Understanding Expected IIC and STC of Assemblies – Case Study

An architectural firm in Florida is undergoing the process of reviewing standard details in their design assemblies, including the expected IIC and STC of these assemblies. Since these details are used on a number of developments, it is critical to understand how these details are performing in the field, and compare those against the expected values in the laboratory tests.

A drawing package review was completed prior to the site visit. Testing was performed with representation from the Architecture team and Construction team present.

This report includes findings from the design review and site observations, as well as all testing data compiled in Appendices A-E.

Findings

  1. WF-9 Tenant-to-Tenant Wall

The first test was conducted on WF-9 Tenant-to-Tenant Double-Stud Wall (Appendix A). This wall had a 10” top plate spanning the two sets of 2×4 studs. The shared top plate diminishes the sound-blocking capacity of this wall from an STC 55 to STC 51 (see Appendix H, figures 10 and 11) below, since it allows direct propagation of noise through the wall along the top plate. Since there is only a top plate connection, and no bottom plate, the expected STC may be closer to 53. Upon discussing with the architect, this top plate is necessary for fire-stopping and draft control. However, if another means of fire stopping may be implemented, such as plugging the 2” air gap with plywood, then the wall may perform closer to its lab value.

After the field test was complete, a leak check was performed on this wall, to determine if more sound was transmitted through it in some locations than others. The SPL (Sound Pressure Level) Meter peaked about 3-5 dB at the base of the wall, indicating there was some flanking at this location. While not as significant as some field tests, adding a thin bead of acoustical sealant just along the bottom of the wall may improve the field STC of the system by several points.

Overall, the ASTC of 50 is above the Florida Building Code minimum.

  1. WF-4 Breezeway Corridor-to-Unit Wall (Kitchen)

The next test was conducted on WF-4 Breezeway Corridor-to-Unit Wall (Appendix B). This wall utilizes resilient channel, but the contractor also used blocking to support cabinets in the kitchen. This compromises the integrity of the resilient channel, which works by decoupling the drywall from the studs. By screwing into the blocking through the drywall, the effectiveness of the resilient channel is greatly reduced.

While an STC of 56 is indicated on the Wall Schedule, no Acoustic Test # is referenced, unlike Acoustic Test # TL-93-265 which was referenced in WF-9 in the wall schedule (See Figures 1 and 2 below).

The attached Figure 12 in Appendix H indicates that this assembly will test to an STC of 50.

As a rule-of-thumb, STC ratings referenced in the wall schedule should have the accompanying Acoustic Test # available for review. The actual Acoustic Lab Test report should also be provided in the design package when possible.

The door appeared to be the primary flanking path in the kitchen. A door STC specification was requested from the construction submittal package, and is included in Appendix F. The STC of 24 for the door is much less than the STC of 50 for the walls. Using a heavier-gauge door, and improving the weather stripping to acoustic seals and sweeps would further improve the performance of this wall system.

Figure 1: WF-4 From Wall Schedule

Figure 2: WF-9 From Wall Schedule

    3. WF-4 Breezeway Corridor-to-Unit Wall (Closet)

As a control, a field test was performed on WF-4 between the unit closet and corridor. While there was substantially less wood blocking used in the closet, due to the lighter weight shelves compared to the kitchen cabinets, it still appeared to affect the performance of the wall assembly.

The ASTC of 43 is slightly below the Florida Building Code allowable limit.

To improve the ASTC of the wall, a different resilient mount system may be used (such as Genie Clips) or a differing wall system that incorporates a soundproofing membrane rather than a resilient mount. See Appendix G for options.

4. Kitchen Flooring (FC-1)

The Kitchen Floor was tested, and results are available in Appendix D. The flooring system consisted of 20mm thick wear layer Luxury Vinyl Tile, ¾” Gypcrete, AccuQuiet D18, ¾” OSB, 20” deep Wood Floor Truss, R-13 Batt Insulation and Resiliently Mounted 5/8” Type X Drywall.

There were a few concerns associated with the location of the underlayment:

  • The underlayment was used under the Gypcrete layer, but was only located under the section of the floor where LVT was used. This creates a number of flanking paths. For instance, structure-borne noise (from footfall or other sources) may travel through the Gypcrete, around the underlayment, and into the OSB subfloor. This bypasses the underlayment layer, reducing the effectiveness of the floor. Furthermore, since the underlayment is below the Gypcrete, additional layers cannot be added in the future, and it cannot be used to spot-treat as a topical sound mat can. Overall, this type of underlayment is effective, but must be used throughout the entire area where the Gypcrete is isolated.
  • The Floor Perimeter Isolation Strips were only installed in the kitchen area. This introduces additional flanking paths. Also, it makes it very difficult to retrofit the apartment for future purposes, since removing the carpet for LVT would then be well below the Building Code requirements.

Beyond the location of the underlayment, the product selection raised a few questions. Upon inspecting the submittals and contacting the manufacturer, there was no acoustical testing available for the AccuQuiet D18. While the manufacturer claims it may improve IIC from 6-12 points, no further testing or documentation was available.

Figure 3: AccuQuiet D18 Sound Mat – Specifications

There is no Acoustic Test listed in the Construction and Referenced Assemblies (A 1.04A). Similar to the wall assemblies, an IIC and STC of the floor should be made available in the design package.

The AIIC of the floor was measured at 43, which is below the Florida Building Code.

5. Living Room Flooring (FC-1)

The Kitchen Floor was tested, and results are available in Appendix E. The flooring system consisted of Carpet with Padding, ¾” Gypcrete, ¾” OSB, 20” deep Wood Floor Truss, R-13 Batt Insulation and Resiliently Mounted 5/8” Type X Drywall.

