Per Hammer

Analysis of Sound Transmission Loss of Double-Leaf Walls in the Low-Frequency Range Using the Finite Element Method:

The sound transmission loss of double walls in the low-frequency range is studied by means of structure-acoustic finite element analysis. The analysis simulates standard experiments to determine sound transmission loss of walls. The model is a detailed description of the geometry of the system, including both the double wall and the rooms acoustically coupled to the wall. The frequency range studied is in the 1/3-octave bands between 40 Hz and 200 Hz. Aparametric study is performed to investigate the influence on the sound transmission loss of various material and geometric properties of the wall and the dimensions of the connecting rooms. The model confirms the importance of primary structural resonance and the size of the connecting rooms in determining the degree of sound transmission loss. The primary structural resonance is mainly determined by the distance between the wall studs and the properties of the sheeting material. Wall length is also important; if the length is such that the wall studs of the last wall cavity are closer together than those of the other wall cavities, the primary structural resonance will be at a higher frequency, thereby decreasing sound transmission loss over a broader frequency range. Similar dimensions of the connecting rooms results in poor transmission loss, mainly at frequencies below 100 Hz (for the wall and room dimensions studied here).

Prediction Models of Impact Sound Insulation on Timber Floor Structures; A Literature Survey

To develop new types of lightweight wall and floor structures it is important to increase the knowledge of the transmission and radiation processes for such structures. To do so, detailed models based on deterministic and statistical assumptions may form a valuable tool. In lightweight floor structures, impact sound insulation is perhaps the most important factor to consider. This paper gives an overview of various solution strategies that may be useful in finding a prediction model for impact sound insulation.

Measurement of the Acoustic Properties of Resilient, Statically Tensile Loaded Devices in Lightweight Structures

Resilient devices are commonly used in lightweight structures to decrease sound transmission in a broad frequency band. Applications of such devices may be found in e.g. resilient mounted ceilings in aeroplanes, ships and buildings. A measurement method to characterise the frequency dependency of the transfer stiffness and the input stiffness of the resilient device is presented. The mechanical characteristics of the measurement method are investigated. In addition, some resilient devices used in buildings are analysed with respect to acoustic properties. Parameters such as static load and mountings for the devices are considered and handled by means of statistical analysis.

Vibration isolation on light weight floor

A theoretical and experimental study of vibration isolation for a source on a lightweight floor structure is presented. The effectiveness of one-stage and two-stage isolator systems is studied. Approximate formulae are presented for both low and high frequency for the receiver, the floor structure. For the mobility, a comparison between approximate formulae, numerical exact results and experimental results are presented. The low frequency asymptote for the approximate mobility is valid up to l/λp ≈ 1/4. The high frequency asymptote is valid from l/λp ≈ 1/2. A straight line can be drawn between these two points for the intermediate range 1/4 < l/λp < 1/2. Finally, a case study is presented. A fan is mounted on a wooden joist floor. The effect of both one and two stage isolation is demonstrated. It is clearly seen that the high mobility situation for the receiver is increased by adding a rigid body to the mount. Hence, in the frequency range of interest, the ‘receiver’ acts more or less as a blocked termination. A two-stage isolator almost completely eliminates the structure borne sound and compared to a one-stage isolator it reduces the sound by 20 dB at the rpm for the fan.

On subjective impact sound insulation classes

The possibility to divide impact sound annoyance into classes is investigated. The experiments, based on human perception, are done in a laboratory environment where various floor structures have been included to produce impact noise. These tests are correlated to studies pertained to real‐life situations for tenants. The statistical tool to test the significant differences between the classes is Rou–Kupper. Real footsteps are used as a noise source. In addition, airborne sound insulation is treated in a similar manner, whereby one may conclude that there are some difficulties finding classes with statistical significant differences. [Work supported by the Swedish Council of Building Research.]

Evaluation of Drum Sound with ISO Tapping Machine

A branch norm, EPLF NORM 021029-3,1 has been established for measuring drum sound on laminate floor coverings. ‘Drum sound’ refers to the sound occurring when an object, e.g. a foot, strikes the flooring in the room in which the receiving ear is located. The norm evaluates the subjective perception of the drum sounds loudness using the ISO tapping machine. A round-robin study of the norm is reported along with the results of a paired comparison listening test using the same floor coverings. The article discusses general aspects of evaluation measures, tapping machines, test environments, etc., that need to be considered when measuring drum sound on various floor coverings, such as linoleum, wood parquet and laminate. It is concluded that loudness as measured according to ISO 532B correlates the best with the subjective perception of the drum sounds loudness. The tapping machine can be used to excite hard floor coverings to produce the drum sound, but should be used with caution in studying low-level drum sounds due to the tapping machines inherent mechanical noise.

Measurements and modeling of commonly used resilient channels in lightweight floor structures

A common part in lightweight floor structures is resilient channels between the joists and the ceiling. The purpose of the channels is to lower impact sound transmission in a broad frequency band. The channels are normally complicated to describe accurately from a structural acoustic point of view. The intention in this paper is to describe the channels by means of a simple structural acoustical model. The channels are divided into two types of elements. The first element is a beam. The second con‐stitutes the mounting of the channels to the joist. The two elements are treated and analyzed both separately and connected to each other. The measurements are done by mainly measuring the accelerations on stiff bodies on the top and bottom of the test sample. The procedure is then repeated with a new set of stiff bodies. From these measured values (four different) one can determine the global two‐port description. As a check there is also the reciprocity. As a comparison a method is used where the actual point ...