Off-axis non-linear distortion

[JohnG]

After some low-level searching on this topic on and off for a few years, I thought I'd post the question here. Is anyone aware of research into non-linear (i.e. harmonic, etc) distortion as a function of an angle off-axis?

I wonder about this and the effect on system sound, namely because it seems to me that the fundamental and harmonics could have dramatically different off-axis responses, which could account for differences in drivers that have a measured low on-axis distortion.

Some ideas to chew upon:

1. Harmonics generated via motor non-linearities could have a much narrower beamwidth than the fundamental due to narrowing of beamwidth with increasing frequency. Listening off-axis might be beneficial in such a situation.

2. Harmonics due to or enhanced by cone breakup would be difficult to predict. If some parts of the cone radiate more than others, all sorts of things could happen. It may be possible that a on-axis measurement of harmonic distortion indicates a low value, while the total radiated harmonic power could be much higher than indicated by an on-axis measurement, and could still be heard via reflection.

I'm no expert in this area, and am not a true audiophile (can't afford to be). At one point in my career, I had to qualify a mobile 2-way radio for FCC, and the analogous issues came up. I was really just curious.

John G

[sreten]

Hi,

I would not worry about it too much, generally axial distortion will be
highest. It is possible an axial null reduces a distortion component
that becomes more prominent off-axis, but you will also have this
problem with the drivers response. Basically the issue is on/off
axis response, possibly effecting distortion harmonics.

I think low distortion per se is the best approach, rather than trying
to use some acoustic mechanism to reduce poor distortion levels.

/sreten.