Hi Nopiano
Thank you for taking the trouble to reply. As I understand it, the job of the surrounds is to allow the driver to move freely and then return to its original position as quickly and precisely as possible, so obviously the manufacturers wouldn't want it to continue to soften and become more flexible past a point of optimum performance. It does seem very odd to me that this process can supposedly take hundreds of hours yet the suppliers of the material are still able to provide sufficiently accurate data, and the designers are able to perform sufficiently accurate calculations, to make all this predictable enough to select the right material parameters for the job of each speker design.
There is a Wikipedia page here
https://en.wikipedia.org/wiki/Thiele/Small_parameters
Here's an extract - the second paragraph mentions change in compliance of the surrounds. Much of it goes over my head but, if I'm understanding it correctly, speakers should be 'run in' after a matter of minutes, not hours -
The mechanical components in typical speaker drivers may change over time. Paper, a popular material in cone fabrication, absorbs moisture easily and unless treated may lose some structural rigidity over time. This may be reduced by coating with water-impregnable material such as various plastic resins. Cracks compromise structural rigidity and if large enough are generally non-repairable. Temperature has a strong, generally reversible effect; typical suspension materials become stiffer at lower temperatures. The suspension experiences
fatigue, and also undergoes changes from chemical and environmental effects associated with
aging such as exposure to ultraviolet light, and
oxidation which affect foam and natural rubber components badly, though butyl, nitrile, SBR rubber, and rubber-plastic alloys (such as
Santoprene) are more stable. The polyester type of
polyurethane foam is highly prone to disintegration after 10 to 15 years. The changes in behavior from aging may often be positive, though since the environment that they are used in is a major factor the effects are not easily predicted. Gilbert Briggs, founder of Wharfedale Loudspeakers in the UK, undertook several studies of aging effects in speaker drivers in the 1950s and 1960s, publishing some of the data in his books, notably
Loudspeakers.
There are also mechanical changes which occur in the moving components during use. In this case, however, most of the changes seem to occur early in the life of the driver, and are almost certainly due to relaxation in flexing mechanical parts of the driver (e.g., surround, spider, etc.). Several studies have been published documenting substantial changes in the T/S parameters over the first few hours of use, some parameters changing as much as 15%+ over these initial periods. The proprietor of the firm GR Research has publicly reported several such investigations of several manufacturers' drivers. Other studies suggest little change, or reversible changes after only the first few minutes. This variability is largely related to the particular characteristics of specific materials, and reputable manufacturers attempt to take them into account. While there are a great many anecdotal reports of the audible effects of such changes in published speaker reviews, the relationship of such early changes to subjective sound quality reports is not completely clear. Some changes early in driver life are complementary (such as a reduction in Fs accompanied by a rise in Vas) and result in minimal net changes (small fractions of a dB) in frequency response. If the performance of speaker system is critical, as with high order (complex) or heavily equalized systems, it is sensible to measure T/S parameters after a period of run-in (some hours, typically, using program material), and to model the effects of normal parameter changes on driver performance.
There is some discussion on the topic at the start of this video from 'Audioholics'. They see to say the same thing (that 'run in' happens very quickly). I have to say though, that even though hey refer to empirical evidence, I find them to be unecessarily cynical rather than taking a mor eschewed, skeptical position.
I think it would be much more sensible for WhatHifi to say something along the lines of - we recommend spending a good few hours if not days listening to your new speakers, before making a conclusive judgement on what you think of the quality of their sound and stereo image they can achieve in your room; it's likely that your brain will take quite a while to adapt to them. Many manufacturers state that their speakers need time for a mechanical 'run in' but the evidence for this is not clear.
