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

Got it! I think you might be OK, but you can get a second smaller sheet if you run out. You don't need another big sheet like that. - Stuart -

So far a box cutter is the best thing I've found for cutting. Do you have any better ideas? Its going very slow...:( EDIT: Actually never mind...I got a long style box cutter blade. Not awesome, but doing the job in a reasonable time frame. :thu:

Email sent. :poke: I'm stuck

Replied: Unstuck now? :) - Stuart -

For the moment anyway. :thu:

Cool! For anyone following the thread and not having a clue what is going on with the above cryptic conversation: Frank ran into an issue cutting the Sorbothane for isolating his speakers, as the calculator provided by the Sorbothane company is not correct: it gives you the wrong answers. When Frank cut it to the correct size, it did not compress correctly. Several of my customers have reported this to me recently, so now I would suggest that nobody should bother even trying with their faulty calculator. So I gave Frank some tips on how to proceed anyway, ignoring what the calculator says and doing it with math instead. - Stuart -

Can you share the formulas you're using to get correct results? Personally, I have just thought to use 1 1/2" thick chunks where possible and make sure to get 20% deflection through trial and error. Greg

Hi Stuart, Make sure to read my whole string of emails to avoid confusion. I was spitting them out as I ping ponged through my trials! :mrgreen: To the rest of the crowd: Sorry for not being more informative guys. As soon as I get the soffit work done, I'll be back to normal levels of content!

:idea: :shock: It's all a little confusing, but I think I understood... I sent you an e-mail, to double check.... - Stuart -

And I was starting to feel like I had a handle on things :lol: :shot:

Can you share the formulas you're using to get correct results

Hey Greg. Sorry I missed your post: The actual equations are on their website. You can download the engineering design guide in PDF, and they are on the first few pages, with examples and graphs on the rest of the pages. Not too complicated... just long, boring, lots of calculations... But I'm working on a simple way to still use the calculator, by adjusting with a "correction factor". Right now it seems that you need to adjust your area to be only 92% of what it really is, and put that number in the calc. Or stated another way, divide the number that the calc gives you, by 0.92 to get the REAL area you need. So if it says you need 20 cm2, then make that (20 / 0.92) = 21.75 cm2. Still working to confirm that this correction factor is true for all cases... Sorbothane is non-linear, so it might not work out that simple... Also, this only applies to their V2 calc: the V1 is also wrong, but in a different way.... Right now I have them both open with the exact same data in each, v1 says the deflection is 23.75% and the frequency is 16.8 Hz, V2 says the deflection is 19.3% and the frequency is 12.9 Hz So there's MAJOR differences here! Don't trust the calculators. I'll be talking to them probably tomorrow, to see what they say. Frank already made contact.

Personally, I have just thought to use 1 1/2" thick chunks where possible and make sure to get 20% deflection through trial and error.

That's one way to do it, but you need a very accurate method for measuring, and it takes a while to do that! And you need to account for the fact that a lot of the vibration in a speaker is in the front-to-back direction, not so much up-and-down.... Plus you have to account for the fact that speakers are not weight balanced: the center of gravity is not over the center of the bottom panel with most speakers, so it will tilt one way or the other if you don't compensate.... And for pads that don't have weight on them, only pressure, or a combination of weight and pressure, you can force them to have 20% deflection WITHOUT having the correct pressure... and you can also force them to have the correct pressure WITHOUT having the correct deflection! :) - in both cases the frequency will be wrong, and it won't isolate properly... (Don't ask... too complex to explain here, and I'd be giving away too much proprietary stuff anyway...) - Stuart -

Back to you sir! :jammin:

Ping----pong! Check your email. Time to get out your pet octopus, and start assembling that sucker! - Stuart -

I have a bit of a problem. lets see what we can do about it....email sent. :?

Ready for the next Phase! :yahoo: Email sent!

We have a winner! :thu:

Update! Frank has assembled his speaker enclosure boxes with the speakers inside them, and they worked out great! We had to adjust some of the mounting process, because of the error in the Sorbothane calculator (as mentioned a few posts back), but with the correction factor that we figured out, it all came together nicely. Photos of the assembly process, and the final outcome: Note that some things are hidden in those photos on purpose, as there's some parts of how I do this that I'm not prepared to reveal in public yet. Maybe one day. Those folks who take the time and think it through carefully might be able to figure it out for themselves. One reason I don't want to reveal it, is because it is complex to get right: Frank can testify to that! :) What you don't see here is the ten pages of instructions that I wrote for him, on how to put it all together, and you also can't see the headaches he went through to make it happen. You really can't see it in the photos, but that's precision carpentry and assembly, right there. It is all accurate to 1/64"... But happen it did, and the effort will be well worthwhile! Nice work, Frank! :thu: Next up: mount them in the soffits, and put baffles on them... - Stuart -

more headaches! messages sent... :(

Hmmmm... thinking about what to do about that. For those following the thread, Frank discovered some symmetry and plumb issues with his soffit framing. I'm trying to figure out if it is serious, and if so, what to do about it... - Stuart -

On another note.....I'm looking at the desk and wondering if I can make it bigger? I would follow the outline of the room of course. I could conceivably add more surface area for mix gear and what not. For everyone out there.....This is the desk in question. I will be building it from scratch. I want to push out in the directions shown. :mrgreen:

You could make the desk a little larger out to the sides, yes (extending the "wings" a bit) without too much acoustic penalty, but it might start getting in the way of the access path through the doors if yu go too far. And you could extend it towards the window exactly 1" :) Why? Because that's how far you'll be moving it backwards to compensate for the soffit issues! :shot: I would suggest not going further than that towards the window: we don't want reflections from the desk surface hitting your head and we don't want to create acoustic zones above and below the desk surface that are wildly different in response. I also have some ideas about how to reduce the total surface area of the desk faces, especially the legs, so when we are done with the soffits, cloud, and slot walls above the door, I'll do a bit of re-design on the desk to see how big I can make it, and also to optimize other aspects. - Stuart -

Cool, I want as much desktop as I can get. I was also looking at ways to get increased rack space as time goes on. Not needing to add it right away, but having the option to do so later. Maybe in between the legs under the racks or adding side modules later. There's a decent amount of space before you get to the midpoint of the sliders. 8) I'm optimistic....

