Four Aspects of Sound Isolation

Four Aspects of Sound Isolation

When it comes to sound isolation for your recording studio environment, you only need to keep four things in mind.
Mass: The first line of defense in soundproofing
Decoupling: Break the connections that sound vibrations use to get from one side of a wall to the other.
Distance: Gain better overall sound reduction and increased low frequency isolation.
Absorption: Control mid to high frequency and also damp the individual wall panels.

DOUBLING MASS:

With every doubling of mass you can expect to get a 5-6 dB increase in isolation. This is important to know.

Using the above example of a typical wall assembly found in any home, if you add another layer of 1/2” sheetrock to one of the existing sides, you could expect the STC value of 33 to go up to 36 or 39 points.

In reality it may only get you up to STC 35. This is where flanking and the coupled elements of the wall assembly work against you in the hunt for isolation.

WALL ASSEMBLY AND ISOLATION:

(REF: Gypsum Board Walls: Transmission Loss Data | IRC-IR-761)
A typical wall assembly in a residential home may be where your search for a better isolated recording room will begin.

So we have to understand this wall to move forward and understand with a greater degree of certainty what other wall assemblies will produce in the way of higher sound isolation.

The typical residential bedroom wall, ½ inch sheetrock both sides with no insulation will get you an STC of around 28.

A standard 16 inch center, 2” X 4” wood framed wall with ½ inch sheetrock on either side and standard building insulation in the interior bays, will yield an STC of 33 with Transmission loss values that show an increase as mass is added.

If we look at this data side by side we can see that there is an overall transmission loss increase in the wall assembly where mass has been doubled on one side.

Single ½ inch sheetrock layer on both sides Single ½ inch on one side, two 1/2” layers on the opposite side.
50 Hz 20.1
63 Hz 16.7
80 Hz 20.5
100 Hz 14.1
125 Hz 8.6
160 Hz 16.4
200 Hz 30.5
250 Hz 33.9
315 Hz 36.0
400 Hz 43.4
500 Hz 43.8
630 Hz 44.2
800 Hz 49.4
1000 Hz 51.1
1250 Hz 53.0
1600 Hz 53.9
2000 Hz 53.1
2500 Hz 44.8
3150 Hz 40.4
4000 Hz 43.4
5000 Hz 49.2
6300 Hz 54.1
50 Hz 21.8
63 Hz 19.0
80 Hz 23.2
100 Hz 16.2
125 Hz 11.5
160 Hz 19.5
200 Hz 33.6
250 Hz 37.1
315 Hz 38.0
400 Hz 44.7
500 Hz 45.0
630 Hz 45.1
800 Hz 49.5
1000 Hz 50.8
1250 Hz 53.3
1600 Hz 55.1
2000 Hz 55.2
2500 Hz 47.7
3150 Hz 43.8
4000 Hz 47.3
5000 Hz 53.0
6300 Hz 57.7

To further diagram the increase in TL values we simply look into the color coded chart that reveals visually how the wall assembly with the extra sheet of sheetrock has increased the TL values almost entirely across the frequency spectrum that were used in the test.

wall assembly chart

Mass Air Mass:

room in a room

In an ideal situation the highest degree of sound isolation is gotten from a room floating inside another room.(See the couple in the picture?)

With the vibration of sound limited to only the interior room and any exterior sound limited to the exterior room this is perfect for keeping a quiet musical environment.

Unfortunately, this is hardly possible. How would you make a room float, unattached in any way to the room that surrounds it? You just cannot do it with our current technology on a shoestring budget.

At the very least we do have an image of what it is we are attempting to do when it pertains to a high degree of sound isolation.

We have a perfect visual for what is called “mass air mass” construction.

There are three things to consider when constructing an assembly of a high isolation type besides the four aspects:
1. High Mass
2. Low Rigidity
3. High damping

These are the properties of sand and Mass Loaded Vinyl.