Attic Shaped Studio

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endorka
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Re: Attic Shaped Studio

Postby endorka » Sat, 2019-Sep-28, 20:40

Soundman2020 wrote:
As you say, isolating room 2 a bit more will help. I reckon some batwing gasket style seals and a drop seal in the room 2 door, like I have to room 1, will solve this sufficiently.
Take a look at Zero International for that type of thing. They have a bunch of seals specifically designed for studio doors and windows in their catalogue. You should be able to get what you need there. Particularly look at the adjustable seals, that you can tweak after they are installed: doors and windows can sag, warp, swell, shrink, etc. over time from gravity and from changes in the weather, so it's great to have the ability to just pull out a screwdriver and fix that in seconds, if needed. Yes, there's stuff is expensive, but I've found it to be good. Hopefully they have a distributor near you.


Just had a look, they have UK suppliers. Their door drop seals are very similar to the one I have on the door to room 1, a Lorient LAS8005si, but a little cheaper. Nice!

You sound a bit like a trekkie there" "Make it so, Mr. Sulu..." :)


Absolutely! We're just watching The Next Generation from start to finish again. Marvellous stuff :-)

Here's a scary graph to give you nightmares: it shows how much isolation you lose from very small holes/cracks/gaps in your wall.


Scary indeed. A quick calculation reveals that the combined surface area of holes behind the sockets is 0.17 m2 - an acoustic hole almost the size of three sheets of A4 paper. That's 0.27% of the total studio surface area. Since the holes are only in the first drywall leaf, let's assume a transmission loss of 28 dB (one sheet of drywall) if the surface was fully sealed. In that case, the holes decrease that by 5 dB. Ouch. Suddenly the not amazing sound reduction from room 1 to the rest of the house is starting to make sense.

I think I'll have a look behind the skirting boards to check the wall / floor joins as well, and seal with acoustic caulk if required.

Perhaps what you could do is to look at just ventilation for now, but do it in such a way that you can add a mini-split later, if the need arises. Don't paint yourself into a corner! For example, have the register where the fresh air comes in directly above where you would install the mini-split in the future, so the fresh air would be sucked right in to the mini-split, to be cooled / heated / dehumidified before it goes into the room. Etc.


That sounds like an excellent idea - thank you for giving me the kick required to do it properly. In truth, I had no idea a mini split was ductless and installed in addition to a ventilation system. As you say, that is within my reach as a DIY install. I've had a few ideas for placement of the outside component should it become necessary, but will focus on the ventilation aspect for the moment.

Here's a design that came into my head when I looked up at the house and noticed a bathroom extractor fan vent coming out of the roof soffit;

2019-09-28 10.54.18.jpg


The roof soffit already has many long thin wire mesh covered holes for roof ventilation. Having the studio ventilation inlet and outlet there as well seems preferable to breaching the actual roof, in so many ways. And since there are already so many holes in the roof soffit, adding the inlet and outlet with proper silencers should not make the acoustic isolation any worse.

Another positive is that most of the roof soffit can be accessed from inside through a large panel from the landing into the eaves, so installing the vent, ducting and silencer would be possible with very little disruption or redecorating required.

panel - landing.png


The only potential issue I am aware of with soffit extracter fans is the danger of expelled moist air rising back into actual soffit roof vents. I think that directing the outlet duct at a bit of an angle outwards rather than straight down, and having the fan close to it will solve this.

Here's the tentative rough design sketch. Very much at the idea stage - nothing to scale, no calculations done yet, and the duct routing needs work. The fan I'm thinking of is an inline centrifugal quiet type designed for mounting in loft spaces. I'm assuming oversized slow running ones can be used here, and floated on the rafters to prevent vibration transfer if required.

The inlet duct emerges at the ceiling. I think just below this would be a good place for the mini split if required.

ventilation 1.png

ventilation 2.png

ventilation 3.png


This is all just the speculation of a beginner really, so your comments would be most welcome. If the general idea is good I can do proper calculations, spec up some parts and do a proper design.

I am also seriously contemplating having the radiator behind the left speaker soffit removed.

Cheers,
Jennifer
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Re: Attic Shaped Studio

Postby endorka » Sun, 2019-Sep-29, 17:13

Soundman2020 wrote:Still playing catch-up on Jennifer's epic post! ;)


And I can't thank you enough for doing so. My initial post was absolutely the peak of my abilities after months of study and planning, I couldn't see any way to develop the design further with any certainty. You've already pushed it way beyond that, and I deeply appreciate it.

To be certain, there's a procedure I developed that I call the "walking mic" technique, and I'll post some instructions for doing that


Sounds like a good plan.

I would try to shoot for less than 45° if you can. It looks to me like it might be possible. I developed a dynamic tool for Sketchup that helps me lay out rooms, and I'll try find time to apply that to your room, to see what I can come up with... but I'm pretty tight on time right now!


I reckon we could get it to less than 45 - the initial midfield position was almost as widely spaced, and less than 45 degrees. I actually really liked the mega separation, and so did musicians and listeners. I miss it with the current nearfield setup. I think this might be what Dan Dan refers to as "big headphones" ? Most of my mixes are LCR so a soundstage that's a bit overwide isn't going to confuse placement significantly, or even at all.

