Quantcast
The difference between Bass Traps and Mid / High Frequency Absorbers? - Gearspace.com
The No.1 Website for Pro Audio
The difference between Bass Traps and Mid / High Frequency Absorbers?
Old 3rd March 2014
  #1
Lives for gear
 
Miiko's Avatar
 
🎧 10 years
The difference between Bass Traps and Mid / High Frequency Absorbers?

So what exactly is the differnece? Is it just the depth of the absorbing material? Or is it more about the placement of the absorption? Or is it more about the material itself?

I mean, if I do 4" absorption panels on the side walls, they would be considered high frequency absorbers, correct?

What if I put the 4" panels in the corners, are they now considered bass traps?

Or, let's say the same situation for 8" deep panels. Assuming that it is all OC 703, would an 8" panel on the side wall be considered a high frequency absorber, or just a poorly placed bass trap?

Confuzzled.
Old 3rd March 2014
  #2
Gear Guru
 
Glenn Kuras's Avatar
 
🎧 15 years
Rigid fiberglass (and others) (broadband) work best in the bass range when in the corners for the most part. The following talks about different kinds of bass trapping.
Understanding Different Bass Trapping - GIK Acoustics
Old 3rd March 2014 | Show parent
  #3
Lives for gear
 
Miiko's Avatar
 
🎧 10 years
Quote:
Originally Posted by Glenn Kuras ➑️
Rigid fiberglass (and others) (broadband) work best in the bass range when in the corners for the most part. The following talks about different kinds of bass trapping.
Understanding Different Bass Trapping - GIK Acoustics
Yes I understand OC 703 or OC 705 are the best for absorption. My question is, what determines if something is a bass trap or a high frequency absorber?

Is it more about location, depth, or material? Or a combination of all three?

I mean, a 2" piece of OC703 in the corner wouldnt really be a bass trap, it would need to be at least 6", right?

But then, would the same 6" of OC703 be considered a bass trap if it were moved to the side reflection wall? Etc...
Old 3rd March 2014 | Show parent
  #4
Lives for gear
 
GIK Acoustics's Avatar
 
🎧 5 years
Quote:
Originally Posted by Myrok ➑️
Is it more about location, depth, or material? Or a combination of all three?
All three. A bass trap is an absorber that reaches down to low frequencies. For velocity based absorbers (broadband bass traps), simply put: the thicker the trap, the lower down in bass it absorbs. Also, an air gap can push the lower cutoff of absorption further down as well. A 4" absorber in a corner can work well down to about 75 Hz, so I would consider it a bass trap. A 4" absorber on the wall would absorb well down to probably 150 Hz or so, depending on how it's built and materials, etc. So in that case it absorbs some bass, but not a lot of the sub bass region. Some people might classify that as a bass trap, some might not.

A lot more of this is covered in the link Glenn posted above.
Old 4th March 2014 | Show parent
  #5
Lives for gear
 
jim1961's Avatar
 
🎧 5 years
Quote:
Originally Posted by Myrok ➑️
Yes I understand OC 703 or OC 705 are the best for absorption. My question is, what determines if something is a bass trap or a high frequency absorber?

Is it more about location, depth, or material? Or a combination of all three?

I mean, a 2" piece of OC703 in the corner wouldnt really be a bass trap, it would need to be at least 6", right?

But then, would the same 6" of OC703 be considered a bass trap if it were moved to the side reflection wall? Etc...
I would argue pink fluffy, when thick enough, does a better job at all frequencies, especially bass than 703 or 705 at any thickness.
Old 4th March 2014 | Show parent
  #6
Lives for gear
 
Miiko's Avatar
 
🎧 10 years
Quote:
Originally Posted by jim1961 ➑️
I would argue pink fluffy, when thick enough, does a better job at all frequencies, especially bass than 703 or 705 at any thickness.
Do you have numbers to back that up? Everything I've read says rigid fiberglass is the best option
Old 4th March 2014 | Show parent
  #7
Lives for gear
 
jim1961's Avatar
 
🎧 5 years
Quote:
Originally Posted by Myrok ➑️
Do you have numbers to back that up? Everything I've read says rigid fiberglass is the best option
Here is one discussion. There are dozens more of them available by a simple google search.

