摘要:

Because of the large demands for space today, massive multipurpose buildings are being constructed. This presents a problem to architects, owners, and managers. Arenas that have temporary seating which may be changed for concerts, theatre‐in‐the‐round, church meetings, basketball, and wrestling may use a speaker system which can be raised or lowered according to event requirements—presenting tremendous problems for management. Fixed speakers can be more than adequate for a few setups, but when the setups are changed drastically the acoustics change also. Overhead speakers work well for very large banquets, but not over a bare concrete floor such as for auto shows. The artist seldom arrives before the actual performance, and this leaves little time for the stagehands to balance the complicated systems being used. Many promoters bring in their own amplification, which, when installed by the promoter ten minutes before the doors open, creates absolute catastrophe during the event. When everything from drums to tambourines is electrified, the load may far exceed the output of the building system. Promoters are normally the last to hear of bad acoustics or amplification; however, the manager of a facility is constantly taking the heat.

ISSN:0001-4966    

DOI:10.1121/1.1975764

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

With Vatican permission, we made acoustical measurements in St. Peter's Basilica in May 1970. The reverberation times for this largest church in the world (20 000 000 ft3) are much shorter than expected; those for the empty Basilica at midfrequencies being about 7.5 sec. This unexpectedly low value results because St. Peter's is a group of five large churches and a number of smaller spaces weakly coupled acoustically. Analysis by standard reverberation theory and simple considerations of acoustical coupling between the spaces agrees with the observations. Measurements made in 1966 with a large congregation gave reverberation times of about 5 sec. In 1964, when the Basilica was filled with highly absorbing seating for the Ecumenical Congress, the reverberation times were about312 sec. For the 200th anniversary Beethoven celebration on May 23, 1970, a complete concert‐hall stage was installed in the rotunda and the acoustics for Miss Solemnis were judged excellent by critical musicians. The exceptional acoustical properties are due to the multiple coupled air spaces into which the Basilica is divided, and to the diffusion produced by the wealth of architectural detail and sculptural ornament.

ISSN:0001-4966    

DOI:10.1121/1.1975776

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

Prior investigations by Plomp and Mimpen have concluded that the ear can hear and identify separately only the first five to seven particles of a tone, in agreement with limitations deduced from the critical band theory. With somewhat different equipment and procedure, a set of experiments was conducted for the purpose of discovering whether such variations of timbre as are typical of musical performance may affect a replication of the conclusions of Plomp and Mimpen. Oscillators were phase locked to a common fundamental frequency and adjusted to uniform sound levels, which were checked by a wave analyzer; the resultant complex tone could be deprived of any partial (except its fundamental partial) by means of interruption by an electronic switch; an observer was asked to duplicate the frequency of the interrupted partial, and the chosen frequency was checked with a frequency counter. Results indicate a less categorical limitation of the ear's capability, in which, at least in the middle frequencies, partials as high as the 11th and the 12th may be separately heard with some consistency. (Research sponsored by North Texas State University.)

ISSN:0001-4966    

DOI:10.1121/1.1975784

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

The radiation resistance of a panel, vibrating in a single mode, is theoretically determined from the acoustic power radiated. The panel is supported in an infinite baffle. The supports include hinges on all four sides and either hinged or clamped supports on two opposite sides with the other sides unsupported. Asymptotic solutions are found and curves covering the entire frequency range are obtained through numerical integration. Well below the critical frequency, the radiation resistance of a panel hinged on all four sides is a minimum for square intranodal areas. By considering a panel or beam either hinged or clamped at each end and vibrating at a given frequency well below the critical frequency, it is found that the ratio of the radiation resistance of the clamped beam to that of the hinged beam is 0.851 for the first mode and 0.711 for the second mode, and approaches 2 as the mode number tends to infinity. For both hinged and clamped supports, the radiation resistance of all modes increases with the beam width‐to‐length ratio. [Supported by the National Research Council and the NASA Langley Research Center.]

ISSN:0001-4966    

DOI:10.1121/1.1975798

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

A critical step in mechanism noise reduction for data‐processing equipment is identification of sources. Techniques such as disabling mechanisms, microphone probing, and frequency analysis are useful here. We have discussed procedures based on noise‐time analysis within machine cycles at past Acoustical Society of America meetings as being particularly useful for this work. For high‐speed impacting machinery, normally used analog acoustical instruments are inadequate for noise‐time analysis. Procedures have been devised using a high‐speed electronic switch attenuator in a “stroboscopic” mode to overcome these limitations. This technique has been useful for source identification and examples are presented. Digital procedures have considerable potential for these applications. Fast Fourier transform digital filtering, and related techniques are useful and we have used these procedures where applicable in noise‐time analysis using an IBM 1130 computer system. The practical limit here is in processing time and/or computer size (and cost). Our present direction is combining the best of both digital and analog techniques in a hybrid system. The resulting approaches will be discussed as more nearly optimum than other approaches and most usable for mechanism noise identification.

