CR Treatment and Tuning---The home stretch!!

[Stadank0]

Looks like the decay is steadily climbing. Any idea about the dip around 171 hz...It seems to be getting worse. Not alarmed. Just wondering what you think of it.

[Stadank0]

I know I'm pushing my luck here but any chance of a weekend project to keep me busy?

All in good fun...

[diedushka]

F=54.59 * SQRT (height-of-hole / (height-of-volume * depth-of-volume * effective-neck-depth) ) * 1000

All of those measured in millimeters.

The last term, "Effective-neck-depth" refers to the thickness of the slats plus a "mouth correction factor". Remember I mentioned the slug of air trapped inside the slot? Well, the slug that moves in and out is actually bigger than the slot: it includes some air on either end, just outside the slot, so the "effective depth" of the slot is the thickness of the wood plus 20%, because it extends about 10% more in either direction.

What a killer explanation Thanks! Im still far from building acoustic treatment, but boy.. Will this thread help me with engaging that! I guess ill need some private counseling when the measurements start and i will actually start designing the things

For this we used "pink fluffy" insulation, which Frank pulled apart even further with his fingers, to make it very light. 701 would have worked, but the thinnest you can get is 1" thick, and that's too much for here.

My thought was that it had to be around 5 milimeters thick, correct? And you cant glue the insulation to the slats very firmly to not compress it too hard.

But it won't be the deepest dips that I look for: it will be the modes that ring the longest (decay the slowest). Dips MIGHT be modal, but they might also be SBIR, or reflections. I don't go after dips at this stage, usually. If it turns out that Im' left with some modal dips still at a later stage, I might go hunting for them in other parts of the room to see how bad they are, then decide what I'm going to do about it.

Indeed. I havent thought about that. One thought: I am designing a large desk in my studio that will hold equipment and some gear. I did design it as low profile as possible but I know for sure it will still present some acoustical problems. I designed everything with smooth angles and with comaprtmens along these angles so i would later be able to add insulation or other treatment in these if i need. Do you often treat the front of studio equipment to prevent reflections from its surfaces? ANd how thick do you treat them if you do?

One word of warning: It sounds real easy to do, but in reality it is not easy at all! I do not encourage first-time studio builders to go this route: designing and using tuned low frequency devices is hard, even for experts. I much more strongly recommend using only absorption for first-time studio builders, since it is so much simpler, and really hard to get it wrong!

I see why you reccomend that But I will choose the hard way if need be With some help here, some dedicated time on reading and careful craftmanship - I think ill be able to reach the goal of at least a good sounding studio

However, this fact does not seem to stop home studio builders from splattering diffusers all over their rear walls of their small rooms! You see that EVERYWHERE! Ignorant people doing silly things to their studios. The problem is that they see pictures of pro-level studios with diffusers on the rear wall and think "That looks cool! If they need those thingies, then I need them too!" So they go buy them, without realizing what damage they are doing. And of course, the manufacturers don't bother telling them that it's a bad idea! They just want to sell more diffusers, so they don't care who buys them....

Tell me about it.. Its like guys just put any type of fu*** up weird looking thing in front or behind them just because it 'looks cool'. With your point in mind - it only looks cool if you have no fucking idea what youre doing )

It's complex to tune a room, when you want it to be very accurate, as Frank does. You can't just hang a few things on the walls because you saw them in a photo of a high-end studio, and figured you need them too! For high precision, it's a long process, done one step at a time. For someone like John, who has a lot more experience than I do(!), he can skip some of those steps by just using his knowledge and expertise gained from many, many past studios. But I like to test every step, to make sure it is working as expected, before going on to the next step. Maybe when I have as much experience as John does, I'll be able to do the same! Until them, I'm a "repeat tester"... .)

What range of accuracy are you aiming at exactly with Franks room?

Especially those curved log siding ones! They would be very good for avoiding specular reflections from flat planks.

Great idea! But these usually come in very fixed widths and depths. I assume knowing how wide and deep they are you would differentiate the distances between them to get the effect you need?


All in all - a great thread, Stuart Thanks for sharing you experience and know-how! It is very much appreciated

You have a good weekend
Cheers.

[Soundman2020]

Im still far from building acoustic treatment, but boy.. Will this thread help me with engaging that! I guess ill need some private counseling when the measurements start and i will actually start designing the things

It would be good if you start posting your initial designs in your thread, so we can get an idea of where are right now, and where you want to go. Sometimes it-s good to have some extra pairs of eyes "looking over your shoulders" to see what you are doing, and maybe notice things you hadn't seen.

