Home cinema audio design is often an overlooked area. Clients ask for a massive screen and 50 seats and surround sound, and that's usually where it ends. But the soundtrack of a movie is easily as important as the picture. As well as providing the dialogue, we use audio to create ambiance in a movie. The soundtrack stimulates an emotional response and is usually provided by an orchestra where the dynamic range can be huge. Although there are some very notable exceptions. Tarantino uses contemporary music to great effect, Pulp Fiction being a superb example. Guy Ritchie is also known to use music and songs from the popular music genre rather than orchestrated music.
So let's take a look at how to produce great home cinema audio.
Limit your volume
As we discussed in Part 1 – Picture, as we add more rows of seats to a home cinema design, we start to build tiered levels so that everyone has a clear line of sight to the screen. It follows that more ceiling height will be required so people don’t bump their heads when they stand. All of this is adding to the volume of the room. That volume needs to be filled with sound. And so better, more powerful amplifiers are required to move all that air and create a convincing soundscape.
As I’m sure we all know, to create sound we move air. A speaker will compress air to create sound waves. The more air we have in a home cinema room, the greater the engineering challenge to fill the space, whether it be a car crash, an explosion, or the tiniest, quietest whisper.
But this brings with it challenges of it’s own. Making sure that the sound from each speaker is balanced in a large room, so you don’t hear one speaker louder than the others is a difficult engineering task. And so when considering a home cinema design, by limiting the volume of the room to what is actually required, rather than just going as big as possible, you can get much better results pound for pound.
Speaker placement for better home cinema audio
Surround sound has been around for a while. But as technology develops we are able to place a sound with pinpoint accuracy. 5.1 surround sound simply means you have 5 speakers that handle 5 separate channels of audio and one subwoofer that handles the low frequencies. The subwoofer is what provides those floor-shaking rumbles and booms.
So now we have three speakers across the front. Ideally, we would place these behind an acoustically transparent screen so that the sound of speech is coming from the centre of the screen rather than above or below it. Then we have two speakers on the rear wall to give effects coming from behind. That’s great, but you can get a disconnect between the front soundstage and rear soundstage. When a sound is moving from front to back we want that transition to be smooth. So we add another pair of speakers on the sidewalls giving us 7.1. Add two more speakers and you get 9.1. Add another subwoofer and you have 9.2.
Low frequencies are a really important part of the soundscape. Anyone who has stood in front of speaker at a concert or in a nightclub will know the feeling of the bass going through your body. Elephants hear more through their feet than their ears, and although we don’t put as much emphasis on the sound that we feel, it definitely plays a part in our emotional response. Subwoofer placement needs to be done with care. The goal is an even, deep bass performance for all listeners. A single sub will always result in lumpy, uneven bass – too much here, too little there, so they should be placed in pairs ideally.
As technology advances we are able to add further channels above us in the ceiling. This means that if the movie shows a helicopter hovering overhead, the sound comes from overhead, rather than a synergy created by all the speakers on the walls. Adding these “voice of God” speakers to your home cinema audio design is a great upgrade, so even if you don’ think you want it now – run cables to the ceiling positions so it is easy to add speakers later. Any decent home cinema design professional should suggest this at the planning stage.
Using acoustic treatment in home cinema audio design
Acoustic treatment as part of your home cinema can be an entire post in it’s own right. So we’ll do a very brief summary here and perhaps do a dedicated acoustic treatment post another time.
There are a few different schools of thought when it comes to using acoustic treatment in a home cinema. This is the approach that our room designers take if the opportunity is there (which it isn’t always if we are brought into the project at a late stage).
Everything in your home cinema room will affect the sound that is produced. From the seats to art hanging on the wall. Appreciating how much each items will affect the sound is the art of acoustic treatment. Correcting those anomalies is science. It is certainly true to say that a mid-level system in a treated room can outperform a top-level system in a non treated room.
Many of the imperfections that you find yourself trying to correct either digitally or with panels at the end of a project could be designed out entirely if the room is constructed correctly. When you walk into a Cineworld or Odeon you will notice that the room is not a perfect rectangle. The corners are not right-angles, this helps the sound reproduction immensely. By understanding the conditions at the beginning of a project, and identifying where problems are going to be, many of them can be designed out of the room without the need for digital manipulation post-project.
But when this is not possible, then we look to treat the surfaces to make them disappear.
This video from acoustic panel manufacturer Vicoustic explains excellently how acoustic treatment panels work.
Aircon, heating, the electronics and hardware used… All of these items generate noise. And so, it is vital that your home cinema professional is involved early in the design process so that we can advise on how to limit the ambient noise in your room. Sometimes it is about the silences rather than the noise. Being able to hear a pin drop, or a stifled breath might be the crucial tension builder in a thriller. But if all you can hear is the cool air being blasted into the room through some narrow vents, the effect is ruined because you simply can’t hear it.
That means, playing films properly is a difficult engineering job and needs the right equipment. Whispers must be audible and distinct, but screams, explosions and orchestral crescendos have to be clear and clean. The sound mustn’t distort and the dynamic range should be maintained.
Keeping electronics out of the room helps keep the ambient noise of the room to a minimum and large air ducts for heating and cooling are good too.
Soundproofing also needs to be considered. It’s as important to keep external sound out as it is to keep internal sound in.
We’ve really only skimmed the surface of what is involved in designing the audio system for a home cinema. There are many technical calculations and formulas that we employ to make sure you are going to get the best experience from your home cinema room that is possible. It is important to speak to a home cinema design professional as early in your project planning stages as you can so that they can advise on room design, and limit the amount of correction that has to be done once the room has been built.
Part 3 of the Home Cinema Design Blog will look at everything else. Room construction, control and the environment, and making your home cinema your own with decor.
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