Abstract: An audio analysis system visually displays a variance of sound intensity in each of several discreet frequency bands from the average sound intensity across all frequency bands. The audible sound is detected and converted to a first electrical signal which represents the ambient sound detected. A second electrical signal is developed as a function as the average DC level of the first signal. The DC level of the first signal is then shifted in accordance with the average level of the second signal to develop a level shifted signal. The level shifted signal is then graphically displayed in the discrete frequency bands so that the plus or minus deviation from the average level signal is displayed in each of those bands. The display may be provided with a visual representation, such as a graphic overlay or multicolor display, showing the probability of risk to hearing loss produced in each of those bands.

Abstract: The intensity profile of an ultrasound beam in an ultrasound imaging system is adjusted by driving the individual piezoelectric crystals with drive signals having adjustable pulse durations. The duration of the drive pulse determines the frequency spectrum of the pulse and therefore determines the amplitude of the emitted ultrasound wave. The pulse durations may be selected such as to compose a desired profile of the ultrasound beam.

Abstract: A system for detecting and monitoring blast noise, the invention provides ncentrically arranged cylindrical windscreens having a pair of vertically spaced microphones mounted centrally therein, the windscreens acting to reduce interference from wind-generated pseudosound yet being acoustically transparent so as not to interfere with the reception of acoustical data incident on the microphones. The present system also includes a signal processing subsystem which receives the output of the respective microphones for analysis.

Abstract: Method and apparatus for evaluating the auditory distortion of an audio system, wherein an audio signal, whose auditory distortions are to be evaluated, is filtered by a notch filter to remove its fundamental frequency, and is then fed through a primary weighting network comprising three high pass filters followed by a secondary weighting network. The filtered, weighted signal is then amplified, recitified, further filtered, compared by taking the ratio with the magnitude of original signal and finally fed to a display unit to sow a figure that represents auditory distortion characteristics consistent with what is actually perceived by human auditory faculties.

Abstract: The present invention is directed to providing an inexpensive, yet effective, simulation for measuring the sound level of the muffler contribution to the total sound created by a truck during a drive-by. The simulation method includes disconnecting a drive shaft of the drive mechanism of the truck and installing a dynamometer. When the throttle of the engine is increased, the dynamometer applies a load so that the acceleration rate of the drive mechanism compares similarly to the acceleration rates of a truck during an actual drive-by test in accordance with CFR 40, part 202. Sound barriers are placed around sounds sources other than the muffler of the truck. Microphones are used to sense the sound during the test for recording by strip-chart recorders.

Abstract: Sound intensity is determined by simultaneously measuring instantaneous acoustic pressure and instantaneous particle velocity at a single point. A condenser microphone having a vibrating diaphragm generates an output voltage proportional to the instantaneous acoustic pressure. A laser Doppler vibrometer measures the velocity of the vibrating diaphragm and a Doppler frequency tracker converts the velocity measurement into another output voltage which is proportional to the instantaneous acoustic particle velocity. The sound intensity is then calculated from the known components.

Abstract: A tamperproof noise alarm for use in a school classroom to detect noise exceeding a predetermined intensity and duration and, in turn, warn both teacher and students when excessive noise has been detected. The noise alarm aids the instructor in preventing excessive classroom noise which can and does disrupt and destroy a given learning situation. A sensitivity control is provided to allow the instructor to determine the noise level at which the alarm will automatically respond. Alarm circuitry is not enabled until a first excessive noise occurs. A closely spaced second excessive noise causes an audible alarm to sound. When switched to a "delay" mode, the noise alarm is more tolerant of occassional classrool noise and will not sound a warning unless additional noise occurs subsequent to a timed delay of several seconds.

Abstract: Apparatus for measuring the power of radiation that includes float means (16) and force balancing means (48, 50, 60, 80). The float means includes a target (46) for the radiation and is constructed such that the net gravitational force, including buoyancy force, if any, acting on the float means tends to accelerate the float means in a first direction. The force balancing means includes drive means (80) for providing a drive signal and means (50) responsive to the drive signal for exerting a balancing force on the float means in a second direction opposite the first direction, such that the magnitude of the balancing force corresponds to a characteristic of the drive signal.

