Holy crap dude! I was hoping to get a detailed answer, but dayum! Thanks so much
You are very welcome! That's what the forum is all about.
Secondly - I am not using an EQ. PCIe sound card SPDIF > Avocet > 8Cs (XLR). That's it.
Ummm... yes you are! You said so yourself: "
After taking a bunch of new REW measurements (in a "mesh", as it was called), I was aided in setting up the filters in the mons; ". Your speakers have built-in parametric equalization: that's what you used, and it is very evident in the REW graphs you posted.
Next - why did I choose that placement for desk and speaker? No speacial reason; I just picked a spot. The desk used to house a pair of Yamaha HS8s (and then Focal twins), and I placed the desk with the idea that the speakers should be close to the wall, but not right on the wall. I did, however, want to make sure the speakers were equidistant from the side walls. The desk can be moved if need be.
It's not the desk that needs moving: it's the speakers. Speakers should never be on top of a desk, nor on a meter bridge, because that invariable creates very uneven response in the mid range, due the reflections from the desk surface and also the interference between those reflections and the direct sound. There might also be other issues, such as vibrations induced on the desk itself, and the resultant possible early-early sound (which arrives at your ears BEFORE the direct sound from the speakers). There is some indication of that uneven response in your REW data. There's no indication of early-early sound in your case, but there might be some resonance and vibration in there.
Speakers should be on stands beyond the desk, up against the front wall, not on the desk. Yes, you do see photos of supposedly high-end studios with speakers on the meter bridge... but that doesn't mean that it is the right way to set up speakers! There's plenty of direct evidence from laboratory testing, as well as real-world empirical data, showing what a bad idea it is, and the what a mess it makes of speaker response.
Next: The reason why the speakers need to NOT be far away from the front wall, is something called "SBIR". That stands for "Speaker Boundary Interference Response". It's a fancy technical term that basically means that the low frequency sound waves leaving your speaker head off in BOTH directions: some towards you, and some going the other way, hitting the front wall, then bouncing back... and interfering with the copies of themselves that already headed your way.
Some people find it easier to picture this as a "Mirror image" speaker: Instead of a reflection from the wall, imagine that there's another identical speaker exactly the same distance behind the wall, then imagine that the wall has gone, so all you have is the two speakers producing the same sound. If you could see the sound waves, this is what you would have:
sbir-interference-patterns-mirror.jpg
You can see how the waves interfere with each other, creating dips and peaks in the frequency response: That pattern of dips and peaks is different
for different locations in the room, and different frequencies.
Obviously, there's a slight delay between the two waves: the wave that took the longer path, bouncing off the front wall then coming back at you, is delayed slightly with respect to the wave that came at you directly. A time delay implies a phase shift. So the "bounced" wave is out of phase with the "direct" wave, and that interference between them causes a massive dip in the frequency response for all frequencies where the delay happens to be a phase shift of 180°. So there's a massive dip at some very low frequency directly related to the distance between the wall and the speaker, then a series of smaller dips, that repeat in a regular pattern all the way up the spectrum: this is called "comb filtering".
This is what the actual frequency response looks like for comb filtering:
SBIR-effect-dip-and-comb-filtering-frequency-response-graph.jpg
There are equations for calculating that.
If the room is large enough, then you can position your speakers far enough away from the front wall that the first huge dip occurs at a frequency below the audio spectrum, so you'd be fine. That distance is about 4 meters! So if you have a room about 20 meters long, then you can do that.... But most home studios are nowhere near long enough to permit that. The second-best option is to put your speakers tight up against the front wall, which forces the first SBIR dip up into the lower end of the mid range, where it is less audible, and can probably be treated.
The best option of all is to flush mount your speakers IN the front wall, such that the front baffle of the speaker is level with the wall surface: in that case, there is no SBIR at all from the front wall! Because the speakers are no longer in the room, so there's no interference pattern, and no SBIR. This is sometimes called "soffit mounting" and is the single best thing you can do for a control room: it solves so many problems all at once, not just SBIR.
Looonnngggg explanation to show the reason for the suggestion: Get your speakers close to the front wall, off the desk, on stands.
Then, set up the desk at the correct location in the room. Or rather, set up your chair at the correct location, then place the desk in front of your chair, so that you can operate your gear comfortably.
Next, the new pic has the location of the diffusors. They are from GIK acoustics... wood w/fabric. What is meant by "tuning" the diffusors. How do you tune them?
You can't tune them after you buy the: you buy them already tuned. There's a certain frequency range that any diffuser affects. For Schroeder type diffusers (which includes Skylines), the depth of the well determines the lowest frequency, and the width of the well determines the highest frequency. Below the lowest frequency, there's no diffusion. There's probably scattering for about an octave below, but not real diffusion. And above the highest frequency, there's also no diffusion. You only get diffusion in the range that the device is tuned to, around it's "target frequency". So you should first determine what frequency range your room needs diffusion for, then buy the right diffuser that treats that frequency range.
