John Sayers' Recording Studio Design Forum Archive

Hi
I have another thread where I've been exploring a design for a studio in my garden built from the ground up. As I've been designing I've been watching the costs mount and so I'm just also looking into whether I could make a ground floor room of our three storey town house work as an alternative option.

Current construction:
- The room is 5.4m long, 2.42m wide and 2.4m high.
- Walls are plasterboard glued to breezeblock
- One of the shorter walls has a sliding glass patio door to a car port outside.
- The Ceiling is plasterboard nailed to the underside of the above floor joists.
- One of the longer walls has our ground floor hallway on the other side. The remaining shorter and longer walls have soil on the other side (our house is on a slope).

Current issues:
- The floor above is noisy - the floorboards squeak and you can hear footsteps, and the dishwasher etc when running in the kitchen above.
- The room has two dimensions that are almost identical.

Proposed use:
- Primarily as a mixing room, with the odd vocal or guitar recording.

My plan for improving the room:
- Take the plasterboard off the wall to release as much width as possible
- Take the plasterboard off the ceiling, and affix OSB or Cement Bonded Particle Board to the underside of the floorboards.
- Build a new inside-out stud wall with 2 layers of 19mm plasterboard on the outside. This new room will be 2.1m tall, 2.24m wide and 4.85m long. This appears to be the best compromise of size and modal response. I've brought the ceiling down that much because I need to keep the width as wide as possible. This design allows for a 5cm air gab between the leaves, to be filled with rock wool, although hopefully after taking the plasterboard off the walls as they are I'll get a slightly bigger gap.
- Build a new inside-out ceiling on the new stud wall frame, with 2 layers of 19mm plasterboard on the outside. The gap between the new ceiling and the underside of the floor above will be filled with rock wool.
- I would like to keep some natural light, so I'm planning to put a window between the soffits which would get light from the glass patio door (which will always remain locked shut).

The above should give better isolation from the rest of the house and better room ratios.

Treatment:
- Soffit mount my Mackie HR824 monitors
- Absorption across the back wall
- Possibly a cloud, if required

Questions:
1. With this limited width and limited height, is this the best design option?
2. With these limitations on dimensions, is this going to work at all?

Photo's of room as it currently is - we've only lived here for a couple of months and this is a temporary studio set up.

- The room is 5.4m long, 2.42m wide and 2.4m high.

Rather long and thin.... and square!

- Walls are plasterboard glued to breezeblock

Strange! Why would somebody glue plaster board to masonry? Why not just plaster the wall directly?

- The floor above is noisy - the floorboards squeak and you can hear footsteps, and the dishwasher etc when running in the kitchen above.

IT might be an idea to deal with the squeak while you are working on the underside of the same floor. Shims from below, screws from above... Make the most of the opportunity!

- The room has two dimensions that are almost identical.

Not good.

- Take the plasterboard off the wall to release as much width as possible

Then seal the surface. If you expose the masonry surface, you'll need to seal it, since it is porous. Any good quality masonry sealer will do.

- Take the plasterboard off the ceiling, and affix OSB or Cement Bonded Particle Board to the underside of the floorboards.

Or drywall! Both OSB and fiber-cement board are hard to work with (cut), and since you'll be cutting many little strips and bits and pieces, it would make sense to go with something that is dead easy to cut and shape... drywall.

Also, the plan is good but do get a structural engineer in to check the load capacity of your joists. You'll be adding hundreds of kg of material to that floor, so you need to make sure that the floor is able to carry that, safely and legally.

- Build a new inside-out stud wall with 2 layers of 19mm plasterboard on the outside.

Inside out walls? How much air gap will you leave?

This new room will be 2.1m tall, 2.24m wide and 4.85m long. This appears to be the best compromise of size and modal response.

What ratio does that give you? I'm not aware of many good ones where one of the dimensions is around two and a half times one of the other dimensions. Also, that leaves you with a VERY low ceiling.

I've brought the ceiling down that much because I need to keep the width as wide as possible.

