Attic Shaped Studio

[endorka]

Source of the postJust the thought of this would keep me up nights.

Indeed! I'll probably lay a 100mm wide plank of OSB along the ceiling noggins under the silencer as well, just for extra catching power

Also, today I rebuilt the stud part of that knee wall and reinforced it with noggins. It is now extremely solid. I am sure I could do chinups from it, if I were really short.

Cheers!
Jennifer

[endorka]

Emergency silencer catching OSB plank laid. Hopefully the first and only time it will be used was when it gently caught the silencer as I slid it into the bay for the install.

And here we go. In most of the way at 90°, then rotated to proper orientation once mostly in. It's propped at both ends by specific wood offcuts established during the test fit. A wooden wedge is used to trim the "roll" orientation so it is vertical. The silencer is big and the fitting tolerances into the bay small, so measuring during the test fit & getting all six axes in 3D space correct has taken a substantial amount of time.

The silencer is screwed into a noggin under the outlet to support it. A temporary OSB support is at the top to hold the position while this is being done.

Screwed into another noggin along the top. There is also a "noggin" attached to the top ears of the silencer here. This way the good shear strength of the OSB can be used to full advantage. This attaches the silencer very firmly to the stud wall, it barely moves at all even with a lot of force.

The props at this end have been removed and the silencer is floating. Fortunately the measures and fit were sufficiently accurate to line up the ducts from the filter box to the silencer and attach the flex hose.

First layer of the wall, 18mm OSB, ready to fit. This is the top half. I did it in two halves, one above the vent, the other round and under it.

Second layer of plasterboard added. Edges sealed, and electrical sockets re-attached. The placement of those looks odd, but will make sense when it comes time to build the soffits.

By listening I can tell you that the sound attenuation from these walls and silencers is sufficient. Better than the windows, which are already pretty good.

Another observation when running the fan with window trickle vents closed. I can hear no significant sound from the airflow coming through this supply vent. So presumably the low frequency noise from the exhaust silencer is related to the fan and/or the turbulant forces it enacts on the air it is moving. This knowledge is useful to inform the design of the silencer extensions that will form part of the soffits. A beefy one required on the exhaust side, no so much on the supply side.

Cheers!
Jennifer

[Starlight]

One of the amazing thing about studios, cinemas and other acoustically treated places is someone looks at a wall or a vent and has little idea of quite how much planning, measuring and labour went in to give it such a great, quiet sound.

If I was your teacher, Jennifer, you would get a 10/10 from me!

[endorka]

Thank you for the encouragement Starlight. It's good we have this forum where there are people who do recognise these things

I've done a very quick test routing of flex pipe to the rear of the room, on the opposite corner to the exhaust vent.

With the fan set to medium speed it is holding room temperature at 26°C, despite the midday sun blazing straight overhead through all that glass. This is excellent - normally it would be excruciatingly hot in those circumstances. This speed gives 6 air changes per hour, and is the "design speed". With more efficient ducting it will perform better.

A funny thing though, it has revealed some non airtight parts of the window frame, you can feel and hear air being drawn through them. The main culprit is along these seams; masking tape is sufficient to stop it.

From the Velux install manual it looks like they are something of an interference fit to the joist;

I reckon I'll be able to wedge them apart very slightly and seal with translucent caulk to make them airtight. Once the wedge is removed they clamp back together again. Hopefully this will avoid the need for a caulk bead along the internal corner.

The window gaskets are airtight apart from a couple of corners. I think I'll be able to beef the weatherstripping up there a bit without too much trouble.

When proper supply ducting with a lower static pressure is installed it will also take some of the strain away from the window seals!

Cheers,
Jennifer

[SoWhat]

Greetings Jennifer,

A usual, your attention to detail is amazing, as is the documentation of your build.

electrical sockets re-attached

Are they switched as a series? Just curious.

translucent caulk

Do you mean "transparent" ?

All the best,

Paul

[endorka]

Source of the post

electrical sockets re-attached

Are they switched as a series? Just curious.

The electrical wiring there is indeed a bit curious!

They are two sockets on the lighting circuit for that floor. The one with the round plugholes is wired to one of the switches on the light switch for the room, a 3 gang. For ambient light in the corner. Not my install, it was there when we moved in. There is another socket of the same type at the back of the room with its own independent switch, the second on the 3 gang. The other is for the ceiling lights.

The socket with the square holes is also wired to the lighting circuit, but not to one of the switches. It really should have "lights only" on the socket, I usually have a sticker with that on it. You can buy sockets with that printed on them.

The sockets on the light circuit allow 5 amps in total, whereas the ring main has several 13 amp sockets.

translucent caulk

Do you mean "transparent" ?l

You've made me think now. The tube says translucent. It comes out white, but dries to a not completely clear finish. I do actually have a tube of proper clear stuff in the collection called "Sticks Like Sh*t" - no joke. Now you mention it, I think proper clear might be better for this job. Thank you!

[Starlight]

Source of the post

Source of the post

translucent caulk

Do you mean "transparent" ?l

You've made me think now. The tube says translucent. It comes out white, but dries to a not completely clear finish.

If something is transparent then it allows light to pass through unaltered, much as a pane of glass would. Something translucent allows light to pass through but it may be diffused. Translucent seems to be the right word.

Speaking of translucent caulk, Stuart has said that any colour (including white) is better than translucent for sound isolation purposes simply because the colour pigment adds a little bit of extra mass to the caulk.

[endorka]

Source of the postSpeaking of translucent caulk, Stuart has said that any colour (including white) is better than translucent for sound isolation purposes simply because the colour pigment adds a little bit of extra mass to the caulk.

