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acoustic treatment for a small live room
Old 11th March 2019
  #61
Okay !!!

Here i am.

So far, i placed 2 half superchunks in the rear corners. Isover 38 (AFR 15Kg / Density 38kg/m3)

And in the front, i placed 2 superchunks made of recycled cotton/polyester (AFR supposed 1,5Kg/ Density 20kg/m3) and added in front of them 120mm slats with 1mm slits and i almost finished to seal all their boundaries.

And here is what i get...

i think i missed something between 130 and 230 and beyond 12K.

Well... the noob i am is lost at sea...
Attached Thumbnails
acoustic treatment for a small live room-half_rear_slats_front_spl.jpg   acoustic treatment for a small live room-half_superchuncks_rear_slats_front.jpg   acoustic treatment for a small live room-half_superchuncks_rear_slats_front_wtrfl.jpg   acoustic treatment for a small live room-half_superchuncks_rear_slats_front_wtrfl_zoom_40_1000.jpg  
Old 12th March 2019
  #62
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🎧 10 years
I'd hire an ACCREDITED Acoustician, before you spend more money, you clearly dont understand what you are doing...
better find someone who does...not meant to be rude, just honest and helpful.
Misunderstanding acoustics is VERY EXPENSIVE!

YYMV

Light

Temple
Old 12th March 2019
  #63
Yes... I see that.
I think that the surface of slats is too big. Too relective.
I m going to remove the front slats. And build a smaller HH trap apart.
Then i'll see.
In a nutshell... I m going to follow the advices readen in this forum.

So far...not a big budget. Just some time.
Old 12th March 2019
  #64
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I saw your message before you edited it, but, hire an acoustician will save you some time and money for sure
Old 12th March 2019 | Show parent
  #65
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🎧 5 years
Quote:
Originally Posted by golgoth21 View Post
Yes... I see that.
I think that the surface of slats is too big. Too relective.
I m going to remove the front slats. And build a smaller HH trap apart.
Then i'll see.
In a nutshell... I m going to follow the advices readen in this forum.

So far...not a big budget. Just some time.
in the link below, un cas concret.

Building massive broadband absorbers on wheels.
Old 12th March 2019
  #66
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It is a broadband absorber, not a tuned* absorber...and it's 40 cm deep.

Not the best option in very small room (like OP's one).

*remember a tuned can have a wide Q as demonstrated earlier in this thread

edit:
quote from thread linked just above by dinococcus
"The acoustic designer recommended the back wall to be 60 cm thick (2 feet) and I was ok with that, it worked, but it also ate up quite a lot of room." ostfisk

60cm!!! I won't recommend a 60cm treatment, in a 2,90 X 3,10 meters room
Old 12th March 2019 | Show parent
  #67
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this is not i have readed.
Old 12th March 2019 | Show parent
  #68
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Quote:
Originally Posted by JayPee View Post
60cm!!! I won't recommend a 60cm treatment, in a 2,90 X 3,10 meters room
i think Golgoth21 can read.
Old 12th March 2019 | Show parent
  #69
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Quote:
Originally Posted by dinococcus View Post
this is not i have readed.
Please, read the thread you linked.


From the OP (ostfisk) #1 post

"The acoustic designer recommended the back wall to be 60 cm thick (2 feet) and I was ok with that, it worked, but it also ate up quite a lot of room.

So I came up with an idea to build the middle section on wheels. Then I can move it close to the wall when needing more space and then move it out to create the necessary depth when mixing and writing songs."
Old 12th March 2019 | Show parent
  #70
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Quote:
Originally Posted by JayPee View Post
Exactly what I said in this post


Regarding the Maths behind Soundflow. Ask them, and please, share the answer with us.

Regarding the differences between Acoustic Modelling and Soundflow:
You will get different results even with very simple porous absorber designs. So it's not ONLY with Helmholtz resonators.
The official answer from AFMG:

yes, if you see differences of about 10% or more, please let the density at zero (not used).
Your 300 mm thick sonorock with 30kg/mΒ³ will produce the main effect, compared with the slats in the plate.
Since the sonorock is between the plate and the rigid wall, we cannot expect, that the "plate"-property of the absorber will contribute much to the overall behavior.
Second, the density could be used, if the absorber has a very high flow resistivity, I guess.
So, use 0 kg/mΒ³ at first and check the deviations for the real density then.
Old 12th March 2019
  #71
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Please, copy and paste your exact question.
Old 12th March 2019 | Show parent
  #72
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Quote:
Originally Posted by JayPee View Post
Please, copy and paste your exact question.
I am currently testing the Soundflow software and am so far very
impressed. I have a question regarding the Absorber density (optional)
setting.

