Car Audio, Custom Fabrication

LIS Audio How-To: Speaker Mounting Material Moisture Test

Introduction

Are you looking to add some new speakers to your vehicle but don’t know what material is best for the application? Have you tried to look it up online only to find tons of different answers, so you aren’t sure which route to take? Then, you’ve come to the right place. Some materials will act very differently when the elements of the external environment are introduced into the door cavity of a vehicle, mainly moisture. Hot and cold temperatures can play a part but moisture is the main ingredient to the deterioration of may common speaker mounting materials, and speakers themselves. In this blog we will go into detail about the most popularly used materials when making speaker mounts and, just how they may interact with prolonged exposure to moisture.

Why does the material even matter?

Lets talk about some the initial advantages, and disadvantages, to the different types of materials we may use to build speaker mounts for our aftermarket speakers. If a speaker mount material is allowed to come into contact with moisture, the material itself could begin to change and exhibit new properties. It could also begin to warp making for an uneven, or curved, mounting surface for the speaker to rest on. This can create gaps or cause the speaker’s frame, or basket, to become bent. If the basket bends too much it could cause the voice coil to misalign in the motor gap and eventually rub or impact a part of the motor structure. Hopefully, if we use the best materials offered, this will not be an issue.

One more property we may see change depending on the material we choose and it’s introduction to direct moisture, is it can begin to wear down or deteriorate. This means the material could begin to break-up into chunks and possible fall apart, leaving an unattractive and not ideal mounting surface for the speakers. From here the speakers can become loose and cause rattles to appear, the music cutting in and out, or we could see “grounding out” issues arise due to the terminals and wire being allowed to move too freely. This can cause permanent damage to the vehicle wiring, the aftermarket audio components, or even destroy mechanical moving parts inside the door if the speaker happens to come loose and become a more of a projectile inside the door.

A couple more disadvantages to using the wrong material, that aren’t as important but are worth mentioning would be; material color and direct speaker oxidation. If the speaker material absorbs and holds water for long periods of time, it can then begin to directly deteriorate the materials the speaker is made from, thus making it more likely to fail mechanically. When we us ABS it comes in many colors but we tend to choose black. Using black allows the speaker mount to fall away from the eye if the sun were to catch the speakers just right through the factory grilles illuminating the new speakers and the installation. It is common that wood be painted to help perform the same duty, which we will cover more at the conclusion of the experiment. Lets get into the experiment and the result we found!

What do we expect to happen?

Lets start off with addressing the variables to the experiment and what we have been told to expect when moisture is introduced to these different materials. The most commonly used wood will be MDF and then Marine Grade plywood, and one ABS Plastic ring. Out of 6 pieces, we will find Raw MDF, Painted MDF (using cheap spray point), Coated MDF (speaker box coating), Fiberglass Resin added to MDF, raw Marine Grade plywood and raw ABS Plastic. I have included the starting point for the thickness of each material below so that we can compare sizes before and after prolonged exposure to moisture. I will also take this chance to mention we have not included materials like birch, particle board or cheap untreated plywoods as it is well known they do not last when exposed to moisture over time.

We plan to take one small ring made from each material and submerge it under water for a prolonged period of time. We will be using two clear plastic bins, a stop watch, a shop camera phone, a Digital Caliper (set to inches), and tap water; while recording the Data we collect onto the computer. The rings will be left fully submerged under water for most of a work shift, overnight, and then through some of another work shift the next day. So, approximately 24 hours to give each material time to absorb plenty of moisture, and hopefully start to cause a physical change in the shape and make up of the materials we predict to be altered.

In car audio there is often advice handed out stating that if raw MDF wood is used, it is more likely to absorb and hold moisture than, if it were covered in spray paint, fiberglass resin, or speaker box coating. Generally, the theory here is that “the wood would absorb the coating into the outer pores making it harder for moisture to enter the wood, now that the space is occupied.” This could mean longer lasting mounting materials due to the fact that less moisture is allowed to absorb deep into the material contributing to the disadvantages we broke down earlier in the article.

The theory behind using ABS or a Marine Grade plywood, is that it is made to hold up against large amounts of moisture much better then most traditional sheet woods on the shelf, that can be commonly found being used for mounting.  It is a common theory, which we share as well, that the ABS plastic will not warp or deteriorate due to being introduced to lots of moisture. In theory, the Marine Grade material is generally expected to absorb less moisture and dissipate any moisture it has absorbed, quicker than the non-marine woods. Now, lets get into the Data that was gathered from before and after the experiment.

