Sholling,
So I’ve read through this thread and I’m slightly confused. What is you actual goal? Are you trying to reduce cabinet resonance by physically reducing the amount of acoustical energy being transmitted to the cabinet walls, or are trying to absorb energy to prevent it from being reflected back into the cabinet?
It is my simple understanding that these are two complete different beasts and must be approached in different manners.
The foam+MLV that you are getting may be a good material for reducing transmission of energy to the outer cabinet, but it is a less than ideal product for reducing internal reflections.
I will differ to Wmax for the discussion of cabinet resonance, as he is definitely the expert, and I’m merely a neophyte.
But if you are trying to reduce internal reflection I can tell you that, the closed cell foam (CCF) is inferior to fiberglass for sound absorption.
This says it better than I can while at work.
Acoustics:
Because CCF is generally more rigid and dense than fiberglass insulation, it does not absorb sound as well as fiberglass. This
is especially true when one compares noise reduction coefficients and sound transmission classification between the
materials. Laboratory tests performed in reverberant chambers confirm that discharge sound values are several decibels
higher when using CCF than with fiberglass product. See Acoustic Property Comparison chart.
Conclusion:
The use of Closed Cell Foam Insulation in HVAC appliances is a viable alternative to fiberglass insulation. CCF offers
several advantages over fiberglass with regard to moisture absorption and its resistance against microbiological
contamination. It is a superior product in its durability when compared to fiberglass. CCF however does not perform as well
as fiberglass acoustically. If acoustics are not the primary concern on a project then CCF is an acceptable alternative.
Hopefully moisture and durability should not be a concern inside of a speaker cabinet.