A previous paper [Woodhouse et al., Acta Acustica 5, 15 (2021) https://doi.org/10.1051/aacus/2021009] showed acoustical measurements of an American 5-string banjo alongside similar measurements on a guitar, revealing a strong contrast in bridge admittance. Theoretical and numerical modelling is now presented to probe the physics behind this contrast. Without the bridge and strings, the banjo membrane has a rising trend of admittance associated with its modal density, and it has a distinctive pattern of sound radiation because an ideal membrane has no critical frequency. When the bridge and strings are added to the banjo, three formants shape the amplitude envelope of the admittance. One is associated with local effects of mass and stiffness near the bridge, and is sensitive to bridge mass and the break angle of the strings over the bridge. The other two formants are associated with dynamical behaviour of the bridge, analogous to the “bridge hill” in the violin.
Measurements of vibrational response of an American 5-string banjo and of the sounds of played notes on the instrument are presented, and contrasted with corresponding results for a steel-string guitar. A synthesis model, fine-tuned using information from the measurements, has been used to investigate what acoustical features are necessary to produce recognisable banjo-like sound, and to explore the perceptual salience of a wide range of design modifications. Recognisable banjo sound seems to depend on the pattern of decay rates of “string modes”, the loudness magnitude and profile, and a transient contribution to each played note from the “body modes”. A formant-like feature, peaking around 500–800 Hz on the banjo tested, is found to play a key role. At higher frequencies the dynamic behaviour of the bridge produces additional formant-like features, reminiscent of the “bridge hill” of the violin, and these also produce clear perceptual effects.
A physically-accurate time-domain model for a 2 plucked musical string is developed. The model in-3 corporates detailed dispersion and damping behaviour 4 measured from cello strings, and a detailed descrip-5 tion of body response measured from a cello body. 6 The resulting model is validated against measured 7 pizzicato notes using the same strings and cello, and 8 good accuracy is demonstrated. The model is devel-9 oped in a form that makes extension to the case of a 10 bowed string very straightforward.
In automotive industry, engine vibration isolation has been a challenging task, and given the emergence of new vehicles with more stringent performance characteristics, engine vibration isolation has become an even more demanding issue. Most engine mounts are passive — that is, their parameter values and characteristics are fixed — and as a result, they may not properly attenuate the complicated vibration transmitted from the engine. In this paper, the development of a new active mount is described. This paper describes modeling, development, and experimental analysis of an active engine mount, which is specifically designed to address the Variable Displacement Engine (VDE) isolation problem. An electromechanical actuator is fabricated and retrofitted inside the inertia track plate of a hydraulic engine mount. The plunger of the electromechanical actuator moves upon receiving the signal from the controller, and it changes the dynamic performance of the mount accordingly based on frequency, amplitude, and phase of the activation signal. Experimental results are presented for different control signals. Simulated and experimental results are compared to validate the mathematical model. The experimental results demonstrate the performance of the designed active engine mount to deal with complicated vibration patterns, specifically those created by VDEs.
This paper describes the design of a versatile and fully controllable active engine mount. The proposed active mount is capable of addressing vibration isolation requirements at various driving conditions. This design addresses a better ride quality that has always been demanded by the automotive industry, as well as satisfying sophisticated vibration isolation requirements for the unconventional engines, i.e. variable displacement, and hybrids. The proposed engine mount replaces the decoupler of the original design with a solenoid actuator. The mathematical model of the active mount is obtained. The dynamic characteristics of the mount are shown to be highly controllable over the operating frequency range of excitation in engines. The effectiveness of the developed active engine mount for various working conditions of engine is also evaluated. Several driving conditions are investigated and proper control strategies are utilized to demonstrate the mount's capability to fulfill the isolation requirements for each condition. The promising results, in addition to compactness, low cost, fail safety, and durability are the main advantages of the proposed active engine mount, which makes it viable for automotive applications.
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