witzendoz
Senior Member
For any type of bass trapping you need rigid insulation, to trap bass you need mass.
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eyeballing
New member
Even for the thick soffit traps like about 16"x16"? I saw some people say the opposite, so I would love to hear your explanation here. Also was wondering how much of mass or density you are talking about when you said rigid insulation.
witzendoz
Senior Member
It is physics, bass low frequency requires mass to either insulate or trap. The insulation in my bass traps can stand up on its end without support, if its floppy soft stuff then you need much more of it to obtain the same mass.
Who says the opposite?
Who says the opposite?
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eyeballing
New member
Ok maybe not exactly contradicting what you said since you also mentioned need more stuff when using soft material. I am really new to whole this acoustic, and what I couldn't understand is the part when you said any bass trap need rigid insulation. I think saw some other people, the famous Mr.Ethan to be one, said for bigger size soffit bass trap fluffier material would work better than having same volume of denser material. I think they were talking about something like 16"x16"x8' or so.
witzendoz
Senior Member
I never remember Mr Ethan ever saying that? 16" x 16" is not big, the bass traps in my control room are across the corners 102" x 48" x 6" thick. 2.6 mtrs high x 1.2 mtrs wide x 150mm thick. I think you mean feet not inches, ' = feet, " = inches.
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eyeballing
New member
When I was searching I found this post: https://gearspace.com/board/bass-tr...etc/1056941-20x20-inch-soffit-bass-traps.html , and here Ethan says fill the cardboard with fluffy. I think I saw more posts by him or by others, but this is the one I could find for now.
I was inspired by this post initially https://www.audiocircle.com/index.php?topic=125742.0, and I thought that is big enough for a home recording studio, and that must be why I was talking about "big". Sorry for being unclear here.
witzendoz
Senior Member
Well we started off talking about tube traps and now we are talking about something very different. The rule is if you use dense insulation you will need less of it, if you use fluffy insulation you will need a lot of it. how much of your room do you want the bass trap to take up? The second link is to a trap with some pretty dense insulation, and a lot of it. By the way Soffit design does not mean soft and fluffy.
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eyeballing
New member
My room is 12' x 10' x 8', and while I don't have a way to measure nor I know the exact units and numbers and terms to use here.... I am trying to control low ends below 300hz, and was hoping that I can reach somewhat decent numbers at 50hz. Reason I am saying this is that I know small rooms like mine usually tend to have bass problems, and I was hoping that I could treat new room so I could hear lower ends better than my older room. My original plan was to put "stacked wrapped fluffy insulation" like I stated in my first post. Now I am leaning toward soffit bass trap design, and I did ask you about the tube trap because I was hoping you could compare tube trap and soffit. Hopefully this makes what I am saying little more clear, and again sorry about weird English.
Yes I am aware. I was looking for fluffy because of some people like Ethan or Andre suggested it in other forums. I heard Safe and Sound also works well, which is denser, and so I am still trying to decide should I go for S'n'S or something fluffier, or something denser.
rob aylestone
Moderator
The basic principle here is fairly straight forward. Converting sound pressure energy into heat. Kinetic energy transfer and the wavelength is important. The bass end has powerful wavefronts and transfer from medium to medium is efficient, hence why outside a nightclub you hear the thud thud but no music. The building doesn’t absorb it but transmits it through the structure. The HF wobbles the rock wool or fibreglass strands and the wobble converts to radiant energy. The bass passes through, following the curve in the specs. The wobbly heavier membranes do the same job for lower frequencies. You need a LOT of static fibre to soak up bass, and in a small room that’s not practical. I can’t find it because I don’t think I’m using the right words but there was a design that used a corner box full of suspended strips of canvas painted with car underseal type stuff. That horrible stick black tarry stuff. Looked like vertical window blinds all hanging vertically. The article claimed really good bass reduction from a small size. Probably smells awful till it cures though. This would have been on the net around 2004 I think because I saw it when I was doing a studio. Apparently it was important to arrange them so none were parallel with others so loads of reflections in the box.
Folkcafe
Well-known member
A whole lot of experts in acoustics and building studios. Your statement takes a few principles and mashes them up into something incoherent. Frankly there is more acoustic misinformation in this one thread than I have seen in a long time. Thanks for adding to the pile, I got a good chuckle out of this.
witzendoz
Senior Member
So what misinformation have I said here?