ISSN:0001-4966    

DOI:10.1121/1.1975806

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

Normal‐hearing listeners were adapted for from 1–30 sec with pure tones of 0.25, 1, or 4 kHz presented at 30, 50, 80, or 100 dB SPL. Adaptation was measured with delayed or simultaneous single loudness balances using a method of constant stimuli for comparison‐tone presentations. Delayed balances yielded essentially no adaptation. When simultaneous binaural stimulation occurred, a modest amount of adaptation was recorded. No apparent frequency or duration effects were present with either delayed or simultaneous balances. Intensity had a noticeable effect with the simultaneous‐balance method only. Differences among subjects were great. The apparent absence of adaptation with the delayed‐balance method and the lack of a duration effect with the simultaneous‐balance method both suggest that the loudness of a steady tone does not change significantly over time. The “adaptation” measured by the simultaneous‐balance method does not appear to fit the commonly accepted pattern of perstimulatory adaptation.

ISSN:0001-4966    

DOI:10.1121/1.1975812

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

Threshold for periodic tone pulses as a function of duration and repetition rate in the normal auditory system is controlled by a time constant of the order of 200–300 msec. Thresholds measured in the neurally impaired ear are greatly influenced by the fact that neural adaptation increases as (1) the time interval between pulses decreases (below 200 msec), and (2) the duration of the signal is prolonged. Threshold measures further reflect variations in response behaviors such as reaction time. For any one individual, the time constant of the ear is related to a critical “decay” time that depends on both signal duration and interstimulus interval. In standard audiometric practice, lengthened signal durations combined with short off‐intervals strain already altered time constants in neurally impaired ears, leading subjects to trade intensity for the critical times necessary to perceive the signal. An adaptive method in which signal duration, off‐interval, repetition rate, and time for subject response are controlled and defined will avoid the adverse intensity‐for‐time trade that can occur during conventional psychoacoustic measures of threshold in auditory pathology. [Research supported in part by grants from the NINDS of the U. S. Public Health Service.]

ISSN:0001-4966    

DOI:10.1121/1.1975826

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

The presence of glottal closure during phonation was determined by transmitting continuous‐wave ultrasound through the larynx and detecting it on the opposite side. In a series of glottal stops, vocal‐fold vibration does not always completely cease during the glottal stop, although the pitch drops rapidly at that time, the vocal intensity is reduced, and the closed phase of the vocal‐fold vibratory cycle is proportionately long. Phonation of this sort may be similar to vocal fry. [Supported in part by a U. S. Public Health Service grant.]

ISSN:0001-4966    

DOI:10.1121/1.1975840

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

A preprocessing technique which enhances speech intelligibility in noise when the noise entersafterpreprocessing has been described recently [I. B. Thomas and R. J. Niederjohn, “The Intelligibility of Filtered‐Clipped Speech in Noise,” J. Audio Eng. Soc.18, 299–303, (1970)]. The preprocessing technique involves high‐pass filtering (cutoff 1100 Hz, slope 12 dB/oct) and infinite amplitude clipping. In the present experiments, we have determined the intelligibility of speech which has been passed through this same system but in which noise is addedpriorto filtering and clipping. Ten subjects took part; all signals were presented binaurally in phase through headphones. The noise signal was white noise, bandlimited from 250 to 6800 Hz. Intelligibility scores (percent) for Harvard PB words at signal‐to‐noise ratios of 0, 5, and 10 dB (measured at the microphone) were as follows: forunmodifiedspeech, 40, 65, and 80; forfiltered‐clippedspeech, 47, 82, and 96; forfiltered‐clipped‐differentiatedspeech, 47, 74, and 95. [Work supported by NIH.]

ISSN:0001-4966    

DOI:10.1121/1.1975846

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

A small inexpensive anechoic tank (2.5 ft high, 3 ft wide, and 4.5 ft long) was designed, built, and tested for use in ultrasonic research. The tank is shaped like a pair of “butterfly wings” in all three principal planes passing through its center. This reduces the effects of standing waves and provides for a trapped mode of operation that forces reflected energy into the corners of the tank. The walls are lined with flexible polyurethane sheets, specially designed for maximum absorptivity in the frequency range 0.5–2.0 MHz. A simple manually operated transducer‐positioning system allows for variable‐range separation along a track and enables rotation and tilting of the transducers through their acoustic centers. Data on the acoustic properties of the tank are presented to demonstrate such design parameters as pressure reflectivity and absorption of the liner, reverberation time, and critical angles for trapped‐mode operation. Some examples of its use as a research tool are given. [This work sponsored by the U. S. Navy Office of Naval Research.]

ISSN:0001-4966    

DOI:10.1121/1.1975866

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP