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PostPosted: Tue Jan 30, 2018 1:51 am 
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So Stuart you design these bass traps/treatment once you've made a proper analysis of the test results correct?
Right.

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In other words you can't fully predict what's required when it comes to treatment until you know how sound gets thrown around the room?
Right. Prediction will get you close, especially for a rectangular room, but this room is not rectangular: it is closer to square (it has to be: it's a "corner control room"), but with one corner chopped off, angled side walls, and soffits. It's more of a 7-sided trapezoidal polygon, so it's hard to predict the outcome. And it's always best to check the actual response, even with a perfectly rectangular room. Construction materials are not perfect, dimensions can vary, there might have been changes during the construction for unexpected reasons, etc.

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PostPosted: Tue Jan 30, 2018 1:52 am 
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In case Stuart doesn't reply shortly, the short answer is yes.. he can predict the behavior of a room when he designs it, but not completely.. What you're seeing is how the process works when you hire Stuart.

LOL... looks like we did it again Stuart


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PostPosted: Tue Jan 30, 2018 2:47 am 
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Excellent! Thanks for the explanations! I love learning more about this stuff! Keep up the great work!


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PostPosted: Tue Jan 30, 2018 4:25 am 
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Frank has put the insulation on the ceiling, and sent me his latest REW measurements, so here's some more "before" and "after" pairs, where "before" is with just the rear corner treatment in, and "after" is with the ceiling insulation in too:

WATERFALLS:
Attachment:
Frank-REW-WF-20-500--Rear-Corner.png


Attachment:
Frank-REW-WF-20-500--Ceiling-Insul.png


You can see the very nice effect that this is having on the modes at 113 Hz, 177 Hz, 205 Hz, and 232 Hz. Those have pretty much gone now, as well as general low end smoothing.

This is a real "slap in the face" for those folks who insist that a couple of inches of insulation has no effect below about 400 Hz or so! Much to their chagrin, the result here is glaringly beautiful: That's some pretty major changes, especially at 113 Hz... and all Frank did here was to put insulation in between the ceiling joists. Just a few inches thick, nothing more, and nothing special: just ordinary insulation.

Got any photos of that Frank, to permanently silence the noisy "insulation doesn't work down low" mob? Showing what you did, and how thick it is?



(For those who don't know what I'm referring to here: there's a vocal bunch of detractors of the benefits of thin porous absorption, who loudly voice their ignorance all over the internet, insisting that insulation can only be effective if it is 1/4 wavelength thick. According to them Frank would need insulation that is two and a half feet thick to have any effect on 113 Hz (the wavelength is 10 feet, so the quarter wave is 2.5 feet). Even worse, what Frank did here also had a nice effect on the problem at 86 Hz, where the Wavelength is 13.1 feet, so you'd need 3 and a quarter feet, according to the silly folks. But you can clearly see that just 8" of insulation is having a very, very nice effect, even down at these low frequencies. 8" is just 6% of ten feet, and 5% of 13 feet, which proves Andre's theory that good porous absorbers is still effective down to 3.5% of the wavelength for random incident sound, and 7% for normally incident sound. And if you look closely, you'll see that this treatment even had some effect on 74Hz. Not a lot, but it's there. The wavelength for 74 Hz is 15.25 feet, so according to the nuts, he would have needed nearly four feet thick insulation to do that... :) 8" is 4.3% of that, still within the 3.5% theoretical range...

--- Sorry for the rant, Frank, and for hijacking your thread to do it, but this is one of my pet peeves! People spouting off about stuff they know absolutely nothing about. I just wanted to mention that, since your carefully done tests highlight their ignorance so beautifully! The ONLY thing you did was to put the insulation in, and the results clearly show that it works very decently.)




SPECTROGRAMS:
Attachment:
Frank-REW-SP-20-500--Rear-Corner.png


Attachment:
Frank-REW-SP-20-500--Ceiling-Insul.png

You can see the same thing here, and also something more important: The SBIR null at 144 Hz is filling in nicely too. I highlighted that with the cursor. (I'm pretty sure that is SBIR, not modal, since there's also a phase shift going on at that point.)

(You have to be careful when looking at this pair, since REW has automatically adjusted the scale between the two! Because the overall level went down, REW modified the color scale and intensity, so it looks like the low end got louder, but it didn't. REW just shifted the scale so that the highest level is now at 89 dB, instead of 91 dB before. So refer to the key color-strip on the right side of the graph for clarification.



FREQUENCY RESPONSE:
Attachment:
Frank-REW-FR-20-500--Rear-Corner.png


Attachment:
Frank-REW-FR-20-500--Ceiling-insul.png


Nice changes, smoothing out neatly.... The 144 Hz issue is highlighted there, with good improvement.


RT-60:

Attachment:
Frank-REW-RT-20-20k--Rear-Corner-B.png


Attachment:
Frank-REW-RT-20-20k--Ceiling-Insul-B.png


The decay times are coming down, especially in the high.mids and highs. But I'm a little concerned that we might be going too far in the high end: the very top end is already down to about 230 ms, with plenty of treatment still remaining. So well need to do something about that.

