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Summary of Contents for Atlas AA-SMG
- Page 1 A technical guide to achieving effective speech privacy in open-plan offices and other environments Sound Masking Systems by Ashton Taylor, Hoover & Keith Inc. for Atlas Sound...
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Page 2: Table Of Contents
Part 1 INTRODUCTION ..... . . 4 WHAT IS SOUND MASKING? THE ECONOMIC BENEFITS OF SOUND MASKING 4 DEFINITION OF TERMS (ALSO SEE APPENDIX A) . - Page 3 BOOTS ........34 No part of this white paper may be copied or used without the written permission of Atlas Sound.
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Page 4: Introduction
Introduction and Executive Summary A sound masking system emits low-level, non-distracting masking noise designed to reduce speech intelligibility and thereby improve speech privacy. This improvement in speech privacy can be of great value in open-plan offices, doctors’ examination rooms and other environments where confi- dentiality is important. -
Page 5: Definition Of Terms
Other situations, in exist- ing structures, may involve significant acoustical problems or building layout issues. In these cases, Atlas Sound recom- mends the services of a qualified acoustical consultant. Court Rooms... -
Page 6: Buildings Near Major Roads, Railroads
Buildings near Major Roads, Railroads, and Airports In most buildings, it is not feasible to com- pletely mask higher-level noises like those from heavy trucks, trains, or aircraft. However, sound masking can soften the impact of these noises. If a client wants masking to cover up these sounds, make sure their expectations are not too high. -
Page 7: Benefits Of Masking To The End User
Benefits of Masking to the End User Cost-Effective Speech Privacy Normal (not confidential) privacy can usual- ly be achieved with floor-to-ceiling walls between workspaces. However, sound masking allows normal privacy to be achieved in an open-plan office with simple partitions between cubicles. This is a cost- effective solution that allows a building owner or leasee to retain the flexibility of an open-plan office. -
Page 8: Three Steps To Successful Sound Masking
Part 2 Three Steps to Successful Sound Masking Carefully planned acoustics, combined with masking sound, make it possible to achieve the goal of increased speech privacy between workstations. There are three steps to successful sound masking: Attenuate the Direct Sound “Direct sound”... -
Page 9: Evaluating The Acoustical Environment
FIG. 1 - In Part A, direct sound from the talker and reflected sound off a hard ceiling con- tribute to poor speech privacy. In Part B, an absorptive ceiling and screen reduce the direct and reflected sound level, and masking sound provides effective (normal) speech privacy. -
Page 10: Attenuation Of Direct Sound
Attenuation of Direct Sound The direct sound is speech from a talker that arrives directly at the ear of a listener without being reflected. Figure 3 shows the direct peak sound levels for male and female talkers at a distance of one meter. FIG. -
Page 11: Sound Transmission Class
′ FIG. 5 - Screens should (a) be high enough to reduce sound passing over them, (b) provide a good barrier to sounds passing through them, and (c) absorb incident sound. Sound Transmission Class Sound transmission class (STC) is a standard way to specify the attenuation of sound through a wall, an open-plan office screen or other bar- rier. -
Page 12: Layout
POOR LAYOUTS FIG. 6 - Examples of good and bad layouts for workstations in open-plan spaces. Reduction of Reflected Sound Energy Layout Simple layout changes can often improve speech privacy in an open-plan office. And, even though these changes will disrupt daily routine in an existing space, clients with severe privacy problems are usually willing to comply. -
Page 13: Ceiling
Ceiling The ceiling in an open-plan office affects speech privacy more than any other acousti- cal element. A hard ceiling reflects sound from one workstation to another, bypassing the sound barrier provided by the worksta- tion screens. This problem is worse when the angle of reflection is between 40º... -
Page 14: Lighting Fixtures
FIG. 7 - Speech frequencies reflect off the flat lenses of ceiling fluorescent fixtures. If the fluo- rescent fixtures are mounted over workstation partition screens, this reflected sound can reduce speech privacy. Lighting Fixtures Typical ceiling-mounted fluorescent lighting fixtures have flat plastic lenses flush with the ceiling. -
Page 15: Boots
FIG. 8 - Install boots above open return air ducts in ceiling plenums. and the masking sound coverage will be uneven. These are very undesirable results. Lighting fixtures with open grid diffusers can cause similar problems. Other Causes of Unwanted Reflections Ceilings aren’t the only source of reflected sound problems in an open-plan office. - Page 16 FIG. 10 - Walls, doors, windows and curtain walls can reflect sound into adjacent workstations. faces such as shelf covers and drawer faces. Of course, workstation partition screens must be highly absorptive. Hard walls, doors and windows can serious- ly degrade speech privacy in both open-plan spaces and in standard offices.
