Sound proofing versus sound treatment

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Zukatoku - Mod Scientist
This type of question comes up often

"How can I soundproof my room?"

and the body of the question goes on to indicate that they want to use sound treatment tools and methods to soundproof their room.

In some cases they actually mean treating the room (taming the [frequency] response, reverberation and resonances of the room), in other cases they mean stopping sound getting out of the room.

So what is the difference between Sound treatment and Sound proofing?
Sound proofing
Sound proofing is the control of sound within a structure, so that it does not escape that structure

Sound treatment
Sound treatment is the taming of sound within a structure so that the room has a known (flat) frequency response and reverb signature

Achieving Sound proofing
To sound proof structure you need to create a room within a room - the air gap between the inner and outer walls is what stops the sound getting out to the outside world.

Normal construction techniques will suffice in achieving this with one exception; the internal wall studs need to be mounted on a flexible barrier that decouples the walls from the floor - this is so the floor does not end up transferring the sound mechanically from internal wall to floor to external wall.

Windows should be manufactured with double or even triple glazing - the air gap again stops the transmission of sound - the frame should be inserted into the structure with the same flexible barrier attached to avoid the frame undoing the work of the glass-air gap-glass in stopping sound moving through.

there is much more on construction than can be possibly covered here

See John L. Sayers - The recording manual - Studio Design for more

Achieving Sound treatment
Sound treatment is about taming the response of the room and controlling the reverberation signature of the room as well.
Room response/resonances are the first hurdle in getting a room that works acoustically/musically

Response is the overall frequency profile of the room - its tendency to emphasise a set of frequencies over others in the spectrum of human hearing.

A resonant peak is equivalent to having a 6db acoustic power boost at the mid-point of the particular dimension.

It is why when doing live sound you never set up in the middle of the room as at every other point in the room the acoustic power is much less and so you mix will be much quieter than what you perceive in the middle of the room

A resonant peak for a dimension will occur at the frequency whose wavelength is the same as the distance of that dimension.

In addition every whole number multiple of that frequency will also experience a boost in resonance.

Every room has three modes of resonance
Axial - along the mid-line of the room dimensions Height (H), Width (W), Length (L)
Tangential - along the joins of any two two dimensions - HW, HL, WL
Oblique - in the corners where all three dimensions meet - HWL

There are formulae and calculators on-line to calculate these different resonances.

Creating a room profile based on the acoustic resonance is part of taming the room - it will tell you what frequencies need to be absorbed

Reverberation is the diffuse repetition of audio within a room - it is different to echo only in the time between repetitions - echoes are discreet (as in countable) whereas reverberation is effectively continuous.

The time it takes for a sound to die away in a given room is the Reverb time of that room - the sound is generally referred to as an impulse

Construction materials and room furnishings can affect reverb time, making it shorter, or longer, brighter or darker.

Reverb consists of 4 components
  • initial sounds (pre-delay) - point of origin,
  • early reflections (earliest points where the sounds start to bounce back to your ears) - listeners position in the environment,
  • room/environment size (the overall density of reflections heard in the current environment) - overall environment,
  • die-away time (how long before these reflections fall beneath your current level of perception) - overall environment plus listeners perception limits

The difference in arrival of the initial signal and the early reflections at your ears is also called the pre-delay - which is another characteristic of the rooms reverb signature.

Treatment options
Most treatment should focus on 3 things
  • Bass resonance control
  • Room resonance control
  • Early reflections control
Bass resonance control
Bass traps are the solution here.

Mass and size are the keys to a good bass trap - they should be built to cover a broad range of frequencies rather than just one and should be targeted to go into the front and rear corners of a room if at possible

If you have room height, then using a range of hanging absorbers is also an option.

Some rooms may have a variable height that is a straight line slope or a curved/flared slope - these do change the overall resonant profile of the room, and are beyond the scope of much small room treatment discussions

Steven P Helm's bass trap design and construction
John L. Sayers - The recording manual - Studio Design

for more

Room resonance control
Broadband absorbers/diffusers are the key to both room resonance and Early reflections control

They should target your mids and high frequency resonances

See John L. Sayers - The recording manual - Studio Design for more

Also see this Hofa Acoustics 20 questions for a different perspective

Early reflections control
Foam on the walls at the points of early reflection are an important tool in stopping mid and high frequency reverberation. The foam serves to break up the reflection path and so control the amount of sound that is reverberated around the room.

You can determine the points of early reflections by taking a piece of string from your speaker cones straight out to where the signal hits the wall in front of it and behind it - that's right early reflections can occur both in front and behind the speaker, as most speaker cabinets are designed to radiate the signal both forwards and behind.

Some Additional Resources
Bob Golds Acoustic Coefficients
Why Your Bass Traps Don’t Work | Home Recording Blog
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Beats By Gambit

New member
Awesome post! I hate it that people do not understand the difference in the too! I recently made about 13 panels with rockwool and rigid fiberglass for my studio. Next I am going to make some diffusers out of wood blocks.
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