I would not do that. Yes, room ratios are important, but so is ceiling height. If I had to choose here, I'd go with a slightly worse ratio and take the treatment penalty, rather than lower the ceiling so much. With a ceiling that low, you are pretty much guaranteed of getting ceiling reflections at your mix position, and there's not enough height to hang a suitable cloud...

This design allows for a 5cm air gab between the leaves,

That's very thin! Did you do the math? What MSM frequency does that give you? I suspect it will be rather high with such a thin cavity, despite the massive concrete block wall as the outer leaf... I try to never go less than about 10cm on the air gaps, as that just pushes the frequency too high, and damages low frequency isolation..

- Build a new inside-out ceiling on the new stud wall frame, with 2 layers of 19mm plasterboard on the outside.

Inside out ceiling? Have you looked into how you will do that? Have you calculated the dimensions that you will need for your new joists, based on the load they will be carrying?

The gap between the new ceiling and the underside of the floor above will be filled with rock wool.

What density?

- I would like to keep some natural light, so I'm planning to put a window between the soffits which would get light from the glass patio door (which will always remain locked shut).

How much isolation do you need (in decibels)? There's conflicting signals here... on the one hand it seems you are aiming for good isolation, on the other it seems that isolation is not a top priority.

- Soffit mount my Mackie HR824 monitors

Yes, but carefully... those have passive re-radiators on the back, which is sort of like having a rear bass reflex port. It's not a huge issue to deal with but it does need to be taken into account in the soffit design.

- Absorption across the back wall

I would suggest either superchunks plus absorption in between, or hangers across the entire rear wall, of varying depth: much deeper in the corners, then less deep across the middle. You have plenty of extra length, and with a long thin room like that you will need stacks of real wall treatment, so I'd make the most of it and go for deeeep hangers.

- Possibly a cloud, if required

Required it will be! Doubt there is not. But space there also is not.... (Excuse my lousy Yoda...) With such a low ceiling, you won't have enough room to hang a suitable hard-backed, angled cloud.

1. With this limited width and limited height, is this the best design option?

The best design option os not to limit the height!

2. With these limitations on dimensions, is this going to work at all?

I would suggest looking for a better ratio by shortenint the room, rather than by lowering the ceiling. A good, chunk, hard-backed cloud can help deal with vertical modal issues to a certain extent, and so can good ceiling design, especially if it is inside-out. You could, for example, vary the height of your ceiling modules, so some have a higher acoustic ceiling than others, without changing the line of the visible ceiling.

- Stuart -

Hi
Thanks for your replies Stuart.

- Walls are plasterboard glued to breezeblock
Strange! Why would somebody glue plaster board to masonry? Why not just plaster the wall directly?

This seems to be quite standard practice in modern homes in the UK, called Dot n Dab: https://www.google.co.uk/webhp?sourceid ... asterboard

Quote:
- Build a new inside-out ceiling on the new stud wall frame, with 2 layers of 19mm plasterboard on the outside.
Inside out ceiling? Have you looked into how you will do that? Have you calculated the dimensions that you will need for your new joists, based on the load they will be carrying?

Quote:
2. With these limitations on dimensions, is this going to work at all?
I would suggest looking for a better ratio by shortenint the room, rather than by lowering the ceiling. A good, chunk, hard-backed cloud can help deal with vertical modal issues to a certain extent, and so can good ceiling design, especially if it is inside-out. You could, for example, vary the height of your ceiling modules, so some have a higher acoustic ceiling than others, without changing the line of the visible ceiling.

I had looked at the room modes from these dimensions and they weren't "too bad" (given what I have to start with) but I'm happy to revise these following your advice about maintaining ceiling height. Given the difficulties in getting plasterboard on top of the joists, if I raise the ceiling it will end up being normal construction rather than inside out.

Without dismantling the ceiling, assuming the joists there are 170mm tall (I know it's an assumption), I reckon I could build an interleaved normal (not inside out) ceiling with internal height of 2.31m. This allows for two layers of 19mm plasterboard underneath the current floor above, a 5cm air gap, 145mm joists for the new ceiling (from this table: https://www.broxbourne.gov.uk/resident- ... span-guide) and 2 layers of 19mm plasterboard for the new internal ceiling.