In the manual it states:

When the FLOW RESISTIVITY is specified, the ABSORBER DENSITY can be
entered optionally. If the latter value is given, additional effects due
to the
conduction of sound by the vibrating structure are included in the result.
However, this should account for a small correction only, otherwise the
plate
or perforated panel type should be used for the material.


Can you clarify what would be considered a "small correction"?


For example if modelling a slat resonator, the density setting can have
a drastic effect on the centre frequency of absorption. In the attached
images you can see that adjusting for density the centre frequency drops
more than 100Hz. I have been unable to find any literature theoretical
and measured that show such a dramatic centre frequency shift with the
addition of absorption to a Helmholtz system. Is this a case where
density should not be used and only Flow Resistivity entered?
Old 12th March 2019 | Show parent
  #73
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Once again:

Quote:
Originally Posted by JayPee View Post
Regarding the differences between Acoustic Modelling and Soundflow:
You will get different results even with very simple porous absorber designs. So it's not ONLY with Helmholtz resonators.

Acoustic Modelling is still a fantastic tool to get familiar with acoustic modelling. It's a great starting point. But I don't know whether professional have been using and relating on Soundflow or AcousticModelling for years for their designs...
Check the measured graph and compared to Soundflow prediction:

acoustic treatment for a small live room

+

Boggy
"Density is still important parameter, whatever online calculators tried to convince you" original poste here


+ many messages here on GS showing (proving?) the importance of density. No matter the design.
Old 12th March 2019 | Show parent
  #74
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You asked for Maths here but I guess you didn't get a Maths answer from Soundflow.

That specific quote lets me very perplex to say the least:

Quote:
Originally Posted by DPower View Post
the density could be used, if the absorber has a very high flow resistivity, I guess.
"I guess"...

Where is the Science here?

Sorry, but, this is not the answer I hoped for. (Check my message just above regarding density).

Maybe the answer you're looking for is in the other calculators.

Let's see the problem the other way around:

We've seen that Soudflow predicts exactly the measured results. (See previous posts from Jens and I).

So, why do other calculators show a different results compared to real measurements?

Should we trust reality measurements or free calculators?

Once again, I never used these calculators since I use Soundflow.
Like you said, it's very impressive, because the prediction are very very closed to reality considering the right parameters entered.

I don't know if there is another software similar to Soundflow. Would be interesting to see if the results match with Sundflow/reality.

Last edited by JayPee; 12th March 2019 at 07:57 PM..
Old 12th March 2019 | Show parent
  #75
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🎧 10 years
Quote:
Originally Posted by JayPee View Post
You asked for Maths here but I guess you didn't get a Maths answer from Soundflow.

That specific quote lets me very perplex to say the least:



"I guess"...

Where is the Science here?

Sorry, but, this is not the answer I hoped for. (Check my message just above regarding density).

Maybe the answer you're looking for is in the other calculators.

Let's see the problem the other way around:

We've seen that Soudflow predicts exactly the measured results. (See previous posts from Jens and I).

So, why do other calculators show a different results from real measurements?

Should we trust reality measurements or free calculators?

Once again, I never used these calculators since I use Soundflow.
Like you said, it's very impressive, because the prediction are very very closed to reality considering the right parameters entered.

I don't know if there is another software similar to Soundflow. Would be interesting to see if the results match with Sundflow/reality.
The math uses the Transfer Matrix method. I discovered that through further reading on the subject in other fora.

My issue with the model is not based on free calculators, but the scholarly research in which prediction and testing correlate almost 100% and in which a centre frequency change of over 100Hz does not occur with the addition of absorption to the Helmholtz model. There is clearly an issue in Soundflow with how the density effects Helmholtz models with a greater perforation percentage. With a lower perforation percentage the density effects the resonant frequency, but at a much tinier level (Less than 10%), which follows the published mathematical models. Given that, the answer from AFMG themselves was that if there is greater than 10% change, then the density parameter should be ignored.

Now, if you have impedance tube measurements that can demonstrate this 100Hz drop in centre frequency after the addition of absorption, then by all means share it. Otherwise, I consider this subject closed.
Old 12th March 2019
  #76
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Do you know impedance tube measurements under 100 Hz are not valid?
Old 12th March 2019 | Show parent
  #77
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🎧 5 years
Quote:
Originally Posted by JayPee View Post
Please, read the thread you linked.


From the OP (ostfisk) #1 post

"The acoustic designer recommended the back wall to be 60 cm thick (2 feet) and I was ok with that, it worked, but it also ate up quite a lot of room.

