AVE Preliminary common mistakes
AVE Preliminary · Understand the traps and how to avoid them.
Treating dB values as linear and adding them arithmetically (e.g., summing two 3 dB gains as 6 dB of power) instead of converting to linear ratios, combining, then converting back.
Candidates memorize the 3 dB doubling rule for power but apply it to voltage/amplitude quantities or to non-coherent sources without checking whether the signals add coherently or incoherently.
What to do instead
Before any dB arithmetic, write down the reference (dBu, dBV, dBSPL, dBm), the quantity type (power vs. amplitude), and whether sources are coherent. For incoherent acoustic or random-noise sources, convert to linear power, sum, then re-convert; for coherent signals, sum amplitudes instead. Practice with a worked table of 10 log vs. 20 log conversions.
Confusing balanced and unbalanced interfaces and miswiring a TRS or XLR connection, resulting in ground loops, lost signal, or phantom power appearing where it should not.
The pin numbering and the meaning of Tip/Ring/Sleeve differ between consumer and pro conventions, and candidates assume a TRS jack is always balanced when it may be a stereo or insert connection.
What to do instead
Learn the standard pinout for XLR (1 shield, 2 hot, 3 cold), TRS balanced (tip hot, ring cold, sleeve shield), and TRS unbalanced stereo. For every cable, state its function before connecting. Never send phantom power to a ribbon mic or unbalanced line input; verify with a multimeter or a phantom-blocking adapter.
Miscalculating loudspeaker impedance loads on an amplifier, such as paralleling two 8-ohm cabinets and assuming the load is 16 ohms or safe on a low-power amp.
Series and parallel formulas are inverted in the candidate's memory, and candidates forget that the amplifier's minimum impedance is a hard limit that varies with frequency.
What to do instead
Memorize the parallel formula (1/Rt = 1/R1 + 1/R2) and the shortcut for equal loads (R/n). Always compare the calculated load against the amplifier's rated minimum impedance at the lowest expected frequency, and leave headroom. Check whether the amp is rated per channel or bridged.
Confusing display resolution, aspect ratio, and pixel density, and assuming a 1080p projector and a 1920x1200 monitor will map one-to-one without scaling or letterboxing.
The terms are used loosely in marketing, and candidates do not distinguish native resolution from supported input signals or from the display's physical aspect ratio.
What to do instead
For each display, record native resolution, aspect ratio, and supported input timings. When integrating a source, compute whether the aspect ratios match; if not, decide on scaling, letterboxing, or pillar-boxing explicitly. Verify with a test pattern rather than assuming the EDID handshake produces the intended result.
Ignoring EDID and HDCP in signal chains, then blaming a cable when a source shows a black screen or drops to a lower resolution after passing through a switcher or extender.
Candidates treat HDMI as a simple one-way cable and do not know that the source negotiates capabilities and content protection with the sink through intermediate devices.
What to do instead
Learn the EDID handshake sequence and how matrix switchers, splitters, and extenders can corrupt or clone EDID. Check HDCP version compatibility on every link, and use an EDID manager or a known-good direct connection to isolate the fault before replacing hardware.
Designing a control system without defining the control protocol and network topology first, then discovering at commissioning that devices cannot be addressed or that the control network shares traffic with streaming video.
Candidates focus on the user interface and device list and defer the transport layer, assuming all devices speak a common protocol or that one flat network is acceptable.
What to do instead
Produce a control architecture document before programming: device addresses, protocol per device (IP, RS-232, IR, relay, CEC), VLAN or subnet plan, and bandwidth budget. Separate control, streaming, and general data traffic, and confirm that each device's API or driver exists and is supported.
Assuming a network cable run will work because it is under 100 m, without verifying category rating, termination standard, and PoE budget for the connected devices.
The 100 m limit is the only rule candidates remember, so they overlook that Cat5e may be inadequate for higher bandwidth, that T568A and T568B must match at both ends, and that PoE class determines available power.
What to do instead
For each run, document cable category, termination standard, length, and PoE class. Sum the PoE draw of all powered devices and compare against the switch's total budget, not just per-port limits. Certify runs with a cable tester and record results in the commissioning report.
Skipping the site survey and as-built documentation, then discovering during commissioning that conduit, power, or structural conditions make the designed mounting or cable route impossible.
Candidates treat design as a paper exercise and underestimate how field conditions (ceiling structure, existing pathways, power availability) change the installation.
What to do instead
Always perform a documented site survey before finalizing design: photographs, measurements, existing infrastructure, and power locations. Produce and update as-built drawings and a cable schedule throughout the project, and use a commissioning checklist that ties each test back to a design requirement.
Troubleshooting by swapping components at random rather than following a signal-flow or divide-and-conquer method, which wastes time and can mask the original fault.
Under exam time pressure and in the field, candidates jump to the most familiar failure (the cable) or the most expensive component instead of localizing the fault systematically.
What to do instead
Apply a consistent method: verify power, then input, then output; substitute a known-good source or sink at the midpoint of the chain; and record each test result. Use test signals and measurement tools (multimeter, cable tester, signal generator) rather than trial-and-error substitution.
Overlooking electrical safety and standards obligations, such as working live, neglecting lockout/tagout, or ignoring grounding, conduit fill, and fire-rated cable requirements.
Candidates concentrate on audiovisual performance and treat safety, codes, and standards as secondary, and they may not know which local codes or standards apply to their jurisdiction.
What to do instead
Before any installation, identify the applicable electrical code, fire-rating requirements, and workplace safety rules, and confirm which tasks require a licensed electrician. Build lockout/tagout, PPE, and de-energization into the procedure, and document compliance. When a standard is uncertain, state that it must be verified locally rather than guessing.