DE20003666U1 - Helmholtz resonator - Google Patents

Description

Description:

Helmholtz resonator multi-stage

In technical sound insulation, Helmholtz resonators are used to reduce the sound level of noises with a constant frequency composition and are designed for the main interference frequency. A typical application example is fans running at a constant speed, whose main interference frequency is determined by the parameters speed and number of blades.

The Helmholtz resonator is known to work in a similar way to a spring-mass system, with the vibrating air column in the resonator tube acting as a mass and the compressible air in the Helmholtz volume acting as a spring. The damping effect is limited to the very narrow frequency range for which the Helmholtz system is designed. For noise sources where the main frequency changes noticeably during operation (e.g. a second fan speed, change in the medium temperature), the Helmholtz resonator is ineffective for the changed operating conditions.

According to the current state of the art, a remedy is to provide a second Helmholtz resonator in the overall acoustic system, which can attenuate the changed main frequency.

This entails considerable construction effort, especially in terms of volume requirements.

The invention set out in the protection claim is based on the problem of creating a Helmholtz resonator which is effective in more than one main frequency and thus meets the acoustic requirements with a low construction volume and weight.

This problem is solved with a Helmholtz volume that can be changed via a switching element or with a Helmholtz tube that can be changed via a switching element and has the features listed in the protection claim.

This allows a second main frequency to be attenuated by switching a Helmholtz volume on or off.

The switching element can also be used to change the effective pipe length or the connected pipe geometry.

With appropriate combination and series connection, this is possible for several main interference frequencies.

In general, the effectiveness of a Helmholtz resonator is enhanced by the invention.

The selection of the switching elements with regard to stress is largely uncritical, since they are not flowed through by the medium but are located relatively far away.

Embodiments of the invention are explained with reference to Figures 1 and 2. They show:

Figure 1 Schematic diagram of a Helmholtz resonator with switchable second volume

Figure 2 Schematic diagram of a Helmholtz resonator with switchable second tube length

List of reference symbols:

1 Helmholtz tube

2 Helmholtz volume

3 Switching element closed

4 Switching element open

5 Second volume

6 Second pipe length

Claims (5)

1. Helmholtz resonator for reducing the sound level of at least two different, independent, main frequencies, characterized in that a second volume can be coupled or decoupled by a switching element. 2. Helmholtz resonator for reducing the sound level of at least two different independent main frequencies, characterized in that the effective tube length can be varied by a switching element. 3. Helmholtz resonator for reducing the sound level of at least two different independent main frequencies, characterized in that the effective tube diameter can be varied by a switching element. 4. Helmholtz resonator according to claims 1-3, characterized in that combinations of the features listed therein can be switched by several switching elements. 5. Helmholtz resonator according to claims 1-3, characterized in that the individual elements (volume, tube) are connected several times in series.