However, as I already mentioned, there's a minimum distance from the diffuser to your head. The reason for that is because of the way numeric-sequence diffusers work. The mess with the timing and phase of the sound. Some parts of the wave go down one of the wells, bounce off the bottom, and come back up... with a time delay (because of te extra distance for the "down and back" path), and that implies a phase change. But the well right next door has a different depth, and therefore a different phase change. The interference patterns between the various phase changes causes the reflections from each well to go off in a different direction, with different timing and different phase: ie, diffusion. But close up, those time, phase, and level differences are audible: if you move your head just a bit, you hear a DIFFERENT set of time, phase, and level differences: the diffusion is not smooth close up. It needs space for all those things to merge together again, into a coherent but diffuse sound field. The minimum distance is about ten feet (3m), but if the diffuesr is tuned low then you might need an even larger distance.
If you could see the sound waves after they come off the diffuser, here's what it would look like:
QRD-Diffusion-lobing--pattern-graph-SML-ENH-2.PNG
As you can see the "lobing" patterns are very intense close up, and it's only at a reasonable distance that you actually get a smoothly diffuse field. Thus, if your head is closer to the diffuser than the minimum distance, then even moving your head slightly places your ears in a different part of that field, so you are hearing the lobing patterns, not the diffuse sound field.
I can not remove the carpet. I am not sure about adding a hardwood surface - I would have to look into that, to see how it might be done.
The effect in your room is not too terrible: just a bit of roll-off in the high end, so I wouldn't worry too much about that.
I am assuming the difference in the early reflections is due to the fact that the window is there behind the l speaker?
It's possible, yes. Or it might be something else in the room that isn't symmetrical. For example, the closet on only one side of your rear wall... Or stuff on your desk that isn't symmetrical. It might even be in the structure of the room, such as a different type of framing for the side walls, or a different thickness of drywall, or different insulation. That's not so likely, but it is possible.
I have no bass trapping right now. Not if we are talking about actual bass traps in corners. There is nothing currently in any corner, top or bottom.
What treatment do you have in there, apart from the diffusers?
RCSW = room correction software. Again, I have none.
Ahh, but you do! That's what the parametric filters in your speakers are doing... EQ is still EQ, no matter what fancy name the speaker manufacturer might decide to give it. "DSP" seems to be a common disguise these days: but at the end of the day, it's still just EQ....
Yes. I can move the desk back, so the speakers are closer to the wall.
Again, don't mode the desk: move the speakers off the desk, onto stands. Then set the desk in the correct location for the mix position, not for the speakers. You have to sit at the appropriate location in the room, where you get the best acoustic response, then you move the desk so you can reach everything on it comfortably. The desk location is dictated by where your ears have to be.
In terms of your next comment - I am not familiar with the term "acoustic axis".
The acoustic axis of any speaker is the spot on the front baffle where all of the sound "seems" to come from. The manufacturer normally shows that in the documentation for the speaker, or on their website. For a two-way speaker, it's about half way along the imaginary line that joins the center of the tweeter to the center of the woofer. For a 3-way speaker, it's more complex. But ask the manufacturer. They should be able to tell you that the acoustic axis is located on the front face XX cm from the left side of the cabinet, and YY cm from the bottom- Some manufacturers even mark it directly: Eve Audio, for example, positions their logo to mark the acoustic axis. Genelec publishes one single booklet that shows all of the acoustic axes for all of their speakers.
Actually, all of the above is about the acoustic center of the speaker: The acoustic axis is an imaginary line that extends out from the front of the speaker, starting at that point, and perpendicular to the speaker face.
Once you find the location of the acoustic axis, your speakers need to be set up with that more or less at your ear height, or a bit higher, and the speakers should be toed in a little, such that the acoustic axis points slightly outboard of the tips of your ears. Thus, the axes from the two speakers will meet each other, intersecting, about 12" to 18" behind your head. That's the theoretical ideal situation.
The top to bottom I didn't choose either; it just wound up that way when I placed the speakers on my desk.
Yet another reason to get them off your desk!
There's an optimal setup for the speakers, the mix position, and the room. If you don't have things set up in that optimal arrangement, then you don't have the smoothest, cleanest, flattest acoustic response.
The aim point is the middle of my head (proper triangle here).
Ahh yes... the infamous "equilateral triangle" strikes again... Don't get me started on that!
Too late! You already got me started! ...
OK, here's the thing: I'm sure you already know that the very best sound from your speaker is "on-axis": when the speakers are pointing at your ears: Because the further "off-axis" you go, the less even, smooth, and clear the sound gets. At 90° off axis, it's a totally mushy disaster, for any speaker, and at 180° off axis, al you get is deep rumbling mud. The cleanest sound is on-axis. It's logical. Now, if you set up your speakers so that they are pointing at the middle of your head, then the acoustic axis is NOT aimed at your ears!
