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Discussion Starter #1
I am using REW on a Mac with an RS-33-2055 through a MOTU 896 converter, sound played back through a pair of old Mackie HR824's. My room dimensions are 7'4" wide, 11'4" long and 94" high. Basically a finished shed. Untreated as of yet, but full of other stuff. I am wondering about the waterfall plots. Is it possible for the decay to continue to climb throughout the time window? I know my room is bad, but from the response, it looks like its about 15db louder AFTER 500ms. And that's just from 20-200. It's much magnified above that. Can this be right? or am I doing something wrong that someone here can see from the details I've given?
 

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Technically, it's possible for a mode at one frequency to increase in volume if you continue playing that frequency. As a mode rings, it loses energy. If you replace that energy at a higher rate than it's being lost/dissipated, the volume will increase. That's not what you're doing though, with the swept sine wave REW should be generating. In some physical systems, it's possible to exicte the system with something other than it's resonant frequency and have it ring at it's resonant frequency. I suppose this would be true of a mode as well, at least if you fed it an impulse. But again, that's not what you're doing.

Go to our post padding thread, get yourself up to 5, wait an hour for the system to update, and post your waterfall and FR plots, making sure the FR has the soundcard and mic calibration traces on it. There are instances of MACs not playing nicely with REW.
 

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Discussion Starter #3
Cool. Thanks. Tomorrow I'll get all that together. What are the soundcard and mic calibration traces? Are they visuals on the FR plots or is it the text info on the left of the graph area?

I do, for now, use the space for storage of all my music instruments when I'm not rehearsing is the house. There is a drumset sort of setup and a couple bass guitars just sitting in the room. Like you said, I don't think they would continue to feedback the sounds at a higher level, but just in case I'll be moving the stuff back into the house before I test again tomorrow.
 

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When looking at your FR plot on the Filter Adjust tab, underneath the plot you'll see radio buttons for the mic cal and soundcard cal, checking each box will put the respective trace on the plot.
 

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Discussion Starter #5
I think I got it. Now looking at it again, I'm even more confused. The place where all this weirdness occurs is far below my 75db test level. Like noisefloor low. Maybe its just random noise i'm looking at. But then again, I dont start seeing any decent response from my speakers until around 200hz and I know that isn't right.
 

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Your soundcard calibration trace shows that something is very wrong with your setup.
Is that a firewire soundcard you're using? Firewire + Mac = No REW
 

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Discussion Starter #9
By the way, I also have a PC laptop laying around here. Windows Vista Ultimate,32-bit, SP2, Intel Core Duo 1.73, 2G RAM. Might I use this with my FW converter? If not then, like I said, time to go shopping.
 

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FW should work fine on a PC. Should. :D
 

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Discussion Starter #11
Well, things went well today. After a lot of trials. Borrowed my friends USB interface to try with my Mac. Same nonsense. I could not get it to work, no matter what. The readings I got were ridiculous. Utter nonsense. Hooked up the same configuration, changed no wires around or anything, to my PC and everything worked fine. No problems creating a soundcard calibration file, loading the mic calibration file or SPL calibration. FR plots, Waterfall, impulse response... Everything looks great! Well, not great, but at least now I know a little more about what's going on in my room.

Still haven't tried my FW interface with my PC though. Need a 400 to 800 cable.
 

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Rescale your FR plot to match the waterfall. Whic is the 11'4" dimension? Any chance of changing room layout?
 

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Given how narrow your room is, Broadband absorption is going to be the best option. Membrane absorbers will "work" for bass, BUT as far as midrange and high freq's you would be simply moving the too-close walls even closer! They are almost never prescribed for small rooms.

Near reflections have NO place in good sound, even if diffused. Any nearby reflections reaching your ears will be integrated with the direct signal by your brain, resulting in blurred imaging and articulation; your brain will know you are in a small room no matter what track you are listening to. Only reflections received >~10 milliseconds after the direct signal are not detrimental.

Simple corner traps (like a "Super Chunk" made of R-19 fiberglass) in every available corner (including wall-to-ceiling junction) would be a minimum start, and will make some impact 45 Hz. Don't use dense fiberglass or rockwool board, unless just using as a thin face panel over the "chunks".

That's my 2 cents.
-- Mark
 

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For the rear wall, you don't need full range absorption as the surround field should be a bit more lively.

While chunks will help with decay times, if the axial length mode is really the issue, then thick panels centered on the rear wall will be your best option. You can use a damped membrane by using an FSK facing on the absorptive material. Even so, you're probably looking at something around 8" thick to do the job.

You can try a sealed panel membrane also and get by with a little less depth though it will be much narrower in function than the damped membrane described above. They will also be less efficient per square foot overall.

Bryan
 
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