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SAC · 14th March 2010

So, you do indeed have a few choices.

The usage I proposed is NOT intended to make the space dead. If you want a dead space, then I would suggest you might have entitled the thread something other than "treating a LIVE room ceiling".

Also, flutter echo is a non-starter with such a configuration - a complete red herring as the surfaces above the grating would not be appreciably parallel. Rather, the goal was to enhance the qualitative aspect of the room while reducing the specular nature of the sound field and while also significantly reducing the gain of any focused reflected energy without deadening the space.

But using them in conjunction with absorption in this case, depending upon the spacing, may or may not increase their absorptive qualities, But duplicating the phase grating with absorption for the control of flutter echoes is an exercise in redundancy. And it will not augment your live room while controlling undesired focused specular reflections. It will simply render it more 'dead'.

And decay times? The purpose of the diffusion is not only to temporally diffuse the energy reflecting off the ceiling, but to significantly reduce the spatially distributed energy returned over a much larger area as well, as is a fundamental feature of diffusion.

In the situation expressed above, quality 2D diffusion on the ceiling would essentially accomplish the same goal that the use of phase gratings would. The difference is in the total cost and complexity of the build - if you buy or build them. Additionally, the phase grating an also be used to augment the aesthetics of the space by providing a porous ceiling allowing light to flow through unobstructed while still functioning to obscure an 'industrial' or otherwise unattractive ceiling space - if such be the case.

Phase gratings are very easily made if you have access to a saw. All that is necessary is to rip the panel into slats and to clamp and make spaced 90 degree slots of an appropriate depth and width at the proper spaced intervals in the clamped slats allowing for a snug compression fit. A frame is also easily fashioned of similar material or 1/4" ply - if desired.

Constant references to "tests" amuse me. I guess someone here who has lots of time and money is welcome to sponsor a myriad battery of tests after they define the myriad potential uses for such of a fundamental tool. But then they would have to define exactly what specific purpose they e are intended to prove and that presumes a knowledge of how collimating phase gratings have been used historically and in principle - which rather renders many such tests unnecessary.

Having dealt with collimating phase gratings in optics for far too many years, and by others for centuries, I have never seen a formal "test" that proves they work. But we employ them all the time in practical and theoretical applications. Instead those that employ them understand the physics involved and find myriad uses for them in all sorts of situations based upon their basic collimating behavior. This feature is then combined with other tools and materials in order to accomplish a desired goal. But I guess the difference is that some understand the basic behavior of the tools, and others demand that others prove their use as their basic behavior is not well understood by those who need the tests made by others. Thus, one should not expect to see many formal tests, as the potential uses are not standardized. And simply testing myriad combinations and permutations of possible uses is prohibitive at best. And CASI (scatterometer) tests, or ETCs, of simple fundamental collimating functions are, for all general purposes, a waste if one does not understand their applied uses! And if one already understands collimation, such are not necessary.

Thus a collimating phase grating can be used to enhance absorption or diffusion based upon their use within a complimentary system of components. And understanding the behavior of the other components, collimation simply is a behavior that serves to augment this.

And in the manner described, Russ Berger has actively employed them in conjunction with scattering surfaces for over 20 years to enhance the 'liveness' of small rooms. And that is simply one application of them. And all of his designs are verified with proof of performance metrics. The fact is, they can also be used for a variety of diffusive purposes, as well as to augment absorption. The simple understanding of the effectiveness of the collimation of incident signals is sufficient to allow one to think of MANY uses, in many situations.

They are a wonderful tool. One of many that a creative designer, cognizant of how the basic physics operate, can employ to create many tailored effects. And their effects can be varied by the spacing and orientation relative to reflective, diffusive or absorptive surfaces.

And anyone who understands the basic physics can easily configure many applications as well as measure the effectiveness of their application sufficient to provide adequate objective proof of performance without waiting for someone else to 'test' all of the myriad potential applications.

Thus, in this case it is one technique of several that can be employed. One would be wise to consider all of the possible alternatives in light of their overall goal, be it acoustics, aesthetics, cost, complexity, and any others that may bear on the situation and make a selection that best suites their criterion.

