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Advice with a multipurpose Hall
Old 1st April 2021
  #1
Here for the gear
 
Advice with a multipurpose Hall

Hi everyone,

I would be very grateful if I could get some advice regarding the acoustic conditioning of a highschool multipurpose hall (my son’s highschool assembly hall). I’ve been searching for threads about something like this and I’ve found some useful information, but most of it regarding smaller spaces and mainly for recording or mixing/mastering. If I missed the right thread, my apologies.

As I said, it is a multipurpose hall. There are lectures, piano, choir and guitar concerts and they also project video and reproduce music with an stereo system. My ideal would be a RT60 around 1 sec.
Because they are on a Budget, and they have a workshop and skilled handyman students in the higher grades they want a DIY approach.


The dimensions of the hall are (length x width x height) : 12.4 x 7.3 x 4m . A volumen of 363 cubic meters. 40.7 x 24 x 13 feet (12796 cubic feet). (picture attached). It has a capacity for 80 spectators, so its ratio volume/spectator equals 4.5, below the ideal ratio for large spaces (6-8m3/spectator) but close to the allegedly ideal of 5m3/spectator established for theaters.
The hall is shoebox shaped and has actually a horrible sound. Room modes up to 180Hz and a lot of high frequency absorption (it has stippled walls and ceiling). (picture attached).

Room modes. My priority would be to get rid of the room modes by using thick panel absorbers separated from the walls, placing the higher percentage of them at the rear Wall, and at the Wall-ceiling joints. They don´t mind losing space in the four floor to ceiling corners so I could fill those corners with absorbers (floor to ceiling layers of 60x60x84 cm - 2x2x2.6 feet triangles). Because these triangles have a máximum depth of 42 cm -1.3 feet , I’d go for an airflow resistance of 3 kPa*s/m2.
I would like to avoid pressure based bass traps, as they have narrower bandwidths, are tricky to build and it’s difficukt to get the desired tune frequency.

High frequencies. In order to recover the high frequencies I am considering the following:

1.Covering the bass traps. By using panel absorbers for the bass traps and for the corners, the problem with the high frequencies would get worst. We could cover the bass traps with plastic, but I’d rather cover them with a more aesthetical material, like White 1mm PVC panels. Would this affect the low frequency absorption?

2.Using Binary Amplitude Diffusers. We could use Binary Amplitude diffusers instead of simple absorbing panels

3.Hanging wood panels. We could perhaps hang wood panels from the ceiling to create direct reflections to the audience and, in doing so, avoid reflections from the stippled ceiling. This panels would be hanged, angled, above the audience. We could also hang panels above the scenario.

4.Hanging stepped diffusers We could also hang stepped diffusers (not difficult to build, made of styrofoam covered with PVC) to avoid reflections in the stappled ceiling

5.Using poly diffusers. We could also build poly diffusers for the ceiling or walls.

6. Remove the texture from the stippled walls and ceiling. From what they told me it's a hard task. It looks it'd be easier to cover walls and ceilings with high frequency reflective panels (if possible with absorption at low frequencies) or with diffusers.

Regarding where to place absorption and diffusion, I think the hall is not large enough for an approach like the one with a reflective scenario, a diffusive middle zone and an absorptive rear area. Am I wrong?
It’s a lot of information, so I hope it is a clear explanation. Any advice would be welcome!

Thank you!

P.S. The brown panels do not exist. They give an idea of how the scenario could end, and how the panels/diffusers could be hanged. The red columns are two existing columns.

P.S.2. I also measured the waterfall graph with the audience seated
Attached Thumbnails
Advice with a multipurpose Hall-captura-de-pantalla-2021-04-01-la-s-17.43.06.png   Advice with a multipurpose Hall-captura-de-pantalla-2021-04-01-la-s-17.40.35.jpg   Advice with a multipurpose Hall-audience.jpg  
Old 1st April 2021
  #2
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Kyle P. Gushue's Avatar
 
1 Review written
🎧 5 years
Helmholtz resonators and perforated panel absorbers would absorb lows and reflect highs. A panel or membrane type absorber would be worth looking into.

You can also make a slat absorber that acts like a high pass filter using wider spacing of slats than a Helmholtz resonator. You get broad band bass absorbsion, and reflect energy above a certain crossover frequncy.