Abstract: A method of determining in a propeller-driven aircraft a propeller pressure ignal from a combined signal derived from the propeller and from the engine exhaust during flight. Where the propeller driven aircraft is powered by a four-stroke internal combustion engine, pressure signals from the propeller and the engine exhaust coincide where the number of propeller blades corresponds to half the number of cylinders in the engine. In order to determine the clean propeller signal from a propeller/engine exhaust combined signal, a succession of combined signals are detected by means of a microphone arranged on the wing of the aircraft behind the plane of rotation of the propeller. In addition to this, the exhaust signals of the individual engine cylinders are measured at the mouth of the exhaust pipe. Both the combined and the cylinder exhaust signals are recorded synchronously on a multi-track tape recorder.

Abstract: A method of determining both the level of sound occurring at a point in an area of interest and the location of the point. The level of sound at a point in the area of interest is sensed, and a first signal is transmitted from the point. This first signal is received at a first location related to the area of interest, and the direction relative to the first location from which the first signal was transmitted is determined. A second signal is transmitted from the first location which is indicative of the direction relative to the first location from which the first signal was transmitted. Similarly, the first signal is received at a second location related to the area of interest. The direction relative to the second location from which the first signal was transmitted is determined, and a third signal is transmitted from the second location which is indicative of the direction relative to the second location from which the first signal was transmitted.

Abstract: A precision acoustic source that is capable of producing acoustic radiation having peak and average power levels that are independently and simultaneously adjustable. The apparatus comprises an acoustic transducer and drive means for producing a drive signal comprising a series of drive pulses to the transducer, such that the transducer produces acoustic radiation having selected peak and average power levels. The drive means comprises means for establishing a series of fixed-length clock cycles, means for generating a series of trigger signals, pulse generating means responsive to each trigger signal to produce a selected number of standard pulses, an amplifier for generating a drive pulse in response to each standard pulse. The amplifier adjusts the amplitude of each drive pulse such that the peak power of the acoustic radiation is equal to the selected peak power level. Each trigger signal occurs either R or S clock cycles after the preceding trigger signal, R and S being positive integers.

Abstract: A method for determining reactive acoustic power density level and its direction in a fluid using a single sensor is disclosed. In the preferred embodiment, an apparatus for conducting the method, which is termed a thermoacoustic couple, consists of a stack of thin, spaced apart polymeric plates, selected ones of which include multiple bimetallic thermocouple junctions positioned along opposite end edges thereof. The thermocouple junctions are connected in series in the nature of a thermopile, and are arranged so as to be responsive to small temperature differences between the opposite edges of the plates. The magnitude of the temperature difference, as represented by the magnitude of the electrical potential difference generated by the thermopile, is found to be directly related to the level of acoustic power density in the gas.

Abstract: A tone discrimination circuit for use with audible smoke or fire detectors or similar audible devices, which automatically emits an output electronic alarm signal, for notification of persons at remote locations, upon input of a proper audio tone from the smoke detector or other audible device. The circuit contains in series a microphone, a two stage audio amplifier, a frequency detector, and a time discrimination circuit. The circuit emits an output electronic alarm signal if and only if the audio input signal has sufficient amplitude, the desired frequency, and the desired duration. In the preferred embodiment the duration must be 20 seconds or longer, though the circuit allows the audio input to cease for a period less than 0.25 seconds, without loss of the output signal. The timing periods are adjustable.

Abstract: A sound level indicating device specifically designed for use by educators to use in teaching students the art of self-discipline when students are arranged in large groups in a large area with means for: (1) detecting noise; (2) distinguishing between noises of different decibel levels; (3) distinguishing between noises of different lengths of time; (4) ignoring isolated sounds of excessive decibel level which may occur in the midst of a general noise level; (5) switching a plurality of SPDT relays; (6) giving visual signals to indicate the rise and/or fall of noise levels in reference to a predetermined decibel level.