https://www.gearslutz.com/board/bass-...-question.html

This is a well known fact. The reason OC703 comes up is that many are space limited. That is to say, at 2" and 4" thickness, OC703 is the best. But at 10" or more, there is no comparison.
Old 4th March 2014 | Show parent
  #8
Lives for gear
 
Miiko's Avatar
 
🎧 10 years
Quote:
Originally Posted by jim1961 ➑️
Here is one discussion. There are dozens more of them available by a simple google search.

https://www.gearslutz.com/board/bass-...-question.html

This is a well known fact. The reason OC703 comes up is that many are space limited. That is to say, at 2" and 4" thickness, OC703 is the best. But at 10" or more, there is no comparison.
Interesting discussion going on there. It seems like the pink fluffy would be good as a cheaper option, but it still seems like OC703 / 705 are better as they are much more dense (essentially compressed R30 fiberglass). So 10" OC703 or 705 would be much more effecient than 10" of pink fluffy, but probably not at the cost of 703 / 705. I do wonder how much pink fluffy / r30 sells for and what the minimum purchase quantity is.. either way I will probably be sticking with OC as it seems much more friendly to work with.
Old 4th March 2014 | Show parent
  #9
Lives for gear
 
jim1961's Avatar
 
🎧 5 years
Quote:
Originally Posted by Myrok ➑️
Interesting discussion going on there. It seems like the pink fluffy would be good as a cheaper option, but it still seems like OC703 / 705 are better as they are much more dense (essentially compressed R30 fiberglass). So 10" OC703 or 705 would be much more effecient than 10" of pink fluffy, but probably not at the cost of 703 / 705. I do wonder how much pink fluffy / r30 sells for and what the minimum purchase quantity is.. either way I will probably be sticking with OC as it seems much more friendly to work with.
No. 10" of OC703 or 705 doesnt do as well as 10" pink fluffy. The greater density is why pink fluffy works better when thick. The higher density stuff is better when thin only (compared to fluffy).

http://www.acousticmodelling.com/mli...1=400&v41=5000

Have a look for yourself. Here I modeled 250mm and 400mm of fluffy vs OC703.

Keep in mind, any figure below about a 0.8 coefficient isnt helping much.
Old 4th March 2014 | Show parent
  #10
Lives for gear
 
Miiko's Avatar
 
🎧 10 years
Quote:
Originally Posted by jim1961 ➑️
No. 10" of OC703 or 705 doesnt do as well as 10" pink fluffy. The greater density is why pink fluffy works better when thick. The higher density stuff is better when thin only (compared to fluffy).

http://www.acousticmodelling.com/mli...1=400&v41=5000

Have a look for yourself. Here I modeled 250mm and 400mm of fluffy vs OC703.

Keep in mind, any figure below about a 0.8 coefficient isnt helping much.
How does that work? If you take 10" of fiberglass, one being more compressed than the other, wouldn't it work out that the more compressed version has better absorbing properties?

I see only rigid fiberglass numbers on that link? Which of those lines is OC703 and which is pink fluffy? Your key says they are all rigid porous absorbers...
Old 4th March 2014 | Show parent
  #11
Lives for gear
 
jim1961's Avatar
 
🎧 5 years
Quote:
Originally Posted by Myrok ➑️
How does that work? If you take 10" of fiberglass, one being more compressed than the other, wouldn't it work out that the more compressed version has better absorbing properties?

I see only rigid fiberglass numbers on that link? Which of those lines is OC703 and which is pink fluffy? Your key says they are all rigid porous absorbers...
Actually it doesn't.

Look at the densities. 16,600 is OC703, 5000 is fluffy. (the blue and red are OC703)
Old 4th March 2014 | Show parent
  #12
Lives for gear
 
Miiko's Avatar
 
🎧 10 years
Quote:
Originally Posted by jim1961 ➑️
Actually it doesn't.

Look at the densities. 16,600 is OC703, 5000 is fluffy. (the blue and red are OC703)
Interesting, that seems to conflict with the information from other members on the link you sent me. What were the testing conditions?

At what point does the crossover in effeciency happen? I mean, at 4", OC703 is more effecient, right? Or, why wouldn't everyone just use pink fluffy and stuff it into a 4" area.

I just don't see how a less dense version of the same material can have an equal level of absorbing as its more dense counterpart. How is that possible?
Old 4th March 2014 | Show parent
  #13
Lives for gear
 
jim1961's Avatar
 
🎧 5 years
Quote:
Originally Posted by Myrok ➑️
Interesting, that seems to conflict with the information from other members on the link you sent me. What were the testing conditions?

