Octave Frequency Bands Research Articles

Derived auditory brainstem response audiometry

This study was designed to establish an accurate and practical means for obtaining objective frequency-specific threshold of auditory brainstem response (ABR).The derived ABR presumably contributed from the cochlea tuned to octave frequency band was recorded in 16 young subjects with normal hearing and 23 patients with various types of cochlear hearing loss. A frequency-selective method was applied to yield the derived ABR, using high-pass filtered noises with five different cut-off frequencies of 0.5kHz, 1kHz, 2kHz, 4kHz and 8kHz, and with a definite cut-off slope 96dB/octave. Measurement of the derived ABR threshold could result in frequency-specific information initiated from the cochlea.The average threshold of the derived ABR for each of the octave-frequency bands was determined as representing a reference level for objective audiogram estimation with the derived ABR in the 16 young subjects with normal hearing. The derived ABR audiograms based on the reference level had good correlations to the pure-tone audiograms in cochlear hearing loss. This derived ABR technique was found promissing for the objective reconstruction of the audiogram with the derived ABR.

Analysis of variability in laboratory airborne sound insulation determinations

In an investigation of the overall precision of airborne sound insulation determinations in laboratory conditions 10 different samples were measured, according to the general procedure described in ISO 140/III, in an horizontal transmission chamber, with lateral flanking transmission. Measurements were carried out according to a prescribed programme to investigate the repeatability, r, and reproducibility, Re, in the results, within the same laboratory. Two different operators carried out 15 replicates, five per day during three consecutive days. Each operator performed the test under repeatability conditions: that is, using the same instrumentation, without removing the samples and with the environmental conditions kept constant. Between operators, certain parts of the experimental set-up were different: i.e., the measuring samples had been removed and reinstalled and the environmental conditions were slightly different. The statistical parameters, r and Re′, were first obtained for each sample level separately in order to investigate any dependence with level. Successively, in order to get an improvement in precision, an overall factorial variance analysis was carried out for all levels simultaneously. The whole treatment was performed for each third octave frequency band between 100 and 3150 Hz separately, as well as for the weighted apparent reduction index, R′ w .

Sources and mechanisms of wheel/rail noise: state-of-the-art and recent research

A review is presented of wheel/rail research studies, published since 1978. Additionally a study is presented which is focussed on the magnitudes and relative importance of vertical and horizontal forces in the wheel/rail contact zone. In the specific case and the frequency range 50–2000 Hz the vertical force appeared to be 3–10 times larger than the lateral (axial) force. Nevertheless radiation due to axial excitation of the wheel dominates the wayside sound pressure level in several one-third octave frequency bands. Another significant contribution to the wayside A-weighted sound pressure level is attributed to vertical excitation of the rail.

A simplified field method for measuring the aggregate adverse deviation of partitions

This paper describes the investigation of a simplified field method of measuring the aggregate adverse deviation of a partition. In this study, the source spectrum in the source room was assumed to be flat over the sixteen one-third octave frequency bands of 100 Hz to 3150 Hz. Measurement of the overall level difference in dB(A) is proposed. Using real transmission loss data, it was found that there was a linear relationship between the aggregate adverse deviation and the level difference in dB(A). The correlation is very good. The investigations show that a simplified method can be developed to rate partitions according to the criterion specified in the British building regulations. The simplified field method can also be applied to situations which use a different grading curve such as the grading curve for flats in Scotland.

Measurement of background noise in sound-insulated rooms

Problems concerning measurement of stationary background noise levels below the dynamic limits of normal transducers are studied. The use of very sensitive large transducers is possible, but in general is restricted to rather low frequencies due to their extreme directional characteristics. Thus a 10 inch transducer may be used up to approximately 250 Hz. Two-transducer approaches based on correlation techniques cover a much wider frequency range because ordinary small transducers are applicable. Measurement errors due to diffraction or to unavoidable spacing of the two transducers generally become significant for transducer diameters in excess of one-quarter of a wavelength at the upper limiting frequency, although an exception to this occurs in the particular case of a plane progressive wave. The use of extremely small insensitive transducers is restricted by the necessity of having very impractical integration times. If measurements of levels down to −20 dB re 20 μPa are carried out with condenser microphones in one-third octave frequency bands a practical compromise seems to be employment of 1 2 inch microphones in the range of center frequencies from 25 Hz to 5 kHz. This range may in practice be doubled (e.g., extended to 10 kHz) if measurements in the range 2·5–5 kHz are carried out with both 1 inch and 1 2 inch transducers so that corrections can be obtained for extended range measurements from 5 kHz performed with 1 2 inch transducers only.

