Glossary of Terms - D

A glossary of terms covering lighting, audio, vision and staging in the event and theatrical industry.

There can be a number of meanings for some terms which can vary from country to country and manufacturer to manufacturer. Information within this guide is indicative and every situation can require a different approach and solution. All care has been taken, however, Image Group NZ accepts no responsibility for inaccuracies. If you have any suggestions, comments or queries regarding this list please contact us.

D

DAISY-CHAINING
Connecting items of equipment together by linking from one to the next in a chain. Used for connecting demux boxes to dimmers etc.

DAMPING FACTOR
The ratio of the speaker impedance to the amplifier's internal output impedance. Damping factor is a measure of how well an amplifier can actually control the movement of a speaker cone or diaphragm by preventing it from moving farther than it is supposed to. Damping factor is arrived at by dividing the speaker impedance by the amplifier's internal output impedance. The internal output impedance of any amplifier is determined by the transconductivity (internal resistance) of the output devices. Everything connected in the speaker line (including the speaker cable itself or a crossover) looks to the speaker like an increase in the output impedance of the amplifier, thus lowering the effective damping factor. Because any speaker is a mechanical device, it will have its own resonant frequencies, which will cause the cone to continue in motion after the electrical signal has stopped. [see transient distortion]. An amplifier with a high damping factor will damp out the unwanted speaker cone excursion.

DANCE LIGHTING
Lighting design for Dance is reliant on a great deal of sidelight from BOOMS at the side of the stage. There are normally at least three lanterns on each boom, and three heights - SHINS (to light feet and lower legs), MIDS and HEADS.

DATA
Information represented in digital form, including voice, text, facsimile, and video.

DB (DECIBEL)-
A unit for describing the ratio of two voltages, currents, or powers. The decibel is based on a logarithmic scale; when measuring differences in sound pressure level (SPL), the amount of change in sound pressure level perceivable is directly proportional to the amount of stimulus (the more sound present, the greater the change must be, to be perceived).

DBO (DEAD BLACKOUT)
See BLACKOUT.

D-CHANNEL
The Data Channel on the ISDN circuit is used to carry control signals and customer call data at 16 kbps (BRI) and 64 kbps (PRI).

DC
Short for DIRECT CURRENT.

DECAY
The gradual reduction in sound energy once the sound source is turned off.

DE-RIG
The process of removing lanterns & cabling from flying bars or grid - returning the venue to its normal state, or as preparation for the next production.

DEDICATED ACCESS
A private connection between a customer's equipment and a company providing transmission services. The connection bypasses the local switched telephone network.

DEDICATED NETWORK
Sometimes referred to as a private or leased line. This transmission circuit is used exclusively by a single customer.

DEAD

    A pre-plotted height for a piece of scenery or lighting bar - "that bar's on its dead". The positional indicators on the rope (either PVC tape, or more traditionally cotton tape passed through the strands of the rope) are called DEADS. Sometimes flying pieces are given a number of extra deads, that may be colour coded, in addition to the "in dead" (lower) and "out dead" (higher - out of view). In the US, TRIM has the same meaning.
    Scenery or equipment not needed for current production - "that table's dead".
    An electric circuit that has been switched off or has failed - "the circuit's dead, you can change the lamp now".

DIAGONAL SCREEN
A method of measuring the size of a screen or a projected image. It measures from one corner to the opposite corner.

DIAPHRAGM

    See IRIS.
    A thin flexible sheet that can be moved by sound waves as in a microphone, or can produce sound waves when moved as in a loudspeaker or compression driver.

DICHROIC FILTER
Glass colour filters which reflect all light except that which is the colour of the filter, which passes through. Normal gels absorb the unwanted colours, turning the light into heat. Dichroic filters run cooler, and produce a much cooler beam of light. Longer lasting, but a lot more expensive, they are predominantly used in moving lights or architectural applications.

DICHROIC LAMP
A low voltage display lamp with a reflector that lets heat pass through it, rather than reflecting it. Results in a much "cooler" light.

DICHROIC
A mirror or lens that reflects or refracts selective wavelengths of light. Typically used in projector light engines to separate the lamp's "white" light into red, green and blue light. Also used to remove the Infrared and Ultra-violet.

DIFFERENTIAL AMPLIFIER
An amplifier whose output is proportional to the difference between the voltages applied to its two inputs. Used to balance or offer common mode rejection of interference signals.

DIFFRACTION
The bending or redistribution of acoustic sound waves in a room caused by some obstacle, such as a column or divider. Only low frequency wave forms can be diffracted.

