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Acoustic measurements of an odd shaped rehearsal room.
Old 12th February 2019
  #1
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Acoustic measurements of an odd shaped rehearsal room.

Hi! I'm Ray from Mexico City.
Attached you can find an image describing my rehearsal room and my first measurements with REW.For the measurements I'm using a calibrated mic (Dayton) EMM-6, a focusrite interface and a Motus Bass rig wich is flat from 40Hz to 10kHz

I'm trying to follow general guidelines regarding room measurement as well as I can.

Let me start with some findings from my research and experiment. Any advice, confirmation or bulling to my conclusions is welcome!.

- Room is not rectangular. So, calculating room modes is not so easy without expensive software.
- I suppose to aim for a flat freq response but it is most important to achieve a consistent decay time.
- In a control room you position your speakers in the best place possible first, then set the mic where your head will be and start measuring. In a rehearsal room you have a lot of things that will change. Position of the sound sources and the people are not fixed.
- I'm a bass player and a bass cabinet designer and builder, so for me the bass treatment is going to be a priority.
- There are a lot of possible placements for my bass rig but really there is only few that are practical. So I picked the one that I liked the most by ear.
- The place where I stand is my sweet spot or my measurement point.
- The most important "sound quality" to be achieved should be 1) How the bass player hears the bass rig 2)How they bass player hears the kick drum 3)how the drummer hears the bass.

So, looking at the graphs I have BIG questions.

Should I try to chase and correct every single peak or null?
How to choose what are the most offending ones?
Should I forget freq response and try to control decay times of the bass region?

What your experienced eyes can see en those graphs?
Attached Thumbnails
Acoustic measurements of an odd shaped rehearsal room.-music_room.jpg   Acoustic measurements of an odd shaped rehearsal room.-ba_bp.jpg   Acoustic measurements of an odd shaped rehearsal room.-ba_bp_t60.jpg   Acoustic measurements of an odd shaped rehearsal room.-ba_bp_wf.jpg  
Old 13th February 2019
  #2
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Ok well.
This is a new completely empirical non scientific approach to help me visualize the problems in my room.

You need to stop me!

Here is what I did.

- I took 8 relevant measurements in my room:
1) Bass Rig measured from the bass player's ears position.
2) Bass Rig measured from the drummer's ears position.
3) Bass Rig measured from the guitar player's ears position.
4) Bass Rig measured from the center of the room.
5) Bass Rig in the kick drum position measured from the bass player's ears position.
6) Bass Rig in the kick drum position measured from the drummer's ears position.
7) Bass Rig in the kick drum position measured from the guitar player's ears position.
8) Bass Rig in the kick drum position measured from the center of the room.

- Calculated the average SPL per octave for each measurement.
- Calculated the absolute difference of the measurement to Its own averages.
- Multiply each abs diff curve by a "weghting factor" to give more importance to some measurements than others. (all factors add up to one).
- Add all curves.

This should give a graphical representation of the frecuencies that are showing more variance across the important points of sound source and listeners that are going to be tipically used in a rehearsal.

Some of the most problematic frecuencies showed by this approach are coincident with the frecuencies where I have the larger delay times.

Could I say that those are the ones to atack first?
Attached Thumbnails
Acoustic measurements of an odd shaped rehearsal room.-imagen1.jpg  
Old 15th February 2019
  #3
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akebrake's Avatar
 

Quote:
Originally Posted by RayGlz View Post
..So, looking at the graphs I have BIG questions.

Should I try to chase and correct every single peak or null?
Only if they happen to coincide with the positions of source/ listener.
A "mapping" of the nulls in the room is helpful here.

Quote:
How to choose what are the most offending ones?
Now we are into opinions of different musicians.

Quote:
Should I forget freq response and try to control decay times of the bass region?
IMHO yes.

Some questions:
What kind of walls/ceiling floor? Concrete/plaster,wood? Opening to other room?

How much treatment are you prepared to add to this room?
Easily removable Traps like Gobos, framed panels, or more stationary sttached to walls and ceiling?

Best

Last edited by akebrake; 15th February 2019 at 04:43 PM..
Old 16th February 2019
  #4
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Thank you for your time akebrake!

Quote:
Originally Posted by akebrake View Post
Only if they happen to coincide with the positions of source/ listener.
A "mapping" of the nulls in the room is helpful here.
Yes! I tried to find a balance of the listener positions potentia problems. A mapping of the nulls? Playing a sine wave at each freq and measuring spl every 2 feets like in a virtual mesh algong all the the walls and ceiling?

Quote:
Originally Posted by akebrake View Post
What kind of walls/ceiling floor? Concrete/plaster,wood? Opening to other room?
Wood floor over concrete slab, painted brick walls, closed room with sealed (and super heavy) door.

Quote:
Originally Posted by akebrake View Post
How much treatment are you prepared to add to this room?
Easily removable Traps like Gobos, framed panels, or more stationary sttached to walls and ceiling?
I'll do what it takes to make the bass and drum kick sound great. I'll go to the point of diminishing returns with the rest. Fixed or built monstruous things in the corners and ceiling are not a problem, there is enough space. For the rest of the surfaces mobile traps.

