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 Post subject: Box light as posible
PostPosted: Wed Mar 01, 2006 10:42 am 
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I got a MDF (wooden) case 12mm thick. It has a 60l. volume, and weights around 20kg's.

Now my question is, how can I create a box that is very light (I want to keep my 3 cylinder performance), 20kg is alot for my swift :P

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PostPosted: Wed Mar 01, 2006 11:17 am 
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Well the lightest would be a fiberglass enclosure but they are typicaly more difficult to build than a comparable wooden enlcosure. If your stuck with wood you can look into using low void plywood. Same thickness weighs less than MDF.

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PostPosted: Wed Mar 01, 2006 1:45 pm 
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Like a 7-ply 1/2" birch playwood box, braced appropriately.

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PostPosted: Wed Mar 01, 2006 2:33 pm 
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Location: Adelaide, Australia
free air sub...

cos, 12mm MDF is nowhere near thick enough for a 60litre enclosure, and I also doubt it even weighs 20kgs, ya weakling... :p (sub weight not included) either way, 20kgs isn't that much... whats a full take of fuel weigh, like 30Kgs? do you always run half empty to save weight? have you removed your spare wheel? taken out the rear seat? gone on a diet? :p


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PostPosted: Wed Mar 01, 2006 2:48 pm 
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I have always wondered how those MCM 8" woofers with a low pass , ran off of a head unit would sound. You know for light weight. You can probably mount those in the hatch.

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PostPosted: Wed Mar 01, 2006 2:51 pm 
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don't run anything off the headunit, especially a speaker you're expecting to get bass from!!! :p

6X9s can sound half decent, if they have enough power :) thats a possibility too!!!


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PostPosted: Wed Mar 01, 2006 3:13 pm 
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12mm...oops...didn't convert it...assumed 3/4" MDF. 4x7' 3/4" thick sheet weighs 100lbs though so I don't doubt that his enclosure weighs a lot. You can't run the sub freeair in a hatch either without great difficulty to pull it off properly. Fiberglass is really the best option but also the most difficult. Guess it depends on how light you want the enclosure. Might be time to look at a sub that doesn't require so much volume....

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PostPosted: Wed Mar 01, 2006 3:25 pm 
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the mdf and fiberglass sub box i was running weighed a ton, too. that's why my new design incorporates the spare tire well as the enclosure for three 10" subs. that keeps the use of mdf to a minimum as well as the weight in that only the mdf baffle board is required.

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 Post subject:
PostPosted: Wed Mar 01, 2006 3:47 pm 
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3 10"'s in the spare tire well?? Does that fit with them all facing straight up? Or do you have to angle them?

I didn't think it was that big.

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 Post subject:
PostPosted: Wed Mar 01, 2006 3:52 pm 
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t3 ragtop wrote:
the mdf and fiberglass sub box i was running weighed a ton, too.



Then you made it wrong :-P.

They can weigh an aweful lot but if you build them with lightweight in mind they can be a LOT lighter than wood. The enclosure that took up the back seat of my Swift look, I'm retarded weighed around 60-70 pounds. It had an MDF back on it. Sounds like a lot but the enclosure I had before was half the size and weighed closer to 100lbs. Last year I did a chicken wire "frame" and wrapped it in glass...weighed very little after it was done. I plan to do a couple more this year and once I get it the way I want it I can see some very light enclosures with excellent rigidity.

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PostPosted: Wed Mar 01, 2006 4:29 pm 
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if you think ahead and use reinforcement techniques, you SHOULD be able to build a fiberglass box that is extremely rigid with nearly NO weight (or... if $$ is no object... go Carbon Fiber!). It may be worth it to use some Kevlar/Glass mix tapes as reinforcement, as the Kevlar is quite a bit stronger than glass cloth and TONS stronger than glass mat.

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 Post subject:
PostPosted: Wed Mar 01, 2006 4:39 pm 
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http://web.njit.edu/~cas1383/proj/main/index.htm

have alooksies

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 Post subject:
PostPosted: Wed Mar 01, 2006 6:11 pm 
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make an airtight enclosure and fill it with helium :P

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 Post subject:
PostPosted: Wed Mar 01, 2006 6:49 pm 
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amxdreamer wrote:
make an airtight enclosure and fill it with helium :P


i know that you were kidding but i have sub enclosures that i build years ago that have mylar bladders filled with nitrogen. the rate of compression is different for different gas. helium would be a pretty sensible choice only the molecules are smaller and will pass through the bladder walls easier.