DIFFUSION

    See FROST.
    The scattering of sound waves by a solid object.

DIGITAL
Many electronic devices use digital logic. Information is handled in separate bits (either ON or OFF) rather than continuously variable analogue signals. Most computer lighting boards give a digital multiplexed output, and more and more sound equipment is going digital. In digital audio the continuous analog signal is converted to an encoded discrete value or digital word.

DIGITAL DIMMER
The new generation of dimmers that can respond directly to the digital multiplexed output of the lighting desk. The technology also permits the dimmer to report faults and other data back to the control board.

DIGITAL LIGHT CURTAIN / DLC / D.L.C.

    A remotely controllable motorised batten fitted with an integral colour changer. The DLC can now be controlled via DMX (via an interface) although it originally used software called Light Moves running on a Mac. The effect produced by this lantern is a wall of light (when used with a HAZE MACHINE).
    See also LIGHT CURTAIN.

DIGITAL LIGHT PROCESSING (DLP)
The commercial name for this technology from Texas Instruments (TI). The technology inside is often referred to as either "micro-mirrors", or DMD. It works this way: build a few hundred thousand tiny mirrors, and line them up in 800 rows of 600 mirrors each. Now attach a hinge to each of those 480,000 mirrors. Attach each of those 480,000 hinges to its own very tiny motor! Power each motor with electrostatic energy. The motors tilt their mirrors up to 20 degrees at incredible speeds. This allows the mirrors to modulate light from a lamp, and send the "modulated signal" out through a lens on to a screen. The most amazing part of DLP micro mirrors, is the scale of size. The 480,000 mirrors (actually 580,000 are used), hinges and motors are packed onto a "wafer" a bit larger than your thumbnail.

DIGITAL TRANSMISSION
A way of sending coded information via a series of electric or light pulses through the air, over wires, or through glass fibres.

DIM OUT
Reduction of lighting level for a scene change, that isn't quite a BLACKOUT.

DIMMER
Electrical or electronic device which controls the amount of electricity passed to a lantern, and therefore the intensity of the lamp.

DIMMER LAYOUT
See CHEAT SHEET.

DIMMER PER CIRCUIT
A lighting installation where there is no patching system. Each lighting circuit / socket has a dimmer always connected to it. This has advantages in that you never run out of dimmers, but allows no flexibility and can have cost disadvantages in a large space.

DIMMER RACK
A number of individual dimmer circuits mounted in a cabinet.

DIN
Deutscher Industrie Normen. European standard covering audio connectors and tape equalisation characteristics.

DIP

    Small covered trap at stage level containing electrical outlets. (US equivalent is FLOORPOCKET)
    Lighting equipment on stands at stage level. (e.g. "We're just focussing the dips now")
    Low lighting intensity when cross fading between two higher states - "there's a dip between these two states".
    Transparent lacquer for colouring lamp bulbs - known as "Lamp Dip".
    An audible reduction (attenuation or cut) in gain at a certain frequency also called a notch.

DIRECTIVITY
Area of coverage of a speaker or microphone.

DIRECT CURRENT

    Electric current that flows in one direction only (e.g. from a battery). Abbreviated to DC.
    Also see ALTERNATING CURRENT.

DISCHARGE LAMP

    A high-powered source of light produced by means of an electrical discharge between two electrodes. An arc light, for example uses a discharge between two carbon rods which are manually or automatically fed together as they are burnt up. The use of this type of lighting is restricted to non-dimming applications such as followspots and projection, where dimming is achieved by mechanical means. Many of the new generation of moving lights use discharge lamps, dichroic filters and mechanical dimming shutters.
    Also see BALLAST, CSI, CID, MSR, HMI, HTI, Xenon, MBI.

DISPERSION
The spread or distribution or coverage of sound generated from a horn or loudspeaker. For any given frequency, the area of dispersion is defined as that area between the -6 dB down points of that frequency plotted against amplitude. It is measured in degrees related to an imaginary line descending from the center of the speaker cone. As you move away from the imaginary line, up or down, right or left, the loudness level of the sound decreases. When the sound level decreases rapidly on either side of the imaginary line, the dispersion in degrees is relatively small and the speaker is said to be highly directional.

DISSOLVE UNIT
Interface connected between two or more slide projectors and a tape player. Synchronisation signals recorded onto the tape are detected by the dissolve unit and fade up the lamp in one slide projector while changing the slide in the other, and then vice versa, producing a dipless crossfade between the two images.

