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When you put a straw in your soda, and suck the air out of the top, then why does soda rise up from the other end of the straw?Does the sucking out of old air automatically suck in new air from the other side of the room? Interesting but can't wrap my head around why it would work
That makes sense, glad I came onto the forum now as I was going to use 2 fansGregwor wrote:That's exactly how it works. Removing air creates a void that must be filled -- so new air comes in from the path of least resistance.That is even better but, how exactly does that work? Does the sucking out of old air automatically suck in new air from the other side of the room? Interesting but can't wrap my head around why it would work
I totally understand your desire for storage space.The garage door opens upward as you will see and I was hoping to keep our bikes/ kataks there so I have easy access out the house when I go riding or kayaking else have to lag all that stuff up the stairs and through the house. I think I understand what you mean though and I would prefer not to have two silencers inside the actual room. Question: Is it absolutely necessary to have 2 silencers. What happens if I just have a silencer on the outside?
- You could mount the boxes in the ceiling
- You could mount them in between your inner and outer leaf like you did before, but you would eat up space either in your room or in your storage area.
- You can have 1 silencer, it just doesn't work as well and will only provide mediocre insertion loss. If this is the route you decide to go, let us know so we can tell you how to do it.
- You can have a silencer on the outside, yes.
You mean make each baffle a different size within the silencer so if there are 3 you can make the middle one a bit bigger and the 3rd one even bigger?Having the change occur at the outlet isn't good as there will then be turbulence there. It has to happen within the actual silencer. Usually it happens right at the inlet (when talking about your supply silencer, this would be on the end of the box opposite your room, furthest point from where your room is). Introducing several different impedance changes will increase it's performance. So within your baffles, adjusting the size can achieve this.When you say "at some point" do you mean at the outlet or within the actual silencer.
do you have a design that I can look at that is designed correctly or could you point me to one/several that will teach me?They were designed incorrectly.Most silencers I have seen built don't have any variation in the size. The baffles are all equal size and the path way within the silencer stays the same.
What happens if it is?Either way, it looks like your inlet is larger than the path through the baffles.Here is a plan I have of a silencer. it looks even all the way through.
Why does having it the same size cause only one impedance change? I would have thought that you would have no impedance change by keeping the same size throughout.Basically, let's say you have an 8" round inlet duct, your cross sectional area of that inlet is 50.27 sq inches. If you only wanted to introduce a single impedance change (having the size the same throughout),
Ok I understand but in this small blue diagram attached (which is what I wanted to do for my room) the outlet is very close to the silencer and indeed very close to the last "corner" within the silencer. So if I have understood you correctly, would this not work?the interior path of the silencer (the inner dimension of the box - this is INSIDE of the 1" duct liner) must be double 50.27 sq inches. So, 100.53 sq inches. Now, based on the CFM required for your room, you also need to calculate how big your silencer needs to be after the last corner in it in order to achieve equal to or slower than 300 feet per min air velocity. This could require you to have your path get larger. Or, maybe 100.53 sq inches will be big enough and you can just retain that size. Now, the outlet itself needs to be away from the last corner (where the last corner or impedance change happens) by at least 3 times the smallest dimension in your box. So, let's say the interior dimensions of your box, in order to achieve 100.53 sq inches is 10", your outlet must be 30" away!
Thanks for the reminder. I saw your last message at a time when I couldn't respond and then I totally forgot to check back into your thread!Please don't forget me
aaah that does make sense, glad I understood thisSoundman2020 wrote:Adding to what Greg said...
When you put a straw in your soda, and suck the air out of the top, then why does soda rise up from the other end of the straw?Does the sucking out of old air automatically suck in new air from the other side of the room? Interesting but can't wrap my head around why it would work
There's your answer...
- Stuart -
buttermuffin wrote:aaah that does make sense, glad I understood this
Right! It is also possible to use just one fan "blowing" into the fresh air intake end of the duct, and some people do that instead. There are pros and cons for doing it that way. And it is possible to use two fans as well, and miht even be required under certain conditions, but it's a huge pain to implement, because you have to make sure that you get both fans set very carefully to move the exact same amount of air: if not, then one fan will be forcing the other to "over-speed", because it will be moving a little bit more air than it should, so that second fan will wear out sooner than it should, and make more noise than it should. The first fan (the one that is doing the forcing) will also be over-worked, because it is facing a higher load than it should be (forcing the other one to run faster), and therefore it too will wear out faster. If the speed difference is larger, then one of the fans will suffer "aerodynamic stalling" due to air not being able to flow properly over the blades, thus greatly increasing turbulence in the air flow, and noise as well. Thus, for those cases where you do need two fans, it is very important to balance the flows exactly, and monitor them all the time to make sure they stay balanced. Either that, or provide a "relief" path that bypasses the main duct, allowing the excess unbalanced flow to go somewhere else... but that' wastes energy and efficiency....That makes sense, glad I came onto the forum now as I was going to use 2 fans
Ok thanks for the recap and that makes total sense. It is incredible just how much intricacy there is to this aspect of studio building.Soundman2020 wrote:buttermuffin wrote:aaah that does make sense, glad I understood this
Right! It is also possible to use just one fan "blowing" into the fresh air intake end of the duct, and some people do that instead. There are pros and cons for doing it that way. And it is possible to use two fans as well, and miht even be required under certain conditions, but it's a huge pain to implement, because you have to make sure that you get both fans set very carefully to move the exact same amount of air: if not, then one fan will be forcing the other to "over-speed", because it will be moving a little bit more air than it should, so that second fan will wear out sooner than it should, and make more noise than it should. The first fan (the one that is doing the forcing) will also be over-worked, because it is facing a higher load than it should be (forcing the other one to run faster), and therefore it too will wear out faster. If the speed difference is larger, then one of the fans will suffer "aerodynamic stalling" due to air not being able to flow properly over the blades, thus greatly increasing turbulence in the air flow, and noise as well. Thus, for those cases where you do need two fans, it is very important to balance the flows exactly, and monitor them all the time to make sure they stay balanced. Either that, or provide a "relief" path that bypasses the main duct, allowing the excess unbalanced flow to go somewhere else... but that' wastes energy and efficiency....That makes sense, glad I came onto the forum now as I was going to use 2 fans
That's the reason why one single fan is best.
