Ohio Basement Studio

Stuart I probably could have worded that better (insulate the metal ductwork). I have seen pictures in the past where existing metal duct work in the basement ceiling was wrapped with some kind of insulation. I believe the purpose is to minimize vibration and transfer of sound through the duct work feeding the rest of the house. However, my searches have not yielded any helpful results. I have the typical square ductwork in the basement ceiling feeding the upper floors for send and return and 6 inch round metal duct work to some of the rooms. I do Not plan on replacing that duct work with something more sound proof. So I was interested in finding out what process is used to minimize sound transfer to the rest of the house via the existing duct. The new duct work will be as you mentioned (insulated on the inside). As far as the Kerfs go. There are already several cuts in the basement. They are there so that as things shift over time, the cracks in the basement concrete will tend to break at those kerf cuts. It has worked, because I can see the crack along the existing kerfs. Which has caused clean separation. There is no additional support in those areas either. We had the house built and I saw how the slabs were poured. I would be doing the same thing. I am not raising the floor, so I was planning on this approach. This was not something I discussed with the Structural engineer. Just something I have seen done in other studios. I have done simple sound transference tests with a hammer and there is a difference where kerfs are located. I would rather not add kerf cuts if the payback is minimal, so I am open to discussion on that matter. Thanks Joe

Stuart Attached is a photo of some of the existing duct work I am referring to. The steel post on the right looks crooked. I must have something set wrong on my camera, because that post is perfectly level. Anyway, this gives you a better idea of the existing duct work. Thanks Joe

Technically, those ducts are part of your outer leaf: So probably your best bet is to just soffit around them with plywood or OSB, carefully sealed to the joists and sub-floor above, and with insulation inside to damp resonance, then just build your inner-leaf ceiling below that, keeping it fully decoupled. - Stuart -

Stuart Thank you for the response. I'm weighing the cost of time and money verse just how much isolation I want to the floor above. I currently do not plan on placing drywall on the subfloor above. Maybe I will just leave the Duct as is. If I do decide to isolate, your idea sounds like a logical approach. Joe

Maybe I will just leave the Duct as is.

Probably not really an option. Think of it this way: that is just thin sheet metal, undamped, formed into the shape of a resonant chamber, and interconnected with several rooms around the house. If sound gets into that (and it will), then it has a free path to go any place in the house, loudly. So you probably do need to do something about those ducts! If not, then you'll have practically no isolation at all. - Stuart -

Well it finally happened! After several years working on things that do not directly relate to the recording rooms like building the break room, the bathroom, resolving water issues, I finally had my first day of construction on the Recording Studio. We started on the Phase 1 portion of the studio. We are beefing up the floor above the basement ceiling. I am following the approach Rod mentions in his book using two layers of 5/8 drywall under the floor . Since I have wooden engineered Ibeams instead of the standard floor joists I had to make special braces to hold the drywall in place. They are made out of 1 inch thick poplar. I was not sure how far apart they should be and did not see any mention of the spacing of the supports in Rod's book. I am looking for some guidance here. Could someone comment on how far apart they spaced their supports? Are things holding up well? The attached photos show some of the detail of the supports I created. In several of the bays there is 6 inch round metal duct going to floor vents in the floor above. I think I will be replacing that duct with sound isolated flexible duct to minimize sound transfer. Since the distance from the basement floor to the floor above is 10ft, I quickly grew tired of climbing up and down the ladder while caulking. I made a scaffolding with rear wheels so that I could move it around. It was worth it. I have 20 more bays to do.

I'm curious if anyone has built a basement studio where the first floor joists are Engineered Composite Wood I-beams? As I mentioned previously, I am beefing up that area above where my control room and ISO rooms will be. The ceilings will be completely isolated from the floor joists above. I'm placing two layers of drywall between the I-Beam floor joists and supporting the drywall with wooden blocks made out of Poplar. I have attached a drawing. Rod's book shows the typical floor joists you might find in a house (Not the I-Beams that I have). These Composite I-Beams are very strong and are 12 inches tall. My question is: Do I need to provide X-bracing support to these I-Beams after placing drywall between them? I am wondering if they need it due to their construction. Anyone have experience with this? Thanks Joe