I think the maximum inside width could be 2.25m. The best I can get from the Bob Golds calculator gives a length of 4.2m. (see attachment at the bottom).

Quote:
This design allows for a 5cm air gab between the leaves,
That's very thin! Did you do the math? What MSM frequency does that give you? I suspect it will be rather high with such a thin cavity, despite the massive concrete block wall as the outer leaf... I try to never go less than about 10cm on the air gaps, as that just pushes the frequency too high, and damages low frequency isolation..

I did do the maths, and the frequency is 39.5Hz (using 100Kg/m2 for the breezeblock). See comments below regarding main isolation requirements.

Quote:
- I would like to keep some natural light, so I'm planning to put a window between the soffits which would get light from the glass patio door (which will always remain locked shut).
How much isolation do you need (in decibels)? There's conflicting signals here... on the one hand it seems you are aiming for good isolation, on the other it seems that isolation is not a top priority.

Fair point. Perhaps I should start with a statement of the problem: The room has issues with sound from above and from the front through the sliding patio door to car port. Isolation issues with any of the other walls are not a great concern as all our other living space is on the floors above, and this room is on the side of the house with no immediate neighbours.

My aims:
- produce a room that sounds good for mixing
- minimise sound going through the ceiling above and patio door to the front

I assumed, perhaps incorrectly, that building a room in room structure with a new ceiling on the new wall frame would provide me the isolation from above and from the patio door. This is why I wasn't too concerned about the small 5cm air gap around the walls.

Question:
- is a room in a room the best way to deal with these problems? If so, I'll rebuild my sketchup model with the dimensions above and hangers across the back wall. I may even look to see if I can squeeze a storage space in the 'left over' bit of length
- if not, what could be a better approach?
- worst case I'll return to my wooden garden building from scratch idea!

Thanks
Gareth

Given the difficulties in getting plasterboard on top of the joists,

It's actually not hard to do.... if you build the ceiling as a "backbone" of larger joists, more widely spaced, and put individual "modules" in the gaps... build the modules on the floor, 2x4 framing with the drywall on top, then raise them up, bolt and seal...

I reckon I could build an interleaved normal (not inside out)

You'll never be able to get your height as good like that, as you can with inside-out. You can have the inner-leaf drywall just a cm or so lower than the existing joists... Practically touching... You should be able to get your ceiling height up to about 236cm, with a bit of luck. Maybe 235.

I did do the maths, and the frequency is 39.5Hz

So you won't have any useful isolation until 56 Hz, and only good isolation above about 80 Hz... Hope you don't plan to play drums, bass, keyboards, or electric guitar in there! Piccolo and alto-soprano singers should be fine, though....

iolation issues with any of the other walls are not a great concern as all our other living space is on the floors above, and this room is on the side of the house with no immediate neighbours.

You canot isolate a room in only one or "some" directions! That0s a physical impossibility. It is "all or nothing" Isolation is a system that affects the entire room and everything around it to the exact same extent. At least, for airborne sound it is. Impact sound is not quite the same, but not far off. So you can't have a room where 5 sides isolate to 40 dB and the fifth side isolates to 60 dB: What you get is a room where all six sides isolate to roughly 40 dB...

- minimise sound going through the ceiling above and patio door to the front

Sorry! Can't happen. That's like saying "I want to build a fish-tank that minimizes water leakage to the front and left, but I don't care how much spills out the other sides." Can you build an aquarium that has glass in only the front and the left side, and expect it to hold water? It will only hold as much water as the leakiest side allows... Same with your room.

- produce a room that sounds good for mixing

ITU BS.1116-2 That's your goal.

I assumed, perhaps incorrectly, that building a room in room structure with a new ceiling on the new wall frame would provide me the isolation from above and from the patio door. This is why I wasn't too concerned about the small 5cm air gap around the walls.