I would add that load bearing, mounting methods, and fire code all come into play. You will probably need a structural engineer to sign off on it. You need to make sure building and fire code are adhered to, as a catastrophe could be tragic, landing people in jail, and causing fatal injury.

You really don't want to be liable for this.
Old 1st April 2021 | Show parent
  #3
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Hi Kyle,

thanks for your response. I´ll have a look at slat absorbers (I'd rather avoid Helmholtz resonators).

Quote:
Originally Posted by Kyle P. Gushue ➡️
I would add that load bearing, mounting methods, and fire code all come into play. You will probably need a structural engineer to sign off on it. You need to make sure building and fire code are adhered to, as a catastrophe could be tragic, landing people in jail, and causing fatal injury.
Thanks also for having security into account. I did not mention it in my previous post, but it was the first thing I digged into.

The building is a public one, and there is a structural engineer (public servant) that supervises changes in the structure. I already contacted him, and gave him the weights of the panels (which I'm not sure I´ll be hanging). He told me they are considered ornamental objects, and not a structural part of the building (weird, I know).

Regarding fire, only problematic material would be plywood. Rest of materials (absorbers and PVC) are fire compliant. Again, due to its weight and due it is not considered as a part of the structure but as an ornamental object, the code allows hanging wood panels. But although allowed, I'd rather hang styrofoam diffusers (either painted or covered with 1mm PCV) for my ease of mind, which are really lighter.
Old 1st April 2021
  #4
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🎧 10 years
You should not consider a fairly large room with this purpose and budget as a kind of studio for spoiled rappers with binary or stepped diffusers, 50.000 dollar Fender Strats, 20.000 bath cables and Rolex Yachtmasters.

Act as a professional in stead of an amateur. Go for a decent room without expensive stupid treatment
Old 1st April 2021
  #5
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avare's Avatar
 
🎧 15 years
Welcome to Gearspace!

You have a great resource with the students. Where are you? That is for material in your area. Low end increase is normal. For initial treatment 200 mm deep absorbers evenly spread.
Old 1st April 2021
  #6
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avare's Avatar
 
🎧 15 years
Welcome to Gearspace!

You have a great resource with the students. Where are you? That is for material in your area. Low end increase is normal. For initial treatment 200 mm deep absorbers evenly spread.
Old 1st April 2021 | Show parent
  #7
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Thanks for your welcome, Andre.
Students are a great resource, indeed! And so is the workshop. :-)
I'm in Madrid.

Thanks for the tip!I was thinking 150mm, but maybe I should go for 200mm. The high frequencies would then be the problem
Old 1st April 2021 | Show parent
  #8
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Quote:
Originally Posted by bert stoltenborg ➡️
You should not consider a fairly large room with this purpose and budget as a kind of studio for spoiled rappers with binary or stepped diffusers, 50.000 dollar Fender Strats, 20.000 bath cables and Rolex Yachtmasters.
Sorry Bert, I don't follow.

Quote:
Originally Posted by bert stoltenborg ➡️
Act as a professional in stead of an amateur. Go for a decent room without expensive stupid treatment
Any advice? :-)
Old 1st April 2021 | Show parent
  #9
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avare's Avatar
 
🎧 15 years
Quote:
Originally Posted by Ricardo1971 ➡️
Thanks for your welcome, Andre.
Students are a great resource, indeed! And so is the workshop. :-)
I'm in Madrid.

Thanks for the tip!I was thinking 150mm, but maybe I should go for 200mm. Problem are still the high frequencies...
You are welcome!

From what we know, the biggest point is the ceiling. How do you feel about multiple poly diffusers? They can be designed to absorb at lower frequencies.
Old 1st April 2021 | Show parent
  #10
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Quote:
Originally Posted by avare ➡️
You are welcome!
From what we know, the biggest point is the ceiling. How do you feel about multiple poly diffusers? They can be designed to absorb at lower frequencies.
That is one of the ideas I'm considering...
Old 1st April 2021
  #11
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avare's Avatar
 
🎧 15 years
What are the current acoustics? Data frm REW would help.
Old 2nd April 2021 | Show parent
  #12
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I attached the waterfall graph when I wrote the first post. If you can't see the images I can upload them again.
Old 2nd April 2021 | Show parent
  #13
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avare's Avatar
 