Also, use the space under the speaker shelf inside the soffit, for bass trapping. Hangers are good there.


I'm up for putting some hangers in, you reckon there's enough height and space for them to be worthwhile versus just filling with light fluffy stuff?

You know, I really like Genelec, both for their great speakers and also for their great documentation, but their flush-mount kits are something I've never been able to figure out! Leaving the speaker half outside the baffle, poking out by several inches? Hmm.... :shock: :?: And to be even more honest, I've never seen anyone actually mount their speakers like that.


Makes sense. I thought it looked a bit dodgy! Proper flush mounting seems like a good option then.

Speakers move and vibrate in all three directions, at once, all over, top, bottom, sides, front, back. Just putting pads under them isn't enough when they are soffited. I have a proprietary method for fully floating them, which is the sensible way to do it, to minimize transmission into the soffit itself. I'm not a big fan of the "bolt the speaker down tightly in a rigid box" method. I prefer to fully float the speaker. But as I say, it's a proprietary method that's taken me years to perfect, so I can't really just put it out there in public!. Sorry.


I totally respect that, no problem at all. If the standard Genelec method wasn't good enough, my next plan was based around this design by "Guit-picker". It floats the speaker on sorbothane pads, and holds them in place with similar pads on the top and sides. A flat plate can be bolted to the bottom of the 8030 speakers for this;

floating soffit mount.png


Considering 25mm MDF for this.
Too thin: not enough mass. I usually build up the baffle from several layers, and aim for the highest surface density I can get, with the least thickness. There are ways of doing that too... :)

Sure thing!



Yep, but you are forgetting something! You need a ventilation path up the rear of the speaker, plus some "air" around it. Don't wrap the poor thing in a blanket!


The lack of ventilation was only for the standard Genelec flush mount design. They don't have any, presumably it isn't required because there is such a huge air gap around the half of the speaker that is actually in the soffit :-)

Determining the size of the front baffle (including the recessed portion) and hole for speaker was a little tricky. The portion of the front wall that isn't a window is about 4.5 cm longer on the left side than the right. This means that the baffle width on the right is 82cm, on the left 88cm.
:shock: Red flag! Symmetry is critical, so you'll need to work on that to get your soffits identical.... You currently do have a difference between your left and right channels, so it would be a good idea to aim to fix that in your soffit setup...


Thanks for the warning. How about this? It's a continuation of the soffit baffle to bring that part of the left wall into symmetry with the right wall. Hinged and flush to the soffit baffle so it swings inwards with the door, and closes automatically when the door closes. It should extend back far enough to get out of speaker reflection influence at the mix position. Perhaps 18mm MDF would be thick enough here to save a bit of weight? It would be covered with the same absorption as the opposite wall.

I already have a similarly hinged door panel in the studio at the moment, it works really well.

panel - hinged door.png

panel - hinged door 2.png


Cheers!
Jennifer
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Re: Attic Shaped Studio

Postby endorka » Tue, 2019-Oct-01, 12:00

Here are some ventilation calculations for the following rough design. The calculations are copied from the approach detailed by John Steel on his thread;

viewtopic.php?f=5&t=19

It has been a fascinating exercise. That will allow me to refine the design. From reading Everest, it would seem that circular cross section ducts are preferred to the rectangular ones I've used in the sketch. The plan is to use an inline fan at the very end of the chain, between the outlet from the exhaust silencer and louvre.

ventilation 2.png

ventilation 3.png


Comments of course welcome :-)

Studio room 1 volume is 31 cubic metres (1094 cubic feet)

6 changes per hour gives 6564 ft3 or 109.4 f3 / min or 186 m3

gives 4.44 inches so let's use 125mm diameter duct.

Outer louvres:
3906 mm2 * 3.142 * 2 = 24547 mm2
sqrt 24547 mm2 = 157 mm

So external louvres should be 157 x 157 mm. There is a bit of oversize margin in the calculation so let's say 150 x 150 mm as it is a standard size and will easily fit in the roof soffit. Going to 200 x 200 might be a bit of a squeeze.

Silencers

Two silencer boxes in the eaves, attached to plasterboard side walls going into the studio, made of 25mm MDF, lined with 25mm of duct liner, with a CSA of:

Silencer calculations:
Radius of duct = 6.25cm, duct cross section area is therefore 123 cm 2
Minimum cross section of silencer path is 246 cm2, therefore 16 cm on each side.

From Gregwor's silencer design for 3 baffles, with X=16 cm, 25mm duct lining, 25mm walls, silencer outer dimensions are

93 x 50 x 26 cm

This will definitely fit in the roof eaves on the left side of the studio. If the small eaves on the right side are similarly constructed, it will fit there too, but I'll have to remove a bit of plasterboard to take a look to make sure. If there is extra height available, I could make them higher and therefore have more cross section area.

