How Waterproof Speakers Are Designed ?
Waterproof speakers are highly adaptable gadgets. They have an edge over regular speakers in that they can be used outdoors as well. They are specially engineered to take on the elements and last longer out-of-doors. But, waterproof speakers are not so different from non-waterproof ones. They have the same basic components; only the way the components are built and put together is different. Further, waterproof speakers are not the same as water-resistant speakers, although we tend to use the terms interchangeably. Today, we will talk about waterproofing in sound systems, and walk you through all you need to know about waterproof and water-resistant speakers. Let’s get started.
Before we go into the details of waterproofing technology, let us first understand how speakers are made. All speakers have 3 fundamental parts: drivers, crossovers and enclosure.
Drivers are acoustic parts that convert electrical energy into mechanical energy and create soundwaves which are picked up by our ears as different sounds. They rely on diaphragms which are the external funnel-shaped components attached to the driver. Diaphragms produce a disturbance in the air which is translated by our brains into understandable sounds like words and music. Large drivers that produce low frequencies are called woofers, smaller ones that process high frequencies are called tweeters and the ones that generate the frequency in between are called midrange drivers.
Crossovers are electrical filters that split up the incoming audio signal into low, midrange and high frequencies. These frequencies are then channeled towards the respective drivers designed to handle the specific frequency band. A 2-way-firing speaker, for example, has a tweeter and a woofer, whereas a 3-way-firing speaker has the full set – a tweeter, a midrange and a woofer.
The enclosure is the cabinet or housing of the speaker. It holds all the parts together, assigning a specific place to each component for the best sound production.
Details Of How Waterproofing Is Achieved In A Sound System :
Fundamentals of waterproofing :
All speakers, whether waterproof, water-resistant or non-waterproof, have all of the above 3 components. The difference lies in the manner in which they are developed and assembled. The design of the components and the manufacturing technique is what sets them apart. Let us now try and understand how these different speakers are made.
At the outset, we would like to clarify that although a lot of brands market their speakers as waterproof, they are in reality only water-resistant, not waterproof. A waterproof speaker is a highly sophisticated device. It can produce sound underwater for hours at a time, and in fact, does not sound very good out of water. It is not very common, and even the ones that are available, are expensive high-end speakers. So if you see a brand aggressively pitch its waterproof speakerbar for UTV, you might want to read the fine print before going in for a buy.
IP Code – A measure of waterproofing :
Waterproofing in electronics is denoted by the IP or Ingress Protection Rating. It is a measure of the protection the enclosure provides to the electronic device and the user. It is depicted by the letters ‘I’ and ‘P’ followed by two digits between 0 and 9. The first digit represents protection against solid foreign body ingress like body parts (fingers, hands), dust, insects, tools, etc. It also represents protection for the user against moving parts of the device like motors, fans, electrical conductors, etc. So it is a two-way protection level, i.e. it concerns both the device and the user. The second digit in the IP code signifies the level of protection against liquid ingress. It shows the extent to which the device is sealed against moisture, humidity, spraying and submersion. It is a one-way protection level and only refers to the protection of the electrical device.
The thumb rule is that the higher the IP number, the greater the level of protection. If a digit is zero, it means the speaker has no protection in that respect. If a digit is replaced by the letter ‘X’, it means enough data has not yet been collected to assign a protection level.
The following chart shows IP ratings and the corresponding extent of solid and liquid protection.
As we have seen the IP code and its relevance to electronics in the above chart / image representation, now we will apply the findings to stereo systems.
Kinds of speakers :
A speaker that is not waterproof, does not have any protection against water. Even a few drops or a mild splash is enough to damage its internal parts. A water-resistant speaker can withstand exposure to water. It can take a hosing-down or even an accidental dip in the pool, but will probably not make it through total immersion for more than a minute. A waterproof speaker is the hardiest of the lot. It is designed to function underwater and under high pressure for longer periods of time.
Non-waterproof speakers :
These are regular indoor speakers for home and office use. They mostly have steel enclosures that pose no problem indoors, but are vulnerable outdoors. They are prone to moisture-induced damage like rusting and corroding. Indoor speakers have paper diaphragms which work fine in dry conditions, but when exposed to humidity and extreme heat, tend to get warped, and lose their acoustic abilities. Also, the cabinets of indoor speakers are not water-tight as they are not meant to be used in wet environments.
Water-resistant speakers :
Water-resistant speakers are also called marine speakers and weatherproof speakers. They are rough-and-tough outdoor speakers built for marine conditions. They are tested for fog, salt sprays, mud and snow. They can take heavy splashes of sea water and can be hosed down at the end of a day to wash off mud, sand and dirt. Wake-tower speaker, marine subwoofer, ATV speaker, motorcycle speaker, snow-mobile speaker, swimming earbud, floating Bluetooth speaker, etc. are examples of water-resistant speakers.
