Problematic room needs taming. Advice needed!

[The Sound Guy]

Hi Stuart,

I'm about to start the calibration process. I think I'll attempt this with my Digi003, which is what I use for day to day audio tasks. The measurement kit came with a Focusrite Scarlett Solo, which doesn't have balanced outputs.

Listening to the empty room, I'm getting more and more afraid of the results, actually... I'm aware the dimensions of this room are far from ideal: bad ratio's, for one. And, listening, I'm also getting painfully aware of street noise. Now, this hasn't been an issue for me in the past: I've delivered mixes from this far-from-ideal room in the past that clients were happy with. But now, I want to make it (a lot) better. Occasional street noise may not be very detrimental to mix results, but it can affect the measurements...

I'm well aware this room will never be up to par with pro studio's. And it doesn't have to be. But I'm beginning to wonder if I have bitten off more than I can chew...

More later!

[Soundman2020]

Listening to the empty room, I'm getting more and more afraid of the results, actually... I'm aware the dimensions of this room are far from ideal: bad ratio's, for one. And, listening, I'm also getting painfully aware of street noise

Right! An empty room really does reveal all the ugly warts and wrinkles.

If you are concerned about street noise, maybe you should consider doing something about the isolation?

For example, if you can identify that the noise is coming in through the window, then sealing up the air gaps around the window, and/or replacing the glass with something much thicker, or even building a window plug could get you some additional isolation.

Occasional street noise may not be very detrimental to mix results,

You'd be surprised... Not trying to scare you, but having annoying background noise can mess with your concentration.

but it can affect the measurements...

Yes it can, for sure. Try to take your measurements in quiet moments, when there isn't much street noise.

But I'm beginning to wonder if I have bitten off more than I can chew...

Treating a room isn't that hard. Simple isolation (such as sealing doors and windows), isn't that hard either. More serious isolation is a bit tougher...

I'm not sure if I already gave you this, but here's the procedure for calibrating and testing with REW: How to calibrate and use REW to test and tune your room acoustics


- Stuart -

[The Sound Guy]

Thank you Stuart!

I've found and read your instructions on how to set up and use REW.
I've also done the measurements (3, not using the subwoofer yet) and attempted to share the Dropbox folder they're in.

https://www.dropbox.com/home/JohnSayers_Forum

What I can interpret from the results is that there is a GIANT!!! suck-out at 90Hz or so. And, as expected, quite long RT60 across the board.
Now, I'd like to hear first hand, from you, what the verdict is...

The speakers are positioned facing the short wall, opposite the window (hence the "Config1" suffix in the name). Would it be advisable to turn averything around 180 degrees and repeat the process?

TSG

[Soundman2020]

Your link wants me to sign in... You need to share that publicly, not privately.

- Stuart -

[The Sound Guy]

Please try again..?

Configuration one: speakers firing toward the short wall, away from the window.
https://www.dropbox.com/s/4gh8g5zcejax4 ... .mdat?dl=0

Configuration two: Speakers firing toward the window.
https://www.dropbox.com/s/t5w1pjdblszbv ... .mdat?dl=0

In both cases there is a desk with an iMac in front of the monitors, the sofa is on the opposite side of the room.

TSG.

[The Sound Guy]

I've done my measurements in an (almost) empty room, my speakers positioned symmetrically from both sidewalls.
Theyre were positioned at my normal listening height, tweeters at ear level. I'm not sure of the exact distances to sidewalls, floor and ceiling. I did not pay attention to the positioning relative to the front wall.
I've been thinking about that. To find a good place to set them up, I took a good look at Carl Tatz's Phantom Focus System. Based on the axial mode calculator on his website, I think I found a good spot to place my speakers (see attached image). But I can't get those exact numbers from the spread sheet. Does anyone know of a way to find those measurements?

The only correlation I think I can see, it that all circled points in the image are at about 3/8th of that dimension of the room.

My thinking may be off, but I think I need to get the positioning of the speakers and listening postions correct, before I can apply basic treatment (trapping/absorption of first reflections).

