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Post by rock on Aug 15, 2016 4:32:50 GMT
Maybe using harmonic is the wrong terminology...but maybe not. All I'm saying is that 105Hz is 3 times 35Hz so by definition,105Hz is the 3rd harmonic of 35Hz.
Now, the 1/2 wavelength of 35Hz is 4.9m which is the length of Wei's room. That means the wave "fits" evenly between the two parallel walls and bounces back and forth and is either constructive (peak) or destructive (null). I actually don't know which but from Wei's measurements, it looks like it means it's a peak so if the reflection is in phase, the interference is constructive=peak. Each multiple (or harmonic) will also fit evenly because it will divide into 4.9m. In the case of 105Hz, it's wavelength is 3.27m and that fits into 4.9m about 1.5 times. In this case, the reflection is out of phase so we have destructive interference = null.
When you think about it, room modes are certain frequencies resonating between the walls, quite similar to a string and soundboard resonating in a piano or guitar.
Yes, I do believe the harmonic series is a concept we find pops up in audio and acoustics almost everywhere you look...depending on how you look at it. If you play with that room mode calculator, you will see the harmonic series in the modes as they increase in each axis.
Cheers, Rock
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Post by rock on Aug 14, 2016 19:10:12 GMT
I did not know what a french cleat was so I googled it. It turns out I DID make one before, I just never knew what it was called. So just google "french cleat" for images. As you will see, it is used for hanging stuff on walls. If you want to make one out of wood, you need a table saw. You can also buy metal channel ones. Google is your friend.
Take Ethan's advice and screw into studs.
Cheers, Rock
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Post by rock on Aug 14, 2016 17:12:51 GMT
Hi Wei, I was curious about your 35 Hz peak and especially your 105Hz null and as you may realize, they are related to your length of 4.9m. If already know this, please forgive me for missing this fact until now. This website is easy to use to calculate room modes: amroc.andymel.eu/?l=490&w=310&h=277&st=false&so=false&r60=0.6So you can see 35 is fundamental and 105 is the 3rd harmonic of the length so that would indicate you need to make sure the front and back walls and corners are completely treated. So to be clear, that's the front wall/ceiling, front wall/floor and front wall vertical corners PLUS rear wall/ceiling, rear wall/floor and rear wall vertical corners. The front wall area and rear wall area should be treated too. As you install the insulation, taking incremental acoustic measurements will confirm you are on the right path and the null and peak should improve. Cheers, Rock
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Post by rock on Aug 14, 2016 16:39:00 GMT
Hi Wei,
I want to assure you, we are interested in your acoustics, nobody is here to judge you on the aesthetic appearance of your room so don't feel that you need to edit your photos. It's actually better if you don't so we can see exactly what you are doing. Please feel free to take pictures of the front and back and ceiling of your room. Stand as far back in the room as you can so we can see as much as possible. Remember, a picture is worth 1000 words, it is really true! Please don't worry at all about how pretty it looks, that is not important to us. We know you can take care of that later.
As far as using the 703 to fill behind your corner traps: that is OK if you have enough but the reason fluffy is recommended is because it's less expensive and does Almost as good as solid denser absorbers. Superchunks are essentially solid 703 or other insulation cut into triangles and stacked in the corners.
As we all learned from Ethan, it's better to have your absorption distributed all 12 corners (and walls) than a lot in only a few corners (and walls)
On the other hand if you have lots of 703 but you don't have all 12 corners trapped yet, you can use the 703 for the rest of the corner traps. The easiest corners are the floor/wall corners, you can simply lean them against the wall. If you calculate you will have more than enough 703 for that, you can use it for wall or ceiling panels too. If you still have enough left, maybe you should consider building super chunks but takes a lot of material so you really need to run some calculations and see exactly where you can use the material you have.
About your 105Hz deep null, don't worry about it too much before you finish installing all your absorption.
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Post by rock on Aug 12, 2016 13:45:50 GMT
Just my opinion but I don't think you need to go to extremes to keep the fluffy from compressing itself. Keep in mind, it is compressed in the package and naturally expands when un-packed so I would not worry too much about it compressing itself under it's own weight. You might need a couple of vertical wires or mullions to keep it from falling forward but if it's 24" wide, I don't think there is much of a chance of that either. After you stretch and staple fabric in place, that would probably be enough but if you want insurance, it cant hurt.
Cheers, Rock
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Post by rock on Aug 12, 2016 13:36:44 GMT
Hi Wei,
Just out of my curiosity, can you post wide view photos of your room from a few angles so we can get the "big picture"?
