Motoki Yairi

Sound radiation from a double-leaf elastic plate with a point force excitation: effect of an interior panel on the structure-borne sound radiation

Abstract The sound radiation from a double-leaf elastic plate subjected to a point force excitation is investigated theoretically, to gain a fundamental insight into the sound radiation from an interior panel of a double-leaf structure in buildings. The effects of the interior panel on the sound radiation, which show a negative effect at low frequencies due to the mass–air–mass resonance, are discussed in detail. The theory is validated experimentally. As a measure of the efficiency of the interior leaf in reducing noise radiation, the radiation reduction is defined in this study, and it is found useful for predicting the sound radiation due to the structure-borne sound in building elements. Parametric studies through theoretical results are made to clarify the effects of the parameters of the sound radiation system, and to gain a fundamental insight into the control of structure-borne noise radiation. It is shown that it is difficult to reduce the radiated sound power by an interior panel alone, even if its mass is increased.

Role of pinna cavities in median plane localization

This paper investigates the role of pinna cavities in median plane localization. First, sound image localization tests were carried out under the conditions of progressively occluding three pinna cavities: scapha, fossa, and concha. Second, HRTFs were measured under the same conditions as those of the localization tests. Finally, the results of the localization tests and those of HRTFs measurements were compared. The results of the localization tests and the HRTFs measurements show: (1) Concha plays a great role in median plane localization regardless of the source elevation. (2) The amplitude spectrum of HRTFs shows a significant change in cases of concha occlusion. The comparisons of these results suggest that (3) the spectral cue in median plane localization is mainly formed by concha. (4) However, the degree of localization error which was caused by the occlusion of the pinna cavities depends on the subjects.

Effect of acoustical damping with a porous absorptive layer in the cavity to reduce the structure-borne sound radiation from a double-leaf structure

Abstract Structure-borne sound radiation from a double-leaf structure with a porous absorptive layer in the cavity is studied theoretically as well as experimentally. The study is for establishing a countermeasure to reduce the structure-borne noise radiated from an interior leaf into rooms and for clarifying its reduction effect. The sound field radiated from a double-leaf elastic plate with layers of arbitrary media in the cavity set into vibration by a point force excitation is theoretically analyzed. The effect of the bulk vibration of an absorptive layer is also considered by a simple model into the present theory. Radiation reduction of an inner-layer derived from the theory is experimentally validated. Parametric studies reveal that increasing the ratio of an absorptive layer thickness to the cavity depth is effective to reduce the structure-borne sound radiation but high flow resistivity of the absorbent material is not necessarily required. A practical equation to predict the mass–air–mass resonance frequency for absorbent cavity case is given in a simple form.

An experimental study on a cylindrical microperforated panel space sound absorber

A microperforated panel (MPP), which is widely known as one of the most promising alternatives of the next-generation sound absorbers, is typically used with a rigid-back wall with an air-cavity. However, a multiple-leaf MPP space absorber, which does not have any backing structure, double-leaf MPP space absorber (DLMPP) and triple-leaf MPP space absorber (TLMPP) is proposed. However, these are panel-like structure which are limited to where they can be used. In order to develop an MPP space absorber that can be used in more various situations, a trial production of a cylindrical MPP space sound absorber (CMSA) is made with an MPP shaped into a cylindrical. The sound absorption characteristics of a CMSA are measured in a reverberation chamber. As a result, although the absorption coefficient is not very high, a CMSA shows sound absorption characteristics similar to a DLMPP and TLMPP: a resonance peak by a Helmholtz resonator and an additional low frequency absorption by its acoustic permeability appear. The results suggest that a CMSA can be used as a space sound absorber in practical situations

Effect of a honeycomb on the absorption characteristics of double-leaf microperforated panel (MPP) space sound absorbers

Sound absorbers using a microperforated panel (MPP) is usually not strong enough for room interior surfaces because MPPs are in general very thin. In order to solve this weakness, the authors proposed to use a honeycomb attached behind an MPP in the air-back cavity. In the authors previous studies a honeycomb is effective to improve the sound absorption performance of an ordinary wall-backed single-leaf MPP sound absorber. The honeycomb can also be applied to a space sound absorbing structures such as a double-leaf MPP space absorber (DLMPP). In this study, the effect of a honeycomb in the air-cavity on the sound absorption characteristics of a DLMPP is theoretically analysed. In the theory a Helmholtz-Kirchhoff integral formulation is utilised. The theory is validated with experimental results. The effect of the honeycomb on the sound absorption characteristics is discussed through the numerical examples calculated by the present theory. The results show that the honeycomb enhances the resonance peak and shifts it to lower freqeuencies. Although the honeycomb is effective to improve the sound absorption performance of a DLMPP at around resonance peak, it does not affect the additional low frequency absorption which is particular to a DLMPP

