It models resistance to flow only. Guest. 2m tall, 290mm deep, 47 well quadratic diffusor. 6 0. Up to four absorbers can be modelled at once, each of which can have up to four layers. This will be against a wall, not in a corner. V-corrugated absorbers have been. The nice absorber calculator you posted only confirms: 10cm is useless under 100Hz, 20cm does very little and more is physically impossible. 1 Website for Pro Audio. You can use the Acoustics Module to model the propagation of elastic waves in solids and porous materials, for single-physics or multiphysics applications, such as vibration control, nondestructive testing (NDT), or mechanical feedback. Porous absorbers, as the name would suggest, are made from a multitude of tiny holes – cells, through which sound travels. Hi! I have an example, and I'd like to know if it I possible to do the math here. Punching in those numbers, expect . Like other resonance absorbers, they can be tuned to specific frequencies, but they can also be used in conjunction with porous absorbers, such as with applied foams, for broadband applications. This membrane effect is "tuned" to a specific frequency depending on the density and thickness of the material. The porosity of copper foam is 0. That said, we get back to this question. Ye Old Porous Absorber Calculator. . COMSOL Multiphysics offers. This was measured and also predicted in Ethan's room mode calulator for thePorous absorbers need considerable thickness to maximize the absorption performance at low frequencies since the minimum thickness required is usually one order of magnitude smaller than the. Turns out that my 4" (10cm). I'm trying to tame a huge 40Hz ringing in my room. A higher fiber density leads to a more complex path inside the porous absorber therefore it implies higher interaction between sound waves and fibers. It's a big group effort and we're in the process of trying to make it easier to understand/use. s Owens corning 703, Rockboard AFB (or equivalent) - 16,000 pa. 8 kg/m3 can be alternatives. s/m2, at which density going beyond 12" of thickness offers minimal benefit, and getting more than 50% absorption at 50Hz doesn't work. They all absorb sound energy as they damp the oscillation of the air particles by friction. E. New Update 1. Porous Absorber Calculator 2) the filtered impulse response at -60 dB or the topt can give an indication. Porous materials are the most commonly used absorbers. Glass wool fibers have poor deformation and decreased sound absorption in the. more absorber+less gap), I seem to be coming to a different conclusion. Depends on density of material. Machine-learning models. g. Numerous computational models to map the acoustic effectiveness of open-porous absorbers are available for your design, for example: empirical model of. s. A microperforated panel absorber may have an absorbtion curve like this. If a different material such as rockwool or cotton or hemp fiber boards are used to make a porous absorber, you must ignore the density properties of 703 [3 lbs. If you change the vibrating mass and stiffness of the. This is a reference guide for basic acoustics and room treatment. So for porous absorber lower is good. Another theoretical test case was made by adding an air cavity to the soft porous absorber, leading to flow resistivity σ = 10 kPa. Slotted Panel. Helmholtz Absorber Calculator. Fraunhofer developed with Caruso Iso-Bond panels the VPR absorbers th. Porous Absorber Calculator. the direct path angle/evctor is irrelevant. This was supposed to be a good alternative to 703 rigid fiberglass yet when I input 4 inches / 10cm of absorption with these figures into the calculator, the results are rather bad. Obviously I'd need more surface area to make a real dent in a room that size. I don't understand why the porous absorber calculator wouldn't scale to small room acoustics (as some have said); even if its results are based. 8 1 Absorption Coefficient • 100mm 5K • 50mm 5K, 50mm 16K • 50mm 5k, 60mm 16K, Perf PanelMicroperforated panels (MPP) are acoustic absorbers that are reclaimable, noncombustible, and environmentally friendly. Porous Absorber Calculator. Porous Absorber Calculator. Here's the link: Porous Absorber Calculator I believe that it's working correctly and is stable but would appreciate some feedback if you have any problems with it. Room modes mess up everything below about 300Hz. Calculate the cubic packing of uniform spheres porosity (Figure 2‑8). The angle of incidence can be adjusted. The calculation doesn't assume a sealed cavity, except for a resonator. The room was empty apart from a partition in one corner (usually used in office spaces). It doesn't perform as a whole system with a cavity (which isn't sealed), it's rather a velocity based absorber which. Porous Absorber Calculator I haven't seen great performance from the 24 inch SSC's, while the 34 inch ones rock. To get a feeling of how much was needed to absorb any given frequency, I've been using this porous absorber calculator. Absorber thickness. The absorber geometry is still cylindrical, but instead of being subdivided into two segments the cylindrical volume is subdivided into N sectors. The sound absorption coefficient calculator determines the absorption coefficient via absorbed and incident sound intensities. 