Well it's been exactly three months since starting the build. I did not realize I would spend so much time with the Phase 1 isolation of the Ceiling (floor above). I had 22 bays to attach two layers of 5/8 drywall to, and then cap off the ends to minimize flanking. This involved removing all of the duct work on that side of the basement. Quite a chore! I did not cap off all ends yet because I still need to address the HVAC portion of this project and need to run the new ducting. I ended up using about 40 28oz tubes of acoustic calk and 2,100 ft of backer rod. I was not expecting to use that much material just to minimize sound transfer to the floor above. The Ceiling of the two rooms in phase 1 will not have any connection to the floor above. My plan was to have this portion of the studio have the most isolation. The phase 2 side will use RC clips and will not have the same level of isolation to the rest of the house. The thought process behind that (beside saving money) is that the Control room and large ISO booth can be used any time of day or night. Usage of the large live room (phase 2) will be limited to non-sleep time hours. I have attached some pictures of the completed bays and endcaps. I would not say it was difficult, but was extremely time consuming, especially when working by myself. There was also a lot of fabrication involved in making the poplar drywall supports. I think I made about 300 of them. It feels good to be done with this phase. It's now time to start planning out the HVAC portion of the project. I am meeting with an HVAC installer this week to discuss some options. The last time I had a company out they suggested using the existing HVAC system and just adding another air handler. I'll know more after our meeting. I'm going to surf the site to see what other basement studios have done. I don't have a huge budget so am not really interested in installing a completely separate system.

"My question is: Do I need to provide X-bracing support to these I-Beams after placing drywall between them? I am wondering if they need it due to their construction. Anyone have experience with this? Thanks" Cross or X bracing was used decades ago to stabilize a wooden flooring system. It assisted in making the floor a "system" rather than a group of individual joists. So a deadload/live load and the deflection could be trusted mathematically. It was thought to help to prevent in roll over (collapse) of the system but there is not much proof that this situation was ever even happening. With engineered wood i beams and joists this is not the case so a retro fit as you suggest is not needed. If it was not there in the first place(cross bracing) then it does not need to be there after the fact.

Brien Thank you for that information. I was thinking that was the case. It's nice to have confirmation. Joe

Well I'm at the point now where I am meeting with HVAC installers to get quotes for tapping into the existing HVAC for the studio. The first person I met with said that he did not think I could control temperature and airflow seperately from the house. I am not sure if that was really the case, or whether he just did not want to do that kind of an installation. He recommended an additional split system that would be dedicated to the basement. While I am sure that is the ultimate approach, I think his bid is going to come in way more than I can afford. I have done some initial research on installing a split system (doing the work myself). Some things like the compressor lines and charging the coolant system I would have to contract out. I think I could afford it, especially if I bought a used system. I see plenty of them on CraigsList in our area. Some only a few years old and in excellent operation. Problem is, I know doing this myself will really extend the time of my build. I have another HVAC company coming out in the morning. They are the original installers of the HVAC in our house which is about 11 years old. I'm hoping to hear better news from him. Here's a question for the forum. Has anyone else tapped into the house HVAC for a Basement Studio and made it work? Are you using Zones with Dampers? Something else? Are you satisfied? Thanks Joe

I haven't done it myself, Joe, but some of my clients have, successfully. However, it does depend on the capacity of the existing system. It is quite possible that it was not designed originally with any additions in mind, and in that case it won't be able to handle the additional load: the static pressure might end up being too high, in which case the fan motor will be overloaded, run inefficiently, and burn out early, before its normal lifespan is up. The heat pump might also not be able to handle the extra load, in which case the duty cycle will be too long, and it too will burn out too soon, as well as causing humidity issues. So if your second HVAC guy says more or less the same thing, then I would not attempt to tie into the existing system: You'll just have to bight the bullet and do a split system plus the ventilation system with its own ducts, fans, dampers and silencer boxes, all of which need to be calculated properly. - Stuart -

Well I met with the second HVAC contractor today. They recommended the “Zone” system using automatic dampers, control electronics etc., which would tap into our existing system but add a new Supply Trunk. This supply trunk would then feed the basement area. Today the basement is fed off the house system and heats and cools quite well, but it cannot be controlled separately from the house. The guys that came out today work for the company that installed the system when the house was built. They agreed that the addition of another split system would work fine but thought that would be a lot of extra money for something they felt could be accomplished with a Zone system which is less expensive. I still need to see what their quote comes in at. If that quote is still out of reach, I don’t think I would try to tackle a zone system on my own. Though less expensive than a complete system, it sounds much more complicated. They explained how everything works together to make sure that each zone is getting only what it needs and the processes that take place to insure that the heater does not overwork itself. There are lots of safety/reliability measures built into the controlling electronics and sensors. These must be tuned. Stuart Did your customers use a Zoned System, or did they just tap into the Supply and Returns of the house system? Am I overthinking all of this? It’s a basement that stays relatively comfortable all year long. I just knew this was going to be the piece of construction that was going to cause me the most stress. Thank you Joe

