Noise, Vibration & Harshness
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Noise, Vibration & Harshness
Many products will produce unwanted noise and vibration under normal operating conditions. This excessive noise and vibration, also known as NVH, is often interpreted as poor quality and can negatively impact consumer perception. It also negatively affects desired performance of the device through accelerated wear and tear, decreased efficiency, or in extreme cases, shortened product life through mechanical failure. Control of these noise, vibration, and harshness (NVH) issues often fall to a variety of add-on treatments applied to a product’s structure with the goal to: absorb or block the transmission of noise, isolate the transmission of vibration between components and damp excessive vibration by reducing the structure’s resonant behavior through solutions like sound absorption, vibration damping and shock absorption.
Boyd offers a wide array of custom converted solutions utilizing highly engineered materials that are tailored to the specific application. The treatment design and material selection is made with a detailed understanding of the structure itself, the governing dynamics driving the NVH issue, and the environmental requirements to be met.
DAMPERS: Vibration damping can be added to a structure in many ways and is predominately used to reduce excessive resonant behavior. The most common type is material-based damping created by straining visco-elastic materials (VEM) in either shear or tension/compression. Performance is optimized by selecting a VEM with maximum loss factor in the temperature and frequency range of interest, and with a stiffness range that maximizes strain energy in the damping element. A constrained layer damper (CLD) combines a rigid constraining layer with a thin damping layer to create cyclic shear stresses in the VEM. An unconstrained layer damper is placed between two components moving relative to each other so cyclic stresses are imparted on the damping pad or link that connects the components in tension/compression. Vibration damping requires optimization through material selection, treatment design and placement to ensure good performance.
ABSORBERS/BARRIERS: For conditions involving excessive radiated noise, a common countermeasure is to enclose the noise source with acoustic absorbing materials to reduce noise levels before they are transmitted to the receiver. Often a dense barrier layer is incorporated to reduce the transmission of noise through the enclosure. These absorbers and enclosures are often die-cut treatments cut to shape with pressure sensitive adhesive backing for installation. Design parameters like foam type, thickness and cover films laminated to the foam are adjusted to achieve good acoustic absorption over the needed frequency range. These same materials can be converted to create air flow paths that direct noise to appropriate areas or force it through an extended or a “torturous” path to increase sound absorption or shock absorption.
ISOLATORS: A common method to mitigate vibration transmission is to insert compliant materials that isolate and de-couple the vibration, blocking the structure-borne path. These isolating materials are converted into many different part shapes: from die-cut isolation gaskets, grommets, bumpers or cushions, to molded rubber components. The isolator is selected to be as compliant as possible and with optimum damping to control unwanted amplification of rigid body modes of the isolation system while maximizing isolation performance.
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