How to ventilate an underground garage/basement studio

[Waka]

My only doubt now which I am researching is figuring out how to make the connection to the register at the end of the duct. I will be using duct board so I am guessing the best way is to cut a hole and simply stick the register in it.

How rigid is your duct board? Also, is the ducting going to be inside the room? If this is the case, will you be boxing it in with plasterboard, because you will be attaching your register to the plasterboard/facing board not the duct board itself if this is the case? Usually the register will have a flange around it that you can screw through into your board.

[Waka]

Im following your threads with great interest, keep up the good work

Thanks very much I should have some more progress to post on my threads over the coming week so stay tuned!

Dan

[Gregwor]

Did you decide on your register? I've been researching the Nailor catalogue for myself and it seems the NC rating of 40 is pretty much as low as I can get it unless I get an absolutely MASSIVE diffuser.

Say I need 400 CFM, I'd use two of the Nailor 5010 1" 4 slot 48" long diffusers. You can see at 200 CFM is states NC of 40. Far from the NC 15 for super pro studios. How the hell can we achieve low NC from grilles/registers/diffusers? Did I mention getting 6 of these (which I'd need for 2 of my 3 rooms) will run me between $1134 and $1470 Canadian depending on the finish!!!

Anyone?

Greg

[Soundman2020]

Say I need 400 CFM, I'd use two of the Nailor 5010 1" 4 slot 48" long diffusers. You can see at 200 CFM is states NC of 40. Far from the NC 15 for super pro studios. How the hell can we achieve low NC from grilles/registers/diffusers?

Don't forget that you'll be measuring the NC-number at the mix position, not at the register. With a well designed room the registers are hopefully not even visible at the mix position, or at least are far away from it... So the actual air noise will be much lower when you measure it.

- Stuart -

[Gregwor]

Stuart, in my control room, my ear to the closest corner of the register/diffuser is just over 8 feet.

My ISO room, however, is only only 9 feet from register to register. So, let's say a singer is standing just off center in the room, they're going to be between 3 and 4 feet away. Should I be concerned? I REALLY am doing my best to make sure there is no audible hiss in the room even with heavy vocal compression.

Greg

[buttermuffin]

My only doubt now which I am researching is figuring out how to make the connection to the register at the end of the duct. I will be using duct board so I am guessing the best way is to cut a hole and simply stick the register in it.

How rigid is your duct board? Also, is the ducting going to be inside the room? If this is the case, will you be boxing it in with plasterboard, because you will be attaching your register to the plasterboard/facing board not the duct board itself if this is the case? Usually the register will have a flange around it that you can screw through into your board.

Pretty rigid. I attached a pic for you to have a look at the product. I believe it is as rigid as a standard duct board.

To answer your other question: The duct board will run inside the room but inside my ceiling cloud (see image). I could isolate it if I wanted to but I am going to see how loud it is first to see if it is necessary. The ceiling trap is going to span the whole ceiling kind of like a framed acoustic ceiling and be around 50cm thick so I don't think the air will be audible, especially since when it enters the room I am aiming for around 200CFM which is pretty slow. Your comment about the plasterboard housing the register got me thinking. So is it not possible to attach the register/grille to the duct itself? Does it have to be attached to the plasterboard? I suppose I could have a piece of drywall just to house the register in that location.

[Waka]

Your comment about the plasterboard housing the register got me thinking. So is it not possible to attach the register/grille to the duct itself? Does it have to be attached to the plasterboard? I suppose I could have a piece of drywall just to house the register in that location

I haven't had any experience with duct board, but for it to house the register it would have to be able to take screws.

[buttermuffin]

Your comment about the plasterboard housing the register got me thinking. So is it not possible to attach the register/grille to the duct itself? Does it have to be attached to the plasterboard? I suppose I could have a piece of drywall just to house the register in that location

I haven't had any experience with duct board, but for it to house the register it would have to be able to take screws.

You're right. Found some stuff on you tube. I will just use some plasterboard to house the register. I was going to use pieces of plasterboard to house the lights anyway.

I noticed that a lot of the videos that talk about ventilation and air conditioning seem to use a bigger return grille and a smaller supply register. Do you know why?

[Waka]

You're right. Found some stuff on you tube. I will just use some plasterboard to house the register. I was going to use pieces of plasterboard to house the lights anyway.

Sounds good.

I noticed that a lot of the videos that talk about ventilation and air conditioning seem to use a bigger return grille and a smaller supply register. Do you know why?

Yes it seems to be quite common. Supposedly the idea is to have smaller supply in order to keep velocity higher (not what we want at all!) to improve throw at the register to push the air to even the corners of the room, then the return is sized larger to balance the system and stay within the system's static pressure limits.
When it comes to studio design though, high velocity supply is definitely a no-no. We tend to size our ducts the same.