The AIIC of the floor was measured at 58, which meets and exceeds the Florida Building Code.

Conclusion & Recommendations:

Overall, of the 5 tests conducted, 2 tests met the Florida Building Code, Section 1702.2 and 1702.3 for Sound Attenuation. The tests that did not meet the Building Code were the Floor-Ceiling test in the Kitchen, Corridor-Unit test in the Kitchen, and Corridor-Unit test in the Closet.

The tests that did not meet code were generally within a few points of the field test requirement, which is an ASTC and AIIC of 45.

Options to consider for further improvement of acoustical performance include:

  1. Specify an acoustically-rated underlayment under the Luxury Vinyl Tile in the kitchen and bathrooms, and include the lab test and floor IIC ratings in the Floor Schedule (see Appendix G)
    1. If using a sound mat under the gypcrete, ensure it is used throughout the entire space, and ensure perimeter isolation strips are used, to prevent flanking
    2. If using a sound mat above the gypcrete, this is not necessary
  2. Remove the shared Top Plate on the Double-Stud Wall Assembly and instead meet the fire blocking requirements with a separate material along the top
  3. Use a different assembly for the corridor-unit wall that does not rely on resilient channel, since this is compromised by the use of blocking in the closet and kitchen
  4. Add thicker, acoustically-rated weather stripping (door seals and sweeps) to the front door to reduce corridor-unit noise transfer
  5. Use a thicker, heavier-gauge door in the kitchen to reduce transmission through the door

Conclusion & Recommendations:

Overall, of the 5 tests conducted, 2 tests met the Florida Building Code, Section 1702.2 and 1702.3 for Sound Attenuation. The tests that did not meet the Building Code were the Floor-Ceiling test in the Kitchen, Corridor-Unit test in the Kitchen, and Corridor-Unit test in the Closet.

The tests that did not meet code were generally within a few points of the field test requirement, which is an ASTC and AIIC of 45.

Options to consider for further improvement of acoustical performance include:

  1. Specify an acoustically-rated underlayment under the Luxury Vinyl Tile in the kitchen and bathrooms, and include the lab test and floor IIC ratings in the Floor Schedule (see Appendix G)
    1. If using a sound mat under the gypcrete, ensure it is used throughout the entire space, and ensure perimeter isolation strips are used, to prevent flanking
    2. If using a sound mat above the gypcrete, this is not necessary
  2. Remove the shared Top Plate on the Double-Stud Wall Assembly and instead meet the fire blocking requirements with a separate material along the top
  3. Use a different assembly for the corridor-unit wall that does not rely on resilient channel, since this is compromised by the use of blocking in the closet and kitchen
  4. Add thicker, acoustically-rated weather stripping (door seals and sweeps) to the front door to reduce corridor-unit noise transfer
  5. Use a thicker, heavier-gauge door in the kitchen to reduce transmission through the door

Appendix A: ASTC Test – Wall Between 4206 Living Room and 4207 Living Room

Figure 4: ASTC of Wall Between 4206 Living Room and 4207 Living Room

 

Appendix B: ASTC Test – Wall Between 4206 Kitchen and Corridor

Figure 5: ASTC of Wall Between 4206 Kitchen and Corridor

 

Appendix C: ASTC Test – Wall Between 4206 Bedroom and Corridor

Figure 6: ASTC of Wall Between 4206 Bedroom and Corridor

Figure 7: AIIC of 4206 Kitchen and 4106 Kitchen (Luxury Vinyl Tile)

Appendix E: AIIC Test – Floor Between 4206 Living Room and 4106 Living Room (Carpet)

Figure 8: AIIC of 4206 Living Room and 4106 Living Room (Carpet)

 

Appendix H: Supporting Lab Testing

Figure 10: Lab STC of Double Wood-Stud Wall

Figure 11: Simulated STC of Staggered Wood-Stud Wall with Shared 10” Top Plate

Figure 12: Lab STC of Wood-Stud Wall with Resilient Channel

 

Cancer Treatment and Research Center – Case Study

A cancer treatment and research center is undergoing a renovation to replace wood flooring with terrazzo. The reverberation in this space has already raised some complaints, and the more reflective floor covering is expected to create more. These issues are most noticeable during events hosted in the atrium with amplified loud speakers.

A reverberation test was set up in the main atrium to determine the reverberation at A-weighted frequencies and speech frequency ranges.

Test Method:

3 different impulse noises were used as the noise source. First, a loud speaker with white noise was cut off to allow measurement of reverberation. Secondly, hand claps were used as an impulse. Both methods failed to produce conclusive readings in the frequencies below 1000 Hz. Finally, 2”x4” wood studs were clapped together to create the noise source. The results were averaged together to yield the RT60 (“reverberation time”) value at each location.

A Type 1 SPL (Sound Pressure Level) meter was used to capture the amount of time it took the initial noise to decay by 60 dB at each frequency range. These results are displayed below in Table 1.

