Machine acoustics

Overview and introduction

Work conversion processes convert energy from machines into dynamic forces that cause the machine structure to vibrate. These vibrations (structure-borne sound) are transmitted to the air via the machine surface and are converted into airborne sound. If this air vibration is sufficiently large, we perceive it as noise. In the case of a very high intensity, this can even be a noise that is harmful to human ears.

Furthermore, large vibrations can damage the machine structure in the long term. It is therefore necessary to identify the causes of unwanted noise through noise measurements and derive measures to reduce it. We are happy to support you in this.

Origin and elimination of unwanted noise

The field of machine acoustics deals with the sound caused by machines. If this sound increases in volume, unpleasant noise is created. The focus is therefore often on reducing or modifying them. In order to gain an understanding of the possibilities for change, it is first important to understand the starting point. For this reason, the origin of one of these noises is explained in more detail in the following section.

Origin

First of all, a mechanical process is required to convert the energy. This often involves converting electrical energy into dynamic forces or torques. This is the case, for example, with an electric motor in a metal-cutting machine. Multiple conversions can also occur within a machine. The electric motor drives the tool, but the interaction between the tool and the workpiece also generates forces (cutting forces). For this reason, various location-dependent dynamic forces act inside the machine structure. It can therefore be stated that the dynamic behavior inside the machine is superimposed with working forces.

Consequences

The internal dynamic forces also cause the surface of the machine to vibrate. As soon as this occurs, the vibration is also transferred to the air surrounding the machine. In concrete terms, this means that the air is pressed and compressed, which in turn can lead to a dynamic air pressure fluctuation that spreads throughout the room. If this air pressure fluctuation is sufficiently large and at an audible frequency, we perceive it as a sound. The intensity and tone of the sound are in turn directly dependent on the amplitude and frequency of the air pressure fluctuation. The following illustration shows the described generation mechanism graphically.

Solution

Along this acoustic chain of origin, machine acoustics takes the approach of eliminating the noise as early as possible. Ideally, in such a way that the disturbing noise does not arise in the first place.

Nevertheless, it may be the case that no sensible or economical solution can be found for a machine that eliminates the source of a noise. In such cases, passive elements are used to reduce or absorb the resulting noise. A typical example of this is the noise barrier in road traffic.

In which production stages are machine acoustic analyses used?

Machine acoustic analyses are used in various phases of the product life cycle of machines. HoloMetrix GmbH offers you its experience and services for noise reduction in every phase. The following list presents a few typical use cases in the most important phases where we are happy to support you:

Software Development

At this stage, it may be of interest to record the actual acoustic condition. Acoustic measurements are used for this purpose. Typical questions that are asked in this context are Is the target being achieved? Are further acoustic measures necessary? Such measurements can be supplemented by benchmarking (comparative measurements). Furthermore, identification measurements also play a decisive role in detecting acoustic problem zones.

Production

Im Produktionsstadium dienen akustische Messungen häufig der Qualitätssicherung. Hierbei bedarf es einem genau definierten Messprozedere, sodass die Ergebnisse auch zu einem späteren Zeitpunkt vergleichbar und ,,kontrollierbar” bleiben. Durch eine Aktualisierungsmessung können die gewonnen akustischen Ergebnisse in die Entwicklung, speziell in die Berechnungsabteilungen einfließen. Dies dient dazu, zukünftige Vorhersagen noch zielgenauer zu gestalten.

Application phase

Particularly in the case of larger stationary systems, which may also represent a larger investment, the acoustic properties should not change significantly over the operating time. Supplementary measurements and their comparison with previous measurement results are therefore also useful at this point. Furthermore, acoustic measurements and their subsequent FFT analysis allow potential weak points to be identified and rectified at an early stage.

The field of machine acoustics is very comprehensive and versatile. We are happy to offer you specific advice for your project.

Our services

  • Determination of the current acoustic status of your machine acoustic system
    through the metrological determination of relevant emissions
    (e.g. sound power) 
  • Comparative measurement (benchmarking) for the acoustic optimization of products in the development stage 
  • Identifiying of the causes of unwanted noise by localizing the dominant sound sources
  • Derivation of technical and economically viable measures for noise reduction
  • Determination of transmission paths
  • Frequency and third-octave band analyses