17.06.20

The rights & wrongs of acoustic treatment

thebigpicture1
Photo: Artnovion

This month, Amy Wallington attempts to explore the complex and highly technical topic of acoustic treatments in a home cinema environment.

You might recall a debate in the previous issue of HiddenWires between two industry pundits arguing whether home cinema rooms should be acoustically treated or not. We took this discussion to ISE, threw in another expert and held a panel debate, a video you can find on ISEShow.TV. Leaving the fighting behind, this time we are looking at what acoustic treatments can do in a home cinema and, occasionally, a media room.

Treatment comes in many different forms and how you implement solutions depends on size, shape and physical construction of the room, as well as the furnishings and layout, to name a few. Most people would agree that every home cinema or media room needs some sort of treatment in order to reproduce the most realistic sound for the viewer or listener. 

This is easier in a home cinema environment compared to a media room. Media rooms are often multipurpose and trying to treat a room so that it sounds perfect for every purpose isn’t always possible. 

“The quality of a Hi-Fi or home theatre system is the result of its components, together with the acoustics of a room,” begins Massimo Magliola, international sales manager at Garvan Acoustics. “A medium quality sound system installed in an acoustically correct environment offers a far better performance than an excellent sound system integrated into an environment which has not been acoustically treated.”

Ultimately, the main aim of treating a room is to create a comfortable, natural atmosphere that will make the viewer feel like they are in the film environment rather than watching it at home. 

An acoustic consultant, Chris Adair, the managing director of Adair Acoustics thinks that acoustic treatment is essential. “The sound is what moves you emotionally, and the quality of the sound is key to getting the audience involved in the film. The part the room plays is really key, first to speech intelligibility, and second to creating the illusion of being ‘in’ the movie space. 

“If you design the room acoustics properly, the room will melt away and the audience will become totally involved in the movie experience. However, if you leave the room untreated, the viewer will be constantly hammered by audio reflections coming from all around them that simply shouldn’t be there. They are being showered by room reverberations that muddle the sound, reduce clarity and constantly reminds their subconscious that they are in a small room.”

Garvan Acoustics
Photo: Garvan Acoustics

Before thinking about how to treat a room, the integrator or consultant needs to clarify with the client exactly what the room’s purpose is, how it will be used and what they want from it. Then they can start considering what would affect the acoustics. 

As Nathaniel Bailey, R&D engineer at Artnovion says: “The first thing is the room function, what people expect from a space. Then it’s all about meeting those expectations. Each project runs a similar course: understanding the initial conditions, studying where the main problems lie, and then knowing how to use the available tools to treat each issue. 

“Standard starting points to designing an acoustic treatment are analysing reflection patterns, room resonances, and reverberation time, although the final result is measured in sound quality.”

Of course, the most ideal situation is to be involved from the design stage of a new-build property. That way, the consultant can liaise with the architect or builder and have a say in the materials used to build the room. 

“For sound proofing, it is important to get involved in the building stages and treat the wall cavities with sound dampening material such as mineral wool,” highlights Pieter Venter, general manager of Audio Visual Gurus. “It would be even better to get the architect to speak to a professional with regards to the room dimensions and ceiling height before the building commences. It would eliminate issues and constraints at a later stage.”

Integrator Nic Black, managing director of Pyramid Group says he has had very successful projects where he was involved from the start of the build. “The sooner we’re involved, the better it is and the more successful it is. We have been there before the foundations have been dug on some projects. There are lots of ways in which you can make sure a room performs from an acoustic point of view by using traditional building methods, which is ultimately, from an owner’s point of view, always going to be the most cost-effective way of doing it as it’s done in the build phase rather than being retrofitted.”

Although ideal to get in as early as possible, the acoustics of a room will never be perfect no matter what is done to treat it as everything affects the sound. Venter continues: “Different materials and items all affect the acoustics, like tiles, glass furniture and everything in between which either reflects, absorbs or diffuses the sound. The fact is that even the seats, carpentry and people in the room affect the acoustics. An ideal room will be as natural sounding as possible, without adding noise to the original sound.”

One fits all?
To be able to build a good home cinema for a client, you really have to know your stuff about acoustics, and if you don’t, you must get the help of an expert consultant who does because there are so many things to consider. With every room being different, there is no ‘one fits all’ solution. 

“Acoustic treatments are used to control how the room affects the reproduced sound, be it for music or movie audio,” explains Mathew Moule, managing director of Acoustic GRG. “Most rooms are relatively small, with hard floors, walls and ceilings. Sounds reflect off these surfaces and bounce around the room, interfering with the direct sound. Controlling the acoustic performance of the space can offer the listener a number of benefits: clear reproduction of sound with no colouration from the room, an increased soundstage, improved immersion, and it can make a room feel larger in size.”

"Aesthetics is most certainly important, but to be able to design a room that looks as well as sounds amazing, is an art and a science."

The room size plays a big part in the acoustics as Helin Konnolu, sales consultant at Mikodam points out: “The size determines how far the sounds can reach. Possible acoustic defects include the sound not reaching all parts of the space equally, the sound not reaching the furthest sections of the space, the sound reaching all borders at a high intensity level, causing sound glare, or the sound collecting which causes an echo.”

The surfaces inside the room need to be considered and treated to prevent too much reflection. “The simple rule is the harder the surface, the more reflective it is, and that’s when you mess up the intelligibility and make the space more reverberant,” says Black. 

