Auditorium Acoustics: 8 Factors to Consider

auditorium acoustics

Have you ever attended a lecture or a play in an auditorium and barely been able to make out what the speaker was saying? Chances are the problem was poor acoustics.

Next time you provide acoustical consulting for an auditorium, make sure to consider these 7 key factors:

1. Location

For new auditoriums, the building should be planned as far away as possible from any potential noise sources such as highways, train tracks or industrial areas.

2. Buffer Zones

Isolate the auditorium from the rest of the building and potential noise sources by creating buffer zones.

Hallways and lobbies should separate the main auditorium from restrooms, mechanical equipment, dressing rooms etc. Surrounding space should be used for storage or offices that will be empty while the auditorium is in use.

3. Doorways

All doors should be solid-core, with airtight seals to inhibit outside noise from slipping in.

4. Reverberation

To combat reverb in a large room:

  • Build with sound absorbing material and include sunken panels, undulations and other small irregularities in the walls
  • Sound reflecting materials should be used for the bulk of the building process (thick wood, thick gypsum, concrete)
  • Hang thick, fabric curtains along walls to minimize hard surfaces
  • All aisles should be carpeted to reduce foot-traffic noise
  • Always use fabric seating. Avoid metal and plastic.
  • Create a checkerboard pattern alternating between sound reflecting and sound absorbing materials along the ceiling.

5. Background Noise

Install sound absorbing duct liners and mufflers to reduce HVAC noise.

6. Balcony

Balconies should be included to reduce the distance between the farthest seats and the stage. The overhang should be of small depth and be fitted with sound absorbing material

7. Sound Systems

Speakers should be placed just above and in front of the proscenium opening or arch. The controls for these speakers should be positioned in a central location of the seating area rather than in a separate room in the back of the auditorium.

8. Orchestra Pits

If the auditorium has an orchestra pit, soundproof curtains should be installed that can be opened and closed as the conductor chooses to control the noise level.

General auditoriums play host to a wide range of performances and events which will have no chance of success if audiences aren’t able to hear them. Consider this list the next time you’re working on a general auditorium to create the ideal acoustics.

Have any other tips about auditorium acoustics? Leave them in the comments below!

 

Sofwerx – Tampa Bay, FL

commercial acoustics sofwerx absorption

Sofwerx was a Joint Venture between the Department of Defense and a local non-profit known as the Doolittle Institute. The focus is to develop a training and strategy group that could provide counter-UAV support for our troops.

The team was faced with an extremely aggressive task of converting an old, 33,000 square foot warehouse into an operational site in less than two months. While the architect and design team was busy planning layouts and aesthetics, they realized that there was one challenging element that had not yet been considered: acoustics!

The site had a number of unique elements:

  1. A large auditorium where drones and UAVs (Unmanned Aerial Vehicles) would fly and pilots practice. This was to be converted from the previous “sanctuary” – a large, open space that already suffered from substandard reverberation. To make matters worse, the team needed to remove all of the plush furniture which was helping absorb some of the current echo.
  2. An open office area where pilots, technicians, operators, and management could meet to discuss new counter-drone tactics. None of the office walls went to deck, and most of them did not even have ACT tiles. Furthermore, 90% of the staff were to work collaboratively on large tables out in the open “bullpen”.
  3. A machine shop was directly adjacent to a presentation room. While the machine shop was necessary to quickly manufacture replacement parts, it was to be used simultaneously to the rest of the space. With grinding and milling operations around 110dB, this threatened to make it very difficult to hold meetings immediately next door.

Ultimately, Sofwerx reached out to Commercial Acoustics to provide support in all 3 areas.

