[Harp-L] Comb Materials: the Perfect Test Harmonica?
Thu May 12 19:16:12 EDT 2016
Brendan is among my most-admired performers. However, on this matter which is unrelated to musicianship, I will have the temerity to question his wholesale dismissal of the results. A lot of careful effort was employed to assure a good test and to anticipate possible objections.
The test was designed to allow players to demonstrate their ability to describe the differences in sound attributable to comb materials. The same set of reed plates and covers was re-assembled on combs of different materials. A weight was attached to mask differences of density among metal and non-metal materials. The visible edges of the combs were painted the same color. The half-dozen or so participants were all virtuosos whose names you would recognize. A number of times, each participant played the harp and rated various attributes of the sound on a numerical scale. He/she was not required to name the material.
I reassembled and examined each harp. I made sure that the plates were snug and the screws were tight. I cannot claim perfection, but it did not seem to me that there were gaps severe enough to invalidate the data. Allowing for the sake of argument that there was some leakage, the following limited conclusions are still valid.
* The participants recorded differences in what they perceived. This means that, whatever their source, they were not completely masked by leakage. One participant reported perceiving no differences among all of the attributes of all of the materials. Although this may have been sneering at the test, it may also have been honest and correct. Or…all he was hearing was leakage.
* The attribute ratings for the same materials did not correlate among participants. This means that the perceptions are individual and subjective. A description of a sound by one player would thus mean nothing to another.
* The same material, without re-assembly, was submitted for playing as many as 3 times in succession. Players recorded differences that were not there! This means that the they did not arise from the comb materials.
Whatever the defects of any one test, it remains true that no one has yet demonstrated the ability to reliably distinguish one material from another by listening to or playing harmonicas. Although anecdotes abound, the materials effect remains unsupported by either acoustic theory or hard empirical evidence.
I’ll have to reserve judgment about Tom’s test until he describes for me how he controlled for confirmation bias.
> On May 12, 2016, at 1:13 AM, Brendan Power <bren at brendan-power.com> wrote:
> I had to chuckle seeing "The Great Comb Debate" resurface for the umpteenth
> time. Here are a couple of relevant points:
> Just for the record, the 10-hole diatonic test that Vern and I did together
> at SPAH a few years back was invalidated by an imperfect test harmonica, so
> shouldn't be cited in any discussion. We did our best, talking the test
> through exhaustively beforehand via email, and came up with an excellent
> concept for the harp. It had added weights to mask the differences in comb
> weights - but unfortunately the reedplate fixing was not good enough. You
> could see air gaps between the comb/s and plates; the harp sounded airy and
> there was not sufficient mating between the parts to determine the effect of
> comb materials, if any. That perfect mating of plates to comb is very
> important in any test of this kind, because it is central to the issue.
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