The interest of the air gap is financial and in the extension of the low frequency.Air gap is never a benefit vs filling it out with the correct type of material.
There are two things I'm unclear about.
1) The benefit of leaving an air gap behind absorption panels. I have 50cm to play around with (at least on the front and back walls). I can fill that with 50cm of rockwool, or do some combination of rockwool and air gap (25-25, 30-20, etc). Assuming I don't learn something that makes me opt for some sort of membrane-absorption panel thing, is there a benefit to having an air gap as opposed to stuffing the entire allotment with rockwool?
2) Is there a maximum absorption depth beyond which you get minimal returns? Using the calculator at http://www.acousticmodelling.com/8layers/porous.php, it seems that 40cm seems to be the upper limit, and adding more, even a metre of absorption, gives no additional bass absorption. Is this because of some exponential increase in the amount of absorption necessary, or is the calculator broken?
It's well established now that so much air gap doesn't work and is counter effective. BAD panels are not the best treatment for music. I'm afraid this isn't going to work well.Just a quick update. I put my money where my mouth is, and am applying the lessons I think I've learnt:
https://www.audiosciencereview.com/...atment-plan-the-retirement-gift-update.47375/
I'll update this thread with new information, once I've put the theories into practice and have some actual real-world experience.
Thanks for the feedback, but without your knowledge, or better understanding of acoustic science in general, I don't know what do with that information. If you have the time and patience to help me learn, I'd be interested in learning why air gaps don't help, and why BAD panels aren't a good diffusion solution.It's well established now that so much air gap doesn't work and is counter effective. BAD panels are not the best treatment for music. I'm afraid this isn't going to work well.
From what I understand, your recommendation is to use quadratic diffusers instead of BAD, and not in locations of first reflections. First reflection locations should have pure absorption, but being careful not to over-damp (i.e. treat first reflections on the walls and ceiling, but don't overkill beyond that - maybe on the front wall behind the speakers and subwoofer). Then I assume you deal with room modes using membrane traps in the corners. Is that about right?The calculation with air gap is not trustworthy. The reason is that energy flows out and and looses effect. Besides, there's no good reason to choose an airgap since filling it 100% works far better. The only reason would be to save some financially. But in this case, the cost of filling it with correct material is cheap and the result would be much better. For 40 cm material one could achieve very high absorption down to 100 Hz area and decent effect to 40-50 Hz.
Flat BAD panels will cause audible specular reflections. It's a treatment that's fine for speech, but not for music. Perhaps it can work ok for multichannel movies, if that's the only usage of the room. The absorption is also high with BADs. It's possible to combine improved diffusion and low frequency absorption. That being said, I would not recommend only the usage of diffusion at reflection points unless one doesn't like good imaging and accuracy, and one only desires a more spatial and immersive representation and which will color all the mixes to some degree.
Also, covering the whole ceiling with absorption would create a dead environment and especially remove too much energy for music.
I wish you strength when you try to spread some reason here .First one needs to decide on the goal and the design principles follows.
A standard QRD is never something I would recommend. It's outdated.
Pressure based trapping isn't something one does based on guesses. One needs to measure and apply it appropriately. Corners in acoustics isn't only tricoerners And only treating those would generally not do much.