# RHT 40 vs OC 703



## kadijk (Jan 23, 2011)

I'm having a head time sourcing OC 703 locally, however I can get the roxul rht 40. I thought I had read that they are pretty much interchangeable. Any comments or concerns with that thinking? I'm looking to make panels 2" think for first reflections, and some 3" thick for front and back bass traps( ie behind mains and at the back of the room). You can see a plan of my room in my build thread ( look for the rabbit hole build journal). 
Thanks for your help and interest


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## SAC (Dec 3, 2009)

~3lb/ft^3 Fiberglass or ~4 lb/ft^3 mineral wool are essentially identical.


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## kadijk (Jan 23, 2011)

Thank you! Now...what is it about GOM fabric that makes it the "one" to use in this application? I can't get that locally either and would love to find a substitute.


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## bpape (Sep 14, 2006)

For absorbers you don't need to do Guilford fabric. Any fabric that is relatively breathable will do just fine in this application. It doesn't need to be as transparent as say cloth in front of speakers. 

For your bass absorbers, you'll want to consider going thicker than 3". 6" will do a considerably better job.

Bryan


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## SAC (Dec 3, 2009)

Indeed as Brian mentioned. 

The figures mentioned above were for broadband specular panel absorbers - not bass traps. 

If this is for _bass traps_ or broadband specular traps you will indeed want to go further and make them thicker/deeper'. Optimally, 4" thick with a 4" gap for specular reflection control, and a corner trap with wall facings of at least 24" and a face of about 34 inches for LF corner traps.

An d if you are making bass traps, the 'common pink fluffy stuff' works better and is significantly cheaper than semi-rigid Fiberglass or Rockwool, provided that you make them (at minimum) deeper than ~12 inches - in which case a corner trap (as mentioned above) faced with a minimum 6 mil plastic is your best option.


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## Diskohouse (Jun 2, 2011)

I used RHT 80 for my panels because it was locally available so I was able to avoid the shipping cost. They have the spec sheet available at roxul.com. RHT 80 had better low end absorption when compared against the lover RHT numbers. I am definitely happy with the result I was able to achieve. Once I have figured out REW completely, I will do some measurements and post my finding. I used the 2" for the FRP and then 4" panel for bass traps and the whole front wall. My room is 14.5' x 14' x 8' ... so the room is an acoustic nightmare. You can find the z-clips really cheap online too.... http://www.monarchmetal.com


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## kadijk (Jan 23, 2011)

I realize the topic of this discussion is slowly shifting...is it beneficial to space FRP away from the wall equal to their thickness as well? Or us that redundant or unnecessary? I'm not basing my treatments on testing or measurements yet... Simply on what I've read on the GIK website


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## Diskohouse (Jun 2, 2011)

I'm new to this too....but from what others have said and what I have read, there is a benefit for having the space behind the panel, but it should not be any larger than the thickness of the panel. I remember reading that someone said it's better to have a 4inch panel with no space compared to a 2 inch panel with a 2 inch space behind it. I would definitely like to see what the more experience members have to say. My FRP are built to have a two inch space behind them.....


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## bpape (Sep 14, 2006)

All else equal, you're better off with full thickness. To save money, you can do say 2" with a 2" gap, 4" with a 4" gap, etc. It's not so much the air behind as it is where the leading edge of the absorption is in relation to the hard boundary behind it. 

The only advantage of the gap is if the panel is not framed and you can get anything bouncing off the wall and being caught by the rear side of the panel.

Also note that you can certainly go less than the thickness, just not as much added benefit. So, there's no problem with using a 4" panel and a 2" gap.

Also, agree with SAC that once you get beyond say 6" of thickness, the less dense material can actually perform better than the higher density material. 

All of that said, we do have to consider the reality of a home living situation where looks and available space play a part. Many rooms are pretty narrow as is and simply don't have the usable space to do 4" panels with a 4" gap behind them nor are the owners likely to be terribly tolerant of that look. If you have the space and can live with that kind of thickness and look, sure, go for it. If not, do the best you can with the space available and within the aesthetic limitations placed on the space.

Bryan


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## kadijk (Jan 23, 2011)

Thanks guys. Bryan, you've got me thinking. Framed or unframed...I could easily do 4" panels as I have the room width. However, I would want to frame them. Would 2" unframed with a 2" gap be somewhat equal to 4" framed? I realize the frame presents a reflection issue, so could one frame a panel and then insert absorptive material around the frame on the outside and hold it there with the cloth? I'm just thinking that frameless is hard to hang, and 4" is significantly more money than 2". Or one could slice a "dado" of some sort into the panel and insert a frame into that...then the cloth becomes part of the structural strength(not sure I like that idea now that I spit it out).


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## bpape (Sep 14, 2006)

Frame, it, do a 2" panel and a 2" gap, and route holes/slots in the sides. 

Bryan


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## kadijk (Jan 23, 2011)

Great idea Bryan. Thank you. That's why you're the pro AND they pay you the big bucks...


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## bpape (Sep 14, 2006)

Uh, sure.... You need to tell Glenn about that big bucks thing... :spend: 

Bryan


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## kadijk (Jan 23, 2011)

Bryan...I found some "acoustic" fabric locally, but it has what seems like a backing on them. Does the GOM fabric have something like that? Or does it feel "fabricy" on both sides?(sorry for the homemade word).


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## bpape (Sep 14, 2006)

The GOM is pretty much the same on both sides. 

Bryan


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## kadijk (Jan 23, 2011)

Thanks. That's what I thought. I found something called twill, it's a cotton poly blend, looks a little like carhart pants fabric( that's the best I can describe). I think it'll work. Stiff enough to pull tight without stretching, won't look saggy, and can be stapled to the frame.


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## bpape (Sep 14, 2006)

twill can be pretty tight. Look for something more like a Muslin or broadcloth. Stretching isn't a problem.

Bryan


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