Audio Spectrum Research Articles

Listening enhancement device

A listening enhancement device in which a flat body (18) with a ear-hook (14) cutout can be converted to a sound gathering acoustical scoop by engagement of a fastener system located on the body (18) of the device. Once fastened into its functional shape the device can be independently engaged wtih the ear. The device is made in mirror image pairs so one device is specifically for the left ear and the other for the right. The device is reversible as to which side of the body (18) forms the sound gathering acoustic scoop. When reversed the device that is specific to the left ear becomes specific to the right ear and visa versa. Each side of the body (18) of the device has its own acoustic properties. By reversing the device the user can choose which acoustic properties most benefit them. The device is adjustable in acoustic gain. This is accomplished by different fastener engagement positions, which in turn change the size and shape of the sound gathering acoustic scoop. The body (18) is soft and flexible, providing resistance to damage and reducing discomfort and skin irritation to the user. The body (18) has acoustic properties that preserve a natural spectral balance, being free of colorations or resonances in the audio spectrum.

Reciprocal, subtractive, audio spectrum equalizer

First Page

Acoustical testing of the Harris County Domed Stadium (the Astrodome) in Houston, Texas, preparatory to a new sound system design

In preparation for a new sound system design, a study of the physical acoustics was performed in the Astrodome, Houston, Texas. The goat of this 4‐month study was to determine reverberation time, echo‐producing surface locations, noise levels, and resonant conditions in preparation for sound system design and possible future acoustical treatment. Measurements were carried out using conventional instrumentation (sound‐pressure level meters, real‐time audio spectrum analyzers, scientific data recorders, etc.) and with a TEF (time‐energy‐frequency) analyzer. Specific findings of the physical acoustics study and how these findings affected sound system design formed the basis of the design philosophy and resulted in a new sound system with improved intelligibility, pattern control, and sound pressure compared to the old sound system.

Instrumentation for the investigation of the extracranial carotid circulation.

The original ultrasound Doppler shift flowmeter was a non-directional velocity sensing device. Various methods of signal processing, including phase-quadrature detection and heterodyne detection were developed in order that flow direction could be resolved. In the past ten years the advent of the real-time audio spectrum analyser allowed both the flow direction and the Doppler shift spectrum to be displayed. It is this latter development which has been the major contribution to the clinical acceptability of Doppler flowmeters. The combination of a pulsed Doppler flowmeter with a real-time ultrasound imaging system has meant that velocity information can be gained from specific blood vessels, non-invasively. The development of the colour flow mapping systems has demonstrated that haemodynamic information can now be incorporated into the ultrasound image in real-time. These sophisticated systems are capable of displaying functional and anatomical information simultaneously.

Accurate noninvasive method to diagnose minor atherosclerotic lesions in carotid artery bulb.

In a prospective study using a multigate pulsed Doppler system, minor (less than 30% diameter reduction) carotid artery lesions were diagnosed by detecting not only abnormalities in the blood flow pattern, but also local changes in artery wall distensibility. For the diagnosis of more severe lesions, additional information was obtained from disturbances in the Doppler audio spectrum. Biplane arteriography was used as a reference. The observed agreement, sensitivity, and specificity were 86.6%, 90.3%, and 88.6%, respectively, for all lesions and 85.7%, 82.1%, and 88.6%, respectively, when only minor lesions were considered. kappa (a chance-corrected measure of agreement) was 81.7%. If only blood flow abnormalities were used to detect minor lesions, 43.5% would be missed. Our results indicate that minor carotid artery lesions can be diagnosed noninvasively more accurately when both local blood flow irregularities and local changes in vessel wall distensibility are taken into account.

Sound power level and directivity pattern determination of a space shuttle solid rocket booster

The sound power level and directivity pattern of sound were determined for a space shuttle solid rocket booster motor during a horizontal test firing at the Morton Thiokol Wasatch Test Facility in Utah. Six Bruel & Kjaer type 2230 precision sound level meters were placed at 60‐deg intervals around the rocket motor at a distance of 1000 ft, except the location directly behind the nozzle (2600 ft). These analyzers were used to determine the overall sound‐pressure level, between 20 and 20 000 Hz, at each of the six locations during the test. Two Cetec‐Ivie model IE‐30A audio spectrum analyzers were used to determine the shape of the spectrum at a one‐third octave band resolution. The equipment was turned on approximately 2 h prior to the scheduled test and was unattended during the test. Various adjustments were made to the data to account for topographic and atmospheric effects. The sound produced was predominantly low frequency, and the directivity pattern exhibited major acoustic lobes 60 deg to both sides of the line of fire. A total overall sound power level of 196 dB was determined. [Work funded by NASA Stennis Space Center, Mississippi.]