Water-resistant speakers have stainless steel, aluminum or brass cabinets. These metals and alloys are impervious to water, dirt and salt, and hence, keep the internal parts safe. The enclosures have a special hydrophobic polypropylene coating to ward off water. The different parts may also be sealed tight with a Teflon finish to prevent water from seeping into the device. Marine speakers have mylar diaphragms for standing up to moisture and heat. They are more adaptable and rugged than paper diaphragms.
Weatherproof sound systems have an IP rating of 2 to 6. They can withstand condensation, vertical sprays, angled sprays and powerful water jets. They can be used in the rain and stormy sea conditions. They also work in extremely scorching and freezing temperatures.
Waterproof speakers :
Completely waterproof speakers have an IP rating of 7 to 9. They can survive total immersion in water under pressure for varying lengths of time. An IPX7-rated speaker, for instance, can be submerged in one-meter-deep water for up to 30 minutes, an IPX8 speaker can be submerged in deeper water for longer, and an IPX9 speaker still deeper and still longer. The basic idea is, the higher the figure, the greater the ability of the speaker to prevent water entry.
But how does a waterproof speaker achieve this feat ? How does it prevent water from flowing into the device at such great depths ? We will discuss this in our main and final segment where we will take a closer look at how waterproof speakers are designed.
How waterproof speakers are designed ?
The engineering that goes behind creating a waterproof speaker is astounding. There are so many levels of protection, so many sophisticated techniques, it really is worth knowing more about.
Conformal Coating :
Conformal coating is done to protect printed circuit boards (PCBs) from moisture, chemicals, salt, solid debris, and extreme hot and cold temperature. It shields critical electrical marine audio parts from corrosion, humidity and UV rays. The process involves applying a thin polymeric film that ‘conforms’ or closely adheres to the surface of a circuit board. The conformal coating material hugs every tiny contour on the board, forming an almost imperceptible layer over it, typically around 25 to 250 micron (micrometer) thick. Conformal coating, however, is not a total sealant. It is more of a breathable protective layer over a PCB, protecting it from environmental stress. It allows water vapor trapped in the circuit to escape, thus prolonging the life of the circuit board and the marine receiver.
Different chemistries are used as conformal coating material. The most commonly used compounds are: Acrylic, Epoxy, Polyurethane, Silicone and Parylene. Acrylic is the easiest to apply and remove. It dries easily, is highly resistant to moisture and has a high fluorescence level. Epoxy is an excellent electrical insulator. It prevents short circuits and moisture-damage, and is effective till about 150ᵒC. Polyurethane has good dielectric properties. It is extremely resistant to water and solvents. Silicones display a wide temperature tolerance from -40ᵒC to 200ᵒC. It is resistant to water and impact, and provides good dampening. Parylene is chemically inert. It has excellent deposition rate uniformity, and serves as a dielectric and moisture barrier against the environment.
There are various ways to apply conformal coating. It can be brushed, sprayed, or poured over the surface, or the object can be dipped in the conformal coating material. It can also be selectively applied, rapidly and accurately, to different parts of a circuit board using a machine. Once the coating is applied, it needs to undergo a curing and drying process. Solvent coatings are normally air dried unless the process has to be sped up in which case it is heat cured in special industrial grade ovens. UV conformal coatings require UV curing with arc or microwave lamps. This technique is widely used in consumer electronics like marine audio systems.
Another major breakthrough in waterproofing technology comes from the field of nanotechnology. Now nano-sized particles as small as one billionth of a meter (one billion nanometers is equal to one meter) are used to make waterproof, oilproof and anti-UV coatings. Nano-coatings are mostly made from Fluoropolymer chemistries. The atoms and molecules of the compound penetrate the narrowest gaps and crevices in a PCB to form an intimate bond with the surface of the board. It acts as a barrier against moisture, corrosion, salt, dust and chemicals, and protects the circuitry from the elements. The coating also has high lubricity, and is resistant to extreme high and low temperature.
Nanotechnology is being harnessed to develop superhydrophobic non-conductive sealants (discussed in detail in the following section) for electronics as well as multi-purpose water-based breathable coatings for masonry. Ultra-thin nano wires and nano tubes with diameters as small as 1 nanometer are used in transistors in electrical circuits. The nano tubes are 5 to 6 times stronger and more resilient than steel, but weigh half as much. These benefits make nanotechnology an emerging science in electronics, aerospace, and various other disciplines.
