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PostPosted: Sun May 13, 2018 7:03 am 
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Gregwor wrote:
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1) Are these dimensions for the control room reasonable or is there a room l x w that would be more favorable design? I'd like to keep existing drop ceiling of 94" in control room

I unfortunately don't have time to type in the dimensions and look into different possibilities. You know the rules for dimensions, so I think you've got it under control. I can't see anything wrong with the dimensions with a quick look.

Ok thanks.

Quote:
2) I have the vocal booth drawn out as a 6 x 10 booth (1 " between front and rear framing = 6" air gap between drywall) Should I extend the length longer than 10 feet?

Extending the 10' closer to 12' will make it a multiple of the 6' so that would be bad.

One of the things I'm wondering is, for the booth, is it better to go with specific dimensions that fall within the bolt area, or go with a larger room which falls outside of the bolt area? Is it better to focus on a good ratio, or larger room for the vocal booth?

Quote:
The vocal booth will not be inside out as previously mentioned, but instead will be standard MAM design with 2 drywall layers with gg in b/w

There is no reason you shouldn't at least build the ceiling inside out. You really would be crazy not to.

I will look into this some more. Do you know of any good references here or elsewhere on how to construct the ceiling? Im haveing a hard time conceptualizing how to actually build and lift into place. I've heard that building it in modules is best, just wondering if there are any sketchup examples somewhere or other diagram I can look at to better visualize. Also, can I make the ceiling out of 2x4s or structurally do I need to use larger studs to attach double drywall with 5/8 gg between?

Quote:
I am also thinking about just installing a solid core door (no window to booth), and using video and monitor to see artist in vocal booth instead.

You mean two solid core doors, right?

Yes I mean two solid core doors

Quote:
3) there is about a 15" soffit in the front of the room. I was thinking about removing the interior drywall and using that area to put the bass trap hangers. If the space in between is less than 15" can i still use smaller hangers to achieve similar effect with taming the low end?

Deeper is always better, but around here, most of us just work with what we have. So if 15" is all you have, then cool. But if you an spare more, cool. Remember, bigger hangers = more material = more expensive. Hangers are far from cheap to make correctly.

rough estimate, what kind of cost we are talking to build diy hangers for that back soffit area? Rough estimate. Also, is there another option (cheaper) for bass absorption in the back wall other than the hangers?

Quote:
4) If I remove the drywall as mentioned in step 3, would my new length extend to the drywall on the other side of the soffit (basically include the soffit area as part of the length of the control room?)

Yes. The acoustic size of your room is measured from the hard surfaces. So basically your inner leaf.

Thanks
Greg


I've attached a couple drawings of a new plan where I will be adding a window and door on each wall so that i can see inside the booth. I think Id rather spend the money here to get the look and feel of recording in the booth. Not sure if I am going to go with a 4' x 5' window, or a 3' x 4' window (h x l). Cost will probably determine this.

For my wall thickness on the control room side I will have a single layer of 5/8" drywall. On the vocal booth side, I will have 2 layers of 5/8" drywall with gg between. Therefore, what size glass should I use on each side? Should I be doing 1/2" and 3/4" or something less because of the single wall? I don't want to overbuild the window.

I was thinking of making the booth dimensions 6 x 7.8 x 11.4 (w x h x l) or 5.75 x 8 x 12.5 (w x h x l) depending on how high I can get the ceiling after i frame it out and see where I am. As mentioned above, Do you think it would be wiser to make the booth more spacious even if the ratio isn't ideal, or focus on an ideal ratio?


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PostPosted: Tue May 15, 2018 9:50 am 
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That's looking much better. But I'm wondering about that wasted space on the left side of the booth: What's that for? Storage? If so, how do you get to it? There's no door...

Quote:
I will be adding a window and door on each wall so that i can see inside the booth. I think Id rather spend the money here to get the look and feel of recording in the booth.
:thu: Definitely! Good move.

That said, the door between the CR and booth is in a complicated place, right where your speaker needs to be. I'd suggest replacing that window between CR and booth for a door with glass in it. The door could be nice and large, with a decent sized window. It could even be a sliding glass door (or rather, two such doors, back to back).