Silencer box flow calculations using the equivalent duct length method:

16cm Equivalent diameter round duct area = 18.06 cm = 7.11"

Equation for converting a sharp 90 degree bend into an equivalent length of straight duct is:

Duct Diameter x 60

7.11” x 60 = 427” or 36’ for each 90 degree turn

x 8 for each silencer = 288 feet of straight duct

Using the engineeringtoolbox.com friction or head loss calculator this results in

"Friction Loss (inH2O): 0.124
Friction Loss (inH2O/100 ft): 0.0432
Air velocity (ft/min): 397
Air velocity (ft/sec): 6.6099999"

Results

Giving a combined loss for all 2 silencers of .248 (inH2O) or 61.78 pascals and apparently achieving an air velocity of 397 ft/min at the point it enters the plasterboard wall.

N.B. this should be less than 300 ft/min at the register. Is this going to be a problem? Presumably a silencer with larger cross section would give a slower speed. Hopefully the height in the eaves will permit this.

I've still to work out the duct routing, so going with John's at the moment as a "worse case" as I don't think mine will be any more than this;

Adding in the losses for 2 outer louvres with insect screen [2x 0.05 in.wg], 2 plenums[2 x 0.01] and 4 metres of additional 5” ducting [0.101 in.wg] (with 2 x 90 degree turns [2 x 0.04] and 4x 45 degree turns [4 x 0.03] ) => .381 in.wg

Total = .505 in.wg or 105 pascals.

Cheers,
Jennifer
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Re: Attic Shaped Studio

Postby Soundman2020 » Tue, 2019-Oct-01, 12:00

I think I'll have a look behind the skirting boards to check the wall / floor joins as well, and seal with acoustic caulk if required.
Acoustic caulk is great, but its often expensive. Ordinary bathroom/kitchen caulk works very well for this, and is cheaper. Get the type that sticks like crazy to all surfaces, and never hardens: remains soft and rubbery, even when fully cured. I have had good results with Sika brand "Sikalfex 11FC", which seems to be commonly available in many places around the world. But any good quality caulk will do the job.

In truth, I had no idea a mini split was ductless and installed in addition to a ventilation system.
There's two types of mini-split. One is ductless, the other ducted.

HVAC--mini-split-ahu-and-typical-indoor-unit-ducted-and-unducted-non-ducted-compare-NOLBL.jpg
The one on the left is the ductless or non-ducted type (what you typically see on the wall im houses, shops, etc.), and the one on the right is the ducted type, often also called an AHU for "Air Handler Unit" (which would be mounted in the ceiling space or wall space, normally, or maybe in the attic or basement, connect to the ducts that go to the room(s) ). Both types are mini-split, and in both cases there's some type of compressor unit outside, such as one of these two types:

HVAC-heat-pump-outdoor-4-both-types.jpg
The reason these systems are called "split", is because they work the exact same way as the typical old-fashioned "through the wall" or "through the window" type of air conditioner, but "split" into two parts, instead of all being inside one box. The compressor section is mounted in one unit that goes outdoors, and the condenser is mounted in the other unit that goes indoors (either on the wall if it is a ductless, or in the attic space if it is ducted/AHU). There's a bundle of pipes and wires that connect the two units. Principle of operation is simple: it is a closed loop system, filled with a pressurized refrigerant gas that circulates between the two units. The compressor (outdoors) compresses the gas into a liquid, which makes it hot, then passes it through a radiator with a big fan behind it to cool it down. One of the pipes then conducts that cool liquefied refrigerant to the indoor unit, which is basically just another radiator (coil of copper pipe with fins attached). Just before the refrigerant gets to that "radiator", it passes through an expansion valve that suddenly drops the pressure and turns it back into gas again... with the result that it get very cold, very fast. That icy cold gas then passes through the coils of the radiator, picking up heat from the room air, before finally being sent back down another pipe, back to the compressor, where the whole operation is repeated, ad infinitum.

In the indoor unit radiator, that very cold refrigerant cools down the coils and fins, and there a small fan in the same box that passes room air through the radiator, then back into the room. And two things happen: Because the room air is warm and humid, as soon as it touches the cold surface of the fins, the humidity condenses out as liquid water (hold a metal spoon in the vapor rising from a boiling kettle, and watch how this happens: the vapor condenses on the cold metal and drips off. The same with a cold windscreen in a car, misting up from the vapor condensing on it). So that action removes the excess humidity from the air passing through the radiator... and it also warms up the fins and copper coils WITHOUT cooling the temperature of the air! This is an important point to understand! The simple fact of the water changing phase from gas to liquid releases a lot of heat into the fins and the air. Just like evaporation is a cooling process (which is why you feel cooler when you sweat), so too condensation is a warming process: it releases the latent heat in the water vapor, as the water condenses. Thus you end up with liquid water on the fins, and they also get warmer... which uses up some of the cooling capacity of the mini-splt system! Important point! If the fins are still colder than the air AFTER the condensation has taken place, then the fins can also cool down the air, so the unit blows cool dehumidified air back into the room.

