Engineers are increasingly looking for ways to design and construct loudspeakers to be more rugged and durable. You may have specific goals around your speakers’ Ingress Protection (IP) rating, resistance to extreme heat, or even the ability to withstand the force of a rocket launch.
By selecting the right materials (metals, polymers, elastomers, and composites), loudspeaker components can be engineered to withstand a greater range of temperatures and pressures as well as environmental stresses, such as humidity, dust, and vibration.
When your goal is an audio solution that will endure, you need to consider both the speaker driver and the enclosure/grille that’ll be protecting the sensitive moving parts inside. Let’s start with the inner workings.
Resource: Video Blog on the Parts of a Loudspeaker
More Rugged Speaker Drivers
The driver consists of the magnet and voice coil; the suspension, which includes the spider and surround; the diaphragm or speaker cone; and the basket/frame/chassis that holds it all together. Here’s guidance on how each component can be engineered to increase the overall toughness of a speaker.
Magnet
The default choice is ferrite, and it’s likely the one to go with when extreme heat is any sort of consideration. The alternative is a neodymium magnet. Neodymium magnets are stronger, so they can be smaller. They are more expensive, and they will begin to lose their magnetic properties as temperatures go above 176 degrees Fahrenheit (80 degrees Celsius). However, if keeping the speaker’s weight down is important, a neodymium magnet may be a good choice.
Voice Coil
Again, the default material for wiring, copper, will stand up better to heat than the second most popular option, which is aluminum. Your material options for the bobbin that the wiring goes around are paper, aluminum, fiberglass, or Kapton. Paper and aluminum are inexpensive and work for most normal applications. Kapton was created by DuPont and handles temperature extremes well, from as cold as below 450 degrees Fahrenheit (minus 268 degrees Celsius) to as hot as 500 degrees Fahrenheit (260 degrees Celsius). If that’s not extreme enough for you, fiberglass is rated to withstand 1,000 degrees Fahrenheit (538 degrees Celsius) and not melt until it gets to 2,700 degrees Fahrenheit (1,482 degrees Celsius).
Suspension
If keeping water or dust out is the goal, two possible choices for a speaker surround are Santoprene and nitrile butadiene rubber (NBR). Santoprene is a vulcanized polymer that handles extreme temperatures well. NBR is a synthetic rubber that is resistant to oil, fuel, and other chemicals.
Speaker Cone
Many speaker cones are made from composite papers, not ideal if waterproofing is your goal. To get a tougher or waterproof speaker, you’ll likely want a cone material from this list: aluminum, Nomex paper, Kevlar, or polypropylene. Nomex and Kevlar are both DuPont products that offer high inherent dielectric strength, mechanical toughness, flexibility, and resilience. Nomex is flame resistant. Kevlar is resistant to cutting and heat and has a high tensile strength. A speaker with a Kevlar cone may be a good choice for an outdoor environment where humidity and water will be ever-present.
You can get good water protection from a less costly aluminum cone as well. MISCO makes a 1″ wide-range speaker with an NBR rubber surround and aluminum cone that achieves IP67 performance. Mounted in the proper enclosure, this speaker can be submerged in up to a meter of water for 30 minutes.
Note: An IP rating has two numbers in it. The first refers to protection against solids like dust and the second to protection against water.
The MISCO Guide to
Ingress Protection
Polypropylene cones can withstand extreme temperature ranges and are lightweight. This is a good option if you’ll be ordering a large number of speakers because polypropylene lends itself well to mass production.
Basket
A speaker’s basket is typically either stamped steel or cast aluminum. Both are rugged, durable options. Painting or plating a stamped steel basket helps it hold up against corrosion and rust.
Enclosures
Both the enclosure and grille will impact sound properties, so it’s important to consider these early on and not just once the driver is selected. Putting a carefully engineered driver into the sturdiest metal box you can find will hurt the sound quality dramatically.
Many stand-alone speakers are enclosed in medium-density fiberboard (MDF). This manufactured wood is durable, relatively inexpensive, and absorbs vibrations well. Its burn temperature is between 425 - 475 degrees Fahrenheit (218 - 246 degrees Celsius). Water and MDF don’t mix well (there are versions that are more water-resistant but nowhere near waterproof).
Plastic is also relatively inexpensive (especially for larger orders), durable, and lightweight. Waterproof polymers (which are nonconductive) are good options for marine speakers. Some types of plastic can also withstand significant temperature swings, exposure to chemicals, or be thermally conductive.
However, plastic enclosures generally are not as good at damping vibrations and resonance as wood ones. A plastic enclosure may impact the accuracy of sound reproduction.
Grilles
Speaker grilles offer some protection but they must also be open enough to allow sound waves through without distortion. Detailed testing at MISCO’s audio labs has shown that a metal grille should be 60% open for optimal acoustical transparency.
From an engineering standpoint, each hole in a grille must be wider in diameter than the metal is thick. Aluminum and stainless steel are durable choices because they don’t rust. Mass-produced consumer goods often rely on plastic grilles which can be integrated into the housing of a unit.
Today, 3D printing allows for more customization and the ability to create enclosures and grilles with smaller tolerances. Working with a speaker manufacturer who offers this capability can speed up the design, prototyping, and testing phases of an audio project.
If you have specific questions about creating more rugged speakers and sound systems for harsh environments, please reach out to our team at MISCO, and we’ll be happy to talk with you.
