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How to treat this room?
Old 8th September 2019
  #1
Gear Head
 

How to treat this room?

I would like to treat my space for mixing.

The room has an opening towards another room on the right of my desk, which can be closed by sliding wooden doors. The studio room is 5.30 x 3.60 meters, and the ceiling is 3.10 meters.

This is the REW measurement (not ideal, I'm sorry):
https://imgur.com/a/inknLww

There is no treatment at all right now aside from Auralex Mopads below the monitors. The studio room is also kinda empty but I do have bookshelves to add eventually. I am ready to spend some money in treatment, though.

The room might be a bit complicated being two rooms connected (again, I can slide the doors and obtain a single rectangular room that way, but part of one wall would be wood instead of concrete) and also due to the windows. Right now, the right monitor has a wall besides it at around 130 cm away. Behind the monitors there's a combination of wall and windows, 60 cm away.

First, my listening position is right now at around 25% of the length of the room rather than 38% as I have read it would be a good idea to be, so should I move the desk and the monitors at 25% instead and my listening position at 38%? By doing so, though, the right monitor will have the OTHER's room wall far off on the side, OR the wooden door if I shut them. It would be an asymmetric setup, which I don't know if it's good.

I don't anymore know what's the better monitors position here, and how to treat the room. I am ready to buy Roominators, the base GIK Acoustic kit, or bass traps. But I don't know what I should buy, I need a plan.

I absolutely cannot hang anything on the ceiling at this time - most everything else at around 500 to 1000 euros, I can do.

Hope to get some good advice. Thanks in advance.
Attached Thumbnails
How to treat this room?-sketchup3.jpg   How to treat this room?-sketchup1.jpg   How to treat this room?-sketchup2.jpg   How to treat this room?-room4.jpg   How to treat this room?-room3.jpg  

How to treat this room?-room2.jpg   How to treat this room?-room1.jpg  

Last edited by purpleduck; 8th September 2019 at 04:38 AM..
Old 8th September 2019
  #2
The room size is nice but your budget is too small for anything off the shelf.

If you can live without the view, turn the desk around so you'll have more symmetry and only the rear wall will be asymmetric.

Please also post your .mdat, not screenshots.
Old 9th September 2019
  #3
Gear Head
 

Quote:
Originally Posted by johannburkard View Post
The room size is nice but your budget is too small for anything off the shelf.
Thanks. It is pointless to apply two or four bass traps? I am not expecting perfect treatment, but I've read just some, anything goes a long way. It's not worth it for the purpose of having a better mixing environment?

And what about this? https://www.gikacoustics.com/product...kit-package-1/

4 bass traps, 3 acoustic panels and a cloud. 580 dollars. Wouldn't that be of benefit?

I will post the .mdat.
Old 9th September 2019
  #4
Quote:
Originally Posted by purpleduck View Post
It is pointless to apply two or four bass traps?
No, it rarely is, but you want the right bass traps.

If I can go with the images you've posted, you have a room mode at around 100 Hz and one at around 35 Hz. At some point, I opted to ignore for the time being my 33 Hz 1-0-0 room mode but that wasn't a popular choice at Gearslutz so you'll have to work on that eventually.

For the 100 Hz mode, six or eight 244 panels on the side walls should help.

However, you also have a huge hole between 100 Hz and 35 Hz and you'll need something thicker like the Monster Bass Trap to attack that.

So you could start with four soffit bass traps, two Monster Bass Traps and six 244 panels. And a pair of stands so you could put your speakers against the wall.

Quote:
Originally Posted by purpleduck View Post
And what about this? https://www.gikacoustics.com/product...kit-package-1/

4 bass traps, 3 acoustic panels and a cloud. 580 dollars. Wouldn't that be of benefit?
You don't need the thinner stuff and shipping with GIK isn't exactly free.
Old 9th September 2019
  #5
Gear Head
 

Quote:
Originally Posted by johannburkard View Post

So you could start with four soffit bass traps, two Monster Bass Traps and six 244 panels. And a pair of stands so you could put your speakers against the wall.
I don't understand why four Soffits and two Monster Bass. Four on the four corners, and the other two where?