However, if all of the cooling capacity was used up just in condensing the water, then the air does NOT get cooler: it just gets dehumidified. In fact, if the condensation process released more heat than the capacity of the unit, then the air can come out warmer, not cooler! This is something that people don't expect... and it's the reason why you need to do the math carefully, when dimensioning the cooling capacity of the unit: it needs to have enough capacity to deal with the "latent heat load" of dehumidifying the air, AND ALSO the heat in the room air itself, which is called the "sensible heat load". The sensible heat comes from things like your equipment, lights, your nicely steaming coffee maker, that huge piping-hot pizza that everyone is enjoying, sunlight through the windows, heat coming through the walls, floor and ceiling, ... and from another biggie that most people forget about: body heat. Half a dozen musicians jamming hard can put out as much body heat between them as a decent size electric space heater... A person at rest produces about 100 watts of waste heat, and an Olympic athlete in full exertion at maximum potential can put out nearly ten times that. A musician playing hard can be producing maybe 250 to 350 watts (give or take a bit). So half a dozen of those, is between 1 and 2 kilowatts.... 1 watt is 3.4 BTU/Hour of heat, where "BTU/Hr" is the way HVAC engineers measure heat movement. So just to cool down that bunch of musicians, you would need a mini-split capacity of between (1000 x 3.4) = 3,400 BTU/Hr and (2000 x 3.4) = 6,800 BTU/Hr. Add in the gear and lights, coffee and pizza, sunlight, walls, floor nad ceiling, and you get to maybe 8,000 or 9,000 BTU. If you just did that math, and forgot about the humidity problem of latent heat, then you went out an bought a 9,0000 BTU mini-split system thinking it would be fine, you'd have a problem! On a humid day, with all those people huffing and puffing humidity out with every single breath, there could easily be 3,000 BTU of latent heat to deal with in that humidity... and since the mini-split condenser uses up its capacity FIRST in dehumidifying, if it has 9,000 BTU capacity and 3,000 of that is used up just to remove the moisture from the air, then only 6,000 is left over to actually cool the air... but there's 9,000 units of heat to deal with, and only 6,000 units of "cold"... soooo.... the room does not get cooler, even with the poor thing running full out at maximum capacity.

Thus, the importance of considering BOTH sensible heat AND ALSO latent heat when you dimension your mini-split system. In this hypothetical case above, you would need a 12,000 BTU/Hr unit to do the job...

In other words, you need to dimension your system to be able to handle the worst-case: the room packed full of hot sweaty hard-working musicians with their amps, instruments, and other gear, as well as your own gear, on the hottest day in mid-summer with high humidity outside... and it also needs to be able to handle the opposite extreme: just you sitting quietly alone on a freezing cold day in mid-winter.

I forgot to mention that the majority of mini-split systems are not just "air coolers": if you reverse the flow of refrigerant through the tow units, then the indoor unit become an "air heater": the compressor sends hot refrigerant to the indoor unit, so it heats up the air, instead of cooling it. And in fact, this is the most efficient method for heating a room. A modern HVAC system can produce many times more heat that the electrical power it consumes, because it is the phase-change of the refrigerant that does the heating or cooling: the electricity just runs the compressor and fans, but the hard work is done by the refrigerant changing from gas to liquid and back again as it circulates around the system. So a mini-split system that uses 2 kilowatts of electricity can provide 4, 5, 6, 8, or maybe even 10 kilowatts of heat, depending on the unit and the design. Very high efficiency. Great power saver!

OK, long rant here, to say basically: take care when defining the capacity of your system!

Other points to take into account: the "bundle" that connect the indoor unit to the outdoor unit has two copper pipes in it (usually one is small diameter, the other a bit larger), plus a cable with several wires inside, plus a condensate drain: that water that condensed on the fins of the indoor unit has to go somewhere! So there's a drain pipe to carry that away, and dump it some place. All of those have to go through your isolation walls! Oops! Potentially, that bundle of pipes and wires can create a flanking path through the wall, carrying sound and vibrations in both directions. There's a method for dealing with that. And of course, you need to figure out where the condensate drain can go to dump its water... Maybe just on the grass outside, or the garden, or into a drain if there's one nearby.

OK, I'll stop now, before I wear out my keyboard...


Here's a design that came into my head when I looked up at the house and noticed a bathroom extractor fan vent coming out of the roof soffit;
That looks like a good plan. The vents under your eaves are to vent the roof deck itself, so don't interfere with those too much, but adding your intake and exhaust registers under there would be fine. Do make sure that the intake and outlet are far apart from each other, as you don't just want the intake to be sucking the same old exhaust air right back in again! Keep them at least 2m apart.

The only potential issue I am aware of with soffit extracter fans is the danger of expelled moist air rising back into actual soffit roof vents. I think that directing the outlet duct at a bit of an angle outwards rather than straight down, and having the fan close to it will solve this.
If the HVAC mini-split is doing its job, the exhaust air should not be too humid. Or you could consider adding an ERV unit, which recovers the humidity and waste heat in the outgoing air, and adds it back into the incoming air... but that's extra expense, and extra complexity, and you likely don't need that.

Here's the tentative rough design sketch. Very much at the idea stage - nothing to scale, no calculations done yet, and the duct routing needs work. The fan I'm thinking of is an inline centrifugal quiet type designed for mounting in loft spaces. I'm assuming oversized slow running ones can be used here, and floated on the rafters to prevent vibration transfer if required.
Looks like a good plan to me! However, if you are planning to have a mini-split at some point, then I would suggest putting it high in the rear wall/ceiling, and bringing in your fresh air just above it, so the incoming air gets sucked through the mini-split before going into the room.

