HSW/STC SOUND ENVIRONMENT LEARNING AND HEALING BY: United Plastics Corporation 511 Hay Street Mount Airy, NC 27030 (800) 577-3931 www.dbsoundcontrol.com
Learning Objectives Upon completion of this course, you will have a better understanding of: What is Noise How does it effect us, what s it s affect on Healthcare, Education and Quality of Life? db and Frequency scales Acoustical treatments per frequency range Transmission Loss Tests and how to read the data STC: Sound Transmission Class STC of various wall assemblies Acoustical value of Wood versus metal studs Value of stud spacing (16 versus 24 on-center spacing) Value of sustainable acoustical barriers Value of batt insulation Multiple layers of drywall Best Practices to meet desired STC targets Cost Comparison of wall assemblies Making it simple: Design criteria
Definition of Noise Noise is simply unwanted sound noise n. 1. a. Sound or a sound that is loud, unpleasant, unexpected, or undesired. NOISE IS Televisions on while you are trying to sleep NOISE IS Neighbors talking in the adjacent apartment NOISE IS Washers / Dryers running while trying to watch TV NOISE IS Not being able to concentrate in a loud workplace NOISE IS People walking on the floor above your apartment Noise do not have to be LOUD to be an annoyance It just have to be louder than any other noise in the surroundings. The number one complaint with all US law enforcement is NOISE
What is a decibel (db)? The decibel (db) is commonly used in acoustics to quantify sound pressure levels relative to some 0 db reference. 0 db is the reference point where the eardrum no longer vibrates and sound is not heard. db scales allow one to use a logarithmic rather than a linear scale. It has the distinct advantage of allowing one to do calculations within a scale of small numbers rather than over an extremely large scale of numbers.
quiet moderate loud The db Scale It is important to understand what the db scale is and what the levels mean. One does not need to achieve 0 db in a room to eliminate Noise. 140 db Apollo Rocket 90 db Loud manufacturing environment (ear protection is required limited exposure OSHA) 60 db Car interior while driving 50 db People Talking 40 db Ambient Noise (outside during the night with limited background noise) Goal: To achieve Sound Pressure Levels (db) below 40 db (which for many environments, will be void of any noise issues). 0 db Threshold of hearing (eardrum begins to detect vibrations)
Noise Levels In Education Cognitive development is impaired when homes or schools are near sources of noise such as highways and airports. Noise affects learning, reading, problem solving, motivation, school performance, and social and emotional development. Children who live in noisy environments have been shown to have elevated blood pressures and elevated levels of stress-induced hormones. American National Standards Institute calls for a maximum ambient noise level of 35 db
Noise Levels In Healthcare Excessive noise, and its effect on rest, are high on the list of complaints made by patients on post-discharge patient satisfaction surveys. Excessive noise can induce headaches, cause irritability, prolong wound healing and increase sensitivity to pain. Noise levels in hospitals are twice what they were a few decades ago. Sound levels inside hospitals average 72 decibels during the day and 60 decibels at night WHO standard, for night time ambient sound is 40 decibels In 1859 book Florence Nightingale called noise "the most cruel absence of care."
Adding and Subtracting db s If one was to DOUBLE the Sound Pressure Levels, how many db increase is this? If one wanted to reduce the noise levels by 50%, how many db decrease is this?
