Setiawan Posted February 7, 2018 Share Posted February 7, 2018 I've got some ideas for the corners and ceiling that I'm reasonably comfortable with, but for the side walls, there's no clear solution that's jumping out to me. I spent the last weekend DIYing 6 frames that are 80cm x 120cm x 11cm, and want a 10cm air gap behind them. Ideally, the solution would: Not involve too much work (e.g. mounting four brackets per panel * six panels * four screws per bracket = nearly a hundred screws, which seems a bit tedious for a non-carpenter like me) Not be too unsightly (you'll see the side profile upon entering the room) Allow for some flexibility in placement once installed Be easily removable if necessary Not be too expensive (keeping it under $200 would be good) Be sturdy/low risk of dropping While it would be good if I could hit all of the above goals and it's what I'll be aiming for, I don't expect that I will get them all. The 'best' system I've come up with so far: Screw a hang track into the wall studs (horizontally, one piece for three panels: https://www.bunnings.com.au/flexi-storage-1800mm-white-hang-track_p2660962) Hang slotted wall strips from the hang track (vertically, two pieces for each panel: https://www.bunnings.com.au/flexi-storage-762mm-white-double-slot-wall-strip_p2660951) Hang two double slot brackets on each wall strip (https://www.bunnings.com.au/flexi-storage-120mm-white-double-slot-bracket_p2583641) Find some way to secure the panels to those double slot brackets (each panel is held up by four double slot brackets) In case this is not intuitive enough a description, see dodgy diagram below: Only thing is that I don't really know how I would secure the brackets to the supporting bars on the panel. Otherwise, this mostly hits my criteria. Alternatively, I could hang each panel like a picture frame, and place a spacer behind each panel (or attach the spacer to the panel). This seems like a rather inelegant solution though, and doesn't allow for lateral repositioning without putting more holes in wall. If anyone has any input on the above ideas (ways to improve or overlooked flaws), or have alternate solutions, please share. I'm hoping to possibly do this this coming weekend, though if no good ideas come to mind, I might just do the corners and/or ceiling instead and postpone these until the following weekend. Thanks! Some extra pictures of last weekend's job, still to be covered with fabric (and maybe painted black first). 1 Link to comment Share on other sites More sharing options...
Krispy Audio Posted February 7, 2018 Share Posted February 7, 2018 I've just done exactly this in my shop, with a 100mm air gap. I'll post some pics of the mounting system tomorrow, but basically used some heavy duty steel angle wall mounts, then notched out the ends. On the frame itself I used a biscuit tool to cut a notch in the frame to match. 5 Link to comment Share on other sites More sharing options...
LogicprObe Posted February 7, 2018 Share Posted February 7, 2018 I thought it was always better with a calculated gap.....................if you have the space. Link to comment Share on other sites More sharing options...
Setiawan Posted February 7, 2018 Author Share Posted February 7, 2018 1 hour ago, Krispy Audio said: I've just done exactly this in my shop, with a 100mm air gap. I'll post some pics of the mounting system tomorrow, but basically used some heavy duty steel angle wall mounts, then notched out the ends. On the frame itself I used a biscuit tool to cut a notch in the frame to match. Wow, looks great! Very interested in more pictures Link to comment Share on other sites More sharing options...
Krispy Audio Posted February 7, 2018 Share Posted February 7, 2018 Crude but does the job! The lower one just pushes the bottom away from the wall so it's just in place resting against the lower part of the frame. 1 Link to comment Share on other sites More sharing options...
Guest Posted February 7, 2018 Share Posted February 7, 2018 (edited) Might be worth noting that the gap behind the panels doesn't really make acoustic improvement unless it is sealed to the panel, as in sealed air gap to the wall. Hanging or placing the panel against the wall would have the same effect. Edited February 7, 2018 by Guest Link to comment Share on other sites More sharing options...
