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Join Date: Aug 2002
Location: Toronto area, Canada
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tvuong: for whatever reason I can't access your mdat files. But I just thought I'd throw this in, one more great use I've got out of the REW distortion measuring capability.
Anyway, I found that when some (quality) speakers measured elevated THD, and I mean over a small fraction of a %, it turned out that indeed the mid and "mid-bass" drivers were damaged. The higher the test level, the more the distortion increased, and I mean significantly increased, out of proportion. If your scenario seems a bit like this, do what you need to do to make sure it's not the amp channel that's at fault before saying it's the driver.
We also need to consider that speaker THD below 3% is traditionally actually considered "good". I can assure you that in a modern decent speaker, in the mids and highs at least, THD below 0.1% at a reasonable listening SPL (assuming capable amp), the levels we normally measure at, is very common. I'd say 1% is too much outside the bass range, if we're talking an indication of something "wrong", and not necessarily audibility to any specific individual.
Remember I can't see your graphs! Another clue to a damaged driver is look for the THD significantly peaking at a frequency (resonating). This could indicate a loose cone, or a damaged surround, or maybe even a damaged spider. Many modern drivers, and I'm talking even quite expensive ones, use glue to hold many (all!) of the parts together. I have seen this glue come loose in areas, and when fixed (quality adhesives) the distortion completely went away. It was kind of hard to find & figure out, until after I saw it the first time, but something to consider.
Last edited by cfraser; 01-24-2015 at 12:36 PM.