Chapter 13 - Audiovisual Systems

Question 1

A properly designed overhead paging system will provide an SPL for the voice page that is at least ___ dB, but no more than ___ dB above the ambient noise level

a. 3, 6
b. 6, 6
c. 3, 20
d. 6, 20

Answer 1

d. 6, 20

p 13-84:
If the 6 dB level is not followed, the voice pages:
• May be lost in the ambient noise of the room.
• Will be unintelligible.
If the 20 dB ambient noise level is not followed, the paging will be far too loud in areas closest to the loudspeakers and horns.

Question 2

The ___ is the preferred pattern for loudspeaker distribution because it provides the most uniform coverage.

a. Hexagonal
b. Square

Answer 2

a. Hexagonal

p 13.85

Question 3

In areas with less than ___ dB noise level, the distance between ceiling loudspeakers in a row should be approximately ___ times the ceiling height.

a. 40, 1.5
b. 30, 2
c. 70, 2
d. 50, 1.5
e. 80, 2

Answer 3

c. 70, 2

p 13-86

In areas with less than 70 dB noise level, the distance between ceiling loudspeakers in a row should be approximately twice the ceiling height.

In areas with a noise level greater than 70 dB, the distance between loudspeakers should be decreased.

Question 4

For appropriate sound coverage, wall-mounted loudspeakers should be mounted ___ ft to ___ ft above the floor.

a. 7, 9
b. 8, 12
c. 8, 10
d. 9, 12

Answer 4

b. 8, 12

p 13-86

For appropriate sound coverage, wall-mounted loudspeakers should be mounted ≈2.4 m (8 ft) to ≈3.7 m (12 ft) above the floor. Wall-mounted loudspeakers should not be directed toward each other.

Question 5

For heavy traffic hallways, use ceiling-mounted loudspeakers placed along the center of the hallway ___ ft intervals whenever possible. Place the first loudspeaker ___ ft from the end of the hall and work toward the other end.

a. 8, 8
b. 8, 20
c. 9, 10
d. 9, 20

Answer 5

a. 8, 8

p 13-87

For heavy traffic hallways, use ceiling-mounted loudspeakers placed along the center of the hallway ≈2.4 m (8 ft) intervals whenever possible. Place the first loudspeaker ≈2.4 m (8 ft) from the end of the hall and work toward the other end.

Place a ceiling loudspeaker at hall junctions. In a normal traffic hallway, place loudspeakers at intervals equal to twice the ceiling height.

Question 6

Where ceiling loudspeakers cannot be used, use wall-mounted bidirectional loudspeakers placed at intervals of ___ ft on alternating sides of the hallway. Place the first bidirectional loudspeaker ___ ft from the end of the hall and work toward the other end.

a. 8, 8
b. 8, 20
c. 9, 10
d. 9, 20

Answer 6

b. 8, 20

p 13-87

Where ceiling loudspeakers cannot be used, use wall-mounted bidirectional loudspeakers placed at intervals of ≈8 m (26 ft) on alternating sides of the hallway. Place the first bidirectional loudspeaker ≈6.1 m (20 ft) from the end of the hall and work toward the other end.

Question 7

Horn loudspeakers have a directional projection pattern and are appropriate for use in environments with more than ___ dB of noise.

a. 40
b. 30
c. 70
d. 50
e. 80

Answer 7

c. 70

p 13-87

The loudspeakers may be installed indoors or outdoors or where larger areas must be covered by each loudspeaker. Horns commonly have a higher power rating than ceiling-mounted loudspeakers.

Question 8

In ambient noise levels above ___ dB, coded tones or strobe lights may provide an alternative to standard paging.

a. 80
b. 90
c. 100
d. 110
e. 120

Answer 8

c. 100

p 13-87

In ambient noise levels above 100 dB, coded tones or strobe lights may provide an alternative to standard paging. Many paging controls can activate these devices.

Question 9

A 70 V line can be run ___ times farther than a 25 V line for the same loss.

a. 6
b. 8
c. 10
d. 12

Answer 9

b. 8

p 13-89

A 70 V line can be run eight times farther than a 25 V line for the same loss.

