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Old 10th January 2004, 02:04 AM   #1
amo is offline amo  United States
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Default 5 inch walls?

There are a few people that follow a doctrine of not worrying about "deadening" the speaker box, and insted they make it "breathe" with the music, much like the wood in a nice violine or chello. Others believe in making the box as innert as humanly possible (while others do not use boxes at all ). I want to build the innert veriety, and in true DIY spirit, I want to over-build the heck out of it. The question is, how much is too much? MDF resonates at one frequency and ply at another, so sandwitch construction with braing should be good... But what if your sandwitch has 6 layers? I am not talking about the front baffle, as it has its own considirations. But all the sides, i think, can benefit from the extra mass. Also, it seems joining such thick panels together should be very easy, since the surface area of the joints is so large... Perhaps another benefit is that with joints being as large as the cavity itself, minimal bracing will be needed. Am I wrong? Will I just end up with a wooden mess? Thanks in advance.
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Old 10th January 2004, 03:59 AM   #2
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Default SAND SANDWICH

Have you considered a sand filled sandwich box? Thick well braced inner cabinet, thinner skin outer cabinet with 1"-2" of sand in between. The heat generated by the vibrating sand absorbs the bass speaker's energy. Plus you can vacuum out the sand if you need to move. Even a dipole baffle can benefit from sand dampening.

The baffle around the speaker cannot be so thick that it creates reflections or limits air flow. Aluminum plate or steel reinforcements might be worth considering.

Midrange and tweeters generate little vibrational energy and packaging is not as difficult as long as they are isolated from the bass cabinet's vibration.
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Old 10th January 2004, 04:03 AM   #3
navin is offline navin  India
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sand filled is a very nice concpet but i found it diffcult to execte because it was diffult to keep the 2 wood layers independant. somewhere they had to meet.

so i decided to use curved sides to pre stress the wood and to form non parallel sides.

i also used ply - mdf combo.

see pic.
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Old 10th January 2004, 04:05 AM   #4
cowanrg is offline cowanrg  United States
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overbuilding is AWESOME. i think my pre-amp will weigh in at around 70 pounds or so

if you wanna be really cool, do granite walls. or as LineSource suggested, do a sandwich of granite, sand, then granite again
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Old 10th January 2004, 04:08 AM   #5
Variac is offline Variac  United States
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Nah, granite, sand, aluminum
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Old 10th January 2004, 05:42 AM   #6
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I believe there are a few threads around about using nonresonant resin molded to shapes.
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Old 10th January 2004, 05:57 AM   #7
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Amo,

I have a few suggestions. Don't just focus on one parameter - ie thickness, but consider the speaker box as a system. There are a number of ways to make an inert box, and if used cleverly together, they create a synergy. A 50 kg box is more impressive if it can match a 100 kg box.

A few ways to get an inert box:
- wall thickness
- bracing
- mass loaded damping
- constrained layer damping
- curved walls

1. wall thickness - I doubt anything thicker than two sheets of 18mm MDF is of any benefit if you use the other methods as well

2. bracing - construct a matrix so that all walls are solidly connected to the parallel wall and each bracing sheet is braced by the connection to other bracing sheets

3. Mass loaded damping - one member of the bass list recommends using a layer of non-curing oil based modelling clay applied to the internal walls of an enclosure. This method can be quite heavy.

4. Constrained layer damping - a box within a box - two separate layers which are joined by a flexible adhesive such as liquid nails. This is considerably more effective than doubling the thickness of the walls. This is a technique which has long been used in applications such as industrial noise control.

5. Curved walls - this makes it possible to make the walls thinner.

I think the ideal overkill design would include all of the above, perhaps with the omission of mass loading. Say with 36mm walls. I like the idea of overkill, but I dont' like the idea of excessively heavy. It means I need to get someone to help me lift thing, and so my DIY projects become less autonomous.
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Old 10th January 2004, 06:51 AM   #8
Variac is offline Variac  United States
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It depends on the frequencies that the drivers in the box are reproducing I think. Bass boxes tend to require bracing and stiffness to keep the walls from flexing as a whole. If you can get the resonance of the panels higher than the freqs that you are reproducing, then they are less likely to resonate.

Higher frequencies require more damping of the box I believe.
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Old 10th January 2004, 05:21 PM   #9
amo is offline amo  United States
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Thank you everyone!!!

My original intention was to machine "slices" of marine ply and press them together like TAD's model 1. I actually found a place that will do CNC routing for me. This design incorporates very thick curved walls and built in cross-bracing, and has no joints, other then horisontal... But I expect this method will set me back a good $600 USD for the unfinished cabinets (just wood and glue and CNC). So I decided to do a scaled down version of this project for now, using fewer drivers and going 3-way instead of 4-way. I also though I could use a more "standard" cab design. The reason I like the idea of such thick walls, is because they in fact eliminate the need for bracing and other more complicated tasks. I guess I will try it because it should be quick and I probably have all the wood already. I will see how it looks and sounds and if it is no good, I will go back to plan one and CNC thin layers. I also really like the idea of all that mass simply because there will be 2 ten inch drivers, and I feel like they need a sturdy base to play from...... Will see, and I will keep everone posted. Thanks again.
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Old 10th January 2004, 05:41 PM   #10
Mark Kravchenko --- www.kravchenko-audio.com
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Default Speaking to an Excess

In 1989 I designed and built a line of loudspeakers that went nowhere . They sounded great but could't be marketed. Here's why.

They consisted of a box withan extra thick baffle using you idea of constairned layer dampening. The interior of the box was made using a concrete pier tube that was cut and fitted in grooves on the baffle , the bottom and the top. We shaped it so that most interior standing waves would kill themselves in two to three reflections. Just observe a drop of water in an eliptical bowl and you will get the drift of the idea. ( just guess where I came up with that brain storm ) The voids in the interior were filled with dry sand. The whole mess was filled and tapped with rubber mallets to create a really ( THe deadest box I have ever seen bar none. Wilson audio is the only player in that field, and I believe that we beat them for a hell of alot less money )dead. It makes for a heavy cabinet. You have to calculate for an elipse in the volume end of things bit it is one of the best systems I have ever seen or heard.

Food for thought.

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