Impact Sound Transmission Research Articles

Responses of bowhead whales to sonobuoy impacts

Air-dropped sonobuoys have been used to record sounds near bowhead whales since 1979. They have not been observed to react to sonobuoys dropped 0.5–1 km from them during numerous studies conducted during the summer; however, on a few occasions they have reacted to sonobuoys air dropped near them during their spring and fall migrations. The sound from an AN/SSQ-57A sonobuoy impact was recorded at distance 800 m in water 90 m deep in the western Beaufort Sea. Hydrophone depths were 3 and 18 m. Analysis of the impact signature and sound transmission paths revealed two reflected paths: one with a single bottom reflection and the second with two bottom reflections. A third arrival, occurring later and very weak, was also noted. The presence of a strong, low-frequency sound source nearby led us to high-pass filter the signal at 1 kHz. Analysis of the received signal amplitude, corrected for spreading loss, revealed a peak source pressure level of 211 dB re: 1 μPa/m. The positive acoustic impulse at a distance of 1 m, assuming no positive pulse spreading and scaling the pressure for spherical spreading, is estimated to be 5.55 Pa/s. The overall sound duration of the single bottom bounce arrival was 0.9 ms. [Work supported by MMS.]

Simplified evaluation of flanking transmission based on the mean mass and mean area of flanking elements

Calculation of the flanking transmission of airborne sound energy in a building according to CEN proposals is rather complicated for the average construction engineer. One should aim at simplifying such calculation methods wherever possible with respect to the relatively simple building construction. This principle has been adopted in the draft of the EN standard CEN/ TC126/WG2, which presents the simplified method for establishing flanking transmission in the case of impact sound transmission. In this paper it is shown that this principle may also be applied to calculation of airborne sound transmission. The known relationship between the weighted sound reduction index R w and the junction velocity level difference D vij (or the junction transmission index K ij ) in relation to the surface mass of the separating and flanking elements enables a simplified method for determining the flanking transmission in a building. The relevant calculations have been conducted on the basis of the CEN prediction model (CEN/TC126/WG2 N111 Draft-ENxyz, Building acoustics — estimation of acoustic performance of buildings from the performance products, part 1: airborne sound insulation between rooms. 1993; Gerretsen, E., Calculation of airborne and impact sound insulation between dwellings. Applied Acoustics, 19 (1986) 245–264) and the method used in Poland (Gösele, K. Berechnung der Luftschalldämmung in Massivbauten unter Berücksichtigung der Schall-Längsleitung. Bauphysik, 3 (1984) 79–84, Bauphysik, 4 (1984) 121–126; Szudrowicz, B., Podstawy Kształtowania izolacyjności a Kustycznej pomieszczén w budyn Kach mieszkalnych. Edition ITB; Warsaw, 1992 (in Polish)).

L. Cremer’s contributions to sound transmission through and within structures

Professor L. Cremer was avidly interested in the transmission of sound through walls as part of his practice in architectural acoustics. The frequent use of masonry constructions for partitions and exterior facades in Europe, and their documented departure from ‘‘mass law’’ sound transmission performance led him to study this phenomenon in detail. He first identified what we now call the wave-coincidence effect (i.e., the matching of sound wavelengths in the surrounding fluid with the flexural wavelengths in the panel) as the mechanism which produced the non-mass-law performance in the 1940s. This work influenced London, Beranek, Watters, and Feshback in this country, leading to our present understanding of this phenomenon. His later work in impact sound transmission for masonry floors, and the transmission of flexural waves through wall junctions for flanking transmission also had a pioneering quality. Cremer systematically and significantly altered our understanding of sound propagation in buildings and other structures. This paper will review these several pioneering investigations to help us appreciate this giant of our field, on whose shoulders we all stand.

Sound transmission through wood joist floor/ceiling systems: A study of the effects of sound absorbing materials and changes to the ceiling structure

A wood joist floor system was constructed in the Acoustics Laboratory at NRC. Measurements of airborne and impact sound transmission were made for different types and amounts of sound absorbing material in the cavity. Differences between materials were small. Different makes of resilient metal channels were installed; all gave about the same results. Methods of improving an unsatisfactory floor were examined. Over 20 floor systems were measured. The study was funded by Canada Mortgage and Housing Corporation. Measurements were made down to 63 Hz and revealed that in many cases there are resonances occurring below 125 Hz that have a strong influence on transmission loss values at and above 125 Hz. While the causes of the resonances are not always clear, measurements to these low frequencies give a clearer picture of the effect of changes to the structure. This paper will give a summary of the results obtained.

