Earl R. Geddes

Internal ported band pass enclosure for sound cancellation

A transducer arrangement for active noise cancellation in conduits, for example, in motor vehicles where an electronic control produces a drive signal for a transducer that emits cancellation pulses phased 180° from the sound pressure pulses passing through an exhaust conduit, where both front and rear sides of the transducer are acoustically coupled to improve the efficiency of the transducer operation. Preferably, the acoustic coupling comprises an enclosed chamber partitioned to expose a first transducer side to a chamber portion and a second transducer side to a second chamber portion. A first port couples one of the chambers to the other and a second port couples one of the chambers to the conduit. Each port for communicating with the conduit can be tuned to resonate at predetermined frequencies. When both sides of the transducer are so coupled to the conduit, the transducer has increased efficiency over a band of frequencies, to accommodate the frequencies generated by a source of noise while limiting access of fluid or heat in the conduit to the transducer. A tandem transducer mounting arrangement according to the present invention reduces vibration of the housing. The system is particularly suitable for use in adapting noise cancellation techniques to replace or combine with passive mufflers on motor vehicles.

Integrated active vibration cancellation and machine diagnostic system

A machine analyzer is connected to an active vibration cancellation system in order to identify the operating status of the moving machinery while using a minimum of additional parts and taking advantage of signal processing already occurring in the active vibration cancellation system. A preferred embodiment employs a neural network pattern classifier in connection with detecting operating states such as cylinder misfires in an internal combustion engine.

Protective anc loudspeaker membrane

A transducer arrangement for active noise cancellation signals provides an acoustically permeable membrane between ports in direct communication with the noise propagating conduit and the transducers delivering sound pulses to the port. A housing defines at least one chamber exposed to at least one face of a transducer diaphragm, and each chamber is connected in fluid communication with the conduit through at least one port. The chamber is partitioned by the membrane to include chamber portions with a predetermined volumetric relationship. In a preferred embodiment where the transducer arrangement is coupled to a motor vehicle exhaust conduit, the membrane is preferably a silicone impregnated polyurethane film reinforced with aromatic polyamide fibers. Such a member provides a waterproof, acoustically permeable partition between the port and any adjacent speaker face that can withstand high temperatures. In a two transducer arrangement, two diaphragm faces are exposed to a common chamber including two membranes positioned on opposite sides of the port communicating with the chamber.

Signal processor for sound image enhancement

A signal processor for sound image enhancement of stereophonic signals provides fluctuating coherence between the left channel and right channel outputs by crossfeeding a high pass portion of the left channel to the right output and a like portion of the right channel to the left output. Preferably, the crossfeed path includes a high pass filter to eliminate crossfeeding of lower frequency range components which are often reproduced monaurally in prerecorded materials. The filtering is compensated for by a shelving filter introduced in the respective channel input to boost the power of the lower frequency components to be added with the crossfed signal to produce the channel output. In the preferred embodiment, an automatic gain control varies the gain of the crossfeed in accordance with the stereo content in the input channels. In addition, the gain control includes a control for user variation of the amount of coherence to be generated at the output. Furthermore, the present invention also provides a stereo detector circuit.

Tandem transducer magnet structure

An active muffler for use in motor vehicles comprises a sensor, an electronic control responsive to the signal generated by the sensor for producing a drive signal delivered to a transducer which emits cancellation pulses phased 180° from the sound pressure pulses passing through a conduit, where both front and rear sides of the transducer are acoustically coupled to the conduit to improve the efficiency of the transducer operation. Preferably, the acoustic coupling comprises an enclosed chamber including a port for communicating with the conduit which can be tuned to resonate at predetermined frequencies. When both sides of the transducer are so coupled to the conduit, the transducer has increased efficiency over a broad band of frequencies, and the frequency band can be broadened at the low end as required to accommodate the frequencies generated by a source of noise. A tandem transducer mounting arrangement according to the present invention reduces vibration of the housing while minimizing the mass and size of the transducers by juxtaposing or consolidating the magnet structure for a pair of transducer diaphragms. The system is particularly suitable for use in adapting noise cancellation techniques to replace or be combined with passive mufflers on motor vehicles.