🎧 15 years
Quote:
Originally Posted by Ricardo1971 ➡️
I attached the waterfall graph when I wrote the first post. If you can't see the images I can upload them again.
I am thinking of the RT plots. I awwas trying to help you. Good bye.
Old 2nd April 2021 | Show parent
  #14
Here for the gear
 
Hi Andre,

it was not my intention to bother you. I thought maybe you were not able to see images in the first post (I had some trouble uploading them and I was not sure I did it properly) , that is why I offered to upload them again. I was not implying you had just skipped the images. I apologize if it looked so.

I will upload the RT plots, in case you are still in the mood of helping.
Attached Thumbnails
Advice with a multipurpose Hall-rt.jpg  
Old 2nd April 2021 | Show parent
  #15
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🎧 10 years
Quote:
Originally Posted by Ricardo1971 ➡️
Sorry Bert, I don't follow.



Any advice? :-)
In my opinion you talk like an expert to noobs about fancy acoustical tools you don't need to treat such a room.
Old 2nd April 2021 | Show parent
  #16
Here for the gear
 
Hi again Bert,
sorry if it looked like a pretentious post.
I was just asking for advice because I'm no expert in the field, though during many years my field of expertise was very related (I was into psychoacoustics almost 20-25 years ago). I spent some time doing tests in anechoic chambers and echo chambers and though I'm no expert I think I have a some basic understanding of the theoretical physics behind absorbers and diffusers, and some basic understanding of the physics involved in room acoustics. At that time I read papers related to diffusion, absorption, auditorium acoustics, and many other subjects, because it was related with what I was doing. But never went deep into it, and of course I have no practical experience in the area.

I apologize if my text sounded pretentious to you. I was simply asking for advice, because I'm no expert in acoustic conditioning and have never done something like this.
I don't mind which tools to use. The simpler to build, the better (I did not think as this tools being fancy or not).
They came to me (the principal at the highschool), because he knew I had some general knowledge in the area and he thought it would be a good project for the students. I am really glad to help them, but being aware of my limitations in this field, I tried to find books or relevant information, but all I found was aimed either to small recording studios/home theaters or to large auditoriums.
Then I asked for advice here, before making the students build tools (the simpler to build the better) that won't work.
I still would appreciate any suggestion,

Thanks!

P.S. If I thought about stepped diffusers or binary amplitude diffusers is because they look to me simpler and cheaper to build than Schroeder diffusers (maybe I'm wrong), in case diffusion is needed. I'm no stranger to diffusers or absorbers. While I was into Psychoacoustics, we had to share the anechoic chamber and there were PhD. students testing diffusers and testing the absorption coefficients of different materials.
Old 2nd April 2021
  #17
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avare's Avatar
 
🎧 15 years
We can be as precise, which is not at all, as you are. If it is going to be of value to you, this thread will grow significantly in size. I asked you mpolitely to put in your location in your profile.

What on is simple to you for construction? About the simplest in type of construction is a Schroeder type diffuser. Straightforward and tedius. Simplest in mayerials is a polydiddussor. Once you have the initial jig for the curve(s) it is quite simple.

Keeping to your level of detaiil, cover the the ceiling evenly with polys, varying the radius to a maximum of 900 mm and a 4 to 1 ratio at 1:2:4 ratios of radius. The largest with ~1/6 circumference.

Enjoy!
Old 2nd April 2021 | Show parent
  #18
Here for the gear
 
Sorry, you are right. I updated the location in my profile.
Thanks for the info Andre. As you say, I thought building Schroeder diffusers may be tedious to build. That's why I asked about the option of stepped diffusers, which look easier to build without the fins.

I'm very interested in your proposal of using polys.
What other information would you need to be more precise? More REW graphs? More accurate dimensions or positions?