Test Results:

Location

800 Hz

1 kHz

1.25 kHz

1.6 kHz

2 kHz

2.5 kHz

3.15 kHz

4 kHz

5 kHz

6.3 kHz

RT60

Point 1

3.41

3.16

3.21

2.97

2.78

2.42

2.27

2.3

1.89

1.44

2.8

Point 2

3.51

3.13

2.67

2.58

3.14

2.33

2.04

1.88

1.73

1.26

2.67

Point 3

2.71

2.62

2.48

2.53

2.25

2.04

2.11

2.01

1.6

1.39

2.39

Point 4

3.95

3.9

2.48

2.61

2.46

2.25

2.13

2.11

1.75

1.5

2.47

Point 5

3.68

2.82

2.97

2.75

2.37

2.28

2.13

2.03

1.78

1.34

2.59

Average Reverb

2.58

Table 1: Reverberation Results

Figure 1: Reverberation Test Locations

Figure 2: Reverberation Criteria with Various Venues

Recommendations:

In order to achieve a desired reverberation time of 1.45-1.9 seconds for a multi-purpose auditorium or venue, additional absorption materials will need to be added to the space.

After discussion with the client, it appears that installing these closer to the floor will yield significant savings due to the 56’ height of the room.

Using a simple Sabins calculation, the use of 48 panels at 2’x4’x2” thick, with an absorption factor of 1.05 NRC, will be sufficient to reduce the reverberation down to acceptable levels. While this characterization may be over-simplified due to the cavities and non-parallel surfaces in the space, it has been normalized to the readings taken in the field.

Luxury Timeshare Case Study – Orlando, FL

Testing and analysis were performed for a luxury timeshare in Orlando,

2 walls were tested: The wall between units 209A and 210A and the wall between 211A and 212A.

Both tests were performed late in the afternoon, around 5PM, when the construction on the adjacent job site was sufficiently low, but at times, still audible.

 

Description of Tests (2):

  1. Airborne Test (ASTC) was performed in accordance with ASTM E336 between units 209A and 210A in their respective kitchen/living room areas
    • This test was used to determine how much sound the wall assembly blocks between adjacent A Units.
    • The wall assembly tested was:
      • 1 Layer of 5/8” Type X Drywall Each Side, 1 Layer of 1/8” Wall Blokker Membrane One Side, 25-Gauge Steel Studs 16” o.c. and R-13 fiberglass insulation batting in the cavity
      • The wall assembly also included a hollow-core door in the center, a 4” air gap, and another hollow-core door. Each door had automatic door sweeps that were engaged.
  2. Airborne Test (ASTC) was performed in accordance with ASTM E336 between units 211A and 212A
    • This test was used to determine how much sound the wall assembly blocks between adjacent A Units.
    • The wall assembly tested was:
      • 1 Layer of 5/8” Type X Drywall One Side, 2 Layers of 5/8” Type X Drywall One Side, 25-Gauge Steel Studs 16” o.c. and R-13 fiberglass insulation batting in the cavity
      • The wall assembly also included a hollow-core door in the center, a 4” air gap, and another hollow-core door. Each door had automatic door sweeps that were engaged.

Summary Findings & Recommendations:

The two tests had very similar results, due at least in some part to hollow-core doors in the center of each wall. The test with the soundproofing membrane did perform at 2 points higher, achieving an ASTC (Field or Apparent Sound Transmission Class) of 46, while the gypsum-only wall achieved an ASTC of 44. The Florida Building Code, Section 1207.2, requires an ASTC of 45 for walls between adjacent dwelling units.

After testing was complete, a brief leak check was performed to determine where the majority of the sound was located. In the case of the first room, the sound level at the wall was 60.8 dBA, but reached 69.8 at the base of the door. The second unit had similar results.

Ultimately, combining the wall containing the soundproofing membrane with solid core doors between the units, and ensuring the door sweeps are adequately sealed, may result in an ASTC of 50 or more.

Figure 1: Door Sweep from 3” off of ground

 

Figure 2: Door Sweep from 1” off of ground

 

As you can see in the images above, the door sweeps may appear to be engaged just a few inches off the ground. However, by laying flat, you may be able to see any small gaps or “tilted” engagement of the sweep in a closed door.

 

Sarasota Aerospace Office

Testing and analysis were performed for a property manager working for a commercial property. One of their commercial tenants, an aerospace center at the property had concerns about sound attenuation between adjacent tenant units. Two adjacent legal firms, with very low background noise in their offices, could occasionally hear muffled conversations being held in the office next to them.

3 Airborne Tests were performed in accordance with ASTM E336.

  1. Between Suite 840 and 860, the eastern-most office
  2. Between Suite 800 and 840
  3. Between adjacent office space within Suite 840

 

Description of Tests:

3 Tests were performed at the property

Test #1: ASTC Test between Suite 840 and Suite 860

  • Measured ASTC of 43
  • Receiving room – general description: The room was furnished, with carpet and acoustic ceiling tile.
  • Source Room – general description: The room was furnished, and filled with numerous files and cabinets. It was an active legal office.
  • Relationship between rooms: The Source room was located directly adjacent to the receiving room and shared a wall.
  • All adjacent spaces were closed off with doors during testing.
  • Description of Test Assembly
    • 25 Gauge Metal Studs
    • 5/8” Type X Gypsum Board Each Side
    • R-13 Batting in Studs

Test #2: ASTC Test between Suite 840 and Suite 800

  • Measured ASTC of 39
  • Receiving room – general description: The room was furnished, with carpet and acoustic ceiling tile.
  • Source Room – general description: The room was lightly furnished. It was an empty office.
  • Relationship between rooms: The Source room was located directly adjacent to the receiving room and shared a wall.
  • All adjacent spaces were closed off with doors during testing.
  • Description of Test Assembly
    • 25 Gauge Metal Studs
    • 5/8” Type X Gypsum Board Each Side
    • R-13 Batting in Studs

Test #3: ASTC Test within Suite 840, between a conference room and an empty office on the westward side of the conference room.

