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Page 12
When measuring the room’s response use a minimum resolution of 5Hz. Figure
3 on the previous page shows a theoretical illustration of a room’s response.
Before you plot your results however, it’s important to note the Radio Shack
sound meter is not totally "linear" in its accuracy down low. All similar meters
are off by the similar amount depending on the frequency; so while its sensitivity
below 20Hz is not what it is at 50Hz, there is a simple way to compensate for this
deficiency. It's called a compensation chart.
Simply look to the below frequencies and add the required decibels (dBs) at the
frequency in question. So if your system seems to be measuring 70dBs with a
20Hz tone, then really it's putting out 77.5dBs. This is a VERY substantial differ-
ence, roughly TWICE the acoustical energy, requiring several times the amplifier
power to achieve. You can see then how critical the below chart is if you are us-
ing your PEQ to even out or “flatten” the room response of your bass.
Add the following to your measurements:
10Hz add 20dBs
12Hz add 16.5db
16Hz add 11.5dB
20Hz add 7.5dB
25Hz add 5dB
31.5Hz add 3dB
40Hz add 2.5dB
50Hz add 1.5dB
63Hz add 1.5dB
80Hz add 1.5dB
100Hz add 2dB
125Hz add .5dB
Explanation of the controls. Now that we have dis-
cussed how to measure the room’s response, the next
step is to correct the problem areas with the paramet-
ric equalizer. Before we start turning the controls we need to understand what the
adjustments are and how they work.
“Q”. This control determines how wide the correction will be. Each “hash mark”
on the amp’s front plate represents roughly 0.1 octave adjustments. The “HI”
mark is equal to 0.1 octave (narrow) and “LO” mark is equal to .9 octave (wide).
In Figure 3 the highest peak is located at 40Hz and becomes flat again at 50Hz
(the Highest Frequency of the peak). To determine the Q adjustment the follow-
ing formula is needed. More on “Q” in a moment.
Formula 1 (Highest Frequency [X] – Center Point [Y])
Center Point (Y)
SVS PEQ Controls