Method for Measurement of Impact Sound Transmission through Floor and related Standards-The State-of-arts

Method for Measurement of Impact Sound Transmission through Floor and related Standards-The State-of-arts

Comparison of impact noise transmission using experimental impactors

Preliminary experience with the modified tapping machine proposed by Schultz was described at the 96th meeting of the Acoustical Society of America. Since that time the impact sound transmission through more than twenty floor systems has been measured using the standard ISO tapping machine, the machine proposed by Schultz, an experimental system, and two live walkers. Although the system suggested by Schultz is an improvement over the ISO machine it appears to have an impact velocity that is too high. The experimental NRC hammer with a lower impact velocity and added mass and compliance gives data that correlate better with the live walker results. Some development work remains to be done but these initial results are promising.

On Ranking the Impact Sound Transmission of Wood-Framed Floor-Ceiling Assemblies

A masking procedure has been developed to rank apartment floor-ceiling systems in order of their resistance to the transmitted sound of footfalls. Results obtained subjectively show that the current international standard for rating impact noise transmission using a tapping machine incorrectly ranks some wood-framed floor-ceiling systems. When the described procedure is used to mask tapping machine noise, the floors are also incorrectly ranked. This inadequacy continued even though low frequencies, below the 89-Hz cutoff of the 100-Hz 13 octave, were included in the masking procedure. Because the masking procedure described is subjective, the problems associated with the development of an objective test are also discussed. A simple objective test method is suggested for future development.

Ranking the impact sound transmission of wood-framed floor-ceiling assemblies

A masking procedure has been developed to rank apartment floor-ceiling systems in order of their resistance to the transmitted sound of footfalls. Results obtained subjectively show that the current international standard for rating impact noise transmission using a tapping machine incorrectly ranks some wood-framed floor-ceiling systems. When the described procedure is used to mask tapping machine noise, the floors are also incorrectly ranked. This inadequacy continued even though low frequencies, below the 89-Hz cutoff of the 100-Hz 1/3 octave, were included in the masking procedure. Because the masking procedure described is subjective, the problems associated with the development of an objective test are also discussed. A simple objective test method is suggested for future development.

How to assess the sound-reducing properties of floors to impact noise (footsteps)

After reviewing recent studies where it is assumed that noise resulting from the footsteps of adults, mainly women wearing high-heeled shoes, is the determinant criteria for classifying the impact-sound transmission of a floor, the author discusses the principal studies on the subject and the modifications proposed for an improvement of the ISO method.

Relation between the Normalized Impact Sound Level and Sound Transmission Loss

An expression relating the normalized impact sound level (Ln) and the sound transmission loss (TL) of a floor is derived. It takes into account both the resonant and the forced response of the floor, thus extending the utility of the formulas derived previously by Heckl and Rathe into the frequency range below the critical frequency. This relation between normalized impact sound level and sound transmission loss permits an experimental evaluation of the potential TL of a floor partition in the presence of certain types of flanking.

Connection Between the Impact Noise Level and Sound Transmission Loss

Based on the results presented in the preceding paper, an expression connecting the impact-noise level (Ln) and sound transmission loss (TL) of a floor is derived that takes into account both the resonant and the forced response of the floor; it thus extends the utility of the formulas derived previously by Heckl and Rathe into the frequency range below the critical frequency. It is shown how this connection between impact-noise level and sound TL can be used for the experimental evaluation of the potential TL of a floating floor in the presence of certain types of flanking.

Measurements of the Sound Absorption Coefficient and the Sound Transmission Loss at the Kobayasi Institute of Physical Research

During the past three years, five reverberation chambers were constructed in our institute. These chambers are now used for the measurements of the sound absorption coefficient and the transmission loss. Chamber No. 1 has a volume of 513 m3 surrounded by nonparallel walls, and the reverberation time of this chamber is greater than 20 sec at 500 cps. In this chamber, the position of the microphone and test specimens does not affect the absorption coefficient. Chambers No. 3 and No. 4, which are used for transmission loss measurements, have a volume of 164 m3, respectively. The shape of these chambers is similar to chamber No. 1. The opening between these two chambers is 3.3 m by 3.3 m. Under chamber No. 4, there is chamber No. 5, which is used for the receiving room for impact sound transmission loss measurements.

The New Reverberation Chambers for the Measurements of Airborne and Impact Sound Transmission

The New Reverberation Chambers for the Measurements of Airborne and Impact Sound Transmission

Field Testing for Sound Transmission

Accurate sound transmission tests in the field have been made with portable equipment which will be described. A method of test of STL using recorded half octaves of broad band noise has been found to agree with the more conventional laboratory tests. Simple methods will also be given for tracing vibration-borne sound energy and measuring impact sound transmission. Emphasis has been placed on convenience and portability without sacrificing accuracy. Examples will be given from a large number of field experiences.

The Measuring of Impact Sound Transmission through Floors

The Measuring of Impact Sound Transmission through Floors