This paper presents a high-order, lumped parameter, jet-dynamic model for laminar proportional amplifiers (LPA’s). The governing equations for the lumped-parameter representation of the flow regimes found in the input of an LPA are derived in the Laplace domain, and an equivalent electrical circuit is obtained. The input governs the overall response of the LPA and may be modeled in its simplest form by five reactive components. The transmission of the signal from input to output is delayed by a transport time (determined by observation of flow visualization of a step response) equal to twice the average particle transit time. A pressure difference is then developed at the splitter that is proportional to the loading and the vent conditions. This signal is acoustically fed back to the control region of the jet, augmenting jet deflection when in phase. The vent inductance is found to have a significant influence on the low-frequency gain. Resonant regions determined by this model correspond closely to edgetone eigenfrequencies reported in the literature. Experimental data have shown good agreement with theory for the amplitude frequency response of LPA’s and excellent agreement for the phase shift. An engineering guide developed for the bandpass characteristics of LPA’s indicates that operating bandwidths of up to 14 kHz can be expected for amplifiers with a nozzle width of 0.25 mm, and ultrasonic operation appears feasible with devices having nozzle widths as large as 0.1 mm.
An acousto-fluidic sound augmentation system has been developed which provides adequate sound coverage in worship spaces accommodating as many as 1600 persons. Because of the unique religious restrictions of Orthodox Judaism, use of electricity and sound reproduction per se are prohibited while sound augmentation is permissible as long as the original sound is preserved and no apparent sound amplification occurs. A kosher sound system has been built and tested with essentially 0-dB sound-level gain but about 50 dB of power gain when operating with a 10-psi air source. The system frequency response is flat from 700–3500 Hz, and cuts off at 200 and 6000 Hz, respectively. A single-channel output comprises two 180° out-of-phase ElectroVoice HB640 horns. The monaural sound quality is good enough for recognition of the speaker’s voice with good reproduction of sufficient overtones to render singing pleasant. Sounds can be transmitted up to 25 m through 5-cm-diam PVC pipes thereby allowing speakers to be placed far enough away from the inputs to ensure good aural reception at the furthest reaches of worship spaces. The inherent acoustic delay obviates the need for the introduction of artificial delays and consequently results in very natural sound propagation and rendition.
This paper presents a computer aided procedure for the design of laminar proportional fluid amplifiers and gain blocks. The procedure is based upon a fundamental analysis of the flow regimes in an amplifier. With the aid of a computer, amplifier static and dynamic characteristics, required in control system design, may be determined as a function of geometry and fluid properties. The procedure is illustrated and evaluated by comparison of predicted design and experimentally measured performance. The procedure has been applied to individual elements designed by three different organizations, multistage gain blocks, and laminar jet rate sensor preamplifiers. The results of the procedure are shown to be quite accurate over a wide range of amplifier geometries (eleven different amplifiers with aspect ratio from 0.25 to 3 – a range of 12 to 1 – and nozzle sizes from 0.5 to 10 mm) and operating fluids (both air and oil). Experimental measurements were within 10 percent of the design predictions for amplifier gains, operating resistances, and bandwidth for all examples investigated.
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