My thought was that it had to be around 5 milimeters thick, correct?

It's about half an inch, roughly 12mm. Thick enough to rob the slug of energy on each pass, but not so thick as to over-damp it. Going back to the "kid on a swing" analogy: you do want him dragging his feet through the water, and maybe even his ankles too, but you don't want the water up to his waist!

And you cant glue the insulation to the slats very firmly to not compress it too hard.

You can, as long as you are careful, and assuming that the slats are wide enough: just a thin bead of glue up the middle of each slat, but taking care to not get glue anywhere near where the air will be moving. Another option is to use something like chicken wire stapled to the side walls, and shaped to hold the insulation in place with just light pressure.

[quote I am designing a large desk in my studio that will hold equipment and some gear. I did design it as low profile as possible but I know for sure it will still present some acoustical problems. I designed everything with smooth angles [/quote]By careful use of ray-tracing, you can make your desk do the same as the RFZ concept, and redirect reflections away from your head.

Do you often treat the front of studio equipment to prevent reflections from its surfaces? And how thick do you treat them if you do?

Where necessary, I do use insulation on the rear side of the entire desk. Studio Three, for example, has about 4" of 703 on the front: I don't recall exactly... it might be only 2". But it was necessary to deal with some reflections from there that were getting reflected a second time from the soffits, and getting back to the mix position. There's also insulation on top of the wing surfaces, for the same reason: It's fairly dense and covered with thin carpet, so there's a reasonably solid working surface on those, at least for putting down your coffee mug or pizza plate...

What range of accuracy are you aiming at exactly with Franks room?

That depends on him! We can take it as far as he wants to go until we hit the physical limitations of the room and equipment, if he wants to do that. But there's a point of "diminishing returns", where each successive tweak makes smaller and smaller changes to the response. You get to the situation where you can no longer hear any change at all, even though the graphs are getting flatter and smoother: once you pass that milestone, there's not much point in going further, except for "bragging rights". If the acoustic response fully meets ITU BS.1116-3 specs (or EBU TECH-3276 specs, if you prefer), and you can't hear further improvements, then there's no more acoustical reason or psycho-acoustical reason to carry on... unless you just want to be able to say that your room response is perfect! It takes time to do each new tweak, and of course "time is money" ... in this case Frank's money, so when he runs out of money, then his room is done!

Great idea! But these usually come in very fixed widths and depths. I assume knowing how wide and deep they are you would differentiate the distances between them to get the effect you need?

Right, but what we are building now with Frank is not a tuned slot wall. It looks like it, but it is not sealed, and the gaps are far too wide to be tuned. Yes, it is "tuned" in a different sense: the width of each slat is designed to reflect a certain frequency range, and the gaps between them allow lower frequencies through, to be absorbed. So it is tuned in that sense, but not as a Helmholtz device.

- Stuart -

[Soundman2020]

I know I'm pushing my luck here but any chance of a weekend project to keep me busy?

All in good fun...

We are getting too many specular reflections like this, with those flat planks, so I'm thinking of taking this in an entirely new direction.... if you are up for it! The construction gets to be a little complex, and a little boring at the same time, but I think it's the right approach for the rest of the side walls. It will also look really cool!

The basic plan is this: another slotted poly, but with very different design: a whole bunch of 1x1s or maybe 2x2s, or 2x1s, or something like that, standing up vertically, but with the front edge rounded (or beveled), and built similar to the huge rear monsters that we already did in the rear corner, along a poly-cylindrical path, shaped like a slight "wave" coming out of the wall.

It's hard to describe in words, but this is the basic concept:

poly-slat-SML.jpg

However, yours would not be that deep, and would not follow that circular pattern: it would be a reverse catenary curve, that starts out smooth and tangential to the wall, then bulges out a bit at an increasing angle, then curves back in again, ending up tangential again. You don't have much space to spare inside the room, so I can't bring it out very much, but there's some room to do that. It will be a smooth organic curve, not a sharp angled curve.

Acoustically, this would be the best option, since it provides reflection and diffusion at the same time, without being specular. We can get the needed increase in mids and highs, and probably also take another bight out of the SBIR, with the curve itself.

