At low frequencies, the acoustical coupling of the listener and loudspeakers with reflections from the room’s boundary surfaces and its modal pressure distribution cause significant acoustical distortion. At the listening position, constructive and destructive interference between the loudspeaker’s direct sound and reflections from adjacent boundaries causes severe peaks and dips in the frequency response. In addition, acoustic resonances or room modes cause substantial acoustical gain at frequencies determined by the room’s dimensions. While it is important to provide uniform modal frequency distribution by optimizing the dimensional room ratios, the degree of acoustic gain at each frequency depends solely on the location of the listener and loudspeakers with respect to the room’s sound pressure distribution at that frequency.
Thus, even if the room dimensions are "ideal" according to some criteria, only proper positioning of the listener and loudspeakers can minimize low frequency acoustic distortion. Placement of the listener, multiple loudspeakers, and subwoofers becomes even more complex as we move from stereo to multi channel digital surround formats.
In conventional approaches it is impossible to arrive at an optimum solution by treating the speaker boundary interference response (SBIR) and the modal coupling independently because minimizing the speaker boundary interference may not optimize the modal coupling at all frequencies and vice versa. Thus, the need for an automated, computerized, multi dimensional optimization approach becomes necessary.
Room Optimizer™ is the industry's first Windows 95 / 98 program that automatically and simultaneously optimizes the SBIR and modal coupling. The program utilizes modern geometrical image model prediction techniques along with powerful multi dimensional optimization to achieve the smoothest and flattest bass response in a rectangular room. This result is accomplished quickly, effectively, and automatically by properly positioning the listener and loudspeakers.
In addition to optimizing the bass response, the program also calculates first order reflection positions for mid to high frequency acoustical surface treatment. Absorptive surfaces minimize comb filtering and improve imaging. Diffusive surfaces enhance envelopment and sound distribution throughout the room.
The Iterative Process
With the computational desktop power now available, sophisticated positioning and evaluation algorithms can be used to automatically search for the best listener and low frequency loudspeaker positions in a rectangular room.
First, a random set of listener and loudspeaker locations is evaluated by calculating the energy impulse response via an image model.
Then, two FFTs are performed on the impulse response to reflect the transient and long term aspect of the way we perceive music. A windowed 65 ms short term FFT of the low order reflections determines the speaker boundary interference response (SBIR). A long term FFT of the entire windowed impulse response extending to 15 or more reflection orders determines the "modal" response. A weighted sum of the standard deviation of each response over a definable low frequency range, typically between 20 to 300 Hz, is determined.
If the error is below the specified tolerance, the program ends. If the error is above this tolerance, the optimization enters a simplex search routine that suggests the next potentially best trial locations and the process is repeated.
This iterative process continues until the program finds the listener and loudspeaker locations with the smoothest and flattest combined spectra. The program also lists the optimum locations for acoustical surface treatment. Symmetry and displacement relationships between independent and dependent speakers are used to speed the automated search for the global minimum.
Problem
No existing software automatically determines the optimum listener and loudspeaker locations to minimize all forms of low frequency distortion caused by the acoustic coupling with the room.
Solution
Room Optimizer™ combines image model and multi dimensional optimization techniques to determine the best listener and loudspeaker locations that simultaneously optimize the SBIR and modal coupling to produce the flattest bass response.
|
RPG Optimizer Highlights
