Why does the Beetham Tower hum?

With storms predicted over much of England tonight, I wonder if the Beetham Tower in Manchester will put on another howling performance? This is my recording of the last time the Hilton hummed in 2012:


Simon Jackson (@stjackson), of the acoustic-consulting firm Arup, tweeted, “Quick sound level measurement at Beetham Tower – 78dBLaeq,1s main freq in 250Hz 3rd/oct band”. Simon later told me this was from about 100 metres away. No wonder people complain, that is similar volume to hearing a performance from a nearby tenor saxophone. Although given the way the hum starts and stops as the wind picks up and slows down, producing a single note which varies slowly in loudness, people more often liken the sound to an alien space ship coming into land.

The glass blade that causes the hum

The glass blade that causes the hum [1]

The problem is caused by the glass and metal sculpture at the top of the building. When the wind rushes past the edge of the glass panes turbulence is created. This is very similar to how turbulence generates sound within a recorder. Inside the recorder there is an edge called the fipple, which breaks up the air flow when a musician blows into the mouthpiece.

Turbulence generation by a recorder fipple

Turbulence generation by a recorder fipple [2]

On its own, the turbulence from an edge doesn’t create very much noise, and both the recorder and the Beetham Tower need a way of amplifying the sound. In the recorder this is done via the resonance of the air in the tube. For the Beetham Tower, I suspect it is the resonance of the air between the deep glass panes which allows the hum to achieve such loud decibel values.

How to solve the hum?

You either need to stop the turbulence being generated, or reduce the resonant amplification. This sounds simple, but this sort of noise problem is notoriously difficult to solve. [3] Work has already been done to reduce turbulence, most recently by connecting 1800 aluminum profiles to the glass panes. These reduced the turbulence but the building still hums at very high wind speeds. To stop that humming, maybe the next thing to tackle is the resonance. This could be reduced by altering or removing some of  the glass panes, as was done in for other whistling towers. [3]

Notes

[1] http://www.ropetask.com/index.php/case-studies/beetham-tower/

[2] http://course1.winona.edu/fotto/music/Notes/Day20.html

[3] “Buildings that whistle in the wind”. New Scientist Tech. 4 August 2006.

About these ads

3 responses to “Why does the Beetham Tower hum?

  1. Hello again Trevor, thanks for posting this, first time I’ve seen it set out in plain English.

    I live nearer @AngryBeetham now and on Wednesday night it was quite insane, I thought it was howling through my roof. Hard to explain that even inside my flat it was less of a “hum” and more of a “Martian-death-machine-from-Geoff-Wayne’s-War-of-the-Worlds”.

    Very glad the wind just dropped at half-7…

  2. Pingback: Beetham Tower HUMMMMMMMMM | The Pirate Party in Manchester

  3. Thank you for the interesting article Trevor. I wonder could the humming have been predicted before the building was completed?

    The humming on Wednesday was the loudest I’ve heard, particularly in Piccadilly Gardens. Would the sound be loudest in the flat at the top of the tower or would it be louder downwind?

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s