Question 10

Voltage step-down transformers are used at each loudspeaker to convert the 25 V or 70 V signal to a much lower voltage. These transformers are called ___
transformers.

a. Voltage-matching
b. Load-matching
c. Loudspeaker-matching
d. Impedance-matching

Answer 10

d. Impedance-matching

p 13-90

These transformers provide various taps that allow the power to each loudspeaker to be individually adjusted during installation. The tap values may range from
1/8 W to 20 W for most paging applications, up to 200 W for some loudspeakers.

Question 11

Which of the following statement is false about the central amplifier power rating should be based on:

a. The AV source requirements
b. The total sum of the tap wattages of each impedance-matching transformer on each loudspeaker.
c. The total sum of the power lost in the loudspeaker distribution cabling.
d. Power reserved for future growth.
e. Add an additional 25 percent to this number so that the amplifier will normally be operating at about 75 percent of its rated output.

Answer 11

a. The AV source requirements

p 13-91

Question 12

To have a masking system acceptable to those working in the space, the NC should not be higher than ___.

a. 25
b. 35
c. 45
d. 55

Answer 12

b. 35

p 13-92

To have a masking system acceptable to those working in the space, the NC should not be higher than 35. A sound level meter capable of measuring octave band sound levels should be used. For new spaces, the NC can be predicted but should be field verified.

Question 13

The video conferencing camera FOV should NOT be valued higher than ___ degrees or it would be subject to significant optical distortion.

a. 45 degrees
b. 50 degrees
c. 65 degrees
d. 70 degrees

Answer 13

c. 65 degrees

p 13-72

Anything valued higher than 65 degrees FOV is subject to significant optical distortions (e.g., curvature at the image edges eventually extending throughout the image as the FOV gets bigger).

The ratio of optical zoom (e.g., 8:1, 10:1, or 17:1), combined with the FOV number will give the usable range of the camera views

Question 14

Most cameras used in videoconferencing systems use ___ bit processing.

a. 8
b. 10
c. 16
d. 24

Answer 14

b. 10

p 13-73

Most cameras used in videoconferencing systems use 10-bit processing. A 10-bit system has a bright-to-dark range of 1024:1 for all numerical values. A 10-bit system
would limit the potential performance of the camera to resolve about a 1000:1 difference from brightest to darkest elements in a given image.

Question 15

The typical camera used for videoconferencing operates extremely well at ___ lux measured at the subject.

a. 423
b. 526
c. 629
d. 753

Answer 15

d. 753

p 13-75

The typical camera used for videoconferencing operates extremely well at 753 lux (70 fc) measured at the subject. Figure 13.36 shows a typical videoconference light setup.

Question 16

A codec is a small, but critical piece in a videoconferencing system. Which statement is false about a codec:

a. Takes the analog audio and video signals and converts them into digits.
b. Processes the derived digits to reduce the amount of data.
c. Delivers data at a guaranteed rate, reducing the need for buffering.
d. Allows the transmission of the data to a different location over a network.
e. Decompresses the data.
f. Assigns the data to the audio or video decoder, which turns it back into analog signals for listening and viewing.

Answer 16

c. Delivers data at a guaranteed rate, reducing the need for buffering.

p 13-76

A codec is a small, but critical piece, in a videoconferencing system. A codec:
• Takes the analog audio and video signals and converts them into digits.
• Processes the derived digits to reduce the amount of data.
• Allows the transmission of the data to a different location over a network.
• Decompresses the data.
• Assigns the data to the audio or video decoder, which turns it back into analog signals for listening and viewing.

Question 17

In an audio conferencing environment, the microphones are placed at the periphery of the loudspeaker coverage pattern in order to _____ the echo return loss (ERL) of the room.

a. Balance
b. Minimize
c. Maximize
d. Cancel

Answer 17

c. Maximize

p 13-68

The microphones are at the periphery of the loudspeaker coverage pattern to maximize the ERL of the room.

Question 18

When describing digital video signal standards, the serial digital interface (SDI) is for one-way serial transmission of video and audio over _____ cable.

a. Optical fiber
b. Coaxial
c. Shielded twisted-pair
d. Unshielded twisted-pair

Answer 18

b. Coaxial

p 13-24

SDI is for one-way serial transmission of video and audio over standard RG59 or Series-6 coaxial cable. SDI uses BNC connectors (see Table 13.4).

