Regardless of how well designed a set of speakers are, the room in which they are placed will invariably have an effect on how they sound. In an enclosed space, sound waves will reflect off hard surfaces and reverberate around the room. For accurate sound reproduction, you want as much of the audio reaching your ears to have come directly from the speaker, so an acoustically untreated room can make good speakers sound worse than they really are.
As such, it’s important is it to make sure your home theatre is acoustically treated. Even less extensive speaker systems that have been properly treated will sound much better than top-of-the-range speakers placed in rooms with nothing more than drywall. Just because your speakers and your amplifier cost a lot of money doesn’t mean it will automatically sound incredible unless it’s been installed correctly along with the appropriate treatment for the space.
Sitting in a private cinema that has been properly designed and installed is one of those eye-opening (and ear-opening) moments you’ll never be able to take back. A luxury home theatre with proper acoustic treatment is something you can’t unhear – and it will leave you noticing the difference when it comes to an inferior installation.
What does acoustic treatment achieve in a private cinema?
There are two terms that frequently become confused when discussing the acoustics of cinema rooms: acoustic isolation (or soundproofing) and acoustic treatment. While both deal with audio within a room they focus on separate goals. As a simple definition, acoustic isolation is the act of reducing sound being transmitted beyond the confines of the room and from other rooms into the cinema, whereas acoustic treatment looks to maximise audio performance by normalising (as much as possible) acoustic characteristics namely, reflection, reverberation and resonance.
Reflection describes when a sound wave hits a surface and is diverted off at a different angle, in a similar way to that of a ball will bounce against a cushion on a snooker table.
Reverberation is a build-up of sound due to several reflections congregating, resulting in echoes and decay in sound quality.
Resonance refers to the scenario where an acoustic system amplifies sound waves at a frequency that matches the frequency at which it would naturally vibrate.
A room that is properly acoustically treated will address these aspects, usually through careful placement of items such as sound-absorbent panels to reduce or remove unwanted reflections and reverberation, and bass traps to normalise any resonances.
A certain amount of reflections and reverberation is desired as it keeps a room sounding natural and, especially in setups with fewer surround speakers, can give the illusion of a more completely enveloping sound field; however, this needs to be managed carefully as too much reverberation creates muddy, incoherent sound at the cinema’s focal point (i.e. where you will usually be sitting), so a delicate balance often needs to be found between the two.
How sound will behave depends hugely on the original size and shape of the room. In a small room (such as a home theatre room) the resonance of low-frequency sounds (bass) will change significantly depending on the length, width and height of the space and can also greatly vary from location to location within the room.
With any audio system, it is important to ensure that unwanted echoes or reflections are eliminated where possible. This is largely achieved using thick sound-absorbing panelling on walls or ceilings, alongside similar panels which diffuse rather than absorb the reflections. These panels will either use foam or fibreglass to absorb much of the sound and prevent reflection or else have a diffusive surface that scatters the sound in several directions.
In order to reduce early reflections, sound-absorbing panels are typically placed in line with speaker placement, so that sound is absorbed directly and not reflected first. The thicker the panel, the more effectively it will absorb an audio signal with lower frequency, which makes it important to consider when picking the correct material for different parts of the room. Similarly, treatment placed throughout the room can help to reduce the rooms reverberation time, which is a measure of how long a sound takes to decay to 60 decibels below its initial level (which is effectively then silent).
When dealing with resonance, the biggest element to counteract is standing waves (or room modes). Room modes are directly proportional to the size and shape of the room in correlation to a certain frequency. As the sound waves reflect off of different walls, they have the ability to either sum together, boosting a frequency or cancel each other out, cutting a frequency. This results in some frequencies being louder and others quieter in different parts of the room.
Furniture placement will go some way towards resolving this issue, as will carefully planned and positioned bass traps, which act to lessen standing wave effects by absorbing certain frequencies. The dimensions of a room (and aspects like whether the ceiling is sloped) will also either positively or negatively affect room resonance e.g. cube-shaped rooms are fundamentally poor in terms of acoustics. An experienced acoustic expert will be able to layout certain options for achieving an acoustically amenable room layout, which helps hugely when it comes to ensuring that it is effectively sound treated.
Other areas that need to be considered within a home theatre room in terms of audio include the flooring and windows. With the former, you ideally want to avoid hard floor reflections by laying carpet; while with the latter it is better if there are no windows present, as light entry is a separate issue that can affect the cinematic experience. However, if there is no option but to have windows, then it is important to ensure that sound-absorbing curtains or blinds are employed to prevent sound issues caused by reflections of sound waves off the glass.
Building the perfect home theatre room with Acoustica Projects
While there are several DIY enthusiasts that have built their own custom home theatre, a high-quality home theatre room will always look and sound better when handled by an experienced, professional team.
Talk to our acoustic consultants today to discuss building your very own home theatre room at home!
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