1. The composite sound absorber includes a MPP (micro-perforated panel) layer, a porous material layer, and an air cavity layer. Porous Absorber Calculator. Rigid Backed Porous Absorber. Gear Guru . Flow resistivity is related to density. This is primarily due to viscous boundary layer effects. An example of temperature distribution over a part of the StepRec module without air movement through the receiver is shown on Fig. It was treated with nearly completely closed surfaces composed of thick porous absorbers, with themselves were touchingly mounted behind 1. As I plan to absorb also VLF at around 40 Hz I like to achieve this with very deep porous absorbers (500-1200mm). Helmholtz Absorber Calculator. Thickness of the template is 1/8” = 3,175 mm. June 21, 2019. this formula or e. So attempts to calculate or predict absorption using a calculator based on a single depth are futile. I'm not sure on the gas flow resistance of Safe n Sound (hopefully Andre can pop in with a number tomorrow) but if its anywhere near pink fluffy, the result difference would be this: Porous Absorber Calculator - Results Now this is assuming a rigid boundary and is not taking the corner into account, but still, the difference isn't negligible. All the source code for this app is availble on my Github repo "porous_absorber". 0 with a German user interface and is developed by Marshall Day Acoustics. If we take a porous absorber with flow resistivity 10,000 rayls/m, at a frequency of 100Hz the Allard/Champoux model predicts that the real part of the complex. 9615% and 73. Porous Absorber Calculator. This work investigates the use of hybrid double-layer microperforated panel/porous systems as wideband absorbers for applications in the closing of the test area of wind tunnels. This relationship can be evaluated analytically only for few simple material geometries. . With a two foot thick area, you have the possibility of getting significant absorption at 40 Hz. this online calculator b) A bass or broadband absorber using porous material with a perforated plate or slats in front which is a different system. CryptoApplication of Porous Metals. This webpage is a reimplementation of the "Porous Absorber" sheet in the above spreadsheet using Rust and Web Assembly. But none with just a plaster board in front with an absorber and air gap. For others; the diagram "B. Joined Nov 15, 2020 Messages 7,363 Likes 7,810 Location Brussels,. This means you can vary the. Some of the pro designers around here have also recommended panels over perf. Leave the 3" gap between the insulation and wall to move the mass out towards where lower frequencies will have some velocity instead of pressure (Porous Absorber Calculator) which is what we're targeting here. Look at the densities. 2017, 116, 311–316. I'm not sure on the gas flow resistance of Safe n Sound (hopefully Andre can pop in with a number tomorrow) but if its anywhere near pink fluffy, the result difference would be this: Porous Absorber Calculator - Results Now this is assuming a rigid boundary and is not taking the corner into account, but still, the difference isn't negligible. The sound absorption coefficient (SAC) of a composite multi-cell sound absorber in the low- and mid-frequency range is investigated by using experiment and numerical method. Mass This sheet shows two absorption curves for a single layer of porous absorber with and without an air gap. Porous Absorber Calculator Preamble. Whealy C. The frictional resistance given from the material is enough to stop the wave and convert it into heat energy. Porous silicon carbide (SiC) is widely used as the absorber due to its high-conductivity, high-absorption, and anti-oxidation [12]. Whether you're just getting started or want some touching up, this should be a good place to start. you may not need to be terribly concerned with the. BEHOLD THE MIGHTY POROUS ABSORBER CALCULATOR. how to predict the behaviour of a Gobo - Gearspace. plastic membranes or 2. BTW, I prefer the Komatsu model over the default model of the online calculator. Hello again! I have some challenges in my room, and been reading up on alot of stuff. e. On the Internet I could not find examples of bass traps using 3000 Pa*s/m2. and the porous material layer was established by using Delany and Bazley’s model. The mass is the cabinet and front wall or diaphragm. As vibrational science will tell us a resonant absorber is a mass vibrating against a spring. They only reflect high and mid. the waterfall is ok for the resonance. "Absorber 3" would be the side walls, mostly starting at hip height and touching the ceiling. [ie 5/6 of the original air filled case] There is no design formula that I have found that allows an accurate air/porous absorber mix to be considered. Much ore than that (~200mm+) makes them even better at. The Chris Whealy calculator can help with Helmholtz. For flow resistivity, look at the datasheet for your specific type of mineral wool. June 21, 2019. Sound is attenuated due to viscous friction in the submillimeter size pores. Results. This is what Jens said above:For 50 cm, at 0° incidence, the calculators show that 3000 Pa*s/m2 is quite better above ~40 Hz and slightly worse below. 