On a microscopic scale, sound propagation in porous materials is generally difficult to study because of the complicated geometries of the frames. Polyurethane (PU) foams have become the most important class of polymeric foams for sound absorption applications because of their low density, lightweight, good mechanical properties, and. 2. Business, Economics, and Finance. 1 Website for Pro Audio ; The No. 58 and trying to come up with a design. 3 to 2 kg/m² (most probably between 0. . 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). Some carefully placed spacers (smaller strips of insulation) could keep it off the wall. 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. 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. 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. Take a look at every anechoic chamber in the world. (to be used in porous absorber calculator) Share Reply Quote. Multi-layer Absorber Calculator. im using this Porous Absorber Calculator to check how the GFR would help . This only works with absorbers of uniform thickness and triangular bass traps obviously have varying thickness. "ω" is angular frequency, which is defined as 2*pi*f. s/m2, a 2ft thick absorber can be 70% effective at 50Hz. The porous absorber calculator does not offer a complete solution for diagonal traps. The equation is modified to f=50/sq root(1/md). A reset button is provided which returns all global parameters (and parameter options) to their default. But none with just a plaster. Unless care is taken when deciding on the size of the absorber unit, these holes will not add up. Mechel and Ggrundmann. Been playing with the perforated panel/Helmholtz part of the porous absorber calculator spreadsheet. All the source code for this app is availble on my Github repo "porous_absorber". DD Share Reply Quote. Porous Absorber Calculator. Air is a viscous fluid, and consequently, the friction with the pore walls dissipates the sound energy. 4 0. 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. this formula or e. What I wanna try is to build something like this:. Just made a massive front corner trap out of Knauf RS45. The perforated structures are not resolved explicitly but represented by a volumetric porous zone where a volume-averaged pressure gradient in the form of a drag term is applied to. 59 Reliability for Perforated Panel with Porous Absorbe. Porous Absorber Calculator. Delany and Bazley. 5th March 2014 | Show parent #17. -Assume you have a 12 dB peak at 100Hz that you want to treat. This calculator estimates the absorption coefficients of multi layer porous aborbers. Hey Guys, I wanted to try a few calculations of membrane absorbers to see how the different air and absorber depths affected the absorbers. Up to four absorbers can be modelled at once, each of which can have up to four layers. Do you think I can rely on improved insulation in the sub area if I order the 045 Caruso (400mm) and use an airgap? Only with this airgap I would have a much better effect in the sub range. For membrane absorbers, a first approximation is k/sqrt(d*M), where k is between 50 and 60, M is the mass-per-unit-area of the membrane (kg/m^2) and d is the sealed cavity. The distance in mm between the porous absorbent. 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. Hi! I have an example, and I'd like to know if it I possible to do the math here. placed in the middle of the room. It is not impossible to get a theoretical efficiency of 0,5 at 30Hz with porous absorption, if you use a combination of. 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. It calculates the acoustic absorption curve of a variety of absorption devices mounted against a rigid backing such as a brick wall. Personally, I would figure out which materials are available in your area first and then start modeling. e. I would look into tuned devices. Helmholtz Absorber Calculator. DSP like a DCX2496 is cheap and with placement and experimentation and treatment you can achieve a lot. Maybe with tuned absorbers or perforated panels, but there are others here that have more experience with that. 1 Website for Pro Audio. 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. Air gap 1. Porous Absorber Calculator BTW, if you're from Finland: I'd go with Knauf rolls of insulation from Byggmax, which amazingly is the cheapest option and among the best (if not THE best) performer for thick. The setup follows international standards with about 10 m² of slat absorber in an echo chamber. hi all i have 2 rooms that need Treatment at Specific frequency range And I think of making traps with perforated wood my q is how reliable is the Porous Absorber Calculator V1. . I've done the modelling in Pourous Absorber Calculator, Multi Layer. E. 500cm deep. Which Porous Absorber to Get. Porous Absorber Calculator. The calculation doesn't assume a sealed cavity, except for a resonator. A 100mm panel with 100mm air gap gives a 0. Turns out that my 4" (10cm). The calculators can save you from having to tear stuff out that is worse than it was: Porous Absorber Calculator V1. 