Threshold Sound Pressure Research Articles

Comparative study of the effects of infrasound and low-frequency sound with those of audible sound on sleep

In order to compare the effects of infrasound and low-frequency sound on sleep with those of audible sound, healthy students were exposed to two kinds of sound, (a) infrasound and low-frequency sound (10, 20, 40, and 60 Hz), and (b) synthesized traffic noise with peak sound pressure level in low-frequency range (sound composed of low and audible frequency), throughout their sleep with the recording of the students' EEG. The effects were evaluated by the “reaction rate”. Concerning sound (a), the sound pressure level which causes the reactions of over 50% for the first time was used as the threshold sound pressure level signifying the occurrence of sleep disturbance. The threshold sound pressure levels of 10 and 20 Hz could not be evaluated. The threshold sound pressure levels of 40 and 63 Hz were 95 and 90 dB, respectively. With both sounds, the reaction rate was the highest in sleep stage 1 and the lowest in sleep stage 3+4. The pattern of sleep was little affected by sound (a). On the other hand, it was considerably affected by sound (b). These results suggest that audible sound has more harmful effects on sleep, compared with infrasound and low-frequency sound.

Electroacoustic calibration for sound field warble tone thresholds.

Walker, Dillon, and Byrne (1984) suggested reference equivalent threshold sound pressure levels (RETSPLs) for warble tones with specific modulation parameter values audited from a test position at the critical distance in a semireverberant sound field. This study evaluated these RETSPLs in two typical audiometric rooms and with typically encountered FM tones. Thresholds were measured under earphones and in two sound fields for 6-11 normal hearers at six test frequencies. Results indicated that there was a small but statistically significant difference between earphone and sound field thresholds in 4 of 24 comparisons. However, in both sound fields, 99% of the sound field thresholds were within 10 dB of the earphone thresholds. It is concluded that these RETSPLs are appropriate for electroacoustic calibration of sound field warble tones similar to those used in this study.

Reference threshold levels for the ER‐3A insert earphone

Two sets of provisional reference threshold sound pressure levels have been provided by the manufacturer for the calibration of the ER‐3A insert earphone. One set is for use with the B&K DB‐0138 coupler (an HA‐2 2‐cc coupler that comes with a 5‐mm‐diam by 2‐mm‐long stainless steel coupling nipple preceding the 18 mm of 3‐mm‐diam earmold‐simulation portion specified in S3.7‐1973), and the other set is for use with the HA‐1 coupler (the standard “In The Ear hearing aid” 2‐cc coupler) with a foam eartip sealed directly to the top surface of the coupler. Several recent studies have demonstrated that the ER‐3A may be directly substituted, without recalibrating, for a TDH‐39/MX‐41AR earphone in some cases, but most available data have not been reduced to a form suitable for establishing a revised estimate of the reference threshold levels. This paper reports the results of such a data analysis.

Reference equivalent threshold levels for pure tones and 1/3-oct noise bands: insert earphone and TDH-49 earphone.

Reference equivalent threshold sound pressure levels (RETSPLs) were determined for 20 subjects for pure tones and 1/3-oct noise bands. Two transducers were used: a Telephonics TDH-49 earphone mounted in an MX-41/AR cushion, and a Danavox SMW insert earphone coupled to an "HA-2" earmold. RETSPLs for pure tones transduced by the TDH-49 earphone were very similar to those published previously. For each transducer, RETSPLs for 1/3-oct noise bands were essentially identical to the RETSPLs for pure tones near the center of each band. Applications for threshold testing using the insert earphone and/or 1/3-oct noise bands are discussed.

Reference threshold sound pressure levels for the Welch Allyn AudioScopeTM

The Welch Allyn AudioScope has been evaluated as an audiometer screening instrument using a threshold, loudness balancing technique. Two sets of eartips have been compared to determine which eartip configuration would yield the most reliable audiometric data. The AudioScope has also been evaluated by the American National Standard Method for Coupler Calibration of Earphones using both sets of eartips, and reference threshold sound pressure levels for the AudioScope were developed by combining the coupler and loudness balance data. The most reliable eartip configuration for audiometric purposes is identified and guidelines for use of the audiometric screening instrument are proposed.

