first reflection panels density and thickness

[neuro]

hi all

i'm based in France, and i can easily find those rockwool panels :

"Rockwool Rockplus 50Kg/m3 100mm", which roughly equals 3.0 pcf and 4 inches
"Rockwool Alpharock 70 kg/m3 40mm", which roughly equals 4.0 pcf and a bit less than 2 inches.

would any of these be ok for building first reflection panels ?

which one would you choose ?

[PaulP]

Search this forum for "first reflection panels density thickness", and read the threads.

Reading a lot more than that would be beneficial as treating a room is much more than just adding a few panels here and there.

[neuro]

thanks for your reply.

well, i've done quite a bit of searching and reading.
i plan to build a lot of panels, but i want to start off by making only two first reflection panels because i live with someone suffering from lots of allergies..
i don't want to buy a truckload of rockwool only to find out that it must go.
i also want to test out my abilitie to do these panels myself.
last but not least : as i understand it, first reflection panels don't really need to have holes on the sides. so i can do this "test" on my own without bothering my mate, who's a carpenter and who will eventually supply wood for making panels like these if the "test" turns out ok.

as for density and thickness, this is what i think i understand :
- most people use fiberglass. OC703, 3.0 pcf. this is less effective than 705 (6.0 pcf), but cheaper. that's why it has a better performance to price ratio.
- first reflection panels are used to adress first reflexion problems. mids and highs are small or tiny waves, they're directional and act as light rays, they're easy to absorb, they don't need thickness.
bass is omni and biig, and difficult to absorb. bass waves don't "fit" in small rooms due to their length. the ticker a panel will be, the more bass it will absorb.
first reflection panels aren't meant to absorb bass, hence they don't really need to be thick.

am i right ? am i thick ?

sooo,
isn't 4 inches of 3.0 pcf rockwool a bit too thick (overkill) for those panels ?
isn't less than 2 inches of 4.0 pcf rockwool too thin ? and won't it be too thick if i layer two panels ( a bit more than 3 inches of 4.0 pcf) ?
do you understand the dilemma ?

[matucha]

You'll put rockwool in plastic bags. It doesn't change it's acoustic properties much and it is very effective in protecting your environment from any fibres that could come from rockwool when disturbed. I think your allergic mate won't notice anything if you do that.

I'm allergic too in some way and I didn't noticed anything after adding over 30 packs of rockwool to my place. Well I noticed something it sounds much better with every pack you add .

[neuro]

Originally Posted by matucha

You'll put rockwool in plastic bags. It doesn't change it's acoustic properties much and it is very effective in protecting your environment from any fibres that could come from rockwool when disturbed. I think your allergic mate won't notice anything if you do that.

thanks mate but this plastic would reflect highs. it's quite the opposite of what i want for those panels, isn't it ?
i already bought some "spandex" that should hold the rockwool inside the panels while avoiding to reflect too much highs (i think.. or so i've been told).

[matucha]

Thin plastic won't eat much of the absorption in highs and you're going to finish the panel with some fabric that will add some back.

[explorer]

I like this way of making panels:

http://www.basstraps.net/DIY-BASS-TRAPS-MADE-EASY.pdf

Not too much work and the final design is as effective as possible.

[Glenn Kuras]

DO NOT put any kind of plastic on the front of the panels if being used in the early reflection points. It will reflect the highs that you want to absorb.

[neuro]

cheers Explorer. i want to be able to move my panels so i'm not sure i'll use this design, although it clearly is the easiest one to build.
(well, maybe i'll use it for first reflection panels only.. i have yet to decide)

and thanks Glenn, yes i've seen you and others say that before. i've read many of your posts and articles on your site (many thanks for these). What's your opinion about my initial question ?

[Glenn Kuras]

Originally Posted by neuro

cheers Explorer. i want to be able to move my panels so i'm not sure i'll use this design, although it clearly is the easiest one to build.
(well, maybe i'll use it for first reflection panels only.. i have yet to decide)

and thanks Glenn, yes i've seen you and others say that before. i've read many of your posts and articles on your site (many thanks for these). What's your opinion about my initial question ?

Either of the densities will work fine.

[neuro]

sweet.
let me rephrase my question then :
if money wasn't an issue, would you make a 4 inch thick 3.0 pcf panel, or a 3 inch thick 4.0 pcf panel ?

[avare]

Originally Posted by neuro

sweet.
let me rephrase my question then :
if money wasn't an issue, would you make a 4 inch thick 3.0 pcf panel, or a 3 inch thick 4.0 pcf panel ?

4" 3.0 lb/ft3 panel.

Andre

[Jerrick]

Originally Posted by Glenn Kuras

DO NOT put any kind of plastic on the front of the panels if being used in the early reflection points. It will reflect the highs that you want to absorb.

Even 1mil plastic drop cloths? Ive used that while painting a few house, and I remember having .7mil plastic. I always though at 1mil and below it was acoustically transparent for all frequencies, or does that not apply to early reflection points? All reflection points?

[riteup3]

hey neuro, check with leroy-merlin, they stock up on wood fiber panels that are just the right density (55kg/m3)

[neuro]

thanks Andre. i realize density of mineral wool is a highly controversial subject in this field. you say 4" 3.0 lb/ft3 but others would probably tell me something different ( ? ). i will follow your advice, though.

and thanks riteup, i've seen those wood fiber panels, but i don't know, i think i prefer to buy the nasty stuff. i've been to a Leroy Merlin warehouse filled with fiberglass and rockwool and i didn't find it that nasty. i talked to a worker there, who handles the stuff day in day out without any kind of protection, and it didn't seem to bother him at all..

