Tuesday, November 20th, 2018

Jorge Castro of Vicoustic : What are acoustics anyway?

By editorJune 1, 2012

ACOUSTIC DESIGN

Jorge Castro, 32 years old, born in Fafe, Portugal, Studied Sound Engineering at Porto’s Polytechnic Institute (IPP) ; MSc/Pg in Audio Acoustics at Salford University, Manchester; co founder of Vicoustic, currently working as Project/Product Manager and in I&D for the company.  Jorge also lectures at Evora University.

Jorge explains some of the fundemental principles behind acoustics and the problems encountered in treating a studio monitoring environment; and some of the solutions to these issues in order to create a high quality listening environment.

“Why do people buy acoustic products?  For sure there has to be a reason for investing in sound control products, and that is simply the need to take the best out of our sound systems in our rooms.  But in fact, the main question we should be asking is … why does sound need to be controlled anyway?  This question will take us in the next minutes into a journey of sound characteristics and its behavior, especially those occurring inside an enclosed room, whether it is a Studio, a Home Cinema or even an Opera theatre.

Although people may not have conscious of the science facts behind sound, the truth is that most of us have already got into a place where we said or thought: “Such an awful sound in this place”, and we’re not talking about music styles… we’re talking about getting into a room and just knowing that there was something wrong with the sound of it, whether it is long echoes or simply confusing sound. This happens because sound is just like a light from a lamp in a room with a window. The path the light takes is not just the straight line between the lamp and the surface that’s in front of it (whether it is the floor or a wall), instead, light covers the whole free space of the room and even goes into other rooms through the window. So it is with sound. Whatever may be its source, sound will fulfill the whole room in all directions and even fly into other rooms through the floor, ceiling or walls, since sound waves can travel by any solid, liquid or gas material. Well, acoustics is simply the way sound is affected by the physical properties of the space where it is being produced, and this is why clients want good acoustics and therefore why acoustic products companies develop materials that will interfere with the physical properties of the space, so that in the end, we all come up with rooms with adequate distribution of sound, ensuring clarity of speech and “completeness” of music.

When considering the properties of a room, what we’re really trying to avoid are acoustic defects such as: Strong reflections, flutter echoes, reverberation and standing waves.

Keep up with us and we’ll show you, how each one of these things occur in your own room, preventing you to benefit from the full potential of your sound system. Fortunately there are solutions and we’re also going to show them to you!

Low frequency – Standing Waves

Resonating waves, usually occurring on low frequencies, represent the acoustic phenomena of sound waves that are exactly as long as the dimension of the room, or in half proportions of that (other standing waves happen in parallel of the original one). Resonating waves are louder and take longer to disappear and therefore generating more confusion especially when we consider that are at least 6 surfaces in a room.

 

 

 

 

 

 

 

 

I believe 90% of the room’s problems are related to lack of low frequency control.  A typical home studio is usually small, and the smaller the room, the higher the low frequency limit (lowest frequency with resonant support). These spaces are prone to:

  • Significant modal resonances
  • Too much spacing between modal frequencies

Example

  • 3m long room – bass limit of 56 Hz
  • 6m long room – bass limit of 28 Hz
  • Above 300 Hz the modal frequencies are so close together that problems associated with lower frequencies disappear.

The size, shape and dimensions of the studio are very important, they determine a good or bad control of low frequencies.  Aim fora reasonable sized area, shaped to give a uniform distribution of room modes with various accepted ‘golden’ ratios.

Examples:

Height                             Width                     Length

A.1.00                             1.14                       1.39

B.1.00                             1.28                       1.54

C.1.00                             1.60                       2.33

Due to the wave length associated with low frequencies, it’s harder to treat and I believe it takes more than standard absorbent material in the corners to control them.

Each of the examples has it’s own specific resonance and harmonics so it’s very important to analyse the sound’s behaviour, how it disperses, how the pressure reacts and the room’s acoustic mode, before anything else. The Acoustic mode propagates through the air particles and these air particles are subject to pressure and velocity, resulting in compression and rarefaction; this is what we have to focus on to develop a solution.

In truth, some material behave better when exposed to particle compression and other material with particle velocity. This is why it is extremely important to understand the different absorption techniques, that can be more or less effective when applied to these two particularities. We know that Helmholtz resonators and membranes work better in areas with acoustic pressure, and porous/fibrous material have better effect on areas where the air particles build up high speeds.

This is why Vicoustic has developed hybrid absorption solutions that can be placed in a same location and act on different acoustic modes.

The Super Bass Extreme is an example of a 3 in one acoustic panel: one membrane, 2 layers of high density foam and resounded with micro-perforation. When correctly applied, the result can be impressive.

To achieve better control of the studio’s frequency balance, low frequency solutions have been developed to only act on the low frequencies, without affecting the other parts of the sound spectrum.  This is why we use the Wavewood system on the Super Bass Extreme.