  • Measured ASTC of 37
  • Receiving room – general description: The room was furnished, with carpet and acoustic ceiling tile. One line of walls was thin glass, while the opposite wall was windows looking out over the street below.
  • Source Room – general description: The room was lightly furnished. It was an empty office.
  • Relationship between rooms: The Source room was located directly adjacent to the receiving room and shared a wall.
  • All adjacent spaces were closed off with doors during testing.
  • Description of Test Assembly
    • 25 Gauge Metal Studs
    • 5/8” Type X Gypsum Board Each Side
    • R-13 Batting in Studs

Summary:

The design and construction of the walls tested is sufficient to meet the needs of most office tenants.

There are few attenuation codes defined and available for commercial office applications, and no attenuation building requirements.

Per one leading publication (Architectural Acoustics, Marshall Long), the recommended Field STC (now titled ASTC) for Normal Privacy at Normal Voice Levels is 32. Furthermore, Confidential Privacy may be attained at Normal Voice Levels with an ASTC of 38. All 3 of the walls tested meet or exceed this criteria.

Table 1: STC ratings needed to achieve Privacy at Normal and Raised Voice Levels

If further improvements are required by the tenant, they should be focused on the mullions and baseboards, and if significant improvement is needed, then a topical solution on the walls will provide a 4-8 STC improvement above the current configuration. Sound Masking is also a feasible solution, but should only be considered once mullion flanking is reduced to minimal levels.

Findings & Recommendations:

After ASTC testing was complete, we also performed leak checks along the wall in each of the 3 locations. In all 3 circumstances, significant flanking occurred along the mullions on the dividing walls, as well as secondary flanking along the baseboards.

No flanking was apparent along the ceiling. Walls continued up to the deck above the Acoustic Ceiling tiles. We used ladders to inspect the duct and piping penetrations, and all were visibly sealed with batting and caulk. Workmanship in this area was better than we usually see for ducting and piping penetrations.

1. Mullions: In all 3 tested locations, the sealing around the mullion appeared to be airtight. In these cases, the mass of the mullion alone (1/8” extruded aluminum) was insufficient to attenuate the same amount of noise as the metal-stud wall. In this case, the sound traveled the path of least resistance through the mullion itself. In a nearby, untested area there appeared to be a small gap in the mullion gasket.

  • Recommendation 1: The overall goal is to add further mass to the mullion. This is a perimeter, pre-constructed member, so modifications being made should be fully-reversible and made as a last resort. That being said, if there is an option to drill holes into the mullion and add blow-in insulation or other filler that will act to improve the performance.
  • Recommendation 2: Another option would be to adhere a thin membrane (Mass Loaded Vinyl, Wall Blokker, etc.) to the mullion on each side. These membranes are 1/8” thick and may be coated to match the existing

2. Baseplates/Bottom Tracks: In each testing area, there was some secondary flanking through the baseboards.

  • Recommendation: Remove the baseboards and apply acoustical sealant along the bottom of the drywall to make this gap as air-tight as possible.

3. Walls: While the walls themselves are sufficient to meet most client’s needs and expectations, additional soundproofing may be required in special circumstances (especially where confidential or private information is being shared). In this case, there are a few options:

  • Recommendation 1: Add a layer of mass-loaded membrane directly on top of the surface. This may be done rather economically, but outlets and other penetrations along that wall will need to be extended. Thickness of the membrane is only 1/8” thick, and should be applied along the entire surface. Expected sound-blocking increase is 20-30%.
  • Recommendation 2: Add a 2nd layer of drywall on top of the existing surface. The STC increase will not be quite as much as a membrane layer, but may be quicker to install. Expected sound-blocking increase is 15-25%.
  • Recommendation 3: If both of these options are undesirable, then consider implementing a sound-masking solution in the adjacent offices to minimize the speech intelligibility and articulation index of those next door.

Office Space Vibration Testing – Case Study

Scope:

A property management firm has encountered complaints regarding structural vibrations in one of its commercial office properties in Lake Mary, FL. Specifically, occupants complain of annoying or distracting vibrations in the concrete slab, and some occupants have been concerned with potential structural integrity issues.

The property management firm has already hired a structural engineer to inspect the structure and found no safety issues. The engineer has suggested that the vibrating slab may be due to under-loading of the slab, since all of the occupants have not yet moved in, resulting in a lighter-than-designed live load. This results in serviceability issues due to footfall in certain areas.

Commercial Acoustics performed a vibration study to determine the root cause of the unwanted vibration, and whether the structure complies with ISO 10137 Standard vibration serviceability criteria.

NOTE: The criteria assesses only whether the structure complies with vibration related to serviceability and NOT for safety.

Scope

Testing was performed per ISO 10137 “Bases for design of structures – Serviceability of buildings and walkways against vibrations”.

Three uni-axial accelerometers were used to measure the vertical vibrations incurred during a standard work day on the 3rd floor of their building. The sensors were placed initially at workstation 4183, which was the location of one of the chief complainants. The complainant was also present at the time of the testing and noted that she takes motion sickness medicine throughout the day to prevent nausea.

It should be noted that certain individuals are more sensitive and susceptible to vibrations, even if these vibrations are beneath commonly-accepted levels, and our mitigations list some areas in the office that may be more acceptable for those employees.

Vibrations at a second location were also tested, but found to be lower in magnitude than workstation 4183. As identified in the structural layout (Figure 3), workstation 4183 was mid-span between the beams and joists crossing the floor, likely contributing to the greater vibration magnitude.

They were placed in a layout running horizontally across the floor, perpendicular to the W21x44 beams that were spaced 10’ apart.