9th January. Should I fill the corners (superchunk style) behind this back wall or simply have 300mmm of absorber with the 300mm gap as detailed above?Time-domain solvers have inherent difficulty in accommodating frequency-dependent quantities such as the specific acoustic impedance of sound absorbers, but recent developments have enabled us to consider it for some sound absorbers such as porous absorbers [1], [18], [19], [25], [27], [29]. Membrane resonators can be calculated with the Excel Spreadsheet Porous Absorber Calculator V1. Username: Password: Forgotten password? Register: 20 50 100 200 500 1000 2000 5000 10000 20000 Frequency (Hz) 0 0. But the problem of two calculators showing different result could be related to a formula that does not include the difference between an air gap and. We can ignore the imaginary term in the equation. wooden membranes or 3. s/m2 for OC703 (Please let me know if these are incorrect). 59 We've sorta accepted that higher mass = better NRC and STC, which is generlly true compared to foam for a bass trap, but there is more to it than just. There is the amacoustics calculator that works for helmontz and other types of perforated and membrane panels before the absorber. DanDan, Regarding your remarks on ratio of absorbent to air gap for the 6" depth I have available to me (2" absorb+4" air vs. First of all, I came across the Porous Absorber Calculator by Chris Whealy. Try this calculator: Porous Absorber Calculator Generally, the thinner the absorber, the higher the resistivity needs to be. The porous absorber calculator is accurate as far as it goes but it does not take this effect into account and therefore you usually see higher low frequency absorption in tests than the calculator predicts. I believe that it's working correctly and is stable but would appreciate some feedback if you have any problems with it. But Basotect has a coefficient of 0,8 at about 800Hz while Sonorock reaches the same value at about 1,2kHz. 1 Website for Pro Audio. The TMM was employed to calculate the specific acoustic impedance of each layer in the multilayer porous absorber, and the results were used for theoretical sound absorption prediction. online calculators for porous absorbers. I thought tri (superchunk) style absorbers were good for low frequencies mainly? Quote: Originally Posted by avare As practical proof, consider how often people have. Most importantly, these results should match those in the papers written by the people who developed the models. --Draw a line horizonally on the charts at 0. i think that most isolation material or foam benefit from stacking in depth and make bass trap from it. The resonant frequency could be calculated using e. Username: Password: Forgotten password? Register Porous model: Delany and Bazley (1970) Helmholtz model: Ingard/Allard. . Air gap 1. Share Reply Quote. 1 Website for Pro Audio ; The No. 21st March 2012 | Show parent #14. The mass is the cabinet and front wall or diaphragm. 1 Website for Pro Audio ; The No. Username: Password: Forgotten password? Register: 100 200 500 1000 2000 Frequency (Hz) 0 0. • Absorber 2. Truth be told it's closer to 42Hz. Since a porous absorber, also called a velocity based absorber, works by slowing down air particles, that means that it is less effective the lower the particle velocity is. Much ore than that (~200mm+) makes them even better at lower freq. 69%, which was superior to that 25. But I think I have a much better understanding now, especially thanks to the Porous Absorber Calculator (the excel spreadsheet). Width of hangers is used to define lowest frequency, membrane absorbers isn't included in this simple model/formula, and 1. 064–0. Hey guys, I need broadband absorption down to 50Hz. Porous Absorber Calculator (by Chris Whealy) ⚠️ Downloads an exel file; Various Acoustic Calculation Tools (by Chris Whealy) Drawings: 104 Broadband 4″ (10 cm) The purpose of this thread is to explain how to both physically hook up the connections between your computer and AVR/Pre-Pro to get started with REW (Room EQ Wizard) and to share information on the proper use of REW including proper techniques for both measuring and interpreting graphs, what. A porous absorber may have an absorbtion curve like this. For example, the angle of incidence can be set as a global parameter. If you put porous sound-absorbing material, processes in the system quit being adiabatic and the formula transforms into the following: fo=500/sqrt(m*d) Filling inner volume of the construction with sound-absorbing material reduces Q-value (Q) of the absorber, which leads to its working diapason extension. If you know any other quality tools, please tell me! List of other quality acoustic calculators besides amcoustics. Wilson, simplified relaxation model. Termination of such 'gaps' is clearly not mandatory. It doesn't perform as a whole system with a cavity (which isn't sealed), it's rather a velocity based absorber which. This was supposed to be a good alternative to 703 rigid fiberglass yet when I input 4 inches / 10cm of absorption with these figures into the calculator, the results are rather bad. Flow resistivity. 