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Thank you in advance ! G21 
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So once you identify the mode, you'll know where to put the device. :) 
Ok.... So, i can put anywhere on the back or front wall a bass trap. I mean close to the ceiling or close to the floor, it will work for this 55Hz main modal node located between these two walls ?
Thank you. 
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Multilayer Absorber Calculator Either you've entered the data wrong, or Soundflow has an error in their formula. 
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I did say "compared to all other calculators." Chris Whealy, John Sayers, mhaudio, all come very close in agreement in putting the centre frequency between 145 and 165 Hz. 
Soundflow takes more parameters into account as far as I know.
DPower, I'm not familiar with these calculators since I use Soundflow, but can you enter the density of the material into the equation? 
Any calculator that doesn't allow you to enter the density of the wool (or even flow resistivity in some extreme cases) is bound to be off.

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Density while not completely irrelevant, cannot account for a centre Frequency drop of 100Hz. The basic Helmholtz formula 2160*sqrt(r/((d*1.2*D)*(r+w))) (Cox & D'Antanio Acoustic Absorbers and Diffusers: Theory, Design and Application) works out so (Metric converted to Imperial): F=2160*SQRT(.2362/((.7480*1.2*11.8110)*(3.5433+.3262))) Which gives us a basic centre frequency of 163.9Hz. Adding absorption to that will lower the centre frequency slightly, and lower the q, which lines up with the results from Chris Whealy's and the MultiLayer Absorber Calculator (149 & 155Hz respectively). Now, I'm not saying that Soundflow's formulas are incorrect. It's more likely to be user error, given that the error appears to be a factor of 10, which could be something as simple as a mm/cm mixup somewhere. 
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The fact that SF takes density into account is naturally not a small difference. It will completely change the behaviour of the system. Any calculator not including density will give other results compared to Soundflow. This is why I use Soundflow in the first place! 

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In this case we have an occurrence where there is a discrepancy between your results and the results of all other calculators. As I have demonstrated, this discrepancy appears to be a factor of 10. Your explanation for that discrepancy is that the density of the material is responsible. My explanation is that a decimal point has been shifted. Which is more likely to result in a factor ten discrepancy? By all means post the math that shows that the density of the material can shift the centre frequency of a system by 100Hz, and we can throw out all the textbooks on acoustics. So, no, you can please enlighten me. 
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https://www.gearslutz.com/board/atta...1&d=1552222687 Do you belive me now? Soundflow also always matches real world measurements. Something I noticed was a problem before I got my hands om SF. 
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Hello....
I did some changes. I calculate what to do in order to lower the 50. I fixed some slats in the front of my front corners bass traps and i started to seal the boundaries. By the end of the day the 50 was not dead but lowered a lot. But strangely, the 100 appears. And the room started to show a light reverb when talking loudly. Nice. The room seems bigger. Tomorrow i will attach some REW screenshots. In the meantime, can you tell me if this is normal to see the 100, 150, 200, 250, appearing. Even if we are talking about 10dB. Thanks in advance. 
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HH array is made of slats or slots. You can calculate one using Acoustic Modelling  Home Page with the multi layer calculator. Select slot layer.
Inputs are : slot depth (thickness) ; slot width (space between) and slot spacing (the distance between 2 slots : 1/2 slot width + slot spacing) 
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Oh, and what this thread did show if Soundflow is correct in their equations, is that Helmholtz traps are easier to design and build, but only if you have Soundflow, as all other calculations will result in your design being off by more than 2 octaves.

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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. That difference is even bigger with complex designs (Helmholtz resonator in our case). The more it gets complex, the bigger the difference will be. 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... ;) Cheers, J. 
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I m going to download the soundflow trial version. I hope my room will be finished when it expires. 
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I would like to point out that in the manual, it states the following: 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. Bolded for emphasis. A center frequency drop of 100Hz is not what I would consider a slight correction. However, I cannot replicate this. If and when I can, I will send AFMG support an email. 
I recreated this design with Soundflow and got the same results. Are you sure you enter ALL infos, specially the ones related to the perf. panels?
edit: post a screen shot here and let's see where the difference is 
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Hole shape: Slit Hole Dimension: 6.00 Porosity: 6.67 (based on 90mm spacing) Flow resistivity in Hole: 0 Air 5mm Absorber 300mm Flow resistivity 8.8 kPa*s/m2 Absorber density varied between 0 and 48Kg/m3 Rigid Backing 
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Velocity based vs. pressure based absorbers ...then scroll down (but read!) until here: Velocity based vs. pressure based absorbers Worth reading the whole thread as well like I suggested it in my previous post here... kfhkh We already discussed about it. 
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Screenshot please?

OK, got one that's close with a density of 30kg/m3. Close enough to show the centre freq shift well enough to ask AFMG about it.
