HOW does dynamat work?

[jonathanengr1 10+ year member]

I'll tell you what... I need a new computer. AutoCAD crashed so I'll have to redo the drawing... take just a few mins. Yup--that's the bad thing about my setup... not much I can do about that. I thought about mounting the subs separately but wiring them parallel--one in the front and one in the back under the seats. It's tight... only 11" clearance, but it could work. However, the seats are framed with aluminum (but MUCH thicker), so it could still be an issue... maybe???

I just like the space that it's in because it's essentially wasted space. It's made for storage, but since I had the toilet installed in front of the storage space, I can't really get to it. Thus, might as well make use of it somehow!

 

[jonathanengr1 10+ year member]

Okay--here we go. As you can see, the sub has aluminum on three sides. One side is open but is covered with a thick snap-on vinyl cover. The area shaded in green on the image is actually two compartments. The square compartment houses the sub. The second, larger rectangular compartment houses the toilet. Typically this area is down (it flips up with a curtain for privacy), and when down has an outer aluminum door. Aluminum everywhere! Hopefully this pic makes it through:

 

[Phoenix Risen 10+ year member]

is the opening on the bottom or the side?

also if its closed in on all sides then your just building a quiet rattle trap.

 

[jonathanengr1 10+ year member]

Sorry... should have been specific about that. In the picture you see the boat from a top-down view. Same with the zoomed-in sub enclosure. You're looking at it top-down. You only see one sub on the front because the second sub is directly beneath the first. The floor is 3/4" marine plywood, and the top that encloses the cavity is a marine plywood substrate with the vinyl furniture padding/shaping on top. They still haven't approved the other picture I posted or it would make more sense.

Anyway--the little drawing I did in AutoCAD is looking top-down at the sub enclosure.

 

[jonathanengr1 10+ year member]

Let me just see if this image posts and then I'll explain....

 

[jonathanengr1 10+ year member]

Awesome! It worked. Okay--above is pretty-much my exact boat. Same color and graphics, mine just has a rounded front end (the decking), is a bit longer and undoubtedly faster . You can see where I placed the black circle. The sub is under there. The sub system sets directly on top of the floor (34 oz carpet with 3/4" marine plywood underneath). It is in a cavity with three aluminum walls, and one snap-on vinyl wall (separating it from the toilet/changing area). Above the sub enclosure is what you see circled in the picture: a marine vinyl cushion with a marine plywood frame. Hopefully this helps!

I will be heading to the lake Thursday evening, and I'll take my laptop with me. I'll snap several pictures of the enclosed area so it will make a lot more sense. In the meantime, hopefully the drawings and pics help.

 

[sexy 10+ year member]

When you put a sub box inside of any other enclosure be it a car, a car trunk, or a boat storage compartment what you end up with is a fourth order band pass. If the outer box/enclosure is flimsy it will go ferrrap ferrrap instead of boom boom. You may stiffen up all the metal panels and change the tuning of your fourth order combo into something better or maybe worse it’s hard to tell until you try. If it were me I would not put the sub box inside of another box. Set the subs out in the open when you’re wanting to play music and put them back in that aluminum storage area when you want to store them if that’s possible.

 

[jonathanengr1 10+ year member]

Ergh... I was afraid someone might say that. Let's just say that's not an option First of all, this thing weighs a good 70 pounds, and there's no easy way to lift it out. Secondly, if I don't put it in that area, there's nowhere to store it where it's out of the way. Third, without using brackets to tie it into place, it's very likely to tip over. It's very tall, semi-thick and narrow down the sides, making it less than stable. It's a very fast boat, and if I hit a decent wake it would turn over and damage whatever it hits. Thus, I'd have to drive slow, which negates the reason I bought that particular boat with the options I chose.

I guess I could make a custom fiberglass enclosure to fit in the *other* corner in the open, but I've never done that before. I'm pretty handy, but I might botch a few attempts. The *main* problem is it would then be out in the open. These subs are not marine grade speakers, so that's a problem. The area they are in now is cozy and dry... no direct water, sun or kids jumping up and down on them.

Is there no way to make it work in that area? What if I cut a few holes within the chambers and installed o-rings to make it look nice and clean (not that anyone would see them). Obviously, I can't cut a hole in the outer panel. Even if I did this, I still feel I'd have to do something about the aluminum vibrating. As for it acting like a 4th order enclosure, wouldn't the enclosure have to be completely airtight and fairly rigid to truly be a bandpass? No clue here... just asking!

 

[keep_hope_alive Premium Member]

no one has actually told you how sound deadening material should work. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

simply adding mass is not the goal. that is all asphalt based products do. adding mass is an inefficient way to lower resonance. might as well just start using concrete.

viscoelastic and elastomeric are the terms to read up on. that is what true deadening does - it's called damping. you want to add damping to the panels. damping will absorb vibration and convert it to low level heat. damping is how you lower resonance.

a vehicle treated with asphalt products (simply adding mass) and a vehicle treated with the same amount of damping products will sound completely different. the damped vehicle will outperform the mass-added vehicle in every measurable way.

