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Noise Control: Part 1 - What is sound?

Noise Control: Part 1 - What is sound?

- by Peter Koelewijn, 21-02-2018

Randomly ask people what defines the comfort level of an air conditioning system, chances are high the first thing that comes to mind is temperature, which is understandable. Air temperature is one of the main properties of climate as air conditioning is all a matter of thermodynamics, but there is another property which definitely contributes to the level of comfort. That is sound.

When sound is judged to be unpleasant, loud or disruptive to hearing, it is called noise. Super yachts, cruise ships, and even commercial vessels, all are subject to certain noise level requirements. As sound and noise control has a major impact on the comfort level, we want to dig deeper into this topic. What exactly is sound? How do we experience comfort? Which types of noise can be defined and of course what can we do to control them? In this first blog in a series of four I will explain what sound is. The second blog covers comfort and how noise affects this. There are three kind of noise types, which will be discussed in the third blog. In the last blog, we are looking for solutions to prevent or reduce noise issues.

What is sound?

Sound comes in many different forms; it can be harsh and loud, or soft and gentle. Noise can be high and shrill, or low and deep. Sometimes it manifests as a pure note, sometimes as static. What exactly is sound? Well, according to physics sound is a pressure increase which travels - in the form of a wave - through a medium such as gas, liquid or a solid.

You could say that a wave is a disturbance that propagates through space. But what does this look like in reality? Well, imagine there is a speaker standing in the middle of a room. A speaker is capable of producing sound as its woofer makes miniscule movements, which is called oscillation. As the woofer is moving rapidly up and down, the molecules in the direct vicinity of the woofer will move together with the woofer. This causes pressure to increase because the molecules are pressed together, resulting in a chain reaction of oscillating molecules that will travel the room - in the form of a wave - eventually reaching your eardrum. That is how we experience sound.


Image 1: Woofer with molecule pressure increase.

If we want to figure out sound, we first need to figure out the properties of a wave:


The height of a wave taken from the base (middle) is called the amplitude. This says something about the degree of pressure increase and corresponds with the loudness of a sound. The bigger the amplitude, the louder the sound.


A wave has a beginning and an end. At the beginning the wave goes up till it reaches its top, or the crest. From there it will descent all the way down to the bottom - or the trough -  whereafter it will ascent again till it reaches the base. So it is defined to be the time it takes for one full loop up and down.



A wave which exists of only one period is called a pulse. In the world of sound, waves always have more periods. The frequency says something about the amount of periods per second. So how many crests and troughs there will be in a timespan of one second. Frequency is expressed in Hertz. For example when there are twenty periods in a second, the frequency will be 20 Hz.


The wavelength is the inverse of the frequency. It is the distance which a single period travels, so the displacement of the wave. The longer the wavelength the lower the sound.


This concludes my introduction into noise control. Now that we know what noise is, the next step is to examine the effect of noise on human comfort.

Peter Koelewijn | Sales Manager

Peter Koelewijn has been working at Heinen & Hopman since 2001. Starting out as a mechanic, he gained valuable field experience mounting ducts and pipes for various shipbuilding projects. Five years later he switched to engineering, where he worked his way up from draughtsman, to engineer to site manager, leading teams of HVAC mechanics at one of the largest shipyards in Germany. The last couple of years he has been working as sales manager, combining knowledge from the field and the office to find the best solutions for our customers.

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The HVAC systems we design are subject to various noise level requirements. Meeting these requirements is vital to satisfy our customers as noise has a major impact on the comfort level onboard.

Peter Koelewijn

Peter Koelewijn

Peter Koelewijn

- Sales Manager

Peter Koelewijn

Peter Koelewijn

- Sales Manager

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