[neuro]

"Rockwool Rockplus 50Kg/m3 100mm", (4" 3.0 pcf ) wasn't available anywhere near where i live, so i bought some 3" 3.0 pcf rockwool.
should i make a 3" panel ? or should i use two layers and make a 6" panel ?

[Glenn Kuras]

For the early reflection points 3" is fine. 6" is not wrong to use but not the place for bass traps so I would save the other 3" for corners or other points in the room.

[tINY]

Look at the charts and ask yourself if the absorbtion looks even down to about 250Hz.

That's really what you need to do - absorb evenly from 250Hz - 20kHz. Higher frequencies on the bottom are OK in small rooms as the modal issues are at work at higher frequencies and the extension of the absorbtion doesn't buy you anything.




-tINY

[neuro]

thanks again Glenn, i will do that : )

hi tINY, what charts are you talking about ? i don't have any specific data for the panels i bought.. but looking at bobgolds chart, i can see that a product like Roxull RHT40 (3" 3.5 pcf) comes close to what i have in terms of brand, material, density and thickness. Would it be wrong to assume that both products will have quite similar acoustical properties ? if not then yes, it looks like absorption is quite even, at least from 250Hz to 4KHz..

[Glenn Kuras]

Originally Posted by neuro

thanks again Glenn, i will do that : )

Would it be wrong to assume that both products will have quite similar acoustical properties ? if not then yes, it looks like absorption is quite even, at least from 250Hz to 4KHz..

For the most part yes.

[neuro]

sorry, i'm not sure what you mean.
do you mean it would be wrong to assume that ?
or do you mean that both products would indeed have similar acoustical properties, for the most part ?

sorry about my english by the way. i don't have much knowledge (grammar + acoustics), and i struggle to make myself clear so i may well sound like an idiot.

[neuro]

i'm assuming you mean both products would have similar acoustical properties. correct ?

[Glenn Kuras]

Originally Posted by neuro

i'm assuming you mean both products would have similar acoustical properties. correct ?

Sorry I should have been more clear. Yes they do have similar acoustical properties.

[neuro]

no worries, thanks thanks

[avare]

Originally Posted by neuro

thanks Andre. i realize density of mineral wool is a highly controversial subject in this field. you say 4" 3.0 lb/ft3 but others would probably tell me something different ( ? ).

It is not controversial. It is something that people who do not know what they are writing about, like to write about.

Andre

[SAC]

Originally Posted by avare

It is not controversial. It is something that people who do not know what they are writing about, like to write about.

Andre

+1^100

That should be a sticky!

In fact, I am resolved to have a needlepoint wall hanging commissioned and to get a tattoo featuring that all too apropos observation!

[DanDan]

neuro, there are horizontal and vertical modes. Because of this I, and many others, regard 100mm panels with an additional 100mm gap behind them as a good start.
If you include a layer of FRK or other membrane on the airgap side they will have increased LF performance.
Rockwool is quite floppy compared to the longer fibred glass materials.
You will need to include a supporting mesh under your Cloud.

DD

[neuro]

Originally Posted by avare

It is not controversial. It is something that people who do not know what they are writing about, like to write about.

Andre

it may not be controversial amongst acousticians who know what they're talking about, but i swear i've seen quite a few contradictory opinions and recommendations on the subject.
reading online about acoustics - or other subjects for that matter - can get well confusing when you don't know much beforehand.
i have close to zero scientific background so reading about gas flow resistivity and particle velocity is somewhat challenging...
Andre, since i have (tried to) read some of the posts in the "Q4 AVARE thread", i believe 3" is a bit too thin for flat absorbtion down to 250Hz, isn't it ? as i said, i bought some 3" thick (3.0 pcf) material, so i wonder what to do.
wouldn't 6" be best for flatter absorbtion ?
6" thick rockwool + 6" gap ?

PS: this forum seems to be a great source of valuable info but a few stickies wouldn't hurt, imo.

[neuro]

thanks Dan. for now, i'm working on understanding the concepts behind this diy acoustic treatment.. and i've assembled some backing for two sidewalls panels. i'll make corner traps but i don't know if i'll have to build a cloud.
(edit : i will have to post some more specific questions about my set up at some point. i have tested the room with REW but i'm not totally sure i've got the measurements right..)

[mhch]

Originally Posted by neuro

it may not be controversial amongst acousticians who know what they're talking about, but i swear i've seen quite a few contradictory opinions and recommendations on the subject.
reading online about acoustics - or other subjects for that matter - can get well confusing when you don't know much beforehand.
i have close to zero scientific background so reading about gas flow resistivity and particle velocity is somewhat challenging...

...

PS: this forum seems to be a great source of valuable info but a few stickies wouldn't hurt, imo.

May be this is a French disease, but I can't resist backing that up even with my relatively large scientific background. Put another way, most of the information one can find on the Internet is some introductory material about modes and reflexions, and after that mostly vendor recommendations for their main products (panels) and DIY questions.

May I also add that those few stickies would be great if having meaningfull titles. I'm sure this would remove a number of repeated questions. Q4 avare is really a great piece of information, but the title is not quite reflecting its contents tutt

Please understand I'm not ranting ! I'm really glad to have finally found a reliable source of good information. Just trying to give some feedback.