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Originally Posted by David Spearritt  I think this aligns with my thinking and experiences. Observations as follows:
* Widening the spacing tends to reduce the problem, ie moves the coherent frequencies lower |
This agrees with my observations. As little as a 4cm separation increase caused a noticable change.
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Originally Posted by David Spearritt * Moving away from the source, reducing the contributions from coherent additions of direct sound coming from glancing angles. |
I am not sure if I am not coming to the opposite conclusion. Direct sound is largely phase coherent for all frequencies with AB < 1m. It is the indirect sound that is more phase incoherent, as it comes from all directions, and coherency decreases with decreasing frequency. (Or incoherency rises with wavelength.) So as the direct to indirect ratio increases you will notice less of the low-mid buildup. Or the more distant placements will exhibit more of this problem.
As evidence, placements very close or inside the piano do not exhibit the problem. This agrees with your following observation.
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Originally Posted by David Spearritt However, this doesn't gel with the stated phenomenon that two 4060's hanging just over the open piano lid, do not exhibit the problem. |
Is this making sense?