Speakers against the wall. Well, I can just push the desk against the wall. I plan to buy stands anyway but why should the speakers be against the wall? I have read it's good if they are detached from the wall a bit. I took care of positioning them 60 cm away from the wall. The speakers have rear bass ports too (should I plug them? And also there are room EQs switches which I never used).
Old 9th September 2019
  #6
Quote:
Originally Posted by purpleduck View Post
I don't understand why four Soffits and two Monster Bass. Four on the four corners, and the other two where?
On the first reflection points on the side walls.

Quote:
Originally Posted by purpleduck View Post
why should the speakers be against the wall?
While you'll be exciting the 1-0-0 mode maximally, you are minimizing the distance to the front wall which is as far as I understand it at least minimizes any holes in the bass on that path.

Quote:
Originally Posted by purpleduck View Post
The speakers have rear bass ports too (should I plug them? And also there are room EQs switches which I never used).
Speakers are omni at low frequencies, where the bass reflex port is doesn't matter to bass frequencies (bass reflex ports usually let some low midrange through though). Use the room EQ switches to fine-tune after you've found a spot, installed treatment and measured the results.
Old 9th September 2019
  #7
Lives for gear
 

Quote:
Four on the four corners, and the other two where?
A room has twelve corners... Only four of them are vertical... I'm not sure if that's what Johann was referring to, but all of the corners in a room are fair game for bass trapping. The more, the better.

Quote:
I plan to buy stands anyway but why should the speakers be against the wall?
To reduce the severity of SBIR. If you have your speakers very far from the front wall, then SBIR will occur at a very low frequency: too low to be important. But the distance you need for that is around 3m (aprox. 10 feet), so you need a rather large room to be able to do that. The closer you get the speakers the wall, the more the SBIR issues move up the spectrum, into the lower end of the bass range, where they are very audible... and very, very hard to treat. And as you get closer still the issue continue to move up the spectrum more, until with the speakers very close to the wall (just a few cm away), the issues are now completely out of the low end, and into the mid range.... where they are not so noticeable, are probably lower in intensity, and can be treated a lot easier.

Quote:
I have read it's good if they are detached from the wall a bit.
Unfortunately, you heard wrong. There's an awful lot of incorrect information about acoustics floating around on the internet, unfortunately.

Quote:
I took care of positioning them 60 cm away from the wall.
If you mean 60 cm between the rear corner of the speaker and the wall, and assuming your speaker is maybe 25 com from front face to rear face, that places the drivers around 85 cm from the wall.... thus, your primary SIBR dip will be at about 100 Hz, where it is hard to treat.

Quote:
The speakers have rear bass ports too (should I plug them? And also there are room EQs switches which I never used).
It's not necessary to plug the ports, unless you flush-mount the speakers. As long as you leave a gap of about 10cm between the rear of the speaker and the wall, that's plenty.

- Stuart -
Old 10th September 2019
  #8
Quote:
Originally Posted by Soundman2020 View Post
Only four of them are vertical... I'm not sure if that's what Johann was referring to
Yes, for easy stacking.
Old 10th September 2019
  #9
Gear Head
 

Quote:
Originally Posted by johannburkard View Post
For the 100 Hz mode, six or eight 244 panels on the side walls should help.
You haven't mentioned any treatment behind the monitors. Not necessary?

I am not willing to turn the desk around, that other wall is too depressive. I will keep them in front of the window (I am ok with moving them to the longer side wall, but it seems it's not the thing to do for the acoustics).

Behind the speakers is a combination of wall and window glass panes. The glass screams the opposite of "good acoustics" to me. At stupid volumes, they rattle (volumes I never use, and I applied silicone caulk around the frame to minimize the shaking). The glass is also asymmetric on the rear of the speakers. So, no treatment needed there?

Last edited by purpleduck; 10th September 2019 at 05:16 AM..
Old 10th September 2019
  #10
Gear Head
 

Quote:
Originally Posted by Soundman2020 View Post
Unfortunately, you heard wrong. There's an awful lot of incorrect information about acoustics floating around on the internet, unfortunately.
I think I even read it on the official Yamaha HS80M manual, I will check later, maybe I misread it as "keep them as far away as you can" (while still far away from the center of the room because of other acoustic science rules). Maybe they just meant those 10 centimeters. But I think I read that if you could put them 50 cm away, then good! Official Yamaha manual! I'll find it and confirm later.