This is a post from 2007 by Rod Gervais (he literally wrote the book on home studio construction) when responding to someone with a similar question:

OK- that makes sense- you have a total of 36.27 si of supply running free and full - and then you have a return of 50.27si free air trying to return to your system........ so what happens is you create a build up of static pressure in the supply - which increases the retun air rate even more.......

See - this is why I always over size evenrything for studios- you won't see anything less than a 10" round feeding a little room that is only getting 100 cfm if Iminvolved in the project....

and the supply and returns should alwys be the same size......

[Waka]

Did you decide on your register? I've been researching the Nailor catalogue for myself and it seems the NC rating of 40 is pretty much as low as I can get it unless I get an absolutely MASSIVE diffuser.

Say I need 400 CFM, I'd use two of the Nailor 5010 1" 4 slot 48" long diffusers. You can see at 200 CFM is states NC of 40. Far from the NC 15 for super pro studios. How the hell can we achieve low NC from grilles/registers/diffusers? Did I mention getting 6 of these (which I'd need for 2 of my 3 rooms) will run me between $1134 and $1470 Canadian depending on the finish!!!

Looking at that catalogue image. Doesn't that say CFM per ft.? Unless I'm reading that wrong isn't that: 200CFM over a 48" diffuser is the same as 50 CFM per ft or between 7 and 13 NC?

[buttermuffin]

You're right. Found some stuff on you tube. I will just use some plasterboard to house the register. I was going to use pieces of plasterboard to house the lights anyway.

Sounds good.

I noticed that a lot of the videos that talk about ventilation and air conditioning seem to use a bigger return grille and a smaller supply register. Do you know why?

Yes it seems to be quite common. Supposedly the idea is to have smaller supply in order to keep velocity higher (not what we want at all!) to improve throw at the register to push the air to even the corners of the room, then the return is sized larger to balance the system and stay within the system's static pressure limits.
When it comes to studio design though, high velocity supply is definitely a no-no. We tend to size our ducts the same.

This is a post from 2007 by Rod Gervais (he literally wrote the book on home studio construction) when responding to someone with a similar question:

OK- that makes sense- you have a total of 36.27 si of supply running free and full - and then you have a return of 50.27si free air trying to return to your system........ so what happens is you create a build up of static pressure in the supply - which increases the retun air rate even more.......

See - this is why I always over size evenrything for studios- you won't see anything less than a 10" round feeding a little room that is only getting 100 cfm if Iminvolved in the project....

and the supply and returns should alwys be the same size......

Yeah I have his book. I found the HVAC section good but only as a supplementary information. Most the info I got was from this site. There also seems to be a small difference in how Rod says the HVAC needs to be done. He seems to advise that you either need to size your ducts or use a silencer where here it seems that both are advised as being necessary

[Waka]

Yeah I have his book. I found the HVAC section good but only as a supplementary information. Most the info I got was from this site. There also seems to be a small difference in how Rod says the HVAC needs to be done. He seems to advise that you either need to size your ducts or use a silencer where here it seems that both are advised as being necessary

I just reread the section again in the book, I have to agree with you. Rod does give two distinct options:

For a split system, you begin by sizing the outlet from the air handler large enough to reduce the velocity to not more than double your desired total velocity at the outlets...
Then do the following:

1. Provide lining for all supply and return ducts.
2. Install branch ducting again that is sized to provide no more than double your desired velocity at the outlets.

OR: (emphasis mine)

1. Provide a baffle system (sound attenuator) just prior to air entering the room that's designed to double the volume of the supply duct (a doubling in volume cuts velocity in half, thus achieving your desired supply register velocity).
2. Use a good-quality supply register to ensure that there is no buffeting of air at the register

In the example images provided (Fig: 7.3, 7.7, 7.6, and 7.7) there are no silencers pictured, there is the label

Provide Soffit

pointing towards the ducting within the sound room though. He states that the entry must be well sealed and that a canvas connection should be used at the air handler if steel ducting used. He finishes off chapter 7 with the words:

Just remember that high volumes and low velocities are your friends in this endeavor, and don't forget to maintain your room isolation in the process.

.

It is definitely advised by Stuart (and others in this forum) to fit lined silencers at any penetrations though. It appears that Rod Gervais feels that relatively long lined ducting at low velocities (along with a soffit enclosure possibly?) is sufficient, maybe Rod is designing with lower isolation requirements, I'm not sure.

Two Points:

1. When it comes to supply and return though, the pros seem to be in agreement that supply and return should be sized the same (read: low velocity)
2. Thinking logically, if a hole is cut in my isolated wall assembly, a silencer provides greater mass than a thin steel duct... whether this affects much I don't know, considering that there won't be much of a spring for an MSM system within the silencers themselves, and mass law isn't a lot of help here. To be honest looking at it from the (albeit limited) knowledge I have when it comes to the physics, I can't really see how they isolate much at all. If it's simply down to impedance mismatch within the silencers/between two of them, then the same could be achieved with differing sized lined ducting without the need for silencers at all.

