Proper Amplification Research Articles

Amplification for hearing-impaired children: Basic considerations

The importance of the selection of proper amplification for the hearing impaired child is discussed including goals of amplification, specific methods of choosing amplification, and test procedures including speech audiometry. Evaluation controversies discussed include: monaural versus binaural amplification; body worn versus post auricular hearing aids; maximum output; and special hearing aid modifications.

His Bundle Recording in Acquired Conduction Disease

Scherlag and co-workers1introduced a simple technique for recording the electrical activity of the His bundle in the human heart. The technique consisted of passing an electrode catheter to the area of the tricuspid valve. With proper catheter positioning, amplification, and appropriate frequency filtering, the bundle of His potential could be reliably recorded. The His bundle catheter records an atrial, His bundle (H), and ventricular electrogram (Fig 1). Recording of H potentials allows subdivision of the PR interval into three subintervals. These are the following: PA, from the onset of the surface P wave to the onset of the low right atrial electrogram; AH, from the low right atrial electrogram to the onset of the first high frequency potential of the His bundle electrogram; and HV, from the H potential to the onset of surface QRS. The PA, AH, and HV intervals are, respectively, measures of intra-atrial (from high

A simple large-volume cell suitable for multiparameter measurements in the aminco-chance spectrophotometer

In order to better understand cellular and subcellular phenomena it is desirable to observe multiple parameters such as pH, various ion movements, optical density at various wavelengths, and kinetics of oxygen consumption. Instrumentation for the measurement of these kinds of parameters has been carefully described by Pressman (11, who used a rectangular cuvet with a plastic covrr fitted with an oxygen electrode, a I(+ electrode and a pH electrode. Fluorescence and light scattering measurements are made with the appropriate light sources and photomultipliers situated at the sides of the cuvet and after proper amplification the signals from these sensors are recorded simultaneously. In this communication we would like to describe a simple cuvet suitable for multiparameter measurements adapted for use with the spectrophotometer designed by Chance (2) and commercially available from the American Instrument Co. as a dual-wavelength split-beam spectrophotometer. Figure 1 shows the essential features of the cell, including the measurements which are critical for the positioning of the cell in the spectrophotometer. Since the cell is patterned after the Bl-65103 cuvet carrier, it fits without modification into the spect’rophotometer just as one would position the cell carriers which come as standard equipment with the instrument. This also ensures that t’he light beam will strike the cuvet properly. The entire cell was made from cast methyl methacrylate except the optical surfaces, viz., t’he two sides of the stirring chamber and one end which is used for fluorescence or light scattering measurements.

The Noise-Cancelling Headset—An Active Ear Defender

The purpose of this device is to reduce ambient noise at the ear by using a headset to generate a sound pressure equal in magnitude and opposite in phase to the noise. This paper reports the results of pure-tone experiments. A microphone was mounted on each earphone of a conventional military headset. A two-channel system was used in which the signal from each microphone was passed through an amplifier and a phase-shifting network and was then applied to its earphone. The subject wore the headset in a pure-tone field and adjusted the amplifications and phase shifts for minimum loudness. The signal produced by each earphone was then substantially equal in magnitude and opposite in phase to the sound coming through and under its earcap. The proper amplification and phase shift are frequency-dependent and vary among subjects. Eight complete measurements were made on two subjects. The mean values of the two parameters were computed for each frequency. Calculations indicate that a device having these mean characteristics would provide a noise reduction between 100 and 1200 cps that averages 10 db more than is provided by the earcap alone.