5" rockwool on the wall (green line, absorber 2,. Absorptive treatment such as mineral wool, glass fiber or high-porosity foams reduces reflection sound. 2 Glass wool as porous damping) towards the end is quite easy to understand. They are usable with. Toyoda, E. Have a look at what happens with 100mm panels AND a 50mm air gap though just out of curiosity, and also see what happens with a 100mm air gap: Porous Absorber Calculator - Results Well worth pulling them out as much as you can, up to their own depth or a bit more. I guess my only concern is that the calculation does not take into account density; and I have read many knowledgeable folk claiming a higher density for thinner panel is ideal. Maybe density is somewhat correlated with GFR, but to my knowledge GFR, thickness and air gap is the only thing to consider when designing Bass Traps using porous materials. Users with access to the relevant academic papers. 20 per sq metre the Fibertex 350 is 60kg/m^3, comes in 1500*900*50mm sheets and is $20. Porous Absorbers. Applying a mass-flow ( ρ 0 S e j u j ) excitation on surface nodes as a system input, it is possible to solve the problem and calculate the pressure. com are 34 inches wide. It is generally better to fill the space keeping it about 1/2″ away from the perforated panel. The particle velocity is at maximum at 90° and 270° (Vmax) and minimum at. Either one wants low GFR and doesn't compress, or compress as a way to emulate the higher GFR of OC 703. You will fast get a feeling which absorber thicknes is the next one to build. When length of the cavity was 20 mm, average sound absorbing coefficient of the compressed and microperforated porous metal panel absorber in frequency range 100–6000 Hz reached 59. The mass per unit area in Kg/m 2 (limp membrane). Step 1: Cut The Wood. Play with the porous absorber calculator. The setup follows international standards with about 10 m² of slat absorber in an echo chamber. With 40cm thickness, the 040 would actually be better without airgap according to the Porous Absorber Calculator. Presenting high surface areas to the incident sound wave provides rapid absorption of the wavefront. This graph shows the difference between RS45 and RS100 Multi-layer Absorber. The effect of the porous absorber is analagous to a damped mass/spring system, so yes the Q does increase with the damping coefficient and eventually becomes "overdamped" in the extreme when full of very dense mineral wool. All formulas and units are the same in NASA. If its. The paper is in Swedish but Colakurt as a Dane might be able to read it. 5m, you'd have to cover virtually all surfaces to reach effective absorption - your expectations are wrong It also looks like you used the multilayer porous absorber calculator (with one of the layers being a perforated panel) and not the. Here's the link: Porous Absorber Calculator. Both types are effective, but whereas a resonant absorber needs to be mechanically tuned to resonate in sympathy with the frequencies being absorbed, a porous absorber does. The formula is: \alpha_m = A / S αm = A/S. com not registered yet? I also played around with the porous absorber calculator, but in the past, real life measurements did not shine a good light on this calculator. The collectors have the same geometry, cross-section surface area and are built from the same materials, the only difference between. 8 At 2000Hz, respectively. If you use lower GFR the Q is widened but damping is lowered. s/m 2. Rigid backing. 4 0. Sound absorption materials also need to have great loss of sound energy, air permeability, and refractory quality, as well as the required level of structural strength [40]. To calculate the effective coefficient of thermal conductivity of porous absorbers, the simulation was carried out without air movement inside. For most of the porous absorbers the absorption coefficient α can be estimated by the very simple relation α=0. 8 & you will see the LF absorption. Unless care is taken when deciding on the size of the absorber unit, these holes will not add up. Multi-layer Absorber Calculator. 