Acoustic doors and their uses …

Over several months we’ve written numerous articles on acoustic doors – sometimes called soundproof doors – and we’ve covered a very wide variety of topics.

We’ve touched upon what sound is and how it’s transmitted; how the volume of noise is measured and comparisons are made; how to achieve noise reduction in principle; and what are the maximum noise levels permitted (legally) in different workspaces and environments.

Once again we’ll provide a brief refresh on certain topics, just to remind you, but before that – what do they do?

What is the purpose of an acoustic door?

Essentially, it performs two key functions:

• it acts as a sound barrier, to reduce noise levels entering and leaving an environment or workspace
• because of their necessarily solid construction, it is probable that the door will also provide some protection against the spread of fire and smoke

We might often think about acoustic doors providing a barrier to noise getting in, such as in a recording studio, but let’s not forget that equally importantly there are rooms and environments where it’s important not to let noise get out – good examples are interview rooms, board rooms, and, at the other end of the noise scale, concert halls.

Where are soundproof doors used and why?

In our last article on this topic we looked at many of the different places where acoustic or soundproof doors are used; let’s have a quick reminder.

There are many environments where we would want the doors to provide effective sound-proofing – whether it’s partial (some noise getting in or out is acceptable) or total (no sound should be able to get in, or out, or both).  Let’s look at some obvious examples across the range:

Total

• recording studios
• police interview rooms
• operating theatres

As close to total as it’s practical to get

• music halls and concert venues
• libraries
• museums
• galleries
• interview rooms
• board rooms

Try and keep noise to a minimum

• airports (from the outside in of course!)
• hospitals and nursing homes
• hotels
• offices
• educational establishments

So how do acoustic doors work?

To answer this question, we need to revisit what sound actually is, before looking at how barriers to the transmission of sound actually operate.

Sound is a form of energy that is created when air is disturbed such that the air pressure changes and radiates from the source of the sound in waves.

These sound waves vibrate at different frequencies, and are measured in cycles per second (Hertz).  The faster that a sound wave travels past a given point, the shorter is its wavelength and the higher is its frequency.  The “loudness” of the sound – which is a relative not an absolute term, and which is also impacted by other sounds – is caused by vibrations in the medium through which the sound is travelling (typically, in our experience, air); the stronger the vibrations, the greater the amplitude.  Here’s a simple diagram to make things clearer:

A sound barrier simply reduces the amount of noise that can pass through it.  You’ll be aware that closing a normal door will reduce the amount of noise coming through; similarly a standard fence will reduce noise coming from the other side.  These will not stop all noise, of course – since sound waves flow like water they will find other ways of “getting through, or round” unless more sophisticated measures are taken.  What might such measures be?

Sound insulation is about putting up an acoustic barrier.  Sound absorption describes the ability of materials to restrict the reflection of sound, doing this by converting the energy of the sound into heat.  The greater the sound absorption the shorter the reverberation time or echo that is produced.  Sound absorption is measured as a co-efficient from 0 to 1.0, with the best rating being 1.0.

For the most effective sound-proofing, you should consider using both mechanisms.

To put things into perspective, doubling the mass per unit area of a wall or door will improve its insulation by about 6 dB – this is why heavy materials such as concrete are very effective soundproofing materials.  One way of achieving good insulation using less mass (since concrete doors can be unwieldy!) would be to use a double-leaf partition (two walls separated by an air gap filled with a sound absorber).

Put another way, sound insulation affects people in the room or workspace adjoining a sound source, while absorption affects those within it.

	Sound absorption	Sound insulation
Control	Sound reflection within a room or workspace	Sound transmission between rooms or workspaces
Effect Upon	Performing and listening conditions	Privacy and disturbance
Benefits	Room or workspace occupants	Room or workspace neighbours

 

We’re here to help

Enfield Doors have been manufacturing acoustic doors for many years for numerous satisfied customers – and we can give you expert advice and guide you through all of the regulations and complications that you need to be aware of.

As always we’ll be delighted to help and advise you.