I write this because in my line of work I come across people who claim to know about acoustics, room treatments and in particular how to make a cinema “sound good”. I aim to dispel some of the myths and give a simple guide to ways in which you can go about improving the acoustics of you living room to suite a surround sound system or hi-fi.
So, lets start at the beginning.
How does sound behave in my Living Room?
To answer this we need to consider the room its self and what we have in that room. We of course have four walls, each of which will reflect sound. Very simply two parallel walls reflect low frequencies, these are known as Axial Modes, and are the most powerful and troublesome echos we have to deal with.
The simplest solution is to have no parallel surfaces, however we all know in our living room this is impossible. The ceiling and the floor will always be parallel even if the walls are not. The next best thing is absorption, acoustic specialists will tell you to invest in “bass bins”. They are absolutely right technically, but this is your living room not a recording studio, the best this to do is add as many soft furnishings as possible, no leather sofas, plush deep carpets, heavy curtains big cushions etc. This will be no means cure the problem, but it will help.
Sound does not just bounce in one direction, it can bounce of at angles. If the sound remains on one plane, i.e. x or y or z then we say these are Tangential Modes. These are made up predominantly by mid frequencies.
If the sound bounces randomly across all planes, i.e. x, y and z then we say they are Oblique Modes and are generally high frequencies.
This is of course highly simplified, but the principle will ring true. The best way to deal with the frequencies bouncing around that we don’t want is absorption, things like canvas paintings are good for mid frequencies as are light curtains, blinds and even fabric wall paper. The other option is to use diffusers, these scatter the Tangential Modes into the least problematic Oblique Modes, some diffusers can be make to look quite nice. If you want to go down the diffuser route, hunt around but don’t forget, you still want your living room to look homey or your wife will kill you!
I wouldn’t worry too much about Oblique Modes as they scatter and die out very quickly.
The next question to ask is; does it make a difference where I put my speakers?
The short answer is yes. The long answer is it depends on what speakers you have and what you hope to achieve.
If you are looking at setting out your Surround Sound have a read of one of my previous posts How to Setup Your Surround Sound. If you are setting up a Hi-fi or are creating a listening environment then you need to place your speakers at about ear height and 30 - 40 degrees apart as viewed from the desired sweet spot. You should also bring them away from the wall slightly as if they are too close you get something called comb filtering (for the super geeks follow this link to Wikipedia). The best way to check if you have got it right is to have a listen, if the music sounds muddy move the speakers further from the wall. Another tip is if your speakers sound a little weak in the bass area to put them in corners as this will give a 3dB lift to bass frequencies. If the speakers have a port you can also experiment with putting different kinds of foam in the port, this will change the way air flows in and out and consequently how the speakers respond to bass.
As far as setting up the room goes that’s it! Remember to listed to your work and save using your EQ for minor tweaks.