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Should I be doing 1/2" and 3/4" or something less because of the single wall? I don't want to overbuild the window.
For one layer of 5/8" drywall, 1/2" glass is fine. And for 2 layers of 5/8", 3/4" glass is also fine. More than fine, in fact. The general rule is that the glass should be about 33% of the thickness of the drywall, or a bit more. This is because the density of glass is about three times the density of drywall.

Quote:
Do you think it would be wiser to make the booth more spacious even if the ratio isn't ideal, or focus on an ideal ratio?
In general, make it as big as you can. It's not a control room, so ratios are not that important. Room volume and ceiling height are the two key points. Try to get your ceiling as high as possible, and good volume as well. If you don't need that storage space off to the side, then expand the booth into there. If that would get you a very bad ratio, then use some of that space for treatment, to compensate.

You also need to start getting your CR interior in better shape: get the speakers off the desks onto stands behind the desk, and slide the desk more into the room, to get the mix position more correct. Etc.


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PostPosted: Tue May 15, 2018 3:22 pm 
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Soundman2020 wrote:
That's looking much better. But I'm wondering about that wasted space on the left side of the booth: What's that for? Storage? If so, how do you get to it? There's no door...
I am going to use some of that space for the ventilation baffle boxes, but I will probably extend the booth out further also

Quote:
I will be adding a window and door on each wall so that i can see inside the booth. I think Id rather spend the money here to get the look and feel of recording in the booth.
:thu: Definitely! Good move.

That said, the door between the CR and booth is in a complicated place, right where your speaker needs to be. I'd suggest replacing that window between CR and booth for a door with glass in it. The door could be nice and large, with a decent sized window. It could even be a sliding glass door (or rather, two such doors, back to back).
Yeah Originally I was planning on sliding glass doors, but then I got sticker shock! Do you know of any decent places for acquiring doors that would serve my needs with the wall build I have going? Any DIY options?

Quote:
Should I be doing 1/2" and 3/4" or something less because of the single wall? I don't want to overbuild the window.
For one layer of 5/8" drywall, 1/2" glass is fine. And for 2 layers of 5/8", 3/4" glass is also fine. More than fine, in fact. The general rule is that the glass should be about 33% of the thickness of the drywall, or a bit more. This is because the density of glass is about three times the density of drywall.

Awesome, Thanks

Quote:
Do you think it would be wiser to make the booth more spacious even if the ratio isn't ideal, or focus on an ideal ratio?
In general, make it as big as you can. It's not a control room, so ratios are not that important. Room volume and ceiling height are the two key points. Try to get your ceiling as high as possible, and good volume as well. If you don't need that storage space off to the side, then expand the booth into there. If that would get you a very bad ratio, then use some of that space for treatment, to compensate.

You also need to start getting your CR interior in better shape: get the speakers off the desks onto stands behind the desk, and slide the desk more into the room, to get the mix position more correct. Etc.

Thanks, I'll focus on space then, and Yes, you are correct, I kind of just threw stuff in the room for visual, I will work out the placement once I finalize the room dimensions
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PostPosted: Tue May 15, 2018 6:07 pm 
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Another reason to not have your booth door there would be that it will interfere with your bass trap placement. Personally, my ISO room design has the door right in the corner too. The difference between our designs is that you have the ability to change where your door is. Jealous.

Glass is wicked expensive. Remember to price out laminated glass. And to answer your question about how much hangers would cost to build, call around and find out how much sheets of Homasote cost in your area. Then figure out roughly how many you'd need. Then figure out how much insulation will cost to wrap the Homasote. It's expensive where I live.

Regarding the space beside your booth: As you described earlier, you don't have the room necessary to situate silencer boxes in your ceiling. So having them on the sides of your room is a great place for them. As you've been instructed, having your room as large as possible is ideal. Having said that, try to design your boxes so that they are thin pancake style. That will utilize the space the best. Lastly, when I drew up that ghetto version a while back for you, I had a space on each side of your room. One for supply air, and the other for return air. Having your air draw across your room is ideal. You haven't post any pictures of your room or indicated where the existing HVAC trunks are. This is a major detail to nail down right now.

Greg

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PostPosted: Wed May 16, 2018 12:15 pm 
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Gregwor wrote:
Another reason to not have your booth door there would be that it will interfere with your bass trap placement. Personally, my ISO room design has the door right in the corner too. The difference between our designs is that you have the ability to change where your door is. Jealous.