Effects of Damping | Noise Damping – Green Glue Company

The Technical Library tab is a great place for info. Green Glue is a true damping product.

How QuietGlue Pro Outperforms Green Glue At A Lower Cost

Quiet Glue by Serious Energy (formerly Serious Materials) is also a true damping product.

 

[keep_hope_alive Premium Member]

i would start by de-coupling the sub enclosure from the boat. you're inducing vibrations structurally - de-coupling will reduce the transfer of enclosure vibrations to the aluminum of the boat.

i would start by supporting the sub from only the corners with neoprene closed-cell foam. minimize contact area, and any contact area would be de-coupled.

also, if the sub enclosure was more rigid, fewer vibrations would be transferred. decoupling the sub frame from the enclosure is another effective method of reducing structure borne vibrations. non-hardening modeling clay is used to decouple speakers and subs, you just need to enclose the clay with deadening product to hold it in place (gets soft in high temps, which is part of why it works). i've seen silicone used (never hardens) but silicone fumes aren't good for speakers/subwoofers.

 

[i2ain2thunder 10+ year member]

glue not worth it for subs bro just get asphault/buytl matts. totally worth it for mids, but in my opinion not worth it for subs...

 

[keep_hope_alive Premium Member]

asphalt/buytl matts aren't effective for subs, or anything for that matter. without damping you're wasting time and money. besides, no one is going to cover their aluminum boat with cheap matts. that's hideous.

preventing the structure borne vibration is the goal. that's what de-coupling does.

prevention first, always. then the required damping is much, much less and also much more effective.

 

[keep_hope_alive Premium Member]

in open spaces, loading boards tend to work very, very well. i've done subs under the captian's chair in pontoon boats in 4th order bandpass that worked great. bandpass also do well in open spaces, as do horn loaded enclosures. if it works for pro-audio, it works on a boat. traditional car audio sub designs usually fail on boats since they rely on cabin gain.

de-coupling the enclosure, then framing out the inside of that 3-sided aluminum cavity with 3/4 ply (or two layers with Green Glue between) would eliminate the flexing of those panels, and focus more bass energy out of the opening - toward the passengers.

bass wants to go everywhere, you can control it with dense, rigid materials. from that location, you really only want the energy to go horizontally out toward the boat passengers - which means it has to travel through the seats. reinforcing the sides (and top) would get you that directionality.

your main problem is that as long as you fire the sub into a panel and/or surround the sub with aluminum panels, they will rattle. if you put ply between the sub and your passengers, you'll lose output.

you could frame all four sides but leave an opening that essentially tuned it for a 4th order bandpass, assuming that opening faced the passengers and the tuning was appropriate, you'd get great performance and output with minimal vibration/rattles. that's what i would do.

i would build a properly tuned 4th order bandpass that had vents that went under the rear passenger seats and flared out just above the floor (angled toward the floor so no water ingress was possible). then all of your bass energy would be right there in the cabin and would spread spherically from there (with some corner loading off the floor and seats). the enclosure and vent would be fully de-coupled from the boat and the cavity that held the actual enclosure would be reinforced with multiple layers of ply.

if you've never heard a properly tuned and constructed bandpass enclosure in a convertible or boat, you're missing out.

 

[billabongcr 5,000+ posts]

shove pillows inbetween the box and the enclosure!

 

[jonathanengr1 10+ year member]

keep_hope_alive... thanks for all of your input! I have been considering adding mdf panels coated with resin to the inside of the panels... just trying to figure out if there's some way to test the setup before I glue these to the panels where there's no turning back. As for making it a true 4th order bandpass... that sound very, very complicated. I'm just now (with the help of WinISD) beginning to understand exactly how ported enclosures work, and how to actually tune the enclosure to a certain frequency, etc. The guy who built my box suggested a few weeks ago of making a three-sided enclosure to help with the rattling panels... that's one thing everyone has agreed upon.

One thing is for sure--I'll eventually have to build a new box. While the area stays dry from direct moisture (and in running water and/or droplets), it is subject to atmospheric humidity. I'd like to build a new box using WinISD and coat it with resin inside and out to make sure it's sealed well. When that time comes maybe I'll step up my game a bit. As for firing the subs at a panel, I did try firing them at the vinyl cover, but the bass inside of the passenger area was considerably less... no idea how to solve that issue?

billabongcr... you know--that might not be a bad thing to try! I've got tons of extra pillows already at the lake, so I might just try stuffing those in around the enclosure to put some pressure on the panels. Heck--even if there's about a 2% chance it will work it's completely reversible, and if it DOES work, well, that would just be awesome!