Polygonal - Asymmetrical "NIGHTMARE" Room

[StraylionOfficial]

Hello all!

I posted about a week ago, criminally underprepared. So first off, my apologies.

I’m going to start this fresh post with a diagram of the room:

Oh yes.. I know…

Far from ideal…

Zero symmetry….

But since I’m not planning on moving from this house any time in the near future, I’m determined to find a solution to get everything as reigned in a possible before:
- Purchasing further treatment
- Using Dirac RCS as the cherry on top.

Equipment:
ATC SCM45A’s
(with plans to add a ATC SCS70Pro sub early next year)

Treatment:
The room does have treatment, however this treatment was used for a room at my old house.

12 - 2.5 inch thick GIK Diffuse/Absorb Panels
w/ GIK 23.5” wide corner bass traps in each of the corners that function like real corners.

When I first moved, and was in a desperate mood to get the room in working order, I slapped it all up and have been living with it.

Now that I have a bit of time over the holidays, I’m ready to do whatever is necessary to make it better.

I am aware that there is a lack of bass trapping (apart from the "corners") and am working with an acoustic engineer at GIK.

He thinks that I have the speakers in the best place possible in the room and wouldn’t recommend moving them to a completely different position. (?)

So today I spent all day just moving the speakers around, making measurements, and sending them to him for his opinion.

The MDAT file containing these measurements can be dowloaded here:

https://files.fm/u/pdjm38gcmd. (I tried zipping the file but it said it was too large to be posted here, hence the download link)

First 2 measurements (CURRENT) were taken at my original position. Speakers around 12” from the wall and around 78” from mid dome to mid dome.

Second 2 measurements (WALL) were taken with the speakers pushed closest to the back wall as possible but at the same spacing.

Third 2 measurements (TIGHTER) were taken closest to the back wall but at a tighter spacing of 69.6” from mid dome to mid dome.


All measurements were taken with a UMIK1 at 90deg w/ calibration file. To find the accurate listening position I used a laser measure.


Anyways, I thought I would post on here and get some opinions on my scenario…

I don’t want to torture this guy anymore, well.. at least not until I’ve found a great speaker position and am ready to purchase some treatments.

I'm great at making music. But clueless when it comes to room acoustics.


Any help you can offer would be greatly appreciated.

Thanks!!

Stray

 

[ppataki]

Hello all!

I posted about a week ago, criminally underprepared. So first off, my apologies.

I’m going to start this fresh post with a diagram of the room:

View attachment 408058


Oh yes.. I know…

Far from ideal…

Zero symmetry….

But since I’m not planning on moving from this house any time in the near future, I’m determined to find a solution to get everything as reigned in a possible before:
- Purchasing further treatment
- Using Dirac RCS as the cherry on top.

Equipment:
ATC SCM45A’s
(with plans to add a ATC SCS70Pro sub early next year)

Treatment:
The room does have treatment, however this treatment was used for a room at my old house.

12 - 2.5 inch thick GIK Diffuse/Absorb Panels
w/ GIK 23.5” wide corner bass traps in each of the corners that function like real corners.

When I first moved, and was in a desperate mood to get the room in working order, I slapped it all up and have been living with it.

Now that I have a bit of time over the holidays, I’m ready to do whatever is necessary to make it better.

I am aware that there is a lack of bass trapping (apart from the "corners") and am working with an acoustic engineer at GIK.

He thinks that I have the speakers in the best place possible in the room and wouldn’t recommend moving them to a completely different position. (?)

So today I spent all day just moving the speakers around, making measurements, and sending them to him for his opinion.

The MDAT file containing these measurements can be dowloaded here:

https://files.fm/u/pdjm38gcmd. (I tried zipping the file but it said it was too large to be posted here, hence the download link)

First 2 measurements (CURRENT) were taken at my original position. Speakers around 12” from the wall and around 78” from mid dome to mid dome.

Second 2 measurements (WALL) were taken with the speakers pushed closest to the back wall as possible but at the same spacing.

