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PostPosted: Fri Sep 16, 2016 4:33 pm 
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Location: Los Angeles, CA
Hello everyone,

I've just finished building a small room in my garage and started researching treatment ideas. The room is going to be used mostly for practicing, recording and mixing my own stuff (drums, guitars). I could use some help figuring out what type of treatment I may need to tame the room a bit and make it suitable for both tracking and mixing. I was thinking about treating the back wall similar to what was done here (skyline, limp mass membrane diffuser)... https://www.youtube.com/watch?v=l8eSkoT2buA
Do I even need it in my case? Or could I get away with something like a 1x6 frame stuffed with Roxul SafeNSound spaced a few inches from the wall and covered with burlap?

My budget is around $1500 (+/- 200).

First, the room dimensions:

- Length: 17.5 f (5.3m)
- Width: 13.5 f (4.1m)
- Height: 8.5 f (2.6m)

The walls are 2x6 frame stuffed with fiberglass insulation, 2 layers of 5/8 drywall with green glue in between on the outside, 2 layers of drywall with green glue on whisper clips and hat channel on the inside. Floor is concrete and will be covered with vinyl planks.

I'm attaching the REW files and the pictures of the testing set-up. Can you guys help me interpret the REW graphs?

P.S. Stuart, I would really like to hear your opinion. What would you recommend as far as treatment goes?

http://www.viridispython.com/studio_stuff/room_tests.zip

Attachment:
IMG_0007.JPG

Attachment:
IMG_0009.JPG

Attachment:
IMG_0014.JPG


Thanks for your help!
Vin


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PostPosted: Sat Sep 17, 2016 1:51 am 
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Hi Vin, and welcome! :)

Your Zip file contains three sets of REW measurements: 3 for the left speaker, 3 for the right, and 3 for both. But they are the same! There0s no difference between Left-01, Left-02 and Left-03: they are essentially identical. The same for R1, R2 and R3: identical. Ditto for LR-1, LR-2, and LR-3.

So I'm wondering why there are three sets? Did you change something in the room, hoping it would produce a result? There are some very, very minor differences at a couple of points in the mids and highs, but that's mostly likely just anomalies in the measurement itself.

Also, you can take more than one measurement inside the same REW file. You don't need to start all over again: each time you hit "Measure", it adds another set of data in a tabbed window on the left, then you can name that test, and also add comments if you want.

OK, so what does the data show? Firstly, that's an empty room, clearly! Decay times of well over 1,000 ms, and very clearly evident modal issues. It's almost text-book perfect, in fact! Pretty much every single mode is evident. That's good, actually, because you can clearly see where the problems are with the room, so it's easy (relatively) to fix.

Secondly, the room is a nice size: it meets the basic floor area and volume criteria for a critical listening room. However, the ratio isn't so good. Length is almost exactly double the height. So your 2.0.0. axial mode is at 65 Hz, and your 0.0.1 axial is 67 Hz. You can see that far more clearly an octave higher, where 0.0.2 and 4.0.0 line up practically right on top of each other, at about 134 and 130 respectively... hence the huge double-spike in the spectrogram:

Attachment:
amorphis-sp-01.jpg


Clearly visible. And repeated just as clearly yet another octave higher, at around 260 Hz.

So clearly, the room is going to need some major bass trapping. That's the first thing you need to do. Large superchunks in both rear corners initially, floor to ceiling. Make them 24" on each side, so you get 34" on the diagonal, plus thick absorption on most of the the rest of the rear wall. I'd suggest two layers of 4" OC-703. You could cover the entire rear wall like that, or at least put as many full panels as will fit, spaced a bit apart.

ALTERNATIVE: If you are aiming for the best it can possibly be, then I'd do the entire rear wall in acoustic hangers, with 4" of 703 up against the wall surface. Make them about 18" to 20" long, floor to ceiling, and spaced at the 1/2, 1/4, 1/8th, 1/16th, etc. points of the room width.

When you have done the back wall (with either of the above methods), then take another set of REW measurements, to see how that's doing.

Then add some treatment on the front wall and on your first reflection points. 4" thick panels behind your speakers, between the front wall and the back corner of each speaker, and 6" panels on the side walls.

