Noise, is incredibly tricky to communicate without hearing it. Here is a short guide to get to grips with what noise is, how it is measured, and more importantly how it is perceived. The tool at the end is built around the TWT-11 and its estimated acoustic emissions, if you just want the estimate go ahead and skip to the bottom of this page, the next section will get a bit technical! 

The technical bit, first thing to grasp here is that the measurements are done in decibel denoted dB. Decibel means 1/10 of a bel (B). dB is great when you want to describe differences in power or root-power ratios.

Why is this important? Well as it expresses a ratio we can use it to understand how loud one thing is compared to another. With a little math we can calculate that a 50% reduction in energy equates to a 3 dB drop.

Example: 80 dB(A) compared to 77 dB(A) is twice the energy (this is a simplification, exact numerical difference is a little higher). For now just remember a 3 dB drop is a 50% energy reduction, and a 3 dB increase is 2x the energy.

This becomes a bit harder to understand as you need to know how energy relates to sound pressure. Here a change in 6 dB is a doubling of the sound pressure (which is 4x the energy) 

For something to sound approximately twice as loud a change in 10 dB is needed. 

What is the A then? In order for dB to make sense when we are talking about human perception it needs a little tweak. The "A" is one way of applying weights to frequencies within the audible band. Human hearing is way better at picking up mid range frequencies than deep bass and high frequencies, the A handles this translation for us making the number align better with the sound pressure we as humans experience. 

When we are talking about noise in the relation to the TWT-11 wind turbine we need to keep a few things in mind.

1. Sound Power Level:  Acoustic energy that a machine emits. Denoted dB L_WA, the A here refers to A-weighting as well
2. Sound Pressure: What you would hear/feel at a certain distance to the machine, measured in dB(A)

Sound power level is a smart way of summing all acoustic output from a machine, it makes it easy to compare two machines to each other without having other information.

Sound pressure can be calculated from sound power level if you have knowledge of distance to the source and the surrounding environment. Under normal circumstances this allows us to translate the acoustic output of 83 dB L_WA to a given sound pressure in dB(A) at a given distance from the turbine. 

In the TWT-11's case this means that the calculated sound pressure at the base of the tower is 53 dB(A), and 25 meters away is just 47 dB(A). In more everyday terms 53 dB(A) is similar to normal listening levels in front of a TV-set and 47 dB(A) is a quite office environment. 

Another thing to note is that every time you double the distance you drop the noise by 6 dB, a handy heuristic when it comes to selecting installation spots. 

We are currently providing estimates of the TWT-11 as the final measurements are a part of the final IEC 61400-2 type approval. 

Try our noise simulator below!