Yes, but I would have to sacrifice window size if I move the door further toward the middle. Unless i bought a glass door, or sliding glass door $$$

Glass is wicked expensive. Remember to price out laminated glass. And to answer your question about how much hangers would cost to build, call around and find out how much sheets of Homasote cost in your area. Then figure out roughly how many you'd need. Then figure out how much insulation will cost to wrap the Homasote. It's expensive where I live.

Yes I have some quotes out for laminated glass now, curious to see what the difference in price will be between building 2 windows and doors versus buying glass doors and skipping windows. I'll start looking into the Homasote cost. Thanks for the tip.

Regarding the space beside your booth: As you described earlier, you don't have the room necessary to situate silencer boxes in your ceiling. So having them on the sides of your room is a great place for them. As you've been instructed, having your room as large as possible is ideal. Having said that, try to design your boxes so that they are thin pancake style. That will utilize the space the best. Lastly, when I drew up that ghetto version a while back for you, I had a space on each side of your room. One for supply air, and the other for return air. Having your air draw across your room is ideal. You haven't post any pictures of your room or indicated where the existing HVAC trunks are. This is a major detail to nail down right now.

Good Point, I will try to modify the design so that I get some cross circulation. I dont have any existing HVAC, there is a split AC wall unit on the right hand side of the control room. I was thingking about creating duct from control room into vocal booth. And then ducting from vocal booth out through ceiling of outer leaf.

Greg


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PostPosted: Wed May 16, 2018 4:27 pm 
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Quick question...

Would this fan be suitable for ventilation? I'll be building baffle boxes for each leaf also.

https://www.homedepot.com/p/Inductor-6- ... /100067594

Supposedly rated at 52db or 2.4 sones.


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PostPosted: Thu May 17, 2018 6:09 pm 
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Hey I am looking for some feedback on my ventilation/baffle box plans. I currently plan on creating 2 boxes to use for ventilating the vocal booth only.

I have a split A/C in the control room which will be used to cool the control room. Keep in mind this room is not airtight as I am not concerned with noise entering/leaving the control room. So my plan is to pump air from control room into booth, and have air from booth exit out of ceiling or side wall.

I started working on a baffle box design and here is what I came up with.

Please correct me if I am wrong on my calculations or if I can make the box smaller to save space/cost.

Assumptions (based on what I've read):
1) 6 air changes per hour
2) Air velocity should be 300 fpm or lower
3) Use larger duct/register for supply (at least double surface area of supply duct)

Calculations:

volume of room (vocal booth 6 x 8 x 12.5 [ I will probably extend this further if space permits to 13 ft or more) ~ 600 cubic feet

CFM = (6 air changes per hour * 600 cubic feet)/ 60 min = 60 CFM

Cross section area = 60 CFM / 300 feet per minute = 0.2 square feet

0.2 sq ft x 144 = 28.8 square inches

From online charts > a 6" round duct will supply ~ 100 CFM

cross sectional area of duct = PI(r)^2 = PI(3)^2 = 28.27 square inches

Inside of the box needs to be double that = at least 56.55 square inches

Therefore a register grille of 6" x 10" can be used (60 square inches)

Based on these calculations I have determined that I should use a 6" supply duct, and a 6 x 10 grille for my baffle boxes.

I plan on using 3/4" MDF to build the box. 2" owens corning 703 or alternative material (studio foam?) for the insulation, and I have attached plans for the baffle box design. I wasn't sure if the dimensions of the baffles were critical and how much space to leave between the baffle and wall for air to travel.

Also, does it matter which face of my baffle box that I place the grill? Can i place it on whichever side of the box is convenient for my build or does the location of the inlet and outlet of the box matter?

Please review and suggest modifications as seen necessary.

If i could make it smaller/cheaper than what I came up with and still avoid air movement making noise that would hinder my vocal recordings then that would be a plus!

Thank you!


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PostPosted: Fri May 18, 2018 1:52 am 
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As luck would have it, just a few minutes ago, I wrote up an explanation that covers most of your questions, in a response on another thread. So here's the link to that:

viewtopic.php?f=2&t=21546&start=45

Hopefully that covers it! :)

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PostPosted: Fri May 18, 2018 6:06 am 
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Quote:
I plan on using 3/4" MDF to build the box. 2" owens corning 703 or alternative material (studio foam?) for the insulation

You need to have your silencer boxes maintain the surface density as your walls. Two layers of heavy 5/8" drywall is around the same surface density as 1" MDF.
Also, 703 is not good to use as duct liner as it is not designed for this task. You should use real duct liner as it won't release particles into the air.