By the way, how do you have your speaker controls set up? They seem to be rolling off too much in the low end, starting at about 120 Hz. Do you have the controls set flat? What about EQ? Is there anything in the signal path that might be rolling off the low end? Those are Focal Twin 6's, right? They look like it... If so, they should not be rolling off until down around 45 Hz or so.

Also, regarding your speaker / mix position geometry: It looks reasonably close, but check: Your speakers should be 45" from the side walls, and 48" above the floor. I'm talking about the location of the acoustic axis of the speaker, not the top, bottom or side of the cabinet. That will place them 72" apart. Your head should be 78" from the front wall, and the speakers should be angled such that the acoustic axes intercept 96" from the front wall (18" behind the mix position): The easiest way to get that correct is to set up a mic stand vertically at the 96" location, set up a simple laser line on top of the speaker cabinet, directly above the acoustic axis, carefully aligned to be perpendicular to the front baffle, then angle the speaker carefully such that the laser strikes the middle of the mic stand while also checking that the axis of the speaker is 45" from the side wall. Get it as accurate as you can.

When you have all of that in place, test again with REW and post your results. Do three tests in one file: L alone, R alone, and LR. When you calibrate just before the tests, make sure that you are getting 80 dBC from each speaker by itself (with the other turned off).


- Stuart -


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PostPosted: Sat Sep 17, 2016 6:06 pm 
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Thanks a lot for your response Stuart! You really helped me understand what to look for in the REW graphs! Checking them against the Room mode calculator figures (I used the one on Bob Golds' site here http://www.bobgolds.com/Mode/RoomModes.htm) now makes a lot of sense.

The reason I took each measurement 3 times is because I'm still learning how to use the software and didn't quite know what I was doing :) Somewhere in the back of my head I had this thought that each speaker needed to be measured several times just for the sake of "purity of the experiment" :D Good to know I can save all measurements in one file.

Quote:
By the way, how do you have your speaker controls set up? They seem to be rolling off too much in the low end, starting at about 120 Hz.


The speakers and the mic (C414 in omni) are set up flat and the levels are calibrated at 79 dB against the RadioShack meter. So looking at the graphs (considering 79dB signal level), it seems like the LF roll-off starts at around 35Hz... You are right - those are Focal Twin6 Be's.

Quote:
Also, regarding your speaker / mix position geometry: It looks reasonably close, but check


Thanks for the speaker positioning and distance figures! I checked and they were a bit off. Speakers were at about 50" from side walls and pointing directly at mixing position (which was at 78" from the front wall). I do have one question though. The equilateral triangle - is it supposed to be between the speakers' acoustic axes and the center of the mixing position or the intersection point at 18" behind the mixing position?

Thanks!
Vin


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PostPosted: Sun Sep 18, 2016 12:33 am 
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Quote:
Somewhere in the back of my head I had this thought that each speaker needed to be measured several times just for the sake of "purity of the experiment"
That actually is true! But you can do that inside of REW itself... On the "Measure" window, there's a parameter called "Sweeps". That tells REW how many times to run the complete frequency sweep, then it averages out the results. That helps to improve the signal-to-noise ratio, so the results are more accurate. Set "Sweeps" to "2". You don't need to do more than that.

Quote:
The speakers and the mic (C414 in omni) are set up flat and the levels are calibrated at 79 dB against the RadioShack meter.
Are you SURE you calibrated REW correctly? That's not what I'm seeing in the data:

Attachment:
l-1oct-20-20k.jpg


That's the data from your left speaker, smoothed to one octave resolution. The horizontal line marks 79 dB. The entire curve, from about 45 Hz to 15 kHz is well above that. The average level looks to be somewhere around 88 dB. Check your calibration: Are you CERTAIN that you had both the Radio Shack meter and also the internal REW calibration meter set to "C" weighting and "Slow" response?

