What 's the different between MDF and HDF ?

There is much written on the net, about MDF or medium density fibreboard, have a search
trought e.g. Dogfile. There was a site dedicated to MDF
subjects, but I was unable to find it again.
HDF stands for heavy densyty fibreboard, i.e. it is
made from harder, more dens wood.
You often get a better result if you combine some different
materials, e.g. plywood and MDF, glued together.Even glueing
together sheets of MDF, will probably give better results
than using a homogeneous sheet!
If you need more advice about this subject, please feel free
to mail me!
Regards
Håkan Ståhl
Sweden

Sorry,I was in a hurry when I wrote the response.
More correctly: HDF stands for high density fibreboard, i.e.
it is made from harder wood,with higher density.

May I add, that good speakerbuilding takes place at
the crossroads between art and science,because we don´t know all the aspects of it.Harder and stiffer materials give rise to different forms of vibrations, compared to softer materials.

MDF has it´s drawbacks as an material for building enclosures.The negative properties of MDF, can be deminished by combining MDF with a very different material,
with a different modulus (resistence to bending),and a different density. I have obtaind good results with a
combination of MDF and slabs of granite.
Adding a third material, in an unregular fashion, will
still improve the situation.

So, by only using thick walls in a loudspeaker enclosure,
we may have gained too little.
We also have to consider what frequences we want to reject.
I have built large enclosures for my bass drivers, and
these enclosures really withstands the lower frequences
(up to about 80 Hz) that they are intended to deal with .
Trying to drive this speakers with signals up to 700 Hz
was more discouraging....

Regards
Håkan