Understanding Acoustic Curtains - Absorption vs Insulation

Understanding Acoustic Curtains and Which is Best for you Absorption vs Transmission (Insulation)



Before commencing this article, we are going to be looking at the difference between 2 elements and why buying products on the internet knowledge on a subject assists you in understanding which product is best for you. The 2 different areas when it comes to acoustic curtains. Absorption and the other is insulation.


Sound Absorption is used to reduce echoes and sound going around a space See part 1

Sound Insulation this is to stop sound from passing / entering into a space. See Part 2


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Most curtaining products out there in  the market place are beneficial to sound absorption and will have very little impact on sound insulation.


Sound Absorption – Acoustic Curtains

When working with loud echoes in spaces it can be incredibly frustrating to stop sound reverberating around the room. This is where acoustic curtain come in. Depending on the fabric it will have a varying effect on the amount of absorption that It takes and effects the sound passing back around the room.

To see how good a fabric or product is at absorbing sound in a room then you need to complete the

Sound absorption test EN ISO 354. This grades a product between A – E based on how absorbent a material is. When sound is projected into a room it will hit the surfaces and then it will either be transmitted through things like ceilings and walls or it will be reflected back into the room. So in a basic form the test is how much sound is sent out will return.

Example Imagine. 100 units of sound are sent into a room, 80 units are transmitted out of the room and then 20 are recorded back in to the space.

Thus the sound absorption coefficient is 0,8.


Α = converted Energy +  transmitted energy in relation to the incident.

Incident is the sound initially sent out.

The main aim of materials hung around rooms like recording studios and theatres is to stop the sound reflecting back around and ruining the transmission of the direct sound.

By having fabrics that are highly graded like black wool serge and expression dimout fabric you are limiting the amount reverberation back into the room. This is extremely important for recording studios and also quiet spaces like offices.

Imagine being in a large gymnasium with concrete blocks all the way around the room. If you shout you will get a large amount of echo

Here are some example reports for our best selling acoustic fabrics.


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Which Fabric is Best for Sound Absorption.

Overview Direct fabrics will continue to add to the testing list. Direct Fabrics will add additional fabrics as demand for fashion products increases. However the expression product testing has a gorgeous herringbone running through the fabric and the team feel this is a perfect example of

Working with a variety of suppliers we have tested some fashion dimout products aswell as wool serge materials.

The core product for theatres, exhibition centre and performance centres is black wool serge material. This is a chosen due to being cost effective and performance grading of A / B depending on fullness.



Direct Fabrics is now recommending a designer fabric called Expression which is dimout so 90+% light stopping, this means that you get the highest sound absorption and also a beautiful finish with a herringbone effect for a price lower than a coloured wool serge.




Prices at time at writing this article may vary compared date when reading


FabricApplicationFullnessWeightSound ClassTestAW
Coloured WoolStd Shade100%565gmsA100mm0.85
Standard Wool SergeStd Shade100%400gmsB100mm0.85
Standard Wool SergeStd Shade50%400gmsC100mm0.75
Coloured Wool BlackStd Shade50%565gmsB100mm0.8
Kilo Wool SergeStd Shade100%800gmsC100mm0.65


The most common standard absorption wool serge.




Deciding which fabric to purchase

Very simply you have a choice of a low cost black wool serge for a quick and effective drape to reduce the transmission of sound around a space at different frequencies. Or you can use a decorative product that is slightly more expensive that will give you even more than the standard wool



Sound Insulation Curtains – To be complete 2019

This subject is particularly difficult to quantify, and all environments will differ.

A particularly good analogy I like to use when thinking about partitions and blocking sound is when you are driving in your car. You have the windows closed and it is quite quiet but as soon as you open the window even as much enough to slide an envelope through you can hear a large amount of sound. This is because sound is like a liquid and flows to wherever there is a gap. It will bounce off surfaces until it finds a route to go.

When deciding to look for a sound insulation fabric it all comes down to the mass of the product and that it is tightly woven and doesn’t allow anything to pass through it. A common product is mass loaded vinyl. BUT when making curtains from this product you will have a gap around the curtain so although you will see a reduction you will not


What is mass loaded vinyl

Mass loaded vinyl is a heavy weight vinyl product that has a weight generally of between 5kg and 10kg and is ideally suited for stopping airborne sound. It has a greater weight than lead and will be perfectly suited to stop sound passing between spaces when full enclosed between objects. It is usually used a floating wall barrier between stud work and pasteboard for cinema rooms, but Direct fabrics has been trialling this in curtain form. As a barrier it is shown to reduce sound transmission by circa 20db and 30db.


Understanding Sound Transference / Sound Blocking

It is a common misconception that having foam egg carton shapes on the wall will stop sound coming into a wall. This is simply incorrectly. Imagine sound as water, if you made a wall of sponge do you think that it will stop the water passing through. No it wont. Then imagine an aquarium tank made of thick glass, sound will work in the same way as glass and it will stay within the tank. This is the same with sound passing between spaces.

From Direct Fabrics investigation and speaking with sound labs. We have discovered that the best product for reducing sound transmission is a product that acts as a ridgid barrier.

So using an MLV combined with an absorbtion fabric will give an excellent sound reducing curtain. However it should be known that even having a super thick layer of MLV or similar fabric will still let sound pass through any air gaps.

Please speak to the direct fabrics team for specalist products that will work for you windows for a complete sound solution.

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