Stones Posted March 13, 2017 Share Posted March 13, 2017 My MVHR is proving to be a little noisier than I would like, so it is my intention to fit a silencer / attenuator to the supply ductwork between the MVHR unit and manifold. So far so good. Price wise, around £50 seems to buy me a ready made unit: https://www.bpcventilation.com/attenuator-silencer The silencing material in this case is mineral wool enclosed by a woven mesh material to prevent wool fibres entering the air supply. The alternative is a homemade unit / box which I would line with mineral wool and woven mesh, or alternatively, with acoustic foam. The question is what is the best material to use, and what is the best shape to make a silencer if constructing rather than buying off the shelf? Does increasing the thickness of the absorbtion material (wool or foam) dramatically increase performance (reduce noise level)? Link to comment Share on other sites More sharing options...
Jeremy Harris Posted March 13, 2017 Share Posted March 13, 2017 The ones I made are lined with acoustic foam, the fire resistant stuff that is used to line studio walls. It's not that thick, around 20mm in the dips and maybe 60mm at the peaks. It did make a very noticeable reduction in the sound level, though. An additional thing that helps is to make the silencer so the internal volume is as large as you can get, as this not only helps to reduce the sound by itself, but help by giving a larger surface area of foam that's exposed to the sound. 1 Link to comment Share on other sites More sharing options...
JanetE Posted March 14, 2017 Share Posted March 14, 2017 @JSHarris I recall you posted a picture of yours Jeremy, can you look it out for us please? We're just about to commission the supply end too and I'm not sure exactly where the best place is to put it. Link to comment Share on other sites More sharing options...
Jeremy Harris Posted March 14, 2017 Share Posted March 14, 2017 There's some details at the bottom of this blog entry that may help: http://www.mayfly.eu/2014/07/part-thirty-one-its-slow-going-on-your-own/ 1 Link to comment Share on other sites More sharing options...
Stones Posted March 14, 2017 Author Share Posted March 14, 2017 Working on the basis that it's surface area that's going to have the biggest impact, acoustic egg box foam would seem to be the more sensible option simply on the basis that the surface area will be that much greater (double / triple?) compared to a flat surface? Jeremy, you mention a baffle in your blog. Was this simply a piece of foam in the centre of the box with space all around for air to flow past? Link to comment Share on other sites More sharing options...
Jeremy Harris Posted March 14, 2017 Share Posted March 14, 2017 There's a baffle in the centre of the fresh air supply silencer, only because the inlet and outlet from it were inline, and I felt it might work better if there was a central foam covered baffle partially dividing what is just a rectangular box. I'm not sure how effective it is, as most of the noise problem we had before was on the extract side, so it may well be that just an acoustic foam lined box would work just as well. The egg box acoustic foam isn't very expensive, and I'd already bought some large sheets to line the inside wall of the services room, thinking there would be some noise from the MVHR unit itself (there's a bedroom next to it). The silencers were made with offcuts of this foam. Link to comment Share on other sites More sharing options...
Stones Posted March 25, 2017 Author Share Posted March 25, 2017 I've been mulling over what the best shape and size of silencer would be. I think foam is the way to go as the silencing material if for no other reason than there is more surface area available (assuming egg box etc) compared to the mineral wool type I linked to previously. The question really is do I build a box and line it with foam as per @JSHarris or get lengths of 200mm plastic duct (or bigger) line with foam and use reducers to take the diameter back down to 150mm to fit to the existing. I have enough spare MDF to build a box for the supply side 600 x 600 x 300 and for the extract 600 x 300 x 300. I also have half a tin of MDF sealer and some silicone to help make the box airtight. If I were to down the plastic duct route, in effect making my own version of the one I linked to in the OP, I could fit two silencers, in series on both the supply and extract (one horizontal, 90 bend then one vertical into top of plenum). Whilst there would be slightly more foam surface area if I went down the homemade box route, clearly there would be more length and a bend if I went down the duct route. Any views / thoughts about which would be the most effective? Link to comment Share on other sites More sharing options...
Jeremy Harris Posted March 25, 2017 Share Posted March 25, 2017 The commercially available silencers seem to just be large diameter tubes with a sound absorption material lining them, so I would think a home made version using acoustic foam should work as well. The only reason I didn't do this is because I didn't physically have room to fit them, as I only realised the need for them after I'd installed the system. Link to comment Share on other sites More sharing options...
joe90 Posted March 25, 2017 Share Posted March 25, 2017 I intend to make my own manifolds and turn them into silencers as well as I have loads of room and saves me making 4 boxes instead of two. The only problem I have is how to restrict air flow into each distribution pipe as I want to regulate at the manifold not terminal. I intend to line the boxes with foam as previously described. Link to comment Share on other sites More sharing options...
Stones Posted March 25, 2017 Author Share Posted March 25, 2017 I've lived with MVHR in several houses, but this is the first where I've really noticed the noise at night. None of my previous houses had silencers, but all used a main duct run with branches off to individual rooms, with adjustment at each terminal. The two new variables are the MVHR unit (a Vent Axia) and radial ducting. A combined silencer / manifold makes a lot of sense - surprising that nobody seems to make them. Link to comment Share on other sites More sharing options...
joe90 Posted March 25, 2017 Share Posted March 25, 2017 Stones, I wonder if the noise is coming from the air attenuation at the terminal, a reason that I like the idea of attenuation at the manifold? Link to comment Share on other sites More sharing options...
jack Posted March 25, 2017 Share Posted March 25, 2017 1 hour ago, joe90 said: Stones, I wonder if the noise is coming from the air attenuation at the terminal, a reason that I like the idea of attenuation at the manifold? Our manifold is lined with acoustic foam but it's still recommended that a silencer be used. Link to comment Share on other sites More sharing options...