According to the standard, the vibrations were described as Class 3, corresponding to distinctly Perceptible but not strongly perceptible.

Instrumentation

Crystal Instruments Spider 20 Data Acquisition Unit, Serial #: 5462944

PCB Piezotronics Single-Axis Accelerometer, Part #: 393B04, Serial #: 36913

PCB Piezotronics Single-Axis Accelerometer, Part #: 393B04, Serial #: 36795

PCB Piezotronics Single-Axis Accelerometer, Part #: 393B04, Serial #: 36783

PCB Piezotronics Single-Axis Accelerometer, Part #: 393B04, Serial #: 30743

Source of Vibrations

Figure 1: Vibrations due to Walking

After review of the data, there is no pattern to indicate that the vibrations are due to mechanical equipment. This would usually be indicated by periodic changes that were of the same length and magnitude. A brief demonstration was performed by bouncing on the balls of the feet and simulating walking down the hallway. Both demonstrably influenced the transducers, indicating that the source of the vibrations is staff movement. As seen in Figure 1 above, each incident of significant floor vibrations corresponded directly to staff or technician movement. All of the five aforementioned events vary in magnitude and duration but represent the individuals nearest the testing equipment departing their desks for various tasks and returning to their desks.

After discussions with the staff, it was further verified that the vibrations were sporadic throughout the day. This is common in floors with intermediate spans (between 10 feet and 30 feet) because the structure has insufficient stiffness or mass to reduce some vibration.

Figure 2 outlines the five RMS (Root-Mean-Square) signals with the greatest magnitude. All are from the first two hours of the day, with measurements taken between 8:44 and 10:44 AM, presumably because that is when the majority of the foot traffic occurred on site.

Figure 2: Vibration Magnitude for Each Test, m/s2 versus Frequency

These vibration levels are well below the acceptable limits in ISO 10137, shown on the right side of Figure 2. This graph shows the magnitude of vibrations in acceleration (m/s2), which peaked at about one level of magnitude below the acceptable limits.

Figure 3: Structural Drawings of 3rd Floor

A second set of readings were performed at Testing Location 2, as requested once the team arrived on site. As seen in Figure 4, the magnitude of vibration at the second location was significantly less than the magnitude at Testing Location 1. This is likely due to the proximity to the larger beam in the core of the building. Testing Location 1 is located at mid-span between the larger, stiffer beams.

Figure 4: Magnitude of Vibrations at 2 Different Testing Locations

Path of Vibrations

The testing data indicate the vibrations are propagating through the deck from adjacent footfall. The flooring system consisted of thin Carpet on Concrete (3” Concrete on 3-1/4” Corrugated Deck). No cushion or underlayment was installed under the carpet.

Mitigation Options

Since the office space is fully built-out and in use, construction methods such as stiffening the floor with additional beams are not desirable. However, a number of options are still available, listed below.

  1. Vibration-Reducing Mats:
    • Type: Topical or Underlayment: Since the flooring system is already installed, it would likely be cheaper and faster to install a topical sound reducing mat on top of the existing floor system. A pad such as Pliteq’s GenieMat FIT would be acceptable. This mat will isolate the footfall before it becomes structure-borne in the slab, and will result in a reduced vibration load in the nearby workstations. Other products, such as Commercial Acoustics’ Floor Blokker would be acceptable if installed under the carpeting.
    • Location: Hallways or across the entire floor: It is recommended to only install this pad in major walkways, since that is where the majority of the footfall is occurring. While this will not isolate footfall in certain pods, it will address the majority of the footfall while saving significant cost in material and precluding the need to move the existing office equipment.
  2. Rearranging Office Employees
    • As mentioned above, some office employees are more susceptible to vibrations and movement than others. Relocating these staff to more stable portions of the building, especially near the corners and directly next to the central beams will minimize the level of vibrations they feel. Corner locations nearest to two thick beams will be the most stable.
  3. Future Designs
    • By placing beams and joists closer together, the structural engineer may greatly increase the stiffness of the structure so that vibrations due to footfall are not perceptible by employees. Likewise, keeping the same span lengths the same but increasing the depth (and therefore mass) of the floor will result in a heavier floor that will respond less to human-induced movements.
    • Simply implementing a dampening underlayment during construction will also reduce the acceleration induced from human movement on the concrete slab.

Conclusion

The vibrations in the office space, while clearly perceptible, were not above the suggested thresholds identified in ISO 10137. While this is a good indicator of the serviceability of the structure, implementing Mitigation Options listed above will reduce the vibrations felt by employees and staff in the office area.

Tampa Upscale Hotel – Case Study

An upscale hotel reached out to us because they had been experiencing noise complaint issues since opening 3 years ago. During this time period, the hotel has used GSS (Guest Satisfaction Survey) Scores and comments to determine the areas in which noise complaints are derived. The hotel team’s initial observation is that the windows are transmitting noise and that the hotel doors are loud and disturbing the clients. The speakers at the hotel bar are also creating complaints for guests staying within that vicinity.

As these sound transmission issues are post-design and -construction there are limited design modifications and testing is required for successful recommendations to be made. Freeway & Roadway traffic, impact doors closing, loudspeakers, etc. can all generate airborne and structure-borne noise levels louder than other typical sources (speech, television, walking, etc.).

During our walkthrough performed on April 26, 2017 we confirmed with our Class 1 SPL (Sound Pressure Level) Meter that the majority of the sound in several rooms was being transmitted through the windows and sliding glass doors of the rooms. In addition to sound transmission the hotel doors were quite loud and vibrating the interior corridor walls when shut. The speakers in the hotel bar were directly mounted to the concrete allowing direct propagation of structural vibrations into the rooms nearby – this was confirmed with the corresponding noise complaints often filed in this area.

