Room Optimizer, Room Sizer™ 

Software tools

 3 Software Solutions from RPG

Room sizer | Room Optimizer | CHAOS

CHAOS


The animation illustrates how the Shape Optimizer automatically evaluates various shape modifications, within the imposed constraints of surface depth, width and motif, from a specified number of sources (x) to a specified number of observers (square). The first three lines (with the changing numbers) indicate the standard deviation from the desired performance in dB, including spatial penalty constraints. The standard deviations with no penalty are shown to the right. The last line indicates the number of solutions found thus far, the number of iterations and the time in seconds for each interative calculation. The three curves shown are the current shape (teal), the best shape found thus far (black) and the worst shape found thus far (orange).
 
Problem
Architectural designs and acoustical requirements are often at odds which results in compromises between the two. Acoustical shape design software that simultaneously addresses both needs would be desirable.

Solution
RPG® developed the Shape Optimizer™ to acoustically optimize the desired shape while maintaining the desired motif. RPG® offers this as a design service to the specifying community. The program combines powerful Boundary Element Method algorithms with multi dimensional optimization techniques in an iterative approach that minimizes the standard deviation of the scattered sound pressure level at all receivers from all sources over a specified bandwidth. The program requires source and receiver coordinates, desired shape function, symmetry and other constraints, and allowable width and depth. The program exports a .dxf file for CAD/CAM manufacture. The shape can be fabricated in wood, fiber reinforced gypsum, or concrete.

Acoustics was an integral part of classical architecture. Columns, balustrades, balconies, statuary, and other forms of relief ornamentation satisfied both architectural and acoustical requirements. While these types of surfaces offered useful sound diffusion, by today’s standards they are far from ideal. With the advent of ever increasing computer processing power, we can now predict, measure, and optimize the scattering from potential diffusing surfaces. RPG® has taken this capability and developed a software tool to optimize the scattering from various surfaces to provide an expanded palette of complementary acoustical surfaces for contemporary architecture. This process is accomplished by combining multi dimensional optimization with accurate boundary element scattering prediction.

Shape Optimization

First, a desired surface shape is expressed mathematically.

Surface to be Optimized.

Next, the sound pressure scattered by this trial surface from any number of sources is calculated on a field mesh, which contains the locations of all of the receivers. The standard deviation of the scattered sound pressure is determined at one-third octaves over the desired bandwidth.

 
Calculated sound pressure on a field mesh of all receivers for one of the group of sources being modeled at 1KHz. A plot of this average standard deviation from all of the sources versus frequency is called the Diffusion Spectrum.

 
Diffusion Spectrum monitors scattering performance.
Finally, the program evaluates hundreds or thousands of potential surface shapes, while maintaining the original motif, until it finds the shape with the lowest mean and standard deviation diffusion response.

Features  
Choice of curves, amplitude frequency modulated curves, fractals, and amplitude modulated concave convex arcs
Program can accept any number of source and receiver positions depending on the complexity of the optimization
Program accepts symmetry constraints, fixed localized shape constraints (to allow a shape to avoid a structural obstacle for example), periodic constraints, etc.
 
Benefits
Minimize focusing from concave shapes using amplitude modulation
Design stage canopies specific for each project given source and receiver locations
Design optimum audience canopies for uniform coverage
Design optimum stage acoustical shells for uniform coverage
Design optimum rear and sidewall boundary shapes for uniform coverage to complement the architecture
 
Applications
Any architectural acoustic space including performance facilities, theatres, high school auditorium, rehearsal spaces, critical listening rooms, and home theatres 



Room Optimizer
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.
 
Screen Views 
Configuration View
This view lists the room dimensions, the listener and loudspeaker search limits, symmetry, and other constraints. 
Wizard View
This view lists the room dimensions, search limits, and symmetry and displacement constraints for pre configured room wizards. 










Spectra View
This view shows the SBIR and the Modal Response for the worst, best, and current positions. 
Data View
This screen lists the error parameters for the best, worst, and current locations as well as the optimum listener and loudspeaker locations. 












GRP View
This view lists the first order geometrical reflection positions where acoustical surface treatment may be located. 













Error View
This screen displays a plot of the combined standard deviation (error parameter) for all locations in each of the four solution cycles













Features 
Automatic determination of optimum listener and loudspeaker woofer positions
Simultaneous minimization of weighted SBIR and "modal" responses
Listener and Loudspeaker search ranges
Quick setup room configuration Wizards
Optimizes up to 20 independent and 20 dependent loudspeakers of all types with multiple woofer configurations and polarities
Supports symmetry and displacement relationships among loudspeakers
Provides listener/loudspeaker geometry constraints for all surround formats
7 Room Optimizer™ color or black and white screens
Adjustable frequency range
Optional stereo angular constraints
Room configurations and optimization results can be stored, retrieved, printed, and screen captured
Dynamically evaluate placement, spectra and standard deviation (error) graphically during the optimization process
 
