List of Formulas and Symbology Descriptions

Disclaimer: Here are some common formulas; however this is not an exhaustive list and you may not need all of them.	Loudspeaker Impedance ZT = Z1 / N Where ZT is the total impedance of the loudspeaker system Z1 is the measured impedance of a loudspeaker N is the quantity of loudspeakers in the circuit
Video Camera Image Size IS = 2 * D * tan(A/2) Where IS is the image size D is the distance from the lens to the subject A is the lens angle of view	Lumens Output ANSI Lumens = [( L * 10 ) * A ] / 0.75 Where L is ambient light at screen location* 10 is the desired contrast ratio A is the area of screen ** 0.75 is performance derating value 25% * Light units are in either lux or footcandles ** area in square meters or square feet
Loudspeaker Coverage Pattern (Ceiling Mounted) D = 2 * (H - h) * tan (CÐ / 2) Where D is diameter of coverage circle at ear height H is overall ceiling height h is height of the listener’s ears (48 inches) CÐ off-axis coverage angle of polar pattern	Loudspeaker Spacing (Ceiling Mounted) D = 2 * r (Edge-to-edge) D = r * Ö 2 (Minimum overlap) D = r (center-to-center) Where D is the distance between loudspeakers r is the radius of loudspeaker coverage circle
Wattage at the Loudspeaker Where EPR is electrical power required at loudspeaker LP is SPL required at distance D2 H is required headroom LS is loudspeaker sensitivity at 3.28 feet (1 m) D2 is distance from loudspeaker to listener Dr is distance reference value
Power Amplifier Wattage (Constant Voltage) Wt = W * N * 1.5 Where Wt is required wattage W is watt tap used at individual loudspeaker N is total number of loudspeakers 1.5 is upsize of amplifier by 50 percent	Potential Acoustic Gain PAG = 20 log (D0 * D1) / (D2 * DS) Where PAG is Potential Acoustic Gain D0 is distance from source to listener D1 is distance from loudspeaker to mic D2 is distance from loudspeaker to listener DS is distance from source to microphone
Needed Acoustic Gain NAG = 20 log (D0 / EAD) Where NAG is Needed Acoustic Gain D0 is distance from source to listener EAD is Equivalent Acoustic Distance	Audio System Stability: FSM and NOM Final PAG = PAG - 10 log(NOM) - FSM Final NAG = NAG + 10 log(NOM) + FSM Where PAG is Potential Acoustic Gain NAG is Needed Acoustic Gain NOM is number of open mics FSM is Freq. Stability Margin of 6 dB (equalized system) or 12 dB (unequalized system)
Heat Load Total Btu = WE * 3.4 Where Total Btu is the total British Thermal Units released. WE is the total watts of equipment in the room.	Ohm’s Law Related I = P / V Where I is current V is circuit voltage P is power * * Look up amplifier power in owner’s manual before adding to the other AV devices.
Conduit Capacity Where ID is the inner diameter of the conduit OD is outer diameter of each conductor	One Cable Two Cables 3 + Cables
Jam Ratio Where ID is the inner diameter of the conduit OD is the outer diameter of each conductor