The Rule of 3 db When you DOUBLE the noise levels (two speakers in this instance), the sound pressure levels increase by 3dB 70 db 70 db 70 db + 70 db = 73 db For you math experts out there, the logarithmic sum of doubling a noise source is: 73 db db=10*log(2) = 3dB Double the volume
The Rule of 3 db Therefore, when designing a wall system or trying to reduce noise levels, a 3dB reduction is the same as turning down the volume knob 50%. 3dB decrease (or increase) = 50% reduction in sound pressure levels 6dB decrease (or increase) = 75% reduction in sound pressure levels 9dB decrease (or increase) = 87.5% reduction in sound pressure levels And so on
Frequency (Hz) Frequency is simply number of cycles per time interval, or to better visualize, how many times your eardrum moves back and forth per second (cycles / second). At 100 Hz, the eardrum moves back and forth 100 times / second At 5000 Hz, the eardrum moves back and forth 5,000 times / second The human ear responds to a range of frequencies from approximately 20 to 16,000 Hz. The human speech range is approximately between 400Hz and 4kHz. Human speech range 400Hz 4kHz
The Frequency Scale (Hz) The frequency scale is broken up into three distinct regions (low, mid and high). This is important because each frequency region has different acoustic treatments associated with reducing their sound pressure levels. Low Frequency Boom Noise Bass Mid Frequency Speech Noise Television / Radio High Frequency Siren Noise Birds chirping 63 Hz 315 Hz 400 Hz 4kHz 4 khz 10kHz
The Frequency Scale (Hz) Frequency range and corresponding acoustical treatments Low frequencies are reduced via isolation techniques Higher frequencies are reduced via mass and absorption techniques Low Frequency Treat with Isolation techniques. (Like a spring or an isolator ) Mid Frequency Treat with mass layers to block and reflect the noise High Frequency Treat with absorption 63 Hz 250 Hz 400 Hz 4kHz 4kHz 10kHz
Low Frequency: Isolation (< 250 Hz) Low-frequencies are the most difficult to treat (< 250 Hz). Wavelengths are very large and these frequencies carry a lot of energy and drive entire wall systems. Best way to treat (reduce) low-frequencies is to make two separate wall assemblies and isolate the transfer of energy from one wall to another. The Goal is to eliminate the transfer of vibration from one side of the wall to the other. For very loud source rooms (home theaters, for instance), a second wall assembly NOT mechanically attached in any way to the adjacent wall assembly is a preferred method. Other methods: Reduce the number of studs (24 oncenter spacing instead of 16 ) or to significantly increase the mass of the entire wall assembly. Best Practices to reduce low-frequency noise: 1. Add another wall assembly 2. use fewer studs 3. Add Mass
Double the mass Mid- Frequency: Mass-controlled region (250Hz 2 khz) This frequency range where most speech occurs is from approximately 400Hz to 4kHz. This midfrequency range is best treated with MASS of the wall system. The more mass that is added, the less noise is transmitted out the other side. Rule of thumb: For every doubling of mass, the sound pressure levels are reduced by 6 db throughout the spectrum. For example 60 db 20 db 60 db 14 db (6 db less) Best Practices to reduce mid-frequency noise: 1. Double the Mass: Reduce levels by 6 db 2. Add absorption 3. Use Isolation
High Frequency: Absorption Controlled region (> 2 khz) In the higher frequency range, wavelengths are short and are more easily reflected back off of rigid wall systems. Recall that noise travels back and forth approximately 94 times a second in a 12 X 12 room environment. Thus, absorption would have 94 chances to absorb the echo within the room every second. If the noise (frequencies) is not going through the wall, then it is being reflected back (echo). Add absorptive layers throughout the environment to absorb these reflections and minimize the echo in the room. Incoming noise Difference between incoming noise and reflected noise = absorption of the product. Reflected noise Absorptive Fiber Best Practices to reduce high-frequency noise: 1. Add absorption (treat the room where the noise resides and not necessarily the wall)
Chapter 2 Summary: What we have learned thus far DIFFERENT TREATMENTS / METHODOLOGIES ARE USED TO TREAT DIFFERENT PARTS OF THE FREQUENCY RANGE: Low Frequency: Best reduced via isolation techniques Mid-Frequency: Best reduced via mass of the wall system. High-Frequency: Best reduced via absorption within the room environment itself.
Sound Transmission Class STC is a SINGLE-NUMBER CLASSIFICATION used to rate the transmission loss of a wall. The higher the STC value, the more efficient the wall is in reducing sound transmission. STC = 34
Transmission Loss Graph: What it means 5/8 drywall on both sides of wall
STC Assigning a single number to a wide spectrum of frequencies often times does not tell the entire story it is best to look at the entire frequency range and determine the best practices to reduce noise with the appropriate wall system. The more noise the wall system reduces the higher the STC number.
Compare Transmission loss and STC values of various wall assemblies. Metal versus Wood Studs Acoustical Barrier Batt insulation Spacing of studs (16 versus 24 )
Here is the TL performance of both metal and wood studs Metal studs perform significantly better than wood studs! Wood: STC = 34 Steel: STC = 39 Comments: 5/8 drywall on both sides of wall Metal studs perform approximately 6dB to 10 db better wood studs throughout the spectrum. This is significant!
