Are exotic speaker cabinet materials overrated?

@simao  I can't take all the credit. The idea comes from the Northcreek cook book.

To get the stuff to stick properly I coated the inside cabinet walls with contact cement first. Then pumped several tubes of silicon into a bucket and mixed in sand to what I felt was a good consistancy. Then, with gloves, spread by hand the entire interior. No need to smooth it. Just glop it in there. Let it be rather bumpy and irregular. Drys in a day and seals the cabinet as well as adding dampening to every square inch. Goes thick into the corners. Takes a little bit more effort but I believe it's superior to ANY stick on dampening pad.

Thickness is variable but I use about 1/4" thick in some places a little more. It's really up to you. Then goes in the normal foam or fiber fill stuffing.

The stuff stays soft and rubbery for decades and adds a nice amount of mass to the cabinet.

@yoyoyaya  You're right, basic concrete is not a good choice. However, there are additives that can be mixed into concrete that makes it an excellent material to use especially when creating special shapes. It also requires a mold. The complexity becomes far greater.

Polymer modifiers, Latex/Acrylic polymers

• Increase tensile strength
• Increase internal damping
• Improve adhesion between aggregate and cement

Pros for speakers:

• Reduces brittleness

• Adds loss factor (less ringing)

• Improves edge integrity around driver cutouts

MDF is not “cheap” — it is acoustically well-behaved.
Concrete is not “high-end” unless engineered to avoid its own strengths.

The only advantage concrete may have is for molding shapes. MDF remains a superior product if properly braced and dampened.

Adding substances to Board Materials with the intent to improve the board materials Damping Factor, is known about for a long time in circles where there is a importance on such matters being aired.

Modellers Putty from the Brand Newplast, measures with a Damping Factor that is 50% better than Plasticene.

Newplast added to Board such as MDF has created a DF of 0.3, which is very attractive, but intrinsic properties for Dissipation is not attractive when measured.  Dissipation of most board type materials coated with a material that improves the DF, does not produce a board type that match's a RIDWB intrinsic properties.

Control of resonance through Dissipation is an extremely attractive intrinsic property for a material. High Damper Factor alone does not win over, hence Plinths for TT's using such a design have been Superseded in use for many years, where Dissipation is also a highly valued area of the designs. This same practice is now very evident that it is extending into Structures used for Speakers. 

@gdaddy1 thanks for the details. you do this when you have 5 sides of the cabinet glued and b4 the crossover instal?

also my son and I recently put together a Parts Express C- Note and decided to cut our own 3/4 inch BB in lieu of the 1/2 inch mdf you can get if you order the cabinets. 

I would think that availability is a significant concern for those using exotic woods. A guitarist friend of mine who was a performance major at CCM, had a Brazilian Rosewood guitar. It was the envy of every other guitar major in the conservatory because Brazilian Rosewood is under protective status. 

Additionally, my understanding is that acrylic glass is pretty much non resonant. My power amp is made from sheets of acrylic glass with aluminum heat sinks. Its also aesthetically pleasing to look through the acrylic glass whenever the amp is powered up.

Lastly, my previous speaker tech made me a pair of headphones. The value in this headphone is its 50mm driver. The hardware is plastic. I was talking to my local dealer and he advised me to make wooden supports for the drivers, claiming they will sound better. I guess that's my next project.