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Lionzeye
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#1
20th September 2011
Old 20th September 2011
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HVAC, Baffle Box/Silencer

I am aware of all the conflicts that arise when tapping into a system versus installing a whole new separate system, which is definitely not in the budget and not an option as of now. We want a healthy environment for humans in a creative state! I have read countless hours and need more knowledge and guidance in my DIY project. I have gained much insight and influence on design from this helpful post.
John Sayers' Recording Studio Design Forum • View topic - What I have learned about HVAC

Current Design
This is what we are hoping to introduce without straining the system; We will test the unit after installed accordingly, and if it strains the system, then call in a pro:

LR - 1 air supply with shutter to stop forced heat in winter time if the rest of building uses heater (will introduce noise!), 1 return with high quality low noise inline fan to outside and not machine, and 1 fresh air supply from outside with a shutter to stop heat in summer time

CR- 2 air supplies with shutters to block heater in winter, 1 return same config. and same fan mentioned above, 1 fresh air from outside to introduce cold air in winter with shutter to block out heat in. we will have control with fans how much we introduce into the control room as we could possibly have around 10kW at full peak performance.

Both return inline fans speed and power will be controlled in the control room via control dial to stop fan during recordings, if needed. I am also hoping we provide enough isolation to so we don't have to turn anything off to record.

Both rooms inside have 2 layers of 5/8" drywall and one hole in each room for air supply. (see pictures below) We plan on using duct silencers or baffle box's if we can implement them to work properly outside of the rooms. We basically would like to implement ducting/silencers in the hallway or outside the space if we can.

The CR vent has an 8ft flex duct run before it goes through a baffle box lined with 703, so it was not installed properly and is now covered behind drywall. I considered sealing it up and re-route the vent to a new properly designed vet with proper isolation techniques in mind.

Inside CR

P.S. Don't insult our texture. That was a test wall. We have an interested texture going on. Should be cool and not boring! Will be covered up mostly anyway and that's why we didnt want to sand. And the health hazard of sanding I want to do without!

The LR has one hole in the wall with a Temporary 8" duct running through the whole.

Inside LR


outside LR


here are pictures of the hallway, outside of the two rooms





QUESTION

Will it benefit us to use duct silencers/baffle box's outside the space in the hallway and then punch in?

Last edited by Lionzeye; 21st September 2011 at 09:17 PM.. Reason: Simplify approach on topic and add to design idea
Lionzeye
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20th September 2011
Old 20th September 2011
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I just got a sample of JM ductboard! Cool stuff for a baffle box if I build one!
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21st September 2011
Old 21st September 2011
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ok how about a simpler question

Can you have any amount of duct run at the exit of a duct silencer/baffle box in a supply vent?

i.e. trunk - Duct - Silencer (outside room) - duct run (no longer than 14 inches) through MAM(mass-air-mass) assembly - vent/grill???

Anybody??
#4
21st September 2011
Old 21st September 2011
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hi lionzeye! im also currently in the process of making a sound isolated duct. Mine is enclosed with MDF board. Im a little confused with your question, how bout testing how it works?
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21st September 2011
Old 21st September 2011
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Honestly I didn't read your entire post, but it sounds like you need to build some dead vents.

I am currently doing the same; building 2 of these (see attached diagram); one for cold air intake (sucking from almost floor level of an adjacent room that has HVAC and another for exhaust (it'll be on the ceiling, pumping air out into that same adjacent room.... actually, when I say adjacent what I mean is the large industrial unit my room was built in (10" tall room inside a 20" tall room). Next summer we might buy one of those 'portable' A/C units and hook that up to the intake, then switch back normal when the A/c is no longer needed.

To save you the trouble searching, this seems to be the best deal going right now on inline duct fans. You may need to go bigger (6 or 8" vs 4) for your room; these are probably even too small for mine.

4 inch In-Line Fan 165 CFM


.
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HVAC, Baffle Box/Silencer-dead-vent-diagram-profile.jpg  
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#6
21st September 2011
Old 21st September 2011
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Make sure that PVC pipe does not bridge the plasterboard of the two separated stud walls together.
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21st September 2011
Old 21st September 2011
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Greetings Chris

Quote:
hi lionzeye! im also currently in the process of making a sound isolated duct. Mine is enclosed with MDF board. Im a little confused with your question, how bout testing how it works?
Sorry, I try to be detailed as possible, but maybe confusing. I tried to simplify a little. What I am trying to figure out, Is how to go about having a hole in your "room in a room" assembly, and connecting to a baffle box/silencer on the other side of the live room? The other side of the live room, is the rest of basement space which extends twelve feet before hitting the other side of the basement/structure. This is also the lounge.

