Horns as particle velocity amplifiers

Abstract

Preliminary measurements and numerical predictions reveal that simple, and relatively small, horns generate remarkable amplification of acoustic particle velocity. For example, below 2 kHz, a 2.5 cm conical horn has a uniform velocity amplification ratio (throat-to-mouth) factor of approximately 3, or, in terms of a decibel level, 9.5 dB. It is shown that the velocity amplification factor depends on the horn's mouth-to-throat ratio as well as, though to a lesser degree, the horn's flare rate. A double horn configuration provides limited additional gain, approximately an increase of up to 25%.

Motion of a rigid prolate spheroid in a sound wave field

“…The velocity amplitude is directly proportional to the distance and therefore the maxima are certainly located at the two top points of the prolate spheroid, as revealed in Eq. (10). Figure 3(b) demonstrates that at very low frequencies (kL ( 1), the oblique incidence induced velocities at the top point (0, 0, L/2) shows less related to the geometry of the prolate spheroid, and the torsional motion is therefore very slight and could be ignored.…”

“…10 To approximate a homogeneous rigid body, prolate spheroidal solid model must be materialized in the finite element analysis with certain fictitious parameters, including Young's modulus (E ¼ 1e11 Pa), null Poisson's ratio, and varying densities.…”

Acoustic particle velocity horns

“…1, thus minimizing impedance at the throat. As noted in an initial analysis of the velocity horns, 7 an AVH works as a funnel, increasing particle velocity within the narrow throat, compared to the velocity at the wider mouth.…”

“…Here, as in Ref. 7, a conventional "acoustic pressure horn" is denoted APH, to distinguish from an "acoustic velocity horn" or AVH, where the purpose is to amplify oscillatory particle velocity. Unlike an APH, an AVH must be opened at the throat, as shown in Fig.…”

“…7 Here, an in-depth theoretical basis for particle velocity horn amplification is presented, and provides the necessary criteria for broadband frequency horn design.…”