Prepping the basement for drywall

  • Thread starter Thread starter Velvet Elvis
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Rod? Any comments?

I would have to assume that even WITH a second AC system, this is the same problem every studio deals with for TL and flanking between its own rooms (unless you do a separate system for each room)... so this can't be new ground.

Thanks in advance for any helpful hints.

Jim

EDIT: One other thing I'd add... the feeds are shared to the main trunk, but the returns go all the way back to the furnace (about 100 feet). Given that the feeds (when the AC is running) have positive pressure, wouldn't that help the flanking as well? I would assume the pressure of the LF would look for an easy path, which would be back down the air returns (which are pulling negative pressure already). Maybe I'm wrong, but I thought I'd throw that out there.
 
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Given that the feeds (when the AC is running) have positive pressure, wouldn't that help the flanking as well? I would assume the pressure of the LF would look for an easy path, which would be back down the air returns (which are pulling negative pressure already). Maybe I'm wrong, but I thought I'd throw that out there.
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All I can respond with is what Alton Everest says...
The principle of superpositionstates that every infinitesimal volume of the medium(air)is capable of transmitting many discrete distubances in many different directions, all simultaneously and with no detrimental effect of any one on the others.
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From The Masterhandbook of Acoustics, First Edition, page 67. Whether or not pressure in the duct, moving air still can transmit disturbances as "sound" travels faster than the air. However, my disclaimer is STILL in force here Jim:D
fitZ
 
Well, you with your disclaimer is still way far and above me and my knowledge :)

I have a couple of friends who built rooms with similar issues as mine and they both said "works well enough..." etc. So I'm thinking I'm going to continue with the RC and stuff - mainly to cut down on noise transmitting DOWN into the studio (which won't be a 100db kick drum).

My family can deal with a little kick drum bleed throughout the house ;)

What I'm still hoping Rod can tell me is the "best case" for what I should do with my existing HVAC. I'll do that and hope for the best.

Rod?

Jim
 
One last desperate plea for "as good as it can get"

Ok... here's what I think I'm going to do:

Change the upstairs duct runs to R8 flex... just to decouple the metal of the boot from the metal of the main trunk.

I'll caulk with acoustic caulk all around the upstairs boots.

The studio and theater runs will be decoupled from the main trunk with a short run of R8 flex, but then will enter into 5 feet of 8 inch conduit (coming off of a 6 inch). The 8 inch conduit will be lined with Johns-Manville 1 inch acoustic liner. Then transition back to 6 inch metal for the boot. This will hopefully act like a muffler type situation for HF noise and will at least decouple a little for LF noise (yes, I understand that changes in air pressure due to kick drums etcstill creates LF noise).

Does this sound like a reasonable effort? Does it sound like a total waste?

My biggest questions (if this seems ok) are "how do you seal the boot?" IE - is it best to make a custom boot out of OSB or something, because it seems like the flimsy metal ones all by themselves would ruin a walls ability to isolate sound. The other question is how to handle returns IE - I can use flex and give it a few bends, but should it just terminate at a regular AC boot (and again - how would you isolate the boot).

Thanks for any help... as my wife said on the phone recently "I know you are concerned about things being a waste, but it HAS to be better than what you've got now!" (which is a setup in a loft on the second floor of my house).

Thanks again.

Jim
 
Jim,

basically anything you do is an improvement - decoupling will help a lot.

It is so difficult from here to make any sound (no pun intended) descision - because there are so many other things that come into play (flanking that has nothing to do with HVAC for example)

The fact that your buddy did something and it was good enough for him is encouraging as long as your expectations are realistic.

For the record - in new studios - yes - the control room gets it's own system - and we work out the remainder of the rooms with a seperate system (sometimes multiple systems there as well).

Sincerely,

Rod
 
Rod,

Thanks... I'm doing my best to address other flanking issues. Caulk, caulk, caulk and more caulk :) (OSI acoustic sealant)

Did you have any suggestions for dealing with the actual HVAC boots? (the part that penetrates the wall).

Thanks, kind sir. You are a gentleman and a scholar!

Jim
 
There isn't much you can do outside of making custom boots and lining them with duct liner along with the rest of the supply/return system.

That's about as god as it gets.

The most important thing with air is making sure that you have maximum volume at minimum velocity.

So ou can move a lot of air fast - but before entering the room you want duct sizes to increase so that that air is now moving slowly -

the same air volume - but slow moving.

If you can accomplish that - along with some baffles to stop the passage of fan and air noise - ten you did pretty good.

I'll try to post a typical baffle detail tomorrow.

Rod

Rod
 
Rod,

Fantastic. I truly appreciate it.

I can indeed step up the duct size - It starts as a 6 inch, my "mufflers" are being made from an 8 inch right near the end of the runs. I then plan on using oversized registers to keep the air velocity down while keeping volume up.

Just for added security, a friend who does commercial HVAC hooked me up with some electronic damper valves that seal via a rubber valve. That allows me to turn all the feeds off into the studio rooms. Consequently, he also gave me an HVAC computer which will monitor the temperatures at the air returns and modulate the dampers accordingly. The dampers will be set behind my mufflers to control air flow noise.. and the motors themselves are whisper quiet (seriously). I can't even hear them move.

I *really* appreciate the help. Truly. From both you and Rick.

