Gearslutz.com - View Single Post - Above the Schroeder Frequency. Diffraction.

SAC · 31st January 2010

The two categories of measurements (frequency response/CSD/waterfall and ETC) address two regions with differing models of behavior.

And the nature of how the LF treatment is applied has a great potential to adversely effect the region beyond the modal region.

The frequency response and cumulative spectral decay/waterfalls (they are not the same) are appropriate for the modal region. The ETC is appropriate for the region dominated by spectral reflections - and has uses such as signal alignment that go far beyond.

Earlier in the thread we again explained a simple way how anyone here can identify the reflections and how to identify the focused reflection incidence points - allowing one to treat specific points and to subsequently verify the effectiveness of such treatment without removing more energy than is absolutely necessary.

Typically (but not necessarily), absorption is used to treat the early arriving first order reflections. But only enough to remove and define a particular response, a we want to retain and 'reshape' the remaining energy in more productive ways.

We also must address the perception by many that reflections are to be eliminated with absorption or diffused, with little understanding of where, when or why. And the answer to this is dependent upon a number of things. It is not a simple cook book answer. It is a process dependent upon a number of factors. First of which is a determination of the room's use and the desired response.

In a primary acoustical response model, we also want to establish a method by which we create an essentially anechoic short duration response followed by a stimulus to trigger the Haas effect - a psycho-acoustic response affecting how we perceive the signal. To do this in a small room, this may involve the use of a reflecting source - often a LF QRD that acts as a reflector to the mid-HF energy that is reflected back in a controlled manner of sufficient intensity and optimal orientation sufficient to trigger the Haas effect.

To cite a few points from several definitive sources; several factors, each requiring further analysis, are:

1. The direct path between source and listener must be effectively anechoic.
2. This anechoic Initial Signal Delay Gap should be sufficiently long (the longer this ISD, the larger the perceived space will be) and
3. The initial energy return from the reflected sound field to the listening position must be of sufficient level to ensure an effective Haas effect, and that this stimulus be followed by a high density exponentially decaying sound field. The greater the level of this return energy, the livelier the room will be perceived to be. This stimulus effective removes the directional information from the remainder of the later arriving sound field while allowing us to hear their level and tonal contribution.(The nature and design of this stimulus can be explored later.) Similarly, the more diffuse the exponentially decaying sound field is determines the tonality of the sounds heard.

31st January 2010	#59
SAC Registered User Joined: Dec 2009 Posts: 2,622	The two categories of measurements (frequency response/CSD/waterfall and ETC) address two regions with differing models of behavior. And the nature of how the LF treatment is applied has a great potential to adversely effect the region beyond the modal region. The frequency response and cumulative spectral decay/waterfalls (they are not the same) are appropriate for the modal region. The ETC is appropriate for the region dominated by spectral reflections - and has uses such as signal alignment that go far beyond. Earlier in the thread we again explained a simple way how anyone here can identify the reflections and how to identify the focused reflection incidence points - allowing one to treat specific points and to subsequently verify the effectiveness of such treatment without removing more energy than is absolutely necessary. Typically (but not necessarily), absorption is used to treat the early arriving first order reflections. But only enough to remove and define a particular response, a we want to retain and 'reshape' the remaining energy in more productive ways. We also must address the perception by many that reflections are to be eliminated with absorption or diffused, with little understanding of where, when or why. And the answer to this is dependent upon a number of things. It is not a simple cook book answer. It is a process dependent upon a number of factors. First of which is a determination of the room's use and the desired response. In a primary acoustical response model, we also want to establish a method by which we create an essentially anechoic short duration response followed by a stimulus to trigger the Haas effect - a psycho-acoustic response affecting how we perceive the signal. To do this in a small room, this may involve the use of a reflecting source - often a LF QRD that acts as a reflector to the mid-HF energy that is reflected back in a controlled manner of sufficient intensity and optimal orientation sufficient to trigger the Haas effect. To cite a few points from several definitive sources; several factors, each requiring further analysis, are: 1. The direct path between source and listener must be effectively anechoic. 2. This anechoic Initial Signal Delay Gap should be sufficiently long (the longer this ISD, the larger the perceived space will be) and 3. The initial energy return from the reflected sound field to the listening position must be of sufficient level to ensure an effective Haas effect, and that this stimulus be followed by a high density exponentially decaying sound field. The greater the level of this return energy, the livelier the room will be perceived to be. This stimulus effective removes the directional information from the remainder of the later arriving sound field while allowing us to hear their level and tonal contribution.(The nature and design of this stimulus can be explored later.) Similarly, the more diffuse the exponentially decaying sound field is determines the tonality of the sounds heard.