Yes.... here we go again. My original post was a simple answer to a simple question. Someone asked whether headphones burn-in. I pointed out that speakers do indeed show changes in their measured performance over time... Since headphone drivers are built exactly like little speaker drivers, it would only be reasonable to expect similar changes to occur in their performance over time. And, since headphone drivers vary widely in terms of construction and the materials used, I would expect this to also vary widely. It is close to a first principle of mechanical engineering that all flexible springy materials - like rubber and plastic - change their springiness after repeated flexing... (And, since the suspensions of speakers are made from this type of material, this applies to them.) I'm sure you can find the mechanical properties of the plastics used to make headphone diaphragms documented somewhere. To answer your actual questions (about speakers made by Emotiva): - During the development process we DO burn in both individual drivers and complete speakers before measuring or testing them. It is most common in the industry to leave low frequency filtered pink noise running overnight for this purpose - which is what we usually do. (Sometimes we simply ensure that someone has been listening to them for a few days before taking measurements.) Our speaker designers have found, from long experience, that the measured parameters on most speaker drivers do in fact change over the first few hours of use. (As far as I know, that change is always in the same direction; the suspension gets slightly softer and the free air resonance gets slightly lower; although some change a lot while other change very little.) We don't bother to take or keep measurements before the drivers are burned in - simply because we don't consider them to be representative of the speaker's typical performance. (We have no interest in plotting how rapidly the parameters change... all we're interested in is ensuring that the measurements we take will represent their performance through most of their usable life.) - We DO NOT burn in our production speakers before shipping them; and we DO NOT burn in the individual drivers before assembling them into speakers. We DO NOT recommend that anyone burn-in our speakers before listening to them, nor do we specify that they will change after burn in. However, when people specifically ask, we tell them that "they may notice a slight change in sound over the first few days of use". - All of the specifications and performance claims me make for our speakers should be considered to be "after a reasonable amount of burn-in". ("After a week or so of use at typical listening levels".) I have heard that, in the past, some manufacturers burned in individual drivers before initially testing them. The reason was claimed to be that, because of inconsistencies in manufacturing, different units or batches might change to different degrees. Therefore, individual units were first burned in, until they reached a stable operating characteristic, before being sorted, graded, and matched. I suspect that modern construction materials are consistent enough that there is no longer any justification for doing this. With a ported speaker, the cabinet is tuned to the free air resonance of the driver, among other things. When the spring constant changes, the tuning match between the driver and cabinet will also change, which can have a significant effect on both frequency response and damping. The degree to which this affects performance will depend on several different design parameters - which will be different for each speaker model. As a broad generalization, in a sealed enclosure, the driver will generally experience a single-order roll off, which will shift slightly as the resonance changes. This will generally result in a smaller and more benign difference if there is a slight mismatch. (And, as I mentioned above, we have never bothered to measure or record this, since we are really only interested in how the speaker performs once it is "operating normally".) As as aside, although we haven't tested it, I will state that I personally have never NOTICED an audible change during the burn in period with any of our speakers.