Over the last several days I have spoken with many folks educated in the area of HVAC. I think I have talked myself into putting in an air handler. I have a few questions about wrapping my existing metal duct and where to purchase sound insulated flex duct. I'll post an HVAC question in the construction section. Joe

Stuart

If you leave your duct-work in the MSM air cavity without boxing it in and also without silencer boxes on all penetrations

I did not say I was not going to use silencer boxes. In fact I stated that I was. I just did not understand the theory behind it. BTW, Thank you for the excellent explanation. Very helpful. That is all I was looking for. "My CR ceiling joists need to nestle between the first floor joists above."

Why? That is only one of two possible ways of gaining headroom, and in fact it is the least effective of the two

I respectfully disagree. Having a room within a room design is better than having any part of that room attached to the house, including the ceiling. I wanted a completely isolated space. And that is what I have designed with two different acousticians. I realize everyone is going to have their own thoughts on how to do this. This is how I was advised and I respect the expertise of these gentlemen. Others on the forum have agreed with this approach as well, and many other builders on the forum have used this approach. I do not know why you consider it inferior.

I'm going to see if I can pull off the boxing and stuffing with insulation. Hang on a sec! You just said that you CANNOT box it in, and now you say that it is ALREADY boxed in? That's confusing...

You've taken this statement out of context. Please read the whole statement. "My tracking room is a different story. I'm going to see if I can pull off the boxing and stuffing with insulation." I was referring to a different room (I called it the tracking room). Probably not the best name to use, but not important. It is a different room that has different challenges limiting the height of the ceiling. The joists will not penetrate the cavities above, therefore leaving space to "box off" the bay where duct work resides. Stuart, I appreciate your advice on this particular topic and thread. If you don't mind I am going to copy my response here to my build thread to maintain continuity of that build. Thank you. Joe

Link to reply: viewtopic.php?f=2&t=19682&p=134681#p134681

Stuart Good Pics. Yes I am aware of inside-out construction. John was one of the consultants I mentioned in a previous post. He worked with me several years ago when coming up with the construction plans. We discussed several construction techniques including I/O construction. I chose not to use the I/O ceiling because although it raises the acoustic ceiling , it lowers the visual ceiling. It's just not what I was after. Very nice post (minus the mean sarcasm). I have not seen a better assembly of pics in one post showing I/O construction. JK

I chose not to use the I/O ceiling because although it raises the acoustic ceiling , it lowers the visual ceiling. It's just not what I was after.

Actually, it does not lower the final visual ceiling at all. Rather, it raises it, as should be apparent from the series of images. Or rather, comparing two otherwise identical rooms that are suitably treated to give similar acoustic responses, the one with the inside-out ceiling will have a higher visual ceiling, and also a higher acoustic ceiling. What may be confusing you, is the first look at the interleaved-joist ceiling, which SEEMS to have a higher ceiling... but does not yet have the acoustic treatment on it that is needed. The inside out ceiling, on the other hand, needs no additional treatment, since it is already built in. The bottom edge of the joists marks the final visual ceiling. All that is needed is some type of fabric stretched across the joists, and the ceiling is complete, without needing any treatment. If you just look at the structure, then yes the interleaved-joist ceiling appears to be higher, but once you add the treatment, it no longer is higher. And that's assuming that you don't put cross-bracing on the joists, nor nailing strips at the edges to attach the drywall too. Once you drop the ceiling enough to fit those in, you lose any advantage you might have had. Bottom line: in practical real-world construction, a finished inside-out ceiling will always have better acoustics and a higher visual line than a conventionally built interleaved-joist ceiling. The inside-out ceiling will also be cheaper, easier and faster to build, overall, and will use less materials, assuming it is designed and built properly. The only drawback with inside-out ceilings is lifting them into place, but a heavy duty drywall lifter makes short work of that. - Stuart -

Nice clarification and nice idea about basement studio...

