Glossary of AV design terms

Short, plain definitions of the terms you meet in the tool, grouped by subject. Each one says where the tool uses it.

Sound and acoustics#

SPL#

Sound pressure level: how loud a sound is at a point, in decibels relative to 20 micropascals, the quietest sound a young ear can hear. The tool predicts it across each area at ear height and draws it as the heatmap. See Read coverage and the SPL heatmap.

Decibel (dB, dBA, dBm)#

A logarithmic unit for comparing two levels. A rise of 3 dB is double the power; 6 dB is double the sound pressure, which is also what a small speaker in the open loses each time the distance doubles; about 10 dB sounds roughly twice as loud. dBA is a level weighted to match the ear’s sensitivity, used for background noise. dBm is a power level relative to one milliwatt, used for Wi-Fi signal.

Target level#

The level an area has to reach where people listen, set per area. The speaker count, the tuned levels and the verdict all follow it. See Set the target level and size the speaker count.

Uniformity#

How even the level is across an area, as a ± spread in decibels. Smaller is more even.

Headroom#

The margin between what the system can deliver and the target level. The tool checks the continuous level first, then the peaks, and calls headroom good when peaks reach 6 dB over the target.

Noise floor#

The background level in a room with the system off, in dBA. A system has to rise above it to be heard, and a loud noise floor lowers the speech intelligibility.

RT60#

Reverberation time: how long sound takes to die away by 60 dB after the source stops, in seconds, usually given per octave band. Hard rooms have long RT60s and sound live; soft, furnished rooms sound dry. The tool’s venue presets run from 0.4 s for a bedroom to 1.2 s for a gym. Sabine and Eyring are the classic formulas for estimating it from a room’s volume and absorption. See Set room acoustics and RT60.

STI#

Speech Transmission Index: a figure from 0 to 1 for how well speech will be understood, defined in IEC 60268-16. Reverberation and background noise both blur the rhythm of speech and lower it. The traditional bands are bad below 0.30, poor from 0.30 to 0.45, fair from 0.45 to 0.60, good from 0.60 to 0.75 and excellent above 0.75. The tool checks each area against a target of 0.60. STIPA is the quicker form of the measurement used on site.

C50 and C80#

Clarity: the ratio, in decibels, of the sound arriving in the first 50 milliseconds (C50, for speech) or 80 milliseconds (C80, for music) to the sound arriving after. Higher is clearer. The tool looks for a C50 of 0 dB or more, and treats a C80 of about −2 to +4 dB as balanced.

D/R ratio#

The direct-to-reverberant ratio: the sound arriving straight from the speakers against the reverberant sound, in decibels. It is high close to a speaker and falls with distance, and a higher figure generally means clearer sound. The tool can draw it as a map instead of SPL.

Octave band#

A band of frequencies whose top is twice its bottom. Acoustic figures are given per band; the tool predicts levels in eight bands, from 63 Hz to 8 kHz.

Room modes and the Schroeder frequency#

Room modes are low-frequency standing waves set by a room’s length, width and height, which make the bass boom in some places and thin out in others. Below the Schroeder frequency, single modes dominate the sound, so bass predictions there are approximate.

Comb filtering#

The peaks and dips that appear where sound from two speakers arrives at slightly different times, adding in some places and cancelling in others. The Interference layer shows it.

Time alignment#

Delaying the nearer speakers so that the sound from every speaker arrives at the listeners together, which keeps speech sharp.

Amplifiers and wiring#

Low impedance#

Speakers wired straight to an amplifier channel at their nominal impedance, usually 8 or 4 Ω. It suits short runs and a few speakers. Two 8 Ω speakers in parallel present 4 Ω to the channel.

70/100 V line#

Constant-voltage distribution: the amplifier drives a line at 70 V or 100 V at full power, and each speaker has a transformer with power taps, in watts. The taps on a line add up, and the total must stay within the amplifier’s rating. It suits long runs and many speakers, at a lower current on thinner cable. See Amplifiers, low impedance and 70/100 V lines.

AWG#

American Wire Gauge, a cable size. A lower number is a thicker cable: 16 AWG is about 1.3 mm², 12 AWG about 3.3 mm².

DSP#

A digital signal processor, which sets the level, EQ, crossover, delay and limiting of each output. The tool exports a DSP preset sheet as a starting point for commissioning.

Dante#

A way of carrying many channels of audio over a standard Ethernet network, from Audinate. The library lists Dante devices beside the amplifiers, matrices and players.

Network and video#

RSSI#

Received signal strength: the Wi-Fi level a device receives, in dBm. The figures are negative, and closer to zero is stronger. The tool’s Wi-Fi scale runs from −85 to −40 dBm. See Design Wi-Fi coverage.

PoE#

Power over Ethernet: power sent along the network cable to devices such as access points, cameras and touch panels, so they need no socket of their own. It is defined in the IEEE 802.3af, at and bt standards. A switch or a recorder has a total PoE budget, in watts, shared by everything it powers.

HDBaseT#

A way of sending uncompressed video, audio and control over one category cable. The standard allows runs of up to 100 m; the receivers in the catalogue are rated for 40 m or 70 m.

Video matrix#

A switch that can send any of its inputs to any of its outputs, described by its size, such as 8 × 8.

AV over IP#

Video and audio encoded and sent over an Ethernet network: an encoder at each source, a decoder at each screen and a network switch between them. It grows beyond the fixed size of a matrix. See Design video distribution.

HDCP and EDID#

HDCP is the copy protection on HDMI content: every device in the path must support the same version, and 4K premium content needs HDCP 2.2 or 2.3 from end to end. EDID is the description of its capabilities a screen sends to the source, so the source picks a signal the screen can show.

Cameras#

DORI#

Detect, observe, recognise and identify: four levels of image detail defined in EN 62676-4 by the pixel density on the target. The usual thresholds are 25 pixels per metre to detect, 62.5 to observe, 125 to recognise and 250 to identify. See Place and aim CCTV cameras.

px/m#

Pixels per metre: how many pixels of the image fall on one metre of the scene at a given distance. It falls with distance and rises with resolution and a longer lens. The tool’s pixel-density map draws it across the floor.

NVR#

A network video recorder: it records the cameras’ streams to its disks. Its size follows the number of cameras, the retention in days, the codec and the frame rate.

Documents and files#

BOM#

Bill of materials: the list of every product the design needs, with quantities, and prices once you add them. The tool exports it as a CSV file and builds the proposal from it.

DXF and DWG#

DXF is the Drawing Exchange Format, an open CAD file that AutoCAD, BricsCAD, LibreCAD and others read. DWG is AutoCAD’s own format. The tool imports both and exports DXF. See Export CAD drawings.

Rack unit (U)#

The height of one slot in a 19-inch equipment rack, 44.45 mm. Equipment and cabinets are sized in units: a 2U amplifier, a 36U cabinet.