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 thickness of the porous absorbent in mm. There is the amacoustics calculator that works for helmontz and other types of perforated and membrane panels before the absorber. Hello ! First post but i'm reading for years Thank to everybody who shares so much great info ! ( Thomas Northward, Boggy, GE, Jens E. Porous silicon carbide (SiC) is widely used as the absorber due to its high-conductivity, high-absorption, and anti-oxidation [12]. F. As a result, a combination of porous and membrane technologies should be able to absorb the vast majority of frequencies. Actually it doesn't. The resonant frequency could be calculated using e. then throw it into the porous absorber calculator and compare it to OC703. , JH Brant, DanDan, Avare, can't name you all. Porous Absorber Calculator Typical mineral wool is about 8-10K Pa. Some online calculators as well as commercial software are also available for absorption calculation. • Absorber 2. 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. All the source code for this app is availble on my Github repo "porous_absorber". The distance between the holes (centre to centre) in mm. I've been building my own panels using Rockwool as the absorber. The actual average sound absorption coefficient of the microperforated panel + cavity + porous metal + cavity sound absorber in the 100–1800 Hz range reached 62. s. 2017, 116, 311–316. Similar to the resonant panel they take up less depth than porous absorbers for a given frequency. Share Reply Quote. In order to optimize sound absorption, it was generally advised to predict and calculate the absorption based on the dependent parameters and optimize the parameters to obtain the desired absorption. 9, 10,. Parameter Options determine whether certain parameters appear in the Global or Absorber sections. Microperforated Panel. Limp mass material types can never achieve the proper rates of absorption that music and voice require. Your bass and mid-bass will depend heavily on location, and the only cure is multiple subwoofers, and good acoustic treatment. Komatsu model is selectable from the porous absorber calculator's menu and is the best to use. The formulas are partly accessible and sources are clearly referred. 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)!. The purpose of this blog is not to explain any of the principles of acoustics or how to interpret the data plotted on the graphs shown below, but rather to describe the architecture of a browser-based WebAssembly application written in Rust. The angle of incidence can be adjusted. Air gap 2. My comment is. I am using this link Porous Absorber Calculator and using a rockwool product with a 70kg/m3 density and around 30kPa. Just don’t make the air gap deeper than the panel depth; a 1:1 ratio is best. Mounting and. Each layer can be either a porous absorbent or an air gap. The prediction models are usually used to theoretically calculate the energy consumption efficiency of the porous sound absorption materials, which could provide guidance for the structure design of porous sound absorption materials. The first step is to cut the wood to make a frame. by any material. First, the surface porosity, defined as the ratio of the main perforation surface area to the front surface area of the absorber, is much lower than that of a conventional porous absorber. The best gap size for the given frequency =. So, when guys like me and the OVERWHELMING MAJORITY of people on these forums who are looking for acoustic. Is this a good way to deal with modal issues? 2. Porous Absorber Calculator. ↑ top; home; New Product Alert; classifieds; reviews; deal zoneAt high frequencies, i. ↑ top; home; New Product Alert; classifieds; reviews; deal zoneThe rectangular version is easier to build and saves material. 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. Sat fiddlign with it to try to see what configurations would be effective for the materials I have. Gear Guru . Termination of such 'gaps' is clearly not mandatory. Much ore than that (~200mm+) makes them even better at. 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. All. 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. Obviously I'd need more surface area to make a real dent in a room that size. Normal incidence. Being a porous absorbent, carpet produces mid– and high–frequency absorption. Dammit, is it so difficult do download the bloody thing and insert some bloody numbers? OK, here are some values as being written in my secret documents (no actually derived from Porous Absorber Calculator, hehe) for 48 Hz. Now, I haven't been able to find any official numbers on air flow resistivity, but according to this forum post Rockwool has a flow resistivity of 9000 Pa. These Website Terms of Use apply to the entire contents of this website under the. Absorption Area. Thickness of the template is 1/8” = 3,175 mm. Porous Absorber Calculator 2) the filtered impulse response at -60 dB or the topt can give an indication. 