Just a quick update and a question. UPDATE: I decided to use my existing HVAC system in the basement for the studio. I just don't have the budget for another system. My calculations show 12" duct requirement for the CR. After designing an HVAC silencer for the CR ceiling (using two 6" ducts, each with a silencer), I realized it might be better to slightly oversize the duct and go with two 8" ducts since my calculations are right at 12". If there are additions to the existing electronics down the road, it might actually push me over. The problem is, I cannot see how to design a silencer for 8" duct to fit in a 10.25" x 11.25" space. The 6" silencers, barely fit that space. Below is a diagram of the 6" silencer. Input = 6" (area 28q in) Output (56q In) QUESTION: Does anyone have any advice or experience building an 8" round duct silencer to fit in such a space? Thank you. JK

My calculations show 12" duct requirement for the CR.

That sounds rather large for a typical home studio. How did you arrive at that size?

After designing an HVAC silencer for the CR ceiling (using two 6" ducts, each with a silencer),

Two 6" ducts is not the same as one 12" duct. Two 6" ducts has only half the capacity of one 12" duct (half the cross sectional area). You would need four 6" ducts to get the same capacity as one 12" duct.

realized it might be better to slightly oversize the duct and go with two 8" ducts since my calculations are right at 12".

Two 8" ducts is still not the same as one 12" duct. Two 8" ducts is only 88% of the capacity of one 12" duct. Two 8" ducts plus one 6" duct is about right to replace a single 12" duct.

QUESTION: Does anyone have any advice or experience building an 8" round duct silencer to fit in such a space? Thank you.

If you have an 8" duct, then the box cannot be slimmer than about 12", and possibly more, depending on how much isolation you need (in addition to the insertion loss), which defines how much mass you need, and therefore the thickness / type of wood. So for 8" duct, there's no way to make it less than about 12" for each of the minor dimensions. Therefore you'd need at least 14" of space to fit that box in, which means it won't fit in a standard stud bay or joist bay (Or rather it can be made to just fit, but not with good spacing). But getting back to the original issue here: I suspect that you may have made a mistake in your calculations, or your layout. I vary rarely need individual ducts 8" or larger when designing typical studios. I normally use plenums for the main runs, which can handle greater flow, then use small round ducts only for the runs to the individual silencers / registers. What flow rate and flow velocity are you using for your calculations? And what static pressure are you using? Something doesn't seem right. - Stuart -

Stuart It has been a while since I did the calculations. I will go back and review my notes and post the data I used for the calculations. Maybe I missed something or mis-understood a concept. JK

OK. I feel really stupid after reading your response Stuart. It's simple math for the area. (2 - 6inch circles = 56.5 sq inches. 1 - 12" circle = 113 sq inches). Thanks for pointing that out. I may have figured out where my previous calculation went wrong. My room requires 258cfm. I used the calculator at https://www.cdicurbs.com/ductcal If you look at the two pictures (screen shots of the calculator), one of them suggest a flexible duct of 8", the other 10.8" (I still think it was even higher the last time. I must have done something different). Anyway, the difference in the results is due to the number of 180 turns. I entered (3) originally because I thought that is what the Silencer was really doing. Maybe that was a mistake. Please see the screens shots to see the calculations. Do you still think 8 inches will be enough based on my CFM requirements? FYI: The house Furnace is rated at 1600 cfm and the Air Conditioner is 3.5 tons Thank you JK

I'm just wondering if I'm close here, or if there is more information I need. On a side note, it appears to me that folks are using the same size return ducts as the sends. The residential HVAC guides I have seen suggest the return is supposed to be larger. Having said that, I think I read somewhere on the forum that it was suggested that there be some "back pressure" developed in the room, which maybe is the reason I have seen the Sends and Returns the same size. This is all very confusing to me. The more I read about HVAC, the more I read. Not a lot is sinking in. Just the basics. So my outstanding questions are: 1) Am I looking at 10.8" duct requirement or 8" based on previous data given? 2) Should the send and return Silencers be identical in size and design? Thank you JK

As I mentioned in a previous post, there just is not enough room above the ceiling for an HVAC silencer. Especially for one to accept a 10" flexible duct. I have decided to take some length off the room and bring the duct in from the rear. It really is my only other option. I have attached two pictures. One shows the silencer on the rear wall. The other shows an extension off the silencer into the room. I would install an HVAC diffuser at the end of the extension. JK