DISTORTION
Any undesired change in the wave form of an electrical signal passing through a circuit or transducer. Any distortion can be defined as deviation from the original sound, the discrepancy between what the amplifier should do and what it actually does. All distortion is undesirable. Distortion occurs when the amplifier alters the original sound in the process of amplification so that what comes out of an amplifier is no longer a true replica of what went in. Performers, however, will sometimes desire the application of electronically induced distortion for extra-musical effect in the production of their "sound". The undesirability of inherent distortion is associated with high fidelity and should not be confused with the desirability of distortion as it is expected to be produced through circuitry. When reproducing sound, distortion is unwanted.

DISTRIBUTION AMPLIFIER
An amplifier used to maintain a clean noise free signal to the projector over significant distances. Even with good heavily shielded cables, range of video and computer signals is limited to a few metres before noticeable degradation. In ceiling mount situations, where the wiring may pass along side or across electrical conduits, etc. a distribution amp may be needed with shorter distances. Many distribution amps can also split the signal into 2 or more amplified signals for driving multiple projectors and monitors.

DISTRIBUTION BOARD
System of interconnected fuse carriers and cabling that routes an incoming power supply to a number of different outputs. Known colloquially as DISTRO.

DISTRO / POWER DISTRO
See DISTRIBUTION BOARD.

DLP TECHNOLOGY
Digital Light Processing

DMX512
See MULTIPLEXED (MUX) SIGNAL.

DMX512-A
See MULTIPLEXED (MUX) SIGNAL.

DOME
Follow spot location usually at rear of the upper gallery. Also referred to as BIOBOX (shortened version of BIOGRAPH BOX, after its original function as a cinema projection box).

DONUT
A metal plate with a hole in the middle inserted in the colour runners of a lantern to sharpen focus (in the case of a profile) or reduce spill.

DOT PITCH
The distance between pixels in an image.

DOWNLIGHT
A light from directly above the acting area.

DOWNSTAGE

    The part of the stage nearest to the audience (the lowest part of a raked stage).
    A movement towards the audience (in a proscenium theatre).

DOWSER
A metal flag used in larger followspots and projection equipment to cut off the light beam without cutting off the electrical supply. Discharge lamps need a period of cooling down when they are turned off before they can be turned on again, so they should not be switched off if needed again within about two hours.

DPI
Dots Per Inch.

DRESS LIGHTING
Providing a low level of light to an open stage while the audience enter the house up until the performance starts. Also known as PRESET.

DRESS REHEARSAL
A full rehearsal, with all technical elements brought together. The performance as it will be "on the night".

DRIFT WIRE
A length of suspension wire of standard length with eyelets at each end between the counterweight bar and the top of the scenic piece flown from it.

DRIVER
The motor structure portion of a horn loaded loudspeaker system that converts electrical energy into acoustical energy and feeds that acoustical energy into the entry of a horn throat or the narrow end of the horn. Most often used when referring to a high frequency compression driver, called a driver for short. The definition also includes the loudspeaker in a horn loaded woofer or mid bass horn.

DRY ICE

    Frozen solid carbon dioxide (CO2) at a temperature of -87.5° centigrade which produces clouds of steam-loaded CO2 gas forming a low-lying mist or fog when dropped into boiling water. Although non-toxic, caution is required in the storage and handling of dry ice because of its extreme cold. Water is boiled in a large tank offstage, into which the dry ice is lowered in a basket. Fans and ducts then direct the gas onto the stage. Dry ice does not support life, so care should be taken that small animals, actors etc.are not below the level of the dry ice for more than a few seconds.
    See also LOW SMOKE.

DS-1
The Level 1 standard for digital systems operating at 1.536 mbps (24 DS-0 channels). Also known as T1.

DS-3
Digital Signal Level 3. This term is used to refer to the 45 mbps digital signal carried on a T3 facility.

DVI
Digital Video Interface is a connection standard for linking a video card and a display that requires a digital signal, such as a LCD panel. Analogue video signals can also be used with the DVI interface. A normal DVI cable can support 1600 x 1200 resolution at 60 Hz. A special dual link version can support 2048 x 1536 or even higher resolutions.

DVI-D

DVI-A

DVI-I

DYNAMIC RANGE
In a musical instrument, the dynamic range is the difference in decibels between the loudest and softest level of notes that can be played on that instrument. In electronic equipment, dynamic range is the difference in decibels between the highest (overload level) and lowest (minimum acceptable) level compatible with that piece of equipment.

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