Sound Field In Room Research Articles

Analysis of sound fields in rooms using Bergeron's method

AbstractAt the designing stage of an auditorium, e.g., a concert hall or theater, it is imporant to predict its acoustic field via a computer. A conventional prediction method based on geometrical acoustic theory gives only a macroview of the field, and an addirional scale model test is required for a further investigation. to overcome this problem, although a technology to treat the sound field in a room as a wave field has been considered, there have been few examples of hree‐dimensional time‐response solution of the sound field in a room because of the difficulty of handling a wide analytical region, ide frequency band, and complex boundary conditions. This paper examines the justification of application of Bergeron's method to three‐dimensional sound field in a room. This paper also analyzes the correspondence between a three‐dimensional equivalent‐ciruit representation and the sound field, and examines the fundamental nature of a free sound field. Based on the results, a model of a simple rectangular room was considered, and its steady‐state sound pressure distribution (which is a fundamental characteristic the field) and simulation of reverberation (transient phenomenon) were examined. All the successful results show the usefulness of the proposed method.

Transient analysis of three-dimensional sound fields in rooms by Bergeron's method

Transient analysis of three-dimensional sound fields in rooms by Bergeron's method

Analysis of sound fields in rooms by Bergeron's method

The behavior of sound wave motion in rooms is so complicated that it is not easy to treat it theoretically unless simple geometrical shapes or simple boundary conditions are assumed. This study presents a formulation applying Bergeron's method, developed for an electromagnetic field simulation by computer [N. Yoshida et al., Trans. IECE Japan, J62‐B, 6, 511–518 (1979)], to room acoustics. In this formulation, the sound field is represented by an electrical equivalent circuit composed of distributed lines corresponding to the acoustic equation, and nodal equations for each connection of the lines are derived. As an example, consider a cube‐shaped room with uniform absorption by each wall. The transient responses to the sinusoidal waves and the 1/3‐octave‐band tone burst are calculated, and the stationary sound‐pressure distribution and the reverberation time are obtained from these responses. The results show the validity of the formulation and prove the effectiveness of the application of this method to room acoustics.

Evaluation of room speech transmission index and modulation transfer function by the use of time delay spectrometry

The literature shows that the modulation transfer function (MTF) and speech transmission index (STI) can be computed from the squared impulse response of a linear passive system. This paper describes an extension of this method to measurements of systems using time delay spectrometry (TDS). The new method makes use of both the real and imaginary parts of the complex analytic impulse response of the system (the energy‐time response). This allows more accurate determinations of STI and MTF because the calculations are based on a measurement that more closely follows the true energy decay in the room. The method requires fewer samples of the room's sound field and less spatial averaging to yield a given accuracy.

Trumpet spectrum transformation systematics

The spectrum transformation function Tmr(f) converts the mouthpiece spectrum into the spectrum averaged over the room's sound field, Tmr is extremely irregular, and is best represented as the product of other functions. Tmc transforms from the mouthpiece to the standing wave amplitude in the cylindrical main bore. Tcb converts this to the on-axis spectrum just outside the bell. Tbr modifies the latter to give the room average spectrum. Tcr = Tcb ⋅Tbr = [1 + (1343/f)9.9]−0.25, and Tbr = [1 − (f/104)] for f ⩽ 4000 Hz. For a tonal component whose frequency coincides with an input impedance peak, Tmc ≃ 1 at low frequencies, ≃ 0.3 at 800 Hz (near the mouthpiece popping frequency Fp), and climbs past 1.0 at 2000 Hz. At high frequencies Tmc → (arim/acyl), the ratio of mouthpiece radius to that of the cylindrical bore. Harmonics of a played tone may not coincide with the input impedance peaks. If the harmonic moves above such a peak, Tmc rises overall and its dip smoothly changes into a peak. If the harmonic lies below an air column resonance, Tmc is below the resonance Tmc for f < fp increasing to very large values above fp. [Work supported by NSF.]

Prediction of sound fields in rooms of arbitrary shape: Validity of the image sources method

In order to find the sound pressure field in a rectangular room, the classical modal method may be applied. However, it does not apply to polyhedric rooms of any shape, to which, however, the image sources method may be applied. The two methods are compared for several geometric shapes: two parallel planes (a layer), a rectangular wave guide and a rectangular enclosure. It is shown under what conditions the image sources method can give accurate enough results. A comparison of theoretical and experimental results is presented.

Review of Subjective Effects of the Sound Fields and Acoustic Design in Rooms

Review of Subjective Effects of the Sound Fields and Acoustic Design in Rooms

Equivalence of eigenmode and free‐wave models of steady‐state reverberation in rectangular rooms

The eigenmode and free‐wave models of steady‐state reverberant sound field in rooms are sometimes mistakenly believed to be unrelated representations. These two models are shown to coincide for the case of rectangular rooms, for which the axial, tangential, and oblique modes can be decomposed into two, four and eight travelling plane waves, respectively. (This was pointed out by Morse and Bolt [Rev. Mod. Phys. 16 (2), 85 (1944)].) Above the frequency of modal overlap, therefore, the reverberant sound field in a rectangular room may be viewed as an ensemble of many plane waves arriving from many directions in space. This provides justification for use of the free‐wave model.

