Research areas Building Acoustics

Summary

A model for the excitation, transmission and radiation of impact sound and finally an algorithm for auralisation of impact sound is developed. For it, methods and knowledge from airborne and impact sound transmission, signal processing, and psychoacoustics shall be used. This means that a user can listen, e.g., to the sound of a virtual walker in the room above. Parameters like type of walker (weight, velocity, shoes), floor construction and covering, etc., can be chosen and after a simulation, the sound in the receiving room can be listened to. A verification of the model has to be done by listening tests.

Background

Impact sound insulation is in many cases harder to determine than airborne sound insulation. This is due to dynamic interactions between exciting source (mostly the tapping machine) and the floor construction which is not given in airborne sound transmission. Problems occur with the determination of the insulation of light-weight floor constructions and floor coverings on different types of constructions. Furthermore, from the impact noise levels measured with a tapping machine, normally no parameter for the annoyance can be deduced. In the past, some improvements regarding the exciting sources have been made like the use of heavy weight sources (rubber ball/bang machine) or the modified tapping machine by Scholl. In this project, the force-time signal and the impedance of different sources are to be measured (walking persons, jumping children, falling toys, etc.) and a model for the calculation of the sound pressure signal at the ears of a listener in the receiving room is to be developed. The model should be based on typically available or easy to calculate quantities of the construction (impact sound level, impedance). As another important parameter, the type of receiving room has to be selected by the user.

Fig. : Bang machine in action

In the approach, a linear behaviour of the elements is assumed. This is truly not the case in the reality. So it has to be investigated if the effects of this and other simplifications are to be considered, i.e. if they are audible.

Fig. : Model for excitation and radiation of impact sound

The resulting auralisation tool is not only valuable for planning and development of buildings but also for scientific research, e.g. to investigate the annoyance of impact sound in listening tests. Sound samples can be generated very easily and the improvement in acoustical comfort due to floating floors or floor coverings can be evaluated quickly.

First step: Simplified auralisation

In a first step, a simple auralisation model is developed which does not consider the dynamic source-floor interaction. This is possible if the impedance of the floor is much higher than the source impedance. Force-time signals of the tapping machine, the modified tapping machine and a rubber ball were measured and different floor constructions were auralised. For this, the impact sound level of different floor constructions were calculated by a software (see here), the force spectrum of the tapping machine was removed and the force-time signal of the source to be auralised was inserted. A few examples can be listened to in the following.

Aerated concrete, Ln=99dB	Concrete, bare floor, Ln=76dB	Concrete, Additional layer of cement, Ln=60dB	Concrete, Additional Layer of chipboard, Ln=52dB
Tapping machine	Tapping machine	Tapping machine	Tapping machine
Modified tapping machine	Modified tapping machine	Modified tapping machine	Modified tapping machine
Rubber ball	Rubber ball	Rubber ball	Rubber ball

Table: Listening examples: different sources on different floor constructions. Soundfiles in MP3 format, size app. 110kB each.