Thanks for your help!
Old 2nd April 2021
  #19
Here for the gear
 
Here is all I have:

- Room dimensions 12.4 x 7.3 x 4 m (L x W x H). There is a scenario with a height of 60 cm and a depth of 2m.
- It can host up to 80 spectators. Chairs are wooden and not fixed to the floor.
- The hall has stippled ceilings and walls
- It is going to be used for conferences, concerts and sound reproducing (they have two loudspeakers hanged in the front wall, which could be easily moved)
- Doors are on one of the sides (between the red columns in the hall picture ).
- There are nine windows (60cm x 120 cm) on the opposite wall to the entrance. Very close to the ceiling (aprox 40 cm below it).

Next tuesday I'll be able to take pictures from the hall (Highschool is closed due to easter holidays)

Brown panels in the picture are not part of the hall. White columns are neither. They are there just to show where the corners are located.
Attached Thumbnails
Advice with a multipurpose Hall-hall.jpg   Advice with a multipurpose Hall-no-audiende.png   Advice with a multipurpose Hall-audience.jpg   Advice with a multipurpose Hall-rt.jpg  
Old 2nd April 2021
  #20
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avare's Avatar
 
🎧 15 years
You are welcome. What is your acoustical background? You have mentioned working in psychoacoustics.

What I am hearing (pun intended) is a found space to improve with no defined budget and lots of mostly unskilled labor available. You have several world class people in this thread. Full REW files and figures (sketchup is the norm will help.

Can you get carpentry teacher involved in this thread? There is great potentional for education on all aspects.
Old 2nd April 2021 | Show parent
  #21
Here for the gear
 
I updated my profile. I'm an electrical engineer. I studied some elecroacoustics during my degree (electro-mechanical-acoustical analogies, loudspeaker design... very theoretical), and basic acoustic architectonics. Then for my thesis and PhD (and then I worked almost two years in the field) I moved to psychoacoustics. My field was spatial localization. I was into the equalization of headphones for free field and diffuse field binaural recordings with artificial heads.

You are right in your assumptions about the project. I can get the help of the carpentry teachers of the school, and of course of a large group of students (from what they told me some of them with certain skills). I also think there is a great educational potencial in this (one of the reasons I got into it).
Regarding the budget, its still undefined, because the principal is doing his numbers. I think the actual budget would be something close to 1000 EUR or less, but they have the option to ask for some more funds if we present a nice project.

As soon as I have the time I'll try to create the sketchup design and upload the rew files and some pictures of the hall.

Thanks for your support!
Old 2nd April 2021
  #22
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avare's Avatar
 
🎧 15 years
Great!

What I am seeing is curved diffussers with space behind them to centre the absorption.

What is a challenge is the materials available.
Old 2nd April 2021 | Show parent
  #23
Lives for gear
 
🎧 10 years
Quote:
Originally Posted by Ricardo1971 ➡️
Hi again Bert,
sorry if it looked like a pretentious post.
I was just asking for advice because I'm no expert in the field, though during many years my field of expertise was very related (I was into psychoacoustics almost 20-25 years ago). I spent some time doing tests in anechoic chambers and echo chambers and though I'm no expert I think I have a some basic understanding of the theoretical physics behind absorbers and diffusers, and some basic understanding of the physics involved in room acoustics. At that time I read papers related to diffusion, absorption, auditorium acoustics, and many other subjects, because it was related with what I was doing. But never went deep into it, and of course I have no practical experience in the area.

I apologize if my text sounded pretentious to you. I was simply asking for advice, because I'm no expert in acoustic conditioning and have never done something like this.
I don't mind which tools to use. The simpler to build, the better (I did not think as this tools being fancy or not).
They came to me (the principal at the highschool), because he knew I had some general knowledge in the area and he thought it would be a good project for the students. I am really glad to help them, but being aware of my limitations in this field, I tried to find books or relevant information, but all I found was aimed either to small recording studios/home theaters or to large auditoriums.
Then I asked for advice here, before making the students build tools (the simpler to build the better) that won't work.
I still would appreciate any suggestion,

Thanks!

P.S. If I thought about stepped diffusers or binary amplitude diffusers is because they look to me simpler and cheaper to build than Schroeder diffusers (maybe I'm wrong), in case diffusion is needed. I'm no stranger to diffusers or absorbers. While I was into Psychoacoustics, we had to share the anechoic chamber and there were PhD. students testing diffusers and testing the absorption coefficients of different materials.
As usual I apologize if I sound blunt, I am assured by an Israelian friend who visited me that the Dutch are almost as blunt as the good people of Israel :-).