Also, this might be interesting for some people, regarding the importance of correctly and accurately positioning your speakers and mix position, and also the measurement mic. It might be an eye-opener, too, since most people wouldn't expect such large changes in response from such small changes in position, but here it is: Backstory: Frank noticed that some of the wood he had used for the soffit framing had warped, and there were also some additional inaccuracies in the construction, that prevented him from getting the speakers flat, level, plumb and correctly aimed at the mix position while also getting the baffle on straight. Not huge differences (just a couple of inches, in total), but big enough to be of concern. So I explained to Frank how to do a series of high precision REW tests at several carefully selected spots around where the mix position was originally supposed to be, to see if we could find a new acceptable spot without needing to physically modify the soffits (or worse still: tear them down and re-build them! :shock: ). So Frank ran those tests, while getting bored to tears (its a whole bunch of tests, one after the other, with minor moves of the mic in between), and I analyzed them in various ways. Here's one of the results: That's a series of graphs of the DIFFERENCE in level between the Left and Right speakers. Wherever a curve is above the 0 dB line, the left speaker is louder for that frequency in that location in the room. And wherever the curve is below the 0 dB line, the right speaker is louder. Each curve shows the difference in level at a different physical location in the room. As you can see, there's clearly a pattern here as the mic moves from the D-4 position (pink curve) to the D+4 position (dark purple curve). If you take a close look at the area around 48 Hz, and also at around 180 Hz and several other spots too, you'll see that there's a progression in the curve getting smoother and smoother, then getting rougher and rougher again. The light green line marked D-0 is obviously the best, and smoothest, but also clearly not as smooth as it could be. You can extrapolate mentally, and expect that if there were ANOTHER line in there, with the mic somewhere in between the D-0 and D+2 locations, then the line would be flatter still. And that's the reason why Frank is going to move his desk! To get his head on that flattest part of the line, he can either spend days re-building his soffits to correct the warping and construction errors... or he can move the mix position! So guess which one we decided to do! :) 8) Now, you might think that those various curves were taken with the mic at points that are a long way apart, because the differences are clearly very large: you might suspect that the mic moved a couple of feet between tests. And you'd be wrong! Each step is just a couple of INCHES. Between the pink curve and the light blue curve, for example, the mic moved exactly two inches. This is why you often see me harping on the importance of precision, and being extremely careful to always get your mic in the exact same spot in the room when doing REW tests while you are building. I'm sure some folks think I'm nuts when I tell then that the mic absolutely must be in the precise same spot, accurate to with 1/4", for all REW tests, because if not, the readings are not validly comparable. Here you can see that I'm NOT nuts, and there really IS a huge difference in curves from moving the mic just a small amount. Imagine how wrong you would be if you did a REW test with the mic in the "pink" position, then put up some acoustic treatment panel that you just built and measured again, but with the mic 2" off from where it should be, and you saw the light green curve: then you thought to yourself "Cool! my panel worked fantastic! It flatted everything perfectly!". Oh, how wrong you would be! So always make sure that your mic is at the EXACT same point in the room for every test. In this case, I specifically WANTED the mic at several different spots, but that's an unusual case. Normally you DON'T want the mic to move at all. And just to clarify before someone gets confused here: these curves are NOT normal SPL curves. These curves here show the DIFFERENCE in performance between the two speakers. - Stuart -

Success! Frank has just completed the very successful "floating" of his speakers in the soffits! They are now sitting happily in there, fully decoupled from the structure, and just waiting for him to put the baffles on, in a few days. Here's some REW graphs, to show where we are now. The graphs are posted in pairs, with the first one in each pair being the "before" graph from the previous tests (right when the hangers went in to the tops of the soffits), then the "after" graph, with the speakers floated. For the "before" graphs, the speakers were just sitting directly on the soffit shelf, and the "after" graph they are floated. First (and least important) the frequency response graphs. BEFORE: AFTER: --- Then the same as above but with the phase graph added: This is a lot more interesting! You can clearly see how the phase is now rotating much more nearly the way it should be across the entire low end: BEFORE: AFTER: -------- And finally the spectrograph plots, once again showing how the low end is smoothing out more. BEFORE: AFTER: We'll try to get some photos of the soffits tomorrow, after Frank finishes celebrating! Getting the speakers floated in the soffits is an important milestone, and it tool a while longer to do, thanks to the unexpected error with the Sorbothane calculator, but we figured it out in the end, and everything is floating very nicely now. So I expect Frank is having a party right now, to congratulate himself for getting to this point. Things should go a bit faster now. - Stuart -

Indeed this has been hard! No partying here, but the fire is back and I'm pushing 12 hour days now! So spirits are definitely high. :yahoo: To be clear, that was absolutely no fun at all! :lol: I shot some pics over to the man for approval :cop: Peace out :mrgreen: