H - Equations

Question 1

equation for the speed of sound

Answer 1

c = d/t

c = speed of sound (m/s)
d = distance (metres)
t = time (seconds)

Question 2

equation for the speed of sound at a given temperature

Answer 2

C0+ 0.6 x t = ____m/s

C0 = speed of sound in air (331m/s)
t = temperature (°C)

Question 3

Equation to determine the frequency (Hz) of a note

Answer 3

2 ^(#ST/ 12) x reference frequency

use 440 (A) as the reference - descending, #ST is a negative number
ST-semitones

Question 4

equation for the time of a single cycle (period)

Answer 4

t = 1/f

t = time (seconds)
f = frequency (Hz)

Question 5

Equation for the length of a cycle (in m)

Answer 5

λ= c/f

λ = wavelength (metres)
c = speed of sound (344 m/s)
f = frequency (Hz)

Question 6

Equation for determining phase shift (in º)

Answer 6

⌀ = Δt x 360 x f

⌀ = phase shift (degrees)
Δt = time difference (seconds)
f = frequency (Hz)

Question 7

Equation for determining doppler shift

Answer 7

fd = fo x c / (c - v)

fd = doppler frequency (Hz)
fo = original frequency (Hz)
c = speed of sound (m/s)
v = velocity (m/s)

Question 8

logarithm for power (watts, dBm)

Answer 8

10 x log (P1 / P2)

P1 = variable value (watts)
P2 = reference value (watts)
P = power

Question 9

logarithm for pressure ratio (dB SPL)

Answer 9

20 x log (E1/ E1)

E1 = variable energy
E2 = reference energy

Question 10

power equation

Answer 10

P = V² / R

P = electric power (watts (w))
v = voltage (volts)
R = resistance (ohms)

Question 11

to calculate voltage

Answer 11

V = √P x R

V = Voltage (volts)
P = power (watts)
R = Resistance (ohms)

Question 12

dBFS

Answer 12

20 log (sample value / maximum possible value)

Question 13

to calculate the addition of dBs (from incoherent radiating sources)

Answer 13

L ∑ = 10 log (10 ^L1/10 + 10^L2/10)

Question 14

to calculate the subtraction of dBs (from incoherent radiating sources)

Answer 14

L ∑ = 10 log (10^L1/10 - 10 ^L2/10)

Question 15

calculating RMS

Answer 15

1: square the values
2: take their average
3: take the square root of the average

Question 16

to calculate ohms law

Answer 16

V = I x R

V = voltage
I = Current
R = resistance

Question 17

to calculate power law

Answer 17

P = I x V

P = power 
I = current
V = voltage

Question 18

how to calculate total resistance

Answer 18

in series: RT = R1 + R2 + R3…..

in parallel: 1/RT = 1/R1 + 1/R2 + 1/R3……

Question 19

kirckhoffs law

Answer 19

resistors in series: Vin = V1 + V2

resistors in parallel: Vin = V1 = V2

Question 20

Calculating Output Voltage Circuits with Resistors Wired in Series

Answer 20

Vout = Vin x R1/RT

Vin = Input voltage (V)
Vout = Output voltage (V)
R1 = Value of resistor across which voltage is measured (Ω) RT = Total resistance of the circuit (Ω)

Question 21

Equation for the phase offset in cycles (not degrees)

Answer 21

ø = ∆t x f

Question 22

Eq’n for calculating capacitors in series

Answer 22

1/CT​ ​=​ ​1/C1​ ​+​ ​1/C2​ ​+​ ​1/C3​ ​+​ ​…​ ​+​ ​1/CN

Question 23

Eq’n for capacitors in parallel

Answer 23

CT​ ​=​ ​C1​ ​+​ ​C2​ ​+​ ​C3​ ​+​ ​C4​ ​+​ ​…​ ​+​ ​CN

Question 24

Eq’n for time constant for capacitors

Answer 24

τ​ ​=​ ​R​ ​x​ ​C

τ = time constant (s) R =
resistance​ ​(Ω)​ ​C​ ​=​ ​capacitance​ ​(F)

Question 25

Eq’n for capacative reactance

Answer 25

X​C​​ ​=​ ​1​ ​/​ ​(2​ ​π​ ​f​ ​C)

​X​c​​ ​=​ ​Capacitive​ ​Reactance​ ​(Ω),​ ​f​ ​=​ ​Frequency​ ​(Hz),​ ​C​ ​=​ ​Capacitance​ ​(F)