CTS General 2 — Questions and Answers
Question 1: A loudspeaker is rated at 95 dB SPL (1W/1m). How much additional power is required to increase the SPL by 6 dB at the same distance?
- 2 watts
- 4 watts (Correct answer)
- 8 watts
- 10 watts
Correct answer: 4 watts
Every doubling of amplifier power increases SPL by 3 dB. To gain 6 dB, you must double power twice: 1W → 2W (+3 dB) → 4W (+6 dB). Therefore 4 watts total are required.
The acoustic power relationship is: ΔdB = 10 × log10(P2/P1). For a 6 dB increase: 6 = 10 × log10(P2/1), so P2/1 = 10^0.6 ≈ 4. This means 4 watts total (a 4:1 power ratio yields 6 dB gain). This is foundational to amplifier and loudspeaker system design on the CTS exam.
Question 2: Which AVIXA document defines minimum performance standards for projected image size and viewing distances in AV systems?
- AVIXA F501.01:2015 (DISCAS) (Correct answer)
- AVIXA 10:2013 (Rack Building)
- AVIXA 2M-2010 (Audiovisual Systems)
- AVIXA 4C:2012 (Audiovisual Cabling)
Correct answer: AVIXA F501.01:2015 (DISCAS)
AVIXA F501.01:2015 is the DISCAS (Display Image Size for 2D Content in Audiovisual Systems) standard, which establishes minimum and maximum image sizes and viewing distances for projected and direct-view displays.
DISCAS (F501.01) provides the industry-standard calculations for minimum screen width (at least 1/6 of the throw distance from the furthest viewer for general content) and maximum viewing distance (8H for passive viewing). CTS candidates must know this standard and how to apply its formulas in system design scenarios.
Question 3: What is the primary function of a distribution amplifier (DA) in an AV signal chain?
- To increase the resolution of a video signal
- To split and buffer one input signal to multiple outputs without impedance mismatch or signal degradation (Correct answer)
- To convert analog audio to digital audio
- To compress video for network transmission
Correct answer: To split and buffer one input signal to multiple outputs without impedance mismatch or signal degradation
A distribution amplifier takes a single source signal, buffers it (to prevent impedance loading), and distributes it to multiple destination devices with consistent signal levels and impedance matching.
Without a DA, connecting one source to multiple parallel loads causes impedance mismatch, signal reflections, and level drops. A DA provides high input impedance (loading the source minimally), amplifies, and outputs multiple 75-ohm (video) or line-level (audio) copies. Each output is isolated and buffered, maintaining signal integrity across all destinations.
Question 4: In AV system design, what does 'gain structure' refer to?
- The physical dimensions of audio rack equipment
- The systematic setting of input and output levels throughout an audio signal chain to maximize SNR and headroom (Correct answer)
- The increase in screen brightness from front to back of a display
- The wiring topology of a video matrix switcher
Correct answer: The systematic setting of input and output levels throughout an audio signal chain to maximize SNR and headroom
Gain structure is the process of optimizing signal levels at each stage of an audio system — from source to processor to amplifier to loudspeaker — to maximize signal-to-noise ratio while maintaining adequate headroom to prevent clipping.
Proper gain structure ensures that each device in the signal chain operates in its optimal range: strong enough above the noise floor, but with sufficient headroom below clipping. The process typically starts at the source (line level = +4 dBu professional, -10 dBV consumer), sets DSP input sensitivity to align with the source's nominal level, adjusts processing, and trims amplifier input sensitivity so the amp reaches full rated power just as the DSP reaches its maximum output.
Question 5: Which cable type is MOST appropriate for carrying unbalanced composite video signals over short runs in an AV installation?
- Cat6 UTP
- RG-6 coaxial cable (Correct answer)
- Two-conductor shielded cable
- Fiber optic cable
Correct answer: RG-6 coaxial cable
Composite video is an unbalanced 75-ohm signal. RG-6 (or RG-59) coaxial cable is designed for 75-ohm unbalanced video at the correct impedance, minimizing reflections and attenuation.
Impedance matching is critical for video signals to prevent reflections and ghosting. Composite video operates at 75 ohms. RG-6 coaxial cable has a characteristic impedance of 75 ohms, making it the correct choice. RG-59 is also 75 ohms but has higher attenuation per foot and is better suited for shorter runs. Cat6 is 100 ohms (designed for balanced differential signals), and two-conductor shielded cable lacks the controlled impedance needed for video.
Question 6: An AV technician measures the output impedance of a microphone preamplifier at 150 ohms and the input impedance of the following mixer channel at 600 ohms. What is the impedance ratio, and is it acceptable?
- 4:1 ratio — not acceptable; must be 1:1
- 4:1 ratio — acceptable; audio convention requires load impedance to be at least 10× source impedance, but a 4:1 ratio will have minimal level loss (Correct answer)
- 1:4 ratio — not acceptable; source must always exceed load impedance
- 4:1 ratio — not acceptable; impedances must be equal for maximum power transfer
Correct answer: 4:1 ratio — acceptable; audio convention requires load impedance to be at least 10× source impedance, but a 4:1 ratio will have minimal level loss
In professional audio, a 4:1 (load:source) impedance ratio is common and acceptable. The convention is that the load should be at least 10× (or sometimes 4×) the source impedance for voltage bridging. A 600:150 = 4:1 ratio causes minimal (<1 dB) level loss and is standard practice.
Unlike RF systems (which use impedance matching for maximum power transfer), professional audio uses voltage bridging: the load impedance should be much higher than the source impedance. A 10:1 ratio is ideal, but 4:1 or higher is generally acceptable in practice. At a 4:1 ratio (600/150), the voltage drop is only 20 × log10(600/750) ≈ −1.9 dB — negligible for most applications. Modern preamp outputs are often 50–200 ohms driving mixer inputs of 1k–10k ohms.
CTS General 2
A loudspeaker is rated at 95 dB SPL (1W/1m).
How much additional power is required to increase the SPL by 6 dB at the same distance?