I have read 25% of the length of the room would be the optimal position for monitors. I saved that advice as a screenshot that I am attaching (can't find the webpage).

That rule is bogus? 38% ideal listening position, and "in front of the 25% point in the length dimension", it says there.

Additionally, for hi-fi speakers I have read it's recommended to "leave some air around the speakers" rather than having them next to a wall on any side.

A speaker on a corner clearly boosts the bass. This doesn't happen when placed against a wall, especially when there's a bass reflex? When I use some small bluetooth speaker, I put it in a corner if I want more bass, but I admit I use a corner, not just one wall.
Attached Thumbnails
How to treat this room?-screenshot-2019-08-29-02.19.47.jpg  
Old 10th September 2019
  #11
Lives for gear
 

Quote:
Originally Posted by purpleduck View Post
I think I even read it on the official Yamaha HS80M manual, I will check later, maybe I misread it as "keep them as far away as you can" (while still far away from the center of the room because of other acoustic science rules). Maybe they just meant those 10 centimeters. But I think I read that if you could put them 50 cm away, then good! Official Yamaha manual! I'll find it and confirm later.
Perhaps the image below, from Neumann, will help clarify what SBIR is, and the distances. Also the pages from the Genelec speaker setup guide, related to SBIR.

Quote:
I have read 25% of the length of the room would be the optimal position for monitors. I saved that advice as a screenshot that I am attaching (can't find the webpage)
25% if room length is good for one thing ONLY: not triggering the second order lengthwise modes. That's all. Which might not even be a good thing, depending on the room and the speakers. All rooms are different, and all need different treatment, as well as having different optimal layouts. That spot also pretty much guarantees that the speaker will trigger every possible first-order mode, because it is in the exact location in the room where those will form: the quarter-wave peak location. So no, that's not a good location for a speaker. It avoids one set of modes while forcing an even worse set of modes. Whoever wrote that is not thinking things through very well!

There's several other thing in that image you posted that indicate an incorrect understanding of room modes. For example, it says that room modes are caused by "two waves traveling in opposite directions and striking two parallel walls". That is is most certainly not correct! Modes are a form of resonance, and each mode is just one single wave (not two), traveling in one direction only, in a circuit around the room that brings it back to its original starting position, going the same way it was originally, and in phase with itself (not out of phase, which is what would happen if there were two waves going in opposite directions). All modes are exactly the same in that way: just a single wave following a single path around the room repeatedly, in phase with itself at every point on the path. The difference between the various types of mode is that axial modes do that by following a path between a single pair of walls (which do not have to be parallel), while tangential modes follow a path around two pairs of walls, and oblique modes follow a path around all three pairs of "walls" (where the floor and ceiling are considered "walls" for this purpose).

In fact, what that text describes as "two waves traveling in opposite directions " is what SBIR is all about! And is totally unrelated to modes. Those are two very, very different acoustic phenomena, and are completely unconnected. No relationship. Whoever wrote that text seems to be very confused about acoustics and the processes behind how sound works.

Quote:
That rule is bogus? 38% ideal listening position, and "in front of the 25% point in the length dimension", it says there.
The rule is not bogus, but it's also not a rule! Wes Lachot regrets the day he made the public, since he never intended it to become a "rule": he suggested it as a good starting point, but never as a rule. He did some simple calculations based on a series of room modes, and arrived at the conclusion that the 38% location is the spot where there is the least modal activity. That's all. That does NOT mean there is no modal activity at all, nor even that it is the best spot in the room! It might be in some rooms, purely by chance, but by no means is it always the best spot in every room. When I'm designing a room, I often start out by looking at the 38% spot, then work forwards and backwards from there as needed, to get a better location. And if for some geometric reason I have to put the mix position at a spot that is NOT 38% of the room length, that won't bother me in the least! Usually, the listening position ends up somewhere between about 30% and 45% of room length (for a control room) and maybe between 55% and 70% (for a home theater or recreational listening room). That's the normal range. The spots that should be avoided are 25%, 50% and 75%, because that's where the first order modal peaks.