Thanks, Rock
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Post by rock on Aug 11, 2016 1:08:43 GMT
Hi Kevin,
On the less technical side, and at the risk of stating the obvious, you know you need to remove the drywall from your super chunks, right? There is no way to audibly assess the sound of your room with the DW in place. So when you do remove it, paper faced insulation should face the room. I know Ethan has tested rigid FG with FRK but since I'm not positive fluffy with paper facing gives the same increase in LF absorption, I can only guess that it does and ask if anyone else knows for sure. If not, I'd still suggest going with it. (your rear corner traps should have membrane facing the room too.)
As far as how to cover the super chunk: One very simple way is the frame the perimeter with furring strips. Bevel the vertical edges to the wall angle. Then staple and trim cut your material. Finally, attach moulding trim over the staples and around the super chunk.
BTW, you'll notice Hexspa's design is to make the super chunk portable but my description is for a permanent installation.
Cheers, Rock
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Post by rock on Aug 6, 2016 16:54:05 GMT
Wei,
Just to be clear, when I say limit to 300 - 400Hz, I mean on the high end of the graph. The low end should start at about 20 to 30 Hz. In actuality, 30 to 300Hz is probably good enough but if you play with the values, you should see what is most useful.
Cheers, Rock
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Post by rock on Aug 6, 2016 13:03:45 GMT
Hi Wei, I think your big problem is that your measurements are making you second guess your treatments. I agree with m that you should verify your test procedures and speaker response with close miking your speaker. With close micing, you effectively eliminate your room response and see only your speaker response which should look similar to your speaker spec sheet graph if you have one. After you get a good response with close miking, you can make more measurements at incrementally farther distances from the speaker into the room. This should show you the gradual increase in room modes as speaker/mic distance increases. For your low frequency graphs, turn the smoothing off as you want to see all the detail. For the most part, you will be looking at LF response when analyzing room modes so limit your graphs to 300-400Hz. For wide band graphs using smoothing is good because all the peaks and nulls in the upper freqs are unavoidable. Your primary focus right now should be to gain confidence in your measurements. Without that, you'll be forever running in circles. Also experiment with speaker and mic position as that can affect the peaks and nulls too. As far as your absorbers, you mentioned earlier "I used plastic bag with no more than 1mm thickness to package the OC703, then used cotton sheet to package them and install." The 1mm plastic should be attached to only the front; spray glue works good. It's not clear from your description but if you did that already, great. If you have pictures and or diagrams of your room, that may help. Sorry for asking if you have posted them on a previous thread. I'll look to see if I can find them. As you requested, here's a link for Helmholtz absorbers www.mh-audio.nl/acalculators.asp#showcalc but I really think you need to confirm your measurements and procedures before you abandon porous absorbers; they are the most practical solution for small rooms and I don't think there is any reason they won't work for you too. Cheers, Rock
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Post by rock on Aug 2, 2016 0:47:13 GMT
I have to admit I was growing tired of the wrist watch analogy but now I appreciate it and I think that the point has finally been made.
Cheers, Rock
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Post by rock on Aug 1, 2016 21:27:24 GMT
FWIW, in some high school choir and orchestra rooms I have seen, I notice they have installed panels from the ceiling about 1" thick at an angle that look like they would reflect away from the source. They don't appear to be very absorbent but IDK. These are fairly large rooms and flutter echoes are probably what they are trying to control.
Cheers, Rock
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Post by rock on Aug 1, 2016 21:14:26 GMT
Sure, those adapters should work. Cheers, Rock
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Post by rock on Aug 1, 2016 11:21:17 GMT
Hi Amber, Sorry to hear about your situation and your husband. I'm not sure but if you google "Test Equipment" there are some sites dealing with this and they might be interested in used gear. Here's one example www.tequipment.net/ Rock
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Post by rock on Jul 30, 2016 15:39:07 GMT
Regarding unbalanced (phono) to balanced (XLR), there are a couple (or 3 or more?) ways to go about it. 1. From unbal, you can usually just send the signal conductor to the hot (usually pin 2 of the XLR) and the shield conductor to XLR pin1. Ground pin 3 (Cold or inverted signal) to ground (pin 1). I imagine you might find a pre-wired adapter but I don't believe I've seen one. 2. If you want to get fancy, you can use a passive inline transformer, doing this can eliminate ground loop hum you might otherwise have. OR 3. There are active level converters you can buy too. Here is but one example: www.parts-express.com/art-cleanboxpro-stereo-balanced-unbalanced-converter--245-868 Cheers, Rock
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Post by rock on Jul 28, 2016 13:42:49 GMT
Unless you're doing realtime monitoring thru the computer, I don't think latency is a sonic quality issue. Seems to me, if your question is what is the sonic quality of the recorded signal, how long it took to get there should not matter. I think it's apple and oranges.
I don't know the answer to the quality question but I do have an opinion that cheap interfaces today (I have one) compete favorably with expensive Big Time Studio gear. A friend with expensive gear of his own was dubious but could not find fault with my cheap interface.
Cheers, Rock
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