Quote:
the levels are calibrated at 79 dB against the RadioShack meter. So looking at the graphs (considering 79dB signal level), it seems like the LF roll-off starts at around 35Hz...
Take another look at the graph above: the roll-of starts at roughly 150 Hz, roughly where the vertical line of the cursor is. Yes, there is bass buildup happening in the low end, due to the lack of room treatment, but that doesn't detract from the clear roll-off starting rather high up. Yes, that will improve considerably, once you start the treatment, but I'm not convinced it's going to end up where it should be. I suspect that there's a signal path roll-off happening somewhere...

Quote:
I do have one question though. The equilateral triangle - is it supposed to be between the speakers' acoustic axes and the center of the mixing position or the intersection point at 18" behind the mixing position?
The equilateral triangle is not supposed to "be" at all! It's a myth. Or rather, a simplified misrepresentation of how it should actually be. That "equilateral triangle" thing is all over the internet, in all types of books, all over YouTube, and every place else you look. But that does not make it correct. It would only be correct under two very specific conditions:

1) If the speakers and head were set up some place where there is no room around them: out in the open, where there speakers are not loaded by the room, and there are no reflections or reverberant field. And:

2) For all listeners who have had there ears surgically transplanted onto their eyeballs! :shock:

Think about it. Every speaker manufacturer will tell you that the absolute flattest, cleanest sound from there speakers is "on axis": when your ear is lined up perfectly with the acoustic axis of the speaker. Yet all of those "equilateral triangle" diagrams show the acoustic axes interesting in the middle of the engineer head, which means that the ears are NOT on axis! They EYES are on axis... :roll: So if your ears are in your eyeballs, the equilateral triangle is the correct way to set up your speakers. For the rest of us, the speakers need to be set up so that the acoustic axes are aimed at the ears, not the eyes.

In fact, there are many indications that show that the axes should actually be aimed a bit outboard of the ears, not directly at them, since the head itself affects the sound as it approaches the ears, and also to create a wider sweet spot around the mix position.

Hence, acoustic axes from your speakers should intersect at some point several inches behind your head, not in the middle of your head.

But I bet you are thinking "I can do that and still get an equilateral triangle!". Yes you can, but you'd be forgetting point number 1 above: the room. There are good locations for the speakers in the room, and there are bad locations. There are also good locations for the mix position (engineer's ears) in the room, and bad locations. In most rooms, creating the "equilateral triangle" puts the speakers in a bad location, or the head in a bad location, or both. And if yo put them both in good locations, then you no longer have an "equilateral triangle". My answer to that is: "So what?" There's no logical or acoustic reason why the distance between the speaker cones must be identical to the distance between the cone and your ears. Yes, the distance from the left speaker to your left ear must be the same as the distance form the right speaker to your right ear, in order to ensure that the two sounds arrive in phase and at the same intensity: Absolutely. But that has nothing at all to do with the distance between the speakers! In what way does that distance cause the sound to be better or worse? Answer: In no way!

So it's a myth. The truth is that the speakers should be set up at the best point in the room for your speakers in your room, and your head should be set up at the best location for your head in your room, then angled correctly such that the acoustic axes of the speakers intersect several inches behind your head, usually around 12" to 18" back.

But that means they won't be angled at 30° any more! :shock: Yup. So what? There is nothing magical about 30°. It just happens to be the angle you need to create an equilateral triangle, but once you abandon that myth, then you are automatically abandoning the need for a 30° angle: Yes, both speakers must be angled exactly the same, so the angles on each side are identical, but it does not have to be 30°. Anywhere from 25° to 35° is just fine, and under certain circumstance you could even go as far as 20° and 45°. Not more than that, though, for other reasons that I don't have time to go into here.

But you don't have to take my word for it: try it out for yourself! Set up your speakers in the classic text-book "equilateral triangle", 2 feet away from the front wall, 1/3 and 2/3 of the room width, angled exactly 30°, with your chair set up so that the axes pierce your eyeballs and intersect in the middle of your head, then carefully listen to your favorite music like that (flat EQ: don't adjust). Listen to a few songs that you know really well, and pay attention to the bass tightness, accurate definition in the mids, clarity in the highs, as well as the width of the sound stage, and clarity if the stereo imaging. Move your head side to side, and forwards / backwards, to see how that changes, and how big your "sweet spot" is. The quickly and silently (all sounds turned off, so as not to lose the mental reference of what you just heard) move everything around to set it up the way I outlined in my previous post, and listen to the same songs again, at the same volume, once again paying careful attention to all of the above.