So I came up with an idea to build the middle section on wheels. Then I can move it close to the wall when needing more space and then move it out to create the necessary depth when mixing and writing songs."
40cm +. 20cm air gap
Old 12th March 2019 | Show parent
  #78
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🎧 10 years
Quote:
Originally Posted by JayPee View Post
Do you know impedance tube measurements under 100 Hz are not valid?
63 Hz for most commercially available impedance tubes.

100 Hz for reverberation chambers.
Old 12th March 2019 | Show parent
  #79
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🎧 10 years
Quote:
Originally Posted by dinococcus View Post
40cm +. 20cm air gap
Yes, still equal to 60 cm.

I don't got your point dinococus.
Old 13th March 2019 | Show parent
  #80
Acoustician work in progress. Waiting for the quotation.....
Old 14th March 2019
  #81
Found this : Rockwool Alpharock.

As a SCC, should work great, not !

acoustic treatment for a small live room-alpharock.jpg
Attached Thumbnails
acoustic treatment for a small live room-alpharock.jpg  
Old 14th March 2019
  #82
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🎧 10 years
No. Alpharock is way too dense for SSC.
Old 14th March 2019 | Show parent
  #83
Okay.... I still have to read to learm. So what are the average values for SCC ?
Old 14th March 2019 | Show parent
  #84
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Quote:
Originally Posted by JayPee View Post
No. Alpharock is way too dense for SSC.
But clearly from the screenshot Soundflow shows a more than .8 absorption coefficient at approx 50Hz when the gas flow resistivity is set 30 Kpa*s/m2 and the density of 70Kg/m3 is added...
Old 15th March 2019 | Show parent
  #85
Quote:
Originally Posted by DPower View Post
But clearly from the screenshot Soundflow shows a more than .8 absorption coefficient at approx 50Hz when the gas flow resistivity is set 30 Kpa*s/m2 and the density of 70Kg/m3 is added...
And the average depth of 225 for an SCC of 60x60x80cm.
Old 15th March 2019 | Show parent
  #86
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Quote:
Originally Posted by DPower View Post
But clearly from the screenshot Soundflow shows a more than .8 absorption coefficient at approx 50Hz when the gas flow resistivity is set 30 Kpa*s/m2 and the density of 70Kg/m3 is added...
...at random incident.



I'm off.
Old 15th March 2019
  #87
Ok, here are measurements from another resource :

acoustic treatment for a small live room-alpharock.png

Not the same at all.... Not the same range neither.
Attached Thumbnails
acoustic treatment for a small live room-alpharock.png  
Old 16th March 2019 | Show parent
  #88
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🎧 10 years
Quote:
Originally Posted by Jens Eklund View Post


EDIT: I figured it out. I'm running Windows in a VirtualBox on my Mac, and the number pad on my keyboard wasn't inputting. Tried with the numbers along the top of the keyboard and I was able to change it down to 20hz.


300 mm deep HH array incident angle from Soundflow.

One panel has 6 mm gaps and the other one 7 mm gaps between the slats. So even if you mess up by this much; the performance is almost identical. There is no precision required to build a HH array.

A membrane on the other hand due to the high Q requires quite a lot of attention. Membranes are a last resort for me if I need to combat very low frequencies and/or the available build depth is very limited. For all other low frequency absorption needs I rely solely on HH arrays since itΒ΄s she safest bet (easy to predict and build plus offers a wide bandwidth so you donΒ΄t need to worry about missing your target frequency range).
Jens (or anyone using SoundFlow), after learning about SoundFlow from this thread I've downloaded a trial of the Pro version to see if it might suit my needs. I noticed in the graph you posted that it goes down to 20hz. On my screen, the lowest it will go down is 50hz, and when I try to lower it in the option or in that pane, it won't go bellow 50. Is there a trick that I'm missing?

Last edited by logjamparty; 16th March 2019 at 11:53 PM..
Old 17th March 2019
  #89
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🎧 10 years
Scale, under that graph.
Old 17th March 2019 | Show parent
  #90
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🎧 5 years
Quote:
Originally Posted by golgoth21 View Post
Ok, here are measurements from another resource :



Not the same at all.... Not the same range neither.
hello,

this measurement are take in reverberant chamber.


In the link below the explanation of the diffrence between reverberant chamber and our room.
Low end response is fine but low mids are horroble. Why why why?

Me too i readed (a longtime ago) the measurements you show (extract form alphasabine web site). I try the alpharock and i threw them. For the mid only.
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