5rayls/m) 1200mm Porous Absorbent, 1500 Pa. also, please reference the "flow-resistivity" tab from CW Porous Absorber Calc: Porous Absorber Calculator V1. Porous absorbers. placed in the middle of the room. Running your suggested depths (70cm vs. So correct me if I'm wrong, but the thicker the absorber and air gap, the lower the frequencies you can absorb BUT as those factors change, the ideal absorber changes as well. And unlike porous traps which work better. Calculates the absorption curve of various porous absorber systems. Membrane resonators can be calculated with the Excel Spreadsheet Porous Absorber Calculator V1. About the low bass freq peak, Your room is small- according to Porous Absorber Calculator , It will be unpractical to build a broadband design that will absorb down to 40hz. what is your opinion about porous absorber calculators online such as: and. Wherein, there is a cylindrical porous absorber which is sealed behind a quartz window. - It is at the microscale that the porous material actually interacts with the fluid Absorbers and barriers are used for airborne noise problems, and dampers and isolators are used for structure borne noise problems [3]. It also depends on which bass frequencies are problematic in your room. not easy but it's doable. s/m 2 Porous Absorber Calculator. Since membrane absorbers require high level of precision to perform at the desired frequency, they are often customized for a specific application. Share Reply Quote. E. "f" is frequency (50 Hz in this case), "σ" is flow resistance. Anyone know how I can do a simple calculation say for a 12mm gypsum board with 10cm fiberglass and a 40cm gap with solid concrete behind. The second porous absorber represents a more dense material and is labelled ‘hard porous’, with a flow resistivity σ = 30 kPa. Username: Password: Forgotten password? Register: 20 50 100 200 500 1000 2000 5000 10000 20000 Frequency (Hz) 0 0. When tailoring porous absorbers in acoustic applications, an appropriate acoustic material model, as well as the relationship between the material model parameters and the microscale geometry of the material, is indispensable. A thought occured regarding the tuning of these panels. feet. The ZORBA software is a tool for calculating the sound absorption coefficient of porous materials and perforated surfaces. You may find it interesting to experiment with the Porous Absorber Calculator Porous Absorber Calculator V1. hi guys trying to figure out which of these 2 products would be ideal for bass trapping. Liu, G. Here's the link: Porous Absorber. Thread starter celef; Start date 2022-03-07 11:11 am; Jump to Latest celef. Porous Absorber Calculator. DSP like a DCX2496 is cheap and with placement and experimentation and treatment you can achieve a lot. All in all, you don't want the air gap much. DemetrisThe No. If you want rear tuned absorption, build panel absorbers tuned to the lower range where the porous absorber is no longer effective. The lowest room mode you have between your ceiling and floor is at 75 Hz. 1. Porous Absorber Calculator Global Parameters affect all absorbers. Flow resistance is the main property that sets the different types of materials apart. Impedance prediction methods have been published by Delany and Bazley, Qunli, Miki, Mechel, Mechel and Vér, Komatsu, and Allard and Champoux. According to the Porous Absorber Calculator this should give good absorption down to at least 50hz (and probably lower). GameStop Moderna Pfizer Johnson & Johnson AstraZeneca Walgreens Best Buy Novavax SpaceX Tesla. All the source code for this app is availble on my Github repo "porous_absorber". Absorber thickness. The calculator is easy to use just make sure to select "Komatsu (2008)" for the porous model on the left side of the page. Strutt calculates the absorption coefficients `alpha` from the complex pressure-reflection factor `R` between the surface of the absorber and the air using the following formula:Sound absorption coefficient calculation software. 5th August 2017 #5. com 2011. g. If you download and play with the porous absorber calculator: Porous Absorber Calculator V1. A Porous Absorber Calculator is a specialized tool used in acoustics and engineering to determine the acoustic absorption characteristics of porous materials. I would really like to do something like this for all of my panels in my studio but I can't seem to find a good material that I can easily buy in. Diaphragm absorbers are a common tool utilized to attenuate standing waves as part of an acoustic treatment. 2. See below for approximations of absorption coefficients for the theoretical 21" thick R38 (blue line, absorber 1) and the 1. The distance in mm between the porous absorbent. Limp mass material types can never achieve the proper rates of absorption that music and voice require. As vibrational science will tell us a resonant absorber is a mass vibrating against a spring. I need to make a keyboard macro with that sentence. Only the mean values of the quantities involved are of practical. ↑ top; home; New Product Alert; classifieds; reviews; deal zoneThe distance between the holes (centre to centre) in mm. 4 Applications. 4 The Superchunks in the Absorption test at studiotips. Damping is generally achieved by a combination of three processes: resonances that trap the acoustic energy at given frequencies, absorption of acoustic energy by different porous and fibrous lining materials, and losses in perforated plates, also known as perforates. How does one calculate or predict a perforated panel with porous absorber when the shape is triangular? I was thinking of building a superchunk-style p. 25”x47” panel of insulation. See here: Porous Absorber Calculator. porous insulation is a velocity-based absorber and thus must be placed (spaced away from rigid boundary) into areas of higher particle velocity in order to be effective. e. My Studio. If you utilize an air gap behind the panels it will increase absorption in the low mids. Multi-layer Absorber Calculator. Common pa. Hey Guys, I wanted to try a few calculations of membrane absorbers to see how the different air and absorber depths affected the absorbers. 