Sorry to put it sarcastically, but: "I assumed that the glass on the front and left of the aquarium would provide me with leak protection to the front and the left, hence I wasn't too concerned about using carpet around the other sides of the aquarium, instead of glass...".

- is a room in a room the best way to deal with these problems?

Yes! Absolutely! More correctly, the best approach is fully-decoupled 2-leaf MSM isolation, but one of the best ways to do that is, indeed, with a "room in a room". That said, your diagram does seem to be showing that already! As long as you can get consistent mass around the outer leaf (or at least, sufficient mass in the weakest areas) plus good air-tight seals, and the same on the inner leaf, then you are good.

The best I can get from the Bob Golds calculator gives a length of 4.2m. (see attachment at the bottom).

Ummm.... did you notice this part? :

Computed Information:
Room Ratio: 1 : 1.02 : 1.86
1.1w / h < l / h < ((4.5w / h) 4): Fail
l < 3h & w < 3h: Pass
no integer multiple within 5%: Fail (ratio2 = ratio1 * 1)

Nearest Known Ratio:
24) A worst case scenario calculated by RPG" 1 : 1.075 : 1.868

It's not so good, I'm afraid.



- Stuart -

Thanks Stuart.

All points about isolation and dimensions noted and I had of course seen the 'fail' notes on the Bob Golds calculator.

I think the conclusion drawn from this foray/experiment, is that this room is just not going to work as a studio because of its limited width dimension which is the same as the height.

So, I shall return to my garden studio build plan and just keep saving to get the budget to what it needs to be: http://johnlsayers.com/phpBB2/viewtopic.php?f=1&t=20809

It's all part of the learning curve!

After even more research, planning, talking to builders, calculating and not to mention talking to my wife I have a revised plan that I've made a start on.

The garden option is too expensive and too difficult due to the access (or lack of) to my garden. My revised plan is a phased approach to the ground floor room, because we're not sure how long we'll have this house it seems daft to spend too much and do building works that would render the house hard(er) to sell. Isolation is the lower of my priorities compared to the sound of the room.

So, the plan is to remove the patio door on my room and build a new solid wall there with a decent fully glazed UPVC front door to allow light and access to the room. I will then build soffits and install treatment in the form of super chunks across ceiling/wall corners, rear wall corners and add whatever other absorption necessary.

The dimensions will end up as 2.43m wide, 2.4m high and 5.1m long, due to making the new front wall thicker. This gets the room to the 'best' ratios it can be, according to the bobgolds.com calculator. Not ideal, but this is what I have to work with. I'm working on the design and talking to Stuart offline.

So far all I've done is take down a short bit of partition wall, and rebuild it to allow the door to move further away from the wall to allow for super chunks in the corners. It's my first bit of house wall building and it's going OK so far!
So that's one layer of plasterboard up on the 'outside' of the wall, need to add another layer and caulk then insulation and plasterboard on the studio side. Now the doorway is now over 1m from the wall, where before it was about 30cm. Much more useful.

All good fun.
Gareth

Hi

I've spent more time working on my sketchup model and have got a working design to go forward with. Due to the long thin dimensions of the room combined with wanting a window (well a fully glazed door) to the front, the soffit angles have ended up at 28 degrees. I'm pretty pleased I've got this far with my design.

Sketchup models:
Original Room https://www.dropbox.com/s/gkcshliz85acx ... s.skp?dl=0
Working plan https://www.dropbox.com/s/dlc4gkd80ex9t ... n.skp?dl=0

Air
Importantly I've got my air system sorted. I've gone for a 4" heat recovery unit that will be mounted in the front wall, between leaves, above the doorway with an access hatch made to get to it for servicing. This will connect via four silencer boxes each opening to 6" and lined with the correct (hopefully, it's expensive!) 1" duct liner foam. The HRV has a fan in it with two speeds and I'll need it on full speed to overcome the static pressure. I had a helpful discussion with the supplier where we concluded that if once installed I don't get enough air movement that I could add an inline or wall mounted fan and switch off the one in the unit, so that's what I'm going to do.
I'm really pleased with having the HRVU as one of my main concerns with this room is temperature, so to supplement the central heating radiator I will be installing an electric radiator to maintain background heat. The HRVU has a condensation drain and I have a portable dehumidifier that I can leave on when I'm not recording.

