One layer of treatment .... What Next?

[Blenny]

Not your typical theater install

I am getting a large music rehearsal room treated this month, and have most of the first orders of absorption and diffusion installed. I have met the low end recommendations in terms of square footage of treatment from a few different companies that I had spec this room and model it... a few absorbers are waiting on brackets to come in the mail, and then everything will be up.

Before I get to the data and attached files/ pictures.... My ultimate question is, would absorption or diffusion be the next best step to add to this to finish this room off.

I have MASSIVE improvements from before, but this room is not where it needs to be. The room is still quite brightly loud and unintelligible when it is filled with 50 junior high musicians (did I mention I love my job?) So my initial feeling was to add on a few more absorbers to quiet the space. But the RT I took today is showing that I am definitely on the low end for rehearsal rooms like this. (1.0-1.5 RT60 seems to be recommended) I have budget money left, but not unending amounts of budget money. The room can be described as so loud when students are entering or exiting and chairs getting setup, that I have to shout at a student 4 feet away for them to understand me. I have 2 other rehearsal rooms with this many students in it that don't have this problem.. so I know It is not just me.

Original specs from a free consultation from a well known manufacturer. (computer modeled not mic measured) had RT calculated at 5 secs at 1000hz and 9 seconds at 250 hz

The room is 40x26 with 16' ceilings, 16380 ft^3. parallel cinderblock walls, hard tile floor, center "yellow" tiles are a hard reflective fiberglass, white perimeter are the standard 1/2" 2x2 drop ceiling tiles. A few small windows are around the room.





Since that computer modeling, I have installed 19 2'x4'x4" broadband absorbers on the walls (wall corners can't be touched with basstraps due to asbestos tiles ugg)
and 32 2x4 geofusors in the ceiling. the empty spots on the side walls have 2x4 panels coming. The plan was to mount diffusers on the 2 empty spots on each the front and back



As of this morning, my readings are as follows. I can upload a sound test file if needed

RT


SPL- this room has a 2k null, some combfiltering, and some modal stuff in the lower octaves.


Waterfall



Impulse


So, why is the room so loud, when RT is as low as it is? Is this an early reflections issue, and I need more diffusion? Absorption seems like the easy answer, but I don't want to make this room dead.

My remaining budget, and what I can allocate from other rooms that are being treated could put up another

20-30 geofusors (or similar cost diffusion)
or
another 20 or so 2-4" diffusion panels

or some combo of the two.

Edit. I can also stuff the diffusors with backfill to absorb some bass. Right now they are diffusion only.


Thanks! This is perplexing, but quite fun to work on and learn.

 

[Todd Anderson]

Hey Blenny - looks a super interesting project you have there... I dropped a note to one of the experts from GIK to hop in with some advice. I'm really curious to follow this thread.

Thanks for posting!

 

[Blenny]

Thanks! That is a happy coincidence.. I was just looking at their gridfusors, and am looking to buy 5 or 6 boxes for one of my other more straightforward rooms. The new panels are all 2" deep the first picture's worth were all 4" broadband absorbers.

I am working on treating 3 orchestra rehearsal rooms in my district currently... this is the room that is the weirdest, but not by much.. I may post room 2 later.
-------------------------------------------------

I should post pictures after tonight's install of the final panels from the original order. I will do another run of tests tomorrow with the added absorbers.

There are some empty spots on all 4 walls that I had planned on tentatively installing wall diffusor panels... such as right above the chalkboard, high up on the back wall, and possibly between and/ or under the 5 sidewall absorbers. but wanted to hear the room with absorbtion on the walls only before making that decision.

 

[Sonnie Parker]

My thinking is those panels up high need to be brought down low. You are getting more reflections off the walls at the level of where the sound is coming from... mouth and instrument level. Of course that's just logical thinking, I think. When we treat our home theater rooms we typically keep the panels at ear level. I just don't know that they are doing nearly what they can with them up high as you have them. Then again, I'm no expert, so maybe the GIK guys will have the right advice.

 

[Blenny]

Sonnie, I do think I need some panels lower... Finding spots for them is more tricky due to existing furniture, chalk boards, etc. I still have budget left.... so I would likely add rather than move, unless I am going to deaden the room too much in certain frequencies.

The upper ones were needed as I had parallel cinderblock walls that would still be ringing from this morning's practice if I didn't put them up there. If more absorption won't hurt .... below were some ideas on what I would do....

8 more absorbers- probably 4" since bass is untamed (red) could look like below. green are potential 2x2 diffusor spots.. could just as easily be absorbers. yellow is a "seems like it might work, but ask first" type of location for diffusors. I have working on thick curtains for the windows for MONTHS, no answers yet. (school districts... yey....)