Rather, it is aimed at your EYES!
So, for all people who have had their ears surgically transplanted onto their eyeballs, the equilateral triangle is just perfect...
But for the rest of us, with our ears sticking out from the sides of our heads, many inches away from our eyes, the triangle isn't any use at all. Instead, the speakers need to be toed out a little less, so that they are aimed at your ears, not your eyes. In fact, the science of psycho-acoustics shows that it's best to have the axis pointing just a little past the outer edge of your pinna... The "pinna" is the medical name for the fleshy flappy thing that sticks out from your head, with all those folds and wrinkle in it: what most people would just call "ear", but doctors love to invent special names for all body parts, so the called that the "pinna".
So, forget about the equilateral triangle diagrams that you see in many books and internet sites, showing lines coming out of the speakers and meeting in the middle of your head. Rather, pay attention to the more correct diagrams that show the lines coming out the speaker and going past the side of your head, meeting a bit behind your head. Those are the correct ones. That's how you set up the speakers and mix position for the best sound.
But there's one factor missing here: where to put the speakers "side to side". In other words, how far from the side walls, and how far between them. There are some equations for figuring that out too, and one of them just says "About 27% to 30% of the room width": That's where you set up the acoustic axis of your speaker. Call it 28%. So for example, if your room is 10 feet wide, that's 120 inches, so you would set up each speaker at 120 x 0.28= 33.6" from the side walls. And you would then have a distance of about 52.8" between the speakers (acoustic center to acoustic center).
And one other missing factor: where to put your head in the room! There's an interesting and much-debated guideline that says the supposedly best location is 38% of the room depth: 38% of the distance from the front wall to the back wall. So if your room was 10 feet long, then according to this guideline your ears should be about 120 x 0.38 = 45.6" from the front wall. In theory, that's the spot that has the least modal issues in any room. In practice, most engineers seem to prefer being just a couple of inches further forward, so call it maybe 43", or about 110 cm (do the math for your own room! I'm just giving hypothetical dimensions as an example).
So, for the hypothetical room here, the speakers would go with the acoustic axis 48" above the floor and 33.6" from the side walls, with the rear corner 4" from the front wall, and the mix position (engineers ears) set up 43" from the front wall, 47" above the floor, on the room center-line, and the speakers toed in so they both point at a spot about 18" behind his ears. That's the theoretical optimum layout.
Notice I didn't mention any angles there? The famous and sacred "equilateral triangle" insists that the toe-in angle must be exactly 30.00000°, with the engineer's head siting on the tip of that triangle, and the acoustic axes piercing his eyes.... That's silly. Because its the ROOM that dictates where the speakers and mix position go, not an imaginary geometric figure! If you do this setup the way I mentioned it above, you'll find that the angles will NOT be exactly 30°. They will be close, but not exact. Maybe 27°. Maybe 32°. Maybe more. Maybe less. And .... who cares? 30° is a nice figure that is easy to print in the manual, and in fact does work for most rooms... but is not OPTIMAL for ANY room!
That's the reason why you see the infamous triangle in so many places: it works for most cases. But isn't the best for any case. The best is to follow acoustic theory to arrive at the right locations, then tweak that based on actual testing with REW and with your own ears. Theory is one thing, and the real world is another. Every room is different, and in reality there's no such thing as "one size fits all". What the above will do is to get you to a good starting point, which will be much better already than that "triangle", but still probably won't be the best possible. You then do a series of tests with REW, moving the speakers and mix position in a set of small increments, until you find the absolute best spot. In other words, you move the mic forwards and backwards about a couple of feet each way, in steps of 2", and see where the best spot is (smoothest response). Then you move the speakers closer together and further apart in steps of 2" to see what's the best spot for THEM. Repeat as often as you need, until you fine "The Best Possible Layout That Cannot Be Beaten"! It's a slow, boring process, but if you really want to optimize your room, that's the way you do it.
So, in summary: First, turn off the EQ (parametric filtering) in your speakers, so we can get the REAL acoustic response of the room itself, unaffected by the speaker tuning. Then get the speakers off the desk onto stands (very heavy, tough, firm, rigid stands), and do the other stuff to re-arrange the room into the theoretical best layout, the test again with REW like that. Then do the "small increments" procedure (boring!) to find the best spot. Then add some bass traps, some absorbers on the front wall between the speaker and the wall, something on the ceiling, something on the side walls, and a huge amount on the rear wall. Then measure with REW again. Carefully document every REW test you do, noting the exact location of the speakers and mix position for each one, in the comments block for each measurement. That way you can easily see the trends, and get back to any position later, if you wanted to try something else instead.
So, that's what I'd suggest!
- Stuart -