I am also seriously contemplating having the radiator behind the left speaker soffit removed.
I think that's a good idea!

I would also consider improving the insulation in your walls: you say you have access to do that, so if you can make sure that your wall cavities are completely filled with good insulation, that would help with both sound isolation and also with thermal issues: keep you warmer in winter, cooler in summer.

- Stuart -
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Re: Attic Shaped Studio

Postby endorka » Tue, 2019-Oct-01, 21:11

I hadn't realised the mini splits could do so much, what an incredible system. I'll make sure the ventilation inlet can be easily routed above that position should the need for one arise.

Thanks for the tip on using normal caulk, the brand you mention is available here. And there was me going to do all along the plasterboard wall / floor corners with green glue and backing rod!

Thank you also for the checking out the rough design, it's a great relief you think it's a reasonable approach. That'll be the first step of the studio upgrade.

Interesting observation from today: the existing soffit louvre in the photo comes from a bathroom extractor ceiling fan just below and not particularly far from room 1. It's a normal bathroom fan that makes a lot of noise in the bathroom, but it is virtually inaudible in room 1. I left it running all day today by accident and didn't notice!

It will certainly be possible to position the room 1 ventilation exhaust fan close to that location if necessary, seems like a good indicator it will not contribute mechanical noise to the studio, particularly if it is a quiet type.

I have good access to the "other side" of the walls along the front of the studio, and wall in the same position at the front of room 2. It made routing signal cables between room 1, room 2 and the landing very easy. From memory the insulation was pretty good, although I think the small wall at the front of the studio behind the awkward radiator is only one plasterboard thick.

(edited to confirm this - photos follow)

Radiator corner with acoustic panels removed. Since then I've added another couple of 1 gangs for XLR cable snakes to the landing and room 2. There's also a network socket and blanked 1 gang behind the radiator. And the small hole in the wall with cable sticking out needs filled. A pretty big acoustic hole into the eaves - putty pads and caulk to the rescue!

2016-12-08 12.09.34.jpg


The top two 2-gangs are signal cables to the DAW computer on the landing. I plan to relocate these to the outside of the speaker soffit once it is constructed.

2016-12-08 12.24.05.jpg


A photo from the eaves of the same area. The wood type bit on the far left is the side of the balcony. It's completely lined with a large lead triangle on the balcony side. The corner stud looks pretty sturdy. Next to that is a radiator water plastic pipe, and the insulation.

2016-11-27 11.46.30.jpg


Single layer of plasterboard confirmed. Looks like it is foil backed or somesuch. I'll be able to get putty packs onto these and the other out of shot socket backs.

2016-12-05 15.35.51.jpg

2016-12-05 15.39.41.jpg


The short wall on the landing extends further into the eaves, the mottled thing might be insulation?
2016-12-05 15.41.03.jpg


The equivalent short front wall sections on the landing, tech store in room 2 and presumably the bathroom are similar. Do you reckon it would be worthwhile beefing those up a bit where possible, especially for room 1? Perhaps a second layer of plasterboard could be attached to the other side of the studs and filled with insulation, similar to a standard stud wall partition? It occurs to me that I should check building codes first to see if stud partition walls to roof eaves actually have to be single layer.

The room side walls are standard stud construction. From drilling into them I can verify they are already stuffed with insulation :thu:

Cheers!
Jennifer
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Re: Attic Shaped Studio

Postby Soundman2020 » Thu, 2019-Oct-03, 12:03

I'm still trying to catch, up with you, Jennifer!

I'm up for putting some hangers in, you reckon there's enough height and space for them to be worthwhile versus just filling with light fluffy stuff?
I think so, yes. I normally do a combination of treatment in soffit traps, and you'll have plenty of depth for the hangers, due to the slope of your ceiling that forces the speakers to be further out in the room. And especially if the radiator comes out.... and the patchbay and electrical outlets get moved to the outside of the soffit: That would leave plenty of depth for hangers below the shelf, slightly angled maybe. Above the soffit, due to the strange shape there, that pretty much has to be filled with with insulation: Making hangers for that area would be a pain, and they wouldn't be that effective either. So the top section, just fill with pink fluffy at the front, then something a little more dense behind it, up against the walls: maybe 703 or something like that.

I totally respect that, no problem at all. If the standard Genelec method wasn't good enough, my next plan was based around this design by "Guit-picker". It floats the speaker on sorbothane pads, and holds them in place with similar pads on the top and sides. A flat plate can be bolted to the bottom of the 8030 speakers for this;
The concept is OK, but I do a different implementation... :) I've spent several years refining my own proprietary system for floating speakers for my clients. It needs to be tuned, of course. Sorbothane is great, and I certainly use that, but you do have to do some math and tweaking... to use the right type of Sorbothane for each pad, and make the pad the right size, to do the job. The goal is to get the resonant frequency of the floating system way down, to well below half the cut-off frequency of the speaker itself. If you use subs, then the job is much easier because the mains will not go down very low, so you can relax the tuning just a little... But I still prefer to keep it as low as I can. Don't forget that the speaker can potentially vibrate in all directions at once, and that "up and down" isn't the major vibration axis anyway.... Most of the inertia in the speaker is going front-to-back, as the voice coil and cone of the woofer slam back and forth, against the impedance of the air. But there's also going to be vibrations in the other senses too... in many degrees of freedom all at once... even rotational vibrations, since the center of inertia of the woofer is below the center of gravity of the speaker.... So I do the mounting a little different from the photo, attempting to take all of that into account. (And don't forget that the weight inside isn't distribute evenly either: the speaker is usually heavier towards the front, and off to one side.... ) So, basically: it's more complex than you think!

