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PostPosted: Thu Feb 22, 2018 2:42 am 
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Joined: Tue Jun 30, 2009 10:57 pm
Posts: 18
Location: Reading, UK
Hi all,

I am close to finishing the framework for some soffit mounted speakers and have some sheets of 12.mm think Knauf soundboard plasterboard/drywall. Enough to have two layers.

Is this acceptable to use instead of MDF or plywood? As i have it lying around i thought it would be nice to use up.

Ive had a rummage around the site and found only one or two mentions of using plasterboard for this, while most posts mention MDF.

Thanks


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PostPosted: Thu Feb 22, 2018 4:23 pm 
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Joined: Wed Feb 01, 2017 6:03 pm
Posts: 280
Location: Edmonton, Alberta, Canada
I'm pretty confident to say yes.

It's heavy and flat. Those are the only requirements ever mentioned. It might look like crap unless you use a nice edge where you cut the hole for the speaker though. And getting it precise (~2 mm) around the edge of the speaker might be difficult. Also, you will probably need to use speakers that have nice flat fronts on them as cutting a contoured hole to match other speakers would be pretty much impossible as it would just crumble away.

So my answer is: if you do it with care and realize the downsides of using it, yes, you can use it. Make sure you use SEVERAL layers though to get the mass as heavy as possible. Remember, MDF has about twice the mass of fire rated drywall. People are using really thick pieces of MDF for their soffit walls. So, double that thickness with drywall.

Greg

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PostPosted: Thu Feb 22, 2018 9:24 pm 
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Joined: Tue Jun 30, 2009 10:57 pm
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Location: Reading, UK
Thanks for the quick reply, Greg.

The thickest MDF in my local hardware stores is 25mm. So, according to your remarks on the mass of MDF, would I therefore need 4 sheets of plasterboard/drywall on each soffit wall to match the mass of that MDF? i.e. 25mm of plasterboard (which i currently have) would only be equivalent to half the mass of the same thickness of MDF.

Is that correct? My maths isnt that great!

Ive not been able to find any information on the density or mass of the Knauf soundboard, but looking at the relative weights of the two (MDF v soundboard), for equivalent size sheets (1220mmx2440mm), MDF has a weight of 40.187kg (13.5kg/m2), while soundboard has a weight of 30kg (10.08kg/m2). Though not a measure of density, this leads my simple mind to believe there isnt a great deal of difference between the two.

Seeing as i already have the soundboard in the studio sitting unused, would have to pay for delivery for the MDF (and have trouble lugging it!), im tempted to just go with it and see what happens, but will consult with my studio cohorts to see what they think.

Your comments on the issue of cutting the holes accurately is certainly something ill have to consider though. Ill just have to be careful with the knife and surform!

Chris


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PostPosted: Fri Feb 23, 2018 10:13 am 
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Joined: Fri Feb 14, 2003 1:51 am
Posts: 309
Location: Lansing, MI USA
I used two layers of drywall with more bracing than a stud wall. I made the hole about 7.5cm larger on the top and bottom of each speaker and finished the edges. I should have gone wider on each side. Then I made a bezel that fit over the hole to the exact size of the speaker. The green is drywall, the black mdf.
Attachment:
finished control room.jpg


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PostPosted: Fri Feb 23, 2018 7:18 pm 
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Joined: Tue Jun 30, 2009 10:57 pm
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Location: Reading, UK
Thanks Eric, that is just what i was thinking of doing!

Ive come across your room thread on here before but cant remember the results of your room. With using drywall, and from your general experience of the room, do you think there have been any negative consequences with regard to acoustics etc.?

Chris


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PostPosted: Sat Feb 24, 2018 2:49 am 
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Joined: Fri Feb 14, 2003 1:51 am
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Location: Lansing, MI USA
The measurements for the room are in the second half of my speaker building thread.

http://www.johnlsayers.com/phpBB2/viewtopic.php?f=12&t=16933

I think it turned out great. I do have a problem at 80hz but that doesn't have anything to do with the drywall, and I can't hear it either.

I still haven't done final measurements with the room full like I promised Stuart, but I still have 3 more weeks of getting my team through our championship season and then I will have loads of time!

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