Progress to date, with pictures:
- finished partition wall and doorway
- painting the back half of the room
- starting to build the new wall to the front
- tessellating and cutting MDF for four silencer boxes and two speaker boxes for the soffit wall. I'm so glad I have a friend with a table saw, as they are very accurate and straight cuts!
- test built one silencer
- built one speaker box

This week (evenings) I will complete the inner wall and paint the rest of the room, ready for laminate floor being fitted on Friday (the only time the installer has available). Before he comes I will have put a piece of frame in across the floor for the soffit walls in order that a) they are mounted to the concrete for stability, and b) the laminate floor neatly ends at the soffit wall.

When reviewing my plans and work please remember that part of my design is to allow the room to be returned to a 'normal' house room without too much difficulty - i.e. remove treatment, dismantle soffit wall and make good the walls.

Unfortunately I'm getting close to busy season for my band where I start to loose all my weekends. My new external door is being delivered in 10 days so I'll be taking out the patio door and wall, and fitting the new door, silencers, HRVU etc in a couple of days with my brother in law. Unfortunately changing the door/window requires building regulation approval in the UK so hopefully the inspector will be happy with my thermal uprating!

Finally, unfortunately my soffit walls will be concealing the small consumer unit for the room, so I will be designing in a removable access door for the top 450mm of the soffit wall. Unusual I know, but I'm hopeful it will work.

Pictures follow... We allowed 2mm on the height of the speaker so that I can get it in and out to set the switches on the back. I'm thinking that once this is sorted, I'll add 2mm of rubber or similar to the top of the box to hold the speaker tight.

That's it for now!!

Gareth

Just a few random comments:

my soffit walls will be concealing the small consumer unit for the room,

Is that legal? Are you allowed to cover your electrical panel in the UK?

Why is there so much paint on my hand?

Maybe because you aren't wearing gloves?

Test fit silencer from the back

Sadly, the spider doesn't seem to have survived the test....

We allowed 2mm on the height of the speaker so that I can get it in and out to set the switches on the back. I'm thinking that once this is sorted, I'll add 2mm of rubber or similar to the top of the box to hold the speaker tight.

Ummmmm.... Where's the ventilation system that will cool that speaker? I do not see any vent slots in the enclosure box, nor any provision for air going into/out of the soffit. That's a 150 watt speaker, and no more than about 1 watt of acoustic power is coming out of those cones, so the other 149 must be heat, inside the speaker cabinet...

The manual for the HR824 clearly says: "Do not block any ventilation openings". On page 6 it also says: "When the monitor is operated at high sound pressure levels, a fair bit of heat can be generated by the internal power amplifiers. These internal amplifiers are part of the rear panel electronics assembly. To ensure adequate ventilation, the rear of the monitor should be placed at least three inches away from the wall". I don't see a 3" ventilated air gap at the rear of your enclosure boxes.

Also, the HR824 has a passive rear radiator, which is sort of similar to a bass reflex port in terms of what it does (extending bass response), but rather different in how it does that. You'll need to deal with that inside the enclosure box, and that's a bit more complex than for a reflex port, since all those vents on the rear are for both the passive radiator and also for amplifier cooling.

So this is not going to be a good day for you, and you certainly wont want to hear thins, but your soffit design needs some major modifications to be viable. I would suggest that you halt your soffit build right where it is, and don't do any more until you have completely re-designed them.

Sorry I don't have better news for you!


- Stuart -

Thanks Stuart.

I'm not sure that our regulations do allow consumer units to be concealed, but they are allowed to be in cupboards, for example, hence why I will be building some kind of door into the top of the soffit to access the consumer unit. This element of the build will not happen until the building inspector has approved my changed door.

Regarding the speaker boxes, indeed they do not have ventilation holes, but only because I've not cut them yet. I plan to follow John's design of a slot in the top and bottom of the speaker box allowing for air flow.

