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Ed's AV Handbook
Batting practice for the AV Professional
and primer for the novice

Chapter 7  Page 4

An Acoustical Strategy
for the small room

3. The Transition Zone Region

The 3rd region is difficult to illustrate.  The 3rd region begins above 300Hz. 
It is dominated by wavelengths that are too long to be described by specular acoustics, and too short by longer room mode wavelengths.

Acoustical tactics for the 3rd region.
A room full of furniture, plus the tactics of Region 4, provides an adequate solution for Region 3.

4. The Region of Short Wavelengths

Region 4 is the region where the concern of specular reflections prevails.  Room boundary reflections compete with the direct sound from a speaker. 
This competing sound distorts sound field imaging and spatial impression.

Acoustical tactics for the 4th region
Locate the 1st points of reflection at all room boundaries. 
The 1st points are at the reflection of a speaker in a mirror placed at a room boundary, observed from the listening position.

Mount acoustical absorption on the wall at ear level between the 1st points of the front and right speakers in a stereo arrangement.  Mount acoustical-absorption between the left and right rear speakers of a multi-channel-arrangement.  Absorb 1st points at the floor with carpet and extra padding.  Absorb the 1st points at the ceiling with acoustic foam or ceiling tile. 

Experiment with the 1st points of the left and right sidewalls.  Increasing lateral absorption creates the sound of a smaller-less spacious room. 
Less absorption creates a more spacious image.  Adjust the amount of absorption to your subjective desire.


Noisy Loose End

A significant concern remains - noise.  If noise from an adjoining area merges with your room, it will obscure sound fields, musical harmonic detail, and compromise dynamics.  Therefore, suppress the transmission of noise through walls, the ceiling, and the floor.

Begin by closing windows and doors.  Then consider the following construction instructions. Trapped air and mass are the two components that are most effective at stopping the transmission of sound through room boundaries.  However, all construction materials have a resonant frequency at which they virtually become an open window to sound.  Therefore, consider the construction of an acoustic sandwich of different materials such as sheet-rock, acoustic insulation, acoustic vinyl, and air space.  Each layer closes another’s resonant window and further suppresses the transmission of noise.

Sound as air and water will leak through small gaps, including gaps in windows, doors, and electrical outlets.  Seal all gaps.  The HVAC system can also produce noise.  Install a dedicated large trunk line duct, lined with lightly painted fiberglass board.  Suspend the ducting and vent with rubber tie-down straps rather than loose metal straps and nails.  Wrap the metal vent in a noise suppression material such as the vinyl blanket mention earlier.  Keep in mind, closing a door or window can have a significant effect.  Refer to Handbook Chapter Six for more detail.


In summary, the 2nd and 4th Regions are the regions of most interest in small room acoustics.  The management of turbulent standing waves, the evasion of room mode peaks and nulls, the absorption of the 1st points of reflection, and the suppression of noise are the most significant concerns. Successfully managing these acoustical distortions that affect timbre, imaging, spatial impression, and dynamic range will result in a first-rate sound room.

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Ed's AV Handbook   
Copyright 2007 Txu1-598-288 Revised 2024

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