Question 19

When describing digital audio signal sampling, _____ is defined as the range of numbers that can be assigned to each sample.

a. Quantization noise
b. Bit depth
c. Resolution
d. Granularity

Answer 19

c. Resolution

p 13-13

The resolution of a digital audio signal is the range of numbers that can be assigned to each sample.

Question 20

When describing digital audio signal sampling, _____ is affected by the sampling rate and the signal amplitude

a. Quantization noise
b. Bit depth
c. Resolution
d. Granularity

Answer 20

d. Granularity

p 13-14

Granularity is affected by the sampling rate and the signal amplitude; the lower the granularity, the better the signal quality.

Question 21

When using higher sampling rates to digitally represent the analog signal amplitude and frequency, the error between the actual analog signal value and the digitized value is called ___

a. Quantization noise
b. Bit depth
c. Resolution
d. Granularity

Answer 21

a. Quantization noise

p 13-13

This error is known as quantization noise.

Question 22

For video applications that do not require perception of text or detailed images, a factor of up to ___ may be used, which allows for a smaller image size or longer viewing distances.

a. 4
b. 6
c. 8

Answer 22

c. 8

p 13-31

An image detail factor of 6 is typically used for tasks that require some detail but do not include reading of small fonts. For tasks requiring finer detail and smaller font reading, a factor of 4 may be used increasing the minimum screen height.

Question 23

For program audio, adequate electrical SNR greater than ___ dB should be acquired.

a. 20
b. 30
c. 40
d. 50
e. 60

Answer 23

e. 60

p 13-45

Adequate electrical SNR (greater than 60 dB). Factors that contribute to intelligibility are:
–Achieving at least 25 dB SNR (room noise).
–Meeting the required frequency response.
–No perceived distortion (less than 1 percent total harmonic distortion).
–Good direct-to-reverberant sound ratios.’

Key word “Jazz”

Question 24

Which one of the following is not a requirement for speech reinforcement

a. Loud enough
b. Intelligible
c. Clear
d. Stable

Answer 24

c. Clear

p 13-46

The main requirements for a speech reinforcement system are similar to those for program audio, with one addition. A speech reinforcement system must be:
• Loud enough.
• Intelligible.
• Stable.

Question 25

For point source loudspeaker placement, when considering a central cluster system for an environment, a general rule is that D2 should not exceed ___ times D1

a. 2
b. 4
c. 6
d. 8

Answer 25

b. 4

p 13-48

When considering a central cluster system for an environment, a general rule is that D2 should not exceed four times D1.

Question 26

Within a speech reinforcement distributed loudspeakers system, the optimal distribution of the full range of important frequencies, overlap of as much as ___ percent in adjacent loudspeaker distribution patterns is recommended.

a. 20
b. 30
c. 40
d. 50
e. 60

Answer 26

d. 50

p 13-51

For optimal distribution of the full range of important frequencies, overlap of as much as 50 percent in adjacent loudspeaker distribution patterns is recommended. The lower the ceiling, the more loudspeakers are required, and vice versa.

Question 27

Conference rooms should be designed to an NC ___ standard.

a. 20
b. 30
c. 40
d. 50

Answer 27

b. 30

p 13-56

Conference rooms should be designed to an NC 30 standard. An NC 30 rating corresponds to approximately 40 dBA SPL of background noise, leaving about 30 dB of SNR for normal talkers (70 to 77 dB SPL at ≈1 m [3.3 ft]).

Question 28

The ICT distribution designer should keep in mind transformer losses of approximately 1 dB for each loudspeaker and choose an amplifier at ___ to ___ percent larger than the sum of the required loudspeaker power.

a. 20, 50
b. 30, 40
c. 25, 50
d. 20, 55

Answer 28

c. 25, 50

p 13-69

This will allow some headroom for additional loudspeakers or louder transient signals.

Question 29

___ consists of two user channels of 64 Kb each delivered over a single copper pair similar to a regular telephone line and was originally intended to supplant POTS.

a. BRI
b. PRI

Answer 29

a. BRI

p 13-77

BRI consists of two user channels of 64 Kb each delivered over a single copper pair similar to a regular telephone line and was originally intended to supplant POTS.

PRI contains either 24 or 32 channels of 64-Kb service and is delivered over two pairs of copper wire.

