mdf sandwich quessie

mattpman · 28th March 2002, 05:27 PM

Hi all,

My local DIY store, being useless, doesn't have 1" MDF, so I am going to sandwich 3.75 and 0.25 to make it, but on which side do I mount the drivers? 2 out of the 3 have routing holes of 0.25, so surely I mount them on the "thin" side????

Will steel in a cabinet produce a "ring"?

Also, I saw a recomendation to paint the baffles using that "fleck spray" stuff, not as course as sand, I'm sure you all know what it is, but would it degrade the sound by not having a smooth surface????

Thanks for all your help,
Matt

cyclotronguy · 28th March 2002, 05:58 PM

Matt,

I have never had a problem with sheet steel inside a wood product speaker cabinet. The two materials having vastly different resonant frequencies seem to effectivey damp one another. This presumes you have them firmly bonded together.

Cyclotronguy

jam · 28th March 2002, 07:36 PM

Cyclotronguy.

You have discovered 'constrained-layer damping'.

Jocko homo give the man a medal!

Jam

cyclotronguy · 28th March 2002, 09:10 PM

Jam,

Discovered? I'm not old enough for that accolade, but thanks for the boost.

Cyclotronguy

mattpman · 28th March 2002, 11:51 PM

excellent, thanks cyclotronguy, I only need to use a bit, because one of the braces is about 1mm too small

.

For mass I'm going to use sheet lead, I heard that that was good?

Anyway, does anyone have any ideas about my first question, which way I should use the sandwich

?

thanks a lot,
Matt

turbo · 31st March 2002, 06:52 PM

I have the same question, only on the bonding part for the
baffle..Is it best to use something that has some damping --
say liquid nails on MDF<==>MDF bonding, or bond them such
that it is one contiguous piece?

Also curious about the metal sheeting..so would ask this question
for that concept, too.

Tom

mattpman · 31st March 2002, 07:17 PM

Hi Tom, I've found a number of sites reccomending lead sheeting, heres a quick quote:

http://www.humanspeakers.com/diy/cabinets.htm#build

"Lead flashing, which comes in 12" wide, 1/8" thick rolls, and weighs about 2.5 pounds per running foot, makes a wonderful panel damping material. It is easiest to attach with construction adhesive and a few staples. It does not have to be neat or lie perfectly flat. Wear gloves when handling it and don't leave it where children or pets can play with it, since it is poisonous if ingested. It will be safe inside your speaker box."

Hope that helps :-)
Still dont know about the MDF bonding though :-(
Matt

grrrrr, B&Q cut the MDF wrong AGAIN!!!!! grrrrr!!!!!

navin · 16th April 2002, 12:52 PM

I am hoping to build a pair of speakers as follows:

dimensions
46" high
30" deep
8" wide

drivers:
12" Audio Concpets DV12
6" Scan Speak 18W8546
1" Scan Speak 2905-9900

The 12" will be side mounted.

Question:
for all panels but the baffle I hope to use layers of 6mm MDF with lead sheet in between layer 1 and 2 and snd between layer 2 and 3. Does this make sense?

Since the 12" is side mounted how does one mount it on a multilayer baffle (MDF-lead-MDF-sand-MDF)?

Does this mean that I would only be able to use a multilayer baffle on the sides that dont have a driver mounted in them?

Does it make better sense to use only lead sheet and not sand at all on one side (the side where the 12" is mounted)?

Another alternate is a MDF-lead-MDF-RBF-MDF sandwich. RBF means Resin Bonded Fiberglass. Using polyester resin and fiberglass rovings/mat/mesh in a mixture one can spread this across a MDF sheet and then lay the next sheet of MDF on top. Is this any good?

Lastly another idea is that I bend the MDFon the sides thereby flex it and prestrssing the cabinet walls. This can be done before th resin ins dry so that the fiberglass also dries as per the curve of the bend.