Reflections

Reflections are the acoustic phenomenon that happens in any kind of room, regardless of its shape, functionorsize, translating sound behaviorwhen it encounters a plain surface.

 

 

 

 

 

 

As we’ve previously referred, sound doesn’t move only in a straight line from its source into the listener’s ears, instead, sound waves coming from a certain point, spread out in many directions, and when they encounter an obstacle, like a wall forexample, they react by producing “counter-waves” as if they were being produced by another source different then the real one.

Therefore, the result is quite simple to imagine.  Instead of having a clear sound, the listener will feel a lot of confusion coming not only from its audio system but from the whole room itself, as we can see in the image above.

One of the main consequences that reflections can bring is echo, which happens when reflected sound clearly distinguishes itself from the direct sound.  In order to find a solution, science started from a simple question: “If the problem occurs right after sound waves get into touch with plain surfaces, and if that’s not a possible variable to change, what can be done to “catch” those sound waves and stop or diminish them?

The answer would rapidly put foam and other materials in a privileged position on the package of acoustic solutions, namely those related to ABSORPTION.  Acoustic absorption products made from special foam perform like energy converters, catching reflections (sound energy) from a sound source and by a resistive process turn them into heat energy, diminishing their strength and therefore allowing the sound in a given space become clearer, like we can see in the images above.

Another way to treat reflections is DIFFUSION. Diffusion products, act on reflected sound waves splitting them into smaller ones. Once smaller they move across the room but don’t interfere with the direct sound, and therefore preventing acoustic distortion, as you can see in the image below.

When adequately treated, the whole effect of sound diffusion will also be the sense of complete room “fulfillment” and “spaceness”. And because perfect ambience is also about aesthetics, our engineers and designers have conceived a variety of diffusion products. Design will be a variable – good performance won’t.

It is important to note that complete room acoustic solutions will usually be the combination between absorption and diffusion products.

Absorbing all sound reflections and creating a dry room, with no information on the surface reflections is also a common error. The most important thing is to specifically address the energy to achieve an involving and natural ambience. Avoiding anechoic conditions, the aim is for the listener to be surrounded by sound reflections, and in my opinion, the way to go is to design rooms with controlled and linear RT’s across frequency range.

Rooms with RT’s below 0.2 seconds are strange rooms, that deliver, in most cases, non realistic and even deceitful sound images. Mixing Rooms with RT’s above 0.4 seconds produce sound that is closer to the listener’s reality. When designing a studio, we try to balance the reverberation time spectrum instead of obtaining a super controlled RT.

I believe the fundamental principals are the control of the reflections between the monitors and the listener, and the diffusion of the surrounding reflections from the room’s surface.

The absorption coefficient on the lateral walls between the monitors and the listener should be as linear as possible so as not to interfere with the sound spectrum coming from the loudspeakers. A reflection predominant in mid frequencies will increase the energy of the sound coming directly from the loudspeaker, thus resulting in distortion of the mid frequency range. In addition to this, a reflection travels a greater distance than the direct sound from the speaker, provoking constructive or destructive sound energy across the spectrum caused by phase rotation. These particular problems occur in the first reflections from 50 to 80 milliseconds and sometimes can be higher.

Diffusion is a very important way to treat reflections that come from the ceiling, besides attenuating the energy, it breaks them into multiple reflections scattering the sound field. Because the reflections are broken into smaller and less energetic reflections, the listener gets the impression they are coming from a distant source, thus creating the illusion of “spaceness”. Sound diffusion can be applied on the back wall to enhance this effect and proves to be a very useful technique for studio design, especially for home studios that usually are small areas.

I believe the balance between absorption and diffusion is key, and the accurate positioning of specific panels, makes home studios ever more acoustically controlled spaces contributing to extraordinary results.Today, greatly due to the discovery and evolution of different prime material, in line with optimization research, we can design high-performance acoustic products that incorporate the professional studio’s principles, at home and with impressive results.

The biggest challenge is controlling the low frequencies. A phenomenon that makes professional studios spend around 70% of their budget on acoustic treatment, in attempt to solve.

A good low frequency solution, linear absorption panel and efficient diffuser help to improve any room’s acoustics. Once we understand the sound field’s behavior, in the low frequency range, we can accurately place bass traps, making them an extremely efficient product. Psychoacoustics allows us to develop and tune acoustic solutions that are adjusted to our day-to-day life and unique way of experiencing sound, making the room sound natural and easy to use for audio production, (control rooms, mastering rooms, listening rooms).  It’s not about extracting the energy of a room but controlling it in a way that we can obtain a linear response in the different acoustic parameters.”

 

 

 

 

 

 

 

Jorge Castro
Visound Acústica, Lda.
May 2012

Our thanks to Jorge.  If you found this article useful then we suggest a visit to the Vicoustic website at www.vicoustic.com or you can review the company’s history, approach to acoustical treatment and products in the video below.

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