Abstract: An ultrasonic therapy applicator wherein therapeutic heating is provided by creating a diffuse ultrasonic field in a liquid, such as water, in a tank in which living tissue may be immersed. The diffuse acoustic energy is produced by frequency-modulating the driving ultrasonic frequency in a band employing "white noise" modulation. The apparatus consists of a reverberation tank suspended from a support by four wires. The support is used to mount a transducer, a hydrophone, a specimen holder and a stirrer. The tank is surrounded by a temperature bath. The hydrophone is used for measuring decay rates. The transducer is acoustically matched to the water. Ultrasound is coupled from the transducer via an ellipsoidal vertical reflector vertically aligned below the acoustic window of the transducer. To calibrate integral dosage a temperature sensing probe is used, of the differential temperature analysis type.

Abstract: Acoustic intensity measuring apparatus for determining sound energy intensity utilizing a probe having a pair of microphones and an associated ambient noise shield.

Abstract: A noise level monitoring and indicating system includes plural microphones distributed about a classroom, bus, etc. and adapted to drive individual counters to indicate the number of times a minimum sound level has been exceeded by the signal from the associated microphone. Visual indicators are also provided to indicate the instantaneous noise status at selected microphones.

Abstract: This electronic noise detector is an instructional device for classroom teachers to use in achieving academic excellence in educating students. Academic excellence is, among other things, dependent upon good discipline in the classroom and excessive noise in a classroom is disruptive of good discipline. This invention provides the classroom teacher with a means of immediately controlling the noise level in any classroom with any arrangement of the students. It further provides a means for instructing students to accept responsibility for maintaining a level of noise to the classroom which is conducive to achieving academic excellence.Operation of the device is simple. The teacher places it any place in the classroom that may be desired and turns it on. The device is then in a monitoring mode. The teacher sets an adjustable gain control and predetermines a level of noise which will be unacceptable. The device monitors the classroom without further intervention of the teacher.

Abstract: The invention is a ride quality meter that automatically transforms vibration and noise measurements into a single number index of passenger discomfort. The noise measurements are converted into a noise discomfort value. The vibrations are converted into single axis discomfort values which are then converted into a combined axis discomfort value. The combined axis discomfort value is corrected for time duration and then summed with the noise discomfort value to obtain a total discomfort value.

Abstract: An instrument for measuring ultrasound has a chamber through which sound waves can travel from end to end of the chamber. An acoustic focusing device near one end of the chamber concentrates the sound waves at a focal point near the opposite end of the chamber. A rotary shutter is supported within the chamber in a position to be rotated by passage of the concentrated sound waves. Devices capable of transmitting and receiving a ray of light are arranged on the instrument so that the light ray is interrupted by the rotary shutter to provide a series of light pulses. A counter is operatively connected to the light receiving device and the series of light pulses are utilized to actuate the counter and provide a reading indicative of the intensity of the sound waves. The instrument may have an additional indicator of the intensity of the sound waves to supplement the reading provided by the counter.

Abstract: A system for directly displaying steady state waves, such as sound waves, ultrasonic waves, electromagnetic waves, and the like, by instantaneously sampling the amplitude of the waves in a known phase relationship with some other portion of the wave train. The system includes a source of the waves, such as a speaker, and a transducer, such as a microphone, an electrical signal source being coupled to the wave signal source, and the transducer being connected to a sample and hold circuit whose output is applied to a light emitting diode (LED), or other display unit. The transducer is moved towards and away from the wave signal source in the path of the waves eminating from the wave signal source. In the following description the system will be described in conjunction with wound waves traveling in air, eminating from a speaker and transduced by a microphone.

Abstract: A sound level indicator apparatus includes a signal processing element which detects and processes sound pressure waves into quantifiable electrical signals. The indicator also includes an adjustment member which adjusts the quantifiable signals to compensate for intrinsic electrical variations in the processing element. Further included is a monitoring member which detects when the received sound is below a predetermined level. The indicator still further includes an indicator element which displays the quantified quantifiable signals and the low level monitor detection signal. The sound level indicator is operatively combined with a digital watch integrated circuit for containment in a case which is wearable on one's wrist.