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. Calculates the absorption curve of various porous absorber systems. Air gap 1. Perforated panel absorbers have holes in their face and diaphragmatic absorbers have a solid face. They call it "k" but I'll call it Kp for clarity. and a Calculator Porous Absorber Calculator Coincidentally, I found those links another way earlier today and spent some time with them. 2 0. 7 and 1 kg/m²) and would. . e. Porous Absorber Calculator And some more courtesy of Sebq Bradford Rockwool Building Blanket 13000 mks Rayls/m (nominally 30kg/m^3 product) Bradford FIBERTEX ™ 350 Rockwool 22000 (60kg/m^3) Bradford. We’ll be building a frame that can surround a 15. g. 90 cm) through a calculator, the benefit from more depth seems to be rather minimal. When I use the Porous Absorber Calculator, it shows these to be fairly similar in performance. 58 (RPG´s BAD template is 600x600 mm with 512 holes, each Ø12,7 mm. Hello again! I have some challenges in my room, and been reading up on alot of stuff. Common pa. Username: Password: Forgotten password? Register: 100 200 500 1000 2000 Frequency (Hz) 0 0. Using the "stanleyhall" and "whealy" calculator I figured out, that this could be done best using porous material with a quite low GFR at around 1. AdamIf you have 28 inches, less 17 for the speakers, less 6 inches from the speakers to the AT screen that leaves 11 inches. Porous Absorber Calculator. perforated wood over acoustic foam porous absorbers. Here are some common values for absorption materials. The sandwich acoustic structure consists of an air cavity layer in between two MPP layers, which. For a sufficiently thick porous absorber (eg. On one of the 4. I do all my caculation with the Porous Absorber Calculator. The mass is the cabinet and front wall or diaphragm. Flow resistivity. I used the porous absorber calculator and decided that 40 cm thickness would give a good broadband absorption. I have a crazy 125hz problem in my room and I haven't had luck fixing it with corner traps or speaker placement, and being that its quite narrow, I want to build some tuned traps (PPA Helmholtz) but there seems to be differing opinions on whether the heigFig. Calculates the absorption curve of various porous absorber systems. 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. /s/m2 (we don't know) (according to this porous absorption calculator) Porous Absorber Calculator On the other hand a Limp. 8 1 Absorption Coefficient • 5000 mks rayls/m • 30000 mks rayls/mPorous Absorber Calculator V1. 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. I am quite a noob but i’ve been researching a lot about it the past few weeks. The multilayer absorber was composed of an MPP and three additional layers, consisting of polyurethane (PU) foam, jute felt, and an air gap. Corner Bass Traps completely filled with Hemp (3000 rayls/m) and broadband panels 4-6" deep (maybe with membrane in the middle to prevent too much HF absorption) using an. This app is designed to assist acousticians when designing environments such as home cinemas. 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. Microperforated Panel. online calculators for porous absorbers. The thickness of the porous absorbent in mm. Wherein, there is a cylindrical porous absorber which is sealed behind a quartz window. ZORBA is currently available in version v3. The flow resistivity of the porous absorbent in Pa. 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. . Depends on density of material. Figure 2-8: Typical ordered porous medium structures. Whealy C. But in my design, the open area will also be roughly 50%, so I figured the results would be useful anyway. You may find it interesting to experiment with the Porous Absorber Calculator Porous Absorber Calculator V1. Width of hangers is used to define lowest frequency, membrane absorbers isn't included in this simple model/formula, and 1. com, are committed to protecting and respecting your privacy and take this very seriously. Multi-layer Absorber Calculator Please note that there are many factors which aren't taken into account, eg. per cubic foot] and instead seek a material with similar gas flow and impedance properties in order to match performance with 703. I'm only taking axial modes into account. . The impact of using the partially porous media in the absorber on the efficiency of PTC (parabolic trough collector) has been investigated. 2 Glasull som porös dämpning" (B1. This calculator estimates the absorption coefficients of multi layer porous aborbers. C0 is the speed of sound in air, which we'll say is 343 m/s. The composite sound absorber includes a MPP (micro-perforated panel) layer, a porous material layer, and an air cavity layer. Air-backed porous absorber (i. If you download and play with the porous absorber calculator: Porous Absorber Calculator V1. 