Reflection vs. Absorption: Understanding Acoustic Design

Introduction

In this article, we will discuss the issues of reflection and absorption as a treatment process in acoustic design. Reflections are the energy that strikes the room surface and comes back, causing interference with the direct energy from the speakers. Absorption is a common way to balance the reflected energy in a room. Diffusion is the second technology we have to use along with absorption. Diffusion is a technology to make a small room sound larger. Let’s dive deeper into the science and methods of absorption in acoustic design.

Reflections

Reflections are energy that strikes the room surface and comes back, causing interference with the direct energy from the speakers. Primary, secondary, and tertiary reflections are common in two-channel systems. The ping-pong effect of reflections going back and forth can cause a room to sound unnatural. Real acoustic design and analysis aim to balance the reflected energy room sound with the direct energy from the speaker, which is more pure. Each room usage will require a different balance of direct versus reflected energy.

Absorption

Absorption is an energy process that changes from one form to another through friction and heat. It is an effective way to reduce the amount of reflected sound in a room. The most common way to achieve absorption is through materials like building insulation, foam, and draperies. However, the rate and level of absorption should match the position and usage of the room. Companies that design sound absorption products make sure that the product is spaced out from the wall to take advantage of air movement being greatest 2-4 inches from the surface if the material type absorbs energy on both sides of it.

Types of Absorption

There are three main types of low frequency absorption: Helmholtz Resonator, membrane , and diaphragmatic. Helmholtz resonator uses a resonating cavity, which is designed for a resident frequency to absorb sound. Membrane is a cousin to diaphragmatic. It goes as low but doesn’t get as much as a diaphragmatic absorber. The diaphragmatic process is the most powerful of the three. At Acoustic Fields, we use diaphragmatic absorption with our proprietary carbon fill material that increases the performance of each unit by 40%.

Noise

Before we start any conversation regarding the treatment of reflections as they pertain to the direct sound in our rooms, we must consider the noise transmission issues. Noise leaving and entering our rooms creates as much or more issues than the reflections within our rooms. Noise must be kept out of our rooms from outside sources. Noise leaving our rooms must also be managed. All noise issues must be measured for frequency and amplitude. We have processes at Acoustic Fields to assist you with this noise measurement process using your phone and our apps.

Conclusion

Understanding the science and methods of absorption is crucial in achieving the desired sound quality in a room. It’s important to carefully consider the rate and level of absorption to balance the reflected energy with the direct energy from the speaker. This pertains to both low, middle, and high frequencies.. Companies designing sound absorption products use air movement’s greatest distance from the surface to their advantage for middle and high frequencies. Lower frequencies are a pressure wave and therefore one must use Helmholtz, membrane or diaphragmatic. Open celled foam is the most economical and cost effective to treat middle and high frequencies with absorption.

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