Question 30

Typically, up to ___ BRI circuits are linked together to provide 512 kb/s connectivity.

a. 2
b. 4
c. 6
d. 8

Answer 30

b. 4

p 13-77

Multiple channels of BRI are often collected together and operate as a single higher speed connection in a process called inverse multiplexing. Typically, up to four BRI circuits are linked together to provide 512 kb/s connectivity.

Question 31

Systems requiring only a few loudspeakers are typically better served with a constant ___ design

a. Current
b. Voltage

Answer 31

b. Voltage

p 13-83

Systems requiring more than a few loudspeakers are typically better served with a constant voltage design, which provides a voltage of up to 140 V (i.e., typically 25, 70, or 100), eliminating the need to calculate and balance loads.

Question 32

Masking amplifiers should have ___ V outputs.

a. 25
b. 70

Answer 32

b. 70

p 13-93

Amplifiers should have 70 V outputs. Since a masking system should never be turned off, the amplifiers should be of high quality.

Question 33

The required masking tuning equipment in the United States is an ANSI class ___, ___ octave spectrum analyzer and a high-quality flat response microphone.

a. 1, 1/2
b. 2, 1/2
c. 1, 1/3
d. 1, 1/4

Answer 33

c. 1, 1/3

p 13-94

Question 34

Which articulation index range is considered normal for speech privacy

a. 0.33-0.44
b. 0.20-0.32
c. 0.05-0.19
d. 0.00-0.04

Answer 34

c. 0.05-0.19

p 13-95 Table 13.8

Normal privacy is typically the best that the ICT distribution designer can expect from a properly designed sound masking system in an open office.

Normal privacy means that while occupants are aware of conversations around them, they cannot discern the subject unless they concentrate on them.

Question 35

Human perception of light is most sensitive to the ___ spectrum of light

a. Red / yellow
b. Green / blue
c. Blue
d. Red
e. Yellow / green

Answer 35

e. Yellow / green

p 13-19

Human perception of light is most sensitive to the yellow/green spectrum of light, less sensitive to red, and least sensitive to the blue spectrum.

Question 36

When describing the properties of sound, the action of molecules ___ is called rarefaction

a. Exerting pressure
b. Vibrating
c. Compression
d. Moving apart

Answer 36

d. Moving apart

p 13-2

The action of molecules pressing closer together is called compression. The action of the molecules moving apart is rarefaction. The changes in pressure among these molecules create invisible sound waves.

Question 37

Multiple ISDN basic rate interface (BRI) channels are often grouped together in a process called _____ in order to operate as a single high speed connection for videoconferencing systems.

a. Channel clustering
b. Link aggregation
c. Circuit bonding
d. Inverse multiplexing

Answer 37

d. Inverse multiplexing

p 13-77

Multiple channels of BRI are often collected together and operate as a single higher speed connection in a process called inverse multiplexing. Typically, up to four BRI circuits are linked together to provide 512 kb/s connectivity.

Question 38

When describing digital video signal standards, the serial digital interface (SDI) can operate over a maximum cable length of _____ at a bit rate of 270 Mb/s.

a. 300 m (984 ft)
b. 100 m (328 ft)
c. 15 m (50 ft)
d. 3 m (10 ft)

Answer 38

a. 300 m (984 ft)

p 13-24 Table 13.4

Any rate greater than 1 Gb/s can operate over a maximum cable length of ≈ 100 m (328 ft)

Question 39

In audio conferencing environments, if the period between the time a word is spoken and the time its echo is heard exceeds _____ milliseconds (ms), the echo will cause most talkers to stutter.

a. 400
b. 300
c. 200
d. 100

Answer 39

b. 300

p 13-61

In fact, if the period between the time a word is spoken and the time its echo is heard is more than 300 ms, the echo will actually cause most talkers to stutter.

Question 40

When describing control panel standards for audiovisual (AV) systems, IEEE 1394 requires devices to be within _____ of their connection.

a. 9 m (30 ft)
b. 7.6 m (25 ft)
c. 4.6 m (15 ft)
d. 3 m (10 ft)

Answer 40

c. 4.6 m (15 ft)

p 13-29

IEEE 1394 requires that devices be within ≈4.6 m (15 ft) of the connection or bus socket on a computer or other device.

