Diaphragm absorbers are a common tool utilized to attenuate standing waves as part of an acoustic treatment. Another important parameter of sound absorption, besides the absorbers design, is its AREA. P. 3. s/m2 is a good bet. June 21, 2019. Up to four absorbers can be modelled at once, each of which can have up to four layers. Username: Password: Forgotten password? Register: 20 50 100 200 500 1000 2000 5000 10000 20000 Frequency (Hz) 0 0. Bashing all other coefficients on the net IMO, it is not for every single person on this forum to know all these things unless they want to get serious about it. When set to "Absorber", the model can be set individually for each absorber. Rs=r*d [Pas/m] When you have specific airflow resistance Rs then you can calculate air flow resistivity r for any thickness; r=Rs/d. Otherwise your just making another reflection point. If you are making standard porous absorbers and were trying to target say 50Hz even a 1 meter thick trap is not very efficient at that frequency IF the density is 45Kg/m3 and this material has a GFR of 14755Pa. Agreement to Terms of Use This website is offered to you by acousticmodelling. 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. A Porous Absorber Calculator is a specialized tool used in acoustics and engineering to determine the acoustic absorption characteristics of porous materials. s. 2m porous absorber,. As I plan to absorb also VLF at around 40 Hz I like to achieve this with very deep porous absorbers (500-1200mm). Rigid Backed Porous Absorber. This calculator estimates the absorption coefficients of multi layer porous aborbers. Porous materials, particularly polymeric foams, are the most effective sound absorbers among a wide range of existing sound-absorbing materials. A panel absorber consists of a flat panel made of wood, metal, gypsum board, or plastic material that is arranged in front of an enclosed air volume. This only works with absorbers of uniform thickness and triangular bass traps obviously have varying thickness. Can these be converted to Flow resistivity Pa*s/m2 ? (to be used in porous absorber calculator) Share Reply Quote. If you know any other quality tools, please tell me! List of other quality acoustic calculators besides amcoustics. Multi-layer Absorber Calculator. Try this calculator: Porous Absorber Calculator Generally, the thinner the absorber, the higher the resistivity needs to be. -Assume you have a 12 dB peak at 100Hz that you want to treat. A resonant absorber is a vibrational system that “runs” on sound pressure. - 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]. The composite sound absorber includes a MPP (micro-perforated panel) layer, a porous material layer, and an air cavity layer. If overthinking is a. 90 width you are lost in regards to bass if you rely on absorption only. According to Delany and Bazley (and others), the speed of sound in a porous absorber is given by the angular frequency divided by the real part of the complex wavenumber. Helmholtz Absorber Calculator. Modeling the Damping Effect. 21st March 2012 | Show parent #14. The input impedance of the network duct system is needed, with this information it would be possible to calculate the reflection and absorption coefficients of the absorber material modeled. Reticulate porous ceramic reactors use foam-type absorbers in their operation which must fulfill two essential functions: favoring the volumetric effect and increasing the mass and heat transfer. The others perform atrociously, but even the Komatsu won't work correctly for mixing different densities. I believe that it's working correctly and is stable but would appreciate some feedback if you have any problems with it. 8 & you will see the LF absorption. With 40cm thickness, the 040 would actually be better without airgap according to the Porous Absorber Calculator. 1 Review written 🎧 20 years. Porous Absorber Calculator tlindaas, did you, will you, or may I, repeat the content of this post over in the GFR gathering thread? Common Gas Flow Resistivity numbers. Joined 2012. 6 0. 