Small Speaker Research Articles

Acoustic coupling system

First Page

The diffraction of dipole sound by the edge of a rigid baffle

The theory of the diffraction of dipole radiation by a half‐plane [M. Yildiz and O.K. Marwardi, J. Acoust. Soc. Am. 32, 1685 (1960)] has been much used in aeroacoustics work. There has been little experimental work done on the problem however. We place a small speaker near a half‐plane and find an angular distribution which confirms the theory. The half‐plane in effect splits the dipole so that the radiation in its direction is enhanced. [Partially supported by NASA‐Ames.]

Electronic probe for eustachian tube patency and objective tinnitus.

The electronic probe provides a simple means to detect eustachian tube patency, and can be used as a sensitive probe of objective tinnitus. The basic unit consists of a battery-operated, electronic amplifier connected by 18-in leads to a sensitive microphone and to a small speaker (Fig 1). These transducers are each connected to rubber nipples of the type used for impedance audiometry (Fig 2).

Strain dependence of dynamic Young's modulus for human single osteons

The strain dependence of Young's modulus for human single osteons was investigated at frequencies near 10 3 Hz by means of a small acoustic speaker. On average, deviations from linear dependence occurred at 2% strain and plasticity followed at 4% strain. The modulus itself averaged at 12–14 GN/m 2 and is comparable to values obtained both by Black (1972) and by Smith and Keiper (1965) for samples containing many osteons at frequencies of 350 and 500–3500 Hz respectively.

Size, Shape, and Orientation of Sonar Targets Measured Remotely

Interference principles permit remote measurement of size, shape, and orientation of sonar targets. Each pair of scatterers on the target creates a Fourier component in the intensity pattern in space. Fourier-type wave analyses of the pattern observed either (A) over about half a radian of aspect angles at two closely spaced frequencies, or (B) over about half an octave of frequencies at two closely spaced aspects yield amplitude and phase for each wave number. For pairs of scatterers, in method (A) transverse width between scatterers comes from wave numbers of amplitude peaks, radial depth from phase shift with frequency change. In method (B) depth comes from peaks, width from phase shift with change of aspect angle. Combining the n(n−1)/2 oriented separations from n scatterers, a unique outline drawing is obtained. Presumably dolphins use this process. Both methods have been demonstrated acoustically at about 14 kHz with an experimental setup costing $250. Five small speakers with maximum separation 90.3 cm act as scattering sources. Computer analysis yields all dimensions within a few centimeters or degrees for four- or five-source objects.

Effects of nicotine, nicotine monomethiodide, lobeline, chlordiazepoxide, meprobamate and caffeine on a discrimination task in laboratory rats.

Hungry rats were trained on a discrimination task in order to obtain food rewards. During each experimental session, discrete stimuli of 1 min duration were delivered through a small speaker in the experimental chamber at random intervals on the average of once every 2 min. Lever responses in the presence of a light and tone were correct and produced food rewards. Lever responses in the presence of the light stimulus were incorrect and were punished by total inactivation of the experimental chamber. Rats were selected for this experiment based on their inability to acquire the discrimination task even after six months of training. Administration of nicotine, lobeline, chlordiazepoxide and meprobamate produced an improvement in discrimination performance through a reduction of responses to incorrect stimuli. Caffeine and nicotine monomethiodide, the quaternary salt of nicotine, were without effect on the discrimination.

Auditory direction and head rotation.

The orientation of objects appears to remain constant when S changes the position of his head, yet visual judgments of the vertical and horizontal reveal small but consistent errors that vary with the direction and degree of head and body rilt. Aubert (1861) found that tilting the head to the side produced angular displacement of the apparent vertical in the same direction, if there was no visible background-the A-effect; while Mueller (1916) reported that with smaller angles of tilt the apparent vertical was displaced in the opposite direction-the E-effect. Werner and associates (Werner, Wapner, & Chandler, 195 1; Wapner & Werner, 1957; McFarland, Werner & Wapner, 1962) have repeatedly observed the E-effect with judgments of the apparent vertical, for tactilekinesthetic as well as visual observations. They explain their findings in terms of intermodal (sensori-tonic) determinants of perceived space. If there is a unified frame of reference for spatial judgments, the position of the head should influence the apparent direction of an auditory source much as it does visual judgments. Teuber and Liebert (1956) found that body-tilt displaced a stationary sound source in the direction opposite the tilt. In the~r study, as in previous studies employing another sense modality, it was assumed that the system of reference rotates on a fixed origin. If, however, the subjective origin is displaced during adaptation, either an Aor an E-effect might be identified, depending upon where the measurement of displacement is made. The present experiments, which determine the effects of head rotation upon judgments of straight-ahead, minimize the amount of ocular countertorsion and vestibular stimulation, peripheral factors which have been linked to the effects of tilt by previous Es. The auditory apparent median plane was defined by sounds at different distances that were judged to be straight-ahead. When the head was nuned, the body apparent median plane (BAMP) and head apparent median plane (HAMP) were determined in separate sets of trials. The intersection of the BAMP and HAMP provided a subjective origin or ego-center. In each of three experiments, with the same 18 college students as Ss, the blindfolded S stood with head in a headrest. A small speaker, emitting intermittent white noise, moved along a horizontal track, parallel to the aiual axis. S

