This is my experience with breaking in a quartet of Monacor/Number One SPH-250KE 10" speakers (partially copy-pasted from an earlier post):
First step: measuring their free-air resonance, which, according to the specs, should be at 23 Hz.
Oops... all samples show something around 30 Hz. Now certain people would wrinkle their noses and return that crappy stuff, with parameters far from the specified ones. Well, to me as an experienced speaker builder that's not alarming at all... break-in has always helped in these cases. In fact it's a very normal procedure, and I haven't met any new speaker chassis reaching the specified parameters; all of them show a resonance frequency at least 20% higher than specified. If you're into speaker building (am I really the only one at Head-Fi?), you are familiar with this phenomenon, which BTW is described in every better DIY magazine.
Second step: setting the tone generator to ~28 Hz, to achieve maximum voice-coil/cone displacement with minimum current charge. There's not much power needed to move uninstalled speaker chassis near its resonance frequency, and the maximum displacement with this model is very high, so I give them some juice and allow them to vibrate with a displacement around ±8 mm in average, with some 5-10-minute pauses every 2 hours.Results:
Chassis..........0 hours......after 15 hours
No.1..............30.0 Hz..........25.2 Hz
No.2..............30.0 Hz..........25.2 Hz
No.3..............30.2 Hz..........25.4 Hz
No.4..............30.0 Hz..........24.8 Hz
These values are stable, at least 2 hours after «cooling down».
So 15 hours aren't enough to reach the default values -- I expect 100 or even 200 hours. I haven't finished work with these drivers, since I have more or less retired from speaker building. After all these measurings can serve as example for real
, physical break-in effects, which are still denied and considered impossible by some skeptics. What's going on physically is a simple loosening of the suspension -- which in headphones drivers is part of the membrane -- resulting in a higher compliance and thus lower resonance frequency, so potentially extended low-frequency response. Of course the measurable phenomenon doesn't directly prove
an audible effect, but at least it makes it quite plausible.
Since headphone drivers are mini-speakers, similar effects are expectable from them. Now there's often been asked why the effect is almost always positive -- it sounds better after a certain break-in period, never worse. That's a bit more tricky. My theory -- inspired by a response from Stax
(go to posts No.100 and following) to the subject -- is that the suspension, or the elastic membrane, resp., originally has some inhomogeneities of elasticity within its circumference/surface which get evened out by the mechanical vibrations occuring from use. This should reflect itself in lower harmonic distortion and improved transient response.
Even though the break-in scenario is logical and explainable (to some degree) with sound transducers, not every type of headphone will show it (equally). E.g. I haven't experienced it with canalphones with their balanced-armature drivers.Original thread.