Greg

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PostPosted: Fri May 18, 2018 7:35 am 
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Quote:
703 is not good to use as duct liner as it is not designed for this task. You should use real duct liner as it won't release particles into the air.
:thu: Plus, it won't erode over time, reducing the isolation. (Sort of related ...)


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PostPosted: Fri May 18, 2018 12:33 pm 
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Gregwor wrote:
Quote:
I plan on using 3/4" MDF to build the box. 2" owens corning 703 or alternative material (studio foam?) for the insulation

You need to have your silencer boxes maintain the surface density as your walls. Two layers of heavy 5/8" drywall is around the same surface density as 1" MDF.
Also, 703 is not good to use as duct liner as it is not designed for this task. You should use real duct liner as it won't release particles into the air.

Greg

Thanks for the info, I will see if I can find 1"MDF, otherwise I will do 2 layers of 1/2" or 5/8" instead. Also will look into swappint the 703 with duct liner as suggested. Thanks for the info. What about the baffle design? Do I need to maintain the surface area through out the baffle or do i need to reduce and expand at points other than the entrance and exit? Does it matter which face of the baffle box I place the exit register/grille?


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PostPosted: Fri May 18, 2018 4:46 pm 
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Soundman2020 wrote:
As luck would have it, just a few minutes ago, I wrote up an explanation that covers most of your questions, in a response on another thread. So here's the link to that:

http://www.johnlsayers.com/phpBB2/viewt ... 6&start=45

Hopefully that covers it! :)

- Stuart -


This was very informative and helpful. Thanks!


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PostPosted: Sat May 19, 2018 4:23 am 
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Quote:
What about the baffle design? Do I need to maintain the surface area through out the baffle or do i need to reduce and expand at points other than the entrance and exit? Does it matter which face of the baffle box I place the exit register/grille?

Until yesterday, I've always been under the impression that as soon as your inlet duct hits your silencer box, your cross sectional area must double. In a lot of my calculations, the cross sectional area required to achieve <300 ft/min air velocity ends up being less than double the inlet cross sectional area.
So, yesterday, Stuart brought it to my attention (unless I didn't comprehend what he wrote) that your silencer box does not need an internal size that is double that of the inlet duct. As long as there is an impedance mismatch (duct size increase or decrease) somewhere along the path that happens at least a distance that equals 3 times the shortest dimension of your path. Ex: a 6" RD duct would require an impedance mismatch at least 18" from the duct register.
Regardless, introducing the impedance mismatch would yield a pretty bizarre design. What I'm implying here is that to have the outlet on your silencer box all of a sudden be large, that tail end of the box would have to be big. Maybe I'm wrong here. I'm going to have to SketchUp a design like this to see how it would work. But if I'm understanding Stuart correctly, this could mean much smaller silencer boxes than I've initially designed!

Greg

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PostPosted: Sat May 19, 2018 6:03 am 
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Quote:
Stuart brought it to my attention (unless I didn't comprehend what he wrote) that your silencer box does not need an internal size that is double that of the inlet duct.
Maybe I didn't explain that part too well: The cross section does, indeed, need to change drastically, to at least double (or half), at both ends of the silencer box (or at least one of them). I thought what I wrote was clear: " ... the silencer box. Once again, there's a general rule here, that the cross-sectional area must change suddenly by a factor of at least two, where the air enters the box and where it exists the box.", but I guess it could be misunderstood.

The change can be more than half/double, if you want: for example, I sometimes do silencers where the air path splits in two immediately where the duct enters, or shortly after, and each of those paths is about twice the area of the duct, so I'm getting a four-fold change.

The reason this works is simple: Wherever there is a large change in impedance, sound will be reflected back from that discontinuity almost as though it were a mirror, and since the phase is also flipped, the sound partially cancels itself out as it travels back the way it came. Of course, this is impedance, so the effect varies with frequency. But with a large, sudden change you can get pretty good effects down at low frequencies. However, the change has to be sudden. It's no use to have a long, slow change in area, such as with a funnel-shaped duct or sleeve: that would create a waveguide, which MATCHES the impedance.. Like what happens in a speaker, with the tweeter: long, slow smooth transition, to match the impedances. That's not what you want for a silencer: the change should be as abrupt as possible.