Approach to Recreating a Sound Field

To re-create a “concert hall in a telephone booth,” a smaller volume is delineated within the original environment. The surfaces of this sound-transparent volume are covered with microphones, all having a directional pattern facing outwards from the volume. The sampled space is reproduced with an array of loudspeakers corresponding to the microphones, but with their directional pattern pointed inwards. Since the listeners can move freely within the re-created environment, some basic limitations associated with binaural listening are removed. Experiments were made with a 12-channel system. Studies included (a) effects of sampled-volume size, (b) microphone spacing and distribution, (c) space “magnification,” (d) use of small inexpensive speakers for the multiple channels with fewer large speakers for bass, (e) high-absorption listening environments, (f) effects of a finite number of channels.

"Apparent bass" and nonlinear distortion

A discrepancy between the "apparent bass" response heard by the average music listener and anechoic-chamber measurements has been noted for some small loudspeaker systems. This may be caused by the psychoacoustic response to the generation of harmonic distortion by the nonlinear suspension and the inhomogeneous flux gap density in a small speaker. An electrical analog, with controllable distortion, of such a speaker has been subjected to listener tests and evaluation to determine if this is the cause of the apparent bass effect. An analysis of the listener reactions to various music stimuli through the system indicates that this is the case.

A compact instrument for measuring the total salinity of water on pastoral properties.

The management of water supplies on pastoral properties in the marginal rainfall areas of Australia is often hampered by the lack of an inexpensive reliable device for measuring the total salinity of ground water. The instrument described has been developed with this specific function in view although with further elaboration it could fulfil the requirements of an accurate laboratory, instrument for measuring conductivity. Basically the electronic components consist of an oscillator, a bridge, a single stage of amplification and a small speaker. When in use the speaker emits a high-pitched whistle until the bridge is balanced at a null point. By using transistors the current drain is low, the weight and cost of the instrument is Low and the equipment is rugged enough to withstand rough treatment. The total salinity of water can be measured accurately in terms of conductivity over the limited range covering the requirements for sheep and cattle and other ranges could be accommodated by minor modifications.

Light-Coupled Multivibrator

First Page

Experiments and experiences in stereo

A considerable number of observations as well as formal experiments in High Fidelity Stereo sound are reported. Three-channel stereo with corner flanking speakers has been shown to achieve accuracy in both tonality and geometry. A large center speaker with small outriggers is observed to lack both tonality and geometry. A center speaker in the corner with wall outriggers is observed to produce a deeply curved stereo geometry. Limiting speakers to a bass range down to 300 cycles may preserve geometry, but not tonality. Overly large bass speakers lead to a spatial and delay separation of bass and treble events. There is an optimum bass speaker size. Wide spacing of speakers offers improved accuracy of stereo geometry. The array cannot normally exceed the speaker spacing, but because of the focusing effect of the center channel, it may be much narrower than the speaker spacing. Numerous minor observations of radiation angle and polar response point up the desirability of corner speaker placement. Large speakers may be placed at low or high level, but the dynamic range of small speakers is limited. Corner speaker placement affects apparent room size and may be advantageously employed to improve the reverberation effects. Wide Stage Stereo demonstrations using speaker spacing up to 50 feet or more are compared to home applications with 15-foot spacing. High Fidelity Stereo is both high fidelity and stereo, and entails meeting the requirements of both.

