H - Equations

Question 1

how to work out the speed of sound…

Answer 1

c = d/t

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

Question 2

how to work out the effect of temperature at sea level…..

Answer 2

c + 0.6 x t

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

(do multiplication first, then addition)

Question 3

how to work out the frequency of a note…..

Answer 3

2 (n° of semitones above reference/ 12) x reference frequency

(use 440 (A) as the reference, if you go down, subtract the number of semitones)

Question 4

how to work out the period of a wave

Answer 4

t = 1/f

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

Question 5

how to work out the wavelength of a wave

Answer 5

I = c/f

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

Question 6

how to work out phase shift

Answer 6

⌀ = Δt x 360 x f

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

Question 7

how to work out sum and difference

Answer 7

fh + fl and fh - fl

fh = frequency high
fl = frequency low

Question 8

how to work out doppler effect

Answer 8

fd = fo x c / (c + or - v)

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

Question 9

logarithm for power (watts)

Answer 9

10 x log (P1 / P2)

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

Question 10

logarithm for pressure (watts)

Answer 10

20 x log (E1/ E1)

E1 = variable energy
E2 = reference energy

Question 11

dBFS equation

Answer 11

20 log (sample value / maximum positive value)

Question 12

to calculate the addition of dB’s (from incoherent radiating sources)

Answer 12

L ∑ = 10 log (10 to the power of L1/10 + 10 to the power of L2/10)

Question 13

to calculate the subtraction of dB’s (from incoherent radiating sources)

Answer 13

L ∑ = 10 log (10 to the power of L1/10 - 10 to the power of L2/10)

Question 14

calculating RMS

Answer 14

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

Question 15

to calculate ohms law

Answer 15

V = I x R

V = voltage
I = Current
R = resistance

Question 16

to calculate power law

Answer 16

P = I x V

P = power 
I = current
V = voltage

Question 17

how to calculate total resistance

Answer 17

in series: RT = R1 + R2 + R3…..

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

Question 18

kirckhoffs law

Answer 18

resistors in series: Vin = V1 + V2

resistors in parallel: Vin = V1 = V2

Question 19

Calculating Output Voltage Circuits with Resistors Wired in Series

Answer 19

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 20

power equation

Answer 20

P = V² / R

P = Power (watts)
V = voltage (volts)
R = resistance (ohms)

Question 21

Calculate voltage

Answer 21

V = √P X R

P = Power (watts)
V = voltage (volts)
R = resistance (ohms)