 

[Sonnie Parker]

That might work, but you still have a lot of exposed area down low. I would look at using stands, then you can move them as you need the chalk board. That way you can put them across the floor and they will be a little above the heads of those seated, which will keep all of that bouncing off those areas quietened down some. Another thing that would help is carpet on the floor... my slap echo was gone in my room as soon as I installed carpet... and I've seen that work on more than one occasion. Indoor-outdoor carpet is not too expensive and might be considered an option.

 

[Tonto]

I'd concentrate on diffusion only from now on. Center the diffusors at ear level, side walls & rear walls.

 

[Blenny]

Today's charts from yesterday's work. Speaker in the 2/3 off center, 6 feet from the back wall. Calibration mic on the center podium.

Fewer slices.

The SPL is getting better. I have gotten rid of some of the extreme 30 dB peaks.

 

[JWL.GIK]

Nice job testing so far! The biggest issue I see is that you still have a fair amount of ringing at low frequencies under 300Hz, with longer RT60 times there. Your RT60 is definitely leveled out quite a bit, which is good. Clearly the treatment in there has been quite effective thus far.

To take things to the next level, I'd focus on adding bass traps (ie, absorbers effective as low as possible), along with scattering and diffusion at higher frequencies. This will allow you to further improve the low end decay, without making the room even deader at high frequencies (relative to the lows).

Something like our thick Alpha Panels (Alpha 6As, or possibly Corner CT Alphas for corner mounting) would work well to further improve things. If you want to keep visual consistency, you can also use fabric-covered absorbers (like Monster Bass Traps or 244s) with Scatter Plates installed under the fabric.

In general, for reducing RT60 in a big room like this, the exact placement of each panel isn't hugely critical, it's more about having enough of them in the room and having them be more or less evenly scattered throughout the room. However, since the bass needs the most attention in this room, I'd do this listening test to find bass hotspots and put the thick absorbers there. If you do this test, it might be worth getting a ladder into that room and see what the bass is doing in the ceiling corners around the perimeter of the room.

I'll try to keep up and follow this thread as I can. Or if you are interested in using GIK products for these treatments, contact me directly and I can help you one-on-one. Thanks!

 

[Blenny]

JWK, sent you an email!

 

[Blenny]

Ok, to update folks that are following this, JWK from GIK was super helpful and took a crazy amount of questions from me.

His thoughts were similar to what I was worried about- pulling too much treble out.
Pending my accounting department's red tape, We are going to get......

4 2x4" monster bass traps. I was able to find some hot corners that were not near the asbestos.

8 4" Alpha Panel Diffusor/ Absorber with the scatter plate. I am looking at a 2D scatter pattern, since I don't know yet if they will be vertical or horizontal mounted. Most of these will probably be on the back wall.. But I am going to move them around, experiment with locations, and take measurements before finalizing positions. I will for sure test lining the back wall where it meets the floor.

15-20 Gridfusors. Most all of them will be mounted on the wall students are facing. In addition to alternating direction, I will likely mix them up with the Geofusors I already own up that are currently mounted in the ceiling, to avoid repeated patterns in close proximity.

 

[tesseract]

Informative and very cool thread, Blenny. Please keep us posted on the latest developments.

 

[Blenny]

Ok, My order went in today to GIK. I wanted to ask advice about QRD diffusion in banks as it applies to this room, how it relates to the Barker Code, and the height of the panels above ear level. There are multiple "complications" to this next decision.

I am going to put a bank of 13-17 diffusors across the front of this classroom in some shape or form, How is the problem.

Complication #1
The GIK Gridfusor is a 2x2' diffusor with mirrored root 13 QRD patterns. Does that mean if I want to follow the Barker Code, I treat each panel as 2? Does the mirroring make the Barker code not apply past row 2 on the chart below?



Complication #2
I have fire alarms, and other goodies I really can't move.. and have to provide gaps for in the pattern, or bump the up... I sadly can't get a row of 13. I could get two banks of 5 in a row, and one bank of 3 in a row.. (if I can even use the barker codes with a mirrored pattern.) The Purple are places I HOPE to be able to put some diffusion.


Complication #3

Due to the chalk board height, Most of These are all going to be installed above ear height horizontal diffusion will likely slightly help the room, but not directly to the ears of the musicians..


If you look up at the ceiling, I have 36 2D Geofusors from another company. I can swap any or all of them out with the gridfusors. I have 2 other less complicated rooms with a plethora of 2D GEOs and 1D GRIDs I can swap out.


so my immediate options listed in the order of how I think they would work best to worst. The purple panels are the more durable and expensive geofusor, since there is traffic in those areas.

1- Alternate 1d vertical diffusion, 2d diffusion, put more 1Ds in the ceiling, alternating of course.