  1. Absorption panels were manufactured in-house and delivered to the site within weeks. Commercial Acoustics determined the amount of panels necessary for each space and designed the panel layout for optimal effectiveness.  Furthermore, the design team loved the concept of acoustic “teepees” or wings, hanging over 6-person desk spaces. These were uniquely designed, built, delivered, and installed within 30 days.
  2. A sound-masking system was installed and tuned in the main open office area to provide additional speech privacy. Where none of the office walls went to deck or had ACT, the masking system was the only sound solution that would be effective in that space; raising the background dB level and preventing confidential conversations from bleeding into the adjacent spaces.
  3. Finally, soundproofing membrane material was used in the machine shop, to attenuate unwanted noise prior to it reaching the presentation area. We also recommended that the high-NC machinery was moved to the exterior walls and a high-STC solid core door was installed, to avoid an untreated flanking path.

For these varying sound issues, none have a blanket solution and each environment and sound concern needs to be analyzed in order to find the appropriate solution. Our team was on hand to collaborate with the architects, interior designers and clients to ensure that the sound quality, code compliance, aesthetics, and time frame were met. By implementing a holistic approach, the client received great results, and on an extremely tight timeline.

If you found anything in common in this case study with your projects, let us know here and one of our acoustical specialists will reach out to you shortly.

Classroom Noise Distracts Students

classroom acoustics

Classrooms, especially grade school classrooms, are notoriously loud. We tend to credit the noise to students giggling with their friends and playing with their iPhones under their desks, but they may not be entirely to blame when it comes to tumultuous classrooms.

Think back to the last classroom you were in. What did it look like? Chances are there were tiled floors, cement walls, and endless rows of metal desks – the kinds of surfaces sound waves thrive on.

Sound waves deflect off of these hard surfaces, sending noise flying in every direction. This commotion makes it difficult for students to hear and encourages them to add to the chaos rather than strain their ears to listen. If you’re a teacher or educator looking to quiet your classrooms’ noise problem, you need to hear about these sound solutions.

Wreck the Reverb

Acoustic Absorption Panels are the simplest solution to any classroom noise problem. These durable panels can be installed in as little as fifteen minutes; perfect for teachers on a time crunch.

How It Works: Hang your panels around the room, placing a few on each wall. As sound waves are generated from students chatting, tapping their feet and clicking their pens, they will start to fly around the room and crash into any available surface. As the waves hit the panels, they will be absorbed by the acoustical fiberglass and fabric, silencing them and stopping them from further bouncing around the room.

Ease the Echo

Echo occurs as noise bounces off of a surface and returns to the listener as a secondary sound. Bare rooms with hard surfaces, like classrooms, are likely to experience a good amount of echo. For educators on a budget, absorption foam is an affordable solution with high-cost results.

How it Works: Absorption foam is a lightweight product made from open cell polyurethane, allowing for quick and easy installation. The foam can be hung along walls with any construction adhesive approved for foam and can be installed in less than fifteen minutes. The highly-engineered material traps sound waves as they hit, diminishing echo and improving the listening quality of the room.

Loud background noise distracts students and makes hearing difficult. Help your students succeed by treating the noise and providing a quiet learning environment you can all enjoy.

Have a question about the acoustics of your classroom? Let us know in the comments below, at Commercial Acoustics, we’re always here to help!

Save Time & Money – Choose Wall Blokker Over Layered Drywall

Soundproofing is an obstacle general contractors face during both new construction projects and renovations. The mistake of installing 2 or more layers of drywall is commonly made when combating this issue in the hopes that the extra layers will provide a sufficient sound barrier. Multiple layers of drywall may muffle some sound but will not make any drastic impact on noise control.

Drywall, while an extremely useful building resource, is designed for the construction of walls, not for blocking noise. Typical drywall contains a solid gypsum core that vibrates as it encounters sound waves, allowing noise to pass through easily. Not only does layered drywall do little to block out sound, procuring and installing the extra material is expensive and time-consuming.

Wasted time and money can be avoided by installing Wall Blokker underneath one single layer of drywall. Wall Blokker is specifically designed to block airborne noise as well as decouple drywall from underlying studs to decrease structure-borne noise in both walls and ceilings. It is easy to install and requires less time and effort than purchasing and layering extra sheets of drywall.

