16th December 2012
#61
Lives for gear

He needs 1,72meters of absorbtion in all of the corners to take 50Hz at 1/4 wavelenght.
16th December 2012
#62
Gear maniac

Quote:
Originally Posted by Demor
Look for the location of the offending freqs with a SPL meter. Make the superchunks as advised and you will see improvement. The traps you have already just isn't enough. And remember, there are 12 corners in a room.
Great. Thank you.
16th December 2012
#63
3 + infractions, forum membership suspended.
Quote:
Originally Posted by Mctwins
He needs 1,72meters of absorbtion in all of the corners to take 50Hz at 1/4 wavelenght.
Yes, but you think it needs to be 1,72 meters thick and it doesn't. Draw yourself a top side view with reflection lines. You will see that with most of the waves will travel longer through the rockwool than the actual debt of the superchunk.
16th December 2012
#64
Gear maniac

Quote:
Originally Posted by Demor
Yes, but you think it needs to be 1,72 meters thick and it doesn't. Draw yourself a top side view with reflection lines. You will see that with most of the waves will travel longer through the rockwool than the actual debt of the superchunk.
WOW!!! 1.72m thick in each corner? I don't have these space!!! Unless I dynamite my wardrobe and maybe it will not be enough... Any idea?
16th December 2012
#65
Gear maniac

Quote:
Originally Posted by Mctwins
He needs 1,72meters of absorbtion in all of the corners to take 50Hz at 1/4 wavelenght.
Are you talking to have 1.72 of thickness in "each corner"?
16th December 2012
#66
Gear maniac

Quote:
Originally Posted by Demor
Look for the location of the offending freqs with a SPL meter. Make the superchunks as advised and you will see improvement. The traps you have already just isn't enough. And remember, there are 12 corners in a room.
Question:
Should I test with Mic, White Noise and a RTA and find where the 50 Hz shows "louder" in RTA? Then must I "Trap" that point?
17th December 2012
#67
Moderator

17th December 2012
#68
Gear maniac

Quote:
Originally Posted by Tim Farrant
Build some of these for your LF problems

Tim's Limp Mass Bass Absorbers
THANK YOU VERY MUCH!!!!

I 'll take a look!!!
17th December 2012
#69
Gear maniac

Quote:
Originally Posted by Tim Farrant
Build some of these for your LF problems

Tim's Limp Mass Bass Absorbers
Great data m8. Just 1 question...
Should I build these absorbers as a triangle box for corners or will it better square ones?

You're the man!!!

Sorry, but I recently read this...
Quote:
Originally Posted by Tim Farrant
Yes, placing units at a wall/ceiling junction half way along a wall is another good place for absorbers tuned to higher frequencies. Absorbers tuned to the lowest room modes should always be in the wall/wall/ceiling (or floor) corner where possible. I have in the past made absorbers that are also used as coffee tables at the rear of a listening room!.
17th December 2012
#70
Gear maniac

A membrane absorber is used for a specific frequency or limited frequency range, so the larger area of the membrane facing the offending frequency the better it should work. => If it is a front to back mode and you have a membrane width of 1 m, parallel to front wall it will of course be 1 m. Angle it at 45° in a corner and the width facing the frequency will be 1 / (sq root 2) = 0,71 m. Angle it at 60° and it would be 0,5 m facing the offending frequency.

If you make any membrane absorbers it is the surface weight of the membrane + the air volume = distance to backwall in the air tight box behind + glass fiber inside (for dampening) of the box which matters. How the membrane is fixed to the frame also matters for the frequency and the effectiveness. A “stiff fixing” at the edges + a rigid membrane (like plywood) would behave differently than a “loose and flexible“ fixing at the edges (like soft rubber or an accordion type, as the surround on a speaker.) A rectangular or triangular box is no importance except as its suitability in the room.

You can always place a resistive absorber in front of a membrane one, as long as the membrane is not touched.

