Way to go Erin!
I was able to watch the first sixty minutes and I have to go out and do something, but I did capture some excerpts from the first sixty minutes.
At 46:20, the topic turns to the perfect loudspeaker, and particularly to the question of the importance of non-linear distortion. About five minutes later, the discussion of non-linear distortion becomes more definitive, and about five more minutes after that, there is some very interesting discussion of the importance of bass extension.
51:15 Dr. Toole: “The reality of fifty or so years of listening to loudspeakers of all kinds, in numbers of places, is that in the mainstream of well-designed consumer loudspeakers, distortion basically is not a problem. As you go down the price scale, things start getting simplified and corrupted, and distortions do creep in from time to time. You may or may not be able to predict the audibility from measurements, but that’s why we do double-blind listening tests. So unless you’re doing listening tests, I’m sorry, there are no numbers that are going to predict whether the loudspeaker exhibits audible distortion.”
56:22 Dr. Toole: “Bass is the dominant factor, thirty percent roughly of our overall rating of sound quality is based on low frequencies. This is one of Sean Olive’s interesting findings. … In a paper I published in the early eighties, the correlation coefficient between the low-frequency cutoff, the -10 dB down point, not -3, -10, was .5. The correlation between that cutoff frequency and the overall subjective rating - sound quality rating. So we go for bandwidth, not boom.”
A couple of comments. Everything that is capable of being heard is inherently capable of being measured. If it is true that distortion measurements taken in the present era do not correlate closely with audibility, this can only mean that we still have not figured out how to do it. It does not mean that it cannot be done.
With respect to the discussion of bass, the presumptive reason that the -10 dB point is more meaningful than the -3 dB point is that the -10 dB point is the better indicator of bass extension. This is something that I've believed for a very long time, and this may well be the true reason that many people, old timers especially, prefer acoustic suspension speakers over speakers that use ports or passive radiators. This is my personal preference with an exception, the exception being subwoofers where the tuning frequency is low enough to ensure that the bass extension leaves nothing to be desired and that there isn't a strong emphasis at the peak frequency of the port output. This exception obviously does not apply to small bookshelf or stand-mount speakers where bass extension is not going to get anywhere close to 20 Hz even with the port or passive radiator. I will never understand the rationale behind small speakers with ports or passive radiators. It only exaggerates the response somewhere in the mid-bass, to the detriments of bass extension.
