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Old 22nd January 2007, 01:25 PM   #1
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Default Enclosure Construction Analysis

This question came up in a discussion I was having with someone...

What kind of real world effects does the enclosure have on the loudspeaker?

There is a lot of information/opinions floating around about the proper way to build an enclosure. Materials, wall thickness, stuffing, deadening, etc however it all seems to be more opinion and "ear" testing than absolutes backed by test data. This to me goes beyond what is trying to be accomplished with a diy loudspeaker.

Folks test, retest, and test some more when it comes to the drivers and crossovers, however it seems the enclosure just get built by opinion.

I guess what I'm looking for is how much is too much, I have heard opinions from 1/2" thick walls braced with no more than 8" unbraced panel to 1 1/2" walls with no more than 4" unbraced.

Has anyone done any real testing or analysis of what the enclosure construction does with regards to actual sound reproduction? It just seems to me, if you spend so much time tweaking a system to be as "perfect" as possible within reason, that wouldn't you also include the actual construction of the enclosure as high on the priority list?
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Old 22nd January 2007, 01:36 PM   #2
sreten is offline sreten  United Kingdom
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Default Re: Enclosure Construction Analysis

Quote:
Originally posted by elambert

... if you spend so much time tweaking a system to be as "perfect" as possible within reason, that wouldn't you also include the actual construction of the enclosure as high on the priority list? ...
Hi,

Yes you should, but its a different skillset for most.

All you can do is apply some mechanical engineering common sense,
or invest in some serious FEA (finite element analysis) software.

There is a lot of misinformation about what makes a "good" cabinet.

/sreten.
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Old 23rd January 2007, 02:20 AM   #3
Ron E is offline Ron E  United States
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Some will try to sell you on thick walls, double layers or constrained layer damping, etc, but IMO all that thick or double walls gets you is a hernia. Even if you make the walls out of concrete, the cabinet will talk, and the high Q resonances from very stiff materials may actually be a detriment, rather than a benefit, contrary to what some believe.

There have been studies of box materials, one which claimed particle board is better than any other common material because it has better internal damping than plywood or MDF. The enclosure material should have a high stiffness to mass and low energy storage. THere is nothing wrong with Plywood, particle board or MDF in this respect. MDF machines nicer than the others, but plywood is stiffer and lighter.

All that is really required is a well constructed box of 3/4" material, having tight joints and shelf braces and ribs to stiffen large panels. Struts going between panels are ineffective.

I want to eventually make a cabinet out of composite materials, perhaps a glass or carbonfiber/foam sandwich material or commercial honeycomb/fiberglass/carbon fiber composite. This has been done in the past by Celestion and the enclosures were well rated. These panels are a bit more difficult to join than wood and I expect the MFG costs were relatively high.
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Old 28th January 2007, 02:34 PM   #4
Empee is offline Empee  Netherlands
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Too bad its only in Dutch, but this guy did some serious measuring on materials:

http://www.hsi-luidsprekers.nl/kastm...nonderzoek.htm

bottom line; each material had a certain resonance / sound.
It helps making the sheet thicker, but it's best to combine materials so they cancel out each other's resonance.

He's suggesting making sandwich constructions out of different materials.
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Old 28th January 2007, 03:42 PM   #5
holdent is offline holdent  Canada
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Excellent link! I used Babelfish to try translating it from Dutch to English. I think he got the best results using 18 mm of MDF + 11 mm of concrete board (?) + 18 mm of Birch ply with strenghtening ribs (?) and 80 mm of fiberglass. If I understand the translation properly, this will be one thick and heavy cabinet with walls roughly 2" thick!
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Old 28th January 2007, 05:42 PM   #6
holdent is offline holdent  Canada
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Here's another link with test results advocating the use of a sandwich of materials - http://www.silcom.com/~aludwig/Louds...ration_damping . In this case the author used a sandwich of 3/4" MDF with layer of roofing felt and 1/4" masonite called a "constrained layer technique". He also found that
a) bracing did little to eliminate panel vibrations except under 100 Hz and that
b) filling an enclosure with fiberglass insulation was the most effective method of reducing cabinet vibration.

At http://www.speakerbuilding.com/content/1011/page_9.php they advocate a sandwich with a thin outer layer (3 to 6 mm) with a layer of sand in the middle (9 to 15 or 20 mm). The two outside panels should have very little contact. This site also has a number of other tips including use of bracing, how to fasten drivers, etc.

And more... (once you know what to look for!):
http://www.audioholics.com/techtips/...oudspeaker.php

Unbelievably Sony managed to patent this - http://www.patentstorm.us/patents/5949033-claims.html

A neat and related (and easy to build!) way of providing component vibration isolation called the "Seismic Sink" is detailed on the Hawthorne Audio site at: http://www.hawthorneaudio.com/forum/...ghlight=tennis. It uses a platform resting on tennis balls in a box filled with sand.
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