Test Method:

The following rooms were tested during the evening of May 26, 2017. A class 1 SPL meter was placed in room 359 to determine the peak noises occurring throughout the evening from the hotel bar. Hourly tests were conducted in rooms 310 and 231 to measure traffic noises. Qualitative data was measured in room 231 and room 310 as well, including how many audible noises were detected over a 1-hour span.

Test Results:

During that time, the most common audible noise from outside the room was Street Traffic, where a car could be heard passing almost every minute on average. While the cars could be heard above any background noise (Air Conditioning provided a background level of approximately 40 dBA), the sounds often did not exceed 55 dBA on the east side. Street Traffic was more disruptive on the express way side.

Note, the testing for each room was for 60 minutes, and done concurrently. There were other miscellaneous peaks in noise that occurred, including occasional toilet flushing or talking from exterior sidewalks, but these occurred infrequently and at low dB values.

As indicated in the tables above, windows facing the expressway were consistently louder than those facing east side. These were monitored throughout the night, and were measured at 47.1 dBA on the expressway, versus 40.6 dBA on the east, on average. The readings from the expressway were also characterized by higher dynamic ranges (larger differences between quiet and loud) that typically correspond with more complaints.

It should be noted that while the vertical shades in each room are effective at blocking light, they made little or no difference in the sound level coming through the windows.

Doors being slammed were a consistent, disruptive event throughout the night in all 3 rooms. It was noted during the walk-through that the doors are quite heavy, and while that improves the attenuation from the door itself, they make a loud thud when closed due to the lock of door closers.

Summary: Primary Issues and Mitigations

In order to save unnecessary cost, it is recommended to perform a brief follow-up study with a pilot room window to determine exactly how many of the hotel windows should be reinforced. This may not be necessary for many of the windows that do not directly face the east side or the expressway. There are several options to improve the STCs of the windows, with various costs and STC improvements associated with each.

Figure 1: dBA Values in Room 359 by Hour

Apparent Sound Transmission Class (ASTC) Testing:

Description of Test:

1. Airborne Test (ASTC) was performed in accordance with ASTM E336 between units 210 and 212 through the shared wall

a. This test was used to determine how much sound the wall assembly blocks between adjacent units.

b. The wall assembly tested was presumed to be, but not confirmed:

i. 1 Layer of 5/8” Type X Drywall One Side, 2 Layers of 5/8” Type X Drywall One Side, 25-Gauge Steel Studs 16” o.c. and R-13 fiberglass insulation batting in the cavity

ii. The wall assembly also included a solid-core door in the center, a 4” air gap, and another solid-core door. The doors did not have door sweeps or solid thresholds, but instead lightly grazed the carpeting as they closed.

Summary Findings & Recommendations:

The tests indicated an ASTC value of 47 for the walls separating rooms 210 and 212. While this number is above the Florida Building Code for multi-family units (requires a field value of 45), it just below what is typically implemented in hotel designs (design values of 55 to 60).

After testing was complete, a brief leak check was performed to determine where the majority of the sound was located. In the case of the first room, the sound level at the wall was 42 dBA, but reached 46 dBA at the door, and 48 dBA at the base of the door. This indicates that a more substantial door sweep or threshold may be sufficient to reduce noise coming through the entire wall assembly.

Likewise, the doors into the hallway measured 62 dBA at the door, and 69 dBA at the base. A more substantial door sweep or threshold at this location may also further reduce the noise being transmitted from the corridor to the rooms.

Statement of Conformance:

Airborne sound attenuation tests were conducted in accordance with the provisions of ASTM E336-16, Standard Test Method for Measurement of Airborne Sound Attenuation between Rooms in Buildings. Sensitivity checks were performed before and after testing to ensure the equipment was properly calibrated.

The testing described, the results calculated, and this report fully comply with the requirements of ASTM E336-16. No exceptions were made during this test.

The results stated in this report represent only the specific construction and acoustical conditions present at the time of the test. Measurements performed in accordance with this test method on nominally identical constructions and acoustical conditions may produce different results.

The test environment consisted of a furnished hotel room that included a living area. The source side of the experiment was in room 210. The two rooms were mirrored around a separation wall, with length 26 feet, width of 13 feet, and height 9 feet.

All doors were closed to the adjacent spaces.

A Nor131 Sound Pressure Level meter was used for all tests, Serial # 1313740, last calibrated on October 10, 2016. A Nor1251 Sound Calibrator was used for sensitivity checks, Serial # 34824. The meter and calibrator were hand-held.

A Pyle 18” Loudspeaker was used as the sound source for the ASTC tests, with white noise as the sound type.

Appendix A: ASTC Test Data

Table 7: Transmission Loss by Frequency

Figure 2: STC Curve for Rooms 210-212

Gym Sound Treatment – Case Study

A gym reached out to us in search for a solution to the noise issues they’re having. They are located on the 2nd level of a commercial structure surrounded by a day spa, retail store and office space. The structure is dealing with reported sound transmission through the walls and flooring assembly between tenant spaces causing concern and complaints.

As these sound transmission issues are post-design and -construction there are limited design modifications available and testing is required for successful recommendations to be made. Weight drops, impact noise of weight machines, loudspeakers, and other noise sources can all generate airborne and structure-borne noise levels louder than other typical sources (speech, television, walking, etc.) associated with office buildings.