Third 2 measurements (TIGHTER) were taken closest to the back wall but at a tighter spacing of 69.6” from mid dome to mid dome.


All measurements were taken with a UMIK1 at 90deg w/ calibration file. To find the accurate listening position I used a laser measure.


Anyways, I thought I would post on here and get some opinions on my scenario…

I don’t want to torture this guy anymore, well.. at least not until I’ve found a great speaker position and am ready to purchase some treatments.

I'm great at making music. But clueless when it comes to room acoustics.


Any help you can offer would be greatly appreciated.

Thanks!!

Stray

I have a living room that has a similar shape so I have some experience with this type of rooms
Unfortunately the angled wall will mess around with the phase of the bass range - that is the reason why your L and R measurements look like they were done in two totally different rooms

For me moving the speakers around did not help at all; the final solution (that actually worked) was to use a sub (and then a second one too) to make sure the bass response becomes more even
And since your bass range will be mono (below the sub crossover frequency) you will no longer suffer from the room-induced (angled wall) phase issues

 

[Frank Dernie]

Zero symmetry…

Zero symmetry is good for reducing the fundamental room modes. The biggest peaks occur in rooms with parallel walls.

 

[StraylionOfficial]

I have a living room that has a similar shape so I have some experience with this type of rooms
Unfortunately the angled wall will mess around with the phase of the bass range - that is the reason why your L and R measurements look like they were done in two totally different rooms

View attachment 408109

For me moving the speakers around did not help at all; the final solution (that actually worked) was to use a sub (and then a second one too) to make sure the bass response becomes more even
And since your bass range will be mono (below the sub crossover frequency) you will no longer suffer from the room-induced (angled wall) phase issues

Thankyou for your advice! Yes, the angled wall is seriously messing around with the phase response.

I can’t think of a position that’s going to actually rein that in, except maybe moving the speakers around where the drum kit is currently. Nonetheless I don’t think it will help much as there will still be an angled wall behind the left speaker, an uneven wall near the right, and an untreatable closet door behind both of them. So I guess when my sub comes in I will have to experiment with the crossover etc.

When you looked at the MDAT, did moving the speakers help at all? I can’t seem to see a massive benefit to any of the different positions. If there’s no standout option I’ll just move them back to where they were.

I’ll still have to invest in some bass trapping as the decays (low-end wise) are pretty abysmal.

Zero symmetry is good for reducing the fundamental room modes. The biggest peaks occur in rooms with parallel walls.

I just wish my asymmetrical room worked more to my advantage haha

 

[ppataki]

So I guess when my sub comes in I will have to experiment with the crossover etc.

Yes, you will need to find the best location first (using measurements) and then the volume, crossover, delay

When you looked at the MDAT, did moving the speakers help at all? I can’t seem to see a massive benefit to any of the different positions. If there’s no standout option I’ll just move them back to where they were.

There are differences but where one measurement has 2-3dB more in the low end those suffer from bigger dips in the 70-100Hz region....
I would find it very hard to choose 'the best' based on the measurements but I will let others comment on that too

I’ll still have to invest in some bass trapping as the decays (low-end wise) are pretty abysmal.

I don't think they will help at all....using (properly integrated!) one or rather two subs would do a much better job not only with the frequency response but also with the group delay too vs. any kind of traps

 

[StraylionOfficial]

Yes, you will need to find the best location first (using measurements) and then the volume, crossover, delay



There are differences but where one measurement has 2-3dB more in the low end those suffer from bigger dips in the 70-100Hz region....
I would find it very hard to choose 'the best' based on the measurements but I will let others comment on that too


I don't think they will help at all....using (properly integrated!) one or rather two subs would do a much better job not only with the frequency response but also with the group delay too vs. any kind of traps

Today I’ll mess around a bit with position just for the hell of it and see what else I can discover about the space. I’m thinking that if I shift my setup to the left a bit it could help marginally with the phase response, but marginally is better than nothing.