Two scenarios I came up with that could affect TL or sound isolation at the vents and holes for HVAC

1. i.e. drums playing, will leave the live room through the duct and possibly reflect back into live room, and sound escaping the edge of the hole that will need to be sealed with GG acoustic sealant, also sound leak out of the duct perpendicular to the duct run and into the rest of the room.

2. The sound of cars passing, occasional siren, and people talking, which all will come from the rest of the basement space, or lounge, and into the live room via duct or silencer/baffle box and through the edge of the hole in drywall.

The first Isn't a big deal due to our particular isolation needs, but 2 , is what I am worried about. I cant have any noise leaking into duct holes (through the edge of the hole, and through the duct itself from lounge or outside!) and spoil a good recording. So, I may have answered my own question. If I am worried about noise coming from outside the live and control rooms, then the baffle box's and the silencers should be on the outside of the live room. A baffle box/duct silencer would take care of 1 and 2 if butted against the outside of the live room wall. But, I would need to seal up that box with the equivalent mass of my outside wall, 1/2" drywall that is. (not much, but we only need that much isolation according to our calculations and tests so far), but may eventually have 2 layers 5/8".

hope this made sense!
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21st September 2011
Old 21st September 2011
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Quote:
Honestly I didn't read your entire post, but it sounds like you need to build some dead vents.

I am currently doing the same; building 2 of these (see attached diagram); one for cold air intake (sucking from almost floor level of an adjacent room that has HVAC and another for exhaust (it'll be on the ceiling, pumping air out into that same adjacent room.... actually, when I say adjacent what I mean is the large industrial unit my room was built in (10" tall room inside a 20" tall room). Next summer we might buy one of those 'portable' A/C units and hook that up to the intake, then switch back normal when the A/c is no longer needed.

To save you the trouble searching, this seems to be the best deal going right now on inline duct fans. You may need to go bigger (6 or 8" vs 4) for your room; these are probably even too small for mine.

4 inch In-Line Fan 165 CFM
Hey Granny Gremlin, Thanks for input. I will definitely have to read and look into your suggestions when I have more time to look closer. Need to get our doors on order!!
#9
22nd September 2011
Old 22nd September 2011
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nice detail above.

thought i'd add a couple of more points.

don't forget about an acoustic access panel so you can access the fan.
you can also get a product generically referred to as polyflex which is an acoustc rated flexible duct, with hvac ducting you should runn you duct at least 3m in length and have a couple of bends in it for best effect.
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22nd September 2011
Old 22nd September 2011
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Quote:
Originally Posted by Sebg View Post
Make sure that PVC pipe does not bridge the plasterboard of the two separated stud walls together.
I was gonna cut the hole a bit oversize and sprayfoam and caulk it in. Thanks for the reminder.

As for access panels, since I was gonna build the boxes outside the studio (vs in a soffit on the inside as I have seen or in the wall), is there really a need to have a fancy seal on the removable panel? I was just gonna have one side on removable screws with some sort of gasket material (vs glued, screws/nailed and caulked)?
#11
22nd September 2011
Old 22nd September 2011
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Quote:
Originally Posted by Granny Gremlin View Post
I was gonna cut the hole a bit oversize and sprayfoam and caulk it in. Thanks for the reminder.

As for access panels, since I was gonna build the boxes outside the studio (vs in a soffit on the inside as I have seen or in the wall), is there really a need to have a fancy seal on the removable panel? I was just gonna have one side on removable screws with some sort of gasket material (vs glued, screws/nailed and caulked)?

that should work depending on final detail/needs. i was more raising the issue of accessing your fan for services/replacement. you should aim to achieve the same DB reduction as the box itself that houses the gear.
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22nd September 2011
Old 22nd September 2011
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If the construction is a "room in a room" design it´s important to avoid flank transmission path between the walls. Most flexible ducts are too much rigid and have a perforated sheet of steel inside.
in order to obtain as good Rw as possible I recommend using a soft flexible transition between the pipes (pls. see picture) and use a silencer on booth sides of the wall-construction. You can see how I´m building a construction like this here Paradise Studios Stockholm - construction

Enclosed is a sketch about how you can build a silencer. For the box I´m using 22 mm MDF with two layers of gypsum (carefully sealed with butyl rubber). The box has to be mounted directly to the walls with sealant. I use 50 mm acoustic-polyester absorbing material booth for the baffles but also on all surfaces inside the box. The material can easily be cleaned and need no protection cover (I use to have a lid on the top or side of the box that can be opened for inspection).
I hope this will help a little. / Bjorn
Attached Thumbnails
HVAC, Baffle Box/Silencer-hvac_decoupling.jpg   HVAC, Baffle Box/Silencer-dukstos_1.jpg   HVAC, Baffle Box/Silencer-dukstos_6.jpg  
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Lionzeye
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22nd September 2011
Old 22nd September 2011
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Quote:
I am currently doing the same; building 2 of these (see attached diagram)

