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Posted by Matthew Cupper on September 4, 2018
Matthew Cupper

This blog covers off two elements of the black art of acoustics. If you want your home cinema installation to perform to the best of its natural ability and without limitation do not ignore these elements.

One of the most commonly overlooked factors of a home cinema installation is that of the room shape and size and how this effects sound quality and performance, and also how important it is to stop sound leaking out of the room. We will deal with this in two elements of this chapter.

 

Item 1: Room Acoustics

Put quite simply if you play a speaker in an open field it will have not limitations and will play naturally without interference, other than that of background noise.

There is a great video below which demonstrates this:-

 

 

If you put that same speaker in a square room the sound will be very different as the sound will bounce around and cause issues which result in cancellations and peaks in the sound meaning that in certain positions in the room there will be no noise at that frequency or in some places it can be doubly loud!

This is not meant to be a lesson in acoustics, simply to make you aware of the importance to discuss this.

The key points are what have become known as the three R’s:-

  • Resonance - low frequency sounds are very long when they hit a wall they are bounced back on themselves repeatedly causing problems.
  • Reverberation - when a sound is reflected whilst it loses some energy, volume, it does not disappear completely. We can hear these delayed sounds while they decay to nothing when bouncing around the room effecting the clarity of the system.
  • Reflection - Sound travels in a straight line, so when it hits a wall at an angle it is very similar to a pool ball bouncing off a cushion. Some reflections muddy the direction of where the sound appears to be coming from.

Whilst the issues with the room are tricky to deal with the great news is that there is a science to this so a good home cinema designer can help deal with some of the issues early on.

The most common approach to room correction is a combination of room treatment which includes absorb, diffuse and bass trap products in the room which are used in conjunction with some sort of electronic calibration software which can be automated or performed manually by a home cinema specialist.

THINGS TO NOTE:

Two things we see very often in cinema rooms is overuse of absorption which results in a very flat and dead room, personally we do not like this approach as I prefer a bit of life! Also this gives you a feeling of your fingers being stuck in your ears!

Secondly some sound diffusers are not fit for purpose as they are symmetrical which means they simply do not work properly!

Item 2: Sound Isolation

Isolation of sound needs to be discussed as a cinema room can play loud and clearly interfere with people living in the house and also neighbours.

You could write a book on this topic however I will keep this short and sweet, or try to at least!

The main considerations for sound proofing are as follows:-

How important is it to you? 

If you have young children and will want to use the cinema whilst they are in bed above the cinema it may be more important than if your family are more grown up!

Also what is the construction of your home and when was it built, concrete stops more sound than timber frame or SIPS panels.

How much room can you afford to lose inside the room? The more soundproofing you require the smaller the room gets! Our highest level of soundproofing requires around 330mm of additional space!

ProSilence_sound_isolation

Often times we end up with a compromise as many clients do not want to give up too much space, plus the highest level system we offer comes with a considerable cost. For most circumstances losing an additional 100mm of wall space allows us to do an adequate job with the sound proofing which reduces the noise travelling out of the room to something more like ambient background levels.

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