Math

Question 1

Image height to furthest viewer

Answer 1

Height=Furthest distance/4,6,8

Question 2

Decibel formula for distance

Answer 2

DB=20*log(D1/D2)
D1=original distance
D2=new distance
Increase in distance will yield a negative number

Question 3

Decibel formula for Voltage

Answer 3

dB=20*log(V1/V2)
V1=original voltage
V2=new voltage
Adding voltage will increase dB

Question 4

Decibel formula for Power

Answer 4

dB=10*log(P1/P2)

Question 5

Formula for Current Ohm’s Law

Answer 5

I=V/R

Current or Amps=Volts/Resistance

Question 6

Power Formula

Answer 6

P=I*V

Power or watts = Current or Amps / Volts

Question 7

Series circuit impedance formula

Answer 7

Zt = Z1+Z2+Z3……

Question 8

Parallel circuit impedance formula where all speakers have the same impedance

Answer 8

Zt = Z1/n

Total impedance is the impedance of one speaker divided by the number of speakers

Question 9

Parallel circuit impedance with loudspeakers of different impedance

Answer 9

Zt = 1/(1/Z1+1/Z2+1/Z3……)

Question 10

Series and Parallel circuit impedance calculation

Answer 10

First calculate each series branch then use the parallel formula

Question 11

Needed Acoustic Gain NAG

How much gain do you need for listeners to hear

Answer 11

NAG= 20*log(D0/EAD)
D=distance from source to listener
EAD= Equivalent Acoustic Distance or the furthest you can go from the source without needing amplification or reinforcement

Question 12

PAG or Potential Acoustic Gain

Gain before feedback

Answer 12

PAG= 20log[(D0D1)/(D2*D3)]
D0 distance from talker to furthest listener
D1 distance from microphone to closest speaker
D2 distance from furthest lister to their closest speaker
D3 distance from talker to their mic

Question 13

Audio system stability formula

Is NAG less than PAG?

Answer 13

NAG < PAG - 10*log(NOM)-FSM
NOM number of open mics
FSM feedback stability margin

Question 14

Conduit capacity

Answer 14

ID=square root of (Od1+Od2+Od3../FP
ID = inside diaper of conduit
Od = outside diameter of each cable
FP = permissible fill percentage

Question 15

Permissible Fill Percentage in conduit

Answer 15

One cable is 53%
Two cables is 31%
Three cables or more is 40%
Just remember 5-3-4

Question 16

Jam ratio

Applicable to 3 cables only

Answer 16

Jam=ID/[(Od1+2+3)/3]

Question 17

Heat Load formula

Answer 17

BTU = Watts * 3.4

Question 18

Power amplifier heat load

Answer 18

BTU = watts * 3.4 * (1-efficiency)

Question 19

Power amplifier heat load (constant voltage)

Answer 19

Watts = watt tap setting * # of speakers * 1.5

Question 20

Room mode calculation - Frequencies where room mode will be present

Answer 20

Hz = 3* velocity of sound/Rooms smallest dimension

Question 21

Loudspeaker coverage diameter

Answer 21

Diameter = 2 x ceiling to listener’s ears x tan(half of the loudspeaker’s angle of coverage)

Question 22

Loudspakers spacing for ceiling mounted speakers

Answer 22

Edge to edge = 2*radius of the speaker’s coverage
Minimal overlap = radius of speaker’s coverage x sqrt of 2
Centre to centre = radius of speaker’s coverage

Question 23

Digital video bandwidth

Answer 23

bit rate (bits/second) = horz. pixels * vert. pixels * bit dept * frames/second