Guest Posted February 7, 2018 Share Posted February 7, 2018 11 hours ago, LogicprObe said: I thought it was always better with a calculated gap.....................if you have the space. Yea, you are on the right track, but it needs to be sealed/wall panel. Usually has a mass loaded membrane as well, alias, mass loaded bass trap. Link to comment Share on other sites More sharing options...
frankn Posted February 8, 2018 Share Posted February 8, 2018 I think a gap changes the absorption profile of the all panels whether sealed or not. Ethan Winer has a lot of information on his site about absorption, diffusion panels and room treatment. http://ethanwiner.com/acoustics.html#air gap 1 Link to comment Share on other sites More sharing options...
aechmea Posted February 8, 2018 Share Posted February 8, 2018 (edited) Yeah, a gap will make a bit of a difference, but not that much and you may not even detect it. Some background. There are 2 main sorts of treatment. 1. Absorption. ie. slabs of fibreglass, carpets, curtains, soft furnishings, people and the like. The absorption has to be placed in and area of high 'velocity' ie. the absorption stops those pesky little air particles from moving quite so energetically. High velocity occurs at 1/4 wavelength and 3/4 wavelength. So if the absorption is at 100mm, say, from the wall then that will have the required effect on wavelengths of 400mm and 133mm as well as a whole host of multiple frequencies. As the wavelength shortens then all frequencies will be absorbed. The thicker it is the more occurrences of different 1/4 wavelengths it will capture. The denser the material the more it will slow the particle velocity. The further it is from the wall the lower the wavelength it can potentially effect. The larger it is the more waves that will hit it. In many ways absorption is best placed out in the middle of the room somewhere where it has a good chance of absorbing lots of different frequencies (wavelengths). Haha. At one stage I had a 'teepee' of free standing full fibreglass sheets (2400 x 1200 x 100) in an open area of the room. Not very attractive nor practical though, so it didn't last long. 2. Pressure traps. Pressure regions of a wave occur at the boundaries of the room (floors, wall, ceiling, solid objects) and at 1/2 and full wavelengths. This is where pressure traps are positioned. Pressure traps are sealed devices that have a heavy membrane and usually some internal absorption. They must be sealed to have the desired effect. They also only work on particularly narrow frequency ranges ie they need to be tuned by paying very close attention to dimensions. They are in effect a sealed drum (the musical instrument) that absorbs a particular frequency. They are difficult to make for DIY numpties like me and are difficult to tune, apparently. So getting around to the OP... Building a frame and say half filling it with fibreglass is neither one thing nor the other. It is not completely sealed so can't be acting as a pressure trap no matter how close the frame is to the wall. On the other hand being quite close to the wall ( which is a pressure zone) it is only acting as an absorptive device for those waves with a short wavelength proportional to the distance from the wall ie. high frequency. It will have little or no effect on low frequencies. All that leaving an air gap means is that it is now that much further from the wall which will mean a slightly lower frequency is absorbed. Of course not all waves arrive perpendicular to a wall/absorber, most are arriving at various oblique angles in which case the absorption is seen by the wave as being a lot thicker. So absorption will absorb over a slightly wider range of frequencies than one might initially expect. Semi-rigid and rigid fibreglass (or their poly equivalent) are self supporting so there is no need for a wooden frame if you don't want to, or can't. I would play with positioning before going to the trouble of permanent wooden devices. For proper technical information, I like "Master Handbook of Acoustics" Everest and Pohlmann. A readable textbook style. "Sound Reproduction" Toole is liked by many but is a bit of a rambling essay/novel style, to me anyway. On the web Winer is pretty good. Edited February 8, 2018 by aechmea 2 Link to comment Share on other sites More sharing options...
frankn Posted February 8, 2018 Share Posted February 8, 2018 +1 Everest. Winer quotes that for more definitive/ in-depth review. Link to comment Share on other sites More sharing options...
Primare Knob Posted February 8, 2018 Share Posted February 8, 2018 How about using wires and a curtain rail. You can use (2) roller parts on the rail to slide a panel from left to right and mount the wire fixing into the back of the panel, and re-fix at another point for adjustments. You could even come up with a single mounting point on the back of the panel with pre made adjustment points like a single vertical slat. When you like to have maximum flexibility you need to separate the horizontal movement and vertical movement. One movement is restricted to the wall (probably horizontal since the panel width will restrict this movement the most), while the other is restricted to the panel, if you don't want to drill new wholes. Hanging some horizontal timber slats with the minimum of screws which can be used to freely hang en rehang hooks without the need of drilling into the wall, might be practical, but will likely not win the beauty prize. 1 Link to comment Share on other sites More sharing options...