The curve that the slats would be built along, would be more like this:

BUILD-30th-construction--slotted-poly-diffuser-completed--2014-07-23-photo2-SML-ENH.JPG

What do you think?

It's slower to design, slower to build (boring, yes), but I reckon it's your best bet. And it will look rather nice...

- Stuart -

[Stadank0]

I suppose we should do what's best for the room... I say okay.. I'm not sure exactly what we're going to end up with of course but I trust you on this one.. what needs to happen next?

[Stadank0]

So I would have to round off the faces of each board? I'm guessing the only way I could do that is by sanding..That sounds painstakingly horrible. I'll have to figure out a way to do it....hmmm.

Flat boards can't follow the curve? Faces definitely need to be curved? I'll try to figure something out..things always seems harder at first glance.

If we could do beveled, that would be good. That's a no brainer on the table saw...

Also, I can get 1x2 boards in 8' for cheap. Would like to go that route if we could. So it looks like my vote is beveled 1x2 boards!

[Soundman2020]

So I would have to round off the faces of each board? I'm guessing the only way I could do that is by sanding..That sounds painstakingly horrible.

It's MUCH easier with a router!

half-round-router-bit-SML-ENH.jpg

half-round-plank-end-bull-nose-SML.jpg

Use a half-round router bit, sometimes also called a "bull-nose" bit.

Another option is to use a quarter-round bit on both edges, and leave a small flat surface between:

quarter-round-router-bit-and-plank-CRP.jpg

Or maybe even something like this:

louver-router-bit-and-plank.SML.jpg

There's a huge variety of router bits out there, that can be used creatively to get rounded profiles on the end of the wood.

Flat boards can't follow the curve? Faces definitely need to be curved?

Yes, flat boards can follow the curve, but that's not the issue: I'm trying to avoid specular reflections in general, and get better diffusion too. This is the concept:

slatted-poly-mastering.jpg

That's from a mastering studio that I designed a while back, currently under construction. So no photos yet of the finished product. But that's basically just 1" wide lumber routed with either a 1" bull-nose bit, or routed twice with a quarter-round bit (once on each edge).

That gives rounded surfaces on the front of a rounded surface, so no specular reflections at all. Just overall reflection, with scattering (you can't really call it "diffusion", technically, but it's very similar). I might go with slightly wider slats that have a bit of flat in between the two curve edges: not sure yet. I just wanted to get your OK for the concept.

- Stuart -

[Stadank0]

Of course, what was I thinking...I tell ya...first glance and all.Should have thought of that.

So embarrassing

Still, if we can work with 1x2's that would be great for ease of access and price. They're furing strips. I used them on the diffusers in the LR.

I'm guessing that I would shape ribs for the wall contour. I would then attach the boards to the contour and wallah! We have a curvy wall. I did the contour on the LR absorbers by rough cutting then sanding the shape in on a belt sander with a 1" wide strip. I can get concave curves with that for sure.

Actually drawing the complex curve line on the wood ribs will be the trickiest part, but I'll figure that out. Doesn't seem like it will be too boring. Maybe it will boring to model it in Sketchup?

[Soundman2020]

if we can work with 1x2's that would be great for ease of access and price.

1x2 nominal? Actual dimensions 3/4 x 1 1/2"? Please check the real dimensions, to be certain, but that sounds like a good possibility. Rounding the edges off that with a 3/4" quarter round bit would leave a no flat in the middle, or rounding with a 1/2" quarter round bit would leave a 1/2" flat... Sounds like a good option!


- Stuart -

[Stadank0]

YEs,

3/4 x 1 1/2 actual. Always annoys me that the industry adopted that standard...can't call things what they are

Awesome though! I think we're already getting on track...

Check out the crazy wall Universal Audio did down the street in they're LR. I met the contractor who built it and he gave me a copy of construction pics back in 2015...I'm gonna be cool like them!!!

IMG_1609.jpg

[Soundman2020]

I'm gonna be cool like them!!!

Cooler, by far!

- Stuart -

[Stadank0]

How are we looking for this week?

[Soundman2020]

Working on it!


- Stuart -

[Stadank0]

If it saves you time I probably only need the layout line for the curve of the wall... I'll have to trace that and cut it and shape it to make the ribs which will be the shape I'm assuming.. Once you determine the radius of the board surfaces, that should just about do it for me I think.. I may not see the whole picture of course so it may be moot.