Architectural Acoustics

Transcription

1 Architectural Acoustics SUSPENDED CEILING SYSTEMS A Sustainable Integrated Ceiling Platform Presented by: United States Gypsum Company AIA Provider #: K011

2 Credit(s) earned on completion of this course will be reported to AIA CES for AIA members. Certificates of Completion for both AIA members and non-aia members are available upon request. CES for continuing professional education. As such, it does not include content that may be deemed or construed to be an approval or endorsement by the AIA of any material of construction or any method or manner of handling, using, distributing, or dealing in any material or product. Questions related to specific materials, methods, and services will be addressed at the conclusion of this presentation. This course is registered with AIA

3 Course Description A discussion of the physics and nature of sound - this course will use details and examples to cover design criteria such as STC, CAC, NRC, factors of sound control such as use of building materials, flanking paths, and ASTM testing methods related to interior partitions in the architectural environment.

4 Learning Objectives 1. Understanding Principles of Sound Control Construction such as the physics of sound, sound absorption and reverberation. 2. Be able to define STC, CAC and NRC and clearly recognize the differences and benefits of each. 3. Explain the difference between sound isolation & sound transmission. 4. Comprehend the importance of sound design solutions though Construction Details

5 CRITICAL ISSUES in DESIGN Fire Resistance Sound Control Full spectrum of performance attributes Moisture Control Abuse Resistance Aesthetics Sustainability

6 Architectural Acoustics Involves two main aspects of Sound Sound Transmission Speech Privacy Sound Absorption Speech Intelligibility

7 Architectural Acoustics Involves two main aspects of Sound Sound Transmission: That is sound that is transmitted from one space or room to another. The sound can not only travel directly through the wall as indicated, but can also travel from above the ceiling or from below the floor. The aspect of sound deals with Speech Privacy. Sound Absorption: This has to do with sounds within a space or room. Direct sound from a speaker must be controlled so that unwanted sounds, or reflected sounds within the room do not interfere with Speech Intelligibility. 7

8 Impact of Unwanted Sound Employee satisfaction Interruptions Productivity Loss Confidentiality Health and safety It is well established that proper noise control can significantly increase the output and efficiency of workers. Even moderately loud noises can produce auditory fatigue -- an acoustic term for "frazzled nerves."

9 Definitions Wave Length Atmospheric Pressure Complete Cycle The wave length of a sound is one complete cycle of the particles of a medium, usually air moving from their state of rest to a positive pressure back through their starting point and then to equal point of negative pressure and back to their state of rest. Vibrating objects create fluctuations in air pressure as the particles of air move back and forth, these air particles move through the air in a wave motion and are interpreted by the ear as sound.

10 Definitions Frequency The number of cycles per second. Measured in Hertz (Hz) 1 Second

11 Frequency Ranges Acoustical Lab Tests Human Speech Music 20 Hz Human Hearing Range 20 khz Frequency Hz This graph shows the normal range of human hearing. 20 Hz to 20,000 Hz. Acoustical Lab tests are conducted in the range from 63 Hz to 8000 Hz. This is greater than the range of speech but certainly does not cover the full range of human hearing.

12 Definition Velocity of Sound - 1,130 ft/sec Greater the Frequency the shorter it s wave length. Frequency (Hz) Wave length (ft) ½ Since we know that the speed of sound is 1,130 feet per second and that it s Frequency is the number of cycles per second. We can do the math and see that a sound of 63 cycles per second has a wave length of approximately ft in order for that sound to travel 1,130 feet in one second.

13 Definition Decibels (db) Ø The unit of measure for Sound Pressure Ø Sensed by the ear as Loudness.

14 Amplitude of Common Sounds db Example Level 140 Jet engine at 75 ft. Deafening 120 Rock Concert Painful 80 Loud stereo music Harmful 60 Highway traffic Annoying 50 Office environment Moderate 20 Whisper Barely Audible 10 Human breathing Very Faint Various levels of AMPLITUDE of some Common Sounds are shown by the Decibel level in the left column. 140 db level is considered the threshold of pain. At this level of sound, the human ear will be permanently damaged. At 80 db, the human ear over a sustained period of time can be permanently damaged.

15 Amplitude of Common Sounds db Example Level 140 Jet engine at 75 ft. Deafening 120 Rock Concert Painful 80 Loud stereo music Harmful 60 Highway traffic Annoying 50 Office environment Moderate 20 Whisper Barely Audible 10 Human breathing Very Faint A normal Office Environment is considered to be in the range of 40 to 60 Decibels. It is important to note, that at a Whisper, the sound level is still 20 db. Therefore, if a noise being generated at say, 80 db is to be reduced to a Whisper, the difference in sound level is 60dB. We find that a partition with an STC rating of around 60 STC will be effective in reducing 80 db to the acceptable level of a Whisper.