Field-type acoustic wattmeter

The field-type acoustic wattmeter [Olson, U.S. Patent 1,892,644 (1932)] consists of a velocity microphone responding to the particle velocity in a sound wave, a pressure microphone responding to the sound pressure in a sound wave, and an electronic means for combining the outputs of the microphones so the ultimate output of the system indicates the acoustic energy flow in a sound field. The electronic system is all solid state. The field-type acoustic wattmeter is a useful and powerful tool for measuring the sound power output of loudspeakers, the noise power output of machines in place under operating conditions, the sound absorption of walls, ceilings, and floors, the performance of sound-reproducing systems in rooms, the sound field in rooms, etc.

Diffusion of Decaying Sound Field in a Reverberation Room with a Highly Absorbing Sample

Experiments show that the sound field in a room with one wall partially covered with a highly absorbing material is diffuse during the initial portion of the decay. This behavior can be explained by considering the room as a duct with the absorbing material placed on one of its end walls. When a transverse mode is incident on this wall, the reflected wave contains in addition to the incident mode several other transverse modes also, thus contributing to the diffuse state. Maximum power is reflected into modes other than the incident mode if the area of the material is half the area of the wall on which it is placed. This coupling among the modes increases as the specific acoustic impedance of the material is decreased (i.e., as the material is made more absorptive) or as the angle of incidence is increased. An approximate expression for the initial decay rate of the sound is obtained assuming diffuse incidence. The effective absorption coefficient derived from this decay rate depends upon the ratio of the area of the material to the area of the wall. The effective absorption coefficient agrees with the statistical absorption coefficient only when the latter is small.

Statistical Study in Time Domain on Sound Field in Rooms

Statistical Study in Time Domain on Sound Field in Rooms

Some Observations on Sound Fields in Large Rooms

Acoustical observations and measurements have been made in a number of large rooms in Italy where the size, architectural detail, and decorations, especially the sculpture, produce several interesting acoustical phenomena. The wide range of air volume studied permitted special attention to be given to the facility with which sound fields can be established in them. Large variations of room shapes and extremes in the degree of acoustical coupling between airspaces also made interesting observations possible. The buildings studied afforded great variations in architecture and styles of decoration so that the scatterers for sound diffusion covered a considerable range, effecting the character of the reverberation and the effective sound absorption of complex surfaces. In the largest spaces, the effect of air absorption produced significant effects not only at the higher frequencies but also at intermediate frequencies. Measurements made with large variations in relative humidity permitted this effect to be isolated.

The Effect of the Room Shape on the Sound Field in Rooms (Studies on the Measurement of Absorption Coefficient by the Reverberation Chamber Method I)

In order to carry out accurate measurements of absorption coefficient by Sabine formula, the assumption of diffuse distribution of sound energy in the reverberation chamber must be fulfilled. Thus, this work was started from the basic researches of the sound field in the two and three dimensional model rooms. The standing wave pattern of each normal mode was investigated using the dust figures and other methods. At low frequencies, normal mode of vibration existed even when the room shape was made adequately irregular, and for each normal mode, spatial variation of sound pressure did not depend on room shape. However, as the room shape becomes irregular, the nodal lines of successive normal modes distribute at random in space. Also, in the properly irregular room, the variation of decay rate for each normal mode was much smaller than that of a rectangular room.

Spatial Fluctuations of Steady-State Sound Fields in Rooms

The methods used in solving the problems related to the interpretation of frequency response curves of large rooms [M. R. Schroeder, J. Acoust. Soc. Am. 29, 1258 (1957)] are employed for the computation of the principal parameters of spatial response curves in large rooms at fixed frequencies. The results for the rms response fluctuations and the mean level difference between maxima and minima are the same as for frequency response curves, namely 11 and 10 db, respectively. The mean spacing of adjacent maxima depends upon the dimensionality of the space, the wavelength, λ, and the isotropy of the sound field. The mean spacings are 0.50λ, 0.67λ, and 0.79λ for complete isotropy in one, two, and three dimensions, respectively.

The Effect of Room Shape on the Sound Field in Room

The Effect of Room Shape on the Sound Field in Room

USE OF PRESSURE GRADIENT MICROPHONES FOR ACOUSTICAL MEASUREMENTS

The operation of the pressure gradient microphone is compared with that of the pressure microphone It is shown that the pressure gradient microphone may be used to measure particle velocity in a sound wave. The advantages of the pressure gradient microphone in making loudspeaker measurements, particularly outdoors, are pointed out and experimental data are given for some arrangements which were tried out. The characteristics of the distribution of particle velocity in a complex sound field are studied theoretically and experimentally with a ribbon microphone. A method is described for measuring the energy density in a sound field and some measurements which were taken in complex sound fields in rooms are discussed. It is shown that a combination of three pressure gradient or velocity microphones with a pressure microphone, placed adjacent to each other, may be equivalent in eliminating interference patterns to four pressure microphones placed at distances large compared to the wavelength and with random distribution. A microphone for measuring energy flow in a sound field is described.