Home Cinema Acoustics: A Simplified Guide
Home Cinemas are a fantastic way to make that big screen experience a personal one that you can selfishly enjoy away from the queues and the crowds. The most important thing you can do is to ensure the room you are in has been built and acoustically treated properly. Ideally the room would be designed with Speakers, amplifiers, screens and projectors in mind however they can all be replaced. It is very difficult to change the room once it is built and attempts to do this often mean gluing or screwing foam and wood to various positions around the room which invariable looks exactly as it is; an after-thought. For this reason, it is well worth knowing some key nuggets of information, complete with solutions that go along with these to ensure you have the best possible experience.
Resonance related to the shape of the room can play a huge role in the overall feel as uniformed room shapes can suffer from what is known as “Standing Waves”. This is where sound is bouncing back and forth between opposite walls, ceilings or floors creating. This results in different positions in the room experiencing noticeable differences in loudness in some lower end bass or mid frequencies. In the worst cases it can result in pounding bass for one viewer while 1-2 meters away it is barely noticeable.
This effect is rectified at the build stage through use of irregular wall shapes, coffered ceilings and risen rear seating (which also betters the viewing angle).
Echo; Early Reflections; Reverb: They are all the same thing at their core and refer to sound bouncing off object meaning the same(ish) sound is received by your ears at different times.
Echo and early reflections refer to sound that is very similar to the original propagated sound however Echo is a noticeable repeat of the sound some seconds later whilst Early reflections arrive at a similar time and make a sound source appear to be coming from somewhere other than where it is placed. Both of these types of bouncing sound are bad for Cinema and need to be removed by large scale, full range absorption for Echo and a mixture of room design and absorption in key areas for Early Reflections.
Reverb is the effect experienced of many versions of a sound reaching the viewer at ever so many different times resulting in an audible blurring and softening. This is something that is especially pronounced in tiled bathrooms when speaking or singing. Reverb seems like a bad thing to occur and is when not controlled properly however you do in fact need some amount of reverb to make the room sound natural. For this reason, putting in as much absorption as you can fit is not the resolution here. It takes a balanced approach to ensure you take out reflections across all frequencies and place specialised absorption in areas that are going to be most effective.
Top Tip: Corners are an area low frequency energy gathers due to multiple reflections so low frequency traps are most efficient in these locations.
So far we have been solely discussing absorption as a remedy to reflected sound however specially designed dispersion surfaces are also a great tool. They can further soften the reverb by creating many iterations of the reflected sound and can direct reflections in different directions.
As we are talking in the context of a Home Cinema it is worth discussing the front wall as this is where most of the meaningful sound will be coming from and it is certainly worth talking a bit about the acoustical properties of this wall and requirement here.
In order to have proper sound imagery you will likely have a perforated or woven projection screen with speakers behind this screen so that the sound is coming from the image. These screens will require the speaker to be set back by some distance from the screen and it is preferable that these would be mounted into a false wall built out from the actual boundary of the room. Because of this, the first practical reality is that space should be allowanced for this at planning and highlights the need to have a professional involved from the beginning. It is also worth knowing that the screen itself will inevitably reflect sound back at an angle onto the wall behind so proper absorption should be used on this wall.
If done correctly however you will enjoy better bass response and better imagery across the front thanks to a reduction in the boundary effects of speakers sat at a distance from the wall.
It is worth noting that acoustic considerations for the front wall will apply to all walls except for the screen considerations. However generally the front wall really is the most important as this is the focal point.
By acoustically separating your Cinema from the rest of the home you have the benefit of not only being able to play your favourite movies at the kind of levels that rumble your seat but also stop any noise from the outside interfering with your experience.
If this is to be truly achieved you will need to prepare for thicker walls, flooring and ceilings as well as sealed doors. If you really want to take it to the next level, then your environmental controls and air handling will also need to be thought out so that sound is not leaked in or out through this system.
If you are considering installing a home cinema, it can be one of the most exciting things you can build in your home and getting everything built correctly is so important. Get in touch with us here at Micarta if you would like to chat further about an installation or simply want some advice on what to consider.