Reference equivalent threshold sound pressure levels at 5 and 6.3 kHz using telephonics TDH 39 earphones with MX‐41/AR cushions

Reference equivalent threshold sound pressure levels (RETSPLs), were measured at 5 and 6.3 kHz using Telephonics TDH 39 earphones with MX‐41/AR cushions. The purpose of the test was to verify RETSPL values calculated by interpolation from those specified in present International Standards Organization acoustics standards, ISO 389 “Standard reference zero for the calibration of pure‐tone audiometers,” and its amendments. The RETSPL values are intended for the calibration of audiometers using pure tones of fixed frequencies at the preferred frequencies in one‐third octave steps or pure‐tone audiometers having a continuously variable frequency. Mean measured values of RETSPL's at 5 and 6.3 kHz were 10.9 ± 2.6 and 15.1 ± 2.4 dB, in comparison to predicted values which were 13 and 15 dB, respectively.

Normal threshold of hearing at preferred frequencies.

Hearing thresholds have been determined on 10 young normal-hearing subjects at the preferred frequencies for acoustical measurements in steps of 1/3 octave from 500 to 8000 Hz. The study has been done in conjunction with the task given to ISO/TC43/WG1 to produce an international standard on normal thresholds of hearing at these frequencies. The results are given as equivalent threshold sound pressure levels measured on acoustic coupler according to IEC 303 and on artificial ear according to IEC 318.

Calibration data for the Telex 1470-A audiometric earphones

Standard reference threshold levels for the Telex 1470-A audiometric earphones have been determined. The psychoacoustic evaluation of these earphones was completed by loudness balancing at threshold. The earphones were balanced to comparison standard earphones calibrated at the National Bureau of Standards. Coupler calibration was accomplished using the American National Standard Method. Objective (coupler) and subjective (psychoacoustic) data were combined and the resulting reference threshold sound pressure level data are reported herein. These data were compared to previous data for the 1470-type earphone. While good agreement with previous data was noted for low and mid frequencies, sizeable differences did occur at high frequencies. Possible sources of these discrepancies are discussed.

Real-ear calibration of ipsilateral acoustic reflex stimuli from five types of impedance meter.

The Hearing Level scale has been established in national and international standards for tones presented via supra-aural earphones. However, the standards do not encompass stimuli from the probes of ipsilateral impedance meters. This study transfers the calibration of standardised earphones to the probes of five types of impedance meter and therefore enables the intensities of their ipsilateral stimuli to be defined in terms of Hearing Levels. The method used for transfer of calibration is based on equality of acoustic reflex responses elicitied by the impedance meter probe and by a standardised earphone. Ten subjects were tested with all five instruments to ensure comparability between instruments. The resultant calibration data are expressed in terms of Reference Equivalent Threshold Sound Pressure Levels measured in both 2 cc and Zwislocki couplers. The results indicate a considerable variation amongst instruments emphasising the need for a set of calibration data for each design of probe. This variation is less marked for the Zwislock coupler than for the 2 cc coupler.

Suggested Threshold Sound Pressure Levels For Frequency Modulated (Warble) Tones in the Sound Field

The problems inherent in using frequency-specific stimuli in the sound field to determine threshold sensitivity are reviewed, including a discussion of some of the specific problems encountered when introducing pure tones, narrow bands of noise, and frequency-modulated (FM) tones. The results of two experiments are reported. In Experiment I, the relationship between pure tones and frequency-modulated tones is developed under earphones in an anechoic chamber, and in two sound-isolated auditory test rooms (not anechoic). Experiment I resulted in the development of a reference threshold sound pressure level for frequency-modulated signals in the sound field. In Experiment II the reference level was applied to a clinical test facility and evaluated with a group of hearing-impaired individuals. The results suggest that the sound-field reference levels accurately reflect monaural threshold under earphones, when the earphone is calibrated to the ANSI, 1969 standard, and the sound field is calibrated to the suggested standard.