Folkcafe
Well-known member
Got to go to work (got a business to run) but will answer you when I get back later today.
witzendoz
Senior Member
no need to bother, if the things I say are not wanted I'll leave.
Folkcafe
Well-known member
1. it wasn't just you I was commenting on. 2. you are almost on the right track. 3. leave if you want but what would you learn?
I got to go on a service call for a client. I'm hoping it doesn't take too long and will get back to the office early. This will take a bit of time to lay it all out with graphs that will compare materials and how effective they are at low frequencies and when they cease to be absorptive and become reflective. Really, stick around. No one says your voice isn't welcome.
Folkcafe
Well-known member
R value is a rating related to insulative value and doesn't directly correlate to density or GFR. R11 EcoTouch has the lowest GFR value. Here is my list of GFR for EcoTouch aka "pink fluffy"
R-11 = 2450 mks rayls/m
R-13 = 3500 mks rayls/m
R-15 = 5000 mks rayls/m
R-19 = 2900 mks rayls/m
R-30 = 5000 mks rayls/m
R-38 = 3000 mks rayls/m
I posted a link in which you can enter GFR and depth and compare for yourself the performance. That way you have some idea what to expect. Just keep in mind that the models tend to under perform real life. When comparing, remember anything under .7 isn't absorbing enough to be ultimately effective. That and the ratio of absorption to bare wall needs to be substantial in small rooms.
I considered both a hard soffit and hybrid. Opted against it for now and concentrated on getting the acoustics straitened out first. Check out John Sayers' site. Glenn (Gullfo) there is very helpful when it comes to soffits and there are a lot of threads on the topic.
Folkcafe
Well-known member
So what is the answer to all these question about what to use to build treatment? Like so many question with math and science, the answer is, it depends. Like the question "solve for X", the more specific the details, the more specific the solution. If your question is really general, so too will be your answer. Like so many topics on the web, there are truths, half truths and outright falsehoods. It is no different than the myth of using egg cartons on the wall from years ago. It is not an outright lie, I mean you put them up and they do something. Probably something pretty hard to quantify but something. So when I answered the OP question, I stated, it'll do something. Unfortunately, that something is something you'll not be able to predict and
So lets start with the idea that there is no perfect absorber, no perfect reflective surface and there is no such thing as a perfect room. All studio design is compromise. One thing for another. Anechoic chamber, nope, not perfect. Funny thing, an anechoic chamber doesn't even need to be built with absorptive materials. Navy built one that is all stainless steel wedges and is anechoic via diffusion. Talk about a solve for X problem.
Density, what is better, more or less? Answer, it depends. What problem are you trying to solve is a far better question. 25 years ago, Owens Corning 703 & 705 had nearly a mythical place is studio building. It was the gold standard for building treatment and for simple fabric covered panels and a lot of commercial products, rigid fiberglass is still used. So what is the problem with it. Well, within its limits, nothing but either the original testing data was faulty or it has changed as the current test data shows it a lot less effective than the coefficient charts showed years ago. These sound absorption coefficient tables would show how effective they were for 1, 2 and 4 inches thick. It wasn't uncommon to extrapolate that out. You know, more is better. But is it? Data never said it was, people just thought it was. Truth is after 4 inches at low frequencies, rigid fiberglass becomes acoustically reflective and not absorptive. So only so much bang for the buck if you will.
The other irony is that the ratings only went down to 120Hz. Anything below that is in the pressure and not wave region of energy. Does the range for bass stop at 120Hz
Rigid mineral wool such as Safe n Sound is better going deeper than rigid fiberglass but it too plateaus' as it gets thicker eventually. Fluffy fiberglass starting at around 10 inches or so is about dead even with 2.5lb density or 10000GFR mineral wool. After that, fiberglass absorbs lower than rigid fiberglass or mineral wool. You can enter the data yourself as there are a few online calculators that will graph it out for you.