Sound absorption characteristics of a honeycomb‐backed microperforated panel (MPP) absorber

Microperforated panels (MPPs) are typically made of a thin metal or plastic panel and are often unsuitable for an interior finish because thin limp panels do not have enough strength. In particular, an interior finish of room walls requires appropriate strength. In order to solve this problem, a honeycomb structure is attached behind MPPs to stiffen the construction. Thus, it is possible to stiffen an MPP without increasing its thickness, which is important to keep MPPs at their best absorption performance. Furthermore, a honeycomb can increase MPPs’ absorption coefficient in a similar way as a porous layer backed by a honeycomb. In this study, an experiment was performed to gain insight into the acoustical effect of a honeycomb structure behind MPPs and a simple theoretical model to interpret the experimental effects is presented. The experimental results show that the honeycomb affects the absorption characteristics of MPPs: the absorption peak increases and shifts to lower frequencies. This effect beco...

On the Relationship between the Normal Incidence Airborne Sound-excited and the Structurally-excited Sound Radiation from a Wall: A Theoretical Trial with Simplified Models

Sound transmission and sound radiation by force excitation of a plate are both basic and important problems in acoustics. Both the sound transmission and force excited sound radiation are basically the same phenomena, i.e., sound radiation from a vibrating plate, and the difference is the type of the excitation force, i.e., surrounding sound field or mechanical force. However, their relationship has not been explicitly discussed. If the relationship is known, it should be useful for comprehensive understanding of those phenomena, and to gain insight into relevant problems. In this study, simplified theoretical analyses to find a possibility to obtain a relationship between the sound transmission and force-excited sound radiation of a sigle-leaf plate of infinite extent are carried out with simplified models. As a result, it is suggested that there is a conversion factor which relates the sound transmission and force-excited sound radiation, and its behavior is discussed through numerical examples. Even though the present analyses are approximated and simple, this result suggests that there is a possibility, with further sophisticated studies, for practical applications.

Effect of honeycomb structure in the back cavity on the absorption characteristics of microperforated panel absorbers

Since the principle of microperforated panel absorbers (MPPs) was established, many studies have been made on their practical applications. MPPs are typically made of very thin metal or plastic panels to obtain high absorption. However, such a thin, limp panel is in many cases not suitable for an interior finish of room walls because of its insufficient strength. The authors have proposed to use a honeycomb structure attached behind an MPP to stiffen it without deteriorating its acoustical performance. The honeycomb behind an MPP can also be expected to enhance its absorption performance, considering previous studies on porous sound‐absorbing layers with the back cavity completely partitioned by a honeycomb structure. In this paper, the effect of honeycomb structure in the back cavity on the absorption coefficient of MPP was experimentally studied. The results suggest that the reverberation sound absorption characteristics become close to those of an MPP without a honeycomb structure for normal incidence....

Effect of the mass-spring resonance of a slab covered with carpets on the sound insulation performance

It is well known that the overall sound insulation performance between two adjacent rooms in actual buildings is not so much increased even if a high spec wall is used for the partition because of several flanking sound transmission paths. In recent years, the phenomena that a slab covered with carpets increases the sound transmission through the floor have been found. This is caused by the resonance with the mass of the carpets and the spring of those underlying materials, and consequently the sound insulation performance significantly decreases in the mid-low frequency range. The resonance frequency can be shifted to higher frequencies using formed plastic sheets of higher stiffness for the underlying materials. Although this would usually be one of countermeasures to increase the overall sound insulation performance, it is not a fundamental solution for noise control engineering. In the present work, in order to control the mass-spring resonance itself, a method of focusing on permeability of the carpe...

Relationship between sound radiation from sound-induced and force-excited vibration: Analysis using an infinite elastic plate model.

Although sound radiation from sound-induced vibration and from force-excited vibration of solid structures are similar phenomena in terms of radiating from vibrating structures, the general relationship between them has not been explicitly studied to date. In particular, airborne sound transmission through walls and sound radiation from structurally vibrating surfaces in buildings are treated as different issues in architectural acoustics. In this paper, a fundamental relationship is elucidated through the use of a simple model. The transmission coefficient for random-incidence sound and the radiated sound power under point force excitation of an infinite elastic plate are both analyzed. Exact and approximate solutions are derived for the two problems, and the relationship between them is theoretically discussed. A conversion function that relates the transmission coefficient and radiated sound power is obtained in a simple closed form through the approximate solutions. The exact solutions are also related by the same conversion function. It is composed of the specific impedance and the wavenumber, and is independent of any elastic plate parameters. The sound radiation due to random-incidence sound and point force excitation are similar phenomena, and the only difference is the gradient of those characteristics with respect to the frequency.