2- get a pattern of 1D-vertical, 1D-Horz, 2D- repeat or mirror pattern.. put a few 1D gridfusors in the ceiling.




3- put all 2D diffusors at the front of the room, put all 1Ds in the ceiling where every diffusor will aim at some one directly. (alternating both ways of course)

4- put all front of room diffusors as vertical 1D- sections would blend nicely with themselves, but not with the whole group..

5- use the Barker code (horiz. 1Ds), but have the "different panel" be geofusors or vertical 1Ds.. most diffusion will go 3 feet over student's heads.

Any other thoughts? What would you do, and most importantly, why?

 

[Todd Anderson]

I think @JWL.GIK will probably be able to give you the best advice... perhaps @AudiocRaver might chime in?

Wish I had the acoustics background to dig in and give well-grounded opinions. ;-)

I'm really interested to read your impressions once your modifications are made!

 

[Tonto]

And I would love to see some graphs, before and after!

 

[JWL.GIK]

You are on the right track with all these options. And honestly, the difference between them should be pretty subtle. The Barker code just specifies using 2 different well depth patterns, so since the Gridfusors are a mirror-imaged pattern the only way to accomplish it is to go vertical placement for the +1 and horizontal placement for the -1 (or vice versa if that's better for you). You can also obviously mix & match different diffusors. As long as the +1 and -1 units in the Barker code are different, it will work to reduce periodicity.

Also, you can put some space between each diffusor to help reduce periodicity.

I appreciate you wanting to optimize placement! That's great. But my advice is to not spend too much time on this, the differences will be pretty subtle.

 

[Blenny]

Awesome.

Looking forward to mounting, making music in the improved room, and posting some new charts for everyone!

 

[Blenny]

Ok, an update! My GIK order of alpha 4s, monster bass traps, and gridfusors comes this week. I am also writing a grant for a 6" layer of owens corning to be put in the perimeter above the ceiling tiles of the hung ceiling of this room where the dotted line is to absorb some of the bass pressure waves.... I tested the 2x2 tiles, and they soak up treble- but do let the bass frequencies pass. There is 7' of space above that hung ceiling, so plenty of bass frequencies up there that the fiberglass ceiling tiles are not removing. I am also writing a second grant for a load of stackable corner bass traps with the scatter plates on them.

 

[tesseract]

Sounds (pun intended) like great plan, Blenny. Thanks for the update.

 

[Blenny]

Update!

my GIK order arrived. Pictures will be here soon, but first, the graphs.

First, the "not there yet" parts of the room.

Clarity is not super hot. I think this is the chart that shows what I am hearing in terms of loud early reflection muddiness. I love that REW offers C50 and C80 analysis in their latest update... Though I need to spend a little more time learning about the measurements/ formulas to get this

Impulse shows the strong early reflection that I am still fighting

This is the room as of now. It is getting much more even, though the Bass still needs some work- it is better

Now that we are cleaning up a lot of the muck, I can now clearly see where some environmental noise is coming from- The red is the AC when it is on. Everything used to ring ring ring.. and you couldn't see any clarity on the noise.

RT is getting evened out- those HUGE bass nodes that were 5-7 seconds long are being reduced quite a bit. When I do sine wave bursts, I can still hear ringing 4 seconds after the tone up in the ceiling as there is still substantial parallel cinder block surfaces above my hung ceiling., but it is soft enough to not be as disastrous.

 

[leecreek]

And nothing but tile on the floor?.........

 

[Blenny]

4" Alpha Panels- we got 8 of them I am still moving them around to find the ideal sweet spot. I LOVE how these look!



The New Ceiling. I moved the 2D geofusors to other areas, and now have a full 1D Gridfusor Ceiling.



4 Monster Bass Traps in Various corners... still tweaking them for maximum impact.

The Geofusors that were in the ceiling got moved to the wall, simply because they mount easier than the gridfusors. The gridfusors excel at being dropped in a hung ceiling.

 

[Blenny]

And nothing but tile on the floor?.........

Yes, hard tile on top of cement on risers- I hate it. I have a question out to my acoustic tech if carpet will address the early reflection frequency issue I am having. I am worried it won't treat low enough. I also have a little bit of a lens effect coming off of the concrete curved steps on the front of the risers.

Did I mention I hate risers?

 

[leecreek]

Carpet tiles cut to fit and glued to the front of the curved risers might help. and pretty cheap. Just thinking is all......which I know is dangerous....hahaha

 

[Blenny]

The other problem with the carpet option, is while it could deal with the first reflection- it can deaden the room in the Treble range, and make things worse. As it is, I have sucked out most of the treble reverb time that I I feel comfortable with.

most of my absorbing panels are mounted up pretty high as well. I may need to get more 4a alphas, or other absorbent down at ear level.

Once my GIK guy analyzes, we will figure out the next step!