A Methodology for Assessment of Wind Turbine Noise Generation

The detailed analysis of a series of acoustic measurements taken near several large wind turbines (100 kW and above) has identified the maximum acoustic energy as being concentrated in the low-frequency audible and subaudible ranges, usually less than 100 Hz. These measurements have also shown any reported community annoyance associated with turbine operations has often been related to the degree of coherent impulsiveness present and the subsequent harmonic coupling of acoustic energy to residential structures. Thus, one technique to assess the annoyance potential of a given wind turbine design is to develop a method which quantifies this degree of impulsiveness or coherency in the radiated acoustic energy spectrum under a wide range of operating conditions. Experience has also shown the presence of annoying conditions is highly time dependent and nonstationary, and, therefore, any attempts to quantify or at least classify wind turbine designs in terms of their noise annoyance potential must be handled within the proper probabilistic framework. A technique is described which employs multidimensional, joint probability analysis to establish the expected coincidence of acoustic energy levels in a contiguous sequence of octave frequency bands which have been chosen because of their relationship to common structural resonant frequencies in residential buildings. Evidence is presented to justify the choice of these particular bands. Comparisons of the acoustic performance and an estimate of the annoyance potential of several large wind turbine designs using this technique is also discussed.

反射型の指向性マイクロホン系を用いた同軸二重ジェットの騒音源分布の測定

An investigation concerning the noise source distribution of a coaxial double jet in subsonic speed was conducted by means of a reflector-type directional microphone system which operated on the image principle of an elliptical concave reflector of diameter of 40cm.The effect of the velocity ratio of the bypass jet to the main jet on the apparent source strength distribution for flow direction on the jet axis was clarified in one-third octave band and overall frequency. The distribution of pressure fluctuations in the jet flow was also compared with that of the noise source intensities. The sound power generated by unit axial length of the jet flow was calculated by an iterative technique with the measured noise source distribution and the directional characteristics of the microphone. And, the amount of the noise reduction was estimated. The calculated results agreed with the measurement by the non-directional microphone.

Two-Dimensional Dynamics of Tracked Ram Air Cushion Vehicles With Fixed and Variable Winglets

A linearized model of the pitch-heave dynamics of a Tracked Ram Air Cushion Vehicle is presented. This model is based on aerodynamic theory which has been verified by wind tunnel and towed model experiments. The vehicle is assumed to be equipped with two controls which can be configured to provide various suspension system characteristics. The ride quality and dynamic motions of the fixed winglet vehicle moving at 330 km/hr over a guideway described by roughness characteristics typical of highways is examined in terms of the rms values of the vertical acceleration in the foremost and rearmost seats in the passenger cabin and the gap variations at the leading and trailing edges of the vehicle. The improvement in ride quality and dynamic behavior which can be obtained by passive and active suspension systems is examined and discussed. Optimal regulator theory is employed to design the active suspension system. The predicted rms values of the vertical acceleration in the one-third octave frequency bands are compared with the vertical ISO Specifications. It is shown that marked improvements in the ride quality can be obtained with either the passive or active suspension systems.

Noise impact evaluation of a power generating station and a refuse-derived fuel facility

Community noise impact assessment of a planned addition of refuse-derived fuel (RDF) facility adjacent to a fossil-fueled power plant was conducted using a computerized atmospheric sound propagation model. Close-in measurements of power plant operation and coal handling system were used for station input, and specifications of major equipment of the RDF facility and estimated refuse-delivering trucks along plant access road segment were used for RDF noise source inputs. Site prevailing meteorological conditions for winter and summer seasons, and daytime and nighttime periods were used to account for the significant effects of the atmosphere on sound propagation. Topographical inputs of receptor grid such as bearing, ground cover, natural and manmade barriers were input from USGS topographical map. Receptor grid output corresponding to each noise source, each season and time period are computed in octave frequency bands, and A-weighted sound-pressure levels for each source or combinations of sources are presented in the form of scaled contour maps of 2 dB increment overlaying an aerial photograph of the site of the same scale. Land use and population-weighted impact can thus be easily evaluated for the existing and the future noise environment when the RDF facility comes on line. Close agreements were obtained between predicted levels of the existing power plant operation and measured levels, and excess attenuations provided by meteorology and topography contributed to the significant reduction of noise levels in the residential community.

