[Matthew Dougherty]

In Houston Texas, I built a 20ft dome studio as a prototype laboratory to explore 180/360/3D immersive filmmaking and cinema. https://my.matterport.com/show/?m=44tDXYZuvcJ

I get about 5000 people per month for the last 5 years, coming by hanging out to listen to their music, through their phone’s bluetooth, a rent tradeoff I have with the bar below.

Now that I have the optics and projection figured out, I want to better understand the acoustics. The surface is sheetrock with hot-mud plaster, as opposed to acoustical plaster or fabric.

The room has a number of unusual acoustical properties:

1) somebody 20ft away can be heard as though they are 1-ft away, which is producing unusual social interactions.

2) at the center there is a focal bubble, about a meter in diameter. Someone standing in it speaking causes them to hear themselves from all directions, with a delay of 20ms, well within the Haas effect. What is also unusual is a person a foot away listening to the speaker barely notices changes, compared to what is going on in the brain of the speaker.

3) People enjoy the Haas experience and the natural room amplification. and this has become a signature dome experience people return for. On a few occasions I have noticed a group of opera quality voices doing Italian karaoke. One beatbox group from Vegas told me it was the easiest room they performed in, particularly the baritone. I have also been bringing in solo professional musicians with instruments (e.g., guitar, horns, drums, accordion) and they have not objected to the acoustics.

4) I have been running REW tests and have done some Treble simulations. With the simulations using various treatments, I probably could push the room strongly toward anechoic. Some technical papers on Mosques twenty years ago, indicated a simple treatment of the top third of the dome will eliminate most of the dome reverberation, but their primary problems are way beyond the Haas effect.

Besides video editing, I see micro dome rooms to be the audio mixing rooms for 360 immersive film, and the endpoint of watching and listening to cinema in home-dome-theaters. Regular 16:9 videos play without difficulty, and with the correct projector can create a near-IMAX-like experience.

Looking for ideas for acoustical testing.

[Matthew Dougherty]

actually it is a hemisphere capping a cylinder with a 20 degree incline. I am having some CAD drawings made up, I can present blue prints.

as for the bar, I use it off hours, but there are other problems like a light rail system passing 50ft away and other downtown ambience. This prototype was built to study optical projection, but the acoustics quickly became a subject of significant interest. Filmmaking must integrate the two.

For planetariums, Spitz uses a metal surface which has millions of holes. Speakers sit behind it pointing into the audience. Some planetariums put their speakers within the room.

The acoustical challenge is how to craft a dome room (5-8 meters) that is affordable with acceptable acoustics, but scalable on acoustical quality. Acoustical plaster, fabric, metal are proven possibilities. With a larger budget, a 100 speaker atmos system surfaced in speaker cloth would be my first choice.

Subtle modifications at the top of the dome can reduce reflections. Speakers on the floor, not pointing to the top, pointing horizontally, do not produce strong reverberations. When the sound source is at the very center, the reverberations become highly noticeable to the person speaking, but a foot away listening is nearly normal; the Haas effect is limited to the speaker, but an astute listener would hear something.