I think the PFS approach, or something similar, could work for my room, because it is a generic, non-purpose designed room, and I (first) need to tune the sound at the listening position. I can (and probably will) use one or more subs to regulate the low end, including something like a mini-DSP to properly integrate them.
Additionally, the PFS uses stand mounted speakers. Flush mouting is possible, but not a requirement.
(Soft) flush mouting my speakers in a wall (that I have yet to build in the room) has crossed my mind as a good way to eliminate any and all SBIR issues, but I'm worried about thermal management of the speakers, they do get warm after prolonged use. Without proper convection, this could pose a serious issue. So, at this point, I feel that stand mounting my monitors is preferable.

What are your thoughts on this?

[The Sound Guy]

In the mean time I'm doing some thinking and modelling with online tools. Like the "Helmholtz Absorber Calculator".
Knowing that I have a 37Hz axial mode in my room, would this work? (See attached image).
And how much surface would I need?
Since this absorber has a large reflective surface, would it be best to apply it to the backwall ("live end") of my room?

And, of course, I need to figure out which absorber material I need.

37Hz Helmholz absorber.JPG

But then again, referring to AMROC at the start of this post, I have numerous problems below 150Hz.
What would be the best way to go?

- Determining the best position for speakers and listening position (how??);
- 37Hz HemlHoltz absorber;
- Ignoring the very low end for now and first applying low-mid and mid frequency absorption across the room and then determining what to do next, by repeating the measurements?

[The Sound Guy]

Lately I've been reading up on Alton F Everest's Master Handbook of Acoustics and doing some drawing, to get an idea of what the room would look like.

Screen Shot 2019-06-18 at 14.21.50.jpg

Things to mention that are not abvious from the drawings:

- Speakers are positioned 55cm from the front wall (first SBIR problem 156Hz)
- Speakers are positioned 63cm from the side walls (first SBIR problem 136Hz).
- Woofers are 90cm from the floor (3/8 of the rooms' height).

Both SBIR problems should be handled by the aborbers placed on the front wall and side walls. In the drawing they are all 20cm thick with a 44mm air gap.

Absorber model.JPG

There will probably also be two of those absorbers above the desk, maybe slanted. The idea being that the slant might break up the wavefront below the effective range of the absorber.
If I interpret my measurements correctly, there is already quite a lot of absortion going on in the >6kHz region, probably bacause of the carpet in the room.
So, I could replace all the carpet with wood, for example. Failing that, alternatively I was thinking to only use one absorber placed horizontally on the frot wall, behind the speakers and put QRD Skyline diffusors above it. Also put one or two QRD Skyline dissusors on the back wall, same height. Considering the cost of a new floor, I'd rather only do that when necessary. The thought behind that being that broadband absorbers absorb a lot of the high frequency content as well. So a little less absorption and some preservation of the highs.
I might also need one or two helmholtz resonators, but new measurements after treatment will tell me more.

The backside of the room is not yet filled in in the drawing, because I don't yet know what to do with it yet.

Currently I'm dealing with an enormous 40dB dip from about 80 - 100Hz. No idea what causes that. Possibly floor bounce, according to a friend of mine. But I can't figure out how to calculate the effect of the delayed signal from the room bounce. Could also be the standing wave between floor and ceiling. I which case I hope a slanted cloud (with a rigid back) will help break the wave front.

Can anyone tell me more about this plan, so far? I'd like to know if I'm about to waste time and money before I actually start wasting it..!

[The Sound Guy]

I've been trying to do some calculations on how much absorption I would need, based on estimated numbers for the materials used. The numbers come from the appendix of The Master Handbook of Acoustics.

Screen Shot 2019-06-18 at 19.34.56.jpg

The attached image shows a spread sheet with all relevant numbers, all in Metrics and Metric Sabins.
I know these results can't be right. By my ears alone I can tell there is much reverberation. Measurements confirm that. So what went wrong with the calculations?

I was attempting to get an idea on what's actually needed in terms of absorption. But this way I won't be able to do that.

[The Sound Guy]

Could someone (Stuart..?) please take a look at my measurement data?