Metal versus wood studs Why are metal studs better at reducing noise as compared to wood studs? 1 Vibration (noise) going into the wood studs 1 Vibration (noise) going into the metal studs 2 Does not get absorbed in the wood stud too rigid and stiff 2 However, the thickness of the metal stud is only ~ 1mm thick and absorbs like a spring 3 And transfers much of the original vibration out the other side wood 3 Only a small percentage of vibration is transmitted out the other side. metal Less vibration = Less Noise Metal studs transfer much less energy than wood studs
Influences of stud spacing: 16 versus 24 24 on-center 16 : STC = 39 24 : STC = 40 Comments: There are no consistent trends in performance between 16 or 24 spacing 24 spacing offers improved low-frequency performance while 16 on-center improves mid to high frequencies slightly. Since lower frequencies are most difficult to treat, the 24 on-center spacing is recommended as the best design for reducing noise.
An Acoustical Barrier has the following traits: Heavy and dense, yet limp so it does not radiate vibration easily Thin profile (usually ~ 2mm thick) Flexible to wrap around corners Impermeable to moisture Sustainable, recyclable good for the environment
Influence of adding ONE Acoustic Barrier layer With one layer of acoustic barrier Baseline Wall system no barrier w/o: STC = 34 With: STC = 37 Comments: The addition of a 1 lb/ft2 acoustical barrier placed behind the drywall offers ~ 5 db improvement (reduction) in performance throughout the spectrum. This is significant!
Influences of an Acoustical Barrier Layer Conclusion Acoustical Barrier Layers: 1. Reduce Sound Pressure Levels ~ 5dB per Layer 2. Increase STC ratings ~ 3 to 4 points per layer 3. Reducing Sound Pressure Levels increases wellness, alertness and better productivity.
Influences of an Acoustical Barrier Layer with and without Batt Insulation 1-layer of barrier WITH batt insulation None: STC = 34 Barrier (1-Layer): STC = 37 w/ batt insulation: STC = 41 Comments: The combination of a batt insulation AND an Acoustical Barrier Layer reduces sound pressure levels ~ 10 db throughout most of the frequency spectrum.
Influences of one versus two layers of Acoustic Barrier - with Batt Insulation 2-layers of acoustical barrier with batt insulation None: STC = 34 Barrier (1-layer) STC = 37 Barrier / Batt (1-Layer): STC = 41 Barrier / Batt (2-Layers): STC = 43 Comments: Approximately 10 db reduction in Sound Pressure Levels occur with a single layer of acoustical barrier - plus batt insulation Approximately 16 db reduction in Sound Pressure Levels occur with a layer of acoustical barrier on EACH side of the wall - plus batt insulation
Two layers of Acoustical Barrier (No Insulation) Versus One-layer with batt insulation Barrier with Insulation performs better 2-layers of acoustical barrier only (no insulation) Barrier (2-layers): STC = 39 Barrier & Batt Ins.: STC = 41 Comments: A wall system that utilizes a single layer of Acoustical Barrier PLUS batt insulation performs better than two-layers of barrier without insulation.
Two layers of Acoustical Barrier (No Insulation) Versus One-layer with batt insulation Conclusion What is better acoustically: 2-layers of Acoustical Barrier or a single layer of acoustical barrier with Batt Insulation? 1. A single layer of acoustical barrier plus batt insulation reduces Sound Pressure Levels ~ 3 to 5dB throughout most of the frequency spectrum as compared to a wall system with just two layers of acoustical barrier. 2. STC points are increased approximately 2 points with the batt insulation
Learning exercise Lets take what we have learned thus far and create a STC Wall system that achieves levels greater than 50.and greater than 60. 1. Start with a wood stud wall system (worst case) with no treatments 2. Change to metal studs 3. Add Acoustical Barrier plus Batt insulation 4. Increase stud spacing to 24 on-center 5. And finally, add another barrier layer for a total of 2 barrier layers in the system
Add another layer of Acoustical Barrier 2-layers of drywall, 2-layers of barrier, batt insulation Baseline STC = 34 Metal Studs STC = 39 Metal Studs with Acoustical Barrier & Batt Insulation STC = 52 Metal Studs (24 on-center) / barrier / Batt Insulation STC = 56 Metal Studs (24 on-center) / 2 layers drywall / 2 layers of barrier / batt insulation STC = 62
Chapter 6 Alternative Wall designs This chapter looks at other wall designs commonly found in the industry and compares them to the acoustical barrier wall assembly. 2-layers of 5/8 drywall (both sides of the wall) Damped drywall
2-Layers of 5/8 drywall (both sides) Versus Single Layer 5/8 drywall, Acoustical Barrier & Batt insulation 2-layers of 5/8 drywall (both sides) Two layers of drywall STC = 50 The wall system utilizing acoustical barrier performs significantly better than 4- total layers of 5/8 drywall.