Question 41

When describing digital audio signal sampling, the _____ the granularity, the better the signal quality.

a. Higher
b. Lower

Answer 41

b. Lower

p 13-14

Granularity is affected by the sampling rate and the signal amplitude; the lower the granularity, the better the signal quality.

Question 42

A full bandwidth RGB signal with horizontal sync and vertical sync, has the highest quality and stability and requires _____ cables to carry the signal.

a. Five
b. Four
c. Three
d. Two

Answer 42

a. Five

p 13-18 & Figure 13.13

RGB, horizontal sync, and vertical sync:
––Referred to as full bandwidth RGB with separate sync
––Highest signal quality and stability
––Requires five cables to carry the signal, one for each component

Question 43

Most audio equipment operates in an audio range larger than that of the human ear, typically 10 Hz to 30 kHz.

a. True
b. False

Answer 43

a. True

p 13-10

Question 44

In order for an audio conference system to have good intelligibility, the signals heard by the local talker should be at least _____ dB above the background noise level.

a. 25
b. 20
c. 15
d. 10

Answer 44

a. 25

p 13-56

For an audio system to have good intelligibility, the signals heard by the local talker should be at least 25 dB above the background noise level.

Question 45

In a cable television distribution system, the subscriber drop is connected to the distribution system at the:

a. Junction
b. Splitter
c. Headend
d. Tap

Answer 45

d. Tap

p 13-100

Subscriber drop—The taps, cable, and telecommunications outlet/connector where the users connect their TV sets or other video devices. The subscriber drop is connected to the distribution system at the tap.

Question 46

When describing control panel standards for audiovisual (AV) systems, IEEE 1394 supports _____ modes.

a. Synchronous and asynchronous
b. Isochronous and synchronous
c. Asynchronous and isochronous

Answer 46

c. Asynchronous and isochronous

p 13-29

IEEE 1394 supports asynchronous and isochronous modes. The isochronous mode, which delivers data at a guaranteed rate, reducing the need for buffering, is ideal for applications such as real-time video.

Question 47

Lighting is important for a videoconferencing system since the usual dynamic range for such systems is ___, which is significantly lower than the 1000:1 value for a typical camera.

a. 250:1
b. 200:1
c. 150:1
d. 100:1

Answer 47

b. 200:1

p 13-76

Wide differences in light level—The typical camera has a dynamic range of about 1000:1 from brightest to darkest in a given scene. The usual dynamic range of a videoconference system is around 200:1.

Question 48

AV communications signals are controlled by a variety of control protocols. The most common version of serial communication is classified as:

a. SDTV
b. TCP/IP
c. RS-422
d. RS-232

Answer 48

d. RS-232

p 13-26

This is a form of data communications where information is sent sequentially, one piece at a time, down a cable. The most common version of serial communication is classified as RS-232.

Question 49

In a cathode ray tube (CRT) display, the horizontal (H) sync pulse communicates to the electron beam charging the phosphors to turn itself off at the end of each line; a process called horizontal:

a. Cycling
b. Retrace
c. Tracing
d. Blanking

Answer 49

d. Blanking

p 13-16

The electron beam charges the phosphors in a line from left to right. The beam then drops down and scans another line. At the end of each line, the horizontal sync pulse communicates to the beam to turn itself off, which constitutes a process called horizontal blanking.

Question 50

In audio conferencing systems, the absence of a(n) _____ echo canceller will allow loudspeaker audio to be captured by microphones and sent back to the remote participants as an echo of their voices.

a. Line
b. Noise
c. Audio
d. Acoustic

Answer 50

d. Acoustic

p 13-55

In the absence of an AEC, the loudspeaker audio is sent back to the remote participants, who, as a result, hear a delayed echo of their voices.

Question 51

In audioconferencing environments, echoes can overload communication circuits, resulting in a feedback condition called:

a. Gain
b. Squelch
c. Reverb
d. Howling

Answer 51

d. Howling

p 13-61

Echoes can overload communication circuits, resulting in a feedback condition called howling.

