

Then how about with a larger transducer of a full-sized headphone, such as Sennheiser HD650?



Test methods

A brand-new Sennheiser HD650 is to be broken-in for 100 hours straight with XLO's break-in sample(100 dB SPL @ peak), driven with SONY NW-S639f with all of the tone controls turned off. Once the headphone is inserted in EURI's ear canals , its physical placement must remain untouched for the next 100 hours in order to prevent any placement-related deviations. Each 10 times averaged pre break-in & post break-in measurement data are to be compared, and should any type of change occur, they are to be reproduced back utilizing a binaural recording technique to be ABX-compared.



Test results

Impedance
The resonant frequency has been shifted, while the overall impedance lowered a little bit.

Frequency response


Time-domain characteristics

Spectrogram




Harmonic distortion



Subjective Assessment

ATTENTION: In order to accurately reproduce these binaural recordings, listeners must use a flat diffuse-field equalized headphone, such as Etymotic Research ER-4B and STAX Lambda PRO with ED-1. The accuracy of the reproduced result can not be guaranteed otherwise.

Reference sample


A post-100hr broken-in Sennheiser HD650

High quality sample: http://www.4shared.com/music/aqc94845/hd650_post_The_Lion_King_-_01_.html



Conclusion

As previously confirmed by others, 1 2 3 4 5 6 , the physical effect of break-in is quite evident. Moreover, the psychoacoustic aspect of Sennheiser HD650's break-in has been demonstrated for ABX comparison so that listeners could verify the audibility of 100 hours of what-so-called 'warming-up'. Still, a radical sonic metamorphosing quality, of which audiophiles usually refer to, is nowhere to be seen.



Discussion

So far, there is nohing dramatic about the headphone break-in, just like the others have reported. Still, there is a chance for a reasonable doubt: how about all the claims in regards to headphone's break-in then? Did everybody really fall for such a placebo-induced maelstrom?

So another simple test conducted: This time the focus is on HD650's ear cushions.

Here's the measurement with new cushions:

Very close to the reference diffuse-field target, as measured previously.
And Below is the measurement with old cushions, about a year or two old?

Now everything makes sense: While the physical transformation of a transducer is occurring very slowly in an almost inaudible fashion, the ear cushions age relatively faster, thus making more noticeable change in the tonality. The still-firm new cushions sink deeper into the head's shape with repeated usage, and consequently, bring the transducer closer to the listener's ear.

This is such an ingenious fine-tuning technique, almost like of a musical instrument. As HD650 ages, its timbre will turn from a pronounced treble to a laid-back bass, which is a well-known sonic signature of Sennheiser. Now I can never say HD650 does not break-in.

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