Designing a new live / mixing room inside home (continued)

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madebyjuice
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Designing a new live / mixing room inside home (continued)

#1

Postby madebyjuice » Fri, 2019-Oct-04, 05:52

Hi Stuart,

Hope you're well mate! I was in touch with you on the John Sayers forum regarding the design of a new studio space in my house. It has been some time since we've spoken but I thought I'd drop you a line as I've recently moved my setup into the new space so i can start trying to find an ideal position. http://www.johnlsayers.com/phpBB2/viewt ... =1&t=22081

I've been conducting preliminary tests using a presonus PRM-1 and REW as recommended. I've tried various positions so far just to familiarize myself with the program and one common trend I've noticed is that I'm getting a much flatter response between 30 - 500hz when the microphone is placed in the center of the room as opposed to the listening position. This has happened numerous times with the speakers placed at several spots. Pictures attached for reference.

MIC at center of room
MIC at center room.jpg

center room.jpg


MIC at listening position
Mic at listening position.jpg

listening position.jpg


My speakers are 1120mm from the front wall. Speakers are aimed 18inches behind the listening position. Speakers and listening position form a 1260mm equilateral triangle. The listening position is exactly 38% away from the front wall.

Is there something i'm missing? I'm not sure what the room is trying to tell me here. Any advice would be greatly appreciated as always!

Thanks,
Jules



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Soundman2020
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Re: Designing a new live / mixing room inside home (continued)

#2

Postby Soundman2020 » Fri, 2019-Oct-04, 15:12

Hi there Jules, and a big Welcome to the new forum! Very glad you found us over here. I sure do remember you, with your strange shaped room.

I've been conducting preliminary tests using a presonus PRM-1 and REW as recommended.
Great! I have updated the procedure for doing REW tests, and it is here now, on this forum: How to calibrate and use REW to test and tune your room acoustics So please take a look at that new version, as I tweaked some things there.

Your graphs show that you are only running the tests from 20 Hz, to 500 Hz, but you should run them full-spectrum, from 10 Hz to 22 kHz. There's good reasons for that, even if your speakers don't cover that range according to their manuals. So for future tests, please do run the full spectrum.

one common trend I've noticed is that I'm getting a much flatter response between 30 - 500hz when the microphone is placed in the center of the room as opposed to the listening position.
With the strange shape of your room, having that curved front wall, it is indeed possible that you are getting strange results! :) Curves can be a little unpredictable. See this thread, for example: http://spartanew.digistar.cl/Forum/viewtopic.php?f=7&t=22

Also, you are only looking at the Frequency Response curves, which are useful, yes, but they aren't the most important indicator of room response. Time-domain response is more important. In other words, the waterfall, spectrogram, decay, and ETC (Impulse Response) graphs. Those tell you how the room is behaving over time, as the sound dies away, and that's more important than the "steady state" frequency response curves. So you should be looking at those too, in your search for the smoothest layout for the speakers and mix position.

Please post the actual MDAT file here on the the forum, in your thread That way, we can all take a close look at the data, and analyze it in various ways, to see help identify the best layout. (Yes, you can post MDAT files here on this forum! It wasn't possible in the other place, but I gave this new place enough capacity and power to be able to handle that, so feel free to use it! This place is also "drag and drop", so you can just drag the file directly into your message window... Done! much easier...).

To help you find the best location, I would suggest that you do the "walking mic" procedure, discussed here: ( walking mic test procedure. ) That's usually a real eye-opener, and helps you understand the room a lot better. In your case, I would try it with the speakers in two positions: firstly where you have them now, and secondly right right up against the front wall. If you REALLY wanted to get fancy, you could do a whole series of "walking mic" tests, while also moving the speakers in small increments. To reduce the enormous amount of data that you would generate by doing that, I'd suggest going with larger increments, and limiting the "walk" to just a couple of meters either way from the theoretical best mix position.

One other things I'd suggest, is that you swap out your current desk for a much smaller one, and get your speakers off the desk, onto stands behind the desk. When you have your speakers sitting on the desk, that creates a whole slew of acoustic issues that can be avoided by just putting them on stands behind the desk. The manufacturers of those desks never bother to tell you about that (I wonder why= :) ), but the effects are very real, and very measurable. Try to get a desk that is as low-profile as possible, with few large flat surfaces. Maybe if you take the speaker shelf off that desk, it would be decent. Ditto for your chair: Don't use a chair that has a high hard back, but rather one that is more acoustically transparent, such as this one:

CHAIR-open-mesh-back-2.jpg
Open and "airy" is the concept.

And one other thing: Try to get your video screen down lower, so it interferes less with the sound arriving at your ears. A bigger screen further away (ideally, directly on the front wall) is better than a smaller one close up... and a big one close up is the worst of all! Large flat areas create acoustic reflections, diffraction, "shadowing", and other not-so-fun issues, that it is best to avoid.

