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2021-02-24

How to efficiently improve sound absorption in an audio recording room (Part 1)

It’s been a while.
This is Mr.I of Shizuka Co., Ltd..

Today, I’ve translated an article that recently received a lot of response on Twitter. This article is about how to efficiently improve the sound absorption of an audio recording room.

This is a bit of a long article, so I’d like to split it into two parts: Part 1 and Part 2. This will be the first part.
Original text in Japanese (日本語の記事)

In this article, I would like to introduce the selection of materials that can absorb sound (control sound echo) in an audio room.

The higher the performance of the audio system, the better its ability to diffuse and reproduce sound, but there are cases where the size of the room and the objects placed around the speakers cause unnecessary echoes (flutter echoes) and booms (bass echoes). Have you ever had a case where the sound quality sounds different from what you hear at an audio store?

Even if the audio speakers themselves have the same quality and performance, the way the sound resonates changes depending on the height to the ceiling and the size of the room, and the mere presence of tables and chairs around them can have a diffusion effect. Also, although carpets and rugs have a sound absorbing effect, they are effective in absorbing high frequencies (mainly above 2,000 Hz), leaving the mid-range and below (below 500 Hz), which affects the original reproduction ability.

It is recommended to check the performance of any sound-absorbing material before adopting or installing it, as it does not necessarily absorb all frequency bands, and each material has its own special sound absorption range.

In many cases, it is impossible to tell whether the sound absorption performance is good or bad without actually installing the product, but it is possible to judge whether the sound absorption performance is good or bad by using the “reverberation room method sound absorption coefficient” and the “vertical incidence sound absorption coefficient”. Both of them show the sound absorption performance, but they are measured in different ways.

“The reverberation room method” is used to measure the sound absorption coefficient by using 12 square meters of sound-absorbing material in a room (mainly concrete) where the sound-absorbing material reverberates. In the case of “the vertical incidence sound absorption coefficient”, the circular sound absorbers of 29mm and 99mm are placed in the measuring tube, and the sound is emitted inside the tube to measure the ratio of sound absorption. Therefore, if you are planning to control the acoustics of the whole room, you should refer to the “Reverberation Room Method”, and if you have a small area (for example, a wall with a sound absorber of paper size), you should refer to the “Vertical Incident Sound Absorption Coefficient”. Some products may or may not have measurement data, so if you are unsure, please ask the seller or manufacturer and they will be able to provide you with an answer.

In our experience, sound absorption measurement is done according to the domestic standard called JIS, but the size of the room to be measured and the measuring equipment differ from one institute to another. For example, some institutions measure “vertical incidence” in an anechoic room, while others measure it in a semi-anechoic room or a quiet office. Naturally, the results will differ slightly depending on the measurement location, so if you are installing a sound-absorbing material for the first time, you don’t need to be too particular about the 10% or so of sound absorption performance.

SHIZUKA Stillness Panel (our sound-absorbing panel) can measure both “Vertical Incident Sound Absorption Coefficient” and “Reverberation Room Method Sound Absorption Coefficient”, so please use it according to your application.

This is a picture of the vertical incidence measurement. A sound-absorbing material is placed in the black measuring tube to measure the sound absorption coefficient.

This is the test method of sound absorption coefficient by reverberation room method. A test piece of about 12㎡ is set up and tested with and without.

This is the reverberation room method data of SHIZUKA Stillness Panel. The horizontal axis is Hertz (frequency) and the vertical axis is the sound absorption coefficient. The larger the number on the vertical axis, the higher the sound absorption, and the larger the number on the horizontal axis, the higher the sound absorption. As a graph, it can be read that more than 90% of the sound absorption is achieved above 500Hz.

Continue to Part 2 .


神奈川県厚木市金田492-1