Broad-band injected-beam crossed-field amplifiers

The design and operation of injected-beam-crossed-field amplifiers, which provide efficient amplification over octave frequency bands with grid control in compact PM Focused format, are described. Dielectric supported meander lines, which are used to provide the low-dispersion and high-interaction impedance required to achieve octave bandwidth, are detailed. Relationships between space charge, gain factor, beam impedance, circuit loss, and circuit dimensions are derived for design optimization. An electron gun with a negative grid, which provides noise suppression, as well as a nonintercepting current control electrode, is shown to be effective in controlling the beam current continuously from zero to full operating value. Operating characteristics of production CFA's, providing 1 kW of average power in pulsed and CW operation and up to 5-kW peak pulsed power, are presented to illustrate the inherent multimode performance which can be achieved with low-voltage grid control.

Design of 3-screw tuners

The screw spacing for a 3-screw waveguide tuner to be usable over an octave frequency band is investigated; an optimum is one-sixth of a guide wavelength at the lowest frequency.

Volume attenuation in the Labrador Basin

Volume attenuation coefficients for one-third octave frequency bands up to 400 Hz have been determined as part of an underwater sound propagation study conducted in the Labrador Basin in cooperation with the U. S. Naval Research Laboratory. Charge detonation depths, receiver depth and the sound channel axis depth were all roughly 200 m along the 1300-km track. A late summer maximum in the near-surface sound velocity and a water depth greater than 3000 m also helped to ensure nearly ideal measurement conditions. The deduced volume attenuation coefficients were greater than the Thorp predictions [W.H. Thorp, J. Acoust. Soc. Am. 42, 270 (1967)], with attenuation increasing toward both higher and lower frequencies from a minimum (0.002 dB/km) near 60 Hz. Comparisons with results from other areas will be made. Results on the low frequency dependence of propagation loss will also be discussed.

Passenger ride quality within a noise and vibration environment

The subjective response to noise and vibration stimuli was studied in a ride quality simulator to determine the importance of these two stimuli (or their interaction) in the prediction of passenger ride quality. Subjects used category scales to rate noise comfort, vibration comfort, noise and vibration comfort, and overall comfort in an effort to evaluate parametric arrangements of noise and vibration. The noise stimuli were composed of octave frequency bands centered at 125, 250, 1000, and 2000 Hz, each presented at 70, 75, 80, and 85 dBA. The vertical vibration stimuli were 5‐Hz‐bandwidth random vibrations centered at 3, 5, 7, and 9 Hz, each presented at 0.03, 0.06, 0.09, and 0.12g rms. Analyses were directed at (1) a determination of the subject's ability to separate noise and vibration as contributors to discomfort, (2) an assessment of the physical measures of noise and vibration (and certain demographic factors) that optimize ride quality prediction in this type of multifactor environment, (3) an evaluation of the relative contribution of noise and vibration to passenger ride quality, and (4) development of information as to the “most appropriate” subjective scale for future assessments of ride quality in a noise and vibration environment.

Predictions of volume scattering strengths from biological trawl data

A volume reverberation model which utilizes fish distribution data has been developed to permit quantitative predictions of depth−dependent scattering strengths. The model was evaluated by using coincident acoustic volume scattering measurements and biological trawl data collected in the Mediterranean Sea. Biological specimens were collected at discrete depths with an Isaacs−Kidd midwater trawl. Each fish collected was identified and sized, and its acoustic cross section calculated by utilizing regression equations relating fish species, length, and swimbladder volume at frequencies near swimbladder resonance, or equations relating fish length to acoustic cross section at frequencies far above resonance. Scattering strengths for each species were then determined, indicating dominant species at each trawl depth for 1/3−octave frequency bands between 2.5 and 20 kHz. The acoustic data were obtained with surface−vented explosive sources and a shallow onmidirectional hydrophone. These data were processed to yield integrated column strength versus depth profiles, which were then numerically differentiated to produce scattering strength versus depth profiles for each frequency band. Comparison of the model predictions to the scattering strength profiles showed good agreement at the higher frequencies, with the agreement decreasing with frequency below 6.3 kHz. Subject Classification: 30.30, 30.40.