Then tell me which setup works best... 8) Which one gives you the best stereo imaging, clearest sound-stage, and broadest sweet-spot, as well as the tightest bass, best definition in the mid range, and clearest, detailed high end? :)

Don't believe all of the "one size fits all" hype about how so set up your room. All rooms are different. All need different setups. Very seldom does the best setup work out to be a 30° equilateral triangle. Unless your ears are in your eyes! :)


- Stuart -


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PostPosted: Tue Dec 18, 2018 1:38 am 
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Soundman2020 wrote:
The equilateral triangle is not supposed to "be" at all! It's a myth. Or rather, a simplified misrepresentation of how it should actually be. That "equilateral triangle" thing is all over the internet, in all types of books, all over YouTube, and every place else you look. But that does not make it correct. It would only be correct under two very specific conditions:

1) If the speakers and head were set up some place where there is no room around them: out in the open, where there speakers are not loaded by the room, and there are no reflections or reverberant field. And:

2) For all listeners who have had there ears surgically transplanted onto their eyeballs! :shock:

Think about it. Every speaker manufacturer will tell you that the absolute flattest, cleanest sound from there speakers is "on axis": when your ear is lined up perfectly with the acoustic axis of the speaker. Yet all of those "equilateral triangle" diagrams show the acoustic axes interesting in the middle of the engineer head, which means that the ears are NOT on axis! They EYES are on axis... :roll: So if your ears are in your eyeballs, the equilateral triangle is the correct way to set up your speakers. For the rest of us, the speakers need to be set up so that the acoustic axes are aimed at the ears, not the eyes.

In fact, there are many indications that show that the axes should actually be aimed a bit outboard of the ears, not directly at them, since the head itself affects the sound as it approaches the ears, and also to create a wider sweet spot around the mix position.

Hence, acoustic axes from your speakers should intersect at some point several inches behind your head, not in the middle of your head.

But I bet you are thinking "I can do that and still get an equilateral triangle!". Yes you can, but you'd be forgetting point number 1 above: the room. There are good locations for the speakers in the room, and there are bad locations. There are also good locations for the mix position (engineer's ears) in the room, and bad locations. In most rooms, creating the "equilateral triangle" puts the speakers in a bad location, or the head in a bad location, or both. And if yo put them both in good locations, then you no longer have an "equilateral triangle". My answer to that is: "So what?" There's no logical or acoustic reason why the distance between the speaker cones must be identical to the distance between the cone and your ears. Yes, the distance from the left speaker to your left ear must be the same as the distance form the right speaker to your right ear, in order to ensure that the two sounds arrive in phase and at the same intensity: Absolutely. But that has nothing at all to do with the distance between the speakers! In what way does that distance cause the sound to be better or worse? Answer: In no way!

So it's a myth. The truth is that the speakers should be set up at the best point in the room for your speakers in your room, and your head should be set up at the best location for your head in your room, then angled correctly such that the acoustic axes of the speakers intersect several inches behind your head, usually around 12" to 18" back.

But that means they won't be angled at 30° any more! :shock: Yup. So what? There is nothing magical about 30°. It just happens to be the angle you need to create an equilateral triangle, but once you abandon that myth, then you are automatically abandoning the need for a 30° angle: Yes, both speakers must be angled exactly the same, so the angles on each side are identical, but it does not have to be 30°. Anywhere from 25° to 35° is just fine, and under certain circumstance you could even go as far as 20° and 45°. Not more than that, though, for other reasons that I don't have time to go into here.