Calibration Force Levels for Bone Conduction Vibrators

Two bone conduction vibrators (Radioear B71 and B72) and a headband (Radioear P-3333) have been developed to meet specifications of both the International Electrotechnical Commission and the American National Standard Institute. Pure-tone thresholds for air conduction and bone conduction were obtained from 24 normal-hearing young adults at audiometric frequencies between 250 and 4000 Hz. Results of this study are in good agreement with the standard air conduction threshold sound pressure levels (ANSI) and with bone conduction threshold force levels reported in the literature.

Reference Equivalent Sound Pressure Levels for Japanese Audiometric Earphones

Reference Equivalent Threshold Sound Pressure Levels (RETSPL) for 3 different types of Japanese earphone and TDH-39 earphone were determined at 8 audiometric frequencies.Alternative binaural loudness balancing was accomplished by the subject who matched the variable tone presented through the experimental earphone to one ear to the standard tone presented to the other ear three times at 30dB hearing level re ISO 389 in the WE-705A standard earphone, then the standard experimental earphones were reversed and the variable tone was matched to the standard tone.Based on mean attenuator setting of 8 subjects, RETSPLs in the NBS-9A coupler for experimental earphones were derived using B&K sound measuring system. There were found great differences in RETSPLs between earphones made in Japan and in the United States while small among the Japanese.

Acousto-optical and acousto-dielectric effects in a nematic liquid crystal

This paper deals with the optical transmission and the dielectric effects in a nematic liquid crystal film (MBBA) of homeotropic state subjected to ultrasound. As in the case of the application of shear vibration, it is found that not only the transmitted light intensity through the film but also the dielectric constant and the tanδ of the film change with ultrasound intensity. There exists a threshold sound pressure above which the effects are appreciable. The threshold sound pressure is almost inversely proportional to the film thickness and the ultrasound frequency.

Subharmonic Signals during Acoustic Cavitation

Past experiments have indicated that underwater bubbles in a sound field can help to generate acoustic signals at subharmonics of the driving frequency. Furthermore, theoretical evidence indicates that a likely mechanism for subharmonic generation is the nonlinear pulsation of the driven bubbles. This paper describes a computer study of subharmonics that occur in nonlinear bubble pulsations. The threshold sound pressure for exciting the subharmonic of order 12 was calculated as a function of driving frequency for various chosen conditions. The results show that the subharmonic of order 12 can be excited over a broad frequency range, and not just for a driving frequency of twice the bubble resonance frequency. In addition, the amplitudes of the fundamental and subharmonic components in the bubble motion were calculated for pressures above threshold. The computed results are compared to available experimental results.

The sonically induced cavitation of liquid helium

The onset of sonically induced cavitation in liquid helium at frequencies between 30 and 40 kHz has been studied. In helium II, two types of cavitation activity were identified: acoustic cavitation whose characteristic noise can be detected, and visible cavitation in which vaporous cavities grow to visible size. The onset of acoustic cavitation is statistical in nature with increasing event rates as the sound pressure amplitude is increased and whose threshold depends on the waiting time at that particular amplitude. The acoustic threshold sound pressure amplitude in helium II between 1.8° K andTλ was found to lie within 0.15 mb of 0.3 mb, the variation of ±0.15 mb occurring from one determination to another, whereas the sound pressure amplitude corresponding to the visible threshold was about a hundred times larger. These two distinct types of sonically induced cavitation appear to be unique to liquid helium. However, aboveTλ the two thresholds were found to coincide at a sound pressure amplitude within 0.4 mb of 0.8 mb. The characteristics of the onset of acoustic cavitation were found to be independent of applied static pressure of up to 1.5 atm above and belowTλ and in helium II they were unaffected by filtering, heat flushing, or rotating the liquid. The results suggest that liquid helium is nucleated by random events initiated by the ambient cosmic radiation or by vortices generated in the liquid, and they imply that at ultrasonic frequencies this liquid cannot withstand a tensile stress and behaves in this respect like water saturated with gas and containing dust motes. Attempts to determine the onset of acoustic cavitation by scattering light off the bubbles or by detecting sonoluminescence were not successful: The upper limit to the size of these bubbles was shown to be about 30 µm and the intensity of any sonoluminescence must have been less than 10−4 of that from cavitating water. The possibilities of exploiting the two types of cavitation activity in liquid helium in the construction of a posttriggerable ultrasonic bubble chamber for visualizing the tracks of ionizing particles are discussed, as are the theoretical background and future development of the work presented in this paper.