Thanks for the warning. How about this? It's a continuation of the soffit baffle to bring that part of the left wall into symmetry with the right wall.
For your room, I would use absorption rather than reflection on your side walls, where the soffits meet the walls. A thick panel on the back of the door, and a matching panel on the opposite wall. I'd also suggest making the soffit faces a bit wider, going more across the room, then angling the soffit sides back again to meet up with the windows at the front. Not sure if I'm explaining that well enough!

it would seem that circular cross section ducts are preferred to the rectangular ones I've used in the sketch.
A lot easier to install, too! Flexduct is a blessing... but also a curse! If you don't stretch it out fully and support it properly, you end up with kinks in the skin... and even a few small kinks can drastically reduce the cross sectional area, increasing your static pressure. So keep it stretched out properly and well supported... plus make any curves gentle.

Outer louvres:
Don't forget "open area"! Registers have vanes across to direct the air flow, and those vanes take up some of the cross sectional area of the register size. So allow for that: a 20cm x 10cm register doesn't actually have 200 cm2 of open area: probably closer to 150 cm2, or maybe even 100 cm2 if the vanes are large, close together, and angled. Look for registers that have a large open area if you can, and over-size them by at least 25%. Also for outdoor registers, it's a good idea to put wire mesh inside as well, to prevent bugs crawling in and building a new home for themselves...

Giving a combined loss for all 2 silencers of .248 [in wg.]
Sounds good. That should not be a problem.

N.B. this should be less than 300 ft/min at the register. Is this going to be a problem? Presumably a silencer with larger cross section would give a slower speed. Hopefully the height in the eaves will permit this.
Air velocity at the outdoors intake and exhaust is not too much of a problem. What is more important is the velocity at the registers in the room: high speed air is more turbulent, and thus makes more noise which is why you want low velocity inside the room, but for outdoors, that's not really an issue.

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Re: Attic Shaped Studio

Postby Soundman2020 » Thu, 2019-Oct-03, 12:41

endorka wrote: A pretty big acoustic hole into the eaves - putty pads and caulk to the rescue!
:ahh:

The top two 2-gangs are signal cables to the DAW computer on the landing. I plan to relocate these to the outside of the speaker soffit once it is constructed.
:thu:

I'll be able to get putty packs onto these and the other out of shot socket backs.
:thu:

the mottled thing might be insulation?
Looks like it. Possibly polyester, rather than fiberglass or mineral wool. Much nicer to wrk with that stuff, and its reasonably good acoustically.
Do you reckon it would be worthwhile beefing those up a bit where possible, especially for room 1? Perhaps a second layer of plasterboard could be attached to the other side of the studs and filled with insulation, similar to a standard stud wall partition?
Any additional mass you add is going to help some. As will sealing up all those holes and gaps. And from the photos, it looks like you have plenty of empty air in your walls, which you could fill up with insulation. Right now, you seem to have only thin insulation against the walls, but large empty cavities between. I would consider putting ore insulation in there. Insulation does several things, acoustically, in isolation walls: it damps internal resonances in the cavity, it slows down the speed of sound (so the cavity appears to be deeper than it really is, as far as sound waves are concerned), and it changes the way heat is dealt with in there, from adiabaitc to isothermal. Basically, that means that the heat is carried away. This all happens at the microscopic level, but it is important! I'm sure you know that when you compress air, it gets warm (have you ever pumped up a bicycle tire with a hand pump? It gets HOT!). And the opposite too: when you decompress air (suck it apart, instead of forcing it together), it gets cooler. So, think about this: What is a sound wave? It's a compression wave moving through the air, followed by a corresponding rarefaction wave right behind it: As the waves moves through the air, as it passes each point it compresses the air slightly, thus warming it up, but then the "decompressed" wave comes past right away, cooling it down again. So that heat doesn't go anywhere: The average temperature stays the same, since at any given point the amount of cooling perfectly matches the amount of heating. So no energy is lost. That is "adiabatic" air. But when you put insulation in, that changes everything. It is now an "isothermal" system, which means that the tiny fibers in the insulation can conduct some of that heat away: So as the wave passes, the air heat sup a bit, but so does the fiber and the fiber carries some of that heat off... then when the rarefaction wave comes past, it cools the exact same amount as the compression wave did... but some of the energy from the compression wave is gone! It's no longer there. It can't go back into the "back side" of the wave any more. So the rarefaction wave takes energy out of the atmosphere, thus doing work on the atmosphere, thus wasting energy.... In other words, the insulation turns some of the sound wave, into low grade heat. It removes energy from the sound wave as it passes by. Because: isothermal!

And all of the above ramble, implies that having more insulation in your cavity is a good thing for isolation. So filling up your air spaces with more insulation would also help with isolation... as well as with heat: keep you warmer in winter, cooler in summer, reduce your energy bills...