Summary

Our client has been in operation since December 2016, and since that time has encountered numerous noise complaints. These have originated primarily from three adjacent tenants: a spa (directly adjacent), health care facility (below), and to a lesser extent, a retail store (below).

Prior to build-out of the space, our client hired a different acoustical consulting firm to give design guidance and perform structure-borne testing relevant to weight dropping above. This design was reviewed as part of this scope, and found to be sufficient.

The tenant implemented these designs during construction, including the installation of a floated double-gypsum ceiling and sound-insulating underlayment where the sensitive health care facility neighbor was located. Airborne field testing was performed prior to project completion and was found to be effective. That testing was not reviewed as part of this assessment.

Further noise mitigation efforts have been implemented, including the following:

1. Moving free weights from the center of the gym room to the exterior, and moving dead-lift machines closer to the exterior

2. Closing the class training area door permanently (garage-style vertical lifting door) that would otherwise be open

3. Minimizing use of the Combat Training Class (CTC) area, which involved additional weight-dropping (especially medicine balls)

4. Treating the dead-lift area with large, absorption pads to cushion weights dropped

5. Adding signs to minimize weight-dropping in the gym

After performing airborne and structure-borne tests on site (see Appendix A), performing a site inspection, reviewing previous acoustic assessments, and conducting interviews with nearby tenants, the following mitigations are presented as additional options to consider:

Table 1: List of Options to Consider for Further Noise Mitigation

Review of Individual Tenants:

The initial assessment performed by the previous acoustical consultant focused on the health care office space below, and did not address the adjacent tenants. At that time, the company type for the adjacent tenants were unknown. Typically, “Salon and Spa” type businesses require a stricter than usual noise requirement, which was not reviewed.

1. Spa

While testing was performed in this space, a severe vibration was noted approximately halfway through that required the test to be restarted. This was due to the industrial washing machine in an adjacent room that shook the slab violently. The startup and cooldown frequencies of the machine caused the walls and cabinets to shake audibly. This may indicate that the slab lacks sufficient modal mass for this application, and may be treated by using adequate vibration-reducing steel springs/neoprene pads cantilevered under the washing machine.

It was noted after discussion with the construction manager that the pour was done in a continuous manner. We visually confirmed this assessment, as the only “pour break” visible in the slab was at approximately Spa Room 3, where the vibrations were no longer noticeable. By using a single-pour continuous slab in this space, the opportunities to minimize vibration through the slab are extremely limited. While a thicker underlayment may reduce some of the vibration, another option would be to add a control joint in the flooring system. As noted below, it appears that the primary beams run parallel to the proposed control joint location, so that it would achieve maximum effectiveness. A saw cut should run as deeply into the slab as structurally allowed, and should be filled in with acoustical sealant.

We noted that the ropes are almost inaudible in the gym, but once the energy is transmitted into the slab, it transmits easily into the adjacent spa and from there into the walls and air. This may be easily addressed by adding a topical sound-absorbing pad to the area where the ropes are striking the slab. While placing a thick underlayment under the ropes is a simple solution, it will not be necessary if the slab is isolated.

If a thicker padding is preferred, consider Pliteq’s Genie Mat FIT. This is a heavy duty, durable mat that will reduce transmission into the slab.

Figure 1: Floor Slopes Down Where 15mm Underlayment Is Not Applied

Further improvements may be achieved by isolating the spa walls from the concrete slab. The structure-borne propagation in the slab is transmitted directly into the walls since they are connected directly to the slab. A proper isolator or decoupling membrane placed underneath the track will greatly reduce the airborne propagation into the individual spa rooms.

The ASTC test (Appendix A) performed in this space indicated that the gym speakers are not a significant concern for the tenant. Furthermore, it was noted that the gym environment held its speakers at a lower level than similar gyms of similar size. The airborne noise was further masked by the individual, independently-controlled speaker systems in each spa room.

Figure 2: Area Near the Spa Chained Off – Even Jump Roping Caused Significant Shaking

Figure 3: Hallway Next to Spa Where Testing Was Conducted (See Appendix A) – Sufficient ASTC of 53

2. Health Care Facility

It was extremely quiet in this space, so that very little noise was masked from above. This made the structure-borne noises from above more audible than they would typically be in an office space. By using a sound-masking system, the “thuds” from above may be completely inaudible.

While the initial consultant memos suggested using thick underlayment in this area and moving the free weights, it did not specifically call out keeping equipment and machinery decoupled from the floor. It was noted that the machine presses are bolted through the underlayment directly into the concrete below, significantly impairing the underlayment’s ability to break the vibration path (much of the vibration can travel directly from the machine, through the bolts, into the concrete slab). Either unbolting the machines, or using an isolator in this area, may allow the vibrations to be absorbed prior to entering the concrete slab below.

Figure 6: Machine Presses Bolted Directly Through Underlayment Into Concrete

Figure 7: Deadlift Treatment Has Been Largely Effective

A brief demonstration of the previously-treated dead lift areas versus the machine presses indicated the majority of the vibration in the slab below is now coming from the machine presses.

Figure 8: Isolated Ceiling Below

Figure 9: Depth of Isolated Ceiling Seen From Below

3. Retail Store

The tenant has noted that it can occasionally hear or feel the vibrations in the rear of the retail area and in the break room. The complaints are minimal due to the masking music in the retail space, although heavy weights were occasionally audible. The vibrations heard in the retail store are likely from two sources. First, the areas directly above the retail store do not have the thick 15mm underlayments, which may result in some impacts coming through. However, we believe it is more likely that the sound is coming from the machine presses that are bolted to the floor to the west.