Most importantly, Wall Blokker will reduce 75% of airborne and impact noise, something no amount of drywall can do. In addition to its impressive noise blocking abilities, Wall Blokker offers barriers against moisture and air, making it a 3-in-1 solution.

Choosing Wall Blokker allows for the construction of a significantly quieter structure with less material and labor than layered drywall.

soundproofing walls sound barrier

 

MidFlorida Credit Union Call Center – Case Study

call center sound masking acoustics

MidFlorida Credit Union employees found themselves struggling with voice carryover in their headquarters’ call center. With calls being placed continuously by the many employees in the center, background noise built up and became a real problem for workers who were unable to hear over the noise created by their coworker’s calls.

The excessive background noise was distracting workers and creating a difficult environment for them to focus in. The difficulties and frustration created by this type of noise problem can lead to decreased productivity and harm performance.

This Credit Union employed the help of Commercial Acoustics in the hopes of resolving the situation before it became even more problematic. One of our soundproofing specialists assessed the building and recommended the installation of several carefully spaced speakers throughout the center. Once in place, the sound masking speakers play a white noise designed to eliminate background noise in critical listening environments.

The background noise was effectively masked by the equipment we installed, solving the call center’s problem and improving the overall quality of the workplace. The newfound quiet will allow for greater concentration among employees and likely lead to an increase in productivity.

The Commercial Acoustics Team is happy to have played a significant role in the bettering of this credit union’s call center.

Stop Apartment Noise Disturbances Before They Begin

apartment soundproofing multifamily

From luxury suites to affordable complexes, one of the main factors to consider when building apartment homes is sound. Living wall-to-wall with your neighbors can make for plenty of noise disturbances so it comes as no surprise that a quiet and private living space is of value to most apartment dwellers, and they’re willing to pay for it. Yet many apartment buildings overlook this fact when designing their buildings and end up with dissatisfied tenants upset about excessive noise seeping in from neighboring apartments.

If soundproofing is considered during development these issues can be avoided, making the building a more compelling living space for potential renters.

There are many ways for developers to include soundproofing in the design of their apartment complexes. Below are 4 ways to protect an apartment from noise disturbances during the building process.

Insulation

Installing insulation is already a necessary aspect of building a living space, so why not use it to combat noise disturbances? This high-quality insulation is designed specifically with soundproofing in mind and can be used in both interior and exterior walls, ceilings, and attics. By replacing typical insulation with this soundproofing version, the building will become a much more desirable living location.

Sound Barriers

Another soundproofing option is to install a sound barrier below the surface of an exposed wall or ceiling during construction. High-quality noise barriers are able to reduce noise by up to 75%, keeping tenants from hearing their neighbors and their neighbors from hearing them. It also helps protect against unwanted moisture and improves HVAC efficiency, making it an extremely useful addition to any apartment building construction project.

Sound Dampening

One of the most common noise complaints from apartment home tenants involves their upstairs neighbors’ every movement. To stop this issue in its tracks, consider sound dampening during initial construction. The Floor Blokker can be placed onto bare floor surfaces and then covered with carpeting, reducing ceiling noise flow between apartments.

Decoupling

To greatly reduce sound in high-cost environments like luxury apartment complexes, decoupling is an option to consider. This system can be used to reduce noise and vibrations carried from one apartment to the next via walls or ceiling.

If precautions are taken early on, soundproofing can be seamlessly woven into the construction process. The reduced noise disturbances and increased privacy will not go unnoticed by tenants.

Have a question about one of these products? Leave a comment below and let us help!

Commercial Acoustics Hosts Homebrew Hillsborough

commercial acoustics soundproofing presentation homebrew hillsborough in tampa florida

This past Friday Commercial Acoustics had the pleasure of hosting Homebrew Hillsborough’s monthly coffee networking event.

