Yes fill in with some kind of insulation it will become front corners bass trap. I believe bass trapping is another benefit of soffit mounting. see picture below I believe it's John's work
Right, but that's not the final complete structure. With John's design, only the BOTTOM section (under the shelf) is for bass trapping. The section above that (where the speaker sits) is filled with insulation to damp resonance in the cavity caused by the speaker itself, but is not actually treatment for the room. There's large, massive, thick, heavy front panel that goes over that section, which is the "infinite baffle" for the speaker itself.
leave it parallel to the floor to keep it simple to build. So Panel Absorber (Cloud) will be needed to stop early reflection from ceiling
Right. And if you also put a hard back on that cloud (such as very thick plywood), that can also help to break up vertical room modes, to some extent.
in my opinion some stone walls are diffusers.
Yes, but only at very high frequencies. Sound waves are only affected by objects that are similar in size to the wavelength, or larger. So the variations in the stone surface have to be really deep to have an effect on mids and lows. A smooth stone surface, for example, is an excellent acoustic reflector for all frequencies with practically no diffusion, but a very irregular stone surface with peaks and depressions varying by several inches is a good reflector for mid-highs and highs, and a reflector for lower frequencies.
John has written in his article about Slat resonator "broadband low mid absorber is created that still keeps the high frequencies alive" maybe you don't need stone wall to make live room alive.
Right!
:) Slot walls can keep a room sounding natural and bright, depending on how they are set up and tuned.
I red the link about the hangers and I didn't see any formula for calculating the hangers absorption frequency.
As far as I'm aware, there has not been much research done on hangers, and all the evidence for how well they work is empirical. Tom Hidley seems to be the guy who came up with the concept, and John uses it frequently in his designs (me too!). They work, but there isn't much info on how they work.
But they don't need tuning: they are broadband bass traps. Basically, the bigger and deeper then are, the lower they go in absorbing bass.
Anyway it is probably difficult to explain the absorption process with physic laws or exactly with formula .
From what I've seen, they work sort of like wave guides, both re-directing and absorbing low-frequency acoustic energy at the same time. From what I have seen in tests of rooms I designed that were tested both before and after the hangers went in, they extend the path length that a wave must follow, and thus force the mode down to a lower frequency while also damping it. Also, Since John sets them up at quarter-wave points for room modes, I also have the impression that there is diffraction going on too. So it seems to be several principles of acoustics going on at once.
Maybe one day if I have time ( haha! Good joke!
:) ) I'll do some experimenting on angles, sizes and locations, and see if I can figure out something useful.
I guess what make hanger effective would be gravity. When sound wave hit acoustic hanger sound pressure push hanger move and gravity keeps forcing it to swing back to its neutral position. Hanger's Oscillation creates resistance against sound pressure. I think this is how Acoustic hanger able to absorb low frequency.
I doubt it is gravity! The period of oscillation of those things is from maybe one or two per second, to sever seconds long, way, way below even the very lowest infrasonic, or even earthquake frequencies. The very lowest sound wave frequencies (wavelengths longer than the size of the panels) most likely cause vibration in the panel itself, which is damped by the insulation. Somewhat higher frequencies would undergo diffraction and absorption along the surfaces of the panels, and higher still it would just be simple absorption. There might even be some limited diffusion going on, since the panels are really large and regularly spaced.
So for containing the problems with modes and low frequencies is probably tho make as much hangers as room will allow.
To be honest, I prefer to run an acoustic test of the empty room BEFORE any treatment goes in, to see how it is behaving as just a raw shell, then decide how to treat. Then I test again after each acoustic device goes in, to check that it really is working as planned, to see what side effects it created, and to decide on the next step. Predicting things with calculators and software is great, but rooms are seldom built exactly according to plan, and therefore don't respond exactly as expected, so it's better to treat the way it REALLY reacts, than the way it is PREDICTED to react....
And if after the measurements shows you've gone to far with absorption to add some reflective surfaces.
Exactly! That's what I like about "inside out" construction: it pretty much guarantees that you will have way too much absorption in the room, so most of your treatment is about putting things back into the room with reflection and perhaps diffusing, instead of trying to take more out.
- Stuart -