Home > Articles > Networking > Voice/IP Communications

  • Print
  • + Share This
This chapter is from the book

This chapter is from the book

Acoustics

One of the most impressive aspects of the Cisco TelePresence solution is its audio quality. The sound is spatial (emanates from the direction of the person who is speaking) and is full-duplex. (You can talk over each other with no clipping.) The microphones are directional and have a coverage pattern designed to capture the voice of the participants sitting directly in front of them. The microphones also filter out certain background frequencies. The audio compression board in the system encodes the voice from the participants at 48KHz using the Advanced Audio Coding—Low Delay compression algorithm. On the receiving end, the speakers are specifically designed to reproduce the frequency range and decibel levels of human speech so that it feels life-like, as if the person is sitting 8 feet (2.438 meters) or so away from you on the other side of the virtual table.

Other capabilities within the Cisco TelePresence portfolio exploit the acoustic properties of the Cisco TelePresence system. In multipoint meetings for example, the Cisco TelePresence Multipoint Switch (CTMS) relies on the signal strength of the audio coming from each microphone to determine which segment should be displayed at any given time.

Background noise and reverberation in the room can degrade these acoustic qualities and even disrupt the switching behavior in multipoint meetings. Therefore, careful engineering of the environment must be done to ensure that ambient noise and reverberation levels within the room are kept in check. However, you don't want the TelePresence room to be so flat and sterile acoustically speaking that it feels like you're in a sound chamber or recording studio. The goal is to re-create the experience of an in-person meeting, so some amount of ambient noise and reverberation is tolerable—even desirable. Cisco has defined precise targets and thresholds for ambient noise and reverberation levels within a TelePresence room, providing a comprehensive test methodology for measuring those levels and recommendations for remediating typical sources of higher than desired ambient noise and reverberation.

Measuring Ambient Noise

Ambient noise is everywhere and is generated by numerous things. Take a moment to pause and listen to the background noises around you. Have you ever noticed the sound of the air whooshing through the air-conditioning ventilation vents in your room, the gentle humming of the air-conditioning machinery in the ceiling, the buzzing of fluorescent light fixtures above you, the sound of cars and buses and ambulances passing by on the street outside your building, the people talking in the room next door, or the sounds of phones ringing in the offices and cubicles around yours? You probably haven't because your brain has become accustom to those sounds and unconsciously tunes them out, but those are exactly the types of sounds we are interested in measuring and, to the degree possible, eliminating inside the TelePresence room.

Ambient noise can emanate through thin, hollow walls or through the cracks in the door jamb around the door. It can travel up and over walls from adjoining rooms and corridors and permeate through the ceiling into your room. This section discusses methods for treating the walls, doors, flooring, and ceiling materials to remediate these sources of noise, but first, consider how these noise sources are measured.

Cisco uses a Sound Pressure Level (SPL) meter to measure the level of ambient sound within the room. SPL is a logarithmic measurement of the root square mean (or average power) pressure of sound relative to silence. It is denoted in decibels (dB), with silence equal to 0dB. Sound travels through the air in waves. Therefore, SPL is simply a measure of the strength, or pressure, of that wave.

The SPL of human speech is generally 60dB to 65dB. Because of the way the human ear and brain work, background sound that is 25dB to 30dB less than human speech generally goes unnoticed. Therefore, the goal is create a room where the average SPL of ambient background noise is no greater than approximately 36dB. Noise levels exceeding 42dB are cause for concern, and levels exceeding 50dB can cause significant problems with the TelePresence experience.

When measuring the SPL level of a room, the average measurement across the entire environment (that is, throughout the room) is used. This establishes a baseline measurement referred to as the noise floor average. However, because sound dissipates over distance, when measuring the SPL of a specific source, such as an air conditioning vent or fluorescent light fixture, the SPL is taken from a defined distance from the source (for example, SPL = 30dB at 1 meter away from the vent).

As with the lighting measurement techniques discussed in the previous sections, Cisco divides the room into sections, or zones, to measure the ambient noise floor average at various points within the room. Figure 8-37 illustrates the acoustic zones of a CTS-3000 room.