At what point does the crossover in effeciency happen? I mean, at 4", OC703 is more effecient, right? Or, why wouldn't everyone just use pink fluffy and stuff it into a 4" area.

I just don't see how a less dense version of the same material can have an equal level of absorbing as its more dense counterpart. How is that possible?
All the answers you seek are out there. On this very site in fact. At the end of the day, your going to require more than my words and facts anyhow. So dig deeper into the issue and you will find conformation of what I am saying.

The only thing I will add is this. There is a relationship between density and thickness. The thicker you go, the less dense you want the absorbing material to be. What works best at different thicknesses roughly breaks down like this:

2" Best = 705
4-6" Best = 703
10" or more Best = pink fluffy
Old 4th March 2014 | Show parent
  #14
Lives for gear
 
avare's Avatar
 
🎧 15 years
Quote:
Originally Posted by Myrok ➑️
Interesting, that seems to conflict with the information from other members on the link you sent me. What were the testing conditions?

At what point does the crossover in effeciency happen? I mean, at 4", OC703 is more effecient, right? Or, why wouldn't everyone just use pink fluffy and stuff it into a 4" area.

I just don't see how a less dense version of the same material can have an equal level of absorbing as its more dense counterpart. How is that possible?
It does not disagree. For a nutshell of what happens see post #29 in this thread. For more inforamtion read the entire thread. Another thread devoted mostly to the same subject is Q 4 Avare.

Andre
Old 4th March 2014
  #15
Lives for gear
 
Rod Gervais's Avatar
 
🎧 15 years
Myrok,

There is no conflict with this - and getting your head around it shouldn't be all that difficult -

As you begin increasing the depth of a dense material you reach a point of no return - picture it this way if you would - lead is a very dense material - however if you were to take a sheet of lead that was as thin as a human hair - the amount of sound reduction you would get from it would be almost non-existent........

As you begin to increase the thickness (and hence the overall density) it begins to block sound quite effectively.....

So let's say that for the purpose of this discussion you want to examine low frequency absorption - and at your frequency of interest given a 2" thick board OF density "A" is ideal -(and for the purpose of this discussion the absolute value of "A" is meaningless, as is the particular frequency of interest) however as you begin to increase the thickness of that same material you will reach a point where it begins to act more like a wall surface than it does an absorber - which is counter to what you want it to do (this due to the over the all density of the membrane you're examining, much the same as that lead we were just discussing above)

Now the flip side of the coin is a lightweight material, which is a very poor absorber in thin layers...... however - as you begin to increase the thickness of that same material you also begin to increase it's effectiveness from the prospective of absorption. In very thick layers it becomes increasingly effective due to the fact that a given sound is able to more easily pass through it..... and, due to the added depth, more of that sound energy is converted into heat...

There is nothing conflicting here.

Rod
Old 5th March 2014 | Show parent
  #16
Lives for gear
 
🎧 10 years
Quote:
Originally Posted by Myrok ➑️
I just don't see how a less dense version of the same material can have an equal level of absorbing as its more dense counterpart. How is that possible?
(credit: Hannes)



also, please reference the "flow-resistivity" tab from CW Porous Absorber Calc: Porous Absorber Calculator V1.59
Old 5th March 2014 | Show parent
  #17
Lives for gear
 
GIK Acoustics's Avatar
 
🎧 5 years
Simply put Myrok, the density does not strictly model how well the material absorbs. It just isn't the property that tells you that. The gas flow resistance is the property that is used in theoretical predictions / calculations as it tells you much more about the material. Weight per unit area has nothing to do with absorption.
The reason why you think it does, is because it is typically that a material with a higher gas flow resistance usually also has a higher density. But even then, the thicker your panel, the lower the gas flow resistance should be. The crossover point you asked for is different per the material you use. You can use the calculator Jim posted a link to earlier to find the crossover point between two materials you're looking at. Flow resistance for pink fluffy is somewhere around 5000.
Old 5th March 2014
  #18
Lives for gear
 
Miiko's Avatar
 
🎧 10 years
Thank you guys very much for explaining it clearly, I went ahead and got some 9" r30 to make a bass trap out of my 8' x 2' closet. Should I lightly stuff the entire closet with the pink fluffy and then fabric off where the doors used to be? Will that make a good bass trap? It is a close in the corner of the room / back of the room.