Last edited by Adhoc; 17th December 2012 at 02:53 PM.. Reason: Edit: added: = distance to backwall
17th December 2012
#71

Quote:
Originally Posted by Mctwins
He needs 1,72meters of absorbtion in all of the corners to take 50Hz at 1/4 wavelenght.
Yes, 1/4 wavelength of 50Hz may very well be 1.72m, but this does not mean that you need 1.72m thick absorption. Our test data shows absorption at 50Hz in products leagues smaller than 1.72m.

Andre (Avare) has referenced a figure closer to 1/18 wavelength (and I would agree, though I typically have only calculated figures to 1/16)
17th December 2012
#72

Quote:
Originally Posted by Alejandro Varela
You said that those Soffit & TriTraps Traps will reduced low freqs and I get a better decay absorption? Is guaranteed? How to build it? I can't go to your shop and buy it (I live in Buenos Aires) Are any DIY link of those traps?

Thanks
Alejandro,

I was just in Buenos Aires last month. A beautiful city I must say! How do you guys stay up so late every night?!

You would build the soffits just as you would build superchunks (you can search those here on the forums or Google, many building instructions. The soffit traps are the same idea, only square instead of triangular)

We pay to have our products tested at an independent laboratory so that we're sure they're effective. Not every DIY option has been tested at a certified laboratory, but I can say with confidence that superchunks clearly work in many, many rooms.

Edit: I would also suggest putting time into trying different placements in the room as well. Trying out many positions might be annoying - but it ensures you are starting from the best possible place. And just 15cm can make a LARGE difference!
17th December 2012
#73

Quote:
Originally Posted by Mctwins
He needs 1,72meters of absorbtion in all of the corners to take 50Hz at 1/4 wavelenght.
This is not correct. The speed of sound inside a porous absorber is much less than it is in air. For example, inside a porous absorber with a flow resistivity of 5000 rayls/m, a quarter wavelength at 50 Hz is around 55cm.
17th December 2012
#74
Gear maniac

Quote:
Originally Posted by prairiedog
This is not correct. The speed of sound inside a porous absorber is much less than it is in air. For example, inside a porous absorber with a flow resistivity of 5000 rayls/m, a quarter wavelength at 50 Hz is around 55cm.
Interesting! Quite obvious that the speed of sound is lower in a resistive absorber which in turn means a "narrow depth" resistive absorber can work "fairly well" also for lower frequencies / longer wavelengths. Do you know of any chart or diagram on speed of sound versus different gas flow resistance?
17th December 2012
#75

Quote:
Interesting! Quite obvious that the speed of sound is lower in a resistive absorber which in turn means a "narrow depth" resistive absorber can work "fairly well" also for lower frequencies / longer wavelengths. Do you know of any chart or diagram on speed of sound versus different gas flow resistance?
The speed of sound in a porous material can be found from the angular frequency divided by the real part of the complex wavenumber. Depending on which "model" you use you will get a slightly different value. However, bearing in mind that we are using a value of "flow resistivity" within these models that is often not known with a high degree of accuracy... take your pick which model you prefer Delany and Bazley, Miki or Allard et al.?

I have attached an abstract that shows a modified empirical formula from Miki. It is a modified version of the much used Delany model for porous absorbers. The author claims that this model addresses some of the shortcomings of the Delany model (in particular for use at low frequencies I would argue). In general the Miki model gives slightly higher speed of sound results to the Delany. It is fairly easy to put together a spreadsheet of speed of sound calculation from this.... Frequency vs Speed of sound for different flow resistivities?

Hope that helps
Attached Thumbnails

17th December 2012
#76
Gear maniac

Seeing REW Graphics, If I have a 53.6 HZ "mountain" (I.E.) should I build a "Box" for these specific frequency, isn't it?

And build one on each corner (According to most amplitude freq)...(?)

17th December 2012
#77
Gear maniac

Quote:
Originally Posted by GIK Acoustics
Alejandro,

I was just in Buenos Aires last month. A beautiful city I must say! How do you guys stay up so late every night?!
WOW, next time come home!!! And we could take some drinks!!!
17th December 2012
#78
Gear maniac

Thanks Prairedog. My memory is good but short and it is too long ago I had use of any "higher math"... (My hope was for a ready chart to store away in the "library".)