The Effect of Sounds of Varying Intensity on Hatchability of Chicken Egg

ABSTRACT THE expansion of civilian and military air bases throughout the world has caused some concern among poultrymen with respect to their location in close proximity to poultry production areas. Hatcherymen have frequently heard it stated that loud blasting would affect hatchability of eggs. Such noise levels are encountered in areas frequented by jet planes. The purpose of this study was to obtain information on the effects of sound on hatchability of chicken eggs. FACILITIES AND PROCEDURE A popular cabinet type of incubator was used. The incubators set in the sound field had the two top trays removed to accommodate a small speaker which was installed in the top of the machine and connected to sound reproduction equipment described by Stadelman and Kosin (1955). A sound level of about 96 decibels was reached inside the incubator when tape reproductions of plane flyovers were played. The location of the incubator with respect . . .

The Transmission of Sound through Thin Cylindrical Pipe Walls

Measurements have been made on the transmission of sound through the walls (1/16 in. thick) of cylindrical steel pipes (9- and 15-in. diameter). Two source arrangements were used: (a) an approximately uniform distribution of small speakers along the axis, and (b) a speaker in one end, radiating into the pipe, with a ρc termination at the opposite end. The results from the two methods are qualitatively similar but exhibit significant differences in magnitude. The transmission loss (TL) behavior of thin-walled cylinders can be related to two principal resonances at f1≃(5400/d) cps and f2≃1.65 × 103(t/d2) cps; d = diam, ft; t = wall thickness, in. At f1 the walls stretch in a radial, axially symmetric mode of vibration. At f2 the walls bend in a mode of vibration that is symmetrical about a diameter. Above f1 the TL approaches that predicted by a “mass law,” rising with increasing frequency at about 6 db/octave. Below f2 the TL approaches that predicted by a “stiffness law,” rising with decreasing frequency at about 6 db/octave. At f1 and f2 the TL reaches minimum values that are controlled by internal resistance. Between f1 and f2 the TL rises to a broad maximum. These properties are illustrated by approximate agreement between the experiment and a first-order theory. The results are also compared with field measurements on pipes up to 10-ft diameter carrying high level broad-band noise.

The Acoustical Impedance of Closed Rectangular Loudspeaker Housings

Direct-radiator loudspeakers are often mounted with the back of the diaphragm working into a completely enclosed space. Conventional theory states that when the maximum linear dimension of such an enclosure is small compared with the wave-length, the pressure is uniform throughout, and the acoustical impedance presented to the loudspeaker is -j/ω(V/ρc2), where V is the enclosed volume. Although it has not been clearly established how small an enclosure must be before it is “small compared with the wave-length,” the foregoing expression is generally used, at low audiofrequencies, to calculate the acoustical impedance of closed loudspeaker housings. It is shown here that while the acoustical impedance of a closed rectangular housing is capacitive at very low frequencies, it passes through zero as the frequency increases and becomes that of an inertance as the frequency of the first normal mode is approached. For a typical housing 11 in. × 22 in. × 22 in., the frequency at which the impedance presented to a very small speaker passes through zero is in the vicinity of 70 c.p.s.; at this frequency, the maximum linear dimension of the enclosure is less than one-seventh of the wave-length. These results are obtained by using the methods given by Morse for determining the pressure distribution in a room. A point-source loudspeaker is assumed and the pressure at the source is calculated as the summation of the pressures due to the normal modes of the enclosure, losses being neglected. Measurements of the pressure within the enclosure support this analysis. From measurements of the pressure distribution over the surface of the loudspeaker diaphragm, it may be deduced that the magnitude of the acoustical impedance which the enclosure presents to the loudspeaker diaphragm and the frequency at which the impedance becomes zero depend upon the dimensions of the loudspeaker diaphragm as well as the dimensions of the enclosure.

The Polyrhetor—A 150-Channel Film Reproducer*

At the New York World's Fair 150 versions of a fifteen-minute story are carefully sorted to bring each to only four persons seated in comfortable chairs on a moving conveyor. — A verbal description of a diorama along the edge of which the conveyor progresses, carefully synchronized with the motion of this conveyor, is given each group of persons and is repeated to each succeeding group with approximately a six-minute lag. In telling the fifteen-minute story, approximately 150 versions are being repeated simultaneously, each version differing only in its starting time. — In considering possible ways of meeting the elaborate requirements established for this sound system, various combinations of disk, film, and steel-tape reproducing apparatus were considered, a novel form of film reproducer being selected primarily on the basis of proved operating reliability over long periods of time. — The Polyrhetor consists essentially of a rotating steel drum eight feet in diameter capable of carrying 24 continuous film loops past 168 optical scanners and associate amplifiers mounted on seven posts equally spaced about the drum. A multiple system of sectionalized trolleys conveys the sound through sliding contactors to small speakers in the cars, around which sufficient acoustical partitioning is provided to avoid Program interference from car to car.