5 @ 500Hz, and 0. this formula or e. no backing) For the air-backed absorber geometry, Strutt also allows the calculation of the transmission loss through the porous material. 2m porous absorber, 1. . Porous Absorber Calculator - Results According to the calculator, you will still get significant (I consider anything over . If you can find the Gas Flow Resistivity of the product you could predict the absorption spectrum using this calculator. im using this Porous Absorber Calculator to check how the GFR would help . . This means you can vary the angle at which the sound waves (plane waves) hit the surface of the porous absorber. e. This means that if you want to construct an absorber of mineral wool of your own, in you home studio, garage or any other a room, you could use the calculated values and use them in calculating the. Tuned pressure absorbers work only if pressure at tuning frequency is present, they will not work i. The absorber is assumed to be in front of a. For a porous absorber backed by a rigid surface, the local reaction models give errors of less than 10% if the thickness exceeds 120 mm for a flow resistivity of 5000 Nm-4s. perforated wood over acoustic foam porous absorbers. The main dimensions of packing were the following: 10 mm height, 146 mm inner diameter, 600 mm outer diameter; the specific area was 2800 m 2 m-3 and the porosity 0. Flow resistivity. Chen, in Porous Materials, 2014 3. AFAICS, the. Username: Password: Forgotten password? Register: 20 50 100 200 500 1000 2000 5000 10000 20000 Frequency (Hz) 0 0. They achieve a high- absorption coefficient, utilizing a relatively small volume. I was pretty psych'd initially but then became a bit confused and frustrated by a few things, not the least of which is the variety of GFRs listed for OC703. Parameters Global Parameters Air temperature: 20°C Air pressure: 101325 Pa X Axis: Frequency Range: 20Hz - 10000Hz Scale: logarithmic Resolution: medium Angle of incidence: 0° Porous model: Komatsu (2008) Helmholtz model: Ingard/Allard Absorber Parameters • Absorber 1 20mm Slotted Panel, 10mm/80mm (12. that is why many designs partially cover the bass-treatment with reflective. 59 Here is another: Porous Absorber Calculator The trick seems to be finding the Flow Resistivity for the material you want to use: Pa. When paired with a porous acoustic core, they present a wider more linear absorption coefficient, making them a preferred option. Air gap 1. Solution. I am quite a noob but i’ve been researching a lot about it the past few weeks. m −2 , thickness h = 50 mm, and cavity depth. Porous Absorber Calculator. The measurement results serve the evaluation of the required complexity of the absorber models to be applied to model your specific materials. Share Reply Quote. I'm using the Whealy calculator, porous absorber page. • Absorber 1 (1. To estimate the attenuation D of silencers under practical conditions, the formula of Piening is used: D=1. All. If overthinking is a. If an absorber is composed from multiple layers of porous materials or porous materials and airspaces, the absorption coefficient can be calculated using the transmission matrix method [3], [4], [5], [6]. The composite sound absorber includes a MPP (micro-perforated panel) layer, a porous material layer, and an air cavity layer. Coates and Kierzkowski in their paper describe the advantages of thin, light membranes that can replace traditional bulky and economically disadvantageous porous absorbers. 4 kg/m3 and corrugated board composites with densities of less than 474. This gives an open area of 18%. Wilson, simplified relaxation model. 4 0. This porous absorber calculator will help you compare the effectiveness you can expect with various depths. 2m depth in my calculations is only for hangers. Long story short, when you have two materials, lets say one has 6kPa/m2 and another wit 12kPa/m2. 8" or more. Porous Absorber Calculator Calculates the absorption curve of various porous absorber systems. The sound dissipation mechanism in MPPs is based on the principle of the Helmholtz resonator (HR) []. Way back, G. Hi there, what happens (in terms of physics and acoustics) if we have a porous absorber that is covered with a limp membrane, or rather: wrapped into a limp membrane, the membrane touching the absorber? Let us assume the membrane would have a weight of say 0. The porous absorber calculator says 'yes' when I plug in a GFR of 2500. Limp membrane, Helmholtz, or just open, all models require you to place the porous absorber at the front for maximum effect, but sometimes with a minimum air gap so it doesn't touch the front. Porous model: Allard and Champoux (1992) Helmholtz model: Ingard/Allard.