Pressure Threshold for Acoustic Cavitation

The threshold sound pressure for gaseous acoustic cavitation follows from analysis of the equilibrium state, bypassing the initial-value problem and complicating transient effects. Resonance is considered in detail. A simple approximate threshold formula is established.

Improved Method for Studying Tympanic Reflexes in Man

This report describes manometric apparatus developed for registering the involuntary displacements of the human tympanic membrane during the reflex contraction of the middle-ear muscles. Recent tests with the new method have been uniformly successful in 14 inexperienced subjects, as contrasted with only 20 out of 57 previously. The reflex reactions have also been recorded from subjects who had been judged nonreactors in previous tests. Extensive repetitions of tests on one subject have yielded a close quantitative relation between stimulus and response-index magnitudes. In this set of experiments the stimulus was a click-free tone of 500 cps, graded in steps of 1 db. The threshold sound pressure level was about 111 db, and response magnitude rose in sigmoid fashion with progressively stronger stimuli.

Some relations between normal hearing for pure tones and for speech.

Abstract : The experiment was designed to determine the intensity difference between normal hearing for spondee words and normal hearing for a 1000 cps pure tone. A preliminary investigation indicated that sophisticated listeners achieved considerably lower spondee threshold sound pressure levels than unsophisticated listeners, in spite of essentially equivalent pure-tone threshold sound pressure levels. The main experiment, employing 96 young adults with normal hearing, investigated the five factors of threshold determination, order of test administration, sex, ear, and familiarity with test vocabulary. Only familiarity with test vocabulary exerted a major influence on threshold response, yielding sound pressure levels about 3 db lower for those subjects given prior knowledge of spondee vocabulary. The results indicate that an intensity difference of 12-13 db between thresholds for a 1000 cps pure tone and for speech is approximately medial for normal-hearing subjects. It represents a value which might properly be selected as the relationship to be specified for audiometric standards.

Some Measurements of the Threshold for Growth of Air Bubbles by Rectified Diffusion

It is known that a gas bubble pulsating in a sound field in a liquid containing dissolved gas can grow by a process called “rectified diffusion.” If the liquid is undersaturated with the gas at the existing static pressure, growth of the bubble will occur only if the sound pressure exceeds a threshold value. The threshold sound pressure for growth by rectified diffusion has been measured for individual air bubbles trapped at the center of a water-filled sphere resonating at a sound frequency of about 25 kc/sec. The data cover a range of bubble sizes, static pressures, and air contents of the water. The measured thresholds are several times larger than Blake's theoretical values (Acoust. Research Lab. Harvard Univ. Tech. Memo. 12, September, 1949) or values calculated from several refinements of the theory.

Onset of Ultrasonic Cavitation in Tap Water

The conditions influencing the onset of acoustically-induced cavitation in tap water have been investigated, with special attention to the role of air-filled nuclei. Cavitation was induced by exciting the water, contained in a spherical flask, at the resonant frequency of a radial mode near 25 kc/sec. Air-filled nuclei were detected by observing the reverberation decay of sound in the sphere at frequencies from 150 to 700 kc/sec, the presence of undissolved air cavities causing an increase in the decay rate. The results indicate that tap water standing undisturbed for several hours contains no air nuclei with radii larger than 5 × 10−4 cm, even when the water is supersaturated with dissolved air. The smaller nuclei (not detectable by reverberation decay) seem to become progressively smaller, for the measured threshold sound pressure at the onset of cavitation increases several-fold as the water stands undisturbed for several days. The observed influence of the air content on the threshold peak sound pressure Pt is given by Pt≃A1 − A2Pe where Ps, is the equilibrium pressure of the dissolved air, and the constants have the values A1=612 atmos, A2=4, at 22°C and one atmosphere static pressure. The variation of the threshold pressure with varying static pressure P0 depends on the direction of the pressure change; in the increasing direction, dPt/dP0 is larger than it is in the decreasing direction.