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...

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

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.

I saw your message before you edited it, but, hire an acoustician will save you some time and money for sure

in the link below, un cas concret.

Building massive broadband absorbers on wheels.

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

this is not i have readed.

i think Golgoth21 can read.

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."

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/m³ 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/m³ at first and check the deviations for the real density then.

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?

Once again:

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.

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 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.

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.

Do you know impedance tube measurements under 100 Hz are not valid?

40cm +. 20cm air gap

63 Hz for most commercially available impedance tubes.

100 Hz for reverberation chambers.

Yes, still equal to 60 cm.

I don't got your point dinococus.

Acoustician work in progress. Waiting for the quotation.....

Found this : Rockwool Alpharock.

As a SCC, should work great, not !

No. Alpharock is way too dense for SSC.

Okay.... I still have to read to learm. So what are the average values for SCC ?

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.

...at random incident.



I'm off.

Ok, here are measurements from another resource :



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

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?

Scale, under that graph.

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.