Ray
Old 16th February 2019
  #5
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Positions and modes

Quote:
Originally Posted by RayGlz View Post
Thank you for your time akebrake!
My pleasure

Quote:
Yes! I tried to find a balance of the listener positions potentia problems.
As I’m a bassplayer myself I find this an interesting but seldom discussed question in Forums.

Quote:
A mapping of the nulls? Playing a sine wave at each freq and measuring spl every 2 feets like in a virtual mesh algong all the the walls and ceiling?
”Virtual mesh”! That’s a nice description!

A generic ”rule” when positioning speaker and listener in controlrooms is:
”Neither put speaker nor listener in a null by accident” (only by purpose).

The obvious next question is: Where are these nulls (below ≈150Hz) situated?
In a shoebox shaped room with rigid boundaries they are easily calculated.
Your room is ”close to” box shaped. A calculator like Hunecke will give a rough clue (and you also have REW WF & your average calc to compare with)

Sustained notes
The bass rig is fairly point source. Place it in a corner (to drive all modes efficiently)

Run Sines or Pink PN from REW generator (which ever you like best) and watch result on the RTA screen.
And then walk around in the room with the mic and a laptop(?) finding the null lines. Like "Isobars" with low pressure. Mark with tape on the floor.

These null-lines connects to room modes, which in turn connects to certain boundaries. ( Walls or Floor-Ceiling).

We now have low positioned sources (with good coupling to vertical modes) but also seated /standing listeners which affects how they percieve the vertical modes.

As Kick and the other drums are impulse-like signals first reflections will also play it's role.

Will your drummer prefer a rigid back wall (used to) or deep trapping behind his back?

/Ake
Old 19th February 2019
  #6
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Quote:
Originally Posted by akebrake View Post
My pleasure



As I’m a bassplayer myself I find this an interesting but seldom discussed question in Forums.



”Virtual mesh”! That’s a nice description!

A generic ”rule” when positioning speaker and listener in controlrooms is:
”Neither put speaker nor listener in a null by accident” (only by purpose).

The obvious next question is: Where are these nulls (below ≈150Hz) situated?
In a shoebox shaped room with rigid boundaries they are easily calculated.
Your room is ”close to” box shaped. A calculator like Hunecke will give a rough clue (and you also have REW WF & your average calc to compare with)

Sustained notes
The bass rig is fairly point source. Place it in a corner (to drive all modes efficiently)

Run Sines or Pink PN from REW generator (which ever you like best) and watch result on the RTA screen.
And then walk around in the room with the mic and a laptop(?) finding the null lines. Like "Isobars" with low pressure. Mark with tape on the floor.

These null-lines connects to room modes, which in turn connects to certain boundaries. ( Walls or Floor-Ceiling).

We now have low positioned sources (with good coupling to vertical modes) but also seated /standing listeners which affects how they percieve the vertical modes.

As Kick and the other drums are impulse-like signals first reflections will also play it's role.

Will your drummer prefer a rigid back wall (used to) or deep trapping behind his back?

/Ake
Ok so we are going back a little with the source and listener placement issue. I have a preference now for some spots due to practical reasons and from a few months of rehearsals with the band. Anyway, "mapping" the nulls sounds interesting.
Definetly will do!

Just one question:

Do I walk with the measuring mic at ear level and mark the low pressures points at the floor? or should I measure at the bass amp height?

Ray
Old 19th February 2019
  #7
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Quote:
Originally Posted by akebrake View Post

Will your drummer prefer a rigid back wall (used to) or deep trapping behind his back?

/Ake
I think the drummer will prefer whatever is best for the rest of the band. Especially the bass player ja!

I mean, drummers relate differently with their performance. They are hitting things, and they have an imediate reference of their instrument that is way more prominent than the effect of the room. The real problem for them is to hear everybody else.
Old 19th February 2019
  #8
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Quote:
Originally Posted by RayGlz View Post
...Just one question:
Do I walk with the measuring mic at ear level and mark the low pressures points at the floor? or should I measure at the bass amp height?

Ray
Actually three "mesh-layers"!
Floor level for the sources. (Bass and Kick)

Ear level 1.60m standing bass player
Ear level 1.10m seated drummer

Confusing? I will expand on that to morrow.

Cheers
Old 20th February 2019
  #9
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Quote:
Originally Posted by akebrake View Post
Actually three "mesh-layers"!
Floor level for the sources. (Bass and Kick)

Ear level 1.60m standing bass player
Ear level 1.10m seated drummer

Confusing? I will expand on that to morrow.

Cheers
Clear for me! Thank you.

I was reading about a so called "subwoofer crawl" Were you position the source in the place of the listener and the go and listen (or measure) to find the best sounding spots. Then you put your subwoofer in that place and sit where the subwoofer was.

I think I could simplify things a bit doing all this in two steps:
1.- Do as you sugessted and "map" the room at ear level.
2.- Apply that sub crawl "method" and put the bass rig over some table or something to raise it to ear level at one good spot (not null) found ind the previous step. Then measure the room to find good spots for the bass rig and the kick drum.

