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

One other question...Do i need to go with MDF on the backing for the cloud? It adds considerable weight which makes installing it harder and a bit more dangerous.

Unfortunately, yes you do need it. That cloud is designed as "hard backed", because it needs to deal with some modal and SBIR issues in the vertical plane. The only way to do that is to put some decent mass on the top, and hang it at an angle. The good news is that the new design has some holes cut out of the MDF, and it isn't 100% coverage any more. It's not that much harder to install with the hard back on: you still have your "come-along" winches that you used to raise the inside-out walls, right? Or maybe rent a heavy-duty drywall-lifter for a day to help get them up. Or "rent" some friends using pizza and beer, and get them to help you. :) Lots of ways to skin a at. Dangerous? Yes. It's just as dangerous as raising any heavy object up over your head, but if you do it properly, taking precautions, and anchoring it correctly, then the danger is minimized. You've already done far more dangerous things, such as raising the inside-out wall sections, and even more so the inside-out ceiling modules, so you know how to do this. The only different thing here is using chains and bolts to anchor it all in place. Use the normal safety precautions and "rules of thumb" from stag rigging. In other words: everything rated for ten times the weight it will actually support, full-loop hardware (no hooks!), welded not just bent, etc. I'll give you some more pointers when the time comes, but following the safety precautions will make it no more dangerous than anything else you have done so far. And once it it is in place, it is no longer dangerous, as long as you anchored it all correctly. - Stuart -

Oh Yeah, I'm not too freaked out, Just looking for any advantage I can get when it comes down to it. You know I'll figure it out. I raised that entire ceiling and HVAC system by myself. Of course I had that awesome lift.... :wink: I do have a sheet rock lift still. Not as heavy duty, but it should work. Just wanted to know for sure so I could get my head around it while I'm moving along...Thanks. :thu: should have the slats done by late tonight or early tomorrow depending on the paint...

Should I put some center supports mid way on the slats? Thinking about possible resonance due to the span...

Should I put some center supports mid way on the slats? Thinking about possible resonance due to the span...

You can if you want, but only one, and don't make it very wide: I don't want to lose too much slot area. But those slats are really thick! An inch and a half! I don't think flexing and vibration will be an issue. Maybe put one slat up as a test, to see how sturdy it is, then decide if you need a center support. Also, I forgot to mention before, but when you put the slats in place, start from the top, going down: If the bottom slat doesn't work out to that exact dimensions, then that's fine: you can make it bigger or smaller as needed to fit over the door frame, with not too much penalty. But the top few slats are very critical in size and spacing, so start up at the ceiling and work your way down to make sure they are very accurate. - Stuart -

Oh, and don't forget to caulk EVERYTHING! That cavity must be sealed air-tight. So after you get all the framing bits in place, pull out your trusty caulking gun, and go nuts on sealing up every possible crack you see. And he ones you don't see too. I know that you already know this, but it's good to have a reminder: Helmholtz resonators only work if their cavities are sealed.... - Stuart -

Like So? :P

You beat me to it! :) :thu: I should have known you already knew all that... - Stuart -

Today's episode! Got a lot done...Spent the 3 hours getting the insulation..Traffic's always bad on that route. Got the framing and caulking done, insulation installed and slats all cut to finish size...So an 11 hour day. Couldn't get to the paint... But Still... :jammin:

