{"id":3135,"date":"2023-01-31T07:22:42","date_gmt":"2023-01-31T07:22:42","guid":{"rendered":"https:\/\/blogs.qsc.com\/live-sound\/?p=3135"},"modified":"2023-02-22T09:42:00","modified_gmt":"2023-02-22T09:42:00","slug":"how-to-mitigate-sound-propagation-through-materials-in-live-sound-settings","status":"publish","type":"post","link":"https:\/\/blogs.qsc.com\/live-sound\/fr\/how-to-mitigate-sound-propagation-through-materials-in-live-sound-settings\/","title":{"rendered":"How to mitigate Sound Propagation through Materials in Live Sound Settings"},"content":{"rendered":"

You may remember from your science classes in school that the speed of sound is a constant, but this statement is entirely dependent on the material through which sound is propagating. Different medium transmit sound at very different speeds. So, let\u2019s look at some typical materials that most people would encounter in indoor live sound settings, before investigating how to minimize such undesirable sound propagations through structures.<\/p>\n\n\n\n

Sound Propagation<\/strong><\/h3>\n\n\n\n

Sound is a form of energy produced and transmitted by vibrating matter. Low frequency sound waves caused by such vibrations move through a medium (solid, liquid or gas) in all directions from their source and can be described by the wavelengths and frequencies of such waves. However, it is the medium that vibrates back and forth and transfers the energy, as the medium itself is not carried along with the sound waves.<\/p>\n\n\n\n

What is Acoustic Transmission?<\/strong><\/h3>\n\n\n\n

Acoustic transmission occurs when sound waves propagate and pass through a barrier or a material, resulting in noise on both sides of the barrier. Acoustic transmission poses a number of problems in any live sound application, where sound from the performance\/venue transfers from one room to the next and within a building, creating nuisances for neighbors and people living nearby.<\/p>\n\n\n\n

Dense materials are able to block most acoustic transmission for high, medium and low-mid frequencies. However, at low and very low frequencies (with wavelengths of many meters\/feet below 100 Hz) sound waves are able to propagate through buildings, as buildings\u2019 structures and materials start to vibrate, and the higher the speed of sound, the most effective is the low frequency propagation!<\/p>\n\n\n\n

Different Materials Implies Different Speed of Sound<\/strong><\/h3>\n\n\n\n

To understand better what happens when sound waves propagate through materials, first let\u2019s recall that sound wave propagation involves the transfer of kinetic energy between adjacent molecules. The closer molecules are to each other, the faster sound travels. This means that sound travels much faster through solids than through liquids or gas, which have their molecules the farthest apart.<\/p>\n\n\n\n

A second aspect is the elastic property of a material. Materials with higher elastic properties return to their normal shape faster, making it easier for sound to travel through them. This is why sound travels much faster through steel, for example, than rubber, which has very low elastic properties and a speed of sound of 60 m\/s.<\/p>\n\n\n\n

Indoor Live Sound Settings and Environments<\/strong><\/h3>\n\n\n\n

If the quality of any live sound performance is highly dependent on room acoustics, at low frequencies specifically, the propagation of bass energy across the venue structure is not negligible. The most common construction materials that we encounter in live sound settings are: reinforced concrete (with inner steel framing), bricks, gypsum board (single or multi-layered), wood (planks, plywood boards, beams, doors, house framework, etc) and of course glass (windows, winter garden, etc). The list is surprisingly short. Looking at the speed of sound in these solids (see Figure 1), we observe they range between 3600 m\/s and 6000 m\/s (10 to 17 times faster than in air!).<\/p>\n\n\n\n

Even though typical dense materials (concrete or brick walls) block acoustic transmission efficiently, their inherent high speed of sound characteristics allow for efficient sound propagation across structures. The question is now what to do to mitigate sound propagation?<\/p>\n\n\n\n

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Figure 1 – Speed of sound through many different medium (gasses, liquids, solids)<\/figcaption><\/figure>\n\n\n\n

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How to Minimize Sound Propagation through Buildings?<\/strong><\/h3>\n\n\n\n

As mentioned, the most problematic sound propagation across structures occurs at low and very-low frequencies (typically below 100 Hz). Here are a few tips to minimize such sound propagation in typical indoor live sound settings:<\/p>\n\n\n\n