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SAC · 14th March 2010

We are talking of several different intended uses/applications that are basically at odds with each other.

Normal (referring to near 90 degree) incident sound simply passes through he phase grating and would strike a reflective surface and reflect back through the phase grating at the same normal (90 degree) incidence angle!

The way the collimating phase grating works as a diffusor is that signal 'near' 90 degrees passes through collimating phase grating, which is then redirected by a scattering surface 'above/behind' the phase grating. This redirects and scatters the signal about the space until it is oriented such that it passes back out of the the space when it happens to be incident with the phase grating at a 'near' 90 degree angle. A scattering surface behind the phase grating separated by some distance is optimal to further scatter and subsequently diffuse the energy. A surface perpendicular to the incident admitted signal would simply reflect the signal back through eh grating and defeat its purpose in this case.

Using absorption in conjunction with the phase grating in this application is a waste of both the phase grating and the absorption, as our goal is to use the phase grating to augment the scattering surface and to further diffuse and delay the retransmission of the signal into the main room space - And our purpose here is certainly not to absorb the energy.

To absorb the signal above the phase grating does NOT augment the diffusion and later 'retransmission' of the acoustic energy back into the space.

Flutter echo is completely avoided as the energy retransmitted is much lower in energy content/gain then that of the original entering sparse specular reflection.

A collimating phase grating has been used for several hundred years in the optics realm for a great many purposes, and it can be used for a variety of applications. It is not limited in itself, but is a tool that can be used either alone or in conjunction with many configurations for quite a variety of tasks. We risk error if we try to state its 'use', as it can be used in a myriad configurations, either alone or in conjunction with other 'tools' for a myriad of uses.

And as far as being cost effective, phase gratings can be made very easily with a table saw and 3/16" 4x8foot sheets of luaun plywood used to cover interior doors that is available for less than $10 a sheet at any Home Depot or Lowes or foamcore material. And this would be cheaper and more easily accomplished for a given area than than applying absorptive clouds (which would simply deaden the space) or using more complex truly diffusive designs.

And our concern was NOT simply the existence of flutter echo, but of augmenting a more live than dead acoustical space while avoiding the problems of sparse specular reflections - as was stated in the original premise.

14th March 2010	#16
SAC Registered User Joined: Dec 2009 Posts: 2,622	We are talking of several different intended uses/applications that are basically at odds with each other. Normal (referring to near 90 degree) incident sound simply passes through he phase grating and would strike a reflective surface and reflect back through the phase grating at the same normal (90 degree) incidence angle! The way the collimating phase grating works as a diffusor is that signal 'near' 90 degrees passes through collimating phase grating, which is then redirected by a scattering surface 'above/behind' the phase grating. This redirects and scatters the signal about the space until it is oriented such that it passes back out of the the space when it happens to be incident with the phase grating at a 'near' 90 degree angle. A scattering surface behind the phase grating separated by some distance is optimal to further scatter and subsequently diffuse the energy. A surface perpendicular to the incident admitted signal would simply reflect the signal back through eh grating and defeat its purpose in this case. Using absorption in conjunction with the phase grating in this application is a waste of both the phase grating and the absorption, as our goal is to use the phase grating to augment the scattering surface and to further diffuse and delay the retransmission of the signal into the main room space - And our purpose here is certainly not to absorb the energy. To absorb the signal above the phase grating does NOT augment the diffusion and later 'retransmission' of the acoustic energy back into the space. Flutter echo is completely avoided as the energy retransmitted is much lower in energy content/gain then that of the original entering sparse specular reflection. A collimating phase grating has been used for several hundred years in the optics realm for a great many purposes, and it can be used for a variety of applications. It is not limited in itself, but is a tool that can be used either alone or in conjunction with many configurations for quite a variety of tasks. We risk error if we try to state its 'use', as it can be used in a myriad configurations, either alone or in conjunction with other 'tools' for a myriad of uses. And as far as being cost effective, phase gratings can be made very easily with a table saw and 3/16" 4x8foot sheets of luaun plywood used to cover interior doors that is available for less than $10 a sheet at any Home Depot or Lowes or foamcore material. And this would be cheaper and more easily accomplished for a given area than than applying absorptive clouds (which would simply deaden the space) or using more complex truly diffusive designs. And our concern was NOT simply the existence of flutter echo, but of augmenting a more live than dead acoustical space while avoiding the problems of sparse specular reflections - as was stated in the original premise.