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How to
adjust your
equalizer settings to match your transmitters frequency
response.
The
most quantitative and scientific approach would be to measure the power output
of the transmitter when excited with different frequencies. For these tests,
you will need a tone or audio sweep generator. Many software based recording and analysis programs have these
generators built in. I use a free
program called TCUBE.
Here is an
outline of how to test your transmitter frequency response:
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1
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First, make sure you use a
dummy load with the following tests!
Select a 1000Hz tone as a reference with your external tone generator or
computer soundcard software. Make sure that your transmitter power output
control is at full so that it is capable of its full output. Then, adjust
the tone output from the source, not the transmitter, to produce 25watts
from the transmitter. The 0dB reference has now been set up and should
remain there for the rest of the tests.
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2
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The next step is to find the
plus/minus dB points of where the transmitter power either increases or
decreases with certain frequencies. Begin by measuring power output when 25
Hz is applied. Write down your findings. Next measure the output at 100Hz.
Then 200Hz, then 300Hz, etc... all the way up to about 4500Hz. To find the
+1dB, +2dB, +3dB and -1dB, -2dB, -3dB, etc... points in terms of power drop
or gain compared to our 1kHz reference tone of 25w, consult the chart
below:
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I find adjusting the individual frequency bands on the
equalizer using the above method works quite well.
Whatever frequencies your EQ has, apply the above method…Set each band
for 25 watts. For the frequencies on your EQ that are outside your
transmitters frequency response just set them at the lowest position on your
equalizer. (ie. –24db). POWER in watts = Resulting Gain/Attenuation 0dB
Reference - Power = 25Watts @ 1kHz
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Power Output
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Resulting
Attenuation
or Gain
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200w
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+9dB
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156w
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+8dB
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125w
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+7dB
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100w
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+6dB
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80w
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+5dB
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64w
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+4dB
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50w
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+3dB
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40w
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+2dB
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32w
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+1dB
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25w
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0dB REF
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20w
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-1dB
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16w
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-2dB
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12.5w
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-3dB
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10w
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-4dB
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8w
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-5dB
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6.25w
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-6dB
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5w
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-7dB
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4w
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-8dB
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3w
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-9dB
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2.5w
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-10dB
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2w
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-11dB
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1.5w
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-12dB
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1.25w
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-13dB
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1w
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-14dB
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3
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After finding the dB points
with your transmitter tone tests, apply these numbers to your equalizer.
Say, for example, that your transmitter was only producing 12.5 watts at
80Hz. This means the power was down by -3dB in comparison to our 0dB
reference of 25 watts. Adjust your equalizer for +3dB at 80Hz to make sure
that your power at 80Hz is producing 25 watts, our 0dB reference power
level. Go through all of the deficient frequencies the same way and apply
the necessary corrective EQ measures. When you are done, check the
frequencies again to make sure that ALL frequencies within reason are
producing 25 watts. Obviously, there will be frequencies beyond your
transmitter and EQ's ability to compensate for. If you can squeeze a flat
response from 50Hz ~ 4kHz and/or beyond, you're doing great! You should be
able to reproduce most stations with good accuracy!
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After applying the settings to your EQ,
your transmit audio will be very close to having a flat response. Now with
just minor adjustment you can tailor the sound of your microphone to give the
sound you are looking for.
Just
remember, a little audio shaping goes a long ways.
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