By holding events like this one, Homebrew Hillsborough works to create collaborative environments for local businesses and entrepreneurs to grow and flourish together.

Hosting this month’s event was an exciting opportunity for Commercial Acoustics.

commercial acoustics coo presenting soundproofing products like mass loaded vinyl

The meet-up began with a tour of our factory, led by Nathaniel Lamb, our Chief Operations Officer. Nathaniel walked our visitors through our factory and offices, giving them a feel for our day-to-day operations and allowing them to get to know our team.

commercial acoustics ceo presenting soundproofing curtains

Following the tour, Walker Peek, our CEO, discussed the ABC²s of Commercial Acoustics:

 Absorption

  • Echo & Reverb Control
  • Baffles, Clouds, Panels

Blocking

  • Soundproofing Membranes
  • Floor Underlayments
  • Wall Underlayments

Cover

  • Sound Masking
  • Ambient Background Noise

Consulting

We greatly enjoyed hosting Homebrew Hillsborough here at Commercial Acoustics and look forward to their future events!

Soundproofing Walls and Ceilings in Your Gym

soundproofing for gyms commercial acoustics

From SoulCycle to Barre to Zumba, it seems like there’s a new workout craze every week these days, and with all these fitness classes come new gyms on every corner.

Blaring music, loud equipment and stamping feet may pump you up while you work out but for the daycare center and office building next door, the constant noise can be problematic to say the least.

So what can these gyms do to combat noise complaints and keep their neighbors happy? Soundproof, of course!

Floors

Gyms are typically built with hard flooring to fight against damage from heavy equipment. This type of flooring may be great for protecting against dropped weights, but sound easily echoes off of these hard surfaces, creating a lot of extra noise, especially for your downstairs neighbors.

To muffle sound without sacrificing tough flooring, install sound dampening composites directly onto bare floors for an overall quieter structure.

Walls

Many gyms are located in places with thin walls, like strip malls, which do nothing to stop noise from traveling between facilities.

To stop noise from seeping through the walls and into your neighbors’ space, consider hanging “acoustical wallpaper,” which will suppress sound from moving through even the thinnest of walls. This one is easy to install and can even be primed and painted over, so you don’t have to sacrifice style when soundproofing.

Ceilings

If your gym is located in a multi-story facility, you’re likely irritating your upstairs neighbor with every class you offer.

By installing these noise-blocking panels to your ceiling, you will stop noise from escaping through to the floors above you.

If your gym is constantly fielding noise complaints from angry neighbors looking for some peace and quiet, it may be time to start soundproofing. By following these easy tips, you’ll be able to easily trap noise in and keep your bothered neighbors at bay.

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.

commercial acoustics acoustical test

Figure 1: WF-4 From Wall Schedule

commercial acoustics acoustical test

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

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

commercial acoustics acoustical testing astc

commercial acoustics acoustical testing

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

 

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

commercial acoustics acoustical testing kitchen and corridor

commercial acoustics acoustical testing

Figure 5: ASTC of Wall Between 4206 Kitchen and Corridor

 

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

commercial acoustics acoustical testing bedroom and corridor

commercial acoustics acoustical testing

Figure 6: ASTC of Wall Between 4206 Bedroom and Corridor

commercial acoustics acoustical testing

commercial acoustics acoustical testing

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)commercial acoustics acoustical testing aiic test

commercial acoustics acoustical testing living room

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

 

Appendix H: Supporting Lab Testing

commercial acoustics acoustical testing

Figure 10: Lab STC of Double Wood-Stud Wall

commercial acoustics acoustical testing

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

commercial acoustics acoustical testing

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

 

Cancer Treatment and Research Center – Case Study

soundproofing and acoustical treatment for medical centers

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

commercial acoustics acoustical testing reverberation

Figure 1: Reverberation Test Locations

commercial acoustics reverberation criteria

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.