Sub bass energy is the frequency range the subwoofer make, typically below 45 Hz. It’s pretty difficult to buy bass traps large enough to absorb the power being put out by subwoofers. A subwoofer might be rated at 1000 watts. One horsepower is about 750 watts, so a subwoofer is rated as a 1¼ horsepower air pump. What happens to all that power anyway?
ASC President Art Noxon shares his knowledge on sub bass energy.
Well, your neighbor knows where that energy is going, it’s heading straight out of your room, through the house and out into the neighborhood, shaking windows and walls of your nearby neighbors…usually late at night, when most of the neighborhood is trying to go to sleep.
In order to get out of your house the sub bass power has to first move the walls, floor and ceiling of your listening room, which then moves other parts of your house which eventually push and pull on the exterior surface of your house. Once the exterior surfaces of your house begin to move, your house becomes a giant loudspeaker broadcasting sounds into the neighborhood.
If a subwoofer is generating 100 dB inside the listening room, it is probably generating 80 dB sound level just outside the walls and roof of your house. The TL or Transmission Loss is the soundproof rating in some particular frequency range. The more familiar STC is some sort of an averaged version of the TL ratings in the speech range of sound.
The TL of your house in the sub bass range is very low, between 10 and 20 dB for most construction. A 10 db reduction is sound means that 10% of the incident power leaks out of the house. A 20 dB reduction means that 1% of the power leaks out. A 30 dB reduction means that 0.1% of the sound leaks out…and so on.
Keep In Mind…
When doing soundproofing projects two factors need to be included, otherwise the soundproofing project does not work. The first and most obvious factor is to contrive some way to block the unwanted sound. The second and less familiar is to contrive some way to absorb the sound that you’ve just blocked. If you don’t absorb what has been blocked, it reflects back into the room where it adds to the energy being made there and the sound levels build up even louder than before.
Read ASC President Art Noxon’s full article on this subject.