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. not easy but it's doable. I am interested in porous absorption of low frequencies since it is. S. Absorber thickness. (broadband) the glasswool Quietel is 130kg/m^3, comes in 2400*1200*25mm sheets and costs $33. OC discrepancy), 30k for 705 - I think what I have is closer to OC703, but I have a call in to Knauf to see if. A microperforated panel absorber may have an absorbtion curve like this. Up to four absorbers can be modelled at once, each of which can have up to four layers. Use diffrent angels because base resonances come from everywhere. The main advantages of microperforated panels (MPP) as light, clean and easy-to-design sound absorbers were already established in the previous century [1,2,3]. Speech Reinforcement Calculator The damped walls are acting as membrane absorbers below that range, requiring an additional 30-45 cm air gap, to absorb down to 20 Hz. The LSA proposed in this paper is shown in Fig. Look at the densities. There is an excel sheet available somewhere online and also this online calculator at Porous Absorber Calculator Here's a some modeled results for 100 mm thick absorber placed at a wall using different flow. I was planning to buy the Bradford Fibretex 350 - 60kg/m3 batts (3 for $128 - 100mm thick 1200mmx 600mm). There is also a loss in momentum due to. That said, we get back to this question. 2017, 116, 311–316. All. In base traping watch out for high absorption numbers. The porosity of copper foam is 0. The idea behind the "4 inch rockwool is only effective above 850 Hz" is that because porous absorbers work on sound velocity, and particle velocity is zero close to a rigid wall, for maximum efficiency an absorber needs to be placed at least at 1/4 wavelength. This webpage is a reimplementation of the "Porous Absorber" sheet in the above spreadsheet using Rust and Web Assembly. Mounting and. The materials used to fabricate the porous sound absorbers mainly involve stainless steel [62], copper. feet. Personally, I think it's the better option. 65 at 100Hz for an average of 0. Hey Avare, would love to ask you a couple questions to gain deeper insight- Quote: Originally Posted by avare ️ Corner absorbers are good at mid and high frequency absorptio. 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 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. AFAICS, the. Congyun and Qibai (2005) calculated the acoustic impedance for multi-layer absorbers such as perforated plates and air space or perforated plates and porous materials by using an iterative method. The above formula can be recursively applied to calculate the surface impedance of a multi-layered absorbent,. 1. I know I’ve linked this elsewhere, but I think it’s a valuable tool which is worth repeating. Documentation. effect_of_perforated_sheet_open_area. The problem is, I'm not seeing results that confirm the general wisdom -- that. Mechel and Ggrundmann. Turns out that my 4" (10cm). For 60 cm the situation is similar, though with different frequency and angle values. Behind the template is glass fibre filling with density 6-8 lbs/ft³ (96-128. There are generally two types of bass traps: resonant absorbers and porous absorbers. Calculation models and input parameters. Air is a viscous fluid, and consequently, the friction with the pore walls dissipates the sound energy. Some things were way off. Porous Absorber Calculator - About. COMSOL Multiphysics offers. 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 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. 5th August 2017 #5. Jens. Porous Absorber Calculator. A 100mm panel with 100mm air gap gives a 0. When set to "Absorber", the model can be set individually for each absorber. 5" rockwool on the wall (green line, absorber 2,. when using the porous absorber calculator, etc. Porous Absorber Calculator. placed in the middle of the room. 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. If you drop down to about 4K Pa. Flow resistivity is measured with DC pressure loss. Now you can determine which absorption you can expect from what you have. Either one wants low GFR and doesn't compress, or compress as a way to emulate the higher GFR of OC 703. 30th May 2012 #27. The equation is modified to f=50/sq root(1/md). For thicker absorbers and irregular slat sequences measurements are needed. Close inspection reveals that the metal foam absorber plate is cooler than the. 2" wide. Gearspace. Mechel and Ggrundmann. 