frankn Posted February 8, 2018 Share Posted February 8, 2018 (edited) Or mount the panels on free standing frame/stands until you are happy with the placement or keep them on the stands. Edited February 8, 2018 by frankn Typo 1 Link to comment Share on other sites More sharing options...
marten Posted February 8, 2018 Share Posted February 8, 2018 Thanks for your write-up Aechmea, you obviously know the subject and it's good to have some grounding facts for the thread. To the OP, I agree with your and some posters' views that it's preferable to go for a scheme that allows you to shift panels around a bit, instead of locking in their position. Depending on the wall surface, one could also consider 3M removable patches - they are rated per kg and used for hanging pictures. Fibreglass insulation is quite light, so if the frame isn't too heavy, it could be an option. Now, looking more closely at the air-gap issue: 12 hours ago, aechmea said: Building a frame and say half filling it with fibreglass is neither one thing nor the other. It is not completely sealed so can't be acting as a pressure trap no matter how close the frame is to the wall. Then this would mean that just sealing the back of a fibreglass panel adjacent to the air gap, will have no effect. 12 hours ago, aechmea said: High velocity occurs at 1/4 wavelength and 3/4 wavelength. So if the absorption is at 100mm, say, from the wall then that will have the required effect on wavelengths of 400mm and 133mm If the panel is 100mm thick plus a 100mm air gap, the normally incident wavelength with maximum velocity inside the panel (150mm) will be over 550Hz and we would have much reduced absorption at 100 to 200Hz. Generally, I feel that the frequency range I most like to target with acoustic treatments is 100Hz to 300Hz. So the above discussion really says 100mm panels with or without air gaps would be largely ineffective for that range. Are things really that bad, or am I missing something? Link to comment Share on other sites More sharing options...
Bilbo Posted February 8, 2018 Share Posted February 8, 2018 I hang mine on a curtain rod. That way I can move them along the wall quickly and easily. Link to comment Share on other sites More sharing options...
aechmea Posted February 8, 2018 Share Posted February 8, 2018 5 hours ago, marten said: SNIP If the panel is 100mm thick plus a 100mm air gap, the normally incident wavelength with maximum velocity inside the panel (150mm) will be over 550Hz and we would have much reduced absorption at 100 to 200Hz. Generally, I feel that the frequency range I most like to target with acoustic treatments is 100Hz to 300Hz. So the above discussion really says 100mm panels with or without air gaps would be largely ineffective for that range. Are things really that bad, or am I missing something? Hi Marten, No, you aren't missing anything. Your calculation is correct. Divide the distance (in meters) into 343 and divide by 4. That gives the quarter wavelength frequency. 100mm = 850Hz 150mm = 572Hz 200mm = 429Hz 500mm = 172Hz 1m = 86Hz The 1/4 wavelength (and 3/4) is the maximum velocity point of a wave but there is spread on each side of that where, even though the air particle velocity is reducing, the absorption will continue to work, but on a sliding scale (a sine wave). Then if we consider that a reflection from the wall may pass back through the panel then that will reduce the velocity a second time. Then if we consider the oblique waves, our 100mm thick fibreglass is effectively 120mm or 150mm or 250mm or ... depending on the angle of incidence. We therefore find in practice that there is effect lower in freq than the 1/4 wavelength distance would indicate. However when one is thinking in terms of say 100Hz then the absorption has to be big and thick and dense. 100mm semi-rigid fibreglass (32kg/cu. m.) is suitable for mid range and upper bass. Unfortunately thin, rubbery, small (even commercial) bass traps that one too frequently sees, are simply not effective in the bass region. They will be OK in the mid range and up but that is not why they are bought. This always comes as a surprise. To tame the <200Hz I have made tube traps which is a third type of trap. They are (sort of) sealed and made of rigid fibreglass (64kg/cu. m.) so they have both pressure and absorptive properties, but they are still huge (450mm diameter and 1m high and there are 10 of them stacked into 5 columns). They are effective down to 70-ish Hz in my room. Any lower than 100Hz and we are talking those pressure traps with doped vinyl diaphragms etc and Helmholtz resonators. I have only read about them so can't comment on them in practice. That amount of DIY skill is beyond me. Plenty of info on the web though. -------------------------------- Here is a portion of the back wall of my room. Tube traps in the corner. 100mm fibreglass filling window alcoves (dark brown) 2400 x 1200 x 100 sheets propped against wall (fawn) 1200 x 1200 x 100 sheets propped against lounge (cream) (nearly 2m out from wall) 2 x 2 seater lounges hidden in there somewhere More tubes out of view to the left. More tubes, another fibreglass sheet and diffusion panels on the front wall. It looks a lot, but when compared to the combined area of the walls, floor and ceiling it's not much percentage-wise (5-10% maybe) All of this is non permanent freestanding and the room can resume its original look in a few minutes, but in reality, it is permanent. Professionals like Winer are all for it whereas Linkwitz is not, saying that normal furnishings are good enough. Comes down to personal preference. 1 Link to comment Share on other sites More sharing options...