What you think?

Ray

Last edited by RayGlz; 20th February 2019 at 11:27 PM.. Reason: clarify things
Old 20th February 2019
  #10
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akebrake's Avatar
 

Quote:
Originally Posted by RayGlz View Post
Clear for me! Thank you.

I was reading about a so called "subwoofer crawl" Were you position the source in the place of the listener and the go and listen (or measure) to find the best sounding spots. ...
RE "Subwoofer Crawl! (Reciprocal method)
That's a bit easier (but still involved) because in a music-room situation (where you have already decided to sit) you "only" have to put your sub in the listening (ear) location and crawl around on the floor in a possible sub location to find the most even bass response. Better than crawling and listening is REW
Only one unknown position.

In your case: Two listeners and two sources...

The virtual mesh is more like an investigation of your specific room which can be practical information to save for later use.

Cheers
Old 6th March 2019
  #11
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Ohhhh MOG the floor!

Well
I started with the measurements. There is +/- 6dB in some spots and you can start to see a pattern. The speakers and listeners spots chosen by ear previously are not too bad.

BUT during the measurements I noticed a resonance in the floating floor in the 73Hz. The hole system was intended to separate the floor from the ceiling above my bedroom. Despite all the reading and planing I did last year to execute it properly (and of course the investment) I'm now sure that is acting like a giant drumhead

I'm starting to think that It will be a very hard to solve problem to the acoustics of the room (which I favor over the isolation It is providing now).

From top to bottom the floor layers are:
-9mm Laminated Floor
-Very heavy Neoprene
- 12mm OSB
- Green Glue
- 12 mm OSB
- 2" High density Extruded EPR
- 2" Medium density Expanded EPR
- 2" Medium density Polyuretane Foam

What you think?
Old 7th March 2019
  #12
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Quote:
Originally Posted by RayGlz View Post
...BUT during the measurements I noticed a resonance in the floating floor in the 73Hz. The hole system was intended to separate the floor from the ceiling above my bedroom.
Despite all the reading and planing I did last year to execute it properly (and of course the investment) I'm now sure that is acting like a giant drumhead
...
How do you know it's the floor vibrating? How exactly did you test that?
Accelerometer / contact pick up?

Best
Old 12th March 2019
  #13
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Quote:
Originally Posted by akebrake View Post
How do you know it's the floor vibrating? How exactly did you test that?
Accelerometer / contact pick up?

Best
Well, It's pretty obvious if you stand on the floor while reproducing a sine wave at 73 Hz. You can really feell it vibrating. In fact you even can see it moving like a speaker would.

Another no scientifical test I did was using a drums tunning app. If I hit the floor with my fist hard enough to make a loud sound. The app reads exactly 73Hz.

The floor Is damped with a heavy rubber layer and green glue but i think It IS resonating.

Ah! and other thing I found out is that the wavelenght of 73 Hz is 4.7 meters, almost matching the room width.

How could I make myself sure that It is the floor actually making things worst?
Old 14th March 2019
  #14
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???

Help!
Old 17th March 2019
  #15
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Quote:
Originally Posted by RayGlz View Post
...Another no scientifical test I did was using a drums tunning app. If I hit the floor with my fist hard enough to make a loud sound. The app reads exactly 73Hz.

The floor Is damped with a heavy rubber layer and green glue but i think It IS resonating.
Yes, I believe you.

Quote:
Ah! and other thing I found out is that the wavelenght of 73 Hz is 4.7 meters, almost matching the room width.

How could I make myself sure that It is the floor actually making things worst?
Yes, and mode 4.0.0 (room length: 9.81m) is 70 Hz. In fact all three dimensions have coincident or near coincident modes.

Quote:
How could I make myself sure that It is the floor actually making things worst?
The floor will vibrate in sympathy with the air bourne resonances (modes).
Worse? Possibly.

I think it’s better to start treating the acoustics.

My suggestion for a start:
Build floor to ceiling square ”pillar” traps in 4 corners. 60x 60x 300 cm with low GFR ”fluffy”.

Window (south) wall corners.
Drummer right hand corner and east wall mid corner.

That will shorten the decaytime a bit. (make REW measurement)
How much and what kind of treatment do you have in mind?

Then, if the floor is still concidered a problem, one can build heavy platforms for the drums and the bass cab. (Boxes filled with gravel).
That will surely lower (damping) the frequency of the floor vibrations.

Best
Old 1st July 2019
  #16
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Still Me

Hi there!
I tried several times to recover my password with no luck. So i registered again with a different Name.
Old 1st July 2019
  #17
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So I ripped out the floor

Yes! I'm starting from scratch.
So, I will take some time to plan on everything.
I will open a new thread to share plans and measures and hopefully get your help.

Ray
Attached Thumbnails
Acoustic measurements of an odd shaped rehearsal room.-db3698a7-f15a-4b64-9e2d-6cd42868b778.jpg   Acoustic measurements of an odd shaped rehearsal room.-img_5553.jpg   Acoustic measurements of an odd shaped rehearsal room.-img_5569.jpg  
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