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Lining a Speaker Cabinet



 
 
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  #1  
Old January 21st 07, 11:32 AM posted to rec.woodworking
JGS
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Posts: 95
Default Lining a Speaker Cabinet

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


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  #2  
Old January 21st 07, 01:15 PM posted to rec.woodworking
CW
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Posts: 926
Default Lining a Speaker Cabinet

MDF is difficult, if not impossible, to get to resonate. That is the reason
for it's use in speaker boxes. Little is better than none. How much
difference it actually makes is dependant on may factors. Couldn't hurt.
"JGS" wrote in message
...
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




  #3  
Old January 21st 07, 06:55 PM posted to rec.woodworking
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Posts: 58
Default Lining a Speaker Cabinet

On Sun, 21 Jan 2007 06:32:28 -0500, "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


What are the boxes made of? Plywood? Plywood will resonate more in the
midrange frequencies than MDF, MDF will resonate more in low
frequencies. Adding layers of MDL to stiffen the enclosure sounds like
it makes a lot of sense. I am not certain where to get 1/8" MDF and I
don't think it will stiffen appreciably.

I wonder, though, if you can add thicker MDF in part of the side
panels.

You can do a couple of other things. You can run bracing along or
between the side panels. I suggest NOT at 1/2 the height or width;
using a different spacing will effectively break up the panel into
smaller less resonate sections and the amount of resonance will be
reduced, and the resonance frequencies of each section will be
different and so not combine to a larger peack.

You can check out antiresonant Deflex panels from a source such as
Madisound
(http://www.madisound.com/cgi-bin/ind...7226 8.22629),
or perhaps Sorbothane (reputedly not as effective).

By the way, I see Madisound is selling a 1 edition-old issue of "The
Loudspeaker Design Cookbook" for $11 (normally $30) and if you
purchase some Deflex, I suggest you get one of those. It will no doubt
have some very specific info on speaker cabinet construction.
  #4  
Old January 21st 07, 07:00 PM posted to rec.woodworking
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Posts: 3
Default Lining a Speaker Cabinet


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


Speaker enclosures are usually designed from the inside out rather than
the converse. MDF is used for its density (damping ability) and
rigidity, properties that keep the box from vibrating along with the
driver (speaker). The box is also usually air tight unless there is a
port that is tuned as part of the design.

At this point I would question the lining of the sides with only 1/8"
MDF unless it is securely glued to the existing sides, which are
hopefully already pretty substantial.

As an alternative I would suggest a sheet damping material similar to
this:

http://www.partsexpress.com/pe/showd...number=268-035

Good luck.

Wes Stewart

  #5  
Old January 21st 07, 09:33 PM posted to rec.woodworking
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Posts: 1,420
Default Lining a Speaker Cabinet


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

  #6  
Old January 21st 07, 09:47 PM posted to rec.woodworking
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Posts: 192
Default Lining a Speaker Cabinet

You mean the speaker diameter plus 1/4" is all you have for the side space?
If so, could you route out the two front part of the sides on the 3/4" MDF -
the left and right side front edges where the speaker goes into it? Looks
like a common practice for speaker construction where the outer edge or the
speaker comes almost next to the outer box edge if I'm not mistaken.

Assuming the box is not very big, I don't think too many people will notice
the sound quality difference between 1/8" and 3/4" for the side panels after
you fill up the box with insulation material.


  #7  
Old January 22nd 07, 11:44 AM posted to rec.woodworking
JGS
external usenet poster
 
Posts: 95
Default Lining a Speaker Cabinet

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



  #8  
Old January 22nd 07, 02:54 PM posted to rec.woodworking
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Posts: 44
Default Lining a Speaker Cabinet



On Jan 22, 5:44 am, "JGS" wrote:
Hi Robatoy,
I am talking about effectively a box which holds the completed speaker.
Thanks, JG"Robatoy" wrote in oglegroups.com...


In that case, why do you need them at all, or perhaps just use a
product like 1/4" oak plywood. 1/4" MDF would be like spagetti, not a
good product so they don't make it AFAIK. You can get 1/4" masonite of
course, and that is pretty stiff and paintable smooth.

  #9  
Old January 22nd 07, 05:19 PM posted to rec.woodworking
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Posts: 192
Default Lining a Speaker Cabinet

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

Electroacoustics was my favourite subject, btw.

r


I never understood why electrostatics cost so much - $10K for a headphone
and a few X more than that for full panel speakers. Years ago I build one
with some spare parts laying around and I'm sure I could make the sound more
"hi-fi" if I play with it some more. Those spare parts wasn't worth more
than $10 at the time.

I suppose that's the same reason why a local custom wood shop charge over
$20K for a table - custom design with exotic wood.


  #10  
Old January 22nd 07, 05:58 PM posted to rec.woodworking
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Posts: 1,420
Default Lining a Speaker Cabinet


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

Electroacoustics was my favourite subject, btw.

r


I never understood why electrostatics cost so much - [snip]


Electroacoustics is a subject that deals with the conversion of
electrical energy to acoustic energy via a transducer, or backwards (as
in microphone)

Electrostatics on the other hand, are a form of transducers which do
not operate on an electromagnetic motor, but operate on a totally
different principle.
The $10K headphones (I'm assuming you're talking about Stax
Earspeakers?) are simply the most incredible experience for $10K you
can have...with a few caveats like you need to sit on a subwoofer for
the tactility of the bass, and the recording should be made with the
Sennheiser Kunstkopf microphone method.
I have a Stax tone-arm which has never been equalled in any way, shape
or form. That used to be one crazy little company.

Full-range electrostatic loudspeakers have a myriad of problems in
terms of physics limitations as well as reliability issues when pushed
to sound pressures we expect from today's dynamic range-heavy sound
sources. Many need to be sub-woofed, which totally screws any ideas of
a single sound source.

If all you listen to is harpsichord or cello, a pair of Quad ESL63's
will make you weep. (with the right amps, in the right room, yadda,
yadda....)

 




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