Absorption of fiberglass

Posted: Sat Nov 29, 2008 10:40 am

Hi Rod and company,
This is my first post here as ive just found the site from Rods book that im reading - very slowly - as im not to quick.
Id like to thank Rod as it is only because of his book that i stopped throwing money away at my garage conversion.
I have read the sticky and intend to give all details of my project properly for your consideration next year, but i would like to do it justice with some 3D CAD images. Could anyone recommend a free software package that is easy to learn to do this as there seems to be quite a few and im really poor at learning software ?
I do have one other question. Im probably getting this totally mixed up (as i do sometimes), but after reading the fiberglass test results in the book and then the tests on Ethan Winers site, they seem (to me atleast) to be showing different trends for absorption in the lower frequencies when comparing OC 703 with 705. Im confused by this. Could somebody explain this?
Thanks
Peter

Posted: Sat Nov 29, 2008 4:30 pm

Google SketchUp gets a bit of use around here.
Never tried it though.

Posted: Mon Dec 01, 2008 2:39 am

stringmen wrote:

after reading the fiberglass test results in the book and then the tests on Ethan Winers site, they seem (to me atleast) to be showing different trends for absorption in the lower frequencies when comparing OC 703 with 705.

Published absorption data rarely goes below 125 Hz, and my tests went down to below 40 Hz. Published data is also for panels mounted flat on a surface, where my tests had the panels straddling corners as is usual for bass trapping. This is explained in my Density Report.

--Ethan

Posted: Mon Dec 01, 2008 8:08 am

Hi Ethan and thanks for replying,
Your site is a great free resource and im very grateful for it.
Sorry, i must apologies as i wasnt specific enough with my first post, i was just refering to the results on the actual page and not the link to your own set of results-sorry if this was inferred.
Im just confused because the data in Rods book suggests 703 is generally better at all frequencies except at 125Hz - where its much closer. Here the 1 & 2" plain results show 703 being marginally better than 705, and at 2" 703FRK being marginally better than 705FRK. This is different from the second table of results from your site where 6pcf (plain) absorbs better than 3 pcf at 2".
Would it be right to say that 703 is generally better above 125hz but 705 is better below this?
I am a novice with regards to acoustics and im just trying to ascertain which is the more effective density of fiberglass for use as broadband absorbers where low end is the most important. This will just be a temporary measure until my studio soundproofing is done. Then i will hopefully try to make some of your great bass trap plans. Again thanks for these.
Best wishes
Peter

Posted: Mon Dec 01, 2008 8:26 am

Thanks for the link Ethan, the density and room spacing advice from it is much appreciated. I see from it that the frk increases absorption but unfortunately i only have access to the non foil variety of rockwool (of same densities as 703 and 705) at the moment.
Thanks again

Posted: Tue Dec 02, 2008 5:21 am

At different thicknesses 703 or 705 behave differently. What really matters for bass traps is when it's 3 or more inches thick, and placed in corners. In that case 705 FRK is clearly best. If you can't get the FRK type, add your own facing by spray-gluing Kraft paper to the fiberglass.

--Ethan

Posted: Tue Dec 02, 2008 5:25 am

thanks for clearing that up Ethan.
Cheers
Peter

Posted: Wed Dec 03, 2008 6:43 am

Greener wrote:

Google SketchUp gets a bit of use around here.
Never tried it though.

Thanks Greener, had a look and this looks like it could be just the ticket.
Cheers
Peter

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