Looking good, Frank! Nice workmanship, as usual! One more point: It's important that the FRONT layer of insulation (the very light-weight, soft, low density stuff) must be tight up against the slats: The principle of operation here (as in all Helmholtz resonators) is that there's a "slug" of air trapped in the slot between adjacent slats, and that slug acts like a single mass of air that moves in and out of the slot, sort of like a piston on an engine cylinder. Except that it doesn't stop when it reaches the edges of the slats: it "overshoots" a little, beyond the face of the slat, in both directions (inwards and outwards), by about 20% of the depth of the slat. It does that because it is "bouncing" on the "spring" of air that is sealed inside the cavity. That spring prevents it from moving too far out or in, but does allow it a little extra movement beyond the slot itself. The purpose of the light-weight, low-density insulation just inside, is to damp that "overshoot" motion, thus removing some energy from the slug's movement, on every single cycle of resonance. And because the slug's "overshoot" movement only goes about 20% extra (of slat thickness), the insulation MUST be in that region, right up next to the rear face of the slats. So in theory you need about 8mm thickness there to cover that 20%, which is why I specified 1/2" insulation. 1/4" wouldn't be enough (only 6mm), and 1" would be too much: it starts damping the cavity too much, beyond what it is already damped by the insulation at the back. So, right up against the back face of the slats you need thin black cloth (to hide the "ugly"interior from being seen through the slots), then direct pressed up against that, goes the light-weight, low density 1/2" insulation. Once again, I'm pretty sure you already know all this stuff, but it doesn't hurt to have a reminder, especially for folks following the thread at some point in the future. In my opinion, it's important for studio builders to understand WHY they are doing things, rather than just blindly following instructions... - Stuart -

I am aware, but the best I an do in this case is to use screws around the perimeter as stops. I don't have access to staple or fasten the insulation to the backs of the boards. It worked on the wavy walls, so hopefully we get good results here....

Alright Y'alls! Here's the door slats done without trim of course....This conglomeration will get much prettier soon with trim..I don't think Stuart can fit in any more resonators, which pleases me to no end! :) Now we just sit back and wait for graphs and charts to rise... :snack:

I don't think Stuart can fit in any more resonators,

Hmmmmm.... Challenge accepted! Now let me see.... there's gotta be some tiny little miniscule spot here some place! .... Maybe if I ..... :) Seriously, that looks pretty neat, Frank! Let me take a look at the data, and see where we are.... Next up is the cloud, I reckon! - Stuart -

And the wild card absorber above the window...Pretty close now!

Well, dammit Frank! You've gone and made me a liar! Before you did this, I warned you that the results would not be major. And it turns out that it isn't working the way I thought it would... it's working BETTER than I thought it would! Still nothing earth-shattering, to be sure, but I'm pleasantly surprised about how well those things are doing. Considering the small surface area, and remote location, and that I was really pushing the limits of what slot-walls can do, I'm happy! So take a look at some "before" and "after" wiggly lines...: First up: Frequency Response: Purple is "before", light blue is "after". Self explanatory, I think. Now for RT60: Purple is "before", light blue is "after". Very nice smoothing out, especially in the mid range. Very noticeable difference between 300 Hz and 2 kHz. And finally, waterfalls: BEFORE: AFTER: Note especially the large annoying peak that we had at 627 Hz (marked with cursor), and how that is greatly reduced in amplitude. Also note the 54 Hz modal tail, and how that is reduced in length (time). Ditto the "mud" at around 73 Hz, 110 Hz, and 273 Hz. FIY, the large broad slats with the small gaps, along with their surrounding slats, are tuned to 53.5 Hz and 100.5 Hz, while the smaller slats with wider slots are tuned to 275.5 Hz and 627 Hz. So yeah, even though I told you that not all of those might work, I lied: they all did! :) Here's the direct comparison, with the two waterfalls overlaid on each other: Gold color is before, purple color is after. Helmholtz resonators are notoriously hard to tune accurately, especially at these low frequencies where they aren't very efficient anyway, and it requires precision work in cutting the wood accurately, and most of all in getting the slot gaps exactly right. But it looks like you pulled it off wonderfully! The results clearly show that everything is tuned exactly where it is supposed to be, and working very nicely. Color me happy! (Like I said, not earth-shattering, but very nice, very welcome, and better than expected considering the small surface area and unusual location.) - Stuart -