14th March 2010	#19
SAC Registered User Joined: Dec 2009 Posts: 2,622	So, you do indeed have a few choices. The usage I proposed is NOT intended to make the space dead. If you want a dead space, then I would suggest you might have entitled the thread something other than "treating a LIVE room ceiling". Also, flutter echo is a non-starter with such a configuration - a complete red herring as the surfaces above the grating would not be appreciably parallel. Rather, the goal was to enhance the qualitative aspect of the room while reducing the specular nature of the sound field and while also significantly reducing the gain of any focused reflected energy without deadening the space. But using them in conjunction with absorption in this case, depending upon the spacing, may or may not increase their absorptive qualities, But duplicating the phase grating with absorption for the control of flutter echoes is an exercise in redundancy. And it will not augment your live room while controlling undesired focused specular reflections. It will simply render it more 'dead'. And decay times? The purpose of the diffusion is not only to temporally diffuse the energy reflecting off the ceiling, but to significantly reduce the spatially distributed energy returned over a much larger area as well, as is a fundamental feature of diffusion. In the situation expressed above, quality 2D diffusion on the ceiling would essentially accomplish the same goal that the use of phase gratings would. The difference is in the total cost and complexity of the build - if you buy or build them. Additionally, the phase grating an also be used to augment the aesthetics of the space by providing a porous ceiling allowing light to flow through unobstructed while still functioning to obscure an 'industrial' or otherwise unattractive ceiling space - if such be the case. Phase gratings are very easily made if you have access to a saw. All that is necessary is to rip the panel into slats and to clamp and make spaced 90 degree slots of an appropriate depth and width at the proper spaced intervals in the clamped slats allowing for a snug compression fit. A frame is also easily fashioned of similar material or 1/4" ply - if desired. Constant references to "tests" amuse me. I guess someone here who has lots of time and money is welcome to sponsor a myriad battery of tests after they define the myriad potential uses for such of a fundamental tool. But then they would have to define exactly what specific purpose they e are intended to prove and that presumes a knowledge of how collimating phase gratings have been used historically and in principle - which rather renders many such tests unnecessary. Having dealt with collimating phase gratings in optics for far too many years, and by others for centuries, I have never seen a formal "test" that proves they work. But we employ them all the time in practical and theoretical applications. Instead those that employ them understand the physics involved and find myriad uses for them in all sorts of situations based upon their basic collimating behavior. This feature is then combined with other tools and materials in order to accomplish a desired goal. But I guess the difference is that some understand the basic behavior of the tools, and others demand that others prove their use as their basic behavior is not well understood by those who need the tests made by others. Thus, one should not expect to see many formal tests, as the potential uses are not standardized. And simply testing myriad combinations and permutations of possible uses is prohibitive at best. And CASI (scatterometer) tests, or ETCs, of simple fundamental collimating functions are, for all general purposes, a waste if one does not understand their applied uses! And if one already understands collimation, such are not necessary. Thus a collimating phase grating can be used to enhance absorption or diffusion based upon their use within a complimentary system of components. And understanding the behavior of the other components, collimation simply is a behavior that serves to augment this. And in the manner described, Russ Berger has actively employed them in conjunction with scattering surfaces for over 20 years to enhance the 'liveness' of small rooms. And that is simply one application of them. And all of his designs are verified with proof of performance metrics. The fact is, they can also be used for a variety of diffusive purposes, as well as to augment absorption. The simple understanding of the effectiveness of the collimation of incident signals is sufficient to allow one to think of MANY uses, in many situations. They are a wonderful tool. One of many that a creative designer, cognizant of how the basic physics operate, can employ to create many tailored effects. And their effects can be varied by the spacing and orientation relative to reflective, diffusive or absorptive surfaces. And anyone who understands the basic physics can easily configure many applications as well as measure the effectiveness of their application sufficient to provide adequate objective proof of performance without waiting for someone else to 'test' all of the myriad potential applications. Thus, in this case it is one technique of several that can be employed. One would be wise to consider all of the possible alternatives in light of their overall goal, be it acoustics, aesthetics, cost, complexity, and any others that may bear on the situation and make a selection that best suites their criterion.