Useful Line System
Calculations
Amplifier Max Volts Out
Calculator
Problem:
I want to use an amplifier for 100V line operation so I need to find out what
its maximum output voltage is.
How do I calculate this?
This is a straightforward calculation.
First, you need to know the maximum rated power at the rated impedance. Let's take
an example of 400 Watts at 8 ohms. We'll call max. power
A
and rated impedance B.
The calculation you require is :
Max volts out =
Ö(Max
Power*Rated Impedance) Volts
or
Max volts out =
Ö(A*B)
Volts
Substituting the values, the calculation
becomes :
Max volts out =
Ö(400*8)
Volts
Which calculates to
: 56.6 Volts
<- Click HERE to
perform this calculation ->
Minimum Line Impedance Calculator
Problem: I need to calculate the minimum impedance I can
connect to my 70/100Volt line system. How do I calculate this?
You will need to know the amplifier's maximum output voltage and output power.
We'll call output voltage A and
output power B. and use values of
A=100 Volts and
B=500 Watts.
The calculation you require is :
Lowest
Permitted Impedance (Ohms) =
((Output Voltage2 )/Output Power) Ohms
or
Lowest
Permitted Impedance = ((A2)/B) Ohms
Substituting the values, the calculation becomes :
Lowest Permitted Impedance = ((1002)/500)
Ohms
Which calculates to : 20 Ohms
<- Click
HERE to perform this calculation ->
Transformer Loss
Compensation Calculator
Problem: I need to find
out how much power I have to apply to make my loudspeakers produce full output given that
I know I have a 2dB loss in the line transformers.
This is a very relevant calculation. This needs to be
performed for just one of the loudspeakers and then multiplied up to give you the total
system calculation. We'll take the calculation a little further and plug the
amplifier you're using into the calculations to find out how many loudspeakers you can
actually get to full power using the result. For our example we'll use a
single 32W loudspeaker (A) and assume a
transformer loss of 2dB (B) using a 100 Volt
line system (E).
The calculation you require is :
Total power applied
to produce xWatts =
(Max LS input power*(10Transformer Loss/10))
Watts
or
Total power applied
to produce xWatts =
(A*(10B/10)) Watts
Substituting the values, calculation becomes
:
Total power applied
to produce 32 Watts =
32*(102/10) Watts
Resolving to:
Total power applied
to produce 32 Watts =
32*(10(0.2)) Watts
Which calculates to
: 50.71 Watts
Taking this a little further, we can now
calculate the number of speakers that we can actually drive to their maximum output given
that we want to use an amplifier having an output power of 500 Watts.
Next, we can calculate the
transformer primary impedance by squaring the line voltage (E)
and dividing the result by the total power applied (C)
for each speaker.
The calculation you require for this is :
Primary Impedance =
((Line Voltage2)/Total Power Applied) Ohms
or
Primary Impedance =
((E2)/C) Ohms
Substituting Values for our example, this
becomes :
Primary Impedance =
((1002)/50.71) Ohms
Which calculates to
: 197 Ohms
To calculate how many speakers we can use with
our 500W amplifier is easy. We take the amplifier output power and divide it
by the total power required for each speaker. In our case above, we know we
need 50.71 Watts to produce full power (32W) at each speaker.
The calculation becomes :
No. of
Loudspeakers Useable =
(Amp
output power / Total input power per speaker)
Substituting for our example above :
Max No. of
loudspeakers = (500/50.71)
Which calculates to
: 9.85
Therefore 9 is the safe
limit if you want to drive them all at full power.
<- Click
HERE to perform this calculation ->
Derated Transformer Voltage Calculator
Problem: I have a line
voltage transformer rated at 200 Watts (A) input that gives 100V (C)
output on the secondary, but I want to use an amplifier that only puts out 100 Watts
(B). What
will be the voltage on the secondary if I use this smaller amplifier?
The calculation you need is :
Derated secondary
Voltage =
(Ö(New Input Power / Normal Input Power)
* Normal
Output Voltage) Volts
or
Derated
Secondary Voltage = (Ö(B/A)*C)
Volts
Substituting for our example above :
Derated Secondary Voltage = (Ö(100/200)*100) Volts
Which calculates
to : 70.71 Volts
<- Click
HERE to perform this calculation ->