The speakers are 310mm deep including the amp on the back, or 267mm deep to the wooden frame. The internal depth of the box is 332mm and I’d allowed for the speaker to protrude 18mm because that’ll be the thickness of my oak venerred MDF soffit front. This gives a gap of 40mm between the back of the amp and the back of the box.

So, I could pull the speaker another 18mm forward because my soffit front will be 18mm plywood with 18mm veneered MDF on top of it, so rather than mounting my MDF speaker box flush with the front of the plywood I’ll mount it to the back of the plywood. This would give a gap of 58mm, which is closer to the recommended 3”. I’m not sure I could go much further without having to move the soffit wall further into the room.

Regarding the passive radiator, I've seen others soffit mount the Mackie's - what needs to be different compared to a 'normal' soffit mount design for a speaker without a passive radiator? I couldn't see anything in their threads to make this clear... for example this one http://www.johnlsayers.com/phpBB2/viewt ... f=2&t=8205

Thanks!

Gareth

I'm not sure that our regulations do allow consumer units to be concealed, but they are allowed to be in cupboards, for example, hence why I will be building some kind of door into the top of the soffit to access the consumer unit. This element of the build will not happen until the building inspector has approved my changed door

Smart move! As long as he says it's OK, then you are fine.

I plan to follow John's design of a slot in the top and bottom of the speaker box allowing for air flow.

That's fine for cooling flow, provided that you also allow the 3" depth at the back, as recommended by Mackie, but you still need to deal with the rear radiator.

... the speaker to protrude 18mm because that’ll be the thickness of my oak venerred MDF soffit front.

Only 18mm of MDF? That's not nearly enough. The front baffle of a soffit needs to be very massive, and very rigid. Mine often end up 40 or even 50mm thick, built up from various layers. And the baffle also needs to be rigidly braced with massive, closely spaced framing inside. You don't show your framing, so I can't say if it is good or not.

This gives a gap of 40mm between the back of the amp and the back of the box.

3" is 76mm.... plus another couple of inches for the damping...

my soffit front will be 18mm plywood with 18mm veneered MDF on top of it,

Better than just 18, yes, but I'd still shoot for more.

This would give a gap of 58mm, which is closer to the recommended 3”

58mm is only a bit more than 2". You are still about 20mm short, and that's just for the cooling vent. I would allow a total of about 130mm (5") if that were my soffit. That would give me 3" of cooling depth plus 2" of damping.

I’m not sure I could go much further without having to move the soffit wall further into the room.

Bingo! There's your answer....

Regarding the passive radiator, I've seen others soffit mount the Mackie's - what needs to be different compared to a 'normal' soffit mount design for a speaker without a passive radiator?

That radiator moves a lot of air at very low frequencies. So it needs a large volume of emptiness around it, with acoustic damping in it. If you box it up in a tight space, you create a high impedance "resistance" for the radiator diaphragm, so it will not work the way it was supposed to: in simple terms, it will be trying to compress and "vacuum" the air trapped in the back of the box, or trying to "pump" it in and out, if you prefer to think of it that way. It will be working against a spring (the air trapped in the box). So you need a large empty volume around it, at least equivalent to the interior volume of the cabinet itself, and there needs to be acoustic damping material in there to help dissipate that energy. But this implies a conflict: You can't fill the "empty volume" completely with damping material, as you also need the cooling flow! Hence, 3" depth for cooling, as recommended by Mackie, plus at least 2" of damping behind that, plus very large, wide slots on the bottom, rear an sides of your box for both cooling and to provide low impedance coupling to the larger cavity around the enclosure box, with more damping in there.

I couldn't see anything in their threads to make this clear... for example this one

He doesn't say much about the dimensions of his enclosure box, or cooling, or damping, and I wasn't around on the forum back then to ask, so I really don't know what he did. Giles does bring up the subject towards the end, when someone challenged the viability of soffit-mounting those speakers (claiming it is impossible, blah blah blah), but Giles correctly responded that it can be done as long as the necessary precautions are taken. I can only assume that the OP on that thread did, in fact, take those precautions. Giles is a speaker guy, and knows what he is talking about. Pity he's not still around on the forum!