marten Posted February 9, 2018 Share Posted February 9, 2018 Thanks again for the info Aechmea. Impressive - you have a serious spread of absorption on your walls. 3 hours ago, aechmea said: To tame the <200Hz I have made tube traps which is a third type of trap. They are (sort of) sealed and made of rigid fibreglass (64kg/cu. m.) so they have both pressure and absorptive properties With apologies to the OP for asking about panels themselves rather than hanging tips, when you say "sort of sealed", could you expand a little on what that means in practice? Is it simply normal fibreglass insulation (very dense) with some kind of surface wrapping or membrane? Link to comment Share on other sites More sharing options...
aechmea Posted February 9, 2018 Share Posted February 9, 2018 (edited) Yes, sorry OP, we will keep this brief. I bought pre-formed fibreglass tubes used commercially for insulation of air conditioning/heating ducts. It's called sectional pipe insulation (SPI) (look it up at Fletcher Industries) and it comes in all sorts of diameters. The tube walls are about 25mm thick and is made from really dense (64kg) fibreglass. It is so dense that it is just about 'sealed' after a wooden top and bottom are glued on and the side seam is glued shut. Sounds like a bass drum when you give it a thump. [The local installer that I bought all this fibreglass from was pretty amazed at such uses and took a photo for his records.] Most of the DIY instructions use chicken wire frame, less dense FG and would be difficult to make. The pre-formed stuff is great. [Edit: All covered with a linen/hessian sort of material that Mrs A got from Spotlight.] Some commercial tube traps do have an aluminium foil layer or similar covering part of the tube. They say that by rotating the tube so that the aluminium is 'outward' then some of the highs are reflected back into the room rather than being absorbed. http://www.tubetrap.com/tubetrap-technical.htm Edited February 9, 2018 by aechmea Link to comment Share on other sites More sharing options...
Guest Peter the Greek Posted February 9, 2018 Share Posted February 9, 2018 Another option is vertical strips of aluminum duct tape in say 100mm stips. I did something similar with half rounds. Makes them extra diffusive.....apparently Link to comment Share on other sites More sharing options...
marten Posted February 9, 2018 Share Posted February 9, 2018 Why do the Hunter Valley boys have a leg up on acoustics panel use .... something in the air drifting down the valley ..? Great idea to use pre-formed round insulation Aechmea. I had a quick look at the tech page in the link but not clear to me how they work, so I'll have to dig around the web a bit more to come to grips with the how's and the why's; if I get usable info, I'll kick off a new thread for those. Link to comment Share on other sites More sharing options...
Guest Peter the Greek Posted February 9, 2018 Share Posted February 9, 2018 (edited) Here we go - the only WIP shots I had of these. Lined with 25mm of ultratel and then stuffed with whatever I had lining around. Half round poly differs/absorbers.....so you know, those panel that look **** in the last pic, they got re-done....cant hide imperfections with fabric Edited February 9, 2018 by Peter the Greek Link to comment Share on other sites More sharing options...
