How does soundproofing work?
Soundproofing works by combining three core principles to block noise effectively. The three core principles of soundproofing are high-mass materials, absorption and isolation (decoupling). When all these methods are used together, you get effective soundproofing. Alone, these methods will control different aspects of sound but not provide complete soundproofing. Let’s see how this works…
High mass and soundproofing
High-mass materials are able to reflect airborne noises away. This means you are insulating your space against noise entering or leaving, it’s like a locked door on sound. The more mass, the more effective your partition will be. However, because every additional decibel ‘weighs’ more than the one before it, the amount of mass you need does not evenly increase, either. This is because sound is measured on a logarithmic scale. To avoid losing too much space but still be soundproof against loud noises, we need another part of the recipe adding.
Isolation and soundproofing
Isolation, or decoupling, is a great soundproofing method for party walls. Decoupling will help to block more sound for space used than simply continuing to increase the mass. Decoupling a wall usually involves MuteClips which hover the new soundproofing panels away from the existing structure. The reduced contact makes it far harder for vibrations to travel from one side of the wall to the other.
Absorption and soundproofing
Absorption is important in soundproofing systems, but will not block sound by itself. We used absorption in cavity spaces to reduce the drum effect. This is when sound vibrations reverberate around a space and actually result in the amplification of noise. By filling the cavity with acoustic mineral wool, sound cannot reverberate and your system is strengthened.
Airborne noise v/s impact noise
Airborne noise is from sounds that travel through the medium of air, whereas, impact noises occur when two surfaces meet. Airborne noises include talking, music or TVs and impact noises can be footsteps, a hammer or a washing machine drumming.
What are decibels? The science of soundproofing
Decibels are used to measure sound. Decibels, abbreviated to dB, are given a numerical value and as the numbers get higher, the sound measured gets louder. However, each unit is not evenly weighted, meaning that 1dB between 5 and 6 is not worth as much as 1dB between 40 and 41. This is why decibels can be a confusing concept at first and why the science of soundproofing can be difficult to understand.
Unlike money, where every pound in a £20 note is worth an equal share, decibel units do not have the same value as each other. One decibel from 2 to 3dB is far far smaller than one from 30 to 31dB.
One way to help explain this is by remembering that to the human ear an increase of 10dB is heard as a doubling of the sound. This 10dB increase rule sticks whether it’s from 90dB to 100dB or 30dB to 40dB. So, with that in mind, you can understand that as decibels get louder and the numbers get higher, each single unit is worth more.
It’s like saying the ten decibels between 40 and 50 are worth an additional 40dB (because we hear it as a doubling in noise), but the 10 decibels between 90 and 100 are worth a weighting of 90. As you may imagine, to block an additional decibel of sound at a level of 40dB is going to take much more effort than blocking a single unit of sound at 20dB. This also explains why a material that might be able to block 10dB of sound can’t block 20dB by using two layers. Those additional 10dB have a much higher weighting than the first 10dB.
Soundwaves and mass
The next thing to understand about soundproofing is that we are blocking vibrations. It can be vibrations from impact like footsteps, or, from airborne noises like music. Sound waves are measurements of pressure in the air, very much like waves in water. Just like the sea hitting the cliffs, small waves are simply splashed away. But larger waves, with more force, can actually try to move through the cliff and break it with the force.
Likewise, soundwaves that hit a partition with too little force are reflected away. But sound with more energy, more volume, is going to move through the partition (with less dramatic effects of course). Returning to the sea and the cliff, if you think about a small windbreak stood in the way of an incoming tide, you can imagine it will be more easily knocked down. But when the sea hits the cliffs it’s going to need a lot more force. Likewise, soundproofing which is too thin and has a low mass won’t be able to reflect very much noise. But thicker partitions with high mass are going to be able to resist more energy. The more mass a material has, the harder it is for sound to pass through!
Resonant frequencies of materials in soundproofing
However, every material has a natural point of weakness, like an Achilles heel. This is known as its resonant frequency and it’s the sound frequency that can most easily make the partition vibrate in sympathy. It’s like finding a secret passage and moving through more easily than frequencies before it or frequencies after it. On a graph this will be shown as a slight dip in performance. Because different levels of mass have their own resonant frequency, we need to use different materials in conjunction so that the dips in performance get smoothed out. This is why we use soundproofing panels of more than one material.
Sound tests explained
The next thing to cover is sound testing and what test data is showing you. Test data is a funny one because it can be made to look incredibly good even if the soundproofing solution used wasn’t very good. This is why it’s important to have the test data for a partition before soundproofing got installed.
I could test a wall solution and tell you it can reduce an amazing 65dB. That would be incredible! But what I forgot to tell you is that the wall already reduced 64dB by itself. Check the data to make sure it’s referring to the same wall being tested before and after because some just use test data from any old untreated wall so you haven’t got a true comparison. This is why you should also check whether the data is for a brick or for a stud wall. Stud walls do not block sound as well because they have a lower mass than brick.
Now in terms of understanding all the figures and numbers, they aren’t that bad when you know what to look for. A sound test is conducted by creating a sound in one room, and measuring the volume, this figure is called L1. Then speakers on the other side of the partition measure the sound transmission and this is L2. The first thing to note is that a lot of sound tests happen in a lab, and will achieve better results in these settings.
Which sound test results show what?
If you want to know what the average airborne sound reduction for a system was, then look for the letters DnT,w for real-world testing or Rw for lab. Better than this, however, is to get a different average that also accounts for the lower frequencies. Lower frequencies are harder to stop as they have more energy but if a system has blocked lots of mid to high frequency noise and got a good 20dB reduction average, you may install it hoping to drown out next doors bass music, only to find it doesn’t. The DnTW+Ctr , or RW+Ctr for lab, will give you a reading that takes the lower frequency resistance into better account and provides you with a more accurate reading for this range.
For impact sound, so this is for flooring, look out for Ln,w which is the lab measurement and LnT,w for the onsite figures.
Ultimately, though, if you’re trying to figure out the world of soundproofing and want to check you’re getting the right solution for your problem, then reach out to us. We are experts in the world of wall, floor and ceiling soundproofing and can guide you through the process to resolve your noise issue.
