Noise and Vibration Consultants
A noise and vibration engineering project
So many of our projects involve both noise and vibration, so as noise and vibration consultants and engineers, we are able to attend to both by finding the cause and resolving the problem.
As mechanical engineers, we then specify mitigation, design the mitigation device or system, manufacture, install and prove that the mitgation is effective.
Here is a noise and vibration engineering project that we completed in Belgium last year.
The penthouse at the top of Residentie 21, a 20 storey buidling in Koksijde, Belgium was experiencing a vibration noise. This noise was audible at night only - when the background sound level was low enough to hear the vibration sound. Unfortunately, this was most audible in the children's bedroom and kept them awake at night.
Once this was observed, the owners demanded that the telecomunications tower be switched off altogether, making the tower obsolete.
Vibration source
We decided to approach this noise and vibration engineering project by measuring the sound of the noise around the roof installation.
Once we were on the roof, an audible vibration sound was present, and the grid on which we walked was vibrating and felt underfoot.
The source itself was in the white canopy (image). The source excited the walkway grid, and the vibration travelled along the metal structure, that spanned the width of the building, and along the supporting walls as structure borne sound, which then radiated from the walls in the children's bedroom.
What we had to prove, was that the audible vibration sound in the bedroom originated from this canopy.
Noise and vibration analysis
We analysed the sound recorded in the bedroom and on the roof to get this FFT.
In this FFT (image) there are several sound traces. The top trace is the FFT of the sound recorded on the roof of the buidling, and the other were recorded in the rooms in the penthouse.
The FFTs of the room recordings included background noise from outside and the vibration noise radiated off the walls in the room, which were not audible to the human ear at the time of the recordings.
In the FFT trace, it is evident that the FFTs taken in the room overlay each other near exactly at approximately 58Hz. So the vibration in the room stayed constant while the background sound was random.
These results were proof that the vibration on the roof was the cause of the vibration and structure-borne sound in the rooms. We also determined that the vibration source frequency was 58.33Hz
The noise and vibration solution
The solution, an isolation system, had to be designed to fit in the same space as the rigid mounts, which was challenging.
The equipment from which the vibration originated was mounted on isolation mounts or anti-vibration mounts made of rubber to isoalte the vibration fro mthe main structure.
A sound measurement was taken after the installation and no peak was visible in the FFT, and no vibration was felt underfoot when standing on the walkway grid; therefore, the problem was solved
Do you require noise and vibration consultants?
If you have a noise and vibration engineering problem, please call us on 01908 643433, as we can help you.