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. Look at the densities. COMSOL Multiphysics offers. The flow resistivity of the layer in Pa. (Side remark: If you are up to using other devices like membranes in front of your absorber, angled walls or. When modeling porous absorbers, various empirical models are available. It models resistance to flow only. s/m2 flow resistivity. As vibrational science will tell us a resonant absorber is a mass vibrating against a spring. This is the number we're after. 50%) 400mm Porous Absorbent, 4000 Pa. Username: Password: Forgotten password? Register: 20 50 100 200 500 1000 2000 5000 10000 20000 Frequency (Hz) 0 0. And unlike porous traps which work better. I've recently written a porous absorber calculater for my own use and have decided to make it available over the internet. 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. 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. 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. Porous Absorber Calculator V1. I believe that it's working correctly and is stable but would appreciate some feedback if you have any problems with it. Have a play with this: Porous Absorber Calculator V1. Chen, in Porous Materials, 2014 3. 064–0. 117–0. It calculates the acoustic. Fraunhofer developed with Caruso Iso-Bond panels the VPR absorbers th. The distance in mm between the perforated panel and the porous absorbent. Now note that the following must also be true (I'll leave aside for the moment why it must be true): K 0 /K p = C p /C 0. 2. The Chris Whealy calculator can help with Helmholtz. a tuned membrane absorber. This sheet shows two absorption curves for a single layer of porous absorber with and without an air gap. Gushue ️. 69%, which was superior to that 25. Absorptive treatment such as mineral wool, glass fiber or high-porosity foams reduces reflection sound. Flow resistivity. Example 2‑1. I am interested in porous absorption of low frequencies since it is. Let's call C p the speed of sound in the porous absorber. Same Class – Different Performance. 16000, 23400, 27000 (c/o NASA!). s/m2 flow resistivity. 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. Typical mineral wool is about 8-10K Pa. If you utilize an air gap behind the panels it will increase absorption in the low mids. And Using Porous Absorber calculator, air gap (when panels hang to the walls) is giving better performance, and this air gap must be achieved through out all panel ( i mean hanging it using two nails not going be enough) ?. meter. 0 with a German user interface and is developed by Marshall Day Acoustics. Absorber thickness. It will let you model various combinations of panel width, air gap, and material type. A Porous Absorber Calculator is a specialized tool used in acoustics and engineering to determine the acoustic absorption characteristics of porous materials. Wilson, simplified relaxation model. 1 (a) that comprises a cavity, neck, lids and porous material. Corner Bass Traps completely filled with Hemp (3000 rayls/m) and broadband panels 4-6" deep (maybe with membrane in the middle to prevent too much HF. now I get different results on calculations, which are more realistic. 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. Mass Production is often uncommercial, although some companies offer membrane absorbers. (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. 70% of original porous metal absorber and that 31. you may not need to be terribly concerned with the. All in all, you don't want the air gap much. s. The rotational speed of the bed varied from 150 rpm to 1500 rpm, and the gas flow rate ranged from 20 m 3 h-1 to 60 m 3. The others perform atrociously, but even the Komatsu won't work correctly for mixing different densities. Global Parameters affect all absorbers. 16,600 is OC703, 5000 is fluffy. Helmholtz Absorber Calculator. Appl. Thank you Can you help me clarify the difference between "random incidence" and "normal incidence" options in the porous absorber calculator? Share Reply Quote. I'm only taking axial modes into account. We, very luckily, know the density (27 kg/m3) or air flow resistivity, 12900 Nsm-4 (ISO 9053 specifies how to measure it) of the porous absorber, which is known to be well. Absorption coefficient measurements are not easy, where materials are placed and having no regard of their shape or extension. BEHOLD THE MIGHTY POROUS ABSORBER CALCULATOR. 1. s/m2 There seem to be a few available on the web for common insulation materials like Rockwool but you need to hunt around for them. 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. Porous Absorber Calculator. 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. Porous absorber bass traps (or broadband absorbers) are the first-line-of-defense when tackling general problems with room acoustics. Hi all, I have a (at the moment) theoretical question for the experts here: If one wants to try and control frequencies as low as possible in a room, iSound absorbers can be made from porous materials or resonant structures, and the main mechanisms for sound absorption are acoustic impedance matching on the absorbers’ boundary and acoustic. 