---

Hey! Wow! I think I finally caught up with your thread! :yahoo:


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Re: Attic Shaped Studio

Postby endorka » Sat, 2019-Oct-05, 04:06

Soundman2020 wrote:Hey! Wow! I think I finally caught up with your thread! :yahoo:


A Herculean effort - brilliant job, thank you, and I now have many positive changes to incorporate into the design. I'll get that done and the walking mic test, then post both here :-)

Soundman2020 wrote:
endorka wrote: A pretty big acoustic hole into the eaves - putty pads and caulk to the rescue!
:ahh:


Since you liked that one so much, here's another, from the centre of the right wall. Usually this lurks behind an acoustic panel :-)

2019-10-05 07.56.53.jpg


On the upside, these are good opportunities for some easy gains in sound isolation.

Cheers,
Jennifer
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Re: Attic Shaped Studio

Postby endorka » Tue, 2019-Nov-05, 06:01

As a first step I've been making the improvements in sound isolation discussed above. I measured the attenuation to adjoining rooms with the UMIK-1 for both SPL figures and an REW sweep to allow proper checks on these improvements.

Done so far;

- filled in the holes in the plasterboard walls. There were quite a lot of those, some of significant size!
hole - puttied up.jpg


- caulked around the floor / wall corners between the plasterboard and floor.
- Putty pads applied on all the mains, light and signal sockets of room 1, of which there were many. A few more than first count - I think 20 in total, at least half of them double gang.
- Putty pads applied to the mains and signal sockets on the landing where the studio computer is; there are four sockets in the wall behind the computer leading to the eaves;
Studio computer.jpg

- I also put a rubber gasket around the perimeter of the hatch on the landing to the eaves to ensure it was airtight. Previously there was about a 3mm gap between the hatch MDF and plasterboard wall. The hatch itself is made from 18mm MDF so that is fine. In retrospect, some insulation stuck on the inside of that hatch would have been useful too, I will add this next time it's open.
hatch gasket.jpg


Actually quite a lot of work, but I swear I can hear a difference already. Mainly in the tone of transmitted sounds to other rooms, which now sound more "distant", presumably due to a proportionately higher increase in high and mid frequency attenuation than bass. The most bizarre thing was when somebody knocked on the studio door. It sounded like a door being knocked elsewhere in the house, like a floor down. And noise from the studio computer fan used to be distinctly audible in the room below. Now it is not. But of course, we'll have to wait until I measure the attenuation properly again to be sure.

Before that though, there were two unexpected snags I didn't have time to fix on this round of improvements. First was the insulation in the eaves. As Stuart pointed out in a previous post, there wasn't very much of it, indeed current UK building regulations also advise more than this for new builds.

insulation.jpg


I have rolls of the stuff waiting to go in there. However, there is a good reason for this sparsity of insulation. There are two bathrooms below this run of the eaves, and between them they have about 15 halogen ceiling downlighters fitted. These get hot so insulation cannot be placed on top of them, it has to go around it. And of course these ceiling downlighters give large acoustic holes into the rooms below.

Fortunately the fix is easy. LED downlighter replacements are available that are acoustically rated, fire rated, and can be placed below insulation. One they are installed more insulation can be placed in the eaves. They are not much more expensive than the standard ones, so happy days.

The next snag is a little trickier. The wall / floor corner at the rear of the studio is not joined properly, so there is a hole along most of its width (3.5m) to the floor / ceiling void below. It's pretty narrow, and was covered by the skirting board, but still a huge acoustic hole. Probably like having two doors a little bit ajar into the void.

floor - wall - rear - hole.jpg

floor - wall - rear - hole 2.jpg

A very rough sketch, the real rafters and joist system is far chunkier and complex than this;
rear wall floor corner gap 2.png


Caulk added to the crack will just drop down into the void!
rear wall floor corner gap 1.png


A quick fix would be to screw and caulk in section of wood along the entirety of the crack. It would look ugly, but since it is hidden behind bass traps probably be ok. I'd much rather fix it properly though, and here are some thoughts about how this could be achieved.

Here's a side view of the problem. The skirting visibly hides the crack, but provides no acoustic isolation;
rear wall floor corner gap 3.png


A fix might be to extend the floorboard to butt the wall board properly, then attach a small "stud" bottom layer to it. Then caulking can be done as normal. In theory removing a strip of plasterboard behind the skirting board should provide enough access to do this. The plasterboard can be replaced and sealed once the repair is done, and the join concealed behind the skirting; the result should look as good as new, but with the crack sealed.

rear wall floor corner gap 4.png

rear wall floor corner gap 5.png


I can't think of a less destructive but also effective way of solving this, but any comments to the contrary would be of course most welcome!

Cheers,
Jennifer
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Re: Attic Shaped Studio

Postby Soundman2020 » Tue, 2019-Nov-05, 19:41

Good to see the progress there, Jennifer! A lot of hard work, but worthwhile.

Actually quite a lot of work, but I swear I can hear a difference already.

I'm sure you can. Filling up all those holes and gaps is certain to make a difference.