One of the most important properties of nano coatings is that they are ultra thin. This means no masking is required for protecting connectors that would normally be contaminated with conformal coating. This greatly reduces the cost of masking and demasking parts involved in conformal coating. Thus, nano coating has a lot of potential and can be a good low-cost alternative to conformal coating.
Superhydrophobic coating :
Waterproof speakers, and some water-resistant ones, have a special coating known as superhydrophobic coating.
Superhydrophobic coating is a subset of nano coating. It can be made from a number of materials such as Manganese oxide polystyrene nano-composite, Zinc oxide polystyrene (ZnO/PS) nano-composite, Carbon nano-tube structures, Fluoropolymer compounds, and Silica-based nano coating.
Superhydrophobic coating is applied to speakers and PCBs to make them waterproof. It is what gives the device its water-resistant quality. It is a nanoscopic super layer that strongly repels water. It is the opposite of absorbent. It fends off water vapor and liquid water. When a surface that has been treated with a superhydrophobic coating comes in contact with water, the water just slides off of the surface leaving it completely dry. If a jet of water is sprayed at such a surface, the water immediately rebounds off the surface.
Superhydrophobic coatings prolong the life of the object they are sprayed on. They are used in ultra-dry surface applications in industrial engineering. The coating can be applied to electrical parts like chips, batteries and grids to prevent water-damage. It is anti-icing and anti-corrosive in nature, and can easily be cleaned with water.
In stereo systems, superhydrophobic coatings are used to protect the drivers, crossovers, charging ports and built-in batteries from moisture. It makes the individual parts waterproof and makes the gadget more adaptable.
Glue, tapes and gaskets :
Another thing that plays a central role in waterproofing is glue. Let us explain. A speaker is made up of many parts. All these parts are held together with the help of screws and auto-lock sliding clasps. Now, even if the parts are fitted closely together, there is still a gap that remains through which water might seep in. A speaker has many joints and ports, and it’s nearly impossible to plug all the holes. Water only needs a microscopic opening to trickle in and compromise the device. Therefore, in order successfully combat water entry, manufacturers use glue and tapes to cement the different parts together. The glue used in speakers is an industrial-grade sticky rubber-like substance. It creates a water-tight seal preventing water from entering the main housing of the speaker.
The enclosure of a speaker may comprise of two or three parts. All these parts are held together with the help of screws. For example, the outer frame is joined to the chassis with screws. Likewise, the speaker is joined to the grille/outer frame with screws. Once these parts are screwed in together, a thick daub of rubber is dripped in from top over the head of the screws to plug the screw hole and prevent water ingress. The part where the speaker meets the grille/outer frame is also sealed off using a thick rubbery adhesive. A rubber washer runs along the rim between frame and the chassis to make it water-tight. The screws holding the frame and the chassis together exert pressure on the washer making it expand so that all the cracks are plugged off.
Waterproof speakers have plastic or mylar cones which are impermeable. They also have rubber surrounds which repel water. So even though water enters through the grille, it washes against the cone and the surrounds and slides off them like water on a lotus leaf. The circuit boards and electrical wires have superhydrophobic spray coatings and tapes too. Under high water pressure even if the glue and washer barriers are compromised, the coatings and the tapes keep the components safe.
The charging port flap in a waterproof speaker is incredibly thick. It made of rubber and keeps the jack dry. Most speakers also have a second layer of waterproofing around the USB ports on the inside. It involves an extra plastic covering over the charging port and USB slot inside the speaker body. It is held down by screws and has the same rubber sealant as the rest of the device.
Waterproof speakers have rubber gaskets around buttons. Gaskets are rubber rings squished against the inner side of the device. They expand under pressure and plug off the gap between the button and the surface. Some manufacturers also use a boot of silicone rubber that completely separates the part of the button you press from the electrical circuitry inside.
Waterproof speakers are put through numerous tests to ascertain their degree of impermeability. There are Accelerated Life Tests that test the effects of ageing and temperature on the device. There are Acoustic Stress Tests to understand how the speaker would perform with advancing age. The speakers are tested for salt water resistance, ultra-violet radiation resistance and extreme hot and cold temperature resistance. They are checked for gaps and fissures in the physical frame. They are checked for expansion and contraction under different simulated weather conditions. The strength of the gaskets and washers are tested. The hardiness of the cone is tested. In short, a waterproof speaker has to pass rigorous testing to be certified as a waterproof, or water-resistant gadget, as the case may be.
There you go. Now you know the fundamentals of waterproofing. You are better prepared to make an intelligent choice. In future, if you plan on buying a waterproof speaker, you will know what to look for, and no salesman will be able to take you for a ride.