Good point - quite a lot of extra mass too, I believe. I have a figure of almost twice as dense in my head.

For those very thin cracks between the wood I'm prepared to trade off the aesthetic appearance for potential very small isolation gains, I reckon the clear will look far better than white. If the cracks were larger it would be the white, no contest.

Cheers!
Jennifer

[endorka]

The plot thickens - I just weighed new tubes of translucent & white sealant, and they were both pretty much the same. The translucent one starts out white though, it must be said. Only goes translucent when cured.

Apologies for the mess! I replaced the last meter of flex duct with 200mm diameter instead of 150mm. It almost doubles the area at the end of the hose, therefore almost halving the speed of air coming out. It will also lower the static pressure of the system so it is more efficient overall. It's behind the bass trap at the centre of the ceiling / wall corner. Having it come out at that angle seems to work well, although it might get a tiny bit drafty for a tall person singing while standing up at the back of the room.

Not well enough concealed, but no matter, this is only a temporary setup until I build the soffits and cloud.

[SoWhat]

It almost doubles the area at the end of the hose, therefore almost halving the speed of air coming out.

Amazing that it works exponentially (150 vs 200).

it might get a tiny bit drafty for a tall person singing while standing up at the back of the room.

The two tallest musicians I can think of, Tiny Tim and Ric Ocasik, are no longer with us, so I think you're safe.

[endorka]

Source of the post

It almost doubles the area at the end of the hose, therefore almost halving the speed of air coming out.

Amazing that it works exponentially (150 vs 200).

Yes! And the opposite is true too. I calculated two duct and silencer arrangements for the room, one based on 150mm and the other 125mm. Due to the big reduction in cross section in the 125mm version, the static pressure of the entire system was far higher. So much that it would have required the 150mm diameter fan anyway.

The two tallest musicians I can think of, Tiny Tim and Ric Ocasik, are no longer with us, so I think you're safe.

The tallest singer I've recorded here was 6'5" (196cm). Good singer too! Here's how the mic was;

[endorka]

A big effort now to get this part of the project finished!

Finished the plaster skim coat of the knee walls at the front and painted them. Re-attached skiring board, not entirely simple as the knee walls are now a double layer (18mm OSB + 15mm plasterboard) instead of just one layer of 12.5mm plasterboard. So one bit of skirting on each side was too short and another too long. Fortunately the offcut from the long bits filled the gap of the short ones.

I made a simple OSB plate with flange to attach the flex hose to the air supply vent. It's just temporary, eventually all this will be inside a soffit.

Cheers!
Jennifer

[endorka]

I filled the rear bass traps with light insulation. These are 600mm deep. The insulation is "Knauf Insulation Earthwool Combi-Cut Loft Floor Insulation Roll 44 170mm". There will also be another row of 1200x600mm bass traps on the sloping wall when finished.

Measurement mic placed at a very quick guesstimate of the mix position, and speakers placed roughly where they would be in soffits. The corner traps look a bit close to the speakers but there is a clear direct line of sound to the ears at the mix position.

REW tests were of course done, will post soon!

Tomorrow I'll finish building the covers for those built in bass traps and fit them.

[endorka]

I attached the covers for the builtin bass traps today. I had grown used to the visual appeal of those cupboards, so absolutely heartbreaking to cover them up, but there it is. It's all about the sound after all!

I have another row of 1200x600mm traps to attach to the sloping wall above them.
Assembly sequence for the covers. There is no insulation as such, just the fire retardant wadding (as recommended by Starlight) to cover up the interior of the traps. Covered by self coloured calico, sprayed with a fire retardant spray.

[endorka]

Time for REW measurements. Speakers positioned as above, just roughly in the area they will be when soffits are built but a bit closer to the wall. Left and right only roughly aligned for the moment.

I am not aiming for perfection with this positioning, just something decent enough to work with in the meantime. There are a couple of terrible specular reflections in the first 20ms of impulse response. Almost certainly due to wacky primary reflections going on in these corners. Soffits will solve the early one at least!

The main goal of this superdooperchunk at the rear of the room is to reduce the room mode resonances. How well does it perform? Spectrograms for left speaker without and with the superdooperchunk;

It is doing a remarkable job with even some effect down to 40Hz. It absolutely slays the secondary length mode around 60Hz. 50Hz is pretty much untouched but that is to be expected as it is the primary width mode.

The effect is more noticeable in the right speaker;

SPL before and after for left speaker. The speakers (Genelec 8030) have a low frequency cutoff of 55Hz at -3dB, so the bass will drop naturally below this. It is receiving a significant boost from the tri-corner (or 2.5 corner?) placement. I've enabled the bass rolloff on the speaker to -6dB to partially offset the corner boost.

I am absolutely delighted with these results. All the effort was worthwhile. These low frequencies are tough eggs to crack, and the effect has made a huge difference to the sound quality of playback in the room. I took a note of my first impressions when listening to reference tracks.

"First thing, drum ambience / room sound in recordings. Blatantly clearer. Second, stereo doubled guitars sound clearer and jaggier. Much improved stereo imaging - and it was good to start with. Third, the bass is more even throughout the room. Bass is more prominent, even with -6 dB roll off on speakers applied. Sounds like the bass is reaching to lower frequencies too. It is superb, so fat and clear! To be expected form tri-corner - or 2.5 corner? Will need reduced further until I can get these in soffits. Sound transmission to room below tonally as exptected - midrange resonances to room below obviously damped by insulation.