This graphic is a comparison of 2ft thick insulation choices between Safe N Sound mineral wool and R38 pink fiberglass. The blue line is pink fiberglass. If you are looking to build a bass trap, which of these would you choose? The mineral wool because of its density become reflective and starts to bottom out at 400hz yet the low density fiberglass goes nearly 10 times lower in frequency absorption.
I had a decent size problem down low so I went with 2ft deep bass trapping all along my back wall using R38. Had I used a higher density material, I wouldn't have hit my target. It would have trapped bass, just not low enough.
Don't need to take my word for it. There are plenty of ways to verify what I am saying using the tools that are readily available online.
So lets start with the idea that there is no perfect absorber, no perfect reflective surface and there is no such thing as a perfect room. All studio design is compromise. One thing for another. Anechoic chamber, nope, not perfect. Funny thing, an anechoic chamber doesn't even need to be built with absorptive materials. Navy built one that is all stainless steel wedges and is anechoic via diffusion. Talk about a solve for X problem.
Density, what is better, more or less? Answer, it depends. What problem are you trying to solve is a far better question. 25 years ago, Owens Corning 703 & 705 had nearly a mythical place is studio building. It was the gold standard for building treatment and for simple fabric covered panels and a lot of commercial products, rigid fiberglass is still used. So what is the problem with it. Well, within its limits, nothing but either the original testing data was faulty or it has changed as the current test data shows it a lot less effective than the coefficient charts showed years ago. These sound absorption coefficient tables would show how effective they were for 1, 2 and 4 inches thick. It wasn't uncommon to extrapolate that out. You know, more is better. But is it? Data never said it was, people just thought it was. Truth is after 4 inches at low frequencies, rigid fiberglass becomes acoustically reflective and not absorptive. So only so much bang for the buck if you will.
The other irony is that the ratings only went down to 120Hz. Anything below that is in the pressure and not wave region of energy. Does the range for bass stop at 120Hz
Rigid mineral wool such as Safe n Sound is better going deeper than rigid fiberglass but it too plateaus' as it gets thicker eventually. Fluffy fiberglass starting at around 10 inches or so is about dead even with 2.5lb density or 10000GFR mineral wool. After that, fiberglass absorbs lower than rigid fiberglass or mineral wool. You can enter the data yourself as there are a few online calculators that will graph it out for you.
This graphic is a comparison of 2ft thick insulation choices between Safe N Sound mineral wool and R38 pink fiberglass. The blue line is pink fiberglass. If you are looking to build a bass trap, which of these would you choose? The mineral wool because of its density become reflective and starts to bottom out at 400hz yet the low density fiberglass goes nearly 10 times lower in frequency absorption.
I had a decent size problem down low so I went with 2ft deep bass trapping all along my back wall using R38. Had I used a higher density material, I wouldn't have hit my target. It would have trapped bass, just not low enough.
Don't need to take my word for it. There are plenty of ways to verify what I am saying using the tools that are readily available online.
O
Orson
Well-known member
Could just open the window? 
E
eyeballing
New member
better yet... tear down all walls and have no reflection at all! lolCould just open the window?
E
eyeballing
New member
Thanks for an informative answer. I know my questions were not as specific as it should/could been... and I also know there is no perfect answer, and even when following rules and laws it could differ a lot in reality in this field.
Even so I think it is worth trying lower GFR material for my plan. I know it takes a lot of try and fail, and I guess this is only way to know for sure. Thank you for the information.
Just two more question: if you were to choose only front or back wall to place 2 bass traps at the corners, which would be it? For now I am leaning toward 2ft by 2ft chunk like you mentioned, but might go little shallower.
Also, if you by any chance know if which Johns Manville is equivalent to 3000 mks rayls/m? It seems my local store usually do not carry OC for whatever reasons, but a lot of JM.
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Folkcafe
Well-known member
I'm not so sure why it has to be try and fail. My dad used to say, "measure twice, cut once". This thinking applies. Spend more time planning than constructing is about the best advice you can get. No point in trying to prove that 4+4=10.
Here are the JM numbers I have. Don't know what country you are in but this applies to products for North America. Other parts of the world can be different depending on manufacturing and market differences.
Here are the modeled room mode based on the measurements you posted. Look up John Brandt and go to his resources page and download the spreadsheet. The instructions on how to edit the dimension are on the left hand side of the first tab.