16 Acoustics & Building Design Sound Absorption Sound Transmission

17 Noise Reduction Coefficient (NRC) First let s take a look at Sound Control within a space or Noise Reduction. One of the industry standards established to help you make relative comparisons of acoustical products is called NRC or Noise Reduction Coefficient. A ceiling panel s ability to reduce reverberation in a space is expressed as a Noise Reduction Coefficient (NRC). NRC can be defined as the average amount of sound energy a material absorbs at the frequencies of 250 Hz, 500Hz, 1000Hz and 2000Hz. ASTM C423 defines the procedure to determine ceiling panel NRC.

18 Noise Reduction Coefficient (NRC) Average amount of sound energy a material absorbs at the frequencies of 250 Hz, 500 Hz, 1000 Hz and 2000 Hz. The higher the NRC, the less sound is reflected (echo).

19 Measurement of Sound Absorption The standard ASTM Test Method for determining the Sound Absorption (NRC) of Acoustical Materials is ASTM C423 (NRC) A specimen of material approximately 8 feet square is placed in the center of the room on an elevated platform 16 high. Prior to placing the acoustical material in the room, the reverberation time is determined. Then, the reverberation time is measured after the placing of the acoustical material, and the difference in the two measure times is used to calculate the effectiveness of the acoustical material to absorb sound at each frequency and thus establish the Absorption Coefficients. Rotating Diffuser Sound Source Test Sample on Std Plenum Diffuser Panel

20 Noise Reduction Coefficient Frequency (Hz) , , , The absorption of a product is measured at 6 frequencies. Ceiling manufactures take 4 frequencies and average them. The next slide walks thru the calculations.

21 Noise Reduction Coefficient NRC (Noise Reduction Coefficient): Mathematical average of the absorption coefficients at: 250Hz Hz + 1,000 Hz + 2,000 Hz 4 21

22 Noise Reduction Coefficient NRC (Noise Reduction Coefficient): Mathematical average of the absorption coefficients at: 250Hz Hz + 1,000 Hz + 2,000 Hz 4 Example: NRC=

23 Common Building Materials NRC (Absorption) STC (Transmission) Wood Plaster Gypsum Board Non-Perforated Metal First we have a group of hard, dense materials that are good at stopping sound transmission but are poor at absorption.

24 Common Building Materials NRC (Absorption) STC (Transmission) Perforated Metal Polystyrene Fiberglass Next we have a group of products that are good at Noise Reduction because they are very porous, however, sound passes through the material making them poor at stopping sound transmission. Mineral Fiber Finally we have a mineral fiber panel. This product has a unique balance of Sound Absorption and Sound Transmission reducing properties. For this reason most Acoustical Ceiling Panels are a mineral-fiber composition.

25 Noise Reduction Coefficient NRC of.50 is required for a panel to be considered acoustical. (Industry Standard) Open plan environments require higher NRC levels.70 in generally considered a minimum NRC for open office applications.

26 Definition Reverberation The continuation of sound reflections within a space after the source has ceased. A basic acoustical property of a space. Think of it as an echo. It can enrich speech and music in all areas -- or it can slur speech and generate higher noise levels throughout a room, depending upon the room volume, timing, and absorption. In rooms used for speech or music, reverberation time should be long enough to enhance the blending of sounds, but short enough so there is no excessive overlapping and confusion. In general, the larger the room, the longer the reverberation time because sound waves must travel farther between absorptive surfaces.

27 Direct & Indirect Sound Indirect sound Direct sound Reverberation can have a Positive & Negative Effects Too much is distracting Negative effect if the distance the indirect sound has to travel to reach the audience is too far. Enhanced or amplified by indirect sounds which are reflected off walls and the ceiling Controlled with increased absorption

28 Recommended Reverberation times in Seconds Speech Small offices 0.50 to 0.75 sec Class Rooms to 1.00 sec. Work Rooms to 2.00 sec. Music Rehearsal Rooms to 1.00 sec. Chamber Music to 1.50 sec. Orchestra/Choral /Church to 2.00 sec. Organ Music 2.00 to 2.25 sec.