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 thought tri (superchunk) style absorbers were good for low frequencies mainly? Quote: Originally Posted by avare As practical proof, consider how often people have. 2 0. . An example of temperature distribution over a part of the StepRec module without air movement through the receiver is shown on Fig. e. To be honest, real life testing is the only to be sure. 9 log(fd)−X. (Side remark: If you are up to using other devices like membranes in front of your absorber, angled walls. I decided to prepare perforated panel with porous absorber. Porous absorbers are most effective with mid to treble tones. , JH Brant, DanDan, Avare, can't name you all. hi guys trying to figure out which of these 2 products would be ideal for bass trapping. concepts, models, and algorithms developed for porous media in the geosciences are not directly applicable and there is a very strong need for tailored models. When sound propagates in small spaces, such as the interconnected pores of a porous absorber, it loses energy. Hello, a broadband panel effective at 30 hz is not yet invented. I am currently trying to design a slotted panel with a resonant frequency of 133 Hz and I really need to know if I can use PAC at all. According to the calculator, that has an absorbtion coefficient >=0. (i found URSA pureone fibre to be a good product available in my area) here is a great calculator to predict what is going to happen: Porous Absorber Calculator in acoustically small rooms like yours resulting roomresponse is probably too dry after treating the lows. 70% of original porous metal absorber and that 31. A 2" cloud with 16800 Pa*s/m² (which should be about the value for Owens Corning 703) mounted to the ceiling (1 mm gap) absorbs less than 50% below 428 Hz and less than 25 % below 269 Hz, and practically nothing at 75 Hz. My comment is. From the first formula we can calculate specific airflow resistance simply by multiplying airflow resistivity [Pas/m2] with thickness of the porous material [m]. Model: Allard & Champoux (1992) Absorber Parameters. I think I have read that ideally one shouldn't mix materials in broadband absorbers. The. (18), (19)) are used to calculate the Nusselt number and the Darcy-Weisbach friction factor, respectively [46, 47]. Share Reply Quote. g. Another ruff rule is, the lower the frequency, the lower the density which means, for superchunks and corner traps the WLG 045 or 040 with the thickness of min 30cm for round about 100Hz. Its value ranges from 0 to 1, with 1 being the perfect absorber. They have minimal success with lower and bass. Furthermore, if you have a look at Chris Whealy's Porous Absorber Calculator and plug the numbers for the frequency range of absorption for regular fiberglass batt insulation (R-13) @ about 8000 rayls/m compared to 60kg rock wool @ about 22000 rayls/m. 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. Some of the pro designers around here have also recommended panels over perf. Is the “Rigid Backed Porous Absorber” calculator not “correct” (within reasonable limits of course)?. These Website Terms of Use apply to the entire contents of this website under the. The flow resistivity of the layer in Pa. Truth be told it's closer to 42Hz. . meter. 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. 6 0. Porous Absorber Calculator. Porous Absorber Calculator Calculates the absorption curve of various porous absorber systems. 1 (b). This app is designed to assist acousticians when designing environments such as home cinemas. If you blow air through a cloth it gets warm by friction; air flow turns into heat. Perforated Panel. . a tuned membrane absorber. 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. 59 Also for good bass response this room (as a whole) is a good candidate for multi-subs + treatment. Diaphragmatic absorbers are good for going after frequencies below 90 Hz. The available calculators allow you to see the impact of this absorber on the absorbers frequency response for different depths and spacings. Average sound absorption coefficient formula. s. Rigid Backed Porous Absorber. The distance in mm between the perforated panel and the porous absorbent. (Side remark: If you are up to using other devices like membranes in front of your absorber, angled walls or. It is assumed that there is a rigid backing (such as a solid wall) behind the. com - View Single Post - Room treatment advice and help interpreting GIK's published lab results Post 16047038 -Forum for professional and amateur recording engineers to share techniques. If velocity types of porous broadband absorbers are gonna be effective at 100Hz, they need to be about 1 meter thick which is a quarter wavelength of that frequency, or half of that thickness but with an air gap of 0. This is due to the fact that the air resonance in the airgap and porous material layer is further damped by the porous material layer. com. It calculates the acoustic absorption curve of a variety of absorption devices mounted against a rigid backing such as a brick wall. The Whealey porous absorber