90 width you are lost in regards to bass if you rely on absorption only. 16000, 23400, 27000 (c/o NASA!). a tuned perforated panel Helmholtz absorber. com are 34 inches wide. 2 0. Air-backed porous absorber (i. Calculates the absorption curve of various porous absorber systems. I am using values of 10,000 Pa. this formula or e. 2 times the material thickness. A Porous Absorber Calculator is a specialized tool used in acoustics and engineering to determine the acoustic absorption characteristics of porous materials. 9th January. A higher fiber density leads to a more complex path inside the porous absorber therefore it implies higher interaction between sound waves and fibers. s/m2. This app is designed to assist acousticians when designing environments such as home cinemas. Multi-layer Absorber Calculator 20 50 100 200 500 1000 2000 5000 10000 20000 Frequency (Hz) 0 0. If perforated panel with porous absorber trap isnt the way for me to go, then what other options should I consider? Share Reply Quote. Your key says they are all rigid porous absorbers. You can play with the porous absorber calculator to find suitable dimensions. The absorber is assumed to be in front of a. Porous Absorbers. Multi-layer Absorber Calculator. The LSA proposed in this paper is shown in Fig. 6 0. Absorber Parameters: Layer: This field sets the type of layer as follows: Not used; Air; Porous absorbent; Limp membrane; Perforated panel; Thickness: The thickness of the layer in mm. Member. 35 absorbtion at 30Hz and increase to 0. 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 the absorbent and the backing. Porous model: When set to "Global", the model appears as a global parameter and is applied to all absorbers. 45 across the frequency range. The spring is the air inside the cavity of the resonant absorber. Helmholtz Calculator. I'm using the Whealy calculator, porous absorber page. Diaphragm absorbers are a common tool utilized to attenuate standing waves as part of an acoustic treatment. If you drop down to about 4K Pa. Often porous materials with spherical grains have lower porosity than materials composed of non-spherical grain. Absorber thickness. Porous Absorber Calculator V1. See here for a simple porous absorber calculator. 10 PPI) absorber plate was 13. As vibrational science will tell us a resonant absorber is a mass vibrating against a spring. The paper is in Swedish but Colakurt as a Dane might be able to read it. The temperature profile is also shown in longitudinal direction in different angles for the configuration VI and the non-porous state in this igure. 1. These porous absorber models are then used to calculate the surface impedance and absorption coefficient of different absorbents using a transfer. s/m2 for Roxul SNS and 24,000 Pa. Some things were way off. The mesh part shown in Fig. 4 The Superchunks in the Absorption test at studiotips. Both are needed for accurate prediction of porous absorber performance. AFAICS, the. I've recently written a porous absorber calculater for my own use and have decided to make it available over the internet. 52 and download the Porous absorber calculator. Truth be told it's closer to 42Hz. I found Whealy's Porous Absorber Calculator and the math is beyond casual skimming and just typing it in. 300 - 4500 Hz. For the sake of completeness, the technical parameters that I used for my curves: air temperature: 20 degrees Celsius, air pressure: 101325 Pa, Angle of Incidence. Porous Absorber Calculator. ) broadband absorbers. Username: Password: Forgotten password? Register: We, acousticmodelling. 1 Website for Pro Audio ; The No. 4 kg/m3 and corrugated board composites with densities of less than 474. Porous Absorber Calculator. 6 0. com. Reply. 2 coefficient at 50 Hz (about 0. Then I. 10th June 2011 | Show parent #19. . Even if it's peaked in planned location, most probably you'll have to measure and investigate to see results. e. Each layer can be either a porous absorbent or an air gap. AFAICS, the absorbtion-fix is case-closed. the waterfall is ok for the resonance. 3m x 4m). I was planning to buy the Bradford Fibretex 350 - 60kg/m3 batts (3 for $128 - 100mm thick 1200mmx 600mm). Username: Password: Forgotten password? Register: 20 50 100 200 500 1000 2000 5000 10000 20000 Frequency (Hz) 0 0. For instance they assume a full boundary of fibre, like in an Impedance Tube. Standard pink fluffy is ~5,000. Porous Absorpton calculator says: No significant absorption for bass lower than 150 Hz: In a room with 1. Let us take a look at a plane sound wave vertically incident on a rigid wall. Mechel and Ggrundmann. Having that much depth allows me to absorb lower but it creates. Of course I won’t know for sure until I get my hands on the stuff and build some absorbers (at which point I’ll be happy to share my results). Hole spacing. Using the porous absorber tube causes the surface temperature to decrease. However, for basic calculations relating to multi-layer porous absorbers, both calculators should give almost identical results (provided the extra options in Soundflow. m Shows how the open area changes the surface impedance and absorption coefficient of some Helmholtz.