When a product produces unwanted noise, the experience of the user is negatively affected. More than that, they perceive the product as being of a lower quality and also as being less efficient.
Noises may originate from several different components, so it isn’t an easy issue to troubleshoot. However, if design engineers can understand the factors influencing sound levels, they can create products that are more efficient.
In many cases, engineers resolve one sound issue but then discover that there’s another, quieter noise source lying beneath it. For this reason, reducing sound is often a complex operation. It isn’t always solely the level of sound that needs to be considered, but also its characteristics. In fact, in some cases, a louder noise could be desirable.
Motion Systems
When parts move, they’ll always create noise, potentially from sliding contact, vibrations, or motors. If gearing is necessary for the application, the gear type and spacing, the lubrication regime and surface finish all have a significant impact on the gear arrangement’s noise. When it comes to vibrations, motor speed has an impact. When the system operates under no load, the noise level may be acceptable. But at different speeds and loads, resonance may cause problematic unwanted noise.
Air Flow
Many products require cooling, and thus air flow is necessary. There are several ways that air flow causes noise issues when it isn’t considered fully during the design process. It’s common that enclosures require some type of cooling, for example an exhaust fan that removes hot air.
In such an example, the obvious noise source is the bearings and motor of the fan, or the air flow sound as it runs over the blades. In those cases, using a bigger, slower rotating fan that delivers an identical flow rate but at a lower air velocity can solve the problem, although if a small, high-speed fan must be used, it’s possible to optimise the blade design and add quiet bearings to reduce the noise to an acceptable level.
With a high-flow rate, small fan, the rapidly moving air must be managed without causing extra noise. If a disruption occurs to the high velocity flow, or the direction through the ducts changes, sound will be generated. Also, flow restrictions cause fan noise. If the flow is restricted by the intake, the fan works harder and draws more current, producing more noise.
Selecting Components
An acceptable product sound level must be understood from the start of the designing process so solutions to reduce and manage noise can be included in the design from the get-go. Products that have pumps are especially challenging when it comes to sound reduction since they include many sources of excessive noise including fluid flow, sliding or rotating contact, and motors.
Pumps come in many styles, and each has different flow rate and pressure characteristics, which results in different noise characteristics. Usually, noise problems arise if the product requires a pump that is at either a pressure extreme or a flow velocity extreme. Low flow rate – high pressure applications require reciprocating pumps, and these are very loud.
Meanwhile, high flow rate – low pressure applications have high speed motors and high velocity airflow. It’s therefore essential to select the right components and to avoid choosing components that deliver over and above what is required. Design engineers must, therefore, understand the user requirements and needs specification.
Noise Levels – An Overview
An excessive noise level is usually the most obvious sign of inefficiency:
- A noisy bearing will wear out more quickly and will have more sliding rolling resistance.
- Scraping and scratching sounds from sliding linear bearings and bushings indicate poor alignment and surface finish, resulting in increased friction and accelerated wear.
- Loud gears could be spaced incorrectly, be specified incorrectly, or have a poor surface finish.
- Frictional losses and flow disruption can cause loud airflow which leads to pressure increases that cause the colling fan to work much harder.
In some cases, it isn’t possible to reduce noise to a level that is acceptable at its source. Every component has its own minimum sound output which will sometimes still be excessively loud. In such situations, additional sound insulation and damping can help to reduce the sound level exponentially.