Aurally sensitized flat frequency response noise reduction compansion system

A flat frequency response compansion noise reduction system employs both input signal and control signal preemphasis and deemphasis in its encoder and decoder networks respectively. The linear range of the frequency response curve of the input signal deemphasis is selected to approximate the frequency range within the audio spectrum at which the human ear is most sensitive, typically having a high frequency end of 3.617 kHz. The frequency response curve of the input signal preemphasis is a mirror image of the frequency response curve of the input signal deemphasis. The linear range of the frequency response curve of the control signal preemphasis is selected to provide an encoder output signal having a substantially flat response. The frequency response curve of the control signal deemphasis is a mirror image of the frequency response curve of the control signal preemphasis. The amount of preemphasis is maximized to the limits of the recording medium, typically ranging from 0 db to 20 db.

A Theoretically Based Valve Noise Prediction Method for Compressible Fluids

Noise generated by control valves in power generation, chemical and petrochemical plants must be predictable so that proper design measures can be taken to conform to OSHA’s noise regulation. Currently available noise prediction methods are empirically based and not sufficiently accurate. The method proposed is based on jet noise theory for both subcritical and choked conditions, duct acoustics theory in terms of higher order mode generation and propagation, and the theory of acoustics-structure interaction in the development of the transmission loss values for the pipe. One third octave values are calculated over the audio spectrum by incorporating spectral aspects of noise generation, propagation, transmission, and radiation. The predicted values of noise for several size cage globe valves over wide pressure ranges compare well with measured results by two prominent valve manufacturers. The method, at present, is restricted to conventional valve styles, as opposed to the special low noise valve types with their very complicated orificial elements.

Apparatus and method for adjusting the characteristic sounds of electric guitars, and for controlling tones

To adjust the characteristic sounds produced by electric guitars and other musical instruments, the present apparatus and method provide for varying the resistive loading on the electromagnetic pickups of such instruments. This changes the shape of the peak of the resonance curve caused by the self-resonance of the electromagnetic pickup. A predetermined fixed resistance is maintained in the circuit at all times, such that when a control element is at a certain known position, the output curve from the pickup will be substantially flat and, furthermore, the apparent volume generated by the instrument will not be reduced substantially. To change volume, a volume-control potentiometer is provided. In the preferred form, a single control element not only adjusts the characteristic sounds produced by electric guitars or other musical instruments having electromagnetic pickups, but also provides roll-off of higher frequencies at some desired region within the audio spectrum. In one embodiment, the peak of the resonance curve is shifted along the audio spectrum.

Ribbon-type electro-acoustic transducer with low distortion and improved sensitivity

A ribbon-type electro-acoustic transducer has a magnet system which comprises an upper plate (2, 3) and a center pole (1) between which an air gap (8) is formed. A diaphragm (7) on which conductors (9) are arranged is disposed in the air gap. The upper plate (2, 3) comprises two plate-shaped parts (2', 3' and 2", 3" respectively) between which a space (11) is formed in which an edge portion of the diaphragm is located. This results in a more homogeneous magnetic field so that the transducer distortion may be reduced. Moreover, the transducer sensitivity is improved and is suitable for handling signals in the mid-range audio frequency spectrum. The cavity (15) enclosed by the magnet system and the diaphragm (7) can be acoustically coupled, be via an additional cavity to a (bass-reflex) duct or an additional (passive radiator) diaphragm.

Underwater sound generation by breaking wind waves

In a recent paper [B. R. Kerman, J. Acoust. Soc. Am. 75, 149–165 (1984)] the mechanism of sound generation by forced oscillation of bubbles by turbulence was discussed. It was argued that the most intense sound originated from bubbles of radius comparable to the Kolmogorov scale of the turbulence. The consequences of this aspect of the model in terms of the resulting audio spectrum are examined. An extension to the concept of intermittent forcing by shedding wake vortices behind rising bubbles will be outlined. As well, corrections to the original formulation for the source depth and effective turbulent forcing will be discussed.