29 Sound Masking Acoustical ceilings can be very effective at reducing the sound which is reflected back into a space or transmitted into adjacent areas. In some environments, however, acoustical ceilings alone cannot provide the level of control required. In these situations, sound masking is a sensible option for additional acoustical control. This means installing a masking- noise system. Masking noise mimics a ventilation system noise and is created with loud speakers above the ceiling tile. The masking system raises the background sound level to mask distracting noises

30 Sound Masking Engineered Sound Electronically produced sound Ambient background sound is beneficial in exceptionally quiet environments A supplement to acoustical ceilings

31 Sound Masking Covers noise and conversation not absorbed or blocked Works by electronically producing a unique sound spectrum similar to that of softly blowing air Masking system raises the background sound level to mask distracting noises. Increases speech privacy

32 Sound Transmission Room to Room Ceilings & Partitions

33 Sound Transmission CAC Room to Room - Ceilings CAC CAC is an industry standards used to compare the relative effectiveness of different assemblies in reducing sound transmission. CAC is used for ceilings and represents a double pass through the assembly.

34 CAC Between Rooms with a Common Ceiling Plenum (ASTM E1414, CAC) Source Room Sound Source Revolving Microphone Receiving Room 60 STC Wall Revolving Microphone ASTM E 1414 is used to measure sound transmission through a ceiling system. This ceiling test is commonly referred to as a two pass test since the sound travels through the ceiling on both sides of the wall. In E 1414 a common ceiling is installed with a high STC partition dividing the space into two rooms. A source sound is generated in one room and the sound levels are recorded. The source sound goes up through the ceiling in the source room and down through the ceiling above the receiving room. Sound levels are recorded by a microphone in the receiving room to determine the amount of sound transmission loss through the ceiling material. The CAC rating approximates the sound transmission loss between the two rooms in decibels.

35 CAC Between Rooms with a Common Ceiling Plenum (ASTM E1414, CAC) Source Room Sound Source Revolving Microphone Receiving Room 60 STC Wall Revolving Microphone For example, if a source room has a noise level of 60 db and a ceiling panel with a CAC of 40 is installed the sound level in the receiving room will be approximately 20 db (60-40). Rating which ranks the performance of a product in a controlled test environment with regards to the transmission of sound. Sound transmission loss attributed to the acoustical ceiling. CAC performance is most critical in closed office applications where privacy is a major consideration

36 Sound Transmission Class (STC) Room to Room - Ceilings STC STC is single pass through assembly and STC is a single number system to determine sound redux in partition.

37 Sound Transmission Class (STC) ASTM E 90 - Two Room Method Source Room Sound Source Revolving Microphone STC Receiving Room Revolving Microphone The standard ASTM Test Method for measuring Sound Transmission through Wall Systems is similar to testing Ceiling Systems in that two chambers are used during the test. A common high CAC barrier ceiling system is installed (such as concrete) to prevent sound transmission through the ceiling. A dividing wall system is construct for testing. Again a Source Sound is generated in the Source Room, and sound level measurements are recorded by a Revolving Microphone located in the Receiving Room to determine the amount of sound transmission loss through the Wall Assembly.

38 STC Values - Common Wall Designs

39 Sound Control How to achieve Sound Attenuation Increase STC by: Usually the Dimension of the Framing 3 5/8 1. Isolation 2. De-coupling 3. Absorption 65 db 15 db 4. Mass STC = 50 TL = 50 db resilient channel Drywall 50 STC Insulation either SAFB or fiberglass to absorb sound energy

40 Sound Control The Five FACTORS OF SOUND CONRTORL TRANSMISSION : Usually the Dimension of the Framing 3 5/8 1. ISOLATION or the separation of materials from one side a wall from the other side sometimes referred to as de-coupling. 2. MASS - use of a high density material in these examples we will use Gypsum Panels. 3. ABSORPTION - commonly cavity insulation material. 4. DE-COUPLING or inelasticity by the use a material such as Lead resilient channel Drywall 65 db 15 db 50 STC Insulation either SAFB or fiberglass to absorb sound energy

41 25 ga. Steel stud Single Layer 5/8 Type X STC 40 Let s now review the concept of enhanced combination effect with a few wall assembly sections showing typical constructions with increasing STC performance. We begin with a typical gypsum wall partition assembly 25 gauge 3 and 5/8 metal studs with framing spaced 24 inches on center and a single layer of 5/8 Type X gypsum wallboard placed on each side. The resulting laboratory performance is a STC of 40. Sound Transmission Class or STC is a logarithmic calculation. This essentially means that there is a 40 db (decibel) loss through the constructed assembly if built as tested.

42 Absorption Add Insulation STC 49 In the second assembly we have added 3 of insulation (tested with SAFB Sound Attenuation Fire Blankets) or high melt mineral wool insulation. The resulting STC increases to 49. Every 10 points of increased STC performance means that the construction is twice as quiet or effective in reducing the sound vibration energy through the constructed assembly at the tested sound frequencies. Adding 3 of mineral wool insulation almost doubles the performance of the wall assembly in terms of STC performance.

