Relative Sound Intensity Research Articles

Experimental analysis on noise characteristics of surface-mounted permanent magnet synchronous motors

Starting with the analysis on sound pressure level (SPL) spectrum of surface-mounted permanent magnet synchronous motors (SMPMSMs), the reasons for producing main peaks are investigated. According to different causes, different methods for reducing noise are proposed. Firstly, the SPL spectrum of SMPMSMs is obtained by experiment under the conditions of 2000 rpm rated speed, full load and 4 kHz switching frequency. Meanwhile, the frequencies corresponding to main peaks are found out. Secondly, the reasons for generating peaks in the SPL spectrum are researched from three aspects, namely, force sources, natural frequencies, coefficient of relative sound intensity. Then, on the basis of different causes for generating noise, different measures for decreasing noise are presented, namely, single cutting of two end rabbets of motor case in single clamping, waveform reconstruction of radial electromagnetic force density, enhancing of switching frequency, changing of natural frequency and decreasing of the length-diameter ratio of stator. Furthermore, the effectiveness for these methods is studied. Finally, a comprehensive method is proposed to decrease noise. The noise value of SMPMSMs is reduced by 4.7 dB(A) at the rated speed of 2000 rpm, full load and switching frequency of 4 kHz. In addition, the sharpness and loudness are respectively decreased by 0.522 acum and 6.97 sone at no load. The study provides references for the design of SMPMSMs with low noise.

Evaluation of Isolated Impact of Trans Fatty Acids on Short Dough Product

AbstractIn this study, the effects of trans fatty acids (TFAs) on rheological properties of dough (elastic moduli (G’), loss moduli (G”), complex modulus (G*)) and textural properties of dough and cookie (hardness) were studied. Two different groups of fat samples having different TFA composition but similar solid fat content (SFC) were prepared. Samples of the first group (group 1) had TFA between 0.0 and 56.23 %, while the samples of the second group (group 2) contained trans isomers ranging from 0.0 to 44.40 %. Texture measurements of different doughs and cookies prepared with different fat samples were performed. Texture measurements indicated that hardness values of doughs increased from 3950 ± 420 to 5498 ± 506 g in group 1 and 4700 ± 501 to 6787 ± 369 g in group 2 with increased amounts of TFAs. A particularly high, almost three‐fold increase in complex modulus values was observed in the dough samples containing the highest TFA levels compared with samples containing 0.0 % TFA. Although not significantly different, mean hardness and relative sound intensity values of cookies displayed an initial decreasing trend and then both parameters had maximum values when the TFA content was at maximum in both groups.

Improved methods for prediction of electromagnetic noise radiated by electrical machines

Improved methods for predicting the electromagnetic noise radiated by electrical machines are presented. The preferred method is based on the calculation of the sound-pressure and stator-vibration velocity distributions on a finite-cylindrical acoustic model. It results in a simple formula for calculating the acoustic power from the relative sound intensity and the stator-surface vibration, and is therefore eminently suitable for use during routine design. The method eliminates the need to calculate the sound-pressure and air-velocity distributions around a machine, as is required for existing methods. It can also account for the effect of an axial variation of the radial vibration. In an alternative method the relative sound intensity is calculated from a spherical acoustic model in which the radial vibration of a machine is expressed as a function of the circumferential mode order in the form of a Fourier series rather than a Legendre series, as in previous analyses. This makes it possible to use Fourier series throughout the various stages leading up to the prediction of electromagnetic noise. Predictions of the relative sound intensity from the different models are compared, and the sound-pressure distribution and the acoustic power are investigated both theoretically and experimentally on a TEFC 3-phase induction motor. It is shown that methods based on a spherical acoustic model are only geometrical and physical approximations, whilst a finite-cylindrical acoustic model is more generally applicable.

Control of responding by the location of sound: role of binaural cues.

In auditory localization experiments, where the subject observes from a fixed position, both relative sound intensity and arrival time at the two ears determine the extent of localization performance. The present experiment investigated the role of binaural cues in a different context, the sound-position discrimination task, where the subject is free to move and interact with the sound source. The role of binaural cues was investigated in rats by producing an interaural imbalance through unilateral removal of the middle auditory ossicle (incus) prior to discrimination training. Discrete trial go-right/go-left sound-position discrimination of unilaterally incudectomised rats was then compared with that of normal rats and of rats with the incus of both sides removed. While bilateral incus removal affected binaural intensity and arrival times, the symmetry of sound input between the two ears was preserved. Percentage of correct responses and videotaped observations of sound approach and exploration showed that the unilateral rats failed to localize the sounding speaker. Rats with symmetrical binaural input (normal and bilaterally incudectomised rats) accurately discriminated sound position for the duration of the experiment. Previously reported monaural localization based upon following the intensity gradient to the sound source was not observed in the unilaterally incudectomised rats of the present experiment. It is concluded that sound-position discrimination depends upon the use of binaural cues.

