Enclosure Project

[andr3w.4]

Hi,

Im currently working on a project for school that invloves designing speaker enclosures using different materials (really different materials) to prove which is best suited to speaker enclosures. Then measureing this by using pink noise and programs etc, etc.

I currently have brought two 3-way speakers (6 1/2") and running them through an amplifier.

Im currently up to the stage of designing the shape of the enclosure. I have been researching different designs (and heaps of them) and evaluating them.

Is there any particular design or size of an enclosure that is ideal for 3 way speakers? I am currently looking for a few different designs other than your traditional box/square shaped enclosure. Can anyone help me out with this? It cant be to complex of a design as i have to make 6 or so of these designs with different out there materials (villaboard, fibreglass, plastic, etc).

I appreciate any advice and help anyone will be able to give for this project. (Feel free to advise a few materials as well need a few more besides the traditional MDF)

- Andrew -

[sparky77]

I did an experiment already with concrete cabinets, doesn't work so well unless you have MASSIVE amounts of sound deadening material stuffed int he cabinet, concrete reflects sound too efficienly. You can hear the sound reflections through the cones of the speakers. You must take into consider some materials are very well damped and absorb sound while others reflect it.

[WmAx]

For most efficient acoustic absorption material internally, line all walls with 2" high density rockwool board or fiberglass board(4-8lb/ft^3 density)on all walls, except rear, place 3-4"; this is the material as used in commercial/industrial applications and in the highest quality acoustical treatment products. You can create an absolutely reflection free environment internally with proper use of such material.

-Chris

[WmAx]

In order to mitigate panel resonances to very low levels, use the stiffest materials/construction possible. Wood products are a poor choice when compared to metals/ceramics/concrete; or at least when used in full-range band using traditional construction techniques. Do take note that metals/ceramics/concrete have poor internal dampening properties, so you may have to apply mass loaded dampening materials to control this behavior for optimum behavior. If using thick concrete, a single, non-anchored application of dampening may not be sufficient; a constrained layer sandwich technique using this material should be implemented in this case to have maximum efficiency. Alternately, you could mix materials into the concrete to increase it's internal dampening properties. However, wood products can be used with great effect with appropriate construction techniques and/or in specific band-limited applications where you can feasibly push the panel resonances above the passband of the particular speakers being used in the application. Note: Standard 3/4" MDF with shelf bracing every 5-6" typically yields first occurring panel resonances in the 200-350Hz range. In the most extreme building methods using only wood products, first occurring panel resonance modes can be typically pushed to 600-800Hz. What this means is that you could place a woofer or lower midbass limited driver that operates under the respective panel resonant frequencies and the cabinet would be non-resonant. However, for actual mid-range band itself in the upper range, a physically isolated separate cabinet system designed differently to deal with resonances in it's passband would be required. The B&W Nautilus 802D is a textbook example of this design method: it uses a woofer module made of traditional wood products with extreme bracing to push the panel resonances well over the passband of the woofers; a suspension system mounts the mid-range module to the woofer cabinet to isolate them, and the mid-range module is made from a highly dense composite polymer with high internal dampening properties. In addition, the mid-range drivers are fully suspended/isolated from their own enclosures to prevent direct mechanical excitation from the driver frame to enclosure.

One wood technique as an example, that I found works very well for full range use, is to use external shell 3/4" cabinet grade void free plywood. On the inner side of this, adhere 1/8"-1/4" Dynamat or similar material. Using an effective aluminum to wood bonding glue/agent, glue the aluminum exposed side of the Dynamat to 1.25"-1.5" solid oak(you can glue togehter 2x 0.75" pieces to get desired thickness). For bracing, place oak internal braces(in X, Y, Z fashion) leaving no more than 3" radius from any point non supported directly.

-Chris

[ISLAND1000]

If your experiment only involves testing with pink noise then you won't have to bother with any internal treatments.
If your experiment mostly involves using really different materials include; cardboard, MDF hardboard, plywood, various species of real wood (ie: pine, oak, birch), metal, plastic sheets, plastic stoarge boxes, sand filled void walls, cloth, free air, and for amusement bread slices.
3 way speakers usually end up being built in a rectangular box. There are several esoteric reasons for this. There is no reason though that just for experimentation you couldn't use say a gas can . . . . empty.

[WmAx]

I did forget the person would only be using pink noise to test the systems. Unfortunately, simple microphone recording of external output in normal acoustic spaces would be unable to reliably tell the speaker output from the cabinet output. One would need at minimum to use vibration measurement equipment(accelerometer) and analyze several points of each enclosure to quantify the cabinet material/construction differences.

-Chris

[andr3w.4]

I have some professionals in the industry helping me out with the testing so that is pretty much covered its just building the enclosures thats hard.

The 6 materials I will be using will be ply wood, plastic (of some sort), villaboard, concrete, fibre glass, aerated concrete, sand filled void walls (as someone had suggested [thanks!!].

Thanks to everyone for replying

- Andrew -

[ISLAND1000]

Sounds like an A+ to me.