by Aural Stage Studios July 26, 2011

Once we have our base EQ laid in, it’s time to use our coefficients to figure out what else to remove.  You will get much much much much much much better results if you resist the temptation to add to the EQ.  I nearly always subtract from.  Adding EQ get’s muddy very quickly and should be reserved for layered sounds, and giving sound effects or instruments weight and presence.  For natural voice purposes.. and especially for purposes of creating a natural room, we substract.

Let’s go back to our 10 ft x 10 ft room (hardly an ideal sound listening environment, mind you, but the math is easy for illustration).

For purposes of simplicity, we’re going to concern ourselves only with the two parallel walls.  For more accuracy you would want to consider the reflection and absorption of as many surfaces as possible, but you can get effective results by synthesizing just a basic environment using the direct reflective surfaces.

Let’s go with the basics:  Sheet rock walls.  This really helps to narrow our numbers down as three of the surfaces are going to have the same coefficient and effect the sound relatively equally (in an ideal world), leaving only the carpeted floor to deal with.  Keep in mind whether your room is insulated (and what type of insulation is used.), popcorn ceilings are going to diffuse sound just as they do with light, and underlayment under the carpet is going to also affect the sound of the room.  Let’s get some numbers:

Walls and Ceiling (insulated no popcorn):

 Material   125 Hz   250 Hz   500 Hz 1000 Hz 2000 Hz 4000 Hz
Sheetrock 1/2″ 16″ on center 0.29 0.10 0.05 0.04 0.07 0.09
Fiberglass: 2” rolls 0.17 0.55 0.80 0.90 0.85 0.80

Next we add the elements of the wall surfaces together:

  Material   125 Hz   250 Hz   500 Hz 1000 Hz 2000 Hz 4000 Hz
Sheetrock 1/2″ 16″ on center 0.29 0.10 0.05 0.04 0.07 0.09
Fiberglass: 2” rolls 0.17 0.55 0.80 0.90 0.85 0.80
Total 0.46 0.65 0.85 0.94 0.92 0.89

Now we need one more number to determine our EQ settings, the dB Range of our EQ.  This is typically 24.  I set mine manually to 48 for more dramatic results and greater control in the margins.  There are two ways to determine your range.  Some allow you to select a range, which means the range is typically displayed on the interface somewhere.  Some are hardset, but you have the numbers along the sliders as a guide: a range between -24 and 24 dB indicates a 48dB range.  Now we half that (24) for use in calculating our EQ settings.  To do so, all we need to do is multiply half the range (24) by our total coefficients.  This is how much we will reduce our EQ for each frequency:

  125 Hz   250 Hz   500 Hz 1000 Hz 2000 Hz 4000 Hz
Coefficient 0.46 0.65 0.85 0.94 0.92 0.89
x Range 24 24 24 24 24 24
EQ (- dB)  11.04 15.6 20.4 22.56 22.08 21.36

Next, we plug our numbers into the EQ we have set up on our FX bus so the EQ only effects our reflected sound and not the direct sound.  Round as needed.  It may require some tweaking to get the sound to “sound right” since we’re really using a very empty room basis for our EQ settings:

You can just set these levels as-is in a 10-band EQ and roll with that.  It will still get fairly effective results.  Personally I like to smooth out the edges with a 20 or thirty band by rolling off the top and bottom ends and smoothly rolling the in-between frequencies to form a nice curve for blending:

 

 

Here is the result:

Dry Track

With Room Eq

One final trip into reverb to go.  And we’ll have the basics of creating an environment from scratch.

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