# Acoustics/Basic Room Acoustic Treatments

![](Acoustics_basic_room_acoustic_treatments.JPG "Acoustics_basic_room_acoustic_treatments.JPG")

## Introduction

Many people use one or two rooms in their living space as \"theatrical\"
rooms where theater or music room activities commence. It is a common
misconception that adding speakers to the room will enhance the quality
of the room acoustics. There are other simple things that can be done to
increase the room\'s acoustics to produce sound that is similar to
\"theater\" sound. This site will take you through some simple
background knowledge on acoustics and then explain some solutions that
will help improve sound quality in a room.

## Room sound combinations

The sound you hear in a room is a combination of direct sound and
indirect sound. Direct sound will come directly from your speakers while
the other sound you hear is reflected off of various objects in the
room.

![](sound_lady.jpg "sound_lady.jpg")

The Direct sound is coming right out of the TV to the listener, as you
can see with the heavy black arrow. All of the other sound is reflected
off surfaces before they reach the listener.

## Good and bad reflected sound

Have you ever listened to speakers outside? You might have noticed that
the sound is thin and dull. This occurs because when sound is reflected,
it is fuller and louder than it would if it were in an open space. So
when sound is reflected, it can add a fullness, or spaciousness. The bad
part of reflected sound occurs when the reflections amplify some notes,
while cancelling out others, making the sound distorted. It can also
affect tonal quality and create an echo-like effect. There are three
types of reflected sound, pure reflection, absorption, and diffusion.
Each reflection type is important in creating a \"theater\" type
acoustic room.

![](sound.jpg "sound.jpg")

### Reflected sound

Reflected sound waves, good and bad, affect the sound you hear, where it
comes from, and the quality of the sound when it gets to you. The bad
news when it comes to reflected sound is standing waves.

These waves are created when sound is reflected back and forth between
any two parallel surfaces in your room, ceiling and floor or wall to
wall.

Standing waves can distort noises 300 Hz and down. These noises include
the lower mid frequency and bass ranges. Standing waves tend to collect
near the walls and in corners of a room, these collecting standing waves
are called room resonance modes.

#### Finding your room resonance modes

First, specify room dimensions (length, width, and height). **Then
follow this example:**

![](equationandexample.jpg "equationandexample.jpg")![](Resmodepic.jpg "Resmodepic.jpg")![](exampletable.jpg "exampletable.jpg")

#### Working with room resonance modes to increase sound quality

##### There are some room dimensions that produce the largest amount of standing waves.

1.  Cube
2.  Room with 2 out of the three dimensions equal
3.  Rooms with dimensions that are multiples of each other

##### Move chairs or sofas away from the walls or corners to reduce standing wave effects

### Absorbed

The sound that humans hear is actually a form of acoustic energy.
Different materials absorb different amounts of this energy at different
frequencies. When considering room acoustics, there should be a good mix
of high frequency absorbing materials and low frequency absorbing
materials. A table including information on how different common
household absorb sound can be found
here.

### Diffused sound

Using devices that diffuse sound is a fairly new way of increasing
acoustic performance in a room. It is a means to create sound that
appears to be \"live\". They can replace echo-like reflections without
absorbing too much sound.

Some ways of determining where diffusive items should be placed were
found on this
\[<http://www.crutchfieldadvisor.com/S-hpU9sw2hgbG/learningcenter/home/speakers_roomacoustics.html?page=4>:
website\].

1.  If you have carpet or drapes already in your room, use diffusion to
    control side wall reflections.
2.  A bookcase filled with odd-sized books makes an effective diffuser.
3.  Use absorptive material on room surfaces between your listening
    position and your front speakers, and treat the back wall with
    diffusive material to re-distribute the reflections.

## How to find overall trouble spots in a room

Every surface in a room does not have to be treated in order to have
good room acoustics. Here is a simple method of finding trouble spots in
a room.

1.  Grab a friend to hold a mirror along the wall near a certain speaker
    at speaker height.
2.  The listener sits in a spot of normal viewing.
3.  The friend then moves slowly toward the listening position (stay
    along the wall).
4.  Mark each spot on the wall where the listener can see any of the
    room speakers in the mirror.
5.  Congratulations! These are the trouble spots in the room that need
    an absorptive material in place. Don\'t forget that diffusive
    material can also be placed in those positions.

## References

-   Acoustic Room Treatment
    Articles
-   Room Acoustics: Acoustic
    Treatments
-   Home Improvement: Acoustic
    Treatments
-   Crutchfield
    Advisor