43 Decoupling Add Resilient Channel STC 54 In the third wall section, we have added a component known as a resilient channel made of 25 gauge steel. This component is designed to de-couple or assist in separating and isolating sound vibration from one side of the wall partition to the other. Resilient channel is installed horizontally perpendicular to the metal framing and will be used for the attachment of the gypsum wallboard on one side of the assembly. It is important to remember that fastener should be engaged through the 5/8 Type X gypsum wall panel and into the resilient channel, but not into the 3 and 5/8 stud. Doing so will short circuit the STC performance and re-connect the sound bridge through the wall assembly. Proper installation results in an additional 5 points of STC a noticeable improvement.

44 Mass Add Second Layer of 5/8 Type X STC 61 Lastly we will add a second layer of mass in this case 5/8 Type X gypsum panels to each side of the wall partition assembly. The additional mass in combination with the other techniques used absorption and de-coupling results in an additional 7 points of STC performance an excellent improvement again

45 25 ga. Steel stud Single Layer 5/8 Type X STC 40 Absorption Add Insulation STC 49 STC 54 Decoupling Add Resilient Channel Mass Add Second Layer of 5/8 Type X As you can see the enhanced combination effect or the combination of factors of sound control work effectively together to increase performance dramatically 4 times more quiet from the first assembly diagramed to the last while maintaining a small footprint and keeping construction costs affordable. STC 61

46 Improving Sound Transmission Loss Rules of Thumb Doubling Partition Width = 5 db Transmission Loss Improvement Doubling MASS = 5 db Transmission Loss Improvement By only using the factors or either MASS or ISOLATION, it is difficult to achieve high STC ratings. This can however be achieved by combining two or more positive principles of sound transmission.

47 STC 53 2 Layers 5/8 Gypsum Board Insulation Sound Path STC 29 Unsealed This animation first constructs a wall system that can achieve an STC of 53 Then shows that without proper AIR SEAL or Acoustical Sealant, the STC rating can be reduce to just 29STC, unsealed.

48 STC 53 Acoustical Sealant 2 Layers 5/8 Gypsum Board Insulation Correctly Sealed This image constructs a wall system that can achieve an STC of 53. Then it shows that with the proper AIR SEAL or Acoustical Sealant, the STC rating is maintained.

49 Sound Transmission Structure Ceiling High STC For wall assemblies with an STC of greater than 50, we recommend extending the wall directly to the underside of the structure. This will assure the sound control between adjacent rooms. Floor STC = > 50

50 Sound Transmission Structure For wall assemblies with and STC less than 50, it is recommended to first install the ceiling, and then install the partition to the underside of the ceiling. This way, there is sound control compatibility between the wall and the ceiling. Most ceiling manufacturer s make a ceiling system that has a CAC rating of An 6 inch blanket insulation installed above the partition will generally increase the CAC of the ceiling system by 5 points. Ceiling STC = < 50 Floor

51 Sound Control Negative Impacts FLANKING PATHS & AIR LEAKS. This can be correct by the proper installation of Acoustical Sealant. Flanking paths are normally associated with openings in the wall system, such as doors, windows, electrical boxes, and HVAC ducting. Acoustical sealant should be used at all partition perimeters, cutouts for lights, cabinets, pipes, ducts, and electrical boxes. A STC rating of a desired assembly from an accredited laboratory is a first step in achieving your sound performance goals.

52 Sound Control Negative Impacts Flanking Paths Electrical Boxes: Especially back-to-back HVAC Perimeter Seals Doors Other penetrations Example: Back-to-back electrical boxes

53 Flanking Paths Better Best FLANKING PATHS are weaknesses in the wall system regarding Sound Transmission such as when electrical boxes are installed back-to-back for economical reasons. Even electrical boxes that are circuited together within a common wall can allow a path for sound to travel through. Example 2 is an improvement when boxes must be in the same cavity. As always boxes should be caulked and in this case the cavity is filled with insulation. Example 3 is the proper installation.

54 Flanking Paths CUTOUTS Cutouts for Electrical panels or medicine cabinets are another problem area. Material mass that has been removed from the wall should be replaced behind the cutout and sealed. An equal mass of drywall used to seal the area is a economical solution. Cabinet

55 HVAC Far to often seen, this mechanical supply design negates the construction of good STC / CAC assemblies.

56 Flanking Paths HVAC Improving Sound Performance Placing a couple of 90 degree transitions in the layout will significantly improve the condition.

57 Since a door is usually the weak link in a partition, care should be taken to not place doors adjacent to each other on a corridor. This condition in an office building or school creates real sound problems

58 Room Layout The more often sound turns and reflect off of surfaces the more sound energy will be reduced. Quiz Password: 00AA01DE

59 Thank You! Architectural Acoustics Quiz Link