Improving Acoustics in an Existing Room

As you find yourself wanting just that little more from your current audio setup, whether you are starting out in music production or you are just a passionate hobbyist like me, you might be tempted to upgrade your audio equipment. Maybe you are aware of potential flaws in your setup or you just want to take it to a higher level. Well what if I were to tell you this is reasonably easy to do by yourself without spending a fortune? I will take you through the very most basics of acoustics in a room for you to get a better understanding of acoustics and so you can craft a solution to satisfy your needs. I will do this based on what I have experienced whilst improving my room acoustics.

There are a lot of “solutions” out there on the internet and there is a lot of information regarding sound enhancement in rooms and building tutorials for upgrading your setup. I find however that all the information is overwhelming and lot of expensive "one-size-fits-all" solutions are offered even though every situation requires a slightly different solution. Although good sound quality is subjective, there are a few key aspects that can be generalized and viewed objectively. This is what I have focussed on.

Materials:

• Wooden beams (& planks)
• Screws
• Rockwool
• Fabric
• Nails/staples

Tools:

• Power drill
• Scissors
• Saw (& breadknife)
• Nailgun/stapler
• (Gloves & mouth mask)

Two main aspects in room acoustics can be distinguished: flutter echo and resonance. Their influence is largely dependent on the room layout and speaker placement. Since high frequencies are directional, the tweeters of your speakers should always face the listener. This same frequency band can be responsible for flutter echo where soundwaves bounce off of walls before reaching the listeners ear creating a delay and therewith less clear audio. Bass-frequencies (< 200Hz) are not as directional but tend to be susceptible to resonance. When the length of a soundwave corresponds to a primary room dimension (room mode) it will amplify itself in areas of the room where the soundwave pressure is at a maximum and reduce its loudness in other areas of the room where the soundwave velocity is at a maximum, making for an uneven and less pleasant listening experience.

Solutions to treating problematic acoustics in a room are roughly divided into two categories: velocity and pressure absorption. Velocity absorbers tackle soundwave velocity and their effectiveness for lower frequencies increases as their thickness increases. They are most effective in high velocity areas, meaning they may take up usable space when wishing to absorb low frequencies since the velocity near walls is at a minimum. Pressure absorbers use resonance to absorb small frequency bandwidths and are most effective near walls and corners where the soundwave pressure is at a maximum. They are more complex to set up as they have to be tuned to tackle specific frequencies and are often complementary to velocity absorbers. 

Determine one or two primary listening positions as this reduces effort and material cost. If necessary, relocate and repitch your speakers such that the tweeters face the listener as this can have a big impact already.

If your room is untreated, stick with velocity absorption as it is much easier and more capable of yielding a noticable result compared to pressure absorbers. In order for the velocity absorbers to be effective take the following three things into consideration:

1. Orientation and position:

Since axial modes have the biggest effect on sound, the velocity absorbers are to be placed parallel in between two opposing surfaces. In my case this is between the floor and ceiling and between one set of walls since the other two opposing walls are slanted and therefore have no primary dimension. Furthermore, they should be placed near and facing the listening positions as this increases their effectiveness locally. If possible place them further into the room as it will further increase their effectiveness.

2. Size and thickness:

Increasing the absorber thickness will increase their effectiveness on absorbing low frequencies. Therefore, make them as thick as possible in your setup. Design the absorbers so they utilize as much (unused) surface area as possible.

3. Construction:

Use an open frame construction as much as possible to make the absorbers multidirectional. Construction using only planks creates additional surface areas and corners that can generate new room modes!

Make your own velocity absorbers as it is much cheaper and leaves more design freedom.

• Make some frames using thin wooden beams, I used 18x27mm untreated pine wood using a saw to create to correct lengths. construct your frames using at least two screws on each side of the beams to prevent them from rotating. Use additional beams halfway to stiffen up the construction and prevent the fabric from deforming the structure.
• Start securing the fabric on one of the long sides using staples or nails whilst keeping it tight. Do the same for the opposing side and finally do the short sides. Here, fold the corners inwards as it is more foregiving than cutting the fabric.
• Slightly undercut the Rockwool to size using a breadknife or saw (wearing gloves and a mouth mask since the fibres can be itchy) and stuff them in the frames. To prevent the fibres from leaving the frames, close the frames up with additional fabric, making sure to fold it inwards.

A final addition to my treatment are thin foam panels which I bought online. These remove the last unwanted reflecting flutter echo where the thicker absorbers take up too much space. The absorber on my ceiling does not stretch out fully to listening position B as it would’ve required me to purchase a full additional pack of Rockwool. In hindsight however, I could have placed this absorber further from the corner closer to position B as it would be more effective in this higher velocity area. I might do this in the near future.