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Page 17: Ambient Noise
Ambient Noise To the extent possible, keep building and office equipment noises below the level of the masking system. The heating, ventilat- ing, and air conditioning (HVAC) system makes a sound similar to an electronic masking sound. However, the level and spectrum will be different from workstation to workstation and, in many buildings, the system cycles on and off. -
Page 18: Part 3 - The Basic Electronic Sound Masking System
Part 3 The Basic Electronic Sound Masking System The electronic sound masking system creates a “blanket” of background noise carefully controlled in level, spectrum, and coverage. Masking sound should not call attention to itself in any way. It should merely seem to be part of the general building noise. -
Page 19: Sound Masking And Background Music Or Paging
the equipment. Ensure the rack has adequate ventilation for uninteruppted usage 24 hours a day, 365 days a year. For an existing space, include the cost of an electrical subcontractor to provide dedicat- ed AC circuits hardwired into the rack. Consider an uninterruptible power supply (UPS) to prevent system shutdown during brief power outages or brownouts. -
Page 20: Equalizer
with a pseudo-random sequence of at least several seconds. Test equipment noise gen- erators usually repeat too frequently to be acceptable for sound masking. Some masking sound generators have computer controls that gradually reduce the normal daytime masking sound to a pre- set nighttime level. -
Page 21: Part 4 - Multi-Channel Masking, Background Music And Paging
Part 4 Multi-Channel Masking, Background Music, Noise Equalizer Gen. Ch. A Ch. A 4-In 2-Out Mixer Music Source Noise Equalizer Ch. B Gen. Ch. B FIG. 12 - Wiring diagram of a two-channel sound-masking system with zone level controls, background music, and an amplified monitor panel. Very simple masking systems, with only the bare minimum of components, are fairly rare. -
Page 22: Zone Level Controls
Zone Level Controls Larger masking systems may cover more than one workspace in a building. Unless the workspaces are acoustically very simi- lar, each deserves its own masking sound level control. Even in a single large room, it may be useful to provide separate level controls for open areas, walled offices, con- ference rooms and corridors. -
Page 23: Paging Sound Level
Paging Sound Level To calculate the paging sound level of a masking loudspeaker at the listener, first gather the following information: * S = loudspeaker sensitivity (from the manufacturer’s data sheet) This must be given as dB SPL with 1 watt input at 1 meter distance * P = power delivered to the loudspeaker in watts (from the system designer) -
Page 24: Part 5 - Masking Loudspeakers And Self-Contained Masking Units
Part 5 Masking Loudspeakers Masking loudspeakers are special assem- blies designed for installation in ceiling plenums. A typical assembly consists of a 4 or 8-inch cone speaker, a 70.7-volt speaker line transformer, a metal enclosure with baffle, and a hanging/mounting hardware kit. -
Page 25: Downwards Loudspeaker Orientation
Downwards Loudspeaker Orientation Roof decks (above the ceiling on the top floor of a building) usually have sprayed-on thermal insulation that is also an efficient acoustical absorber. In this situation, mount the masking loudspeakers high in the plenum and point them downward as shown in Figure 14. -
Page 26: Self-Contained Masking Units
conduit, make the loudspeaker connections inside the electrical box or inside the enclo- sure to avoid violating local building safety codes. Always comply with all state and local codes, as well as the National Electrical Code, for any masking loudspeak- er installation. -
Page 27: Part 6 - Commissioning The Masking System
Part 6 Commissioning the Masking System “Commissioning” the masking system takes place in two steps: Confirm the proper installation and function of all system components. Adjust the system level, spectrum and coverage to the design specification. Good coverage simply means every listener hears masking sound at the desired level and spectrum given in the initial specification. -
Page 28: Masking Spectrum
Masking Spectrum Figure 16 shows a typical masking spectrum compared to typical “quiet” building sound, pink noise, and white noise. FIG. 16 - Octave-band sound pressure levels of typical masking sound (solid line curve), typical “quiet” building background sound (dotted line curve), pink noise (horizontal straight line plot), and white noise (upward-sloping straight line plot). -
