It actually sounds quite good. I tested it with a cheap 12 inch dual sub and was really happy with the sound and bass output both inside on my home theatre and in the car. I tried it with some dacron inside and without it made no difference. Cloth has its advantages bit I totally disagree on the cloth being stronger. Mat is strong in all directions,cloth is only strong in opposing directions to the weave pattern. Being light has nothing to do with resonance. Its all about wall stiffness and the quality of the lay up,thats why I make and use molds. A fiberglass product from a mold is normally stronger than one made without a mold because I roll out every couple layers of material with a special roller to remove any air. This of course depends on wether you actually know what your doing or not. I have been building speakers for 20 + years,I know a great deal about them. I didnt get too technical because I didnt want this to become a involved discussion. It sounds like you know more than the average guy but I think you got some bad information somewhere about the mat verses cloth thing. I sub contract for a professional composite shop also,we make fiberglass helicopter garages used on battleships and large ocean liners and they are made from 85% mat and 15% woven roving. I have made fiberglass items as big as SUV's entirely from mat and a chopper gun which is really the same as mat. The only time any cloth can even approach mats strength is carbon fiber or kevlar and thats only if its vacume bagged and cured in a autoclave which I also do.

 

I had a real hard time measuring the internal air volume on this box. To anyone wanting to figure air displacement on a weird shape try this. I made a wood box with internal dimensions of 12 inches by 12 inches by 12 inches which is 1 cubic foot. One cubic foot equals 1728 cubic inches. I then bought some play sand and filled the one cubic foot wooden box with it leveling it carefully. Then pour the sand into your strangely shaped sub box. You can add inch marks inside the wooden 1 cubic foot box do some math and calculate how much air space is inside your sub box pretty accurately. This is how I measured this box and many before it. I also design and build 3rd and 4th order passive butterworth crossovers and wind my own air core chokes to any inductance (mh.). I made a jig and simple machine to wind them and sell them also. I also design and build transmission line speakers. Just a little background in case anyone is worried about my speaker experience/knowledge.

 

Well my experiences with cloth and mat has been strictly with boats, both full scale and models. On our RC boats the top deck is laid up entirely in mat, several layers of 3/4 ounce I believe. And the top deck is pretty flexible, and this is with high quality epoxy resins. While the hull is laid up in mat and cloth and is extremely rigid and very solid feeling. I know mat does have it's advantages, but I think in a box situation cloth will really increase each panels rigidity.

It has been several years since I did any reading on building a subwoofer glass box. And I remember reading the more mass the lower the resonance, while the stiffer the higher the resonance. And the tricky part with glass was to make it as stiff as possible while keeping the mass low. Because when you add mass, you would need to make it proportionally more rigid.

I do a lot of my posting stoned, so please excuse anything that just doesn't make sense. My knowledge in this isn't really to deep.

EDIT: I could never imagine building a box without a mold, way to much stress involved. What did you make your plug from, plan old MDF and clay for the weird spots?

I also really like the box, I think I have about the same space in my trunk. I just hope my CVX would fit there and still let the VC breathe. I have to take my sub out every weekend as I squeeze both my 57" and 48" RC boats in my trunk. I think with this box I would be able to keep my sub in the trunk. It's a long drive to the lake so that would be nice.

 

I have a lot of experience with boats also,full size speed boats. my last boat was a hydrostream V-king that topped out at 92 MPH with a 32 pitch prop and Merc 2.5 liter with a sportmaster. I has to re core the entire boat. Talk about a job and a half and it took weeks of grinding away glass and scooping out the rotten balsa core. I replaced it with divinicell synthetic foam that absorbs resin. The sandwich construction is stronger than any fiberglass alone structure. If you want to approach speeds like that your life is on the line on the water. A blow over at 90+ would equal certain death or becoming a quadrapelegic forgive my spelling. Mat was used entirely. For your R/C boats you could add tons of strength by simply sanding the existing fiberglass and gluing on balsa strips and glassing over them. You want to use whats called fiberglass tissue,I have never seen mat in that light of a weight. I have been wanting to make some large scale boat molds for some time. Im interested in the zenoah powered (weed eater converted engine) type. Probally considered 1/4 scale. Last I checked they are about 4 feet long. I want to make a mold a V hull with the same basic design as my old 1984 hydrostream,was a excellent design. I also studied hull design and would add my own twist. If you want to do some interesting in depth reading check out Decware.com for speaker plans and excellent forums and also nutshellhifi.com for exceptional Arial speaker plans (transmission line). I have built a lot of decware designs and they are excellent. The Ariel is in construction now in my garage ...very difficult and time consuming cabinets which I do not sell. I have several hundred hours into them and they are only about 70% done. A lot of the designs in full size boats can be scaled down to work well with 1/4 scale. I have been lucky and have done a lot of prototype building for many things and it has helped me in most all of my interests. I have a lot of hands on life experience in many areas. Those web sites I mentioned are required reading for any audio nut. Just because they are geared for home audio does not mean you wont learn something and can apply it to car audio.

 

Well my large 57" offshore mono has no bulk heads as it tops out at 45mph and the top deck is strong just bends when you press down on it. My 48" boat is a race boat that can do low 60's, and does have bulkheads. I actually stuffed the crap out of her last weekend, the deck slammed into the water at 60mph without even a gelcoat crack.