Dual element headphone

A stereophone includes cup assemblies which are supported over the ears of a user by a headband. Each cup assembly includes a piezoelectric acoustic transducer and a dynamic acoustic transducer. The reproduction of the entire audio spectrum is divided between the two transducers at a crossover frequency which is established by an acoustic filter.

Noninvasive diagnosis of aortic and mitral valve disease with pulsed-doppler spectral analysis

To differentiate normal from abnormal left-sided heart valves, 34 adults (6 normal and 28 abnormal) with 48 valve lesions proved at catheterization were examined using a 3 MHz duplex pulsed Doppler echocardiograph with 2-dimensional verification of sample volume position and on-line display of the Doppler audio spectrum. A uniform protocol was used to position the sample volume for each lesion and to analyze the Doppler spectral data. Intracardiac blood turbulence, manifested by an increased Doppler spectral envelope area, was the noninvasive indicator of disease. The specific lesion present was determined by documenting the intracardiac location and timing of the turbulence. Doppler spectral envelope areas in all normal valve sites were smaller than those measured at the same sites in patients with aortic stenosis, mitral stenosis, and mitral regurgitation (p < 0.01). Except for a single patient with minimal aortic regurgitation, spectral envelope area allowed complete separation of patients with valve disease from normal subjects (p < 0.01). High sensitivity (97%) and specificity (100%) were noted despite the presence of multiple valve lesions in 67% of the patients. The data demonstrate application of a simple, noninvasive method of acquiring and analyzing Doppler echocardiographic data which allows accurate identification or exclusion of left-sided valve disease in adults, even in the presence of multiple valve lesions.

A monolithic audio spectrum analyzer

A monolithic audio spectrum analyzer with 16 channels of bandpass filters, half-wave rectifiers, and postfiltering has been fabricated with double-poly NMOS technology. The chip was designed using switched-capacitor filter techniques. It performs a total of 84 poles of filtering and contains 100 operational amplifiers in an area of 225 × 280 mils. A system dynamic range of better than 43 dB, linearity of better than 1 percent, and center frequency accuracy of better than 1 percent have been achieved.

A Monolithic Audio Spectrum Analyzer

A monolithic audio spectrum analyzer with 16 channels of bandpass filters, half-wave rectifiers, and postfiltering has been fabricated with double-poly NMOS technology. The chip was designed using switched-capacitor filter techniques. It performs a total of 84 poles of filtering and contains 100 operational amplifiers in an area of 225 X 280 mils. A system dynamic range of better than 43 dB, linearity of better than 1 percent, and center frequency accuracy of better than 1 percent have been achieved.

Sound reproduction system

First Page

Design of cross-over network for high fidelity speaker system

A filter network is interposed between an audio amplifier and a speaker system consisting of a woofer, midrange and tweeter. The reactive elements for the filter sections associated with the woofer, midrange and tweeter, respectively, are interrelated by mathematical formulas and there is a capacitor lock connected across the input terminals of the network. The value of the capacitor lock is mathematically related to the values of the reactive elements to achieve superior overall performance for the speaker system. The filter or crossover network is designed for matched or unmatched speakers. This design uses a frequency system based on F1, F2 =8F1 and F3 =16F1, where F1 is a selected frequency in the lower portion of the audio spectrum.

A Digital Signal Generator

Implemented on a single-chip microcomputer, this digital signal generator can provide low-distortion waveforms ofprecise frequency in the low-frequency audio spectrum.

Sonic transducer mounting

A sonic transducer incorporating a rigid plate-like transmitting member coupled to electromechanical compression wave generating means such as a piezoelectric crystal for transmitting sonic energy in a medium. The transmitting means is damped to prevent ringing, and the transducer is particularly responsive to the high frequency audio spectrum. The sheet-like configuration of the transducer enables it to be recessed within a generally flat panel such as a front panel of a speaker cabinet while nevertheless being separated from the inside of the cabinet to avoid interaction with a conventional cone-type speaker that may be mounted in the same cabinet. The sheet-like transducer is resiliently mounted in a direction contrary to the principal direction of sonic energy propagation in the transducer to minimize loss of sonic energy to supporting structure such as a speaker cabinet.

Listening to the Doppler shift of visible light

Doppler shift of light can be reproduced audibly with minimal apparatus: a commercial He–Ne laser, two mirrors, a photodetector, and a stereo amplifier with speakers. A dual-trace oscilloscope and signal generator can be added to obtain a numerical value for the laser wavelength. The method can be extended to display optical spectra directly on an audio spectrum analyzer.