You can see it here:

Old 5th March 2014
  #19
Gear Guru
 
Glenn Kuras's Avatar
 
🎧 15 years
Quote:
Should I lightly stuff the entire closet with the pink fluffy and then fabric off where the doors used to be? Will that make a good bass trap?
Basically yes!
Old 5th March 2014
  #20
Lives for gear
 
🎧 5 years
Quote:
Also, an air gap can push the lower cutoff of absorption further down as well.
Would you say that 2x4 corner traps are a more effective solution than superchunks for this reason? Or is it in fact the exact opposite with the chunks being the more absorbent? IMO the chunks are a bit of a cleaner look and take up slightly less space, but id go with the better results -is the reason im asking.
Old 5th March 2014
  #21
Gear Guru
 
Glenn Kuras's Avatar
 
🎧 15 years
Filling the whole area is going to work better. If you have the funds then go that route.
Old 5th March 2014 | Show parent
  #22
Lives for gear
 
🎧 5 years
Quote:
Originally Posted by Glenn Kuras ➑️
Filling the whole area is going to work better. If you have the funds that go that route.
Thats cool man thanks! Sounds like a lot of work too, but ya know, if i could put a nice frame together to hold the pieces, id do it.

Let me ask since i have ya hear. If i COULD put a frame together that id be happy with, what do you think about going with a face that is 1 foot wide (to save on space, material, and weight) but trapping every bit of the room? Meaning all corners, all floor to wall sections and all ceiling to wall (or as much as i could on the ceiling to wall)

Worth the energy? Thanks again. Really appreciate the time you guys give here.
Old 5th March 2014
  #23
Gear Guru
 
Glenn Kuras's Avatar
 
🎧 15 years
I have never test a 1 foot facing. My best guess, with all the testing I have done, is it is not going to work all that well for bass trapping. Minimum you would want the face to be 24" across the corner. If you are low on funds, then I would make them 24"x48" by 4" thick, straddling the corner.
BTW you did not ask about framing but here is a test I did on the subject.
DIY Acoustic Panel and Bass Trap Frames |
Old 5th March 2014 | Show parent
  #24
Lives for gear
 
Miiko's Avatar
 
🎧 10 years
Quote:
Originally Posted by Glenn Kuras ➑️
I have never test a 1 foot facing. My best guess, with all the testing I have done, is it is not going to work all that well for bass trapping. Minimum you would want the face to be 24" across the corner. If you are low on funds, then I would make them 24"x48" by 4" thick, straddling the corner.
BTW you did not ask about framing but here is a test I did on the subject.
DIY Acoustic Panel and Bass Trap Frames |
Is there a significant advantage to doubling the width of the face? Instead of 2' corner absorbers, would 4' at the same angle be more effective, or not really?

And, what do you think about the depth of corner traps? If I were to make a 4' wide face in each of my front 2 corners with 8" of OC703 / Roxul combination, should that make for an effective corner trap?

Should it be ceiling to floor, side wall to side wall, or should there be a gap / space from the wall like you would normally use for first reflection points and clouds?

Sorry for the rookie / uneducated questions. I know a lot of the info is available in reading which I have tried to comprehend but sometimes it is easier to ask people with the knowledge directly to better understand. Thanks for any help you can offer.
Old 5th March 2014
  #25
Gear Guru
 
Glenn Kuras's Avatar
 
🎧 15 years
No problem on the questions.

Yes if you span the corner 4' that would be great and yes you do want to go floor to ceiling. Just don't give up other corner areas due to less fiberglass. Key is coverage of as much corner area as possible. And yes if you can make them 8" deep then all the better, but once again you do not want to leave other corners open because of it.
Old 5th March 2014
  #26
Lives for gear
 
AwwDeOhh's Avatar
 
🎧 10 years
The main reason you see the 703 touted around the web (and i've done my share..) is that it's a convenient/manageable (and moveable) size that can be mounted in rooms where it then can be taken down quickly. (ie, NON-permanent installations).
If you have the space for it, and/or don't need modular trapping, thicker & less-dense wins out any day of the week*.
*Though that is a general statement that doesn't take into account what exactly the goals of the specific treatment are in the first place. But yes, generally> thicker and less dense will absorb more bass than thinner and harder.

