Types of Sound Wave Reflections

•Unless properly controlled, reflected sounds can be detrimental to accurate monitoring

•Axial – 2 surface reflections

•Tangential – 4 surface reflections

•Oblique – 6 surface reflections

•Sound waves reflecting more than 6 times are usually too weak to cause significant problems

Room Acoustics - Frequency Nodes

•Most rooms have frequency peaks (false increase) and nulls (false decrease)

•Called frequency nodes

•Creates a false sense of the sounds coming from the monitors – the room adds or subtracts frequencies

Room Acoustics – Low Frequencies

•Small rooms suffer the most problems with low frequencies

•The frequency below where the build up occurs depends on the room dimensions

•The frequency below which problems occurs goes up as the room size gets smaller

Room Acoustics

•Rooms with two or three equivalent dimensions have a large amount of frequency build up and number of nodes

•Room corners cause a lot of problems with low frequencies

•Amount of apparent low frequency boost caused by a corner is 9 dB (i.e., 3 times more low frequencies than actually present)

Room Acoustics - Treatment

•Good sounding rooms often exhibit a mix of natural ambience with no flutter echoes or false bass build up

•Most rooms can be treated with a proper blend of absorption, low frequency control and diffusion

Room Acoustics – Absorption Control

•Absorption involves removing (absorbing) some of the sound waves, thus reducing the strength of direct reflections off of surfaces (usually walls)

•Acoustic foam or panels is used in most home studios

•Usually placed on the walls near the monitoring position•To the side of the monitors•Between the monitors•Ceiling above listening position

•Array of smaller panels tends to work better than a large panel

•Thicker foam absorbs more sound and down to lower frequencies

Absorption Control – Placement of Panels

•Sit in the listening position

•Have an assistant hold a mirror along the walls near the monitors

•Glance at the mirror as it is moved around the room

•Place absorption panels on any wall location where you can see the monitors in the mirror

Room Acoustics – Low Frequency Control

•Controls the amount of low frequency build up in a room

•Usually accomplished by placing bass traps in the vertical room corners (wall to wall junction)

•Wall/ceiling junction are also corners, but treating the wall/wall junctions are easier and a higher priority

•Bass traps are usually large and/or thick

•The smaller the room, the more critical controlling low frequencies becomes

Room Acoustics – Diffusion Control

•Breaks up the sound waves to create a wash of reverb and removes some of the direct sound and echoes

•Creates a greater sense of openness in a room without removing acoustic energy or greatly altering the frequency content

•Diffusion panels contain irregular or multiple level surfaces

•Usually placed in the rear part of the room along the side walls and ceiling and, in some cases, the rear wall

•Covering 20-25% of the rear half of the room is usually plenty of diffusion coverage

Room Acoustics – Treatment

•Room treatment order of priority•Low-frequency control•Absorption•Diffusion