The next snag is a little trickier. The wall / floor corner at the rear of the studio is not joined properly, so there is a hole along most of its width (3.5m) to the floor / ceiling void below.
Do you have a circular saw? If so, what I would do there is somewhat scary, but would fix the issue properly... however, you might not like it so much!

I would carefully remove that last floorboard just next to the wall, along the full length of the room, then set my circular saw to a cut depth of the exact thickness of the floor and sub-floor together, run it along floor just a little in from the edge of the second floor board (maybe 1 or 2cm closer to the wall), then take out those pieces of sub-floor, exposing the the joists below. So you'd have a gap a few cm wide along the wall. Then I'd put in a new section of "sub-floor" that butts up tightly against the studs on one end and the cut edge of the existing sub-floor at the other end, carefully sealing the joint with caulk, of course. Then trim off the bottom edge of the drywall to just a little higher than the final floor level will be, add in some extra floor boards nestled under that drywall edge, then fill with backer rod and caulk to complete the job. The problem with this method is trying to match the color and grain of the floor boards. That might not be so easy, and you could end up with a strip of slightly different colored floor along the base of that wall. But that's the only drawback I can think of.

The reason for cutting the sub-floor 1 or 2 cm in from the edge of the floorboard, is so you can have "staggered" joints there: the joint in the sub floor would not line up with the joint between the finish floor boards, which helps to ensure better isolation.

Anyway, that's another option if you are skilled with a circular saw, or know someone who is. But do be careful to set the cut depth accurately, so it ONLY cuts the sub-floor! You don't want the blade going deeper than that: you never know what else might be down there, just below the sub-floor: electrical, plumbing, gas....

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Re: Attic Shaped Studio

Postby endorka » Tue, 2019-Nov-05, 20:25

Cheers Stuart, yes the sound leaking into adjoining rooms seems "tighter" and more directional or somesuch as well, it's fascinating. Probably because leakage to the landing and subsequent stairwell and halls has been substantially cut. I like it a lot; as someone who values silence as well as music, it makes me wish they built houses like this as standard. It would be very little additional work to do at the time of building versus applying retrospectively.

I totally hear what you are saying about avoiding overlapping joins. I do indeed have a circular saw, and the gap in the floor / wall corner is large enough to put the endoscope through, so a prior inspection for reassurance may be possible.

The floorboard is a real wood tongue and groove system, which I suspect would be very difficult to match. If it has not been glued down, it may be possible to simply lift the end boards out and back in though, in which case the following variation would be possible. The caulk (not shown) would go in front of the circular backing rod;
rear wall floor corner gap v2.png


Does that seem sane?

Cheers,
Jennifer
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Re: Attic Shaped Studio

Postby Soundman2020 » Tue, 2019-Nov-05, 21:37

endorka wrote:The floorboard is a real wood tongue and groove system, which I suspect would be very difficult to match.
That would be the big concern, for sure. On the other hand, you could just replace the entire floor! :) :shock: :roll:

If it has not been glued down, it may be possible to simply lift the end boards out and back in though, in which case the following variation would be possible. The caulk (not shown) would go in front of the circular backing rod;
rear wall floor corner gap v2.png

Does that seem sane?
That would work! :thu:


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Re: Attic Shaped Studio

Postby endorka » Wed, 2019-Nov-06, 03:30

Excellent, I will make it so :-)

Looking closely at the photos I took before putting the skirting board back on (there was a recording session today), it looks likely that the wood floor and sub floor don't align perfectly at that edge anyway, which would certainly be useful.

Here's something else I've been considering for bonus points. As they both lead to the same void, it occurs to me that in this case the inner wall plasterboard partition could be thought of as a continuation of the floor. As the plasterboard is thinner & lighter, it is a weak link in terms of sound transmission from the studio into the void. Adding another layer of plasterboard on that short wall would help this, but only if there was a partition across the void at the corner where it meets the roof slope part of the wall. If that partition is not there, then the entire wall would require a double layer.

As it happens, when I checked other parts of the eaves, there is such a partition;
rear wall floor corner gap v3 - 1.png

It's not sealed at the edges, but the fit was very good, and the wood seemed chunky. I assume it can't be sealed to due roof airflow requirements, but even so, I wonder if adding a layer of drywall to the short wall area below would be beneficial? With Green glue between the layers;
rear wall floor corner gap v3.png

Do you reckon it's worth a shot? It's not a huge amount of effort to try, and I'd like to get as much isolation to the room below this section as possible within the scope of these modifications.

Thanks again for you help!
Jennifer
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Re: Attic Shaped Studio

Postby Soundman2020 » Wed, 2019-Nov-06, 11:15

Any time you add substantial mass to a wall, it's going to help, at least a little bit. Any time you improve the air seal around a wall, it's going to help, at least a little bit. Any time you put Green Glue in between two layers of wall, it's going to help, at least a little bit. Three times "little bit" = "bigger bit"! :) So yeah, I'd say to give it a shot!

I sometimes say things like: "If you do ten things to your room that each improve isolation by just a half of a dB, then you improved the total isolation by 5 dB". :)


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Re: Attic Shaped Studio

Postby endorka » Wed, 2019-Nov-06, 11:33

Nice one, that makes sense, thank you :-)

Cheers,
Jennifer


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