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Post by Hexspa on Aug 13, 2016 12:36:35 GMT
You can ignore the peak at 35Hz. You can use 703 and the fluffy one behind it: 4" 703 with FRK at non-RFZ points and unfaced Rxx behind it - up to 3x the thickness (12"). The more you treat your surfaces (rear, front, side, ceiling) the better. The more you fill in corners, the better. Remember, there are 12 corners, not four so unless you have the remaining ones treated somehow they're going to contribute to the standing waves. You can watch this video to see how my room was done: youtu.be/jLkk8X0E9foThe bottom line is: if you have problems, you need more treatment. If your room is already 100% covered then make it thicker! -m
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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 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 Ethan Winer on Aug 14, 2016 18:20:31 GMT
I used 703 to fill the inside instead of fluffy one, is that ok? Because I have so many left. Yes, of course 703 is fine, especially if you already have it. One large thick entire absorbing wall is better than corner traps if you can give up that much space. --Ethan
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Post by Hexspa on Aug 15, 2016 3:42:56 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 Hi Rock. This is the first time I hear about the harmonics producing nulls. I've understood quarter wavelengths causing nulls up until now but this is the first time I hear anything about the harmonic series relating to room acoustics. Can you please shed some light on this for me? Thanks, -m
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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 15, 2016 12:49:26 GMT
I used 703 to fill the inside instead of fluffy one, is that ok? Because I have so many left. Yes, of course 703 is fine, especially if you already have it. One large thick entire absorbing wall is better than corner traps if you can give up that much space. --Ethan Wei, As always, I think Ethan's advice above is the best. Cheers, Rock
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