28th March 2002, 05:27 PM	#1
mattpman diyAudio Member Join Date: Jan 2002 Location: UK.	mdf sandwich quessie Hi all, My local DIY store, being useless, doesn't have 1" MDF, so I am going to sandwich 3.75 and 0.25 to make it, but on which side do I mount the drivers? 2 out of the 3 have routing holes of 0.25, so surely I mount them on the "thin" side???? Will steel in a cabinet produce a "ring"? Also, I saw a recomendation to paint the baffles using that "fleck spray" stuff, not as course as sand, I'm sure you all know what it is, but would it degrade the sound by not having a smooth surface???? Thanks for all your help, Matt

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28th March 2002, 05:58 PM	#2
cyclotronguy diyAudio Member Join Date: Sep 2001 Location: Northern California	Matt, I have never had a problem with sheet steel inside a wood product speaker cabinet. The two materials having vastly different resonant frequencies seem to effectivey damp one another. This presumes you have them firmly bonded together. Cyclotronguy

28th March 2002, 07:36 PM	#3
jam diyAudio Member Join Date: May 2001 Location: Charlotte,NC,USA	Cyclotronguy. You have discovered 'constrained-layer damping'. Jocko homo give the man a medal! Jam

28th March 2002, 09:10 PM	#4
cyclotronguy diyAudio Member Join Date: Sep 2001 Location: Northern California	Jam, Discovered? I'm not old enough for that accolade, but thanks for the boost. Cyclotronguy

28th March 2002, 11:51 PM	#5
mattpman diyAudio Member Join Date: Jan 2002 Location: UK.	excellent, thanks cyclotronguy, I only need to use a bit, because one of the braces is about 1mm too small . For mass I'm going to use sheet lead, I heard that that was good? Anyway, does anyone have any ideas about my first question, which way I should use the sandwich ? thanks a lot, Matt

31st March 2002, 06:52 PM	#6
turbo diyAudio Member Join Date: Mar 2002	I have the same question, only on the bonding part for the baffle..Is it best to use something that has some damping -- say liquid nails on MDF<==>MDF bonding, or bond them such that it is one contiguous piece? Also curious about the metal sheeting..so would ask this question for that concept, too. Tom

31st March 2002, 07:17 PM	#7
mattpman diyAudio Member Join Date: Jan 2002 Location: UK.	Hi Tom, I've found a number of sites reccomending lead sheeting, heres a quick quote: http://www.humanspeakers.com/diy/cabinets.htm#build "Lead flashing, which comes in 12" wide, 1/8" thick rolls, and weighs about 2.5 pounds per running foot, makes a wonderful panel damping material. It is easiest to attach with construction adhesive and a few staples. It does not have to be neat or lie perfectly flat. Wear gloves when handling it and don't leave it where children or pets can play with it, since it is poisonous if ingested. It will be safe inside your speaker box." Hope that helps :-) Still dont know about the MDF bonding though :-( Matt grrrrr, B&Q cut the MDF wrong AGAIN!!!!! grrrrr!!!!!

16th April 2002, 12:52 PM	#8
navin diyAudio Member Join Date: Jan 2002 Location: Mumbai (Bombay), India	I am hoping to build a pair of speakers as follows: dimensions 46" high 30" deep 8" wide drivers: 12" Audio Concpets DV12 6" Scan Speak 18W8546 1" Scan Speak 2905-9900 The 12" will be side mounted. Question: for all panels but the baffle I hope to use layers of 6mm MDF with lead sheet in between layer 1 and 2 and snd between layer 2 and 3. Does this make sense? Since the 12" is side mounted how does one mount it on a multilayer baffle (MDF-lead-MDF-sand-MDF)? Does this mean that I would only be able to use a multilayer baffle on the sides that dont have a driver mounted in them? Does it make better sense to use only lead sheet and not sand at all on one side (the side where the 12" is mounted)? Another alternate is a MDF-lead-MDF-RBF-MDF sandwich. RBF means Resin Bonded Fiberglass. Using polyester resin and fiberglass rovings/mat/mesh in a mixture one can spread this across a MDF sheet and then lay the next sheet of MDF on top. Is this any good? Lastly another idea is that I bend the MDFon the sides thereby flex it and prestrssing the cabinet walls. This can be done before th resin ins dry so that the fiberglass also dries as per the curve of the bend.