Page 29: Masking Spectrum 2
Masking Spectrum 2 Masking Spectrum 2, given in the table below, and charted in Figure 18, is appropri- ate for good open-plan spaces (screens 4 - 5 feet high, some reflective surfaces, and moderate furniture absorption). Compared to Masking Spectrum 1, Masking Spectrum 2 increases the sound level slightly (2 dB) at 2000 Hz, the band that contributes most to intelligibility. -
Page 30: A Comparison Of All Three Masking Spectra
Comparison of All Three Masking Spectra FIG. 20 - Comparison of Masking Spectra: Sound Masking Spectrum 1 (preferred) Sound Masking Spectrum 2 Sound Masking Spectrum 3 Equalizing the System: The Equalization Process After selecting one of the three masking spectra, equalize the system as follows: Use a 1/3-octave spectrum analyzer, measuring microphone, sound level meter (SLM) and oscilloscope. -
Page 31: Troubleshooting
Using an Octave-Band Equalizer for Troubleshooting Although it cannot be used to commission the system, a hand-held, octave-band analyzer is a convenient way to troubleshoot or survey the masking system. Because each band in an octave-band analyzer receives the energy from three 1/3-octave bands, proper levels are approximately 5 dB higher than those given in the 1/3-octave tables above. -
Page 32: Masking Environment
Part 7 As originally discussed, the goal of most mask- ing systems is to increase speech privacy. A well-planned sound masking system achieves this goal by reducing speech sound energy and increasing background sound (with masking sound). But how can speech privacy be quantified? This section shows how to predict articulation and privacy and it discusses how to use the speech privacy... -
Page 33: Normal Privacy
Normal Privacy Normal is usually the best level of speech privacy achieveable in an open-plan office space. A masking installation that achieves normal privacy will reduce distractions from nearby conversations, footfall noise, and the sounds of office equipment. However, even in a normal privacy installation, listeners will still be able to hear speech, and they may even be able to eavesdrop, if they listen... -
Page 34: Part 8 - Case Histories
Part 8 Masking Improves Speech Privacy in a Quiet Space In the open-plan offices of a major oil com- pany, nighttime ambient noise levels were very low. As a result, employees could carry on normal-voice line-of-sight conversations over distances greater than 60 feet and speech privacy was effectively impossible. -
Page 35: Masking Loudspeakers Tapped Too Low
speakers were aimed downward because of the thermal insulation applied to the under- side of the deck above. The contractor could not install boots above the fixtures because there were a great many fixtures, the electrical conduits were in the way, and service personnel would have removed the boots the first time they serviced a fixture. -
Page 36: Medical Professional Building Masking
between two examination rooms and the area just outside these rooms. The improvement in speech sound isolation was immediate and dramatic and the doctors had no problems using their stethoscopes or other instruments. Prior to the test system installation, doctors and patients could hear every word from the next examination room. -
Page 37: Conclusion
Part 8 Basic masking systems are relatively simple to design, install and commission but results are greatly influenced by the acoustics of the ceilings, screens, furniture and interior finishes. When designing a masking system,remember these three steps: Reduce the direct speech sound level (screens, distance) Reduce the reflected speech sound level (ceiling, furniture, wall treatments) -
Page 38: Appendix A - Definitions
Appendix A ambient noise - The background noise in a given environment, usually composed of many sound sources from many direc- tions, near and far. articulation class (AC) the weighted sound attenuation values in the one-third octave bands between from 200 Hz to 5000 Hz. - Page 39 noise - (1) Any disagreeable or undesired sound. (2) A random sound or electronic signal whose spectrum does not exhibit clearly discernable frequency components. noise criterion (NC) curves of curves of octave band sound spectra used for rating the noisiness of an occupied indoor space.
