The wall to ceiling corner can be viewed the same as a wall to wall corner so If you have the space, corner traps would probably be a good Idea! In fact I’m doing just that at the moment in my studio, although two of the ceiling to wall corners already have a 45 slope fitted so standoff traps are being fitted to them. Again I think knocking the wall,wall, ceiling corners out with a triangle absorption would probably work but as the total area is small the effect would be minimal.
Prior to building out my room, I had read about bass build up in the corners, but it seemed like a bit of voodoo as I could not create the problem for first hand experience. As I worked on the build, it all became evident. For some back ground, the room is 12 ½ by 14 ½ by 7 ½ foot tall in the basement, with four cement block walls. I had torn out the ceiling and inserted rockwool between the joists which would later be covered with drywall. The ceiling acted like a very large broad band absorber. I took a cheap radio and moved it around the room, if I put the radio or my head in a corner, I could hear the bass build up in the corners as easily as you could hear I’m not a singer. The front of the room bass traps are I believe 30” by 36” and run floor to ceiling, the rear bass traps are 18” by 18” and run floor to ceiling. What a difference they make. Oh yeah, they are full of rockwool. Of course there are broadband absorbers in the front and back with Helmholtz resonators on the side walls along with some clouds. The reverberation rate is about .35. In a room this size the bass waves never get a chance to develop properly due to their length, but the traps do sop up a lot of their energy. Hope this helps.
Because of the size of my studio I wasn’t able to put bass traps in all wall to wall corners, so I put two bass traps in wall to ceiling corners. One in front of me, over my desk and monitors and the other on the opposite side, behind me.
All my bass traps and other acoustic panels are DIY, filled with Rockwool.
They make a big difference.
Curves as in concave curves as viewed from inside are bad, convex curves better, or non parallel flat walls easier.
Absorption and diffusion are the main treatments.
I always thought the classic Stealth had flat panels because when they were originally designed 70’s? they didn’t have the computing power to compute results from curved surfaces??? They also use radar absorbing paints and materials.
The Raptor F22 has curves and is reported to be more stealthy than the F117, the thing is the curves are convex to radiate away rather than concave which would focus the energy!
Same kind of principles as diffusion and absorption with sound frequencies.
works like lenses and mirrors
Mandatory reading for every DIY acoustics “engineer”:
I knew you were going to pull up that as an example 
We are are mainly concerned initially with low frequencies as the major problem with most rooms, they have long wavelengths are are a lot more difficult to deal with, With a vocal the frequencies are more mid/top and as the wavelengths are shorter they are more readily absorbed by smaller amounts of material due to the fact that you can place the absorption closer to the 1/4 wavelength point without the design needing to be massive. The design constraints on a small portable vocal mic shield mainly produces a mic stand mounted semicircle with a structure designed to not only reflect but also pass through as can be seen in a lot of designs by the inclusion of holes in the reflecting back plate. The vocal sound pressure (frequencies) then have to pass through an absorbent material followed usually by an air gap to the back plate, then any reflections from the back plate then have to pass through the absorbent material again before any reflections (highly attenuated) can get back to the rear/sides of the mic.
Bass frequencies, say below 200Hz, wavelengths are considerably longer, more absorbent material is required to reduce the energy. a 70Hz signal has a wavelength of around 4.9 meters so for maximum efficiency, a simple absorber would need to be place out to 1/4 wavelength, about 1.25 meters from your wall!!! so more efficient designs have been realised, mostly using damped resonance. With a frequency of 2KHz the wave length is about 17cm, far easier to deal with using absorption alone.
Anyway, using concave surfaces (with absorption) in the corners of your room would be very bad for the acoustics particularly at low frequencies, you would be in affect making a low frequency focuser that would result in extremely bad bass pile up. The tried and trusted corner absorbers work well, although not the most efficient designs they are cheap and easy to make and are fairly effective.
Indeed. You only have to remember that half of the pages are (more or less) RPG product ads. If you can filter this out and consentrate on facts on this book, it’ll give you good guidelines on acoustic treatment of the recording studio.
No NO NOOOOO! Concave surfaces are VERY BAD idea. They work only if they are absorbing/reflecting/bypassing/diffusing the sound in precise calculated way (as in case of SE Reflection Filter and other similar products) just like Split was trying to tell you.