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 Post subject:
PostPosted: Wed Mar 01, 2006 9:23 pm 
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Metropwr wrote:
I have always wondered how those MCM 8" woofers with a low pass , ran off of a head unit would sound. You know for light weight. You can probably mount those in the hatch.


If you're talking about the DVC paper/poly cone w/rubber surround, then I can say that a pair of them in vented enclosures that filled the cargo area sounded pretty good. Not fantastic, but they filled the bottom end quite well. Originally ran them off a Kenwood head unit (might've been a KRC-501, but I don't remember) until I got a 75Wx2 amp to run them dedicated.

Lacked definition compared to the set of 10" aluminum cone DVC woofers that I got from MCM a few years later in the same boxes.

I'd go for the 10" aluminum DVC woofers. Same box size and sound much better.


Chris


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 Post subject:
PostPosted: Wed Mar 01, 2006 10:12 pm 
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Forgive me if my info is outdated... but how can you guys accurately give analysis of a sub when you've ran it off of a head unit? I can't imagine that today's head units are making THAT much more power than head units from back when I used to mess with this stuff (oh Gawd has it been 10 years?!!??! ).

Unless the power requirements for an average mid-line sub have come WAY down, or the available output of a mid-line head unit have gone WAY up (and have gotten MUCH better quality).. I dont see how you're going to get enough power to drive a sub well enough to give an accurate account of how 'good' the sub is....


Phil

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 Post subject:
PostPosted: Wed Mar 01, 2006 10:32 pm 
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Grashopr wrote:
Forgive me if my info is outdated... but how can you guys accurately give analysis of a sub when you've ran it off of a head unit?


CJDavE wrote:
Originally ran them off a Kenwood head unit (might've been a KRC-501, but I don't remember) until I got a 75Wx2 amp to run them dedicated.


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 Post subject:
PostPosted: Wed Mar 01, 2006 11:00 pm 
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gotcha

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 Post subject:
PostPosted: Wed Mar 01, 2006 11:25 pm 
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Grashopr wrote:
if you think ahead and use reinforcement techniques, you SHOULD be able to build a fiberglass box that is extremely rigid with nearly NO weight (or... if $$ is no object... go Carbon Fiber!). It may be worth it to use some Kevlar/Glass mix tapes as reinforcement, as the Kevlar is quite a bit stronger than glass cloth and TONS stronger than glass mat.


Resin doesn't saturate kevlar. You would be better off with a Fiberglass box, due to the price. The best would be a pre-preg carbon fiber, but at what cost is saving a couple of pounds?


Go on a diet, it's better for you in the long run and cost a whole lot less.

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 Post subject:
PostPosted: Wed Jun 13, 2007 3:57 am 
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Point to note here:

Just a word or two about Resonance....

If you know much about MDF,
(not the cheap crap, the stuff pressed with Glue and Formaldehyde)
......then you know that it is very dense.
(my saw blade and router bits will attest to it)

Resonance, for those that want to know works kind of like this:

When the Driver (Sub) plays a tone that resonates at the same frequency as the cabinet, the dB (deciBel) output will increase marginally.

Where this becomes problematic as far as sound quality goes, is when the material that comprises the cabinet has such a high tonal resonance factor that you can hear it buzzing when you play music.

Fiberglass can be used but as a rule of thumb:
8-12 layers of chopped strand woven cloth are equal to the density of 1/4" of MDF. Have you ever heard a Subwoofer box made out of 1/4" MDF.... I have... it sounds like a wet fart! :razz:

So, in closing, if you want to put any kind of real power to a sub, remember the rule:
"Do it right, or Pay someone else to do it"

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 Post subject:
PostPosted: Sun Jul 29, 2007 10:49 pm 
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But with fiberglass you can make a circular-dome shape box, which is much stronger than a flat one. With the MDF you are stuck with flat panels.

I loaded an MCM 8" sub into a horn and even with ten watts it is pretty loud. I think in this application a head unit may run the sub decently.

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 Post subject:
PostPosted: Mon Jul 30, 2007 12:43 am 
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Agreed. 1/4" of glass is equal in strength to 3/4 MDF. At this thickness though resonace can still be a problem...unless you know your way around that :P.

