The Sound of the Big Bang … And Other Matters Of Interest …
We have previously touched upon the Decibel scale and how it works, and mentioned the loudest sound ever recorded – that being the volcanic eruption on Krakatoa in 1883! That has led us to research the loudest sound POSSIBLE – another matter altogether and perhaps a topic better suited for the philosophers of the scientific world to consider?
Trying to define a potential maximum loudness of a sound is like trying to explain why nothing can travel faster than light -however, there is, apparently, a definitive answer in that the loudest a sound can be is – 194 decibels! This is based on the fact that anything louder than that sound measurement moves from being a sound ‘wave’ to a sound ‘blast’!
The physicists will explain that sound is associated with pressure waves in air. Such vibrations, however, are only possible under conditions where air can be approximated as a continuous fluid. This approximation breaks down when the wavelength becomes comparable with the mean free path of the molecules that make up the atmosphere. This mean free path is roughly the average distance between collisions of atmospheric molecules. (You still with me?)
The mean free path in air at sea level is about 0/1 micron – if we take the speed of sound to be approximately 300 m/s, then the upper limit on sustainable sound frequencies is –
f_max = (300 m/s) / (10^-7m0 = 3*10^9 Hz = 3 GHz
If you are wondering, incidentally, just how loud the Big Bang was, as it occurred in an airless space – as nothing existed before it – it would have been completely silent – it wouldn’t have made any sound at all – so, really, it was the Big Silence as opposed to the Big Bang!
Recommended Noise Levels
In everyday life we are in environments in which there are many different noise levels – different sorts of workplaces and social settings which require different noise constraints and sound levels. Here are some typical maximum noise levels:
- Offices – 40-45 dB
- Large Offices – 45-50 dB
- Classrooms – 40 dB
- Large Lecture Rooms -35 dB
- Music Room – 30 dB
To put these noise levels into some context, consider the following figures:
- At 20 dB normal speech can be heard
- At 25 dB loud speech can be heard
- At 30 dB loud speech is audible under normal circumstances
- At 35 dB loud speech is audible but difficult to distinguish
- At 40 dB loud speech can still be heard but not distinguished
- At 45 dB shouting will be audible but not distinguished
- At 50 dB shouting will be barely audible
- At 55 dB shouting cannot be heard
Measuring Noise Reduction
Decibels are logarithmic units while the percentage scale is linear – therefore a statement such as “solution XYZ would replace noise by N dB” means absolutely nothing – the Decibel scale has no maximum value so is impossible to calculate a percentage reduction! Instead, a calculation using a “Weighted Sound Reduction Index” – Rw – is applied. This Index expresses the difference between sound intensity hitting one side of a structure and the resultant sound measured on the other side.
Acoustic Doors
Acoustic doors are designed and manufactured to different levels of noise absorbance using the Index outlined above – they are designed to reduce the escape of noise and vibrations from one room or space to any other adjoining room or space. They are manufactured with the different decibel ratings to be applied in the various environments for which they are required.
As we saw earlier, the sound generated in workspaces such as offices demonstrate a need for some noise reduction if effective work is to be performed – typically acoustic doors with a 40-42 dB rating would be appropriate in such environments.
That level of workplace noise would, though, obviously be far less than that required in a factory environment where industrial machinery is in constant use generating much higher noise levels, where you may consider acoustic doors with rating of 48-54 dB would be better installed.
Acoustic doors are manufactured from specific materials with sound absorbent qualities – the combination of the solid materials with the insulated engineering within the body of the door, and the edge seals around the frame, provide a significant reduction in the vibrations that pass through them.
Typical Environments
There are many workplace environments where noise reduction acoustic doors are required – as already stated, offices and industrial settings, but also educational establishments like schools, colleges, universities and many important services such as hospitals, medical centres and surgeries, and police stations. Consider also, the importance of acoustic doors for entertainment outlets such as cinemas and theatres along with some obvious examples such as music recording studios.
Fire Safety
Acoustic doors can be manufactured not only to provide noise absorption and sound reduction, but can also include enhanced fire resistance – another important factor in many of the environments requiring acoustic doors!
