RPG Room Sizer

The First Automatic Room Dimensioning Software
From The Acoustical Products Leading Innovator

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.

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.

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RPG Room Sizer Highlights

  • Simple and Easy to Use
  • Allows anyone to figure out appropriate dimensions for new construction listening rooms or home theaters
  • When used with the RPG optimizer can create an extraordinary basis for a great room
  • Only $100

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Featurs and Benefits
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 modeling of the modal response allows more accurate evaluation of room dimensions than the current eigenfrequency 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 eigenfrequency 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.

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