I installed a few of these. In fact the Restaurant I had my first job in had these wooden slats so it would make the Air cleaners quieter back in the day when we had smoking sections in restaurants. So you saw them a lot more often in the past being installed then today.
There was a formula from what I understand that works on the same principle as calculating port length or box tuning. It would target those frequencies, and in some cases provide acoustic cancelation of a target frequency range.
You notice them more often in older builds since they use to take into account the way a space sounded as well.
This goes back to the days where an architect would take into account all aspects of the structures design and it was deemed a very important part. Something that goes to the wayside these days as costs for doing this often are axed due to cost overruns.
Firms such as
SSA acoustics specialize in materials such as metal panels being tuned in order to be used as sound absorption facades. This is sort of the reason why its not so popular these days since it does take quite a bit of money and time to get all of this up and running and us usually left for Big funded construction such as civic projects that don't bother with cost as these building projects tend to be permanent lasting buildings that often won't see any further updates after final construction.
The slats from what I understand are tuned
Monochords.
The slats (
Tuned metal in this instance) is made to a length, size or shape to give it a desired tuning. This tuneing can either act as a sound absorber,
(attenuation) or amplification
(reinforcement of frequencies) .
--------Hence why you will see ones made out out of wood with shapes trimmed into them to get them to resonate as a certain frequency desired. Therefore, they either amplify or cancel out room acoustics or tune them in such a way for either speech, music etc. Ala,
Symphony Hall is a 2,262 seat concert venue in Birmingham, England.
Architectural acoustics
en.wikipedia.org
A book from 1932:
Source: Digital Library of IndiaScanning Centre: C-DAC, NoidaSource Library: Central Library, Bits- PilaniDate Accessioned: 7/10/2015 22:05The Digital Library...
archive.org
Page 419 goes over school buildings in detial.
It was also used for outdoor applications such as Art installations and Exhibits.
Here is Pioneer Courthouse Square that has this really cool space where everything sounds like you're echoing back to yourself. More like Binaural sound but without headphones. You have to have 2 working ears to hear this.
Some cool people who were the pioneers of this stuff as far as I can find and read up on in the past.
Frederick Russell (Russ) Johnson
en.wikipedia.org
en.wikipedia.org
Russell Johnson, one of the most influential figures in the modern history of concert hall design and the acoustician for some of the world's most admired new classical music venues, passed away on Tuesday, August 7 at his home in New York City. He was 83 years old and had continued working...
playbill.com
Artec - Morton H. Meyerson Symphony Center - Symphony Hall, Birmingham - Wallace Clement Sabine Medal. Hyperleap helps uncover and suggest relationships...
/)
hyperleap.com
The O.G.
Greek Accoustian. 570 – c. 495 BC
Pythagoras of Samos
In the 6th century BC, the ancient Greek philosopher Pythagoras wanted to know why some combinations of musical sounds seemed more beautiful than others, and he found answers in terms of numerical ratios representing the harmonic overtone series on a string. He is reputed to have observed that when the lengths of vibrating strings are expressible as ratios of integers (e.g. 2 to 3, 3 to 4), the tones produced will be harmonious, and the smaller the integers the more harmonious the sounds. For example, a string of a certain length would sound particularly harmonious with a string of twice the length (other factors being equal). In modern parlance, if a string sounds the note C when plucked, a string twice as long will sound a C an octave lower. In one system of musical tuning, the tones in between are then given by 16:9 for D, 8:5 for E, 3:2 for F, 4:3 for G, 6:5 for A, and 16:15 for B, in ascending order.[6]
Honorable Mention:
Jean Nouvel, French architect.
Jean Nouvel
en.wikipedia.org
Archaeoacoustics
Truly fascinating reading on how this sort of field evolved over the years. I sometimes wonder why on earth they don't have people from colleges go into schools for and teach this fundamental of sound to kids. If they did? I bet you music today would be a lot more interesting. And so the same with architecture.
en.wikipedia.org
That reminded me of how pleasant is to hold a conversation in those modernist spaces, without any symmetries, round corners and ceiling decoration...
Why we stopped doing architecture like this? 
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There are more sheep farmers in the world then there are acousticians. Sadly...
.
You don't get these spaces to often as our culture has delved into a throw away Society.
instead of improving the Acoustics we simply use speakers to mask the environment around us instead of improving it. Active noise cancelation being the new fad as its cheaper to install tech then do the proper job of improving the space above.
There are also real world limitations on what you can actually do as far as architecture that will work in the acoustic environment / space. The first being finding anyone that is able to pull it off. You also have to take into account building codes. If the building is in an area that has earthquakes for example? It would be hard to pull something like this
off to code.
Example:
-Section R102 Modifications to ASTM C 635 — Standard Specification for the Manufacture, Performance, and Testing of Metal Suspension Systems for Acoustical Tile and Lay-In Panel Ceilings
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Support and Bracing Requirements for Ceiling Suspension Systems with Lay-in Panels
-
PRESCRIPTIVE STANDARDS FOR SUSPENDED CEILING ASSEMBLIES
-Grid Ceiling Construction Guidance Suspended Acoustical Grid Ceilings 2009 International Building Code
Why did it become such a thing to do in buildings? Well. Its due the 19th century thought that items that suronded people have a way of absoribing their "Soul" voice or aura. This was popularized by a few people back in the day. One notable person that I could find is,
Charles Sanders Peirce who wrote back in 1902:
"Give science only a hundred more centuries of increase in geometrical progression,
and she may be expected to find that the sound waves of Aristotle's voice have somehow recorded themselves"
OTHER Sources:
https://asa.scitation.org/journal/jas
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The Journal of theoretical and computational acoustics
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Journal of Sound and Vibration
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Applied Acoustics is a leading international journal that reports original scientific research in acoustics with broad impact in engineering applications
