Richard H. Bolt

Speaker identification by speech spectrograms: some further observations

This letter reviews recent research on speaker identification by means of comparisons of speech spectrograms by human observers. Various factors affecting the reliability of identification are discussed, particularly those that would be present in practical forensic situations. Our interpretations of the new data lead us to reiterate our previous conclusion: that the degree of reliability of identification under practical conditions has not been scientifically established.

The Aircraft Noise Problem

Aircraft noise presents a system problem which to date has been attacked mainly at the level of individual components. The system includes: (a) aircraft as noise sources; (b) atmosphere and terrain as influences on sound propagation; (c) people, under several classes and conditions, as responders to noise; (d) physical components for controlling noise; (e) operating procedures for reducing noise exposure in communities; (f) public relations; (g) aviation planning policies and economics; and (h) many organizations concerned with characteristics and consequences of aircraft noise. The nature of these components is reviewed in a general way, with emphasis on their inherent interrelations. This discussion provides a framework for unifying the several subjects included in the present Aircraft Noise Symposium.

Orchestra Enclosure and Canopy for the Tanglewood Music Shed

The Tanglewood Music Shed, a large fan‐shaped hall seating 6000 people indoors (approximately 6000 more can be accommodated outdoors on the lawn) was modified in 1959 to improve the acoustics. The acoustical qualities that were to be improved included sectional balance for large orchestra, balance between orchestra and soloist, clarity of music inside the hall, and loudness of music on the lawn. The architectural solution was the design of an orchestra enclosure and a canopy over the orchestra and the front part of the audience. Also, a 14‐ft high chamber music orchestra enclosure was installed in 1960. This paper discusses the details of the construction and presents comments by musicians and listeners following its completion.

The ASA*50 Papers. A record of the plenary sessions celebrating the fiftieth anniversary of the Acoustical Society of America

An introduction to the papers presented at the Plenary Sessions of the 50th anniversary meeting of the Acoustical Society of America, Cambridge, Massachusetts, 11–15 June 1979.

Orchestra Enclosure for the Tanglewood Music Shed

The 25‐year old “temporary” stage shell in the Tanglewood Music Shed at Lenox, Massachusetts, needed replacement for practical reasons. This opportunity was taken to re‐examine the acoustics of the shed in the light of acoustical advances during the intervening years. A new shell, designed to increase the definition and enhance the tonal balance, was completed in July, 1959 and is described in this papr. The shed seats about 6000 inside; more than 6000 on the lawn outside. The stage, which can hold a large orchestra and chorus, is enclosed at sides and rear by angled panels of the new shell. Serrated side walls are sloped inward at the top and fanned outward in plan to aid in directing sound to the audience seated in a pie‐shaped sector of 110°. Above the entire stage, and extending forward approximately 14 the length of the seating area, is a canopy suspended about half‐way between floor and ceiling. The canopy is made of faceted plywood triangles, in graded sizes and thicknesses, joined at corners to fo...

Sound Absorption by Free‐Hanging Resistive Sheets

Absorption, reflection, and transmission coefficients have been derived for a plane wave of sound at an arbitrary angle of incidence on a thin sheet of flow resistance r = R/ρc and specific mass m = M/ρc, freely suspended in anechoic space. At normal incidence, for large ωm, the absorption reaches a maximum of 0.50, which occurs at r = 2. The statistical coefficient (appropriately averaged over angle) exceeds 0.40 over a considerable range of r and ωm. In a room with fully diffused sound, a sheet of dimensions large compared with wavelength, suspended away from room boundaries, introduces a number of absorptive units (sabins) which approaches (at high frequencies) twice the absorption coefficient times the sheet area. Confirming measurements in a reverberation chamber suggest certain configurations of “space sheets” for sound absorption in rooms.

Neighborhood Reaction to Noise: A Survey and Correlation of Case Histories

More than fifteen case histories involving the reaction of people in residential areas to intruding noise have been examined and correlated. In each case, statistical data on the physical characteristics of the noise (such as the level, spectrum, and time character) are examined, and the nature of the neighborhood reaction or response is described. The case histories cover a wide range of neighborhood reactions, which are arranged on a rank order scale from negligible complaints to vigorous legal action. On the basis of this experience, a scheme is suggested for predicting the reaction of a community to an intruding noise from a knowledge of pertinent physical characteristics of the noise in question and of noise to which the community has been exposed in the past. The procedure is to combine the physical properties of the stimulus into an empirical formula, from which a so‐called composite noise rating is derived. The composite noise rating determines (within a range of statistical variability) the neighborhood response to the stimulus. The scheme breaks down in situations where public reaction is strongly influenced by emergencies or other stresses.

Tentative Criteria for Noise Control Design

Presented in this paper is a set of criteria that have been developed and applied on numerous noise control problems. A wide range of confirmatory evidence and experiences has led us to view these criteria with some confidence, although we recognize that they are subject to modification on the basis of additional data which are continuing to accumulate. An essential feature of the criteria is that they incorporate a specification of frequency dependence (usually expressed by octave bands) as well as over‐all sound pressure level. Tentative criterion curves are presented for: (a) risk of permanent damage to the hearing mechanism under habitual exposure to (i) continuous spectrum noises and (ii) single frequency components; (b) speech communication conditions in terms of percentage intelligibility, voice level, distance between talkers, and type of vocabulary; (c) risk of annoyance to residential areas as dependent on type and previous noise conditioning of the community, daytime vs nighttime exposure, and ...

Non‐Linear Effects in Acoustic Resonators and Orifices

Classical analyses of acoustic elements involve the assumption that the frictional force on a plug of air moving in a constriction is proportional to velocity. Similarly, the effective masses owing to the plug of air and its radiation impedance are assumed to be independent of velocity. We find cases in which these linearity assumptions are violated with sound pressure levels as low as 70 or 80 db. Acoustic impedance measurements on orifices show that their reactance decreases and resistance increases as the sound level is increased above some minimum value which depends on the orifice dimensions. Correspondingly, in a resonator the resonance frequency increases and the Q decreases. The absorption coefficient may either increase or decrease with increasing sound level, depending on whether the specific resistance ratio (R/ρc) is less than or greater than unity. This variation of absorption has been observed in reverberation measurements on two arrays of resonators tuned at 300 and 500 c.p.s., respectively. For these cases the decay curves are concave downwards and the “instantaneous absorption coefficient” increases more than twofold as the sound level drops 30 to 40 db below its initial value. We have analyzed these effects theoretically by inserting non‐linear terms into a differential equation and solving by a perturbation method. This analysis shows that a variation in resistance is always associated with a variation in reactance and vice versa. Simplified formulas deduced for special cases agree quantitatively with experimental results.