Anyway, I use a very different method for soffit mounting for my customers, which has taken me years to develop and refine, so I don't go sharing it in public, but suffice it to say that there's way more than enough cooling and damping space with the way I do it, even for very large speakers. I'm not sure if you have seen the Studio 3 thread ( http://www.johnlsayers.com/phpBB2/viewt ... =2&t=20471 ) but that's a good example. Those speakers are Eve Audio SC-407's, which are rather large, rather powerful, and have a huge bass reflex port on the back. I briefly discussed this with the chief engineer at Eve Audio (great people, by the way), and he gave his OK for this method, even though they don't advertise it much, plus a tip on damping. As you can see from the results, it worked out pretty well!

I would still suggest that you re-think your soffits, and re-design them with enough depth and volume, and enough rigidity and mass.

Another thing I noticed from your diagrams and models, is that the speaker geometry is not optimal: you have the speaker axes intersecting in the middle of your head, by the looks of it...


- Stuart -

Thanks Stuart for a very helpful reply.

I've made a sketchup file with a design for a speaker box following your suggestion of 130mm behind the speaker including air gap and dampening.

https://www.dropbox.com/s/bvt2aod2kx5do ... x.skp?dl=0

I have made two alternative back panel options: one is sealed and another has a large hole, as you suggested " very large, wide slots on the bottom, rear an sides of your box for both cooling and to provide low impedance coupling to the larger cavity around the enclosure box, with more damping in there."
This led me to question whether a back to the box is necessary at all, given that it will be within a cavity filled with rock wool (save for the passage for hot air from the top of the speaker box)?

I've dropped this into my sketch for the room, at floor level (for the moment) to be able to see the geometry lines better - I can confirm that currently they intersect behind the listening position.
https://www.dropbox.com/s/dlc4gkd80ex9t ... n.skp?dl=0

It looks like I need to bring the soffit walls further into the room, which will mean an adjustment to the angle. This isn't a problem but if I don't need a back on the box, I might not have to.

Thanks

Gareth

Much better!

This led me to question whether a back to the box is necessary at all, given that it will be within a cavity filled with rock wool (save for the passage for hot air from the top of the speaker box)?

Very much necessary! It gives rigidity to the box. It's the only thing keeping the sides, bottom and top mutually parallel and square. So it's not really doing that much acoustically, but it sure is structurally. It can have a hole in it, for sure,definitely! Or perhaps a couple of smaller holes instead of one large one, but it does need to still provide good lateral rigidity. The way you show it should work fine.

I would suggest putting some type of mesh across the box interior, to keep your rear damping in place, so it can't fall forward and block the airflow. Maybe chicken mesh, or plastic garden mesh. Even a couple of strand of string, plastic strapping, or wire would help.

I've dropped this into my sketch for the room, at floor level (for the moment) to be able to see the geometry lines better - I can confirm that currently they intersect behind the listening position

A couple of things with that: you want the intersect much further back behind your head, ideally 12" to 18" back, but you also need to be careful that the toe-in angle is not too shallow. And right now, your speakers are too close to being in the corners of the room: you don't want them lined up with the corners, as seen from your head. So you will need to fiddle a bit, as all three of the above are in conflict! You need your speakers closer together, further apart, angled in more, angled in less, further into the room, and further back! Somehow you need to tweak and poke at all of those to come up with a good compromise... It's a very small, narrow room, so it's physically impossible to get everything right... you just have to play around until you find a reasonable balance between the conflicting needs.

So, to prioritize:

1. Don't let your angle get less than about 20°, absolute minimum, and preferably more like 25°.
2. Do get the speakers out of the room corners, closer to the middle of the room.
3. Do bring the speakers and soffit more into the room (towards the mix position), so you can fit in the extra depth for the enclosure box, inside the soffits.
4. Least important, but still on the list of priorities; try to get the axis intercept a few inches behind your head.