calculator tells you all: Number one, make them thick, number two alternatively use an air gap, number three, don't make them too dense (see my posts in the link above for a rough understanding of that). Helmholtz Absorber Calculator. com. The spring is the air inside the cavity of the resonant absorber. This membrane effect is "tuned" to a specific frequency depending on the density and thickness of the material. You can confirm what I have said using a porous absorber calculator which is available online. See below for approximations of absorption coefficients for the theoretical 21" thick R38 (blue line, absorber 1) and the 1. with a lot of air behind them, like about 1,2m. A Porous Absorber Calculator is a specialized tool used in acoustics and engineering to determine the acoustic absorption characteristics of porous materials. 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. The pancake absorbers are different from conventional porous materials in two respects. For DIY absorber components please see: Bob Golds Fiberglass/Rockwool Absorbtion Coefficients page Absorbtion coefficents, averaged to the octave bands, do not nessessarily tell the whole story. All the source code for this app is availble on my Github repo "porous_absorber". It is assumed that there is a rigid backing (such as a solid wall) behind the. The need for significant thickness compared to operating sound wavelength makes porous absorbers dramatically inefficient and impractical at low. If you can find the Gas Flow Resistivity of the product you could predict the absorption spectrum using this calculator. 5°, and between the (Flat plate and metal foam 40 PPI) absorber plate was 8. I need to make a keyboard macro with that sentence. It can be used as a guideline for the design of a horizontal multi-layer porous wave absorber. I'm using the Whealy calculator, porous absorber page. This gives an open area of 18%. 1. Here's the link: Porous Absorber Calculator. s/m2, at which density going beyond 12" of thickness offers minimal benefit, and getting more than 50% absorption at 50Hz doesn't work. 6m walls, there is a 2. Acoustic plate absorbers have NRC ratings of 0. 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. with porous absorber assuming you use the good GFR and good surface, you will need a tickness equal at 2,8 m/ 111 inch for maximum absorbtion. 4 0. 8" or more. This may be an old thread, but the problems with the slotted panel graph still persist in the latest version 1. Membrane resonators can be calculated with the Excel Spreadsheet Porous Absorber Calculator V1. Resonant absorbers are further divided into panel absorbers and Helmholtz resonators. But none with just a plaster. 3. For example, I want to absorb. Absorber Parameters. Multi-layer Absorber Calculator Please note that there are many factors which aren't taken into account, eg. Which one would you place closer to the wall when building a porous absorber ? Porous Absorber Calculator. 's most successful trap, after many many attempts, was a panel one. 59 Reliability for Perforated Panel with Porous Absorbe. How would you calculate a triangular trap and compare different flow resistivities? Do you just pick the different depths of the triangle and look for an average?I was playing around with the Porous Absorber calculator but I don't see how to input the difference between 703 and 705. Speech Reinforcement CalculatorThe damped walls are acting as membrane absorbers below that range, requiring an additional 30-45 cm air gap, to absorb down to 20 Hz. They are usable with. I used the porous absorber calculator and decided that 40 cm thickness would give a good broadband absorption. Global Parameters: Air temperature °C. I'm only taking axial modes into account. If you want rear tuned absorption, build panel absorbers tuned to the lower range where the porous absorber is no longer effective. All formulas and units are the same in NASA. s/m 2. . Porous Absorber Calculator. Hey guys, I need broadband absorption down to 50Hz. Hello again! I have some challenges in my room, and been reading up on alot of stuff. . Speech Reinforcement CalculatorNote: I know that the results from Porous Absorber Calculator can't be fully applied to my design, because PAC assumes that slat width and spacing is always the same. 3. Joined Nov 15, 2020 Messages 7,363 Likes 7,810 Location Brussels,. . 