Stones Posted March 25, 2017 Author Share Posted March 25, 2017 1 hour ago, joe90 said: Stones, I wonder if the noise is coming from the air attenuation at the terminal, a reason that I like the idea of attenuation at the manifold? It is fan rather than terminal related noise, as the volume and pitch corresponds to the unit and speed it is set at. What little air rushing noise there is at the terminal (which you only notice at very high fan speed where terminals have been quite restricted) can be dealt with by opening the terminal a little. Certainly something to be said for balancing at the manifold as this would let you have the terminal open rather than restricted, thus reducing any sound of air rushing. 24 minutes ago, jack said: Our manifold is lined with acoustic foam but it's still recommended that a silencer be used. How effective would you judge the foamed manifold to be I'm terms of noise reduction ( difficult I know but say compared to standing next to the MVHR unit itself) ? Link to comment Share on other sites More sharing options...
jack Posted March 25, 2017 Share Posted March 25, 2017 No idea, sorry - it's never been on without the silencer in place. Link to comment Share on other sites More sharing options...
Stones Posted June 13, 2017 Author Share Posted June 13, 2017 Having gathered all the necessary materials, I'll be constructing my silencer tomorrow. I'm planning a timber framed box, sheeted with MDF, lined with acoustic egg box foam. MDF to be screwed to timber frame, sealed with silicone. Duct inlet and outlets 90 degrees from each other rather than inline. I have enough MDF to build either a 600 x 600 x 600 cube or a 900 x 600 x 300 rectangular box. Any views on the best shape to construct? I have enough space to accommodate either. Link to comment Share on other sites More sharing options...
Jeremy Harris Posted June 13, 2017 Share Posted June 13, 2017 Bigger is better, and the longer the air path the better, but other than that, make them any shape you like. One of ours ended up being a sort of trapezium shape, to fit in the space available, with the ducts offset from each other, the other is a rectangular box, sat on top of the fresh air feed plenum, with the ducts at right angles to each other. Both seem to work about the same, as far as I can tell with a Mk1, slightly ageing, ear. Link to comment Share on other sites More sharing options...
Russdl Posted December 1, 2020 Share Posted December 1, 2020 On 13/06/2017 at 18:40, Stones said: Having gathered all the necessary materials, I'll be constructing my silencer tomorrow. How did these work out @Stones ? I'm a bit limited in space for many of the off the shelf version to fit so I may well make my own. Any hints, tips and tricks? Link to comment Share on other sites More sharing options...
CC45 Posted December 2, 2020 Share Posted December 2, 2020 just buy some - it will save you lots of time and they are easy to fit! Link to comment Share on other sites More sharing options...
MJNewton Posted December 2, 2020 Share Posted December 2, 2020 11 minutes ago, CC45 said: just buy some - it will save you lots of time and they are easy to fit! Yes, I'd agree with that. I was going to make some but when I saw how cheap they were (eg the Blauberg ones) I decided it wasn't worth DIYing it. Link to comment Share on other sites More sharing options...
Russdl Posted December 2, 2020 Share Posted December 2, 2020 @CC45 they way I’m set up I only have about 450mm to fit them which doesn’t appear to be enough for any of the shelf ones that I’ve seen. Link to comment Share on other sites More sharing options...
joe90 Posted December 2, 2020 Share Posted December 2, 2020 I made my own from ply and incorporated the manifold as well into one box, extract one side, input the other 1 Link to comment Share on other sites More sharing options...
PeterW Posted December 2, 2020 Share Posted December 2, 2020 I’ve got a couple of issues with noise due to having very short ducts from the manifolds to the supply valves so looking to use some sort of pyrosorb foam in the duct plenum to try and reduce some of the transferred noise but not lose the flow. Link to comment Share on other sites More sharing options...
joe90 Posted December 3, 2020 Share Posted December 3, 2020 8 hours ago, PeterW said: I’ve got a couple of issues with noise due to having very short ducts from the manifolds to the supply valves so looking to use some sort of pyrosorb foam in the duct plenum to try and reduce some of the transferred noise but not lose the flow. yes I lined my “box” above with sound absorbing foam which helped but admit it’s the short lengths that produce the most noise. Link to comment Share on other sites More sharing options...
Russdl Posted December 3, 2020 Share Posted December 3, 2020 8 hours ago, PeterW said: pyrosorb foam Something else I can add to the list of ‘never heard of that before’. It’s quite a large list. I was planning on using that eggbox type foam whatever that’s called, what is pyrosorb? It sounds fire retardant at least. Link to comment Share on other sites More sharing options...
PeterW Posted December 3, 2020 Share Posted December 3, 2020 30 minutes ago, Russdl said: Something else I can add to the list of ‘never heard of that before’. It’s quite a large list. I was planning on using that eggbox type foam whatever that’s called, what is pyrosorb? It sounds fire retardant at least. Pyrosorb is a self adhesive foam sheet that has a class O fire standard but is also quite dense so is good for the lower frequencies which is what I am trying to reduce. https://www.efoam.co.uk/Pyrosorb-class-0-acoustic-foam.php Plan is to both line the plenums using layers of 6mm and also to create a convoluted route through the plenum itself to increase the sound path. Will see next week if it works ..! Link to comment Share on other sites More sharing options...
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