Granny-Gremlin, I think this is a good design concept for our particular situation. The one part of the design I noticed and may not be a problem, but, it seems to create a three leaf system with the middle layer of drywall. I wonder if you left off that middle layer of drywall you might get the same isolation, and possibly even more if that peice was not there. Many tests have shown three leaf assemblies reduce STC value. If this box is lined with sound absorbing material, say, JM ductboard, then it should provide a decent sound lock and the middle layer of drywall is not needed. I am not a pro on this subject, so anyone please fill in here...

we will be using an 8" inline fan for CR and a massive 12" inline fan for LR. They are both high quality, low noise, centrifugal, and will be connected to a fan speed dial at the control room desk. That way we can have full control over fans to adjust power and speed on the fans. That way if the fans are too loud for recording session (we are designing proper sound isolation so we may not need to), we can turn them down or completely off. We will be able to exchange fresh air in our room very fast! In just under two minutes!
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22nd September 2011
Old 22nd September 2011
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What about fresh outside air, anyone? We plan on introducing one fresh air vent from outside into each room!
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22nd September 2011
Old 22nd September 2011
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Quote:
don't forget about an acoustic access panel so you can access the fan.
Thanks Gouge for the tune in!

Oh yeah, we have a nice sized room were fans will be (were handler is located as well), so in our case we might not enclose the fans in the duct box at all. Our fans performance will not be altered from duct run based on our design. As well, the fan speed dial will be an easy solution to noise if at all, I recommend using one. It's always nice to give urself more options to control your environment!

Quote:
you should aim to achieve the same DB reduction as the box itself that houses the gear.
Good point!

here is a GREAT DIY'er trick for silencing a fan to almost no noise at all. I have seen and heard the proof! Not theory.

Take your low noise centrifugal inline fan, and take a piece of r-13,19 insulation and wrap it around the perimeter edge of the fan. Duct tape the ends! Make sure you keep the inl/outlet clear of obstruction for ducting to be connected, and the electrical housing is secure (Very, Very important care must be taken here). Next step, cover the entire insulation which wraps the fan with duct tape until the insulation is gone and no fibers are exposed. That fan will barely be audible, especially if enclosed in a box, but it will be considerable larger due to the insulation!
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22nd September 2011
Old 22nd September 2011
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Quote:
If the construction is a "room in a room" design it´s important to avoid flank transmission path between the walls. Most flexible ducts are too much rigid and have a perforated sheet of steel inside.
in order to obtain as good Rw as possible I recommend using a soft flexible transition between the pipes (pls. see picture) and use a silencer on booth sides of the wall-construction. You can see how I´m building a construction like this here Paradise Studios Stockholm - construction

Enclosed is a sketch about how you can build a silencer. For the box I´m using 22 mm MDF with two layers of gypsum (carefully sealed with butyl rubber). The box has to be mounted directly to the walls with sealant. I use 50 mm acoustic-polyester absorbing material booth for the baffles but also on all surfaces inside the box. The material can easily be cleaned and need no protection cover (I use to have a lid on the top or side of the box that can be opened for inspection).
I hope this will help a little. / Bjorn
Thank You Bjorn for your input!

Is there a name for this type of connector?

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22nd September 2011
Old 22nd September 2011
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Quote:
Originally Posted by Lionzeye View Post
The one part of the design I noticed and may not be a problem, but, it seems to create a three leaf system with the middle layer of drywall. I wonder if you left off that middle layer of drywall you might get the same isolation, and possibly even more if that peice was not there. Many tests have shown three leaf assemblies reduce STC value. If this box is lined with sound absorbing material, say, JM ductboard, then it should provide a decent sound lock and the middle layer of drywall is not needed. I am not a pro on this subject, so anyone please fill in here...
I'm not exactly sure myself. Others here would know better than I.

Also, to be completely honest, in my build I am actually not all that concerned with isolation from the larger space my room is in. Initially we were planning to do proper room-within-room design with floating floor etc, but since the building is mostly deserted after 6pm (we all have day jobs) and we noticed that there are some loud-ass bands (at least one metal/numetal, one classic rock cover band and a few indie guys in another space) that seem to just be jamming in units with absolutely no soundproofing whatsoever (it took me a while to find their spaces because you can hear them clear accross the building, which is huge, a full city block, and 2 floors up), we decided to save the money (it would have easily tripled the cost of the build). I only built a room at all because :
a) I wanted a good sounding symetrical space that I can treat and tune (indeed, even though the space isn't finished yet, I think it sounds great, just obviously a little too live due to bare walls and being empty - the room gain and echo seems, from my vocal tests, to be pretty even across the spectrum so I'm pretty happy).
b) I needed to be able to lock the gear away as the rest of the unit has other uses during business hours
c) if it even takes the edge off the noise (which is does - according to my boom box test - I am so scientific) I will not have any problems with neighbors or building management because I'm not half as loud as the metal band (for example). It might even make it harder to figure out which unit my noise is coming from (the space is up against an exterior corner accross the unit from the entrance).