Configuration one: speakers firing toward the short wall, away from the window.
https://www.dropbox.com/s/4gh8g5zcejax4 ... .mdat?dl=0

Configuration two: Speakers firing toward the window.
https://www.dropbox.com/s/t5w1pjdblszbv ... .mdat?dl=0

In both cases there is a desk with an iMac in front of the monitors, the sofa is on the opposite side of the room.

A few notes on the data: The room is empty, except my desk with iMac, the monitor and a sofa on the other end of the room.
Cfg 1 and 2: The monitors are set up symmetrically in the horizontal plane, at the height they were normally at. No thought was given to distance to any surface. Just convenience (now I know better). I kind of feel that I may need to repeat the measurements with a better placement of the monitors. But I might be wrong. The data could tell more, I don't know. Please let me know.

The Sound Guy

[The Sound Guy]

Did I not follow the forum rules in one way or another? It seems that no-one is willing or able to respond to my questions. Are (all) people just busy? Or did I offend people in some way? Is my room so difficult that no one wants to burn their hands on it?
I want to start with the first round of basic treatment. But as Stuart pointed out in another thread, treating a room without knowing what to do and why, is like having a serious illness and wanting to treat it yourself, without first consulting a doctor. Well, I have made measurements. But I don't fully grasp what I'm looking at. Who wants to help me get started?

[The Sound Guy]

With SuperChunks in the corners of the front wall, the closest I can get my speakers to the front wall, will be about 54cm. First SBIR issue will be at approx. 168Hz.
The distance to the sidewalls will then be 63cm, first SBIR issue at 136Hz. I can only hope that the Superchunks and Absorbers on the front and sidewalls will be able to handle this adequately. 136Hz is quite low...

With this configuration and the mix position at 35% from the front wall (163cm), the angle between the long axis of the room and the speakers will approximately be 38˚. The distance between the speakers will then be 172cm.

Probably tomorrow I'll try a listening test in the room, with these numbers. And if possible, I'll also do some REW measurements.

[DanDan]

Most of us skim these fora. You have presented a vast amount of hypothetical stuff. Well done on the intentions and sketch upping.
I will try to contribute a little.
SuperChunks are great, but the bigger ones only. SoffiTraps of similar size would place double the amount of fibre in the corner.
Jeff Hedback has shown increased LF absorption by adding pegboard. Reflects HF back into the room too.
What is the purpose of your Front Wall Treatment?
If you are trying to combat SBIR I don't think you are presenting enough area.
In which case, both of my points considered, how about a whole front wall treatment. Sink the speakers into it.
You might take a read through my Measurement Primer. Note the point that REW is best used to decide between measured options.
I haven't investigated it's Room Sim yet.
Simple Sine Waves will identify and locate your strongest modes and encourage you to aggressively treat them.

DD

[The Sound Guy]

Hi DanDan!

Thanks for your reply. I apologize for my impatience. I just want to get started, but I prefer to do so with a sound plan, rather than just going ahead and hoping for the best

I will investigate a (soft) flush wall. Right now I get the feeling that my room is not wide enough for optimum speaker placement, which might also mean that flush mounted speakers will not perform their best, because of the proximity of the side walls. Also, I’m a bit concerned about thermal management. But Adam assured me that normal, passive ventilation will “most likely” be sufficient

Updates will follow.

TSG

[The Sound Guy]

After having set up my speakers and listening position according to the method Stuart explains elsewhere on the forum, I’ve found that soffit or (soft)flush mounting of the monitors is not possible in my room. By extending the line parallel to the baffle to the adjacent wall, that line cuts though my door. Even if I move the speakers more to the front wall, I won’t be fully clear from the door. So no can do. Unfortunately.

DanDan, what did you mean by saying that my front wall hasn’t enough absorption surface to combat SBIR? Which image are you referring to? There will be at least to two 600x1200mm 200mm thick absorbers placed symmetrically behind and between the speakers. Two more on either side and possibly two more on the ceiling, over the mix position (slanted?). AlthoughI doubt the latter two will have much effect on the 71Hz mode between floor and ceiling.

I cannot find the cause of the 40dB dip at around 90Hz. Does anyone else have a clue as to what might cause that? Cancellations, because of the interaction of modes, perhaps? And what do I about it?

The Sound Guy