Conclusion

The use of a continuous 4” concrete slab for a second-floor gym introduces a number of vibration paths into local, adjacent spaces. While certain mitigations have been and may be considered, the best scenario is to isolate the slab from adjacent tenants or provide a thicker isolation pad in order to achieve acceptable performance.

Upon completion of this initial assessment and once noise mitigations have been implemented, a follow-on assessment performed over night when few or no tenants are in place (and mechanical and HVAC equipment may be turned off) may allow precise assessment of exactly which equipment is causing the most issues.

Since there are no applicable building codes for a gymnasium-to-tenant wall or floor-ceiling system, and since numerous noise mitigation efforts have already been undertaken, it is our assessment that the gym has made reasonable efforts to reduce the noise in this space to an acceptable level.

By reviewing and implementing one or more of the Options to Consider listed above, further noise reduction may be achieved and audible levels in adjacent tenant spaces reduced.

Central Florida Hospital – Sound Study

Solving Hospital Noise Complaints

The management from a hospital in central Florida requested an assessment and potential solutions to improve their sound rating scores in their facility. Specifically, the intent was to study and improve the HCAHPS question of whether patients find their environment “Always Quiet at Night”, and the corresponding improvement in patient care quality.

Commercial Acoustics planned and executed an acoustic study on premises, and completed related research, to outline an appropriate mitigation plan for the hospital noise levels. All measurements in this sound study were completed with a Class 1 Sound Pressure Level (SPL) meter and included time- and spatial-logged data to determine exactly when and where the various noise sources are occurring. Furthermore, all events were classified by type, and any anomalies were noted.

By addressing the leading causes of sound and implementing a Noise Reduction Program, the hospital is on its way to delivering exemplary patient care in regards to sleep (in addition to other patient satisfaction metrics).

This is a problem that many, if not all, hospitals face – yet few address it comprehensively. A sound study is critical to isolate the source of each of the noise issues, then they are prioritized and mitigated individually. Many of the issues are addressed via behavioral change, while others may require architectural modifications. By implementing a mixed-approach, most hospitals may expect to achieve significant results within the first 3-6 months of a Noise Reduction effort.

Noise Issues with Drop Ceiling

Drop Ceiling Flanking

One of the most common complaints we see in office and educational settings is flanking noise through open plenums between adjacent spaces. This is often problematic when walls between offices don’t go to deck allowing sound to pass directly through the Acoustic Ceiling Tile and allowing clearly audible conversations between neighbors. (Note: ACT are not designed to block sound but rather absorb echo in a large reverberant space). A common solution we see attempted is laying fiberglass batting on top of the ceiling tiles. However this is strongly discouraged because batting is not STC rated and oftentimes maintenance staff struggles to keep it in place when accessing above the ACT.

A university in Florida came to Commercial Acoustics to address noise from their student government area spilling over into staff offices. Our recommendation? A new polymer based tile that installs above existing ACT to prevent the flanking path. Commercial Acoustics’ drop ceiling noise blocker is available in our Florida and North Carolina warehouses and shipped to the university campus during school break for installation. Installation is simple, taking just a few hours for just over 300 tiles.

Drop Ceiling Panels Above the ACT Grid

ABCs of Acoustical Consulting

Acoustical Consulting

Every acoustical consultation is unique, and should be treated as such. Applying a blanket solution on to acoustical problems rarely results in a happy ending. However, the approach should be methodical and systematic, allowing a clear set of principles to guide a cost-effective solution that is likely to yield an acceptable acoustical design. Our team applies heuristics that save our clients time and money, and ultimately lands them with a solution that meets their expectations.

When deciding on a consultant, ensure they are certified with one of the major Acoustical bodies in the US, and that they have experience in at least the areas mentioned below. If you find solution providers focused in Sound Masking, then you’ll receive a Sound Masking answer, even if the problem doesn’t require it. By finding a diverse acoustical solutions provider, you’ll ensure a good chance of finding the most cost-effective solution for your noise issue.

When approaching any new problem, the following areas should be considered:

A – Absorption: This applies to areas with large volumes and parallel, hard surfaces. There are a number of products that can resolve unwanted echo and reverberation, including fiberglass panels and recycled cotton panels, baffles, and clouds. Furthermore, there are numerous perforated products that specialize in low-frequency absorption. Ultimately, absorption is most needed in large spaces such as gyms, auditoriums, and large classrooms. (See our Acoustical Calculator to understand how much absorption your space may need). Absorption requires a soft, plush material to capture the sound waves and turn them into heat.

B – Blocking: Includes soundproofing for transmission from one area to another, including noise passing through floors and walls to adjacent dwellings. To block unwanted sound, it is important to add mass to the barriers, as well as vibrational decouplers for structure-borne noise. We most often use sound-blocking techniques for hotels, multi-family housing, and mixed use commercial-residential developments.

C – Cover: Also known as sound masking, this solution is ideal for open offices when a uniform background ambient noise allows further focus, privacy, and productivity. It can also be beneficial for doctor’s offices or military applications when privacy is a baseline requirement.

C – Consulting: Our team of experts combines 25 years of soundproofing and acoustical consulting experience to bring a blended knowledge-base. While many consultants focus on expert witness testimony, environmental noise surveys, and long-term studies, we focus our expertise on serving the commercial and residential markets in construction, architecture, and development.

Acoustical Consultants should have the skills, expertise, and equipment to clearly frame the problem and then provide an insightful solution. Our team at Commercial Acoustics is well-versed in each of these areas and is dedicated to providing a cost-effective solution to your concerns.

See our Acoustical Case Studies for recent soundproofing and acoustical projects.