Relative Intensities of Sounds at Various Anatomical Locations of the Head and Neck during Phonation of the Vowels

Speech signals from 16 different anatomical locations were recorded as subjects intoned different vowels at a constant level. Power level analysis was made to determine relative intensity of the signals. It was found that significant difference in intensity exists among the anatomical locations. Some locations of lesser intensity were subjectively evaluated as providing more faithful signals.

Relative Intensities of Sounds at Various Anatomical Locations of the Head and Neck during Phonation of the Vowels

Speech signals from 16 different anatomical locations were recorded as subjects intoned different vowels at a constant level. Power level analyses were made to determine the relative intensity of the signals. It was found that significant difference in intensity existed among the anatomical locations. It was found that the composite intensities of the test vowels were statistically equivalent at the larynx, the sides of the neck, and at the angles of the rami. The next rank of intensity was noted at the back of the neck, back of the head, chin, and nose. The next most intense location was the top of the head, with least intensity measured at the six positions of the two temples, midback of the head, forehead, and the sides of the head above the ears. In general, previous observations of “the nearer the larynx, the more intense the sound” is borne out by this study. Some locations of lesser intensity were subjectively evaluated as providing more faithful signals. The consensus was that most faithful reproduction resulted in the vowels recorded from the forehead, with the most intense reproduction afforded by the larynx and neck areas. [Done in connection with contract AF 19(604)-1757, monitored by the Operational Applications Laboratory, Air Research and Development Command, Bolling Air Force Base, Washington 25, D.C.]

Localization of Response in the Cochlea as Determined by Electrical Recording

Electrical responses from the cochlea of the guinea pig were studied by means of an amplifier, a cathode-ray oscillograph and a wave-analyzer. The guinea pig was anesthetized with dial and urethane, put under artificial respiration and placed in a “sound-proof” room. A beat-frequency oscillator, attenuator and speaker provided tones which were delivered to the ear of the guinea pig through a rubber tube and a speculum which had been sewed into the external meatus. The cochlear response to frequencies of 100, 200, 400, 600, 1000, 2000, 4000, and 6000 cycles per second was recorded from selected positions on each turn of the cochlea. For each frequency a series of intensities was used and a log response log relative sound intensity curve obtained. From these curves the relative intensity of sound on each frequency necessary to elicit a response of three microvolts was determined for each recording position. The data obtained make it possible to construct a map of the cochlea which meets the requirements of the place theory of audition, and which confirms a map of the cochlea previously constructed by Culler from data obtained by a somewhat different method.

IV.The loud-speaker as a source of sound for reverberation work

Abstract In reverberation work it is important to have a source of sound of which the activity can be varied in a large known ratio. The suitability of a loud-speaker for this purpose has been studied. A loud-speaker actuated by audio-frequency current of pure sine wave form was set up in a room, and measurement was made of the manner in which the intensity of sound at any point in the room varied with the exciting current. The measurements of relative sound intensity were made by means of a condenser microphone with suitable accessory apparatus for measuring the small electromotive forces involved. An electrodynamic type of loudspeaker was found to be satisfactorily constant and free from lag, and over a wide range to have an activity approxi mately proportional to the square of the exciting current. An electromagnetic instrument tested was, on the whole less satisfactory. As a further test, measurements were also made of the rate of decay of residual reverberant sound in each of two large rooms, using t...

XI. A selective hot-wire microphone

The instrument described in the following paper provides:— (i) A convenient means of detecting a note of given pitch when other sounds are present; and (ii) A method of estimating the relative intensities of sounds of the same pitch. The idea which formed the starting-point for the construction of the instrument—viz., the placing of an electrically heated grid of fine platinum wire in the orifice of an otherwise closed vessel—was originally employed by one of us (W. S. T.) in the construction of a sound-detector for the use of Sound Ranging Sections in the British Army. In its original form, the detector was intended to respond to heavily damped aerial vibrations, such as those produced by the firing of guns. Further experiments, however, showed that the detector could be tuned to respond to any continuous sound of definite frequency by suitably choosing the dimensions of the vessel and its orifice.

XI. On the experimental determination of the relative intensities of sounds; and on the measurement of the powers of various substances to reflect and to transmit sonorous vibrations

XI. <i>On the experimental determination of the relative intensities of sounds; and on the measurement of the powers of various substances to reflect and to transmit sonorous vibrations</i>

On the experimental determination of the relative intensities of sounds; and on the measurement of powers of various substances to reflect and to transmit sonorous vibrations

On the experimental determination of the relative intensities of sounds; and on the measurement of powers of various substances to reflect and to transmit sonorous vibrations

On the experimental detemination of the relative intensities of sounds; and on the measurement of the powers of various sustances to reflect and transmit sonorous vibrations

On the experimental detemination of the relative intensities of sounds; and on the measurement of the powers of various sustances to reflect and transmit sonorous vibrations