The second measurement seems to have the best phase interaction on the top end so I’m going to use that spacing but shift it slightly.

I’m in no rush to order any bass traps just yet. Just keeping an open mind in regards to solutions.

I’ll report back with my findings!

 

[StraylionOfficial]

I feel like todays changes have been quite positive! But I'm not an expert at reading measurements...
Here are the old vs new. What do you think?

 

[Keith_W]

Before we start, have you read this post and taken a proper measurement?

Comparing old vs. new, the high freqs are the same. So we will ignore those. The real differences is in the bass.

In a room like yours, summing the bass to mono is more useful because that is likely what you hear. So in REW, I summed L+R for the old and new curves (Trace Arithmetic A+B). You did not do a mono measurement, but A+B predicts it pretty well. This is the result:

Highlighted is the NEW measurement. I think you can easily see that it is worse than the old one. The peaks are peakier, the dips are dippier.

Since this is a studio, I took a look at the reflections. The Energy-Time Curve shows the timing of reflections. The target: all reflections arriving within the first 20ms should be -15dB below the main signal. You almost meet the target. That single peak arriving at 4ms travelled an extra 4.5 ft. I am guessing table bounce depending where you put your microphone and the elevation of the speaker. I would say this is "good".

The RT60 shows the decay of sound by frequency for "L new". For a small home studio, the target should be about 250ms or less. It should really be calculated against the room volume but I couldn't be bothered doing all that maths with a funny shaped room like yours Yours just meets the target, so I will give this a "pass". That huge spike you see in the bass is not reverberation, it is a room mode.

 

[StraylionOfficial]

Before we start, have you read this post and taken a proper measurement?

Comparing old vs. new, the high freqs are the same. So we will ignore those. The real differences is in the bass.

In a room like yours, summing the bass to mono is more useful because that is likely what you hear. So in REW, I summed L+R for the old and new curves (Trace Arithmetic A+B). You did not do a mono measurement, but A+B predicts it pretty well. This is the result:

View attachment 408282

Highlighted is the NEW measurement. I think you can easily see that it is worse than the old one. The peaks are peakier, the dips are dippier.

View attachment 408283
Since this is a studio, I took a look at the reflections. The Energy-Time Curve shows the timing of reflections. The target: all reflections arriving within the first 20ms should be -15dB below the main signal. You almost meet the target. That single peak arriving at 4ms travelled an extra 4.5 ft. I am guessing table bounce depending where you put your microphone and the elevation of the speaker. I would say this is "good".

View attachment 408285

The RT60 shows the decay of sound by frequency for "L new". For a small home studio, the target should be about 250ms or less. It should really be calculated against the room volume but I couldn't be bothered doing all that maths with a funny shaped room like yours Yours just meets the target, so I will give this a "pass". That huge spike you see in the bass is not reverberation, it is a room mode.

Wow! Appreciate the in depth analysis, Keith.

I read through that list and am confident that I ticked all the boxes when measuring. As I said in my first post: UMIK1 @ 90deg with Calibration file. Listening position located with a laser measure pointed at mid domes with measurement in mm’s etc.

The only difference with todays measurements is that I’m not sure they were taken at the exact same level as yesterdays. A mistake I won’t be making again…

Could today’s level being louder cause it to look worse than the prior measurement?

So the “NEW” is dippier and peakier which is a shame; but am I right in saying the left and right channels look like they’re taken from the same room now? The difference between L&R on the “OLD” looked abysmal to me, and now they seem to be getting more… acquainted.

Regarding the big dip. Is it more likely to be SBIR?
Seems to show all the trademark signs. But I guess modes are not out of the question.

Sounds like I’m far from done yet.
Curious about next steps.
Ready to keep on measuring tomorrow.

 

[ppataki]

Curious about next steps.

IMHO the next step is to get at least one subwoofer

 

[Keith_W]

Could today’s level being louder cause it to look worse than the prior measurement?

Not really, unless your speakers are distorting. I saw that your newer measurements were louder. As you can see from my graph (where I overlaid old vs. new), I aligned the SPL of both graphs so they are comparable.