Quote:
Additionally, for hi-fi speakers I have read it's recommended to "leave some air around the speakers" rather than having them next to a wall on any side.
Hi-fi speakers follow the same rules of physics as all other speakers. The decision of where to place them is usually made based on geometric calculations, along with actual acoustic measurements. If you have them away from the walls, you lose the benefit of the bass boost from the walls... and in a small room, you then also get the severe penalty of SBIR! SBIR stands for "Speaker Boundary Interference Response", and it refers to the problem caused by "two waves traveling in opposite directions" (which has nothing to do with modes.

What happens is fairly simple to understand: for low frequencies, the speaker emits sound in all directions. For high frequencies, the sound is focused in a cone heading out the front of the speaker, but as you go down the spectrum, that cone gets wider an wider, until at some point on the spectrum, it "wraps around" the speaker, and some of the wave goes backwards, behind the speaker. That wave then bounces off the front wall, comes back the way it came, and as it passes the speaker heading back into the room it will be exactly 180° out of phase with itself for some frequencies... thus causing a huge null in the frequency response. That's what SBIR is. It is the wave from the Speaker hitting a Boundary, then Interfering with itself, and messing up the speaker Response. It causes that huge initial dip shown in the image below from Neumann, as well as the wavy jagged comb filtering all the way throughout the rest of the spectrum. In other words, it trashes the frequency response, making a total mess out of it. And it has nothing to do with room modes: they are two different acoustic issues. They might happen at similar frequencies in some rooms, if the dimensions of the room and the speaker layout happen to coincide badly, but they are two distinct issues, and are not related to each other.

SBIR can form between the speaker and ANY wall: not just the front wall. Usually the front wall SBIR is the strongest, but it can also occur with the rear wall of the room, and with the side walls (and even with the floor and ceiling, in some cases).

That text you quoted seems to be a muddled confusion of these issues, but it is wrong in many ways, so you can safely ignore it. For example, it defines the "sweet spot" as the intersection of the 38% length position with the 50% width position... but that's not correct either! The speakers play a major role in determining where the sweet spot is, as do several other factors.

Quote:
A speaker on a corner clearly boosts the bass. This doesn't happen when placed against a wall, especially when there's a bass reflex?
YEs it does, actually! And that's why studio monitor speakers have controls on the rear, to compensate for the bass boost in walls and corners.

It works like this: remember I said that for highs the sound waves are emitted roughly in a cone shape pattern? And for frequencies a bit lower the cone gets wider? And as you go even lower in frequency, the cone gets wider still, until at some point it spreads out completely, and then at even lower frequencies, the sound waves "wrap around" the speaker, and and also go backwards? That's what we are talking about here: For highs, all of the power goes just towards you. For lows, half of the power goes towards you, and the other half goes backwards, away from you. In a free field, where there is no room around the speaker, the part that goes backwards is lost: it never comes back. So half of the power put out by the woofer is gone: disappears into nothing. Thus, the speaker manufacturer puts an amp inside that is twice as powerful, for the woofer, since it has to develop twice as much power as the tweeter, just to send the SAME level of power towards you. (because all of the tweeter power goes towards you, but only half of the woofer power does).

Now, if you then put that same speaker in a normal room, far away from the walls, then some of that power that went out "backwards" hits the wall and comes back to you, so you do hear it... but only slightly if the speaker is far away form the wall. If you move the speaker closer to the wall, then you get more of that power coming back at you, and if it is right against the wall, then ALL of it now comes back to you: you don't lose any of it. But that now means that the woofer is putting out too MUCH power! Instead of losing half of that power into nothing, it is ALL coming back at you. So you need to turn down the woofer amp by half, to make sure you are getting the correct power balance: the same amount of sound level from the woofer and tweeter. Thus, you have "room correction" controls on the rear panel of proper studio monitors, so you can compensate for that problem. Those controls are usually variable, and allow you to roll off the low end intensity across a range of 0 dB down to -6 dB (because a drop of 6 dB is exactly half the power).