Abstract: Acoustic intensity is measured by a pair of closely spaced microphones aligned in a given direction. One microphone is connected directly to an integrator the output of which is connected to a multiplier while the other microphone is connected directly to the multiplier. The multiplier output is proportional to the imaginary part of the cross-spectrum of the two microphone signals which when time averaged represents the absolute value of the sound intensity in the given direction if the microphone systems are properly phased matched.

Abstract: An instrument for measuring the intensity of sound waves has a container partly filled with liquid. An open-ended tube is supported by the container above the liquid. Below the container a clamping arrangement serves to hold a sound-producing device in acoustical contact with a bottom closure of the container. A sound lens carried by the container above the bottom closure concentrates sound waves generated by the device at a focal region located below the surface of the liquid and in vertical alignment with the tube. The resulting column of liquid is supporting by the tube and the column height is measured on a scale to indicate sound intensity.

Abstract: Method and system for the constant amplitude control of an electromechanical oscillator utilizing a phase locked oscillator to generate a secondary a-c setpoint which is compared to the oscillator output to provide a difference signal which is passed as a fast-acting negative feedback signal to stabilize the amplitude.

Abstract: A measuring apparatus employs a target vane suspended from a movable arm and disposed in a water bath. The transducer under test is arranged to direct its energy at the vane. An electric nulling circuit maintains the arm in its initial position. The current required to do so is a measure of the power of the transducer. An acoustic trap is provided to insure accurate measurement.

Abstract: A system for resolving a complex acoustic field, resulting when acoustic energy propagates through a duct, into component unit spatial pressure patterns or modes is disclosed. In each disclosed system arrangement, an acoustic filter, which includes one or more annular cavities, circumferentially surrounds the duct through which the acoustic energy propagates and sound is coupled from the duct into one end of each annular filter cavity via a series of openings which exhibit a relatively high acoustic impedance and a relatively high resistance to fluid flow. Each filter cavity is dimensioned such that it is excited into resonance when the circumferential distance between adjacent nodes of a modal component of the pressure pattern within the duct is mathematically related to the velocity of sound within a filter cavity by a predetermined factor.

Abstract: A radiation balance for testing the power of ultrasonic transducers involves a balance mechanism wholly immersed in transmission liquid in a windowed vessel to avoid surface tension effects. The mechanism comprises a target connected for movement with the coil of a moving coil/magnet assembly, such as from a galvanometer, and a null-seeking servomechanism energizes the coil in response to balance mechanism movement. The balance movement is about a vertical axis to avoid gravitational effects, and the target has neutral buoyancy.

Abstract: An apparatus for detecting ultrasonic energy comprises a chamber, partially filled with a colored liquid, having two sides separated by spacing no greater than about 25 millimeters and having a transparent section allowing for visual observation of the height of the liquid therein. A method of detecting the energy level of a beam of ultrasonic energy being propagated through a fluid comprises positioning the apparatus in the fluid so that the beam of energy strikes the liquid at the surface thereof, whereby the beam generates a visible arc-shaped spray having an amplitude proportional to the energy level of the beam.

Abstract: A system for the periodic sampling and recording of a condition, such as noise. The system employs a transducer which gates strings of pulses to a tape recorder. The gating time is in accordance with the transducer output voltage at sampling time. At each sampling, a delay in recording is provided to allow the recorder motor to come up to speed. The recorded tape may be played back and the grouped recorded pulses counted and presented as noise levels which can be plotted against time.

Abstract: This invention is a device for measuring small differences between relatively high sound pressure levels at two different microphone sites. It provides electrical insertion voltages, "pilot" voltages, as a means for continuously monitoring the gains of two acoustical channels. The difference between two pilot voltages is utilized to force the gain of one channel to track the other channel.