Long story short... I don't know

I'm using silencers though, I'll let you know how it turns out.

***EDIT*** I have stumbled on a thread on https://recording.org from 2014 that shows that Rod Gervais is stating a requirement for silencers (baffles) to maintain isolation:

Air conditioning has to do with comfort levels - you don't have to use it all all if that is not an issue for you - however fresh air is a different thing altogether...... you absolutely need to get fresh air into the space - and if you expect to maintain your levels of isolation this is going to require baffles as well as a fan......

Source: https://recording.org/threads/soundproo ... 026/page-2

[Soundman2020]

OR: (emphasis mine)

I suspect that's a typo, and was meant to be "and" or "plus" or "in addition". Either that, or Rod was talking about only low levels of isolation without silencers, and moderate / high levels with silencers, but somehow that part wasn't made clear.

It's a simple thing to do a practical test and see how much isolation you get from a duct alone: Get fours sheets of 5/8 drywall and seal two of those onto each side of a doorway to completely close it off (take off the door first to make it easier). So you'll have two sheets of 5/8, then an air gap, then 2 sheets of 5/8. Play loud music on one side of that, and measure the levels on both sides with a sound level meter, to see how much isolation you are getting. Now cut a 6" diameter hole in both "leaves", and thread a piece of flex duct through both holes. Play loud music like before, and measure again, like before... How much isolation will you have now?

I think you probably don't even need to do this test in real life: you can simply imagine how well that will work...

there is the label "Provide Soffit"

That suggests that he is talking about using a soffit around the duct, to get some extra isolation. That's certainly better than just duct, but it would only be good for low to moderate isolation.

Just remember that high volumes and low velocities are your friends in this endeavor, and don't forget to maintain your room isolation in the process.

Yup. With silencers!

It appears that Rod Gervais feels that relatively long lined ducting at low velocities (along with a soffit enclosure possibly?) is sufficient, maybe Rod is designing with lower isolation requirements, I'm not sure.

That would be my take: he probably wasn't talking about studios that need high isolation. I'm wondering if some part of his explanation was lost in the editing process, that would have clarified this.

Thinking logically, if a hole is cut in my isolated wall assembly, a silencer provides greater mass than a thin steel duct... whether this affects much I don't know,

Correct, and yes it does make a big difference. In the above "thought experiment", instead of using flex duct, use ordinary round metal duct, and see if you believe that it would make any substantial difference. You could even add to the experiment a bit, by bringing that duct through the drywall, turning it through an angle of 90°, and running it alone the wall a few feet before terminating it in a registers. Now play drums on that room, and go listen in the other room. The sound of the drums will be getting through, loud and clear. If you then put a SOFFIT around that metal duct, yes, that would reduce the level, but there would still be plenty of sound getting through.

considering that there won't be much of a spring for an MSM system within the silencers themselves, and mass law isn't a lot of help here.

Right, but do consider that you have one silencer on the inner-leaf penetration, another on the outer-leaf penetration, and a short section of flexduct joining them. Now you have MSM again. The flex duct doesn't really count here, and you are back to the mass of the silencers on each side with the spring of the air gap between the leaves...

To be honest looking at it from the (albeit limited) knowledge I have when it comes to the physics, I can't really see how they isolate much at all.

They do that in several different ways. First is mass (which is why you make them heavy), second is damping (which is why they are lined with duct liner), third is impedance mismatch (sudden, large changes in cross section at both ends), fourth is baffles (more mass in the direct path of the sound), fifth is multiple turns (the air can go around turns, but the sound waves can't), fifth is path length attenuation (the sound must take a much longer path through the silencer than just the length of the box, due to the multiple turns), and there are some other minor things going on in there too. Plus, of course, the plain old MSM thing, from the silencer box mass on each leaf being separate buy the air spring in between the leaves.

If it's simply down to impedance mismatch within the silencers/between two of them, then the same could be achieved with differing sized lined ducting without the need for silencers at all.

Right, but it isn't! Impedance is only one of several mechanisms that all play their part.

I'm using silencers though, I'll let you know how it turns out.

If you do it right, it will turn out great! And silent...

Rod Gervais is stating a requirement for silencers (baffles) to maintain isolation:

Yup! My bet is that something happened when the publisher was editing what he wrote for the book, and they maybe left out something, or changed the wording in such a way that the meaning was lost. I can't imaging Rod suggesting that a straight-through duct would provide high levels of isolation.