Predictions of volume scattering strengths from biological trawl data

A volume reverberation model which utilizes actual fish distribution data has been developed to permit quantitative predictions of depth-dependent scattering strengths. The model was evaluated using coincident acoustic volume scattering measurements and biological trawl data collected in the Mediterranean Sea. Biological specimens were collected at discrete depths with an Issacs-Kidd midwater trawl. Each fish collected was identified and sized, and its acoustic cross section calculated utilizing regression equations relating fish species, length, and swimbladder volume at frequencies near swimbladder resonance or equations relating fish length to acoustic cross section at frequencies far above resonance. Scattering strengths for each species were then determined, indicating dominant species at each trawl depth for 1/3-octave frequency bands between 2.5 and 20 kHz. The acoustic data were obtained with surface-vented explosive sources and a shallow omnidirectional hydrophone. These data were processed to yield integrated column strength versus depth profiles, which were then numerically differentiated to produce scattering strength versus depth profiles for each frequency band. Comparison of the model predictions to the scattering strength profiles showed good agreement at the higher frequencies, with the agreement decreasing with frequency below 8 kHz. Possible causes of this disagreement are enumerated.

Volume-Scattering-Strength Dependence on Depth and Frequency in the Pacific Ocean off San Francisco

A time series of measurements of volume scattering was made in the N.E. Pacific Ocean at a site approximately 55 miles west of Pt. Reyes (near San Francisco). The technique involved the firing of small explosive charges close to a receiving hydrophone and monitoring the broad-band scattered returns originating nearby (approximately 100-ft radius). Lowering the hydrophone-charge combination to various depths enabled the scattering characteristics in the top 2100 ft of the ocean to be examined. The data are presented as spectra of scattering strength versus frequency at 10 evenly spaced depths between 200 and 2000 ft and also as a set of eight profiles of scattering strength versus depth in each of four octave frequency bands between 0.625 and 10 kHz. These profiles are obtained in the course of a 30-min lowering of the equipment—eight of which were carried out between 0600 PST (about 112 h before dawn) and 2000 PST (about 2 h after sunset). Scattering-strength profiles were integrated against depth to give column scattering strength values which are displayed as a function of time. In addition, a comparison was made between integrated scattering strength versus depth profiles obtained both from a scattering strength versus depth profile and from a surface-fired charge.

An isolator for VHF and UHF bands using a printed circuit

An isolator using a printed interdigital circuit has been considered here. The circuit is fed by a coaxial line with good matching for one octave frequency band. Though the loss characteristics obtained were not satisfactory for practical purposes, because of nonessential causes, the practicability of this device was clearly shown.

Transmission of Sound and Vibration to a Shroud-Enclosed Spacecraft

The flow of high-frequency vibratory energy to a shroud-enclosed spacecraft is discussed. Two paths of energy flow are considered: first, the acoustical path along which energy flows from the external exciting field through the shroud and interior acoustic space to the spacecraft; and, second, the mechanical path along which energy flows from the external field through the shroud and spacecraft mounting trusses to the spacecraft. Theoretically predicted response levels in octave frequency bands for a model of the OGO spacecraft assembly are presented. These predictions show that the spacecraft response to energy transmitted along the acoustic path is at least a factor of 10 greater than the response due to energy transmitted along the mechanical path over the frequency range 250–8000 Hz. Methods to reduce the spacecraft response are discussed. [Research supported by National Aeronautics and Space Administration.]

Measurements of Backscattering from the Sea Surface

Measurements of ocean-surface backscattering were made off Nassau in 2500-f water using 2-lb TNT charges as acoustic sources. Analysis in octave frequency bands between 0.8 and 12.8 kc/sec shows surface backscattering decreasing down to grazing angles of 2° and confirms that scattering strength is proportional to frequency and wind velocity, with wind velocity becoming increasingly significant as grazing angle is decreased. Volume backscattering predominates over surface backscattering at low wind velocities and small grazing angles; the volume backscattering is presumed to be due to the presence of a layer of large numbers of microscopic marine life. General agreement was obtained on backscattering coefficients at grazing angles where previously published data are available for comparison.

Longitudinal Space-Time Correlation Function in Turbulent Airflow

The longitudinal space-time correlation function of the fluctuating pressures at the wall in turbulent flow has been measured in the U. S. Navy Underwater Sound Laboratory'a 3.5-in. turbulent pipe-flow facility. Measurements in octave and half-octave frequency bands at zero time delay and at various spatial separations of the transducers are presented and compared with theoretical investigations to illustrate the effect of finite filter bandwidths on the longitudinal space-correlation function.