Speakers and listening position form a 1260mm equilateral triangle.
I think I need to write an article about the famous "equilateral triangle" myth! It keeps coming up over and over again, but basically it is a myth that you must have your speakers and mix position set up in a perfect equilateral triangle. It simply is not true. Yes, it does work for most rooms, which is why the speaker manufacturers put it in their manuals (sort of like a "one size fits all" approach), but it is never the optimum layout for any given room. It's just a layout that sort of works reasonably OK, sort of... maybe...

Here's the thing: You will not get arrested by the "triangle police" if your speakers are set up differently! :) Nothing bad will happen to your speakers, the roof won't collapse, and your DAW won't explode if you set up your room a bit different. It is perfectly fine to have your speakers angled at something other than 30°: anywhere in the range 25° to 35° is fine, and under some circumstances you can even go to 45°, if you lay things out carefully.

It is still important that the distance from the left speaker to your left ear is the same as the distance from the right speaker to your right ear, yes. Definitely. But that distance does NOT have to be the same as the distance between your speakers.

If you think about it, this makes sense... Pretty much all contemporary studio monitors are designed to have the best, smoothest, flattest sound on-axis to the speaker: the further off axis you go, things start to fall apart and get more uneven.

However, if you set up your speakers in the standard equilateral triangle, with each speaker at one apex of the triangle and your head at the third apex, you'll notice something strange: the speakers are aimed at your EYES! Not your ears... So if you happen to have your ears surgically transplanted onto your eyeballs, then the standard equilateral triangle is fine... but for normal people, with their ears sticking out the sides of their heads, many cm away from their eyes, the triangle doesn't work... because your ears are not on-axis to the speakers! It turns out that ou have to rotate the speakers a little further out, so the acoustic axis is pointing a but past the tip of your ear (the "pinna"). That gets your ears on-axis again... but then the triangle is no longer equilateral!! So, as I said, it's a myth.

"But!... But! .... BUT!....." some people say... "You can still have the triangle if you just move your head forward, so that the axes are pointing at your ears again..... Hmmm.... that doesn't make sense, geometrically.... because if you do that, then obviously your ears are no longer the same distance from the speakers, as the speakers are from each other... so once again, that is not an equilateral triangle! :shock:

In other words, no matter which way you look at it, it is actually impossible to have a setup where the speakers are angled at 30°, your ears are on-axis to each speaker, and the distance from ear to speaker is the same as the distance between the speakers. That is physically impossible. Either you have to roate the speakers, or you have to move your head, and in both cases you end up with a triangle that is NOT equilateral.

Thus it is a myth.

Thus, don't sweat it! Just lay out your speakers in the best positions for YOUR room, and YOUR speakers, to OPTIMIZE the acosutic response at the mix position, then treat the room accordingly, and perhaps re-tweak things a bit after you treat (since the treatment itself will change the location of the optimum layout). This is especially true in your room, which has a very complicated shape, so all of those normal "rules" are out the window!

All that to say: forget about equilateral triangles!

The listening position is exactly 38% away from the front wall.
The 38% location is not a myth... but it is also not a rule! It's a guideline , meant for rectangular rooms. Wes Lachot was the guy who came up with that, as far as I know, and he was merely attempting to find the spot that has the least bad modal response, in a perfectly rectangular room. Not the "perfect" or "best" spot, because there is no such thing: just the spot that is "least bad".

This does not mean that 37.9% is terrible, or 38.1% is disgusting. Not at all. It just means that 38% is the middle of a range of not-so-bad locations, and in reality, anywhere from maybe 33% to 43% is probably just fine in most rooms. In odd-shaped rooms (such as yours), the "rule" does not apply at all. It is only valid for rectangular rules, because it describes the point where the modal response of a rectangular room is lowest. Modal response is easily predictable, using simple math.... but only for rectangles with three sets of mutually perpendicular surfaces. As soon as you angle any of those surfaces, or add more surfaces, or change the shape in any way, then its no longer possible to predict the modal response with simple math, and the 38% point disappears.

So, there's another long convoluted explanation to say: forget the 38% point in your room! There will still be a point where the modal response is best, but it won't be at 38% because the modal situation in your room is far more complex than for a simple rectangle. It would be possible to model it in a computer, using FEM/FEA or BEM, to predict where the best spot is... or you could just do the "walking mic" test to find it.... :)

Is there something i'm missing? I'm not sure what the room is trying to tell me here.
The reason why things don't seem to make sense in your room, based on the conventional wisdom, is because your room is not like a conventional room: that curved front wall messes up all the "rules" and even the guidelines. So in your case, the simplest approach is to use a procedure such as the "walking mic" to help you find the best spot. And not just for the mix position: you'll need to do something similar to find the best spot for the speakers too.

This is the reason why things are so confusing in your room: the shape throws it all off from the "normal" situations, so it's going to be a bit tougher in your case. But by working carefully, we'll be able to figure it out! Don't give up hope!


- Stuart -




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