“To prevent this, you need to make sure that all hard surfaces are as treated as possible. That could be anything from just making sure you have got a decent underlay and a really thick carpet to start with. If there’s a flat ceiling, wherever you can, try to mitigate that with soft surfaces. What is quite prevalent in a lot of standard cinema designs is something like a star ceiling that is typically made up of a foam-based material covered in fabric, which is great from an acoustics point of view.”

Going into more detail, Vicoustic published a whitepaper entitled, ‘Hi-Fi & Home Cinema – Acoustic Treatment Guidelines’ which can be found and downloaded at the company’s website. Within the guidelines, author Gustavo Pires wrote: “It is recommended to treat first reflections with sound absorbing panels, as these will take energy from those early reflections and improve sound clarity and source localisation within the room. It should be noted that late reflections do not present the same issues mentioned for early reflections. These late reflections might even be helpful in avoiding the room from becoming too ‘dead’, as long as these are properly controlled and do not have too much energy.”

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Photo: Adair Acoustic Design

According to Black, in a home cinema, the goal is to achieve an RT60 reverberation time, which needs to be taken at the beginning of the process. “Whenever we design a cinema, we use 3D software and we ultimately work out how the room is constructed, and then we work backwards. We look at what the pre-treatment RT time would be within the space, then we know what we are working with. Typically with a home cinema, it’s probably more about absorption than it is about any kind of reflection.”

As already mentioned, there are a number of different ways to acoustically treat a room, dependant on many factors. According to Moule, Acoustic GRG uses a combination of treatments to give the best quality sound possible. “When we design a room or propose a treatment plan, we will always ensure that we have used the best range of product types to treat the specific problems of the room.

“For absorption, we use panels that absorb frequencies from 100Hz upwards in various thicknesses. Diffusers are used to scatter sound, either in one direction or two, depending on the panel type. We use diffsorbers, which are hybrid panels that diffuse high frequencies and absorb low frequencies. Bass control is used to absorb the low frequency energy from 35Hz up to 500Hz. Some can be tuned to specific frequencies. Finally, we use reflection panels to redirect sound.”

According to Vinter, absorption panels, diffuser panels and bass traps seem to be the most popular ways of treating a room. He adds: “Some people use curtains in some areas for an ‘old school’ cinema look. They also use thick carpets on the floor – which is not suggested to have on the walls – and acoustic ceiling tiles, as well as hanging acoustic baffles and more.”

"If you design the room acoustics properly, the room will melt away and the audience will become totally involved in the movie experience."

There are various materials that can be used to treat a home cinema. Mineral wool, acoustically perforated fabrics, glass wool, polyurethane foam, and hemp fibre are just a few that are sometimes used. Magliola continues: “For our acoustic solutions, we have chosen polyester fibre as a base because of its valuable qualities; it does not release toxic fibres into the environment, it is odourless, durable and resistant, and it can be recycled. Last but not least, this material also features significant thermo-acoustic properties.”

Although treating the walls and ceiling are probably the most crucial parts to concentrate on, Konnolu suggests that they are not the only aspects that should be considered. “Sound waves reflect more on corners with right angles. Using sound absorbing panels on corners will increase the acoustic quality of the space. However, when sound is absorbed excessively it will become dull and unnatural.”

Over the top
Is it possible to over treat a room? Yes, it seems. If an integrator does not know what they are doing in terms of the acoustics within a room, over-treating it can make it sound even worse than having no treatment at all.

“Too much absorption can cause a lifeless sound with a lack of bass, since the energy is sucked out of the room,” reveals Vinter. “This results in an unrealistic experience with narrow sound stages and poor surround effects.

“Additionally, incorrect panel placement may result in sound being reflected and absorbed in areas where it should not and will result in echoes and a lack of realism. Many more examples can be given, but the results could be catastrophic, and worst of all, it will come at a price since the treatment would have cost a great sum of money. Aesthetics is most certainly important, but to be able to design a room that looks as well as sounds amazing, is an art and a science.”

Simon Grattidge, managing director of Sinemas, advises to keep the treatment simple and not overdo it. “Common sense goes a long way here. Acoustic foam behind the screen wall and beautiful panels on the side and rear walls controls nearly everything required; it gives vastly improved intelligibility and looks superb too.”

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Photo: Artnovion

As already mentioned, there is no ‘one fits all’ solution, and using different panels and techniques is the best way to ensure a room sounds as natural as possible. “A properly treated room doesn’t just use one type of panel,” advises Moule. “I have seen many rooms that have been ‘treated’ with just fabric covered panels, all the same thickness and same panel type. All this does is absorb sound in a specific frequency range, sucking all the high frequency energy from a room and leaving all the mid and low frequency problems that haven’t been touched because it’s the wrong type of treatment.”

Acoustic treatments is a very complex topic that could be explored in great technical depth if we had enough space in this magazine. It is impossible to specify one solution to treat all rooms because every room is different and everyone hears differently; what sounds good to one person might not sound good to another. This has caused varying opinions on whether a room should be acoustically treated, and if so, by how much. 

A final thought, what is most important is being able to transport the homeowner to a different place when they are watching a film in their home cinema. Adair concludes: “The acoustic treatment is the equivalent of making the room dark – acoustically we want the room to melt away. Therefore, the treatment must prevent the walls and ceiling from reflecting what has just been heard from the speakers back to the viewer. This makes dialogue much easier to understand, as well as letting the viewer properly perceive all the subtle sound effects while appreciating the divergent locations the sounds originate from.”