Perception of microphone noise in hearing instruments

In a well-designed instrument the noise level is reduced until it is dominated by the front end noise. In a hearing instrument this is the microphone noise. This paper examines the perception of noise in a hearing instrument by both normal-hearing and hearing-impaired listeners. The noise levels are specified as input-referred values in one-third octave bands. Two sets of measurements, the just-objectionable level (JOL) and the just-audible level (JAL), were assessed in third octave bands from 250 to 5000 Hz. The data indicated that the use of a subjectively described acceptability of noise, JOL, is an unreliable measure due to a very large variability across listeners. It is recommended that mean values for the noise threshold level, the JAL, be used as a guide in the optimization of microphone noise design.

The finite element method in acoustics

From the variational field equations for problems in acoustics one can derive the finite element approach to their solution. From this approach the application of a standard finite element method (FEM) program to a problem in room acoustics was performed. The role of the acoustic variables, the material constants, boundary conditions, etc., as required for the FEM program was examined. The need for complex arithmetic in the analysis of a nonconservative system and in the modeling of real sources was shown. The FEM eigenvectors and eigenvalues were then used to assemble the Greens function in the form of a data base. This Greens function was then to be used to examine the acoustic behavior of the room at low frequencies, i.e., below the Schroeder frequency.

A simplified approach to a nonlinear loudspeaker modeling

Exact solutions of the nonlinear equations for a loudspeaker are extremely difficult to solve as they involve Volterra series expansions and higher‐order system functions and impulse responses [A. R. Kaiser et al., J. Audio Eng. Soc. 35, 421–433]. Indeed, these complex methods are required for exact system simulations, however, they can be greatly simplified with a reasonable assumption about the system. By assuming that the distortion (or nonlinearity) is not so large that it causes an excessive amount of distortion, say about 20% THD, a vastly simplified approach can be developed. It is not always the case that this near‐linear assumption can be made, but clearly, it should be accurate for higher performance units. This presentation will show how to use an algebra processor (Maple) to develop these simplified predictions given the nonlinearities of the parameters. These equations will then be used to show the effect that various loudspeaker enclosure designs have on the distortion of a given (typical) loudspeaker using a commercially available software package written by the author.Exact solutions of the nonlinear equations for a loudspeaker are extremely difficult to solve as they involve Volterra series expansions and higher‐order system functions and impulse responses [A. R. Kaiser et al., J. Audio Eng. Soc. 35, 421–433]. Indeed, these complex methods are required for exact system simulations, however, they can be greatly simplified with a reasonable assumption about the system. By assuming that the distortion (or nonlinearity) is not so large that it causes an excessive amount of distortion, say about 20% THD, a vastly simplified approach can be developed. It is not always the case that this near‐linear assumption can be made, but clearly, it should be accurate for higher performance units. This presentation will show how to use an algebra processor (Maple) to develop these simplified predictions given the nonlinearities of the parameters. These equations will then be used to show the effect that various loudspeaker enclosure designs have on the distortion of a given (typical) l...

Evaluation of the perception of input‐referred noise in hearing aids

Hearing‐aid circuitry noise has been a major complaint among hearing‐aid users, especially among those who have normal hearing at low‐frequencies. The purpose of this study is to examine the spectral distribution of the noise‐tolerance range for hearing‐impaired listeners. The primary purpose of this study is to determine the upper and lower fences of the permissible equivalent input noise (in dB SPL) of a hearing aid. First the audiometric threshold is evaluated, then the just‐audible noise level (JAL) and the just‐objectionable noise levels (JOL), measured in dB SPL at the eardrum, are determined in quiet using normal hearing and hearing impaired listeners. Given the audiometric threshold, various prescriptions can then be applied to obtain the target gain values. The JOL minus the prescribed gain values (Rx) and the JAL minus Rx represent the maximum input noise level an individual will tolerate and the just‐noticeable input noise level, respectively. These data will be useful as specifications of inpu...

Improvements in hearing aid transducers

Hearing aid transducers have been around for nearly 50 years and have reached a significant level of maturity. Recent improvements have been made primarily in the areas of robustness, size, and integration of subsystems. This presentation will describe several recent improvements in hearing aid transducers. The author will also discuss areas where future improvements are likely to be made. A discussion of the noise levels in microphones, which are felt to be a concern of the industry, will be made in an attempt to present a manufacturer’s view of this issue.