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If a certain standing wave frequency is acoustically isolated from its modal neighbors, its
effect is more likely to be audible and problematic. This can compromise the accuracy of any
loudspeaker.
To analyse your room for standing waves we would recommend that you work upto about
300 Hz. Beyond this point they become less relevant and difficult to perceive.
Any standing wave below 300 Hz is detectable and should they combine sympathetically the
result will be a lumping together and this is very undesirable. Evenly distributed modes are
the goal.
Characterising the room.
Characterising the behaviour of the room is the first step towards your understanding of
your listening room's contribution to the audio system. Follow the simple procedure below
to obtain a better understanding where changes could be made in order realise
improvements.
1. Record data of the room dimensions onto a simple floor plan. The graph paper can assist
you with this.
2. Apply the data (dimensions) to the formula
3. Make a record of the predicted standing wave frequency characteristic for each parallel
wall dimension of the room.
4. Verify your predictions using the Wilson Benesch test CD which has a number of fixed
frequency tests and swept frequencies. Use these to verify and back up your predictions.
Note 1 big differences in perceived and calculated values will indicate an error
Note 2 If the predicted frequency matches with the perceptible increase in output in the
room this has verified your prediction.
Note 3 The listening tests should be taken whilst seated in the main listening position.
Evaluate the data and look for errors.
5. Assess whether changes should be made and what can be changed in order to overcome
any dramatic and clearly in-accurate increase in sound pressure levels.
Middle and High Frequency Room Characteristics.
The middle and high frequencies are effected more by room contents rather than room
shape. The "sound" of a room is described by the surfaces and how they reflect, absorb or
diffuse the acoustic energy. Like all energy, acoustic energy cannot be destroyed, it can only
be converted into something else or reflected. The shape of the surface will determine how it
is reflected and the material will determine whether it is absorbed. All rooms have a
particular sound, and to appreciate what influences are present in your room you should be
aware of how the objects in your room will respond to sound.
Sound waves behave in the same way as light waves or "rays" and so imagine the driver to be
a flood light.
Reflection: acoustic energy is not converted but reflected in an orderly, predictable fashion.
Diffusion: acoustic energy is dispersed in a random and or disordered fashion.
Absorption: acoustic energy is converted into kinetic energy or heat. All or a majority of the
sound energy is "soaked up" or disposed of by the object surface or room boundary.
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