Burning In

Brian Dunning’s usually excellent Skeptoid podcast this week contains a blooper on the subject of burning in equipment. This podcast was a collection of short answers to student questions, one of which was:

Hello Brian, my name is Julian and I am from Malaysia, and my question is: Do burning in headphones improve sound quality?

His answer:

No, burn-in of headphones and other audio equipment is just one more dimension of the snake-oil world of high end audio, akin to super-duper speaker wire. Burn-in is the process of turning on new equipment, sometimes under extreme conditions, to reveal defects. It’s a common, and almost always worthless, tacked-on optional extra by some retailers of electronic equipment. Once in a while burn-in will reveal a defective component, thus saving the customer the trouble of taking the device home to discover it on his own; but as far as burn-in actually improving the performance of consumer electronics, then no, there is no evidence or plausible reasoning behind this.

Obviously I agree with most of this, but there are two problems. First, Brian seems to misunderstand what ‘burn in’ means conventionally amongst audiophiles. It is not to expose defects. Indeed, it isn’t even to push equipment hard. It is running the equipment normally for some hours, or more typically, tens of hours. Some audiophiles claim that this improves the sound of the equipment.

The second error he makes is in equating the equipment about which the question was asked — headphones — with electronic equipment. These are very different beasts. Headphones are, like loudspeakers, electro-mechanical devices. They convert electrical energy into acoustical energy (which is simply mechanical energy in the form of compression waves in air). They do this by using a linear electric motor to push a cone or diaphragm of some kind. This is designed to be extremely stiff in the frequency range of operation, but nothing is perfect and to some degree or other it flexes. This cone or diaphragm is supported by a suspension system, called a ‘spider’ in the case of a loudspeaker. This is often a stiff fabric rendered springy by means of concertina folding. The edge of the cone or diaphragm is typically also surrounded by some material in order to locate it in space. In speakers this is usually either some kind of foam, or a soft rubber.

All these moving bits change their state with use. The assumption is that they are stiff to begin with and loosen up with use, and this seems to make sense. The assumption also seems to be that they loosen up from their initial stiff state to a normal operational state fairly quickly — say, within dozens of hours of use — and maintain this state for a long time. Think of a tipped over ‘S’ curve.

Whether or not this has any perceptible effect on sound I do not know because I have never done a test. The procedure for such a test would be easy enough. Take two sets of same-model loudspeakers. Use a panel of listeners of sufficient variety and number to generate statistically valid results. Have them listen to both sets of speakers new out of the box, but only briefly, and score any differences in sound.

Run one of the sets of speakers extensively for a lengthy period to burn them in. Get the listening panel back and, double blinded, compare the barely-used and heavily-used speakers again. Score any differences in sound. If this second score is significantly greater than the first score, then the existence of an audible effect would have been established.

Some people swear that burn-in does make a difference in their experience. I suggest that it’s almost impossible to tell without some formal protocol as outlined. You cannot compare the sound of a device from one day to the next in the way that most people do these things. All you can do is compare the sound of a device with your memory of how it previously sounded, and I’d strongly suggest that you shouldn’t trust such a comparison.

But that doesn’t take away from the fact that it is almost certain some physical changes do take place in loudspeakers (and headphones) when they are run.

Electronics? Cables? No way.

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