I do expect to run some lines out to the larger space because the echo in there is disgustingly good - just singing/humming/whistling to myself as we drywall sounds great. We might have some shows/parties occasionally as well, so it'll be handy. Also there's an old vault (vault door removed) that we're gonna try using as an echo chamber on an aux send. The plan for that is to get a small single ended tube monoblock (5ish watts) to drive 2 foster 4" fullrange drivers (forget the model name, but I have a bunch lying around, they're a proto F103 but alnico and much less power handling, like 3 watts - but that's all I need) and use something like an old Shure ribbon for pickup. Maybe an SDC if I can score a cap that'll work with my mv692 (I kinda want one of the nickel ones for the flavour).
#18
22nd September 2011
Old 22nd September 2011
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i don't see it as a problem re 3 leaf system,

having a 2 foot cavity will reduce the resonant frequency considerably.
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23rd September 2011
Old 23rd September 2011
  #19
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Granny-G,
Quote:
but since the building is mostly deserted after 6pm (we all have day jobs)
I share a similar situation, so i am not too concerned with noise leaving the studio and into the rest of the basement space which is the lounge, but more concerned with noise from lounge entering into the space on a precious recording.

Quote:
we decided to save the money (it would have easily tripled the cost of the build).
We are doing the same, and keeping the outside shell only 1 layer of 1/2". Our SPL tests showed we might not need two layers 5/8". I am so so so sick of drywall and mud and tape. So, is our wallet! So, I hope we are mostly done with drywall hang.

Quote:
I only built a room at all because :
a) I wanted a good sounding symetrical space that I can treat and tune (indeed, even though the space isn't finished yet, I think it sounds great, just obviously a little too live due to bare walls and being empty - the room gain and echo seems, from my vocal tests, to be pretty even across the spectrum so I'm pretty happy).
b) I needed to be able to lock the gear away as the rest of the unit has other uses during business hours
c) if it even takes the edge off the noise (which is does - according to my boom box test - I am so scientific) I will not have any problems with neighbors or building management because I'm not half as loud as the metal band (for example). It might even make it harder to figure out which unit my noise is coming from (the space is up against an exterior corner accross the unit from the entrance).
Funny, sounds like the same situation I was in. Fortunately we took over and no more bands for us! We might still rent our space, but we are focused more on recording.
gouge
Quote:
i don't see it as a problem re 3 leaf system,

having a 2 foot cavity will reduce the resonant frequency considerably.
I guess It really depends on your target STC and how important it is to accomplish it. This is my first build, so theories in acoustics such as the "three leaf isolation issues" for me, have only been confirmed by reading results of laboratory testing and not by experience.

Not sure if you are saying this is not a three leaf system, or just not going to be a problem even though it is???
#20
24th September 2011
Old 24th September 2011
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hi lionzeye,

yep it's a 3 leaf system but no i don't beleive it to be an issue because you have a 2 foot cavity and 2 layers of lining.

if you have found once built it was a problem then i would suspect that the issue can be found with either the length of the duct being too short or the lack of insulation within the cavity or it's not sealed somewhere.

i'd be keen to see your test data of 3 leaf walls with deep cavities. have been looking for that ype of test but can't find anything.

i've got equations for calculating resonant feq of walls when masonry is part of the makeup and a spreadsheet for when resonator panels are used (creating a 3 leaf system) but nothing specific to 3 leaf systems like above.
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#21
29th September 2011
Old 29th September 2011
  #21
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Quote:
yep it's a 3 leaf system but no i don't beleive it to be an issue because you have a 2 foot cavity and 2 layers of lining.

if you have found once built it was a problem then i would suspect that the issue can be found with either the length of the duct being too short or the lack of insulation within the cavity or it's not sealed somewhere.

i'd be keen to see your test data of 3 leaf walls with deep cavities. have been looking for that ype of test but can't find anything.

i've got equations for calculating resonant feq of walls when masonry is part of the makeup and a spreadsheet for when resonator panels are used (creating a 3 leaf system) but nothing specific to 3 leaf systems like above.
I have no test data on this particular situation. For practical purposes, this should be o.k.
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