That's for proper studio reference monitors: For low-quality speakers that don't have good bass response, such as your little bluetooth speakers, putting the against the wall can indeed help to improve the APPARENT bass response, because it boosts the tiny bit of low-end that the speaker was just managing to emit, and increases the level by 6 dB. For a poor quality speaker that had no low end before, that can be useful, as now it appears to at least have some low end... However! Doing that also boosts the frequencies that the speaker was putting out just fine before, so now you have a frequency response imbalance, in addition to a power response imbalance! And since typical low-quality speakers like that do not have any controls for adjsuting that, you just have to live with it. Some people think it sounds "cool", as their little speakers are sounding "bigger", but they don't realize that they are not hearing what the music actually sounds like, since the frequency response is all messed up.

All of the above is about having a speaker close to one wall, which gives you a 6 dB boost in the low end. But you can also put the speaker in the corner between two walls (eg, the front wall and the side wall), which will give you a 6 dB boost from EACH of those walls (thus, a 12 dB boost in total, or four times the power), and in extreme cases you can put the speaker in the "tri-corner" or "triple-corner", where the two walls meet the floor: and that will give you an 18 dB boost which is six times the power.

To add a bit more detail: you only get that boost for frequencies that "wrap around" behind the speaker... not for the ones that were going out in a cone towards you. But where is the division? What frequencies are in the "cone" and what frequencies "wrap around"? That's actually easy to calculate, because acoustics is all mathematical. Sound waves are only affected by objects that are larger than the wavelength of the sound. They are not affected by objects that are smaller than their own wavelength. So this is simple: Waves can only "wrap around" behind the speaker if they are bigger than the speaker! Thus, the smallest dimension of the speaker baffle (the front face of the cabinet) determines the highest frequency that can wrap around: all waves of higher frequency cannot wrap around behind, because the speaker face is bigger than the are, so those are the ones that are forced towards you in the "cone". Waves that are longer than that, can wrap around. So all you have to do is to measure the dimensions of the speaker, then do the math to see where the cut-off point is.

This effect is often called the "baffle step response" issue, because all frequencies below the "step" lose 6 dB because the wrap around the back, while all frequencies above that do not lose 6 dB, as they are sent only forwards. It's actually not really a "step" at all: rather, it's a slow, gentle change in the power balance, that covers a range of 4 octaves, with the "cut-off" frequency being in the middle of that range.

So, placing your speaker against a wall can give you a boost for the frequencies below the baffle step point, but not for the ones above it. For very small speakers (such as tiny bluetooth cans), that frequency can be pretty high, but for typical studio monitors it is somewhere in the lower mid range.

Now, it's important to NOT confuse the baffle-step issue with the SBIR issue! They are vaguely related to each other, distantly, but neither of them is related to modes. Modes are relate to one thing only: the dimensions of the room. That's it. Nothing more. Baffle-step response is related to one thing only: the dimensions of the speaker. That's it. Nothing more. SBIR is sort of related to baffle-step, since SBIR can only occur with waves that are "wrapping around" the speaker, so it cannot happen for high frequencies... except that it does.. sort of!! Because the lowest frequency wave can cause SBIR comb filtering, that comb filtering can indeed extend all the way up the spectrum, even into the region above the baffle step response... but you can't get an initial SBIR dip from frequencies above the baffle step response point... that would be impossible.... which is why the best possible way to mount a speaker is IN the wall, so that the front face of the speaker is flush with the face of the wall. That makes the baffle seem very large indeed now, so the baffle-step response frequency is forced way down to a very much lower frequency, and thus front wall SBIR cannot happen at all: it becomes impossible. Which is why pro studios pretty much always have their speakers flush-mounted like that: so they can avoid Baffle Step Response issues, power imbalance, AND ALSO SBIR, and several other nasty issues that happen when speakers are inside the room.

Hopefully, that clarifies the issues here.


- Stuart -
Attached Thumbnails
How to treat this room?-neumann_loudspeaker_boundary_location_v02-sbir-table-wall-bounce-distance.jpg   How to treat this room?-genelec-loudspeaker-boundary-lcation-sbir-info-wall-bounce.jpg   How to treat this room?-speaker-boundary-lcation-sbir-graphs-wall-bounce.jpg  
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