Figure 8-37

Figure 8-37 CTS-3000 acoustic zones: top down view

Within each of the six zones, the ambient noise is measured with the decibel meter approximately 5 feet (1.5 meters) from the floor using a slow sweeping motion to capture the average SPL for that zone. These measurements are done using an A-weighted test. A seventh measurement is taken using a C-weighted test within the middle of the room (front of zone 5) to capture the C-weighted average SPL for the entire room. Note that the C-weighted target is approximately 52dB, compared to the A-weighted target of 36dB mentioned previously. Finally, specific measurements are taken of any particular source of noise, such as each of the air conditioning vents in the room, at a distance of 3 feet (1 meter) from the source, using an A-weighted test. You should be concerned with any A-weighted measurements that exceed 36dB, a C-weighted measurement that exceeds 56dB, or any specific source such as HVAC vents that exceed 36dB at 3 feet (1 meter) distance from the source. For all these tests, you should choose a time of the day that represents the high average, ideally, when the HVAC is actively producing air flow through the vents.

Measuring Reverberation

Reverberation is essentially a measurement of how long a sound continues to bounce around the room before decaying to the point that it can no longer be heard. The measurement used to denote reverberation is called RT60, which is a measurement of the time required for a sound to decay by 60dB. For example, if you have a source generating sound at 65dB, and it takes 200ms for that sound to dissipate to 5dB, the RT60 measurement for that sound is 200ms. The more the sound can reflect off of walls, ceiling, flooring, and other surfaces, the longer it will take for that sound to decay. Figure 8-38 illustrates this concept.

Figure 8-38

Figure 8-38 Reverberation illustrated

The ideal reverberation level for a Cisco TelePresence room is 150ms to 300ms. Levels ranging from 300ms to 500ms are cause for concern, and levels exceeding 500ms can cause significant problems with the TelePresence experience. Reverberation is measured for each of the following frequency ranges independently: 125Hz, 250Hz, 500Hz, 1kHz, 2kHz, and 4kHz. Different frequencies of sound reflect off of (or are absorbed by) wall, ceiling, and flooring surfaces differently. Although the human ear cannot discern all these frequencies, the microphones of the TelePresence system might. Therefore, measuring the reverberation of all these frequencies ensures that we understand the acoustic behavior of the room for all types of sounds, from the low frequency sounds generated by building machinery, through the frequencies of human speech and music, up into the higher pitched sounds generated by electronic devices. For each of these tests, you want to measure from the center of the room, as illustrated in Figure 8-39.

Figure 8-39

Figure 8-39 Reverberation zone: top down view

To measure reverberation, place the decibel meter in RT60 mode in the center of the room on a table surface approximately 5 feet (1.5 meters) off the floor. Use a tone generator and amplified speaker to completely fill the room with > 70dB of white or pink noise for several seconds and then instantly silence the tone generator. The decibel meter measures the time it takes (in milliseconds) for the noise to decay by 60dB. Repeat the test for each of the six frequency levels. For accuracy, several measurements should be taken with the tone generator and amplified speaker at different locations within the room for each of the frequency ranges to ensure that your measurements represent a true average for the room.

Targeted and Maximum Ambient Noise and Reverberation Levels

Table 8-4 summarizes the targets and thresholds for ambient noise and reverberation.

Table 8-4. Target and Maximum Ambient Noise and Reverberation Levels

Measurement

Target

Maximum

Notes

Ambient Noise Floor Average (A-Weighted)

36dB

42dB

Within each of the six zones

Ambient Noise Floor Average (C-Weighted)

56dB

62dB

In the front of zone 5

Specific noise source (@ 1 meter from the source)

36dB

42dB

Air-conditioning vents, light fixtures, or any other specific device such as the fan on a UPS or Ethernet switch

Reverberation (RT60)

150ms–300ms

500ms

For each of the six frequency levels

Controlling Ambient Noise and Reverberation Levels

The primary method of controlling ambient noise and reverberation levels within the room is to use the appropriate wall, flooring, and ceiling building materials. All types of building material have ratings associated with them for the following three acoustic properties:

  • Noise Reduction Coefficient (NRC): The NRC is a rating that represents the amount of sound energy absorbed upon striking a surface. An NRC of 0 indicates perfect reflection; an NRC of 1 indicates perfect absorption. NRC generally pertains to sound within the room and, therefore, applies to wall, flooring, and ceiling surfaces. The target NRC for a TelePresence room is .60.
  • Sound Transmission Class (STC): The STC is a rating that represents the amount of sound energy required to transfer through a surface or structure. An STC of 40 requires greater than 40 decibels of sound energy to transfer through the structure. STC generally pertains to sound leaking into the room from adjacent rooms and corridors and, therefore, pertains to wall and ceiling surfaces and items such as doors and windows that can leak audio. The target STC for a TelePresence room is 60 for internal walls, doors, and windows and 90 for external walls, doors, and windows.
  • Impact Insulation Class (IIC): The IIC is a rating similar to STC but pertains specifically to flooring surfaces. IIC measures the resistance to the transmission of impact noise such as footfall, chairs dragging, and dropped items. This measurement is especially important in multifloor buildings and with plenum flooring. The IIC represents the amount of sound energy required to transfer sound through a surface or structure. An IIC of 40 would require greater than 40 decibels of sound energy to travel through a surface or structure. The target IIC for a TelePresence room is 60.

Table 8-5 summarizes the target and maximum ratings for common construction surfaces within the TelePresence room. The Notes column provides examples of the types of materials you can use to achieve these ratings.

Table 8-5. Target and Maximum NRC, STC, and IIC Ratings

Material

Acoustic Property

Target

Maximum

Notes

Walls

NRC

.40

.30

Acoustic fabric on gypsum or moderate-weighted curtains

STC

60

40

1/2-in. gypsum drywall on both sides with heavy insulation or acoustic panels

Flooring

NRC

.40

.30

Padded carpeting over cement

IIC

60

40

Standard commercial construction practices

Ceiling

NRC

.80

.70

Commercial acoustic ceiling tile

Tile

STC

60

40

Commercial acoustic ceiling tile

Doors

STC

60

40

Solid core door with gasket on top, bottom, and sides

Interior Windows

STC

60

40

1/4-in. double pane windows or acoustical treated coverings

Exterior Windows

STC

90

70

Location near high traffic or airports might want highest ratings

Scenarios for Mitigating Ambient Noise and Reverberation

This section concludes with a few common scenarios for how these ratings apply and what type of remediation tactics you can use.

First, by far the most common problem encountered by customers is the noise created by the HVAC registers. The challenge is that because the TelePresence equipment and the human bodies within the room produce so much heat, either a high level of air flow or a low temperature air flow is required to achieve a comfortable temperature within the room. Finding the proper balance of temperature, air flow, and SPL can be tricky. On one hand, increasing the air flow generally causes the SPL of the register to go well above the maximum of 46dB, either as a result of the air flow through the register or the machinery noise created by the motors and fans traveling through the ducting. On the other hand, decreasing the temperature can cause the air flowing out of the register to be uncomfortably cold for people who happen to stand or sit directly beneath it. It is recommended that you consult an HVAC specialist for assistance in finding the proper balance for your room. However, one general piece of advice is to always use NC30-rated air registers, which diffuse the air flowing out of the register to reduce the air flow noise. The next section "HVAC" reviews the BTU requirements and recommended types and locations of HVAC registers in greater detail.

The second most common area of problems are ambient noise and reverberation levels caused by low NRC and STC values of walls, doors, and windows. Noise can also come up and over the walls from adjoining rooms and corridors and permeate through the ceiling. Figure 8-40 illustrates some of these common scenarios.

Figure 8-40

Figure 8-40 Example NRC and STC scenarios

Simple tactics for remediating these issues include increasing the thickness of the walls (for example, installing a second layer of gypsum drywall to double its thickness), adding sound-absorbing insulation within the walls, installing an acoustic blanket or foam tile inserts above the ceiling to eliminate the sound traveling up and over the wall, and using ceiling tiles with high NCR and STC ratings. Figure 8-41 illustrates some examples of these materials.

Figure 8-41

Figure 8-41 Example ceiling materials used to increase NRC and STC ratings

For rooms that exhibit high levels of reverberation, the best remediation tactic is generally to cover the wall surfaces with acoustically dampening materials, such as small fabric panels placed in strategic locations on one or more walls in the room. Refer back to the "Wall, Floor, and Ceiling Surfaces" section earlier in this chapter for additional considerations.

  • + Share This
  • 🔖 Save To Your Account

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020