BARRIERS
Aside from structure born sound, sound travels by three paths: 1) Direct, 2) Reflected, and 3) Diffracted. The direct path is the "line - of - sight" straight path between the source (people, machines, etc.) of the sound and the receiver(s). We block that path by placing barriers in that path. The ability of those barrier systems and materials to block sound is measured by a test which provides a performance criteria in terms of STC (Sound Transmission Coefficient). This is a single number that defines the average number of decibels blocked by that material, composite or system. The higher the STC the better a material is at blocking sound.

In open plan space those barriers are partial height and their barrier performance (STC) is not as critical as in situations where more isolation is required. Properly designed and specified, partial height barriers can provide an adequate degree of speech privacy for typical office usage. When a high degree of privacy and/or noise containment is required, full height walls must be used.

LEAKS
The problem with full height walls is that they can create a sense of false security with regards to the isolation that they provide. A wall that appears to be a solid barrier may have weak points and/or flanking paths by which sound can find its way to the other side.

A wall with a STC of 45 will block 45 decibels. That's a lot of sound being blocked. If that same wall has a 0.3% (less than 1%) line of sight opening, the STC drops to 25. Perceptually, that is a 75% loss of performance. It will be 400% louder on the other side of that wall than if that barrier wall were tightly sealed.

It's not just clear (see-through) openings that diminish the efficiency of barrier walls. Combinations of weak points and other conditions serve to defeat an otherwise efficient envelope. Examples of these conditions and solutions are, for example:


CEILINGS: Unless the wall extends to the slab above, sound will pass through the ceiling on one side of a wall, bounce off of the slab above and, pass through the ceiling on the other side of that wall. See Barrier systems

Solutions: Specify ceilings with STC equal to the wall. Add materials to the back of the ceiling panels to increase their STC (barrier blankets, trowel able coatings, etc.). Install a vertical plenum barrier between the top of the wall and the slab. Install sound traps over open air grills.

WALL CORNERS: Where walls intersect outside window walls there may not be a tight seal at the mullion. Additionally, the filler piece above a perimeter convector unit between the wall and the exterior wall may be mostly cosmetic (a visual barrier).

Solutions: Use caulking. Add additional materials to these filler pieces. The idea is to have the mass (weight per square foot) equal to that of the rest of the wall. See Barrier systems

CONVECTOR PENETRATIONS: Where perimeter HVAC units penetrate common walls, the hole created to pass the duct or pipe through can be substantially larger than that conduit. The unit metal cover (usually with vents) hides that violation from view, but not from sound.

Solutions: Make smaller holes. Caulk or otherwise seal openings with dense material (spackle, lead, etc.).

DOORS: Typically, doors do not fit tightly in their jambs. Sometimes small rubber buttons in the door jamb are used to cushion the door when it closes; that "slamming" noise. These assure an air space between door and jamb. To avoid interference, doors are usually cut to provide a clearance of the carpet as they open and close. Gaps of 1/2" to 1" are not uncommon. These leaks work to defeat an otherwise tight, acoustically efficient wall. Hollow core doors are often not adequate.

Solutions: Use gasketing around doors. Use "drop" guillotine-like closures at thresholds. Use solid core doors (check STC data from the manufacturer). See Barrier systems

Space at the bottom of door allows transmission of conversations and other distractions. Privacy is compromised.	A threshold seal that engages when the door is closed creates a tight seal preventing noise transmission.

Button cushions at doorjamb assure an air space that enables noise transmission.	Seals at jambs stop the transmission of sound.

Specific tutorials with graphics and/or photos can be accessed by clicking on the following topics:

 OPEN PLAN ACOUSTICS

 OVERALL NOISE LEVELS

 VIDEO CONFERENCING – TELE CONFERENCING

 CALL CENTERS

 NOISE ISOLATION

 HVAC NOISE

 AUDITORIUMS, MEETING AND TRAINING ROOMS

 CORPORATE DINING FACILITIES

Topics in other sections address acoustical issues in facilities such as medical, fitness, and dining.