If it seems like I'm pushy and in a hurry, let me explain my situation a little. I live in Cedar Rapids, IA - the area that was recently destroyed by flooding. Building repair has been on hold for the affected areas, but now they are starting to open the proverbial flood gates. Contractors and supplies are both becoming scarce and expensive.

So, "wait until the rush is over" you might say... well... now the two added twists. The city told me I have until October to clear my permit. AND my wife and I recently found out we are expecting our ***5th*** child this winter.

The bottom line - the studio is part of the same permit deadline that we pulled for the downstairs bedrooms. We need the bedrooms desperately before winter, contractors and supplies are scarce because of the flood and therefore, I have to beat the rush a little and just get this completed.

Thanks again for the help.
Jim
 
Velvet Elvis said:
Rod,

Any luck finding the baffle detail to post for me?

Thanks, man!

Jim
Click to expand...

Jim,

This should give you the idea for a whole system - as well as the baffle......... in this case the baffle was only required for the iso chamber......... the HVAC and duct mains were above the trusses over the room until the point where they could drop down into the tracking room itself - maintaining isolation from the control room.

I hope this helps

Rod
 

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Rod,

That does indeed help.

Would you put those on all the feeds and all the returns?

I'm thinking in the theater area of just using 4 feet of 8 inch round pipe lined with 1 inch Johns Manville acoustic liner. That would be fed by about 10 feet of flex duct coming off the main trunk, complete with at least one 180 degree turn in the flex. Do you think that would work, too?

For the studio rooms, I think I will build boxes as you suggest.

Thanks a ton for your help!

Jim
 
Rod,

Ok... thanks.

Do the boxes go on returns AND feeds? I assume "yes".

Jim
 

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Looks nice, Rick. Always interesting to see my studio in 3D :)

One thing to keep in mind, I have limited ceiling height. The room you have the one baffle in right now has about an 8 foot ceiling, but the room below it (the smaller room) has a shorter ceiling. The good news is, in that room the baffle can be tucked up into the ceiling because there is clearance between the i-beams and the lowered ceiling.

It was lowered to get around some plumbing and HVAC ducting.

My father-in-law is dropping off his extra supply of 3/4 OSB and plywood today so I can start building baffles!

Jim
 
Always interesting to see my studio in 3D
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Hmmm, isn't being IN IT 3d?:D(just kidding)

One thing to keep in mind, I have limited ceiling height. The room you have the one baffle in right now has about an 8 foot ceiling
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Thats the difficult thing about trying to extrapolate info from plans and pics. Theres NEVER enough info.:o However, in the drawing(which isn't finished) I was actually going to extend the baffel to appear as another SOFFIT, with BOTH supply and return baffles within. This way, you could simply RC over framing around them. Anyway, its an idea. But I didn't know ceiling heights.
fitZ
 
Rick,

Yeah... you can never have too much info, which is why I've asked so many questions here. :)

I'm starting to feel somewhat comfortable with how it will hopefully turn out.

Any idea when you might be done with your drawing? The only reason I ask is that I'm quickly approaching the point of needing to do the HVAC work before anything else can continue.

Thanks again for the work!!

Jim
 
Any idea when you might be done with your drawing? The only reason I ask is that I'm quickly approaching the point of needing to do the HVAC work before anything else can continue.
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Well, if you are going to USE my design, then I'll finish it asap. Otherwise, it was just an exercise to learn more of Sketchups potential and illustrate a possible solution. But yea, if you want me to detail these, no problem...except for the custom "boots".
ie...at the register/grills to the box and duct to box connections. I don't know if the flex duct actually needs a "decoupler", but since the grills will be integral to the drywall TL envelope, they need to be decoupled. The box itself MAY need "decooupling" as well, so structual transmission from sound entering and resonating won't occur. Maybe Rod can chime in on this.
fitZ
 
Rick,

Yes, I'd be interested in your soffit design for the one room you were working on especially.

I hadn't thought of building it into the framing and then drywalling around it. But that is EXACTLY what I think I will try to do for that room. Well done.

I don't think the flex needs decoupling, as it acts as the decouple itself. I was planning on doing something (leaving a 1/4 inch gap around the vent area, filling it with backer rod and then acoustic caulk, and then using some sort of gasket for the vent itself.

My guess is that the baffle should be decoupled, but its probably not possible or practical, considering it has to be attached to something and I don't have floating walls.

If you saw my post a few back, I'm going to use my muffler idea for the theater, because a) its something and b) there are other flanking issues in that room that can't be easily addressed. So its going to be more of a "do what I can" scenario.

The studio area however, will have all feeds and returns running through baffles and connected via flex. Basically to do the best I can with my single HVAC unit.

Thanks again!
Jim
 
Hello Jim. Well, I've been working on this but I came across something I thought Rod might comment on, since he is an engineer. Being a Physics/Mathamatics dunce, I can't extropolate the info to bear on the baffle problem. I know there MUST be a principle here that might be applied, but I can't understand it.:rolleyes::o Maybe Rod can chime in whether or not this stuff can be applied.
http://www.jstage.jst.go.jp/article/jpa/23/6/231/_pdf
In the meantime, I'm still working out the details of actually building and installing this thing. Bear with me a little longer. NOT an easy project.:rolleyes::D
fitZ
 
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