Ahh, what the hell.... let's add a couple more, to give Frank some bragging rights here. It's generally accepted that a home studio where the overall frequency response is within +/- 10 dB across the spectrum, is about as good as you can expect. So how does Frank's place stack up on that front? It looks like this: You can see that I have highlighted part of the graph in darker shade, containing the highest and lowest peaks within that rectangle. Take a close look at the red text box, over on the far left hand end. It says that the rectangle covers a range of 15.63 decibels. In other words, +/- 7.8 dB! So Frank's room is accurate to within plus or minus 7.8 dB, from about 31 Hz up to 22 kHz. Not bad at all! Oh, but wait! The graph above is shown at 1/24 octave smoothing, and the specs actually say that you should look at it with 1/3 octave smoothing, because that supposedly better represents human hearing resolution (I don't agree, but that's what the specs say...). Damn. So I got that graph wrong. OK, so let's smooth it some more, to 1/3 octave... So what does that red box say now? Well, gee, to me it looks like it says "7.86 dB" That's the full range, so that means +/- 3.93 dB. Let that sink in a sec, Frank! When viewed at "normal" smoothing, your room is BETTER than plus - minus 4 dB, across the entire spectrum. ---- (PS. We ain't done yet! It can still improve....) - Stuart -

Seems I may be setting the bar high for future do-it-yourselfers such as myself! :mrgreen: Not to worry, John's latest presentation from Taiwan will forever keep me humble. . :lol: All kidding aside, the news is quite welcome. These things are not easy to build..... By the way...The room sounds good!

I am curious, would it be fair to say that 1/6 octave smoothing is as good as I'm going to hear it, or 1/12?

By the way...The room sounds good!

That's music to my ears! Squiggles on a graph are one thing, but actual human ears listening to real music are another. If it is meeting your expectations, then all is well.

I am curious, would it be fair to say that 1/6 octave smoothing is as good as I'm going to hear it or 1/12

That's a real good question, and there's no simple answer, unfortunately. It's different for different parts of the spectrum, and different for different people. Some do have better hearing than others. It even depends on the music itself: Some music has more noticeable detail in the lows, some has more detail in the highs. But as a general rule, I normally look at at 1/48 to 1/24 octave smoothing as being about right for the judging the low end, 1/24 to 1/12 is about right for the mid range, and 1/12 to 1/6 seems to be good for the high end. In REW, there are three different smoothing modes that attempt to simulate what humans actually hear. Here are all three applied to your data: Variable Octave Smoothing: (Starts at 1/48 in the low end, up to 1/3 in the highs, IIRC) Psycho-acoustic smoothing: Varies according to an algorithm that supposedly is a close match for average human hearing perception. And ERB smoothing: I haven't looked into this one much, so I'm not sure what it is based on: But no matter which way you look at it, your room looks great for all of them! - Stuart -

Soundman2020 wrote:

That's music to my ears! Squiggles on a graph are one thing, but actual human ears listening to real music are another. If it is meeting your expectations, then all is well.

I know I'm the only one hearing it with my own ears with regards to the forum, but when you consider how that room sounded untreated...Yeah, its come a long way. The room was pretty much unbearable in the beginning. A big boomy echo chamber of chaos. That was never its intended state of course, but a solid example of what treatment can do. In the end, my ears definitely matter more than the graphs. There's still some things I'm hoping to iron out, but my confidence is high. :thu: Now all I want moving forward, is magic outta you! :lol: no more extraneous building projects! That's for suckers... :shot:

Check your email when you get a chance...Dont miss the first, its the best part. :mrgreen:

Hey all! No updates this week, but I heard back from Stuart, so I'm back on track...Should start seeing some more pics by early next week. Next up is the cloud! Stuart, are you leaving the space under the window unfinished for now? Thanks...

Stuart, are you leaving the space under the window unfinished for now? Thanks...

Right. You'll probably need the space to move your sub around, as we hunt for the best location. Once we find that, then you can finish off that area. Probably just insulation and fabric on a frame. - Stuart -

Hey all, Just wanted to give a quick update....Should have some trim pics and cloud construction pics up by this weekend. Ran into trouble with cabling issues and had to rethink my routing layout. :roll: Nothings ever easy!

Looking forward to your ceiling cloud design, Frank! Your build runs very simultaneously to mine, and I've been quietly lurking here for most of it. Your ideas and Stuart's input has been very helpful, as you've often taken questions straight from my mouth. Can't wait to see how your room looks once it's all done. Keep up the good work, buddy! You're almost there :D 8)