Edit: Ooops, credit to the wrong guy. Sorry about that Icecube, apparentlly I need to go to the optician.

Last edited by Adhoc; 18th December 2012 at 08:52 AM.. Reason: To the deserving ...
17th December 2012
#79

Quote:
Do you know of any chart or diagram on speed of sound versus different gas flow resistance?
Thanks to Icecube1 for his explanation. You can avoid most of the mathematics by using my calculator to estimate the complex wave number. Here is a link to a sample calculation.

Sample Calculation

In this example the speed of sound is given by:

(2 x PI x 50) / 2.88987 = 108.71 m/s
17th December 2012
#80

Quote:
Originally Posted by Alejandro Varela
WOW, next time come home!!! And we could take some drinks!!!
You know, I'm starting to miss Fernet now!

----

Demetris & Icecube, your explanations were great
18th December 2012
#81
Gear maniac

Quote:
Originally Posted by GIK Acoustics
You know, I'm starting to miss Fernet now!

----

Demetris & Icecube, your explanations were great
LOL, Fernet rules!!!!!!!!
18th December 2012
#82
Gear maniac

Seeing REW Graphics, If I have a 53.6 HZ "mountain" (I.E.) should I build a "Box" for these specific frequency, isn't it?

And build one on each corner (According to most amplitude Low freq) and build more Box for other freq too...(?)

18th December 2012
#83
Moderator

Quote:
Originally Posted by Alejandro Varela
Great data m8. Just 1 question...
Should I build these absorbers as a triangle box for corners or will it better square ones?

You're the man!!!

Sorry, but I recently read this...
The idea is to loose the corner and replace it with floppy limp material. Make square boxes and butt the edges up so there is a void behind it. If you look at that thread I give some examples, about page 4 I think.

And despite what others will say, they do not need to have large area to work, believe me.
18th December 2012
#84
Lives for gear

Alejandro...
Don't forgett to make some measurements when the boxes is installed in the room. Same procedure as before.
18th December 2012
#85

Quote:
Edit: Ooops, credit to the wrong guy. Sorry about that Icecube, apparentlly I need to go to the optician.
No worries Adhoc, no room for ego's here it's research by other talented mathematicians anyway that I am sharing
18th December 2012
#86
Gear maniac

Quote:
Originally Posted by Tim Farrant
The idea is to loose the corner and replace it with floppy limp material. Make square boxes and butt the edges up so there is a void behind it. If you look at that thread I give some examples, about page 4 I think.

And despite what others will say, they do not need to have large area to work, believe me.
Yeah I saw that whole thread, realy amazing. Thank you!!!
I' m asking to build just 1 divided Tower of boxes on each corner, since sizes are the same for every freq 60x40xdeep & 30x40xdeep? I guess it'll work the same vertically, isn't it?
Quote:
Originally Posted by Mctwins
Alejandro...
Don't forgett to make some measurements when the boxes is installed in the room. Same procedure as before.
Sure Mctwins. I'll keep you informed.
20th December 2012
#87
Gear maniac

...still building my boxes!!! Last step!!!!
21st December 2012
#88
Gear maniac

Work Finished!!!
I' m very happy
I hope I'd made a great job...
Room sounds better.

Pictures:

Measures:
NW8 before.zip
NW8 after.zip

A & B corners "after" measurements were not made at same Mic position , 'cause I hadn't something to level them (should I put on the floor or at speaker's level? )
Any comment will be welcome...
What's next?

PS1. Thanks again to Tim Farrant
PS2. Cosmetic will be upgrade soon! (ASAP)
21st December 2012
#89
Gear maniac

Today I' m gonna build some Bass traps panels for early reflections...
Side panels can be 1 inch, isn't it?
21st December 2012
#90
Gear maniac

BUMP!

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