- Stuart -
You totally can. You just need to make sure that the box is isolated from at least one of the leaves entirely. Leave a small gap around the sleeve and fill it with backer rod and caulk. You could maybe over-build the silencer (with more baffles) to try and compensate for the lack of a box on each leaf.This is why I wanted to build the inner and outer leaves and have the silencer penetrate both like this (see image and please note changes). Seeing as this driveway is underground and not noisy 99% of the time, do you think that this could work?
I just recently learned about this trick from Stuart. If he reads this post, maybe he would be willing to elaborate more for us. But as far as I understand it, the more impedance changes there are, the more insertion loss will be achieved. Note, each one will add more static pressure though! And to clarify, you wouldn't make each baffle a difference size, but you would make the path itself larger and smaller. I'm talking the cross sectional area of the air path here.You mean make each baffle a different size within the silencer so if there are 3 you can make the middle one a bit bigger and the 3rd one even bigger?
Not handy, but Stuart posted one a few weeks ago showing his very smart design where he splits the inlet left and right into two paths, utilizing the space in a very smart way! When I have time, I can try and post one of my boxes for you.do you have a design that I can look at that is designed correctly or could you point me to one/several that will teach me?
How well do you breath through your nose if you plug one nostril? Same idea.What happens if it is?
If your box had the same cross sectional area as the inlet, then there would be no impedance change. The example I was referring to implied that the single impedance change occurs when the cross sectional area doubles. From the inlet of 50.27 sq inches to the inside of the box at 100.53 sq inches. Assuming your outlet and register path remains at 100.53 sq inches to maintain a large enough path which would allow an air velocity of less than 300 feet per minute, that only equals ONE cross sectional area change. That means only ONE impedance change.Why does having it the same size cause only one impedance change? I would have thought that you would have no impedance change by keeping the same size throughout.
Your blue diagram has no measurements on it. It's impossible to say whether it would work or not. The only way to tell would be to design the box and look at the numbers to see if it works out. If it doesn't, tweak it until it does.Ok I understand but in this small blue diagram attached (which is what I wanted to do for my room) the outlet is very close to the silencer and indeed very close to the last "corner" within the silencer. So if I have understood you correctly, would this not work?
Sweet!! And this longer plenum at the outlet would obviously need to be 3 times the shortest dimension of the silencer right? How big is this silencer?Gregwor wrote:Here's one where the top lid is lifted off like a treasure chest for you to examine. You can see the hole on the right of the picture is much smaller than the hole on the left of the picture. The larger hole is obviously on the studio room side of the silencer box and the small hole is on the air handler side. The wood is 2 layers of 1/2" MDF and it is lined with 1" of duct liner. As you can see, is fed with rectangular duct, not round duct. This silencer does not have multiple sizes throughout it and on it's larger hole side, it is hooked up to a longer plenum which would serve to deal with the turbulence issue.
Ductliner. Only ever use proper ductliner. Do not ever use ordinary insulation products that you would use elsewhere in the studio build. Ordinary insulation will shed fibers and particles over time, poor quality ones will "off-gas" nasty stuff, and all of them will erode due to the air flow. Don't skimp here. Only use the proper stuff, that has been specifically designed for use inside HVAC ducts. You will need the type that is 1" (25mm) thick. It is expensive, yes. Made by several manufacturers.What are my options for lining the interior of the box with?
When you say HVAC ducts, do "flexi ducts" count? Because this is more than likely what i will be using?Soundman2020 wrote:Ductliner. Only ever use proper ductliner. Do not ever use ordinary insulation products that you would use elsewhere in the studio build. Ordinary insulation will shed fibers and particles over time, poor quality ones will "off-gas" nasty stuff, and all of them will erode due to the air flow. Don't skimp here. Only use the proper stuff, that has been specifically designed for use inside HVAC ducts. You will need the type that is 1" (25mm) thick. It is expensive, yes. Made by several manufacturers.What are my options for lining the interior of the box with?
- Stuart -
So that's what I answered...What are my options for lining the interior of the box with?
Ah ok I am sorry I confused you. I did mean thatSoundman2020 wrote:I thought you were referring to your silencer boxes!!! That's what you asked about:
So that's what I answered...What are my options for lining the interior of the box with?
- Stuart -
Where are you using flex duct? If you use this, make sure it's in very short lengths and oversized. If you use flex duct, get the lined stuff. Just make sure you use this where isolation does not matter.do "flexi ducts" count? Because this is more than likely what i will be using?
Ideally, yes, you want as much of your duct work to have duct liner in it as possible. Rectangular duct is obviously pretty easy to line.I also thought that maybe you meant the liner had to be used within the duct too because I know that that is its intended purpose.
Yes.Would there be any added benefit in having duct liner within the duct too?
In this image, the grey part was going to be flexi duct. It is about a meter only. Do you think lining this will make a difference?Gregwor wrote:Where are you using flex duct? If you use this, make sure it's in very short lengths and oversized. If you use flex duct, get the lined stuff. Just make sure you use this where isolation does not matter.do "flexi ducts" count? Because this is more than likely what i will be using?