I watched this because so many people are talking about it – and I even took notes.
The overall thrust of the lecture is, I would say, “objectivity works”. We can make measurements of the hardware, judge them against some fixed criteria, and then demonstrate that these correlate with real, human preferences in blind tests. Hurrah! The age-old debate is over, and we can improve our new speaker designs by building them to maximise their objective scores in the full knowledge that this would correlate with human preferences.
However, I am not totally convinced by the criteria that were specified in the lecture: it seemed to me that there might be gaps in the argument and some circularity.
What he showed:
- Sighted listening tests can be flawed (thereby implying: all sighted listening tests are unreliable).
- Some measurements can be carried out on speakers in an anechoic chamber (dubbed ‘Spin-o-rama’) and munged together to create a performance index related to flatness of frequency response and smoothness of off-axis response. Transient response is not a factor. At all.
- In listening tests, speakers with the ‘best’ Spin-o-rama score are usually preferred by listeners over the opposite (implied: all else being equal).
- Mono allows maximum discernment of difference, and does not contradict stereo listening results in the above tests (implied: therefore mono should be used for all listening tests)
- Trained professional listeners give the ‘statistically healthiest’ range of scores, and do not contradict ordinary listeners in the above tests (implied: therefore trained professionals should be used for all listening tests)
What he didn’t show:
- That it is valid to use the Spin-o-rama score in reverse i.e. as a tool for designing a speaker. He implies it is, but does not prove that a poor speaker could not be designed that achieves an exemplary Spin-o-rama score.
- That transient response doesn’t matter – it is simply ignored. The speakers tested may have had good transient responses, or not, but as most of them were of conventional design they may all have been much of a muchness.
- That various speaker technologies are inherently better or worse than others i.e. no view on whether sealed cabinets are better than bass reflex, or active crossovers better than passive – and his performance index is indifferent to this, assuming that flat steady-state frequency response is all that matters.
- That mono speakers and trained professionals are the best choice for all listening tests.
It is possible to produce different colourations related to phase shifts while still producing a perfect frequency magnitude response (the drivers may have their phases matched perfectly throughout the crossover but the phase is shifted relative to other components in the signal). Similarly, bass reflex configurations distort the time domain response while maintaining a perfect steady state sinusoidal magnitude response. Dr. Toole’s tests don’t address these factors.
I have no doubt that flat frequency response and smooth off-axis response are essential, as he says, but might there be more to it than just that? Any unexplained deviations between the listening tests and the measurements (it isn’t a perfect correlation) could be explained by a multitude of factors including the speaker’s transient response which, after all, is a straightforward difference between what was recorded and what the speaker emits – it is just that someone around 1936 declared that ‘phase doesn’t matter’. Until recently it has not been possible to verify this, because it was not possible to produce a high quality output with close to perfect phase. Comparing different speakers all of which have phase/time distortion and other problems, and finding that listeners cannot tell them apart (in mono using someone’s idea of ‘typical’ music), does not tell us that a speaker without those distortions would not sound better.
Correlation is not causation, but people are talking about the Harman method as if it is. So, if I were a speaker designer doing things by the Toole book, I would always use bass reflex without thinking, as this would have no effect on the Spin-o-rama score but would result in a smaller box. And I would be supremely relaxed about crossover design, ensuring only that it matched the phases of drivers through the crossover. Phase correction and sealed enclosures wouldn’t get a look-in because they offer nothing extra in terms of the Spin-o-rama score but cost more to manufacture.
My opinion is of no consequence, of course, but there are some serious people who do suggest that transient response matters, and it would have been nice if the guru of gurus could have mentioned it, if only to dismiss it with reasons.