If you enjoy driving, you probably want to have a comfortable and quiet ride, especially on long trips. But how can you reduce the annoying noises that come from the engine, the road, the wind, and other sources? And how can you improve the sound quality of your music, podcasts, or phone calls? The answer is: with acoustic materials.
Acoustic materials are materials that can absorb, reflect, or dampen sound waves. They are used to control the noise level and the sound quality inside a vehicle. Acoustic materials can be classified into three main types: porous, resonant, and reactive. Each type has different properties and applications.
Also, keep in mind, that each type interact with each other as well. Previously these categories were sound absorbers, sound barriers and damping material. Note: sound absorber material that gloves over panels (like cast foam) or creates some interference, will add mass damping to that adjacent panel. Similarly, damping material does add some sound barrier properties. You are rarely working in a single silo when it comes to automotive NVH.
Porous materials are materials that have tiny holes or pores that allow air to pass through. They work by converting some of the sound energy into heat as the air molecules vibrate inside the pores. Porous materials are good at absorbing high-frequency sounds, such as wind noise or tire noise. Examples of porous materials are foam, felt, fabric, and carpet.
Also, sound absorbers are used to create a non-reflecting surface (like a rug in a tiled bathroom). When sound absorbers are used in conjunction with sound barrier material, you can create a double-wall effect that increases the sound attenuation dramatically. Again, you will rarely be working in pure sound absorption or pure panel damping. This makes single mode models and test results very limited in their predictive abilities. This is why I always looked at the total, doing an Insertion Loss measurement (the total attenuation from the insertion of that treatment).
Resonant materials are materials that have cavities or chambers that resonate at certain frequencies. They work by creating sound waves that are out of phase with the incoming sound waves, canceling them out. Resonant materials are good at absorbing low-frequency sounds, such as engine noise or exhaust noise. Examples of resonant materials are honeycomb panels, perforated plates, and Helmholtz resonators.
Reactive materials are materials that have a high stiffness or mass that can reduce the vibration of a structure. They work by adding inertia or stiffness to the structure, making it harder for sound waves to pass through. Reactive materials are good at blocking or isolating sounds from different sources. Examples of reactive materials are metals, plastics, and rubber.
To reduce cabin noise and improve sound quality with acoustic materials, you need to consider the source, the path, and the receiver of the sound. The source is where the sound originates, such as the engine, the road, or the speakers. The path is how the sound travels, such as through the air, the body, or the windows. The receiver is where the sound is heard, such as your ears or the microphone.
You can use acoustic materials to either treat the source, the path, or the receiver. For example, you can use porous materials to cover the engine or the wheel wells to absorb some of the noise. You can use resonant materials to line the exhaust pipe or the trunk to cancel out some of the noise. You can use reactive materials to reinforce the firewall or the doors to block some of the noise.
You can also use acoustic materials to enhance the sound quality of your audio system. For example, you can use porous materials to cover the interior surfaces to reduce unwanted reflections and echoes. You can use resonant materials to tune the cabin to optimize the bass response. You can use reactive materials to isolate the speakers from the body to prevent vibration and distortion.
The closer you treat (attenuate) the noise to the source - generally - the lower the cost and the lower the mass of that concern. 1) Reduce the source noise 2) Don't let the noise in (seal the body) 3) Stiffen chassis and powertrain mount attachments to the body 4) Absorb, Sound Transmission Loss (barrier), and Damp what is leftover.
To choose the right acoustic materials for your vehicle, you need to consider several factors, such as the frequency range, the noise level, the weight, the cost, and the durability of the materials. You also need to consider the design, the installation, and the maintenance of the materials.
You can use a sound meter or a spectrum analyzer to measure the frequency range and the noise level of your vehicle. You can then compare the results with the specifications and the performance of different acoustic materials. You can also consult an expert or a manufacturer to get advice and recommendations.
You can also use a scale or a calculator to estimate the weight and the cost of the materials. You can then compare the results with your budget and your preferences. You can also check the ratings and the reviews of different materials to get feedback and opinions.
You can also use a manual or a guide to learn how to design, install, and maintain the materials. You can then follow the instructions and the tips to ensure a proper and safe installation. You can also check the warranty and the service of the materials to ensure a reliable and long-lasting performance.
As mentioned previously, you will not be working in a pure single silo of noise attenuation, always consider total Insertion Loss. Do not rely on single mode models or single mode tests. I prefer fully trimmed / on-road vehicle testing. I know the vehicle and/or weather is not always optimal. My recommendation is to release with a maximum treatment (full coverage, full loft, etc.). Soft tool those treatments. Then when the vehicle is available in the hardware phase, quickly run through a full delete to full treatment iteration of on-road measurements (objectively and subjectively) to release your final package for production.
To test the effectiveness of acoustic materials in your vehicle, you need to conduct a before-and-after comparison. You can use the same sound meter or spectrum analyzer to measure the frequency range and the noise level of your vehicle before and after applying the materials. You can then calculate the difference and the percentage of noise reduction.
You can also use your own ears or a microphone to listen to the sound quality of your vehicle before and after applying the materials. You can then evaluate the clarity, the balance, and the fidelity of the sound. You can also ask someone else or a professional to give you a second opinion.
You can also use your own preferences or a survey to rate the comfort, the satisfaction, and the enjoyment of your vehicle before and after applying the materials. You can then compare the scores and the feedback. You can also make adjustments or improvements if needed.