CTS AV Site Surveys 2 — Questions and Answers
Question 1: During an AV site survey, what is the primary purpose of measuring the room's ambient noise level?
- To determine HVAC duct placement
- To establish the required signal-to-noise ratio for the audio system (Correct answer)
- To calculate the room's reverberation time
- To size the video display
Correct answer: To establish the required signal-to-noise ratio for the audio system
Measuring ambient noise (NC/RC rating) is critical for determining how much signal headroom the audio system needs. The speech intelligibility target depends on having adequate signal above background noise.
Ambient noise level (measured in dB-A or as NC/RC curves) sets the noise floor of the room. For intelligible speech, the direct sound level must be at least 25 dB above the ambient noise floor. Knowing the ambient level guides loudspeaker placement, power requirements, and whether noise-isolation treatments are needed.
Question 2: A site survey reveals that a conference room has an aspect ratio of 2:1 (length to width). According to AVIXA standards, what potential AV design challenge does this present?
- Projection throw ratio will be too short
- Long rooms require distributed audio to maintain even coverage (Correct answer)
- The room cannot support videoconferencing
- Wide-angle lenses must always be used
Correct answer: Long rooms require distributed audio to maintain even coverage
Long, narrow rooms (high length-to-width ratio) create uneven sound coverage from a single front loudspeaker cluster, requiring a distributed or delay speaker system to maintain adequate SPL at the far end.
Sound pressure level drops approximately 6 dB every time distance doubles (inverse square law). In a room twice as long as it is wide, listeners at the back receive significantly less SPL. A distributed ceiling speaker system with delay alignment, or a front+delay fill cluster, is typically required to maintain the AVIXA-recommended minimum speech level uniformity.
Question 3: When conducting a site survey, you discover existing conduit runs from the equipment rack to the display location. What is the MOST important measurement to record?
- The color of the conduit
- The conduit inner diameter and total run length (Correct answer)
- The conduit material (EMT vs. PVC)
- The number of 90-degree bends
Correct answer: The conduit inner diameter and total run length
Inner diameter and run length determine whether the conduit can accommodate required cable bundles and whether pull tension will be within allowable limits. Number of bends also affects pull difficulty but the ID and length are the primary capacity factors.
NEC and AVIXA best practices specify maximum conduit fill ratios. The inner diameter (trade size) sets the maximum cable bundle cross-section allowed (typically 40% fill for multiple cables, 53% for a single cable). Run length combined with bend count determines the tension during cable pull. Both values are essential for materials planning.
Question 4: During a site survey for a new display installation, you measure 850 lux of ambient light falling on the screen surface. According to AVIXA standards, what minimum projector output (ANSI lumens) should be specified for a 100-inch diagonal 16:9 screen?
- Approximately 500 lumens
- Approximately 1,500 lumens
- Approximately 3,500 lumens (Correct answer)
- Approximately 7,000 lumens
Correct answer: Approximately 3,500 lumens
AVIXA's DISCAS standard recommends a contrast ratio of at least 15:1 on the screen. With 850 lux ambient, you need substantial projector output. A 100-inch 16:9 screen has roughly 1.17 m² of area; multiplying by the required screen luminance gives approximately 3,500 lumens as a practical minimum.
AVIXA's Projected Image System Contrast Ratio (DISCAS) standard specifies minimum screen contrast ratios. Screen luminance from the projector must overcome ambient light reflected off the screen. Calculations use: Required lumens = (Required screen luminance in cd/m²) × screen area (m²) × π / projector efficiency. Under 850 lux ambient conditions, approximately 3,500 lumens is the practical minimum for a 100-inch screen.
Question 5: When documenting power availability during a site survey, which value is MOST critical for AV rack design?
- The wall outlet voltage rating
- The available amperage on dedicated circuits at the rack location (Correct answer)
- The building's total service panel amperage
- The type of cable used for branch circuits
Correct answer: The available amperage on dedicated circuits at the rack location
AV racks must not exceed the amperage of their dedicated circuits. Knowing available amperage at the rack location allows the designer to calculate total load, apply the 80% NEC continuous load rule, and specify appropriate PDUs and circuit breakers.
NEC 210.19 requires that continuous loads (on for 3+ hours) not exceed 80% of circuit ampacity. For example, a 20A circuit allows only 16A continuous load. During a site survey, recording the number and amperage of dedicated circuits at the rack determines maximum allowable rack load, which guides PDU selection and equipment power budgeting.
Question 6: A site survey for a boardroom shows ceiling height of 3.2 m (approx. 10.5 ft). What AVIXA-recommended maximum mounting height should guide ceiling microphone placement?
- No limit — ceiling mics work at any height
- 3.0 m (approx. 9.8 ft) maximum (Correct answer)
- 2.4 m (approx. 8 ft) maximum
- 1.8 m (approx. 6 ft) maximum
Correct answer: 3.0 m (approx. 9.8 ft) maximum
AVIXA's Audiovisual Systems Performance Verification standard and general best practices recommend ceiling microphone mounting heights not exceed approximately 3 m (9.8 ft) to maintain adequate pickup sensitivity and avoid excessive room noise pickup.
Ceiling microphones follow the inverse square law: doubling distance quarters the direct-to-reverberant ratio. AVIXA and microphone manufacturers typically recommend a maximum ceiling height of about 3 m for acceptable speech pickup. Above this height, the microphone picks up proportionally more room reverberation and noise, degrading intelligibility. The 3.2 m ceiling in this example is marginally above the guideline and may require boundary mics or a pendant array instead.
CTS AV Site Surveys 2
During an AV site survey, what is the primary purpose of measuring the room's ambient noise level?