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
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
Region 4 is the region where the
concern of specular reflections prevails. Room boundary
reflections compete with the direct sound from a
This competing sound distorts sound field imaging and spatial
Acoustical tactics for the 4th region
Locate the 1st points of reflection at all room
The 1st points are at the reflection of a speaker in a mirror
placed at a room boundary, observed from the listening
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
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