Also, don't forget to beef up the soffit structure, and consider making your front baffle even thicker / more massive.

- Stuart -

Thanks again. I've followed your advice - the speakers are away from the corner (a bit!), and slightly further into the room. The axes intersect 30cm behind the head.

This gives an angle of 25 degrees, and I'm worried that any shallower would bring the speakers even closer to the edge of the soffit, making the soffit ineffective.
Sketchup file: https://www.dropbox.com/s/lfboce5imm2f2 ... s.skp?dl=0

I hope this is a goer for the angle, so I can then work on the concept for framing etc. I will heed your advice for the chicken wire or similar to keep the damping in place in the boxes.

As an aside, last coat of paint tonight, floor on 3/4 of the room fitted friday (the rest will go in once soffits built)

Thanks

Gareth

So it's been a few weeks and I've been busy every spare evening I have, around day job and function band commitments. Thank god I've no studio work on at the moment...

Anyway, in summary, I painted the room and had laminate installed (to most of it - rest to be finished once soffits built). I finished my silencers and lined with 1" duct liner (not cheap).


My brother in law and I spent two days taking out the old patio door and replacing. You'll see from the pictures how rubbish the wall was that held the patio door in place: 9mm plasterboard on the inside, and 9mm MDF on the outside. Several parts of the 2x4 frame weren't even nailed or screwed together!

The build process is set out in the next post, as I ran out of attachment space...

Thanks

Gareth

Continued from previous post...

We then built a new outside wall, installed my ventilation system with heat recovery unit, and the new UPVC normal width glazed door. There's 10m of ducting inside that wall!

I even remembered to put a power cable into the wall in case I need to add a supplementary extractor fan, however, with the HRV on full quite a lot of air comes into the room through the air inlet, so I'm hoping that won't be necessary. Even on slow speed I can feel the air movement at the duct inlet into the room.

We tried our best to minimise mechanical connection between the inside wall leaf and the outside wall, so you'll see in the pictures that the shelf for the HRV is cantilevered off the outside wall frame and doesn't touch the inside wall frame, and similarly the framing and plasterboard for the 'corridor' and access hatch for the HRV between the two leaves is connected to the inside frame but doesn't actually touch the outside frame or door. This might be wasted because both walls connect to the ceiling, but it seemed logical to do our best to minimise it. Unfortunately the flexible ducting does bridge the walls, but hopefully it's not too detrimental. The net result is that the vibration from the HRV is much louder on the outside wall leaf than the inside, so I think it has been worth doing.

I then had to wait a nerve racking week for the building inspector to come back out to check off the work. This was nerve racking because when he came he started asking lots of questions about how fire proof the door was, because it opened on to a car port. He then started looking at the rest of the construction of the car port - wooden ceiling, normal (not fire rated) window to the hallway etc and became more concerned. I attribute much of this to sensitivity over fire because of the very recent london building that burned down - a terrible situation. Seemingly our car port doesn't meet regulation, most likely because in the UK building companies can hire external contractors as inspectors rather than having to use the council ones, like I did. We concluded that the best way around it all was to re-designate the carport as an outside store and never park a car there (we don't, we use it for our teardrop trailer caravan).

Anyway, the door passed inspection! Great news for DIYers like me. Even better news is that our installation is a load better than the original, with two layers of 18mm plasterboard on the inside, 2 layers of 18mm plywood on the outside, insulation, plenty of acoustic sealant and much smaller gaps between door and wall etc (hardly any, and again filled with sealant), with the end result that the noise from outside is much quieter, so a successful outcome!!

Since then I've framed and insulated my back wall absorber - 60cm in the corners and 20cm in the middle of the wall, with RWA45 rock wool. I've also started my ceiling corner absorbers, 40cm x 40cm x 56cm, and started covering with a lovely purple cara material.

Whilst awaiting the electrician to install my fused spurs for electric radiator, HRV and outside power socket, I've booked tomorrow and Monday off work to frame my soffits and get as much of that finished as possible, using the speaker box design above.

Pictures below of the work described above, and one of my dog for luck.

Thanks
Gareth