Question 52

In a(n) _____ vision seating layout, the vertical sight-line of a viewer passes over the heads of the persons in the first row ahead.

a. Aligned-row
b. Sloped-row
c. Alternating-row
d. Single-row

Answer 52

d. Single-row

p 13-34

Typical sightline techniques include single-row vision and double-row vision seating layouts. In single row vision, the vertical sightline of a viewer passes over the heads of the persons in the first row ahead, as illustrated in Figure 13.20.

Question 53

In order for an audio conference system to have good intelligibility, the signals heard by the local talker should be at least ___ dB above the background noise level.

a. 25
b. 20
c. 15
d. 10

Answer 53

a. 25

p 13-56

For an audio system to have good intelligibility, the signals heard by the local talker should be at least 25 dB above the background noise level.

Question 54

The dBu unit used to measure audio system voltage is referenced to _____ across any impedance.

a. 1 V
b. 0.775 V
c. 1 mV
d. 0.775 mV

Answer 54

b. 0.775 V

p 13-11 Table 13.2

Question 55

When describing digital video signal standards, _____ is the version of video compression tools typically used for digital TV signal transmission.

a. MPEG-4
b. MPEG-3
c. MPEG-2
d. MPEG-1

Answer 55

c. MPEG-2

p 13-25

It is named after the international group that established it to standardize compressed video and audio. The version typically used for TV is MPEG-2.

Question 56

Constant _____ centrally amplified paging systems are more common in smaller installations.

a. Balance
b. Load
c. Voltage
d. Current

Answer 56

d. Current

p 13-83

The constant current systems are more common in smaller installations and require more consideration in design because the loudspeakers need to be balanced, based on load rating, typically 4 or 8 ohms.

Question 57

In analog video signaling, RF video is the combination of _____ video with _____ audio channels.

a. Component; two
b. Component; one
c. Composite; two
d. Composite; one

Answer 57

c. Composite; two

p 13-21

RF signals have the lowest video quality. RF video is composite video with two audio channels (see Figure 13.14).

Question 58

Coaxial cable with a solid copper center conductor and copper braid _____ broadband applications.

a. Is recommended for
b. Should not be used in

Answer 58

b. Should not be used in

p 13-101

Coaxial cable with a solid copper center conductor and copper braid should not be used in broadband applications. This type of coaxial cable is not intended for broadband because it does not effectively shield against ingressing or egressing signals.

Question 59

Using the sound pressure level (SPL) method of approximating distance and power, calculate the power required to produce 89 dB at 4 m (13.1ft) with a loud speaker that is rated at a SPL of 95 dB. What input power level (in watts) is required to appropriately power the speaker?

a. 1 watt
b. 2 watts
c. 4 watts
d. 8 watts

Answer 59

c. 4 watts

p 13-69 inverse log equation

1. Calculate 89 dB @ 4 m to 1 m = 89 + 12 (doubling distance 2x or 6 dB + 6 dB) = 101 dB @ 1 m
2. 101 - 95 = 6 dB
3. 6 dBW = 10 log (needed watts/1 W)
4. 0.6 = log (needed W/1 W)
5. 0.6 = log needed W
6. Inverse log ~ 3.98 needed W

Question 60

You are designing a four story retail mall and multiple sound systems within it. Which system should you design to support general music programming within common retail areas?

a. Distributed paging
b. Life safety
c. Sound masking
d. Sound reinforcement and playback

Answer 60

d. Sound reinforcement and playback

Question 61

A space has all hard surfaces including architecture and furnishings. The audio programming produced from the distributed sound system has become unintelligible. Which of the following will NOT mitigate the problem?

a. Add tapestries to the walls.
b. Provide additional speakers at lower output.
c. Increase the volume to the existing speakers.
d. Reduce the distance of the existing speakers to the listener.

Answer 61

c. Increase the volume to the existing speakers.

Question 62

One 15 W horn mounted ≈5 m (16.5 ft) above the floor with a SPL ambient noise of 80 dB angled at 60-degrees will cover how much space?

a. 372 m2 (4000 ft2)
b. 232 m2 (2500 ft2)
c. 112 m2 (1200 ft2)

Answer 62

b. 232m2 (2500ft2)

p 13-87 Table 13.7

Question 63

Within a CATV distribution system, home run design is typically only used in ___ installations.

a. Small
b. Large

Answer 63

a. Small

p 13-102

A home run design is typically only used in small installations.