{the real indicator is the GFR [Gas Flow Resistance], which is usually a harder number to find since most manufacturers don't publish that data... there has been a useful collection of these numbers in this forum ---though be aware that these are general numbers and are always subject to change depending on manufacturing processes... and from batch to batch... but is useful nonetheless.
HERE>https://www.gearslutz.com/board/studi...y-numbers.html)
&https://www.gearslutz.com/board/bass-...ts-norway.html

There are probably a couple of more such threads too if you search}
Old 6th March 2014 | Show parent
  #27
Lives for gear
 
adrumdrum's Avatar
 
🎧 5 years
Quote:
Originally Posted by AwwDeOhh ➑️
The main reason you see the 703 touted around the web (and i've done my share..) is that it's a convenient/manageable (and moveable) size that can be mounted in rooms where it then can be taken down quickly. (ie, NON-permanent installations).
If you have the space for it, and/or don't need modular trapping, thicker & less-dense wins out any day of the week*.
*Though that is a general statement that doesn't take into account what exactly the goals of the specific treatment are in the first place. But yes, generally> thicker and less dense will absorb more bass than thinner and harder.

True, but some glass/rock wool of higher density can act as a membrane and ad a boost of LF absorption. Usually a thin layer(1"-2") of high density and fluffy low density glass wool behind.
Old 6th March 2014
  #28
Lives for gear
 
🎧 5 years
Quote:
Sorry for the rookie / uneducated questions. I know a lot of the info is available in reading which I have tried to comprehend but sometimes it is easier to ask people with the knowledge directly to better understand. Thanks for any help you can offer.
i know right?! and then you look and see 15,000 posts of utter patience and humility....anyway your questions are helping me, so thanks for asking them.

Quote:
I have never test a 1 foot facing. My best guess, with all the testing I have done, is it is not going to work all that well for bass trapping. Minimum you would want the face to be 24" across the corner. If you are low on funds, then I would make them 24"x48" by 4" thick, straddling the corner.
BTW you did not ask about framing but here is a test I did on the subject.
DIY Acoustic Panel and Bass Trap Frames |
Hey thanks youve given me some things to think about for sure. i typed a longish post yesterday and i dont know if i forgot to hit post reply or if something else happened but im not seeing it.

The room EQ wizard tutorial ,which i bumped into on the GIK site from your link has been a big help, but it did raise a couple of other questions if its not too much trouble.

1) mic placement - I didnt *notice any where it was talked about. When taking room measurements do we want it at listening position? In a central point? As far away as possible? none of the above?


2) Room furnishings and existing bass traps. I guess without clouding up the question too much i think im wondering if there are guidelines for preparing the room, before taking measurements.

dont mean to be off topic. Just some thoughts i had after checking out the link.
Old 6th March 2014
  #29
Gear Guru
 
Glenn Kuras's Avatar
 
🎧 15 years
Quote:
1) mic placement - I didnt *notice any where it was talked about. When taking room measurements do we want it at listening position? In a central point? As far away as possible? none of the above?
You want to place the mic where you sit.


Quote:
2) Room furnishings and existing bass traps. I guess without clouding up the question too much i think im wondering if there are guidelines for preparing the room, before taking measurements.
If you want to test before and after treatment then remove the treatment you have. Keep the furniture in the room though
Old 6th March 2014 | Show parent
  #30
Lives for gear
 
🎧 5 years
Quote:
Originally Posted by Glenn Kuras ➑️
You want to place the mic where you sit.
If you want to test before and after treatment then remove the treatment you have. Keep the furniture in the room though
Much respect and appreciation for your knowledge, dedication, and selflessness.
πŸ“ Reply
Post Reply

Welcome to the Gearspace Pro Audio Community!

Registration benefits include:
  • The ability to reply to and create new discussions
  • Access to members-only giveaways & competitions
  • Interact with VIP industry experts in our guest Q&As
  • Access to members-only sub forum discussions
  • Access to members-only Chat Room
  • Get INSTANT ACCESS to the world's best private pro audio Classifieds for only USD $20/year
  • Promote your eBay auctions and Reverb.com listings for free
  • Remove this message!
You need an account to post a reply. Create a username and password below and an account will be created and your post entered.


 
 
Slide to join now Processing…

Forum Jump
Forum Jump