2022-03-07 11:11 am #1 2022-03-07 11:11 am #1Calculate Optimal Gap Size for Given Frequency. PaulRain. Personally, I would figure out which materials are available in your area first and then start modeling. Multi-layer absorbers composed of perforated plates, airspaces or porous materials are used widely to absorb broadband noise [1], [2]. The calculator is easy to use just make sure to select "Komatsu (2008)" for the porous model on the left side of the page. Helmholtz Absorber Calculator. The thickness of the sound absorber was changed from d: [1. Acoust. Yeah, for porous absorbers, lower GFR is better for LF absorbtion, but the thicker the trap needs to be. If you utilize an air gap behind the panels it will increase absorption in the low mids. Absorption Area. Appl. absorption offered by the 3887rayls/m. First start by forming a hypothesis, something like, "The performance of broadband porous absorbers at treating room modes below 100Hz can be matched, or bettered, by narrowband helmholtz absorbers of equal or smaller size in amateur. (the theorical thickness is equal to the 1/4 wave length). What I wanna try is to build something like this:. Up to four absorbers can be modelled at once, each of which can have up to four layers. ↑ top; home; New Product Alert; classifieds; reviews; deal zoneThe rectangular version is easier to build and saves material. s/m2 for Absorber 1, then. Porous Absorber Calculator. How the Porous Media Flow Module Helps Improve Your Modeling Absorber Parameters This calculator estimates the absorption coefficient of a porous aborbent in front of a rigid backing (such as a solid wall) with an optional air gap between. lok the Flow resistivity (Pa. For example, the angle of incidence can be set as a global parameter. Sound-absorbing performance of copy paper composites with bulk densities below 442. 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. For a porous absorber it assumes a rigid backing and that backing (ie the wall) is assumed to be air tight. 0 with a German user interface and is developed by Marshall Day Acoustics. The spring is the air inside the cavity of the resonant absorber. 3 to 2 kg/m² (most probably between 0. Porous Absorber Calculator. Porous absorber calculator is your friend. (download open office if needed, it's a free!) As you'll see, friction absorbers are not particularly effective at such low frequencies unless extremely deep. Helmholtz Absorber Calculator. Gushue ️. Solution. 9 and its pore density. A microperforated panel absorber may have an absorbtion curve like this. In this study, porous packing was used. The room was empty apart from a partition in one corner (usually used in office spaces). You can play with the porous absorber calculator to find suitable dimensions. 1. Username: Password: Forgotten password? Register: 100 200 500 1000 2000 Frequency (Hz) 0 0. Goes up to 170/KG/M3. The No. One or the other is a question of thickness, use the porous absorber calculator to decide what you want, based on your available room space and your needs to absorb the lower frequencies. Take a look at every anechoic chamber in the world. Luca, You don't say whether you want corner bass traps, membrane absorbers or Helmholtz resonators. . They only reflect high and mid. The same porous absorber calculator can model multi layer, limp mass and helmholtz traps - just click the calculator icon to see a drop down to select Off topic - but I'm constantly amazed and impressed with the quality of the audio tools that developers provide for free on the internet such as this one, REW, HornResp, QRDude, Multi Sub. That material still needs to be breathable. AFAICS, the absorbtion-fix is case-closed. The particle velocity is at maximum at 90° and 270° (Vmax) and minimum at. 922. Multiphysics couplings are essential to capture the effects of porous media on transport processes. Thickness of the template is 1/8” = 3,175 mm. The distance in mm between the porous absorbent. I'm playing around with porous absorber calculator and trying to find a good balance between effective and practical. Porous concrete can mitigate noise at a lower frequency than a commercial porous absorber with the same thickness (foams or glass wool) due to high tortuosity. placed in the middle of the room. Share Reply Quote. AdamIf you have 28 inches, less 17 for the speakers, less 6 inches from the speakers to the AT screen that leaves 11 inches. As a result, a combination of porous and membrane technologies should be able to absorb the vast majority of frequencies. m Shows how the open area changes the surface impedance and absorption coefficient of some Helmholtz. 