Again, a question which might work elsewhere but I chose to put it here because perhaps the discussion might be pertinent... As is probably known, there are dodgy companies which sell "audiophile" speaker fuses that are supposed to "improve" the sound. This goes hand-in-hand with the mods often sold to bypass speaker fuses entirely, at the risk of course of damage or destruction to the speaker.
First, let me state for the record that I don't believe a properly rated speaker fuse will cause any audible artifacts in an audio signal. But it is admitted by the manufacturers (such as Littelfuse) that the behavior of a fuse at or near rated current is nonlinear in resistance due to the heating of the fusible element. Nonlinearity in the signal path, of course, does lead to distortion - but how much? Sadly, no one seems to have published any hard data as to the resistance vs. current passed through a fuse. It seems that lower rated fuses would probably show a greater % variance as you approach rated current, because they're higher resistance to begin with; that much is shared by the manufacturers. But then you're more interested in the behavior at a current which is typical of actual use, which for speaker fuses is somewhere around 1/2 - 2A, which is roughly a range of cold resistance somewhere between 40-250 mΩ. Making the fuse larger in order to minimize any putative effect will of course risk damage to the speakers, which is to be avoided.
Has anyone found, or measured, data showing a change in resistance with applied current for a moderate-sized fuse (say 1A fast blow)? In other words, has it been characterized numerically? The only thing I have been able to find was a graph purporting to show distortion vs. applied current, and a vague reference to Bob Cordell's book on designing audio amplifiers - neither of which have been traceable to actual test conditions or discussion. I don't really want to buy the book and then find that the data was taken out of context or that the graph was mis-attributed. I assume that it's probably in a circuit with an amplifier and a ~8Ω speaker, but that still doesn't provide more than vague data (and no analysis) to justify the alleged results. If the data is real, then it would seem unlikely for a fuse to contribute audible distortion just based on the facts that most speakers generate far more distortion over the frequencies shown, and the masking effects of musical signals are quite strong.
Anyone with hard data, a copy of the book, or who has actually done a test and can share? It would be nice to put this one to rest.