HSW/STC

SOUND ENVIRONMENT

LEARNING AND HEALING

BY:

United Plastics Corporation

511 Hay Street

Mount Airy, NC 27030

(800) 577-3931

www.dbsoundcontrol.com

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

Learning Objectives

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.

Definition of Noise

The number one complaint with all US law enforcement is NOISE

•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.

What is a decibel (dB)?

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.

The dB Scale

0 dB – Threshold of hearing (eardrum

begins to detect vibrations)

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).

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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?

70 dB

The Rule of 3 dB

70 dB

When you DOUBLE the noise levels (two speakers in this

instance), the sound pressure levels increase by 3dB

73 dB70 dB + 70 dB = 73 dB

For you math experts out there, the

logarithmic sum of doubling a noise

source is:

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 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.

Frequency (Hz)

400Hz 4kHz

Human speech range

The Frequency Scale (Hz)

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 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.

The Frequency Scale (Hz)

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

Frequency range and corresponding acoustical treatments

•Low frequencies are reduced via isolation techniques

•Higher frequencies are reduced via mass and absorption techniques

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.

Low Frequency: Isolation

(< 250 Hz)

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” on-

center 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

This frequency range where most speech occurs is from approximately 400Hz to 4kHz. This mid-

frequency 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.

Mid- Frequency: Mass-controlled region

(250Hz – 2 kHz)

60 dB

Best Practices to reduce mid-frequency noise: 1. Double the Mass: Reduce levels by 6 dB

2. Add absorption

3. Use Isolation

20 dB 60 dB

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ass

14 dB (6 dB less)

For

example

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.

High Frequency: Absorption Controlled region

(> 2 kHz)

Best Practices to reduce high-frequency noise:

1. Add absorption (treat the room where the noise resides and not necessarily the wall)

Incoming

noise

Difference between

incoming noise and

reflected noise = absorption

of the product. Reflected

noise

Absorptive

Fiber

DIFFERENT TREATMENTS / METHODOLOGIES ARE USED TO TREAT

DIFFERENT PARTS OF THE FREQUENCY RANGE:

Chapter 2 Summary: What we have learned thus far

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 approximately 6dB to 10 dB better wood studs throughout the spectrum. This is

significant!

5/8” drywall on both sides of wall

Comments:

Metal studs perform significantly

better than wood studs!

Wood: STC = 34

Steel: STC = 39

Why are metal studs better at reducing noise as compared to wood studs?

Metal versus wood studs

wood metal

Vibration (noise)

going into the

wood studs

Does not get

‘absorbed’ in the

wood stud…

too rigid and stiff

And transfers

much of the

original vibration

out the other side

1

2

3

Vibration (noise)

going into the

metal studs

However, the

thickness of the

metal stud is only

~ 1mm thick and

‘absorbs’ like a

spring

Only a small

percentage of

vibration is

transmitted out

the other side.

1

2

3

Metal studs transfer much less energy than wood studs

Less vibration = Less Noise

Influences of stud spacing: 16” versus 24”

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.

16”: STC = 39

24”: STC = 40

Comments:

24” on-center

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

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!

Influence of adding ONE Acoustic Barrier layer

With one layer of

acoustic barrier

w/o: STC = 34

With: STC = 37

Comments:

Baseline Wall system

– no barrier

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.

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 an Acoustical Barrier Layer with

and without Batt Insulation

None: STC = 34

Barrier (1-Layer): STC = 37

w/ batt insulation: STC = 41

Comments:

1-layer of barrier WITH

batt insulation

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

None: STC = 34

Barrier (1-layer) STC = 37

Barrier / Batt (1-Layer): STC = 41

Barrier / Batt (2-Layers): STC = 43

Comments:

2-layers of acoustical

barrier with batt insulation

Influences of one versus two layers of

Acoustic Barrier - with Batt Insulation

A wall system that utilizes a single layer of Acoustical Barrier PLUS batt insulation performs better than two-layers of barrier

without insulation.

Barrier (2-layers): STC = 39

Barrier & Batt Ins.: STC = 41

Comments:

Barrier with Insulation

performs better

Two layers of Acoustical Barrier (No Insulation)

Versus One-layer with batt insulation

2-layers of acoustical

barrier only (no 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

Two layers of Acoustical Barrier (No Insulation)

Versus One-layer with batt insulation

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

Learning exercise

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

Add another layer of Acoustical Barrier

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

Chapter 6 – Alternative Wall designs

2-Layers of 5/8” drywall (both sides) Versus Single Layer 5/8” drywall,

Acoustical Barrier & Batt insulation

Two layers of drywall STC = 50

The wall system utilizing acoustical barrier performs significantly better than 4-

total layers of 5/8” drywall.

2-layers of 5/8”

drywall (both sides)

5/8” drywall on both sides of wall

Acoustical Barrier w/ batt insulation versus ‘damped’ drywall w/ insulation

Damped

drywall

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 mid-

frequency 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 Description1 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 3 9 5 6 6 2 5 2 5 5 5 9 5 5

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

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.

Low-frequency

Mid-Frequency

High-Frequency

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