So, Frank, you'll need to get some very thin plastic, around 1 mil, and cover SOME of that insulation in the ceiling, but not all of it. I'd suggest maybe 50% coverage. The type of plastic you need is the very thin stuff, that painters use as drop cloth to protect furniture while they paint. You can buy it in hardware stores (Home Depot, etc.). Cut off reasonably broad strips, maybe 8" or so wide and as long as you need to span between joists, then leave 8" open spaces between them. Don't make them too wide, or they'll be reflecting too much. Also, don't make them too narrow, or they won't do their job. It's not too critical: anywhere around 7" to 9" wide is fine.

So put those up on the ceiling, and try another REW test. There won't actually be very much difference in the graphs with this test at this point, since there's still way to much other stuff going in, that is going to be masking the effect, but it needs to be done now, before moving on to the rest.

- Stuart -


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PostPosted: Tue Jan 30, 2018 4:58 am 
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Stadank0 wrote:
In case Stuart doesn't reply shortly, the short answer is yes.. he can predict the behavior of a room when he designs it, but not completely.. What you're seeing is how the process works when you hire Stuart.


Thanks for the promo and commercial break, Frank! :thu: :)

- Stuart -

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PostPosted: Tue Jan 30, 2018 6:09 am 
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I'm guessing ill only need to do the half of the ceiling that won't be behind the cloud.

I do need to put in a correction in there....The insulation in the ceiling consists of standard rockwool but also an inch of duct liner in the covers... :mrgreen: I forgot to mention it, Sorry Stuart... So we have 3.5" of rockwool and 1" of fiberglass duct liner.

I'll take some pics when I'm adding the plastic food wrap...back in a bit!


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PostPosted: Tue Jan 30, 2018 10:20 am 
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So we have 3.5" of rockwool and 1" of fiberglass duct liner.
Even more impressive! Four and a half inches of typical insulation is giving you some pretty substantial improvements! 4.5" is 3.9% of the 113Hz wavelength, 2.8% of the 86 Hz wavelength, and 2.5% of the 74 Hz wavelength.

So Andre's theory was actually pessimistic! Reality turns out to be even better. The effect goes down even lower than he predicted: porous absorption is slightly effective at thicknesses as small as about 2.5% of the wavelength, and very effective for thicknesses greater than about 3% of the wavelength.

When done correctly, of course!! :)

- Stuart -

(PS. I would do 50% coverage of all of the ceiling, just to be safe: you never know what reflections might make it up above the. Theoretically, it should only be lows and mids getting in there, but in practice, I would not be surprised to find some highs too. The whole concept of RFZ is to get a decent "diffuse field" after the ITDG of around 20ms, that then dies away slowly. So I'll take that field from wherever I can get it! If there's some above the cloud, then that's good for me! :)

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PostPosted: Wed Jan 31, 2018 2:12 pm 
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Here are the pics you wanted Stuart.

I'm ready to move onto the back walls. Let me know if you want anything else done first....


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Attachment:
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PostPosted: Thu Feb 01, 2018 2:14 am 
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I'm assuming you want me to do the same 1 mil plastic on the back walls?


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PostPosted: Thu Feb 01, 2018 2:17 am 
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Not yet! First the insulation, then we'll see how it's going with REW. I might want to do slats on some of that, in which case you don't need the plastic.

- Stuart -

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PostPosted: Thu Feb 01, 2018 2:23 am 
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Actually, I would prefer that because the walls will look boring with just fabric... 8)


oooo...I just had a thought. What about hanging guitars on the wall as part of the reflective scheme? That would look pretty!


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PostPosted: Thu Feb 01, 2018 2:38 am 
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oooo...I just had a thought. What about hanging guitars on the wall as part of the reflective scheme? That would look pretty!
I'm not a fan at all of hanging resonant things in control rooms! :) Acoustic guitars are designed to resonate.... Perhaps a couple of electric guitars would be OK.

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PostPosted: Thu Feb 01, 2018 3:10 am 
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of course, I was thinking solid objects for sure...that actually occurs to me. Not a critical need for me either way.

Will have a test up for the back walls today or tomorrow morning!


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PostPosted: Thu Feb 01, 2018 6:56 pm 
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OK,

So here are some pics of the back walls insulated with panels on them. Nothing exciting to see, but they are now crushing the decay so I'm sure changes will be made. This is not unexpected, so no big deal. Some problem areas got worse and some better. Again, I expect this kind of behavior as the process goes on.

Stuart will probably elaborate more on this.

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PostPosted: Sat Feb 03, 2018 1:49 am 
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To be on the safe side I went back and did a measurement without the covers on. very little change but wanted to eliminate any suspicions all the same. I'll let Stuart post pics of the graphs if he wants cause He'll explain it better... :shot:

There is little difference in a dip at around 175 hz so I'll put em back on!! I absolutely hate insulation!

Ready for the next round! Which will be next? the cloud or the soffits?

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