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Originally Posted by bpape Just for some clarification...
The acoustical cotton is in fact fire rated - and class A at that.
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Lastly, to the original question, if you want to save some $$$, you can do 6" of 703 for 75% of the cost of 4" of 705. It will work just as well if not better due to the additional thickness. Mineral wool will be cheaper than either of those solutions - but harder to work with.
All depends on what you're looking for.
Bryan |
Bryan:
I have corrsponded with many who have used the Cotton Batts successfully and who like the material enormously... though I must admit that a good deal of the attrtaction seems to me to be an irrational fear that mineral fiber being an "industrial" material, it must be bad, whereas cotton is "organic".
My $0.02 is that standard MF panels are cheap, effective, and safe - so cotton is just an expensive alternative to me. But, this may be because I don't find MF to be too much of a PITA to work with if you use some common sense [wear the right stuff - invest a couple $ in a a paper coverall and a filter mask - same as if you were going to paint a house using latex paint and a spray gun - get the right gear on for the job and and its all EZBZ]. Others find working with MF to be irksome - so for them I guess the expense has some justification.
Along similar lines of justifying higher cost materials - you mention perhaps needing to use thicker panels of 3 lbs. fiberglass to match the absorption of 6 lbs. fiberglass [703 vs. 705]. I am aware of no published scientific measurements which support this notion. It is a common claim - but unsupported by science AFAIK. Can you provide a link to any such evidence?
In any event, as you point out, one can buy 703 for half the price, so even granting some small superiority to 705 it makes no sense to use it instead simply treating a few more sf of wall or linear feet of corner with 703 - a product costing half as much.
Given that the price and availability of 703 and other 3lbs. fiberglass products and similar rockwool materials varies enormously from city to city and country to country, the best answer is to use Bob Golds excellent compendium of absorption measurements
http://www.bobgolds.com/AbsorptionCoefficients.htm
to shop locally for best value [ignore brand names - simply shop within a chosen class of materials as Doug describes having done above]. This is the smart way to approach the question - pick a material category that fits your needs and comfort level [or categories] and let your wallet guide you to the sorrect solution.
You may find it useful to have a better understanding of how 4" 703 performs in a corner mount. Below is a graph of showing absorption data for 4" - 703 panels in a corner mount we recently measured at Riverbank Acoustical Laborotory. This measurement is plotted along side data on our RT424 - which is the same material inside one of our RT424B Bass Trap Bags.
Note the jump at 100 Hz - this comes from the fabric increasing the entrance impeadance of the panel and elevating the Mass-Spring-Mass resonance [a property which is expressed in all corner absorbers - both panels and wedges - MF and acoustic foam].
I'll be putting the full report up at our website
http://readyacoustics.com
as soon as I get the certified copies back from RAL in PDF form [probably next week]. In the mean time this chart will help you understand what you can expect to achive from 703 in a corner mounting - and the differences that will arise if you upholster the panels with fabirc which has some modest acoustic mass as opposed to leaving them "naked, or using a ultra light / coarse weave fabric].
Note also how the Mid-Band and HF measurements are uneffected by the impeadance jump... interesting stuff.. more later.