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PostPosted: Mon Jul 30, 2007 4:49 am 
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m wrote:
Agreed. 1/4" of glass is equal in strength to 3/4 MDF. At this thickness though resonace can still be a problem...unless you know your way around that :P.


Hey guy, I don't know what Mobile Audio School you got your degree in a cereal box from, but in the Car Audio INDUSTRY that I was a part of for more than 8 years, we all agree that 1/4" of Glass and mat DOES NOT = 3/4" of MDF.... you'd need about 12 well-soaked layers of chopped strand mat to equal 1/4" of Canadian glue and formaldehyde-impregnated MDF.

Get your facts straight before you make an ass out of yourself. Sorry to verbally bitch-slap you but you just sounded really dumb. If you're unsure.... check out this website... he's an old co-worker of mine and a longtime SPL and SQ competitor, been in several magazines and has written several technical write-ups for the Car Audio industry.

http://www.hzemall.com

Just trying to keep the facts straight here!

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PostPosted: Mon Jul 30, 2007 10:04 am 
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dbadct wrote:
Hey guy, I don't know what Mobile Audio School you got your degree in a cereal box from, but in the Car Audio INDUSTRY that I was a part of for more than 8 years, we all agree that 1/4" of Glass and mat DOES NOT = 3/4" of MDF.... you'd need about 12 well-soaked layers of chopped strand mat to equal 1/4" of Canadian glue and formaldehyde-impregnated MDF.


Fiberglass gets its strength in curves. If your talking flat sheets then yes...you need a lot more glass to equal the strength. In curves..1/4' will get you there. Especialy in an ultra light enclosure. 8 years in the industry huh? Must make you a real expert...I've only been doing this for 15 or so years (I think I'm up to maybe 20-30 glass enclosures and I couldn't tell you how many wooden ones I've done) so you'll have to forgive me if I don't have my facts straight :roll:. Funny though...I've worked in audio shops...worked with installers that have been doing this for well over 25 years...and worked with other that have gone to schools like Mobile Dynamics and Ritop. Thanks for pointing out our ineptitude...we've been doing things wrong up here for far too long LOL.

I just finished up a spare tire enclosure for a Swift. Its 1/4" and I can jump up and down on it without it flexing...and I'm 300lbs. The problem you get with a glass enclosure is, as you stated, resonance. There are a number of ways to combat this. One is for installers to compensate for it by adding more fiberglass to build up density and others use other tricks like sandwiching dynamat between the layers.

Everybody has their own way of doing it. I used to go really thick with fiberglass but after a a few enclosures I realized it just didn't make a difference in the sound and certainly didn't affect the strength or longevity of the enclosure. Try to remember we are talking about a normaly sized enclosure here. On something huge your obviously going to go a bit thicker. On the back seat enclosure in my old Swift I had a 6^'+ enclosure with a pair of 15's getting a touch over 2kw and only the top portion of the enclosure was made thicker...because it was a bit flatter. In the curves I didn't need more than 3/8" and the enclosure was plenty strong.

dbadct wrote:
Get your facts straight before you make an ass out of yourself...Just trying to keep the facts straight here!


I offer the same advice to yourself.

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PostPosted: Mon Jul 30, 2007 4:15 pm 
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Ok, so maybe I came off a bit harsh HOWEVER.........
The original dilemma posted was in regards to getting something that sounded halfway decent.... Sure, curved Glass Enclosures have strength just simply because of the geometrical strength advantages of a sphere.

But for sound quality thin just ain't gonna cut it. And I know you won't argue with me on that. Physics and Acoustics support my argument.

Denser materials have a lower resonant frequency.

End of story.

So in order to build something good AND light... compromise is in order.

A good starting point would be to pick an amplifier with a small footprint.

An MTX RT202 Amplifier if an excellent example. This amp looks small but, performs like a champ!

In order to not have your box "buzz" when the low notes hit and the higher bass resonates, you'd have to have some density to it, no question about it. Otherwise, it'll sound like crap. I don't agree with adding Dynamat. Personal choice I guess.

By the way, you mentioned "Ritop"......Never heard of that place. And isn't Mobile Dynamics a one-day course?

Not to toot my own horn but there's a little magazine called Performance Auto & Sound, and there was an MTX Tiburon with 3 15's in the back. If you read the article, my name's in there on the install team.

Where have you installed? I'd like to know what your work experience in professional shops is. Feel free to email me. It's on my profile.

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