Useful Audio System
Calculations
Loudspeaker Max SPL
Calculator
Problem: How do I
find out the maximum SPL of a loudspeaker ?
If you look at the specification for most
chassis loudspeakers they have both a 1W/1M SPL figure and a maximum input power figure
quoted. These are the only things you need to calculate the maximum output SPL.
If A=
The loudspeaker 1W/1M rating (for this example we'll say
90dB
SPL)
and
B=
The loudspeaker maximum input power (for this example we'll say
32 Watts)
The calculation to find out the maximum
output SPL is:
SPL = (10*(log LSMax
input power)) + LS 1W/1m rating
or
SPL = (10*(log B)) +
A
If we substitute our values above, the
calculation becomes:
(10*(log
32))+90 which calculates up to 105dB SPL
<- Click HERE to perform this Calculation ->
HF Driver Protection
Capacitor Calculator
Problem:
I need
to fit a capacitor in line with my HF driver to protect it from DC.
How do I calculate the capacitor value ?
To do this, you first need to find out the
driver impedance. Let's say for the purposes of this calculation it's
8 ohms.
We'll call this A.
You'll also need the filter frequency required
for the driver. This need not necessarily be the crossover frequency you're using,
but it should correspond to the driver's lower frequency limit. Let's say for this
calculation it's 800 Hz.
We'll call
this B.
The calculation formula you require is:
Capacitor Value in
uF = (500000/(p*(Driver Impedance/2)*Filter Freq. Required))
or
Capacitor Value in
uF = (500000/(p*(A/2)*B))
Substituting the values, using p=3.142
the calculation becomes :
Capacitor Value in
uF = (500000/(3.142*(800/2)*8))
Which calculates to: 49.74uF.
The nearest commercially available capacitor
value is 50uF. Make sure you use a Bipolar (Electrolytic or Polypropylene) type
which is rated greater than 100V (or higher if it's a very high power driver you're
using). You may find that the value you've calculated is not available. Don't forget, you
can add capacitor values together by connecting them in parallel to get
your required value. e.g. a 100uF and a 20uF in parallel is equivalent to a single
capacitor of 120uF. If you do this make sure both capacitors have the required
voltage rating.
<- Click HERE to perform this Calculation ->
SPL Level at Distance x
Calculator
Problem: I have a
constant directivity horn driver capable of 140dB SPL at 1 Metre.
What SPL
level will I get 16 Metres from the driver?
You need to use the following formula :
SPL at xMetres =
(Max.SPL @ 1M) - (20Log (Distance from unit)) dB SPL
For our example, substituting the values,
the equation becomes :
SPL at 16
Metres = (140 - (20Log (16))) dB SPL
Which calculates to:
116dB
<- Click HERE to perform this Calculation ->