Acoustical Barrier w/ batt insulation versus damped drywall w/ insulation Damped drywall 5/8 drywall on both sides of wall
Summary The Acoustical Barrier wall assembly has higher (better) measured transmission loss performance as compared to: Multiple layers of drywall (two layers per side) Damped drywall (with batt insulation) Why?
Summary Because: As previously mentioned the transmission loss in the midfrequency range was best treated with mass. However, that is only half of the story. The remaining variable is STIFFNESS of the wall assembly or more importantly, the ability of a wall to radiate noise efficiently. (radiation efficiency). Drywall is inherently stiff. Recall as a child and taking a glass jar to the drywall to hear the noise on the other side of the wall. You hear the noise on the other side of the wall so well because drywall is stiff and radiates noise very efficiently.
Cost analysis of each system This section examine the cost structure of the most common types of wall assemblies: 1. Acoustical barrier with batt insulation 2. Damped drywall with batt insulation 3. 2-layers of drywall (both sides)
Cost analysis of each system Drywall Description 1 layer of 5/8" dryw all both sides 1 layer of 5/8" dryw all both sides 2 layers of 5/8" dryw all both sides 2 layers of 1/2" dryw all on one side, 5/8" dryw all on other side. 1layer of 5/8" dryw all both sides 1 Layer of 5/8" dryw all both sides 1 layer damped dryw all 1side, 5/8" on other side Full Wall Systems Construction Costs Comparisons Baseline Wall System (Single 5/8" on both sides) db-3 PRO (1 side) db-3 PRO (both sides) Green Glue Assembly 1 layer Resilient Channel Assembly Isolation Clips with Furring Channel Damped Drywall S T C 39 56 62 52 55 59 55 Drywall materials $64.00 $64.00 $128.00 $84.00 $64.00 $64.00 $247.00 Drywall, labor $36.00 $36.00 $72.00 $48.00 $36.00 $36.00 $88.00 Total cost materials + labor $360.86 $650.57 $999.45 $677.74 $595.11 $846.68 $866.52 Cost per Square Foot $3.61 $6.51 $9.99 $6.78 $5.95 $8.47 $8.67 STC values based on published reports: 25 gage metal framing wall system, 24" on-center, 10'x 10' wall assemblies
Building the correct room First thing to do is take care of the rooms themselves with ABSORPTION. Add draperies Add plants Add acoustical panels Add carpeting Noise WILL get into the rooms either through adjacent walls, windows, doors, ceilings from anywhere and everywhere. Absorptive treatments are an easy way to combat these noise levels and capture (reduce) the reverberation as it is bouncing back and forth ~ 94 times per second. ABSORPTION is key
Chapter 7 Building the correct room Proper design and acoustical performance can be achieved if these simple guidelines are followed: Isolation Mass Radiation efficiency Absorption Low-frequency Mid-Frequency High-Frequency Failure to implement any ONE of these variables into your design will significantly degrade the overall performance of the system and sound quality will be compromised.
Course Summary A wall assembly utilizing acoustical barrier: 1. Achieves higher STC values as compared to other popular wall assemblies Due to the heavy mass of the acoustical barrier Due to the low radiation efficiency of the acoustical barrier 2. Is up to 25% lower in overall cost when compared to damped drywall assemblies of similar STC values 3. Using an acoustic barrier will add to the overall performance of the building without extra expense. 2. Acoustic Barriers: Save Money, they not only act as noise barriers, but moisture and insulation barriers as well. 3. Using sustainable products protects the environment for future generations 4. An acoustic barrier is completely recyclable. www.dbsoundcontrol.com