- Stuart -

[Waka]

OR: (emphasis mine)

I suspect that's a typo, and was meant to be "and" or "plus" or "in addition". Either that, or Rod was talking about only low levels of isolation without silencers, and moderate / high levels with silencers, but somehow that part wasn't made clear.

It's a simple thing to do a practical test and see how much isolation you get from a duct alone: Get fours sheets of 5/8 drywall and seal two of those onto each side of a doorway to completely close it off (take off the door first to make it easier). So you'll have two sheets of 5/8, then an air gap, then 2 sheets of 5/8. Play loud music on one side of that, and measure the levels on both sides with a sound level meter, to see how much isolation you are getting. Now cut a 6" diameter hole in both "leaves", and thread a piece of flex duct through both holes. Play loud music like before, and measure again, like before... How much isolation will you have now?

I think you probably don't even need to do this test in real life: you can simply imagine how well that will work...

there is the label "Provide Soffit"

That suggests that he is talking about using a soffit around the duct, to get some extra isolation. That's certainly better than just duct, but it would only be good for low to moderate isolation.

Just remember that high volumes and low velocities are your friends in this endeavor, and don't forget to maintain your room isolation in the process.

Yup. With silencers!

It appears that Rod Gervais feels that relatively long lined ducting at low velocities (along with a soffit enclosure possibly?) is sufficient, maybe Rod is designing with lower isolation requirements, I'm not sure.

That would be my take: he probably wasn't talking about studios that need high isolation. I'm wondering if some part of his explanation was lost in the editing process, that would have clarified this.

Thinking logically, if a hole is cut in my isolated wall assembly, a silencer provides greater mass than a thin steel duct... whether this affects much I don't know,

Correct, and yes it does make a big difference. In the above "thought experiment", instead of using flex duct, use ordinary round metal duct, and see if you believe that it would make any substantial difference. You could even add to the experiment a bit, by bringing that duct through the drywall, turning it through an angle of 90°, and running it alone the wall a few feet before terminating it in a registers. Now play drums on that room, and go listen in the other room. The sound of the drums will be getting through, loud and clear. If you then put a SOFFIT around that metal duct, yes, that would reduce the level, but there would still be plenty of sound getting through.

considering that there won't be much of a spring for an MSM system within the silencers themselves, and mass law isn't a lot of help here.

Right, but do consider that you have one silencer on the inner-leaf penetration, another on the outer-leaf penetration, and a short section of flexduct joining them. Now you have MSM again. The flex duct doesn't really count here, and you are back to the mass of the silencers on each side with the spring of the air gap between the leaves...

To be honest looking at it from the (albeit limited) knowledge I have when it comes to the physics, I can't really see how they isolate much at all.

They do that in several different ways. First is mass (which is why you make them heavy), second is damping (which is why they are lined with duct liner), third is impedance mismatch (sudden, large changes in cross section at both ends), fourth is baffles (more mass in the direct path of the sound), fifth is multiple turns (the air can go around turns, but the sound waves can't), fifth is path length attenuation (the sound must take a much longer path through the silencer than just the length of the box, due to the multiple turns), and there are some other minor things going on in there too. Plus, of course, the plain old MSM thing, from the silencer box mass on each leaf being separate buy the air spring in between the leaves.

If it's simply down to impedance mismatch within the silencers/between two of them, then the same could be achieved with differing sized lined ducting without the need for silencers at all.

Right, but it isn't! Impedance is only one of several mechanisms that all play their part.

I'm using silencers though, I'll let you know how it turns out.

If you do it right, it will turn out great! And silent...

Rod Gervais is stating a requirement for silencers (baffles) to maintain isolation:

Yup! My bet is that something happened when the publisher was editing what he wrote for the book, and they maybe left out something, or changed the wording in such a way that the meaning was lost. I can't imaging Rod suggesting that a straight-through duct would provide high levels of isolation.

- Stuart -

Thanks Stuart, that has been helpful, especially the information regarding the physics of attenuation in silencers. I've designed my silencers and installed the outer leaf ones on my own design and build threads if you're interested in checking the design (Design thread: http://www.johnlsayers.com/phpBB2/viewt ... 7&start=45, Build thread: http://www.johnlsayers.com/phpBB2/viewt ... 9&start=30).

I'm also happy for you buttermuffin in seeing that your design includes silencers . I'd like to see your plans for your silencers at some point when you're finished designing them in sketchup.

[Gregwor]

Looking at that catalogue image. Doesn't that say CFM per ft.? Unless I'm reading that wrong isn't that: 200CFM over a 48" diffuser is the same as 50 CFM per ft or between 7 and 13 NC?

YES!!!!!

I decided to use these linear slot units like 6 months ago and I just re-visited them. I was so surprised that I had picked them seeing that they'd have 40 NC. I can't believe I missed that. Thanks!

Greg