Yeah you can scale full size boats down perfectly and they will handle just like the full scale, My buddy has a 60" truly to scale Apache. The beam is slightly narrower than other RC hulls, because of the scale. My 57 hull is not to scale, and has a 15" beam while his 60" only has a 14" beam.

Zenoah's in the stock form are great reliable motors, they make about 2.9 hp at 12,000. My full mod zenoah makes just over 6hp and 18,000 usable RPM. Recently a new marine engine was brought to the market, that is said to be a zenoah killer. It makes a little over 5hp and 15,000 rpm in it's stock form, and has a much beefier crank and case, and four crank bearings.

If you like full scale boats you'll love RC boats, just instead of the thrill you get pure relaxation.

Here is a shot of my buddy's apache. The hulls is from the early to mid 80's and actually was one of the first gas powered model boats back in the day. He's redone is several times over the years, right now he is running a mid mod zenoah and runs in the 45mph to 50 mph range, and handle a serious chop.

 

Thanks for the compliment about the box. I like it not taking up a lot of space too,I just hope I can sell a couple so the hours making the mold were not wasted. Before making the mold you make a plug which you make the mold from. Making the plug it what takes soooooo much time because it has to fit perfect,be the right size and be super smooth. There is no short cuts to making the plug. I made mine using a special technique I learned from a old school master craftsman I apprenticed under. I would be foolish to post how thats done on the internet...sorry. Thats a trade secret that he would not teach me until many months or pulling fiberglass splinters out of my hands. Thats like a magician showing how his trick is done. The easiest way to make a mold is to buy the product you want to mold and splash it. Kind of unethical but it happens a lot. Splashing it making a copy from a existing finished part. To even explain that would take a great deal of time and tons of posting. Those are some big boats for R/C. Are they zenoah powered and liquid cooled? I wish you lived in N.C. I could splash your boat hulls and give you a hull as payment. I would splash them and then add my own modifications which would be more chines and more set back for the engine as well as a aeration area to increase top speed when trimmed out properly.

 

Looking at your friends boat that hull is easy to build. Just makng sure to get the proportions right is the only tricky part,boats have a lot of R&D involved.Splashing is the best way to go and then add a twist if wanted. When you copy a fiberglass part (splash) you first wax it with a special wax. Then you spray on a coating of PVA mold release that protects the original part from resin. The PVA is key and is quite difficult to spray well because its so thin,like spraying water and trying to avoid runs. Then you can gelcoat over the PVA and finally lay cloth on the gelcoat. Make it good and thick because this becomes the mold. Let it cure in the sun and dont even think of removing it from the boat for a full 24 hours. Green or fresh fiberglass can distort if removed to fast. Then with your mold you wax it 3 to 5 times and spray on PVA carefully. Then You gelcoat it and lay up your glass and insert bulkheads and glass them right in. After 12 to 15 hours you can pop it out of the mold. Water disolves PVA so if something dosnt want to release you hit it with the garden hose and it will float out of the mold.

 

Well you have different classes of RC boats, you've got sport boats and race boats. The sport boats are more to scale and tend to be under 55 mph. While you can scale the hull down, you can not scale the water nor the physics down. So race hulls have been designed over the years for top speed, and handling at this scale. And they use very different techniques than the full scale guys do. Most races boat are over 60mph, with some hydro's and riggers close to 100mph. I think the world record for gas right now is 108mph in a rigger.

Splashing hulls is very frowned upon in this industry, so much time has gone into making the many different plugs and molds to finally get the final revision. And it would take a bit of work to get one these hulls to work as a good plug, as the manufacturers are using the same molds to pull countless hulls from, and fix them instead of replacing them. So the small defects in the original mold, are multiplied when you splash it. What the manufacturers do, to counteract the flaws in the molds, is they just blueprint the ride surface of each hull. Rockers and hooks are even worse on our small hulls then the full scales.

 

Yeah I've made a few custom pieces on my flats boat from a mold. I let it sit in the mold for a solid 3 days before pulling it, but then again I do live on the water and it always very humid here.

 

Splashing anything is frowned upon. All molds take a ton of hours to make and usually some R&D. But its like prostitution or drugs they happen too,and thats not about to change. Besides its different to make a copy for yourself and maybe a friend than it is to sell it. I spent about a week making the plug for the accord box. A week of sweating and sanding and wet sanding and adding more bondo and more sanding. Its not fun work. But when you get to 2000 grit sandpaper and finally buff it out and it shines like a new penny and is nearly defect free you know you did a good job. Once you cast your first part and it cures,then slides out with little to no effort you know you did it right. Theres always a minor pock mark somewheres. The front of the accord box is MDF. I also glass in mdf on the side so the terminal cup has something solid to screw into,mdf absorbs resin and becomes like concrete. I then fit the front baffle (mdf) and fiberglass it in place adding cabosil to the resin to thicken it making it like thick syrup. The box supports my weight 175 lbs without even a hint of flexing. But the curved shape also adds a lot of strength. Its like trying to break a egg the long ways with your thumb and index finger,few can do it. Take the same egg in your palm wrap your fingers around it and it breaks easily. The shape makes this a lot stronger than it looks and once the front baffle is anchored in place its very ridgid.