You have a room you're going to use for amplified music and lectures.
In such a room you need absorption or speechability will be insufficient and music will sound like crap and you can do nothing to correct that.
For the rest of the purposes you can always add when needed a tad of reverb by loudspreakers from the stage.
If you really need diffusion checker the absorbtion pannels with hard surfaces.
Don't bother about numerical diffusers; if you ever need a diffuser the poly as described by Avare will. do.

My ironical intended and prolly not understood bull about expensive fenders, rolexes and rappers was to emphasize that when you have earned a load of money and want to spend it on luxury stuff that's fine, but when you're on a budget of money of other people you should go for a Squier or a Casio
Old 10th April 2021
  #24
Here for the gear
 
Room pics, rew and sketchup

Hi again. It took me longer than expected as I got the Covid vaccine and I've been knocked out for three days. Still recovering.

I attach the rew and sketchup files and also some pictures. Hope they can be helpful!
Attached Thumbnails
Advice with a multipurpose Hall-wall.jpg   Advice with a multipurpose Hall-hall3.jpg   Advice with a multipurpose Hall-hall2.jpg   Advice with a multipurpose Hall-hall1.jpg  
Attached Files
File Type: skp meeting hall.skp (3.78 MB, 0 views) File Type: mdat meeting hall.mdat (5.96 MB, 0 views)
Old 10th April 2021 | Show parent
  #25
Here for the gear
 
Quote:
Originally Posted by bert stoltenborg ➡️
As usual I apologize if I sound blunt, I am assured by an Israelian friend who visited me that the Dutch are almost as blunt as the good people of Israel :-).

You have a room you're going to use for amplified music and lectures.
In such a room you need absorption or speechability will be insufficient and music will sound like crap and you can do nothing to correct that.
For the rest of the purposes you can always add when needed a tad of reverb by loudspreakers from the stage.
If you really need diffusion checker the absorbtion pannels with hard surfaces.
Don't bother about numerical diffusers; if you ever need a diffuser the poly as described by Avare will. do.

My ironical intended and prolly not understood bull about expensive fenders, rolexes and rappers was to emphasize that when you have earned a load of money and want to spend it on luxury stuff that's fine, but when you're on a budget of money of other people you should go for a Squier or a Casio
No need to apologize Bert. Sometimes it is not that easy to detect irony in written texts

Thanks for your advices!
Old 11th April 2021 | Show parent
  #26
Here for the gear
 
Quote:
Originally Posted by avare ➡️
Great!

What I am seeing is curved diffussers with space behind them to centre the absorption.

What is a challenge is the materials available.
Hi Andre!

Materials available should not be a problem. Spain is a country whose economy, besides tourism, relies on construction. Lots of materials available (some of them being cheaper than others, of course).
Old 11th April 2021 | Show parent
  #27
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avare's Avatar
 
🎧 15 years
Quote:
Originally Posted by Ricardo1971 ➡️
Hi Andre!

Materials available should not be a problem. Spain is a country whose economy, besides tourism, relies on construction. Lots of materials available (some of them being cheaper than others, of course).
What do have? Radius of surfaces being significant. The skill of workmanship being paramount.
Old 11th April 2021 | Show parent
  #28
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Quote:
Originally Posted by avare ➡️
What do have? Radius of surfaces being significant. The skill of workmanship being paramount.
Thought you were referring to the difficulty of getting certain materials (getting absorbers...).
Old 11th April 2021 | Show parent
  #29
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avare's Avatar
 
🎧 15 years
Quote:
Originally Posted by Ricardo1971 ➡️
Thought you were referring to the difficulty of getting certain materials (getting absorbers...).
I specifically wrote materials, not products. I HAVE TO PLAY 20 QUESTIONS WITH YOU TO HELP YOU. I have no desire to that. Do you have moldable wood available?
Old 12th April 2021 | Show parent
  #30
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Quote:
Originally Posted by avare ➡️
I specifically wrote materials, not products. I HAVE TO PLAY 20 QUESTIONS WITH YOU TO HELP YOU. I have no desire to that. Do you have moldable wood available?
We have access to moldable wood and any other type of wood. And we have access to any type of absorbent.
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