Sound Deadening or Sound Absorbing: How to Determine Your Needs

February 1, 2021

In the acoustics world – as in any industry – there are some misconceptions that just won’t quit. One of the most common misunderstandings we find among customers is that they aren’t clear on the difference between sound blocking and sound absorbing. Pop culture lets us into plenty of recording studios, and that classic eggcrate foam just perpetuates the confusion.

Here at FatMat all we do is acoustics, and we’re here to set the record straight. We’re going to break down the differences between sound deadening and absorbing, and how they’re best used to optimize acoustics. Keep the dial here.

Deadening vs. Absorbing

Right off the bat, let’s be clear – we aren’t out to ruffle feathers. We also aren’t out to give a detailed physics lecture. The point of this article is to inform the average individual and make their acoustic adventures a success.

That said, let’s delve into these terms a bit: deaden and absorb. You might also hear “sound blocking” and “soundproofing” thrown around – lump these in with deaden, while absorb stands alone. On their face, the terms might not sound very different, but they are. Let’s set some clear definitions:

  • deaden (verb): to weaken; to make impervious to
  • absorb (verb): to take in without echo, recoil, or reflection

The word “impervious” is a good one, because it makes us think of another substance that, like sound, is tough to contain. Much like sound waves, water often finds its way through. Also like water, sound must eventually be absorbed by something. 

If you want to absorb water, you use a sponge, because it’s an airy material that has plenty of free space to be filled. But if you want to impede water or make something impervious to it, you use a heavy or dense barrier that won’t let it soak through. 

The same theory applies to sound. Some materials act like that sponge and simply absorb some of the energy generated by sound waves, reducing what’s reflected – or echoed – back to the ear. But other materials work like a waterproof membrane would, and stop sound in its tracks, bouncing it back and causing echo. And just like with water, this has a lot to do with air space and porosity. The more air space in the material used, the easier it is for sound to get into (and through) it.

When to Do Which

We now understand that deadening and absorbing sound accomplish two very different things. Deadening blocks while absorbing prevents echo. So with those two rough definitions in mind, it should be pretty easy to pinpoint which action is preferred in which sort of scenario. Let’s work through some.

You’ll want to deaden or block sound when…

  • You’re discussing confidential client or patient information and don’t want to be overheard
  • You are practicing and playing music or recording vocals and don’t want to bombard neighbors or family members
  • Others are raising a ruckus around you or you live in a noisy spot and you need some quiet to work or learn

You’ll want to absorb sound if…

  • You’re recording music or vocals and are picking up echoes, high-pitched or metallic sounds, or low-frequency bass-like interference
  • Footsteps or other noises carry and echo across your home, office, or studio space
  • Everyday sounds echo and make speech hard to hear or understand
  • You work in a large, open space with lots of hard surfaces that encourage echo

To put things super simply, sound deadening either contains or shuts out sound, while absorbing lowers intensity. 

Clearly, the uses of sound deadening and sound absorbing products are related but distinct. They are also frequently used together to achieve the all-around best sound quality. Re-enter those eggcrate foam panels. Yes, they were doing their job to absorb excess or extraneous noise. No, they were not blocking sound from entering or leaving the studio.

So if there’s such a difference between deadening and absorbing, what materials besides foam are best to use? That’s next on the agenda.

Materials and Methods

We get the concept behind deadening and absorbing sound, now we want to be sure that the materials we use are best suited to our needs.

Sound Absorbing

When you’re looking to just take the sharp or deep edge off of sounds, you want a material that is porous, with plenty of air space. That way the sound waves have somewhere to collect and settle, so to speak.

Various types and grades of foam are traditionally used to create sound-absorbing panels and are typically installed on walls or ceilings as a finished surface. These can range from stretched fabric systems and decorative or paintable panels to more utilitarian options.

Sound Blocking

As the term suggests, blocking sound keeps noise out. This requires hard, non-porous, and air-tight materials. To block sound from getting through walls, ceilings, or floors, the sound blocking begins within the structure of the room itself – these aren’t just cosmetic applications.

Here are three ways to block sound, and they are often used collectively:

  • Decouple the wall assembly: This happens inside a wall and reorients the wall’s components so that they don’t touch internally. The resulting air space reduces sound transmission. 
  • Increase mass: Adding on sheets of soundproof drywall to a wall increases the sound barrier and decreases porosity. Underlayment layers keep sounds from traveling through floors.
  • Dampen vibrations: Sound isolation clips can be used along with a channel of deliberate air space to reduce vibration and steady the sound barrier. Various adhesives, tapes, and sealants close small gaps that could allow sound through.

As we’ve said before, a two-pronged approach is best. This way sound that’s not allowed to escape a space isn’t echoing but can be softened and controlled. You’ve got to balance the tough and soft materials to get that just-right end result.

Of course, not everyone is in the position to deconstruct their walls, floors, or ceilings. So if you’re looking for a practical solution to noise and echoes, FatMat acoustic technicians are at the ready with expert advice.

Terms to Know

You could see an array of terms when you’re shopping for products. So keep an eye out for these standard industry measurements to steer you in the right direction:

  • Sound blocking: sound transmission class (STC) number or a transmission loss curve (TL)
  • Sound absorbing: sound-absorption coefficient or noise reduction coefficient (NRC)

Knowing what you’re looking for and understanding the application streamlines the process. And having an expert just a call away doesn’t hurt either. Be sure to reach out with any lingering questions or for more detailed product information.

FatMat Knows Sound

At FatMat we have high-quality materials that can both deaden and absorb sound, paired with the skilled know-how to best apply them to your situation. We know acoustics, inside and out – it’s what we do. So if you’re looking to outfit a home studio, office, or school room, or just need to quiet down your living space, remember the experts. If your vehicle is your sanctuary, we can help there too. 

Our technicians can find the ideal products and applications to turn your space into a balanced soundscape. There are lots of options out there, and the right choice isn’t always clear, so get in touch if you find yourself in need of some guidance. Reach out today!

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