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. Wherein, there is a cylindrical porous absorber which is sealed behind a quartz window. s/m2, a 2ft thick absorber can be 70% effective at 50Hz. F. Note the ISD gap of such rooms is very long, infinite perhaps. Porous Absorber Calculator Preamble. The temperature profile is also shown in longitudinal direction in different angles for the configuration VI and the non-porous state in this igure. With a two foot thick area, you have the possibility of getting significant absorption at 40 Hz. 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]. Look up the Porous Absorber Calculator and you can see the graphs for yourself. The porous absorber calculator says 'yes' when I plug in a GFR of 2500. This is primarily due to viscous boundary layer effects. But Basotect has a coefficient of 0,8 at about 800Hz while Sonorock reaches the same value at about 1,2kHz. Air-backed porous absorber (i. Global Parameters affect all absorbers. 1 Website for Pro Audio ; The No. Porous Absorber Calculator Only thing I'd tweak about the post before mine is to buy the bigger/thicker R38 (qty 8 2'x4' batts 13" thick ~$100 at Home Cheapo)!. Each. Tortuosity was essential a capacitance test with a wetted material. 2 Glass wool as porous damping) towards the end is quite easy to understand. 2. Multi-layer Absorber Calculator. 50%) 400mm Porous Absorbent, 4000 Pa. I was thinking of using slats 3cm / 1. On one of the 4. BEHOLD THE MIGHTY POROUS ABSORBER CALCULATOR. The mass per unit area in Kg/m 2 (limp membrane). Username: Password: Forgotten password? Register home | terms of use | privacy policy | links | contact: Copyright. IB Sub. You may be overthinking it. Dennis Foley says: May 4, 2023 at 5:10 pm. you may not need to be terribly concerned with the. . 5rayls/m) 1200mm Porous Absorbent, 1500 Pa. This leads to the question of how much more? In acoustics, we have the ultimate arbiter of test data. 2m wide, 1. Multi-layer Absorber Calculator. Here is a list of other nice acoustic tools you can enjoy. Porous absorber. . The angle of incidence can be adjusted. s/m 2. s/m2 flow resistivity. Play with the porous absorber calculator. The lowest room mode you have between your ceiling and floor is at 75 Hz. This means you can vary the. A porous absorber may have an absorbtion curve like this. My Studio. Calculation models and input parameters. (to be used in porous absorber calculator) Share Reply Quote. I'm using the Whealy calculator, porous absorber page. Above 60°, 5000 Pa*s/m2 is better for all frequencies. Application areas range from micromechanical devices to seismic wave propagation. Slotted Panel. Absorber ParametersHi I just wanted to share an alternative design for absorbers that i made in my listening room. Porous absorbers are in fact thermal materials and usually not effective sound barriers. . 59 You can see by messing with the GFR numbers that unfortunately a higher GFR material (estimates for ultratouch are around 15-20k/rayls?) will work well above 100hz at lesser depths, at the expense of being less effective below. Porous Absorber Calculator - About. 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. Porous absorber bass traps (or broadband absorbers) are the first-line-of-defense when tackling general problems with room acoustics. . Porous Absorber Calculator V1. I changed the concept from slat to perforated absorber. Typical mineral wool is about 8-10K Pa. I do all my caculation with the Porous Absorber Calculator. They have specifiable one-third-octave- center band frequencies between 40 and 100Hz. We measure the total room sound absorption in sabins. If you didn't download it yet grab this: Porous Absorber Calculator V1. Single absorbers: objects such as tables, chairs, people, etc. The actual average sound absorption coefficient of the microperforated panel + cavity + porous metal + cavity sound absorber in the 100–1800 Hz range reached 62. Porous Absorber Calculator I haven't seen great performance from the 24 inch SSC's, while the 34 inch ones rock. The calculator in question does not take into account the mass of the porous material (that has some effect on low frequency performance due to the membrane action it might cause), only flow resistivity, and although the most important factor; the mass can sometimes affect the result quite a lot, even if the FR value is the same. 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]. Multi-layer Absorber Calculator. To calculate the effective coefficient of thermal conductivity of porous absorbers, the simulation was carried out without air movement inside.