almikel Posted February 10, 2018 Share Posted February 10, 2018 On 2/7/2018 at 7:53 PM, Setiawan said: I've got some ideas for the corners and ceiling that I'm reasonably comfortable with, but for the side walls, there's no clear solution that's jumping out to me. I spent the last weekend DIYing 6 frames that are 80cm x 120cm x 11cm, and want a 10cm air gap behind them. Ideally, the solution would: Not involve too much work (e.g. mounting four brackets per panel * six panels * four screws per bracket = nearly a hundred screws, which seems a bit tedious for a non-carpenter like me) Not be too unsightly (you'll see the side profile upon entering the room) Allow for some flexibility in placement once installed Be easily removable if necessary Not be too expensive (keeping it under $200 would be good) Be sturdy/low risk of dropping While it would be good if I could hit all of the above goals and it's what I'll be aiming for, I don't expect that I will get them all. The 'best' system I've come up with so far: Screw a hang track into the wall studs (horizontally, one piece for three panels: https://www.bunnings.com.au/flexi-storage-1800mm-white-hang-track_p2660962) Hang slotted wall strips from the hang track (vertically, two pieces for each panel: https://www.bunnings.com.au/flexi-storage-762mm-white-double-slot-wall-strip_p2660951) Hang two double slot brackets on each wall strip (https://www.bunnings.com.au/flexi-storage-120mm-white-double-slot-bracket_p2583641) Find some way to secure the panels to those double slot brackets (each panel is held up by four double slot brackets) In case this is not intuitive enough a description, see dodgy diagram below: Only thing is that I don't really know how I would secure the brackets to the supporting bars on the panel. Otherwise, this mostly hits my criteria. Alternatively, I could hang each panel like a picture frame, and place a spacer behind each panel (or attach the spacer to the panel). This seems like a rather inelegant solution though, and doesn't allow for lateral repositioning without putting more holes in wall. If anyone has any input on the above ideas (ways to improve or overlooked flaws), or have alternate solutions, please share. I'm hoping to possibly do this this coming weekend, though if no good ideas come to mind, I might just do the corners and/or ceiling instead and postpone these until the following weekend. Thanks! Some extra pictures of last weekend's job, still to be covered with fabric (and maybe painted black first). for the ultimate "no tech" solution you could just lay them lengthwise and lean them against walls straddling floor/wall corners - a tiled floor may be a bit slippery but a few blobs of BluTac might solve that (? - or go bang in the night ), or a strategically placed floor mat. Just an idea. Mike Link to comment Share on other sites More sharing options...
Guest Posted February 10, 2018 Share Posted February 10, 2018 Another simple and effective idea could be hanging them like a large oil painting and letting the bottom of the panels touch the wall on the bottom of the frame, leaning into the room with a tapering air gap. 1 hook per panel Link to comment Share on other sites More sharing options...
Guest Posted February 10, 2018 Share Posted February 10, 2018 19 hours ago, Peter the Greek said: Here we go - the only WIP shots I had of these. Lined with 25mm of ultratel and then stuffed with whatever I had lining around. Half round poly differs/absorbers.....so you know, those panel that look **** in the last pic, they got re-done....cant hide imperfections with fabric very, very cool work there Peter. Link to comment Share on other sites More sharing options...
Dbuns Posted February 19, 2020 Share Posted February 19, 2020 On 09/02/2018 at 10:10 PM, Peter the Greek said: Here we go - the only WIP shots I had of these. Lined with 25mm of ultratel and then stuffed with whatever I had lining around. Half round poly differs/absorbers.....so you know, those panel that look **** in the last pic, they got re-done....cant hide imperfections with fabric I am currently looking into DIY absorption for my Theater. I really like your design. Are the half tube panels Intended to be an acoustic absorber or more bass trap? Are the wall panels next to it absorption as well or just covered in fabric? I had intended on 90mm 27kg/m3 fiberglass in a 150mm deep frame on the wall reflection points. However I like the look of the half tube. Any drawbacks compared to the standard rectangle? Thanks! Link to comment Share on other sites More sharing options...
Guest Peter the Greek Posted February 19, 2020 Share Posted February 19, 2020 6 hours ago, Dbuns said: Are the half tube panels Intended to be an acoustic absorber or more bass trap? They're poly diffusers and provide some trapping, but not really. Mainly poly diffusers and a shelf to put surrounds that could be pointed at the MLP Quote Are the wall panels next to it absorption as well or just covered in fabric? A mix of absorption, diffusion, scatter, and combo panels - each one is different Quote I had intended on 90mm 27kg/m3 fiberglass in a 150mm deep frame on the wall reflection points. However I like the look of the half tube. Any drawbacks compared to the standard rectangle? 50mm 48kg is the standard. I can't speak to your plan. It'd be different for every room, speaker type, and preference. If you want professional help, I recommend the service that Quest AI provide Link to comment Share on other sites More sharing options...
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