Mobile Electronics Australia

If you missed Part One of this series, please check it out first. The first stage of the marine audio build is the new speaker pods that will house a dual array of Clarion’s CMCS7.1 7-inch components. These are mounted into what are effectively the ‘B-pillars’ of the boat, situated just behind the driver’s seat and mounted into what forms the main support structure over the cabin. This bar is constructed entirely from marine grade plywood, and supports the main Bimini cover as well as lights, antennas and a solar panel on its top section.

The original speakers were a pair of Clarion marine 6.5-inch coaxial that were probably as old as the boat itself (around 20 years) and while the white plastic grille covers had aged and degraded the speakers themselves actually still worked. Goes to show you how tough marine gear needs to be to survive the constant barrage of salt, sea water, wind and massive temperature extremes.

The mounting depth of the pillars was not sufficient to support the new, and much deeper, Clarion CMCS7.1 components. This meant that a completely new mounting system needed to be fabricated to increase the depth, while also featuring a neat counter-sunk finish to look professional.

Craig and I opted to go for a dual array of CMCS7.1 speakers to aid efficiency and therefore reduce current consumption placed on the boat’s charging system. The dual arrays would get loud even with modest power input, and unlike with the car in your garage you can’t simply jump start a boat quite so easily if the batteries go flat. This is especially a concern if you’re out at sea! The dual array also looks pretty cool and offers a very symmetrical appearance. Anyway, on to the build.

Stage 1: Building the structure                  

The building material used for the construction of virtually everything in this project is marine grade plywood, since MDF is simply not suitable for marine purposes as it doesn’t resist moisture at all. The original pillar cover panels were removed from the boat and taken back to Craig’s workshop for fabrication, as these were used as a template for the new cover panels. A raised oval ring section is cut out and then mounted on small slices of plywood to create the shape. Note that the inner edge of the oval ring features a small recess. This is what the actual mounting baffle will sit against to recess the speakers.

Stage 2:

Stretching an old t-shirt or some grille cloth over the structure creates a smooth, flowing shape. You can secure the material in position with staples or Quik Grip clue, and the overall size and contour is up to to decide. Note that since we were planning on covering these with vinyl trim it wasn’t necessary to have them perfectly smooth.

Stage 3: Applying resin

Now to give the shape some strength by applying multiple layers of fibre glass resin, which you can pick this up from any Bunnings or hardware store as the resin and the catalyst in separate containers. Mixing is a simple matter of pouring the base resin into a plastic container and then adding the catalyst and giving it a stir. Depending on the amount of catalyst you add the resin will harden quicker or slower, so if you haven’t done this before go ahead and mix some test batches. I tend to add a little extra catalyst and have the resin set a little faster, but not so fast that the resin overheats from the chemical reaction! Around six thorough layers of resin is all that’s needed to form a thick enough layer. Since this construction won’t actually be holding any weight it only needs to be thick enough to support its own weight.

Stage 4: Trimming the cover panel

Once the resin has sufficiently hardened you can check it for soft spots and re-apply resin to increase the strength as required. If it’s sufficiently sturdy all the way around it is time to cover it with vinyl. Here we are simply using white vinyl which is very affordable and suits the marine purpose perfectly. A liberal coat of Quik Grip onto both surfaces is applied prior to leaving it for a few minutes to become tacky. It’s important to make sure the surface of the panel is free from debris and large imperfections as these will show up easily under the vinyl.

Step 5: Cutting the new mounting baffles

When the oval rings were cut out during the first stage these left oval shaped inserts which will fit into the panels perfectly. Using these as templates cut out two further oval shaped panels that are slightly larger in diameter so that they can be inserted under the edge of each ring to create recessed speaker baffles. Once you have calculated their centre positions on the baffle you can cut out the holes for each midrange speaker. Here Craig uses a small sliver of MDF and a drill bit to create a homemade compass that draws perfect circles.

Step 6: Cutting out the tweeter holes

With the new midrange speakers sat temporarily into position with their grilles in place you can now finalize the positions of each tweeter to achieve a symmetrical finish. Once you are happy with their position (and ensuring they don’t foul the cover panel) you can draw some guide lines and cut out the small circular holes into which the tweeters are mounted. With these panels ready it’s time to head over to the boat to continue the installation.

Stage 7: Mounting the cover panels

The new cover panels will only act as cosmetic covers for the speakers and their baffles, as the baffles need to be attached to the main bar for strength. Here Craig places the cover panels into position and sits the speaker baffles inside to position them in place. The cover panels are held in place with self tapping screws around their circumference.

Stage 8: Fibre glassing the baffles into position

With the baffles sitting in position Craig places small rectangular shaped plywood pieces between the bar and the baffles to wedge them into place. These rectangular pieces are then fibre glassed into place permanently to affix the baffles to the bar. Once the baffle is held in place securely by two pieces the cover panels can be removed and additional plywood braces can be added to further strengthen the baffles.

Stage 9: Trimming the baffles

You can trim the baffles or paint them, but in this instance we decided to add a little faux carbon fibre to the installation, which is a theme that will be repeated throughout the installation in other areas. Stick on carbon fibre comes in varying qualities and grades, but the premium 3M stuff will set you back around $100 per 1m x 1.8m sheet. With the baffle trimmed a test fit of the speakers and cover panel can be done prior to wiring.

Stage 10: Wiring and mounting the speakers

There is ample room behind the panel to mount a small passive crossover network, and its simply a matter of securing the supplied speaker wires to each component and to the crossover to button up this stage of the installation. Since the wiring will be the last aspects after all the fabrication work is completed the cover panels are left off for now.

Catch up with us in Part III where we get to work fabricating the large ported enclosure for the three 10-inch Clarion marine subwoofers.