Thickness before exposure to moisture

Raw MDF – 0.50 inch

Painted MDF – 0.51 inch

Coated MDF – 0.52 inch

Fiberglass Resin MDF – 0.51 inch

Marine Grade Wood – 0.48 inch

ABS Plastic – 0.33 inch

Going over the Data…

First off, we notice some pretty big changes in some of the materials. The material submersion portion of the experiment lasted a little over 26 Hours. The materials were allowed to dry for a bout 6 hours passed that so we could see if the moisture dissipating from the materials would cause even more severe changes to the physical appearance of the rings. We’ll use this section to further break down the results of the Data found in the aftermath of prolonged moisture exposure, and the physical changes we did, or did not, see in each of the materials…

Thickness after exposure to moisture

Raw MDF – 0.56 (+0.06) inch

Painted MDF – 0.59 (+0.08) inch

Coated MDF – 0.58 (+0.06) inch

Fiberglass Resin MDF – 0.54 (+0.03) inch

Marine Grade Wood – 0.53 (+0.05) inch

ABS Plastic – 0.33 (+0) inch

The rings were removed from the water at this point of the experiment, and set aside to dry for some time. As the moisture dissipated form each of the rings we could see that some materials had begun to warp more as time went on, and they did not return to the original thickness. All of the rings that did swell maintained the same thickness after being dried out as they had when freshly pulled out of the water. The ring that exhibited the most swelling overall was the Painted MDF, while the Fiberglass Resin MDF appeared to have the greatest amount of warp.

When looking through the slides we can see that the Raw MDF (+0.06 inch) did swell but, not as much as the Painted MDF (+0.08 inch). Though, to the touch, the Raw MDF seems to be a bit softer and gained a slight concave around the lip of the ring. The Painted MDF ring gained a good deal of thickness, feels much softer, and seems to be starting a process of almost falling apart due to the particles swelling independently. What we can gather here is that the Painted MDF does not keep moisture out as well as the Raw MDF, nor as well as speculated in car audio over the years. The Raw MDF ring seemed not to trap the moisture in while drying out as the paint on the Painted MDF ring seemed to do.

Look through some of the slides to see side-by-side comparisons of some of the different rings to the overall thickness of the Painted MDF ring. When we look closely at the Coated MDF ring, which swelled by 0.06 of an inch (the same as the Raw MDF), we can see at the edge it has almost begun to split the coating causing cracks that could potentially expose the wood to more moisture. Seeing as how this material is tied for swelling the second most, this method may not be most ideal when creating speaker mounts expected to be regularly exposed to harsh environments.

The Fiberglass Resin MDF ring swelled (+0.03 inch), but not as much as the Marine Grade Wood (+0.05 inch) ring that we tested. It is pretty apparent the fiberglass resin on the surface of the MDF did not fully absorb into the wood, which allowed for the introduction of moisture. Once the wood started to swell the cured and experiment resin seemed to begin to crack and further open of possible paths for moisture to yet again be introduced into the wood. The Marine Grade Wood ring, and even more so the Fiberglass Resin MDF ring, almost seemed to warp so drastically it wouldn’t be ideal for introduction to an unnecessary amount of moisture.

Here are our materials listed by ranking from least to most of the amount of swelling we encountered after prolonged exposure to moisture… 1) ABS Plastic, 2) Fiberglass Resin MDF, 3) Marine Grade Wood, 4) Raw MDF & Coated MDF, 5) Painted MDF. Keep in mind, this experiment is merely focused on the moisture aspect and has not taken into account fluctuation of extreme hot or cold temperatures, or the fact that the speaker mounts could be inside of a damp cavity while dissipating moisture, and the fact that these materials could exhibit different signs when exposed to moisture and dried multiple different times.

In conclusion…

If you plan to add marine grade speakers and are not worried about how protected from the environment they will be once installed, the best material to use of the ones we have tested here, would be ABS Plastic. It would be perfectly fine to use an Acrylic or HDPE for the material, as it is well known in our industry to be just as efficient as ABS. Personally, I have had luck with using all of the methods above for years, but I always take into environment the natural environment they new rings and new speakers in which they will reside will reside. If you create an ideal home for non-marine grade speakers then it will mostly take care of keeping the speaker mount materials intact as well. If you would like to know more about properly installing speakers, check out the LIS Audio blog How To “Properly Installing New Speakers.”

The main ways we will provide an ideal home for the speakers, or attempt to keep direct moisture exposure from our new parts, will be to; add Hushmat sound deadener in place of weather barriers, create or install reliable weather guards over the speakers location, and make sure the determined location won take on unexpected water due to high rates of speed or a power washer. Some of these are extremely basic principles for speaker installation, but if we abide by them it is most likely to save speaker mount rings that are made of a less resistant material then ABS to stand the test of time. If you would like to know more about sound deadener, how to apply it and its main benefits, check out the LIS Audio blog How To “Benefits of Auto Sound Deadener.”

Thank you for reading our blog and I hope you came away having learned something new. What our LIS Audio Blogs for more “How-To’s” and client features to come!

Call: (913) 912-6990

E-mail: info@lisaudio.com

Address: 631 S. A-Line Dr. Spring Hill, Kansas, 66083

Website: http://www.lisaudio.com

All images are provided and owned by LIS Audio (Limitless Innovative Solutions, LLC) of Kansas City.

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