Regarding the big dip. Is it more likely to be SBIR?
Seems to show all the trademark signs. But I guess modes are not out of the question.

Telling the difference between SBIR and modes from a graph is next to impossible. You have to shift your speakers closer to the wall and re-measure. If the null shifts upwards, it is SBIR. The distance from speaker to wall is 1/4 of the wavelength of the first cancellation. Thus you can predict the SBIR frequencies with this calculation:

• lamda1=4d/1 or f1=c/4d: cancellation
• lamda2=4d/3 or f2=3c/4d: reinforcement
• lamda3=4d/5 or f3=5c/4d: cancellation
• lamda4=4d/7 or f4=7c/4d: reinforcement

Where lamda is wavelength in m or ft, d is the distance from the speaker to the boundary in m or ft, c is the speed of sound 343m/s or 1125ft/s.

Curious about next steps.

Your next step is to see a doctor for some medication

 

[StraylionOfficial]

IMHO the next step is to get at least one subwoofer

Subwoofer is ordered but... wont be in stock until Dec 6th

Not really, unless your speakers are distorting. I saw that your newer measurements were louder. As you can see from my graph (where I overlaid old vs. new), I aligned the SPL of both graphs so they are comparable.



Telling the difference between SBIR and modes from a graph is next to impossible. You have to shift your speakers closer to the wall and re-measure. If the null shifts upwards, it is SBIR. The distance from speaker to wall is 1/4 of the wavelength of the first cancellation. Thus you can predict the SBIR frequencies with this calculation:

• lamda1=4d/1 or f1=c/4d: cancellation
• lamda2=4d/3 or f2=3c/4d: reinforcement
• lamda3=4d/5 or f3=5c/4d: cancellation
• lamda4=4d/7 or f4=7c/4d: reinforcement

Where lamda is wavelength in m or ft, d is the distance from the speaker to the boundary in m or ft, c is the speed of sound 343m/s or 1125ft/s.



Your next step is to see a doctor for some medication

If the doctor can prescribe "acoustic treatment", I'm in!

Today I did Pre/Post Dirac measurements but they look nearly identical...
Why is that? I would have expected it to pull it into shape a bit better...

MDAT attached.

 

[Keith_W]

Today I did Pre/Post Dirac measurements but they look nearly identical...
Why is that? I would have expected it to pull it into shape a bit better...

When you look at the bass response, it is usually helpful to mono it. Issues that were not apparent may become apparent (such as phase differences between L/R), and you listen to your speakers in stereo anyway. Since you did not do a mono measurement, I added the L+R curves. This is a reasonable approximation of what you would measure had you done a mono measurement. I also routinely align the SPL of curves so that they are comparable.

Post Dirac L+R is highlighted, and pre-Dirac L+R is in light brown. Do they look identical to you?

 

[StraylionOfficial]

View attachment 408553

When you look at the bass response, it is usually helpful to mono it. Issues that were not apparent may become apparent (such as phase differences between L/R), and you listen to your speakers in stereo anyway. Since you did not do a mono measurement, I added the L+R curves. This is a reasonable approximation of what you would measure had you done a mono measurement. I also routinely align the SPL of curves so that they are comparable.

Post Dirac L+R is highlighted, and pre-Dirac L+R is in light brown. Do they look identical to you?

Good advice on the mono measurement, much easier to see.
Definitely not identical.
But should it be that jagged?

 

[Keith_W]

The jaggedness is normal. You can make it as jagged or as smooth as you want in REW.

You might be asking about that dip at 120Hz. Let's look at the GD (Group Delay) curve:

See that huge peak at 120Hz? The flat areas are areas of minimum phase. The peaks are excess phase. That huge peak is an area of maximum phase, caused by a reflection arriving at the microphone out-of-phase with the direct sound resulting in cancellation.

You should be able to fix this with DSP. I don't know if Dirac can do it though. I know that Rephase can, and so can Acourate.