Quote:
As long as there is an impedance mismatch (duct size increase or decrease) somewhere along the path that happens at least a distance that equals 3 times the shortest dimension of your path. Ex: a 6" RD duct would require an impedance mismatch at least 18" from the duct register.
I think you misunderstood that part completely. I was talking about turbulent flow and laminar flow, not impedance mismatches there. In other words, after the last "thing" in the duct that creates a lot of turbulence (such as a corner, for example), you need at least three times the shortest dimension of the duct for that turbulent flow to smooth over again and become more laminar. You do not want turbulent flow hitting a register, as that would create a LOT of air noise.

Quote:
Regardless, introducing the impedance mismatch would yield a pretty bizarre design.
Without impedance mismatch, your insertion loss is going to suffer greatly: you won't get good attenuation down at low frequencies. Think of a motorbike exhaust, where some clever "mechanic" has modified the muffler by destroying parts of the internal structure: that kills the impedance mismatch, there is no longer any phase cancellation going on, and the sound coming out the end of the exhaust is much louder, especially at the piston and valve frequencies. The same would happen in your HVAC silencer boxes if there were no impedance mismatch. The design is not bizarre; it is simple. Just have a much larger cavity immediately following the point where the duct comes in.

Quote:
that tail end of the box would have to be big.
Well, at SOME point following the end of the silencer box, the duct MUST expand to be the same as the area of the register! If not, then you'll get serious air noise issues at the register. The basic concept is that the airflow arriving at the register should be laminar. It can't be laminar unless you have a long, straight section of the same size as the register, just before it. You cannot go direct from a round duct into a rectangular register, without generating a lot of turbulence, and hence a lot of noise.

I'm going to do something I almost never do, but there's so much confusion here that it's probably the best: I'm going to share one of my proprietary designs for an HVAC silencer, and ask that people DO NOT copy it. If somebody wants a version customized for their own room, PM me and we can talk fees for doing that, since all rooms are different. Of course, unscrupulous, dishonest people WILL copy it anyway, but whatever... I'll risk it, and hope that there are still some honest people around...

So here's what I'm talking about:

Attachment:
SOUNDMAN2020--HVAC-split-flow-silencer--top.jpg


That's the view from above of a silencer for the supply into a control room. This box sites in the ceiling cavity, between the inner leaf and outer leaf. There's an 8" round duct coming in (cross sectional area: 50 in2), and that expands immediately, since it goes from round section to square section. But then the flow splits two ways, each of which has a much larger cross section. There's three baffles down each "leg" of the silencer, then the airflow takes a dive down through a long sleeve that penetrates the inner-leaf ceiling, and terminates at the registers. Bottom view:

Attachment:
SOUNDMAN2020--HVAC-split-flow-silencer--bot.jpg


There you can see the sleeves and the registers. Each register is 10" x 12", so 120 in2 nominally each, but more like about 100 in2 actual open area each, or 200 in2 total. So I have 50 in2 coming in, and 200 in2 going out. The velocity drops by a factor of four, the flow is laminar at the registers (long sleeve), and there are several impedance mismatches along the way (but I'm not going to say WHERE those are, as that's part of the mystery of the design... :) I chose my view angles carefully, so as to not reveal too much...). And yes, the static pressure penalty is high from such a design, but not as high as you'd think, because the paths are in parallel.

I don't see anything "bizarre" about this. It works, very well, actually.


- Stuart -


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PostPosted: Sat May 19, 2018 8:46 am 
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Awesome. Thanks for sharing Stuart.

When I said bizarre, I referring to how strange the box design would have to be if it maintained a small 50 square inch interior dimension then at the outlet have to get super big (100+). Confirming that the size must at least double at entry voids that point entirely and I'm back to thinking about silencers as I did before. I think the confusion came between double the cross sectional area and the size it would need to be to achieve the proper air velocity. I suppose we should all be choosing whichever is larger.

And thanks for clarifying that the 3x the smallest dimension distance must happen after any turn, not just the impedance mismatch!

Cheers!

Greg

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