Benefits
Automatic multi dimensional optimization replaces tedious physical repositioning of listener and loudspeakers and previous attempts to separately evaluate the SBIR and modal responses
Automatic determination of optimum speaker stand height, listener platforms, and seating
Automatic optimum placement within physically accessible and desirable listener and loudspeaker search limits
Automatic determination and illustration of optimum acoustical treatment locations
Any type, number and combination of monopole, dipole, bipole, multipole loudspeaker woofers can be optimized
Existing room conditions can be evaluated before optimization
 
 
Room Sizer®
Problem
Many methods and optimum room ratios have been suggested over the years to minimize coloration. Essentially these methods try to avoid degenerate modes, where multiple modal frequencies fall within a small bandwidth, and also bandwidths with absences of modes. The assumption being that as music is played in the rooms, the absence or boosting of certain tonal elements will detract from the audio quality. The starting point for these previous methods to determine room dimensions, is usually the equation defining the eigenfrequencies within a rigid rectangular enclosure. All the above methods have limitations. The eigenfrequency solution is only applicable for rigid surfaces. Absorption has a number of effects, for instance it shifts the eigenfrequencies. This is critical for evaluation criteria, as is the case of all the above methods, which examine the modal frequencies or spacing of modes.

Solution
RPG® is now offering a new approach that automatically determines optimal room dimensions in rectangular rooms given an absorption coefficient for each surface and a minimum and maximum dimensional range for the length, width and height. The new method (Read more) uses a theoretical model, which although not perfect, is a more accurate model of low frequency room behavior than the simple eigenfrequency solution. Another effect of absorption is that it acts differently on axial, tangential and oblique modes - for example, axial modes will have the greatest magnitude and least damping. None of the previous methods account for this fully. A further difficulty with previous methods is the choice of criterion used for evaluation. For example, Bonello's method makes several assumptions - such as the use of a one-third octave bandwidth, and that five modes in a bandwidth mask the effects of coincident modes - which are empirical rather than fundamental in nature. The new method acts directly on the modal response of the room, so a criterion based on mode spacing is no longer required. Although an evaluation criterion is still required, as this can be based on the modal response of the room, it is much easier to relate to human perception. This is because the mode spacing is one level more removed from the actual signals received by the listener than the modal response. The new method is based on producing the flattest possible modal frequency response for the room. It uses an optimizing computer algorithm to search for the best solutions.

Modes in small rooms often lead to extended sound decays and uneven frequency responses. In critical listening spaces, this causes unwanted coloration effects that can be detrimental to the sound quality. The problem arises at low frequencies because of the relatively low modal density. Many designers try to overcome the problems of modes by choosing an appropriately proportioned room and by the use of bass absorbers. This paper is interested in the former, the choice of room dimensions to minimise the coloration effects of modes. The paper starts by discussing previous studies by others, which have suggested optimum room ratios or design methodologies. Then a new method is outlined - this is based on numerical optimisation - and the old and new methods are compared philosophically. Results in the form of modal responses are given to demonstrate the power of the new method.

Screen Views:   
Full screen view showing Room view, Optimization data, Frequency responses and Error parameter progress graph.

 
Detailed view of Error parameter progress graph, showing bad guesses (peaks) and good guesses (valleys) during the automated intelligent search for optimal dimensions. Two solutions, with confirmations, are shown.

 
The Room Sizer allows for the use of electronic equalization. If electronic equalization is planned the user will instruct the program to minimize all valleys in the modal response at the expense of peaks, which can be electronically attenuated.



The worst, best and current modal responses are shown, along with predictions of the wall surfaces involved.


 
 Screen view illustrating minimum and maximum entry menu for length, width and height.


  
Features 
Accurate modal response modeling algorithm
Automatic intelligent search engine
Accounts for absorption
Eliminates sorting into 1/3-octave bins
Accurate weighting of axial, tangential and oblique modes
Accounts for electronic equalization
 
Benefits
A more accurate direct modelling of the modal response allows more accurate evaluation of room dimensions than the current eigen frequency equation and provides a modal prediction that is closer to what is actually perceived in the room.
The automatic downhill simplex intelligent search engine provides a fast determination of optimal room dimensions
A more accurate model also allows more accurate prediction of the affects caused by absorption, namely resonance shifting, breath or Q of the resonance, and overlapping of adjacent resonances.
One problem with existing eigen frequency predictions is that modes lying near 1/3-octave borders may in fact be shifted by absorption and hence applied to the wrong 1/3-octave band.
The Room Sizer calculates the modal response and sorting is eliminated.
The Room Sizer model provides inherent weighting of axial, tangential and oblique modes offering a more accurate representation of these modes.
If electronic equalization is to be used, one can instruct the optimization engine to minimize valleys at the expense of peaks, which can be attenuated with equalization.