“Very proactive and extremely helpful, especially with technical queries. I would not hesitate to recommend and will certainly be using them again in the future.”



Under CDM2015 regs we have found CASS ALLEN to exercise a level of professionalism and due diligence which is second to none. We would therefore definitely recommend CASS ALLEN as our preferred acoustic consultant, for all of our projects.’


SF - Taylor Wimpey South Thames

“I was very pleased with their technical knowledge and professional approach when dealing with a very awkward purchaser as well as the local authority.”


JH, Telford Homes

“Cass Allen went above and beyond to help with the Acoustic planning performance and conditions regarding the Greenwich Creekside project…”


LM, Capita plc

“Good comprehensive reports and advice at all design stages. Very flexible and professional, provided attendance at acoustic cladding tests at short notice.”


DF, Berkeley Homes

“Cass Allen have assisted us on a number of our projects. I’ve been impressed with their thorough and professional approach.”


MT, Lark Energy

Singing Buildings: Tonal Wind Induced Noise Caused by Façade Elements

Whenever a new development is built, it impacts the way in which wind moves through an area. This is not a consideration that you may immediately associate with acousticians, however, in tall buildings with certain types of façade elements, it can be a real acoustic problem.

Wind flow across any building will generate noise – this is due to turbulent airflow around the edges of the building. At higher wind speeds this is generally audible as a broadband or slightly tonal ‘wooshing’ sound. People are generally familiar and accustomed to this noise and therefore it is rarely considered to be a problem.

However, under certain conditions, wind can cause building elements to vibrate which can potentially generate high noise levels.

It is quite rare for this to be a problem, however, when it is, it can be quite dramatic. For example, listen to this video of the Beetham Tower in Manchester.

The weird ‘alien like’ sound that can be heard in the video is caused by the vibration of the ‘blades’ on the roof of the building. This vibration occurs at certain wind speeds and directions.

The phenomenon that causes the blades to vibrate is known as ‘vortex shedding’. Vortex shedding occurs when a fluid (e.g. air) passes over an object. Alternating low and high pressure vortices are created downstream of the object, which result in alternating lateral forces on the object. These alternating lateral forces cause the object to vibrate.

The speed of the air flow and the size and shape of the object will dictate the frequency of the vibration. If the frequency of the vibration is the same as the natural resonant frequency of the façade element, or if the wavelength of the vortex shedding frequency is equal to the spacing of repeating façade elements (e.g. solar shades), then extremely large resonances can occur. These large resonances are what generate the high noise levels.

To see what vortex shedding looks like, see this video.


This image shows vortex shedding behind a circular cylinder

Smaller façade elements tend to be most susceptible to tonal wind induced noise, such as architectural baguettes, solar shades, cables, small apertures etc. This is because the natural resonant frequency of these objects are more likely to be in the audible frequency range (20-20,000Hz).

There are general guidelines that can be followed to minimise the risk of vortex shedding problems in the design of new buildings:

  • Any circular façade elements with a diameter of less than 50mm should be avoided where possible.
  • Where small façade elements are required, ensure the façade elements are sufficiently damped and consider modifying the design of the façade elements to break up vortices (this can be achieved by adding fins or other design features designed to break up vortices).
  • If repeated façade elements form part of the development design, they should be spaced irregularly to avoid periodic vortices becoming established.

Testing and modelling can also be carried out to further assess whether any issues are likely to occur including:

a) Modelling the façade elements using Computational Fluid Dynamic (CFD) software or;

b) Conducting tests of the façade elements in a wind tunnel.

If you would like guidance relating to tonal wind induced noise or any other acoustic aspect of your project, please get in contact with us at mail@cassallen.co.uk and we would be happy to assist.

If you’ve found this article interesting, have a look at these other examples of vortex shedding occurring in various contexts; some of them are quite dramatic!

The fall of the Tacoma Bridge

Cloud formations around madeira

Lamp posts dancing on the M62

Aeolian Harp – an instrument that sings in the wind as a result of vortex shedding


Get in touch

We hope you’ve enjoyed browsing our website but if you have any questions feel free to call us to talk through any acoustic issues you may be facing on your projects. The best person who can help with specific queries can be found here.