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Page 40: Appendix B - Worksheet
Appendix B To evaluate the acoustics of an office space, use the worksheet titled “Sound-Masking, Octave-Band, Articulation-Index Worksheet” found at the end of this Appendix. This worksheet has the following sections: * Octave-band data and calculations * Input for talker voice level and orientation * Input for talker-to-listener distance * Input for furniture, screens, and ceiling * Input for masking sound levels... -
Page 41: Section A Instructions
Section A Instructions The worksheet gives data for three voice levels: Raised, ANSI Standard, and Normal. These levels are peak levels for male voices. For female voices use the following data: Use the ANSI Standard level unless the situation clearly fits one of the other descriptions. Section B Instructions This section modifies the values entered in Section A to compensate for talker orientations other than face-to-face. -
Page 42: Section C Instructions
Section C Instructions This section reduces the values entered in Section A to compensate for the normal attenuation of direct sound at increasing distance from the talker. Measure the direct path from the cho- sen talker to the chosen listener. Ignore any obstacles for this measurement. If this measure distance corresponds to one of the worksheet rows, simply copy the numbers from that row to the row entitled “Your Values”. -
Page 43: Section D Instructions
Section D Instructions This section modifies the values entered in Section A to compensate for the acoustics of the furniture, walls, and carpet. The first row of data is entitled “Absorptive”. Use this data if the acoustics meet the following criteria: * Chairs are softly cushioned and covered with upholstery cloth (not leather) * Book shelves and file cabinets have absorptive surfaces where possible * Walls have acoustical wall panels or other absorptive treatment... -
Page 44: Section E Instructions
Section E Instructions This section modifies the values entered in Section A to compensate for the acoustical effect of screens and ceiling. These two elements are grouped together because the effectiveness of one depends upon the other. Use one of the rows for “hard ceiling” if the space has a plaster, gypsum board, or wood ceiling that reflects sound. -
Page 45: Section F Instructions
Section F Instructions Hard surfaces can reduce speech privacy by reflecting sound energy from the talker’s workstation into adjacent spaces. The position of the hard surface, with respect to the talker and listener, is most important. A hard surface that directly reflects sound (a first-order reflection), just like a mirror, is a problem surface. -
Page 46: Section H Instructions
Section H Instructions Enter the background sound levels (including masking sound) in the “Your Values” row of Section H. Measure the actual background sound level or choose one of the data sets in the table. Choose the first row of data for an office with no masking. For a space where masking sound will be installed in the future, use data from the “47 dB(A)”... -
Page 47: Section J And Section K Instructions
Section J and Section K Instructions Section J calculates the actual articulation index (AI). First multiply the values from Section I by the AI weighting factor given in Section J for each octave band. Enter these results in the bottom row. Then, add all of the numbers in the bottom row to calculate the AI. Enter this final result in the box in Section K. -
Page 48: Worksheet Example 1
Worksheet Example 1 Open Plan Environment Part 1 - No Speech Privacy Assume a client wants a masking system in an open-plan space with standard office furniture, 4-foot high screens, commercial padded carpet, mineral fiber ceiling tile, and workstations spaced approximately 8 feet apart. First, determine the speech privacy without masking sound by entering the following data and performing the calculations on the worksheet: °... -
Page 49: Screens
Part 3 - Substitute 6-Foot-High partition Screens Even with masking, there is still no speech privacy. Next, recalculate the worksheet replacing the 4-foot high screens with 6-foot high screens as follows: ° × × × × × Part 4 - Move Workstations Farther Apart The improvements in Part 3 still do not result in effective speech privacy. -
Page 50: Part 5 - Install A High Articulation Class (Ac) Ceiling
Worksheet Example 1 Part 5 - Install a High Articulation Class (AC) Ceiling Part 4 results in marginal speech privacy even with most of the elements correctly implement- ed. To achieve better privacy, install a high articulation class (AC) ceiling and increase the masking level to the maximun recommended setting of 50 dB(A) as shown in the following worksheet: Summary and Conclusions... -
Page 51: Worksheet Example 2 - A Walled Space Part 1 - No Masking Sound
Worksheet Example 2 A Walled Space Part 1 - No Masking Sound The following worksheet assumes that the dividing partition is a standard interior office build- ing wall, the acoustical absorption in Section D is mixed, and there is no masking sound. °... - Page 52 Sound Masking Worksheet _______________________________________________________ _______________________________________________________ ° ° ° ° ° Copy Before Using Page 52...
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- Page 56 1601 Jack McKay Blvd. Ennis, Texas 75119 Tel: 800-876-3333 Fax: 800-765-3435 www.AtlasSound.com PN 484016 AT000369...
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