Hi Robatoy,
I am talking about effectively a box which holds the completed speaker.
Thanks, JG
"Robatoy" wrote in message
ups.com...

JGS wrote:
We are building an entertainment unit for a client. He designed it
himself
and did a nice job. He wanted the boxes that hold the speakers to be
lined
with MDF.
Now that we have built the unit we have found that here is room at the
top,
bottom and back of boxes (cabinets) for 3/4" MDF but because of the size
of
the speakers there is only room for 1/8" (if it's even available) for the
sides.
Is 1/8" MDF going to make a difference? Is there another material to
use?
Or the broader question, is MDF required / desirable at all.
Thanks, JG

This subject is close to my heart.

"the boxes that hold the speakers"... please clarify. Are you talking
about an enclosure that will house a completed speaker box...or the
speaker box itself, containing only the drivers?

I need more information in order to give you an accurate asessment. MDF
'can' be a solution. 1/8" MDF is not going to be a solution to any
vibration as it will act like the skin on a drum and will start to
behave as if it was a transducer on its own (passive radiator-like
behaviour with all its phase complexities.) Stiffnes and mass plus
internal volume will create the box's "Q". MDF has good mass, but is
not very stiff. Balic birch has lower mass, but more stiffness. A
sandwich of baltic and MDF with adequate internal bracing can make a
nice speaker box. Internal reflection has to be dealt with via
dampening/non reflective material as the sound comes off the back of a
woofer with as much vigor as the front. When adding stuffing, keep in
mind that the woofer then thinks the air behind it is actually heavier
than it is changing the resonant frequency of the enclosure. Thin walls
then add to the dilemma by allowing the woofer to think the box is yet
bigger again. Insulation on the enclosure inside walls are only
effective up to the wavelength i.e. a 1" pad will do nothing below
1KHz.

All speaker enclosures are a compromise. You want deep bass or tight
bass? Can't have both with the same driver (woofer). There is only one
way to stop transmitted sound: mass/stiffness. HDF is a nice product,
so is HDPB. Two 1/2" skins of BB with 1" sand in between is VERY
effective, but a bitch to build.

For a solid engineering reference:
http://www.colloms.com/pages/works.aspx

Electroacoustics was my favourite subject, btw.

r