ASTM E 1374-02: Standard Guide for Open Office Acoustics
Excerpts from ASTM E 1374-02: Standard Guide for Open Office Acoustics.

3. Summary of Guide

3.1 Acoustical Privacy- The attenuation of sound between neighboring work stations in an open-plan office is typically much less than that potentially available between closed-plan offices. Nevertheless, a degree of acoustical privacy can be achieved if component selection and interaction are understood. A successful open plan office is the result of careful coordination of the several components, ceiling, wall treatments, furniture and furnishings, heating, ventilation and air-conditioning system, and masking sound system.


4. Significance and Use

4.3 While this guide attempts to clarify the many interacting variables that influence office privacy, it is not intended to supplant the experience and judgment of experts in the field of acoustics. Competent technical advice should be sought for the success in the design of open offices, including comparisons of test results carried out according to ASTM standards.


5. General Open Office Acoustical Considerations

5.2 Attaining acoustical privacy between work stations, open or closed plan, is determined by the degree to which the intruding sounds from adjacent work stations exceed the ambient sound levels at the listener's ear.

5.5 Office layout should be designed to avoid obvious noise intrusion possibilities. Individual work stations should be positioned relative to columns, walls, and each other to avoid uninterrupted sound paths between contiguous work stations. Occupant orientation is also important, because there is a significant difference between the sound level when a talker faces a listener versus the talker facing away from the listener, of the order of 9 dB.

5.6 Loud Noises- Distractions caused by raised voices or loud office equipment usually cannot be controlled by normal open office constructions. It is recommended that some closed plan spaces be provided to contain such loud equipment or enclose noise sensitive spaces such as conference rooms.

5.7 Problem Noise Sources- Computers, business machines, copiers, typewriters, and other noise generating devices should be located in isolated (enclosed) rooms or areas to minimize their noise intrusion into the work station. Where this is impractical, care should be exercised in eliminating or minimizing the noise generation aspects. Telephones and "speaker phones" are a frequent problem. The former should be equipped with flashing lights, rather than ringers (audible annunciators). Large typing pools or word processing centers can generate A-weighted sound levels up to 80 dB. These activities should be contained in special work areas affording adequate noise isolation from the surrounding open plan spaces.

5.8 Undivided Workspaces- Acoustical comfort may be improved in undivided work spaces such as bull-pen offices, drafting rooms, and typing pools by the addition of acoustical absorption to horizontal and vertical surfaces, but no such treatment alone will provide speech privacy.


6. Components of the open plan Acoustical Environment

6.1 Ceilings:

6.1.1 The sound absorbing characteristics required of the ceiling plane for open plan systems are different than those for private offices or conference rooms. In open plan spaces, sound from the source not controlled by part-height space dividers travels toward the ceiling plane, where part can be reflected back into the adjacent work space. To minimize the reflected sound, the ceiling must absorb most of it. In private offices or conference rooms, some lesser absorption or greater reflection may be desirable.

6.1.2 The sound barrier characteristics of the ceiling plane helps provide spatially uniform masking sound from loudspeakers located in the ceiling plenum. If the sound barrier performance is low or variable, it may lead to the perceptions of "hot spots" in the masking sound. Some masking system designs may compensate for these deficiencies or variations.

6.1.3 Lighting fixtures mounted in the ceiling must be chosen with care. Flat, lensed fixtures tend to reflect sound specularly and should be avoided. Parabolic cell fixtures, are preferred because they tend to scatter incident sound. The sound barrier characteristics of the fixtures should also be similar to that of the ceiling, to avoid masking sound "hot spots" underneath them.

6.1.4 Other ceiling elements, such as return air grilles or fixtures, must also be selected with care, to avoid leakage of sound from the masking system or surface reflections of incident sounds.


6.2 Sound Barriers and Vertical Surfaces:

6.2.1 Sound generated within the work station and potentially intruding into adjacent work spaces is of major concern. This potentially intrusive sound is reduced in the following two ways: (1) using barriers that are properly absorptive and appropriately impervious to sound penetration, and (2) reducing the tendency of sound to "flank" or diffract around the perimeters of such barriers.

6.2.2 Sound Reflectors- All vertical surfaces are possible sound reflectors if not specifically treated. Hard, flat, smooth surfaces represent the worst condition. To reduce or eliminate these reflections, such surfaces should be highly absorptive to sound in the frequency range of concern. A particularly difficult area to treat in this regard is the glass in the typical exterior wall of the office area. Note that materials used to achieve sound absorption usually are not effective sound barriers.

6.2.3 Sound Barriers- Reduction of sound transmission through barriers separating adjacent work spaces is normally achieved by adding an impermeable septum to the center of the barrier. Care must be exercised in eliminating any possible "through holes" offering unencumbered passageways for sound to "leak" through to adjacent work spaces.

6.2.3.1 Flanking Transmission- Flanking can be controlled by proper consideration of the height and length of the barrier, the horizontal distance between adjacent barriers, and the sound absorptive characteristics of the adjacent barriers. The most practical method of reducing flanking is to employ vertical barriers that are as high and as long as possible. This may be in conflict with the desire for "openness" or clear view through the office space. The clearance between the bottom of the barriers and the floor should be minimal, although this path is not as critical as clearance above the barrier.

6.2.3.2.1 Barrier Height- Barrier heights of less than 60 in. (1.5m) are not effective in performing as acoustical barriers in open plan offices. As a general rule, barrier heights greater than 80 in. (2 m) provide diminishing returns. "Tradeoff" decisions in the determination of the required height against the original motive for considering the aesthetic factors associated with such systems are required.

6.2.3.3 Electrical Raceways- Current trends are to include the electrical raceway on the bottom of panels; there is also a shift towards including "wire management" features at the top and middle of panels. Unless treated to the contrary, such features can diminish both the barrier and absorptive properties of the barrier.

6.2.3.4 Hang-On Components- Most contemporary open plan office systems incorporate furniture concepts into the overall system. These components include storage compartments, file bins, work surfaces, tack boards, task and ambient lighting modules, communication and power management items, etc. Most of these items will degrade the absorption properties of the system and may also affect privacy characteristics.


6.4 Masking Sound:

6.4.1 Since acoustical privacy is a signal (intruding sound) to noise (prevailing ambient) consideration, precise control of the ambient sound is an essential element for achieving sound privacy in the open plan office. A properly designed, installed, and adjusted electronic sound masking system is the most effective means of controlling the ambient sound...

For the complete masking system standard, click here.



 
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