A brief discussion on resolving systems with a gentleman who makes
single driver speakers in what appears to be a folded Voigt Pipe
design turned briefly to resonances. My general contention was that
since he was using alder as opposed to MDF, that it would result in
additional resonances which would color the sound. Some mild umbrage
was taken. The conversation went like this. Am I somehow missing
something here or is this a combination of spin coupled with some
factual errors regarding wood?

Him: Sure, it will resonate. So will wood, steel, micarta, MDF, and
ANYTHING ELSE that has any mechanical stiffness. How it resonates and
whether it's important depends upon its stiffness, it's internal
mechanical losses, how it's mounted and secured and how it's
mechanically loaded and acoustically excited.

Me: This should not be interpreted as the intentional use of materials
to impart resonances as opposed to MDF which has a more predictable
nature? In ways, it reminds me of the various woods that can be used
in the construction of guitars where I think MDF, apart from being
heavy, might not make for the most pleasing of sounds.

Him: No, you have interpreted incorrectly. A common misconception
though. But yes woods do flavor sound, for guitars and speakers. Part
of woods amazing quality is that it can be made to resonate more, as
in the case of a guitar or piano, but that same piano usues wood to
isolate the vibration (the case) so the most energy can be released to
the room (more music)
What solid wood does in the case of my speaker is resonate LESS. I use
solid wood for it's weight vs ridgidity, it is far more ridgid than
mdf. And contributes actually less in the form of self -resonance. In
addition we have have made this speaker from teak, oak, mdf, plywood,
pine, alder, maple and cherry. All have distinct sonic "flavors". The
solid wood particularly the maple extends bass and allows the very
absolute maximum energy transfer from driver cone to port to room
without imparting audible resonance of it's own. The mdf example
sounded muffled and lifeless. My designs pursue maximum energy
transfer from electrical to the room both from the front of the driver
and the rear.. I once made a xylephone from different species of wood,
the keys all the same size as an experiment. 5 octaves were covered
just from locally growing trees.
One really has to integrate decisions about grain orientation,
thicknesses of wood as well as joint strength to carry this discussion
comparing materials to any logical extent as it relates to
speakerbuilding.

Me: If it's your position that cabinet augmentation is desireable,
then we stand on opposite sides. If you feel that it gives your
speaker a characteristic sound that is pleasing, I can live with that.

Him: The concept that you propose I subscribe to is incorrect, you
mis-nterpret my intention of reducing resonance through the use of
solid wood. MDf does not eliminate resonance. It reduces it
drastically, such that it also reduces musical content via energy
absorption.

If you look at speakerbuilding from another angle, the anthropological
veiw, we see that as forests shrank and skilled labor was replaced
with machinery. The square box (usually sealed or ported0 became the
de-facto method of augmenting the bass drivers own free-air resonance
(fs) or limiting it in the case of sealed enclosures. I submit this
has every thing to do with the advent of high powered solid state
amplifiers as equally as declining skills in our labor pool. MDF was
not created for eliminating resonance in speaker boxes but rather to
utilize vast stretches of inadequate lumber stocks. From an acoustical
standpoint MDF is dampening. It absorbs sound due to it's mass and
weight.

I am trying to allow the energy that would be absorbed by MDF to be
better utilized re-creating acoustical energy in the room. Of course
you do not want your speakerbox to vibrate, but using a "dead" panel
is the easy way out and not neccesarily the best method. ANd I think
Franco Serbelin agrees.