But you don't have to take my word for it: try it out for yourself! Set up your speakers in the classic text-book "equilateral triangle", 2 feet away from the front wall, 1/3 and 2/3 of the room width, angled exactly 30°, with your chair set up so that the axes pierce your eyeballs and intersect in the middle of your head, then carefully listen to your favorite music like that (flat EQ: don't adjust). Listen to a few songs that you know really well, and pay attention to the bass tightness, accurate definition in the mids, clarity in the highs, as well as the width of the sound stage, and clarity if the stereo imaging. Move your head side to side, and forwards / backwards, to see how that changes, and how big your "sweet spot" is. The quickly and silently (all sounds turned off, so as not to lose the mental reference of what you just heard) move everything around to set it up the way I outlined in my previous post, and listen to the same songs again, at the same volume, once again paying careful attention to all of the above.

Then tell me which setup works best... 8) Which one gives you the best stereo imaging, clearest sound-stage, and broadest sweet-spot, as well as the tightest bass, best definition in the mid range, and clearest, detailed high end? :)

Don't believe all of the "one size fits all" hype about how so set up your room. All rooms are different. All need different setups. Very seldom does the best setup work out to be a 30° equilateral triangle. Unless your ears are in your eyes! :)


- Stuart -


Hi, sorry for posting on this old thread but..

I can see you are suggesting moving 30-45cm inside, from the back tip of the triangle.

I modeled that and I can see that my ears will be on axis by just moving 15cm inside. That by leaving speakers as is, on 30 degrees.
I am attaching the design:
Attachment:
Almas speaker axis f.jpg

More I tested that and the best option in terms of tightness, definition , clarity , sound stage, stereo imaging were exactly there. 15cm inside.
More than 15cm returned no actual improvement.

What do you think?


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PostPosted: Tue Dec 18, 2018 3:25 am 
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Quote:
I can see you are suggesting moving 30-45cm inside, from the back tip of the triangle.
Actually, I'm also suggesting angling the speakers a bit less, or a bit more, so they are not at 30°, and/or moving the mix position forward/backward, and/or separating the speakers a bit further / bring them closer together, and/or all of the above....

Quote:
More I tested that and the best option in terms of tightness, definition , clarity , sound stage, stereo imaging were exactly there 15cm inside..
Great! Then you have a good starting point for further experiment. And for checking with REW...

Quote:
More than 15cm returned no actual improvement.
Are you sure about that? Check with REW. Move the mic in small increments, forwards and backwards, and carefully compare the results. You might be surprised at what you see.... :)


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PostPosted: Tue Dec 18, 2018 9:52 pm 
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Stuart thank you for your quick reply !!!

Soundman2020 wrote:
and/or moving the mix position forward/backward, and/or separating the speakers a bit further / bring them closer together, and/or all of the above....


Already did all of the above for and after finding the best spot I tested the "inside triangle" thing.
Without changing the angles though. All tests on 30 degrees

The procedure I followed was this:

I marked the floor with tape and marker that I can erase later.
I had overall 10 widths for the speakers going from 1.2m to 2m in 10cm steps and an extra very wide spot of 2.3m.

For every width I have tested 23 different distances from front wall
going from 35cm (speaker almost touching front wall) to 1.5m in 5 cm steps
which placed the most distant listening position just before half length of the room
(that is after treatment-which is 48% of the length before treatment).

For every combination of width/length I have tested 5 different speaker/mic heights going from 1.05m to 1.49m in 8cm steps.

After painful long measuring and comparing sessions I found what will work best for the room, having in mind after rough measurements that I need to implement the sub also.
I also listened to some music mostly to check the stereo imaging and how the graphs translate on music.

After finding the best spot, I have tested +/-5cm in 1cm steps on every direction including height.



Quote:
Great! Then you have a good starting point for further experiment. And for checking with REW...

Rew already checked as stated above. I can check the different angles though..



Quote:
Are you sure about that? Check with REW. Move the mic in small increments, forwards and backwards, and carefully compare the results. You might be surprised at what you see.... :)


Sitting 15cm closer to center in comparison by a foot closer although it had a stronger center, the stereo imaging was somehow too extreme for my ears and the lows were not so "tight".
The whole mix was just a little more "blurry" but so tiny that was insignificant, if not placebo.
There were differences but not all can be described.

I also got measurements and screenshots of the graphs but they are so many!!!

Maybe it's angling the speakers that is changing the game but I am not sure if it worths, I mean there will be a bunch of options to measure and test just by changing the angle...


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