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SV Subwoofers

 

 

This disc allows the user to play 10Hz through 98Hz in one hertz increments allowing very good resolution over your measurements. Other good examples for test discs are Avia’s Guide to Home Theater and Digital Video Essentials. 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 difference, 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 using 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

SVS PEQ Controls

Explanation of the controls. Now that we understand how to measure the room’s response the next step is to correct the problem areas with the parametric equalizer. Before we start turning the controls we need to understand what the adjustments are and how they work (the controls of your PC-Ultra may be arranged different than pictured).

“Q”. This control determines how wide the correction will be. Each “hash mark” on the amp’s front plate represents 0.1 octave adjustments. The “HI” mark is equal to

0.1octave (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 Fre- quency of the peak). To determine the Q adjustment the following formula is needed. More on “Q” in a moment.

Formula 1 (Highest Frequency [X] – Center Point [Y]) Center Point (Y)