Thanks Starlight for the replies - I've really enjoyed reading through your thread on the build of your studio. I did all of the isolation build for my much smaller room, as per a John Brandt design, and your thread brought back memories!
That is not so much smaller than Jason Baliban's 144x180x104" room, here, also designed by John Brandt.
I had not seen Jason Baliban's room until your link - I read through and it certainly provides a lot of inspiration and food for thought. A couple of things that come to mind:
- After all Jason's work and expense, the speakers are not flush-mounted despite the advantages that have been noted elsewhere.
In my discussions with John, and in reading his book (2008 2nd Edition), he did not seem to be a big proponent of flush mounting. Here is an excerpt:
Do not place your monitors right up against the wall. Due to the boundary effect, your monitors will sound fat or boomy in the corners of the room and likewise to a lesser degree when they are close to the wall in front of you. In order to have the flattest speaker response possible, move them at least one foot from the wall in front of you.
That being said, "right up against the wall" is not the same as "flush mounted inside the wall". But he doesn't mention flush mount at all in his original book...
This seems to have been the philosophy applied in my 2014 design, and also in Jason Baliban's (2018). I found Stuart's comments in favour of flush mounting to be quite persuasive, and am just trying to reconcile the different viewpoints (if possible).
- Again we see a PRD mounted to radiate along a 12' room axis, which is called into question by the Cox and D'Antonio referenced provided by Stuart.
I've just finished reading up to the end of chapter 14 (Schroeder Diffusers) in the Master Handbook of Acoustics (6th Edition, 2015) by Everest and Pohlmann, which includes the following passage in relation to QRD panels:
Comparable polar plots, for single frequencies based on a far-field diffraction theory, show a host of tightly packed lobes that have little practical significance. Near-field Kirchoff diffraction theory shows less lobing.
Question for Stuart: what is the source for the colour image of diffusion lobes you showed in your earlier post? I didn't see it in Cox & D'Antonio, and it provides a lot more information than the polar angle plots used in most of the book. Is it possible that Pohlmann's comment about Fraunhofer vs Kirchhoff models apply to that simulation?
I was able to find an online copy of Acoustic Absorbers and Diffusers by Cox and D'Antonio, for the 3rd Edition published in 2005, but it may take a while to find the relevant parts (any hints from Stuart are welcome!) There is a discussion of the mathematical prediction of scattering in Chapter 8, which seems pertinent. The 2015 Master Handbook has many D'Antonio references, but none more recent than 1999 (and the 2005 book is not one of them).
I'm still just trying to get my head around this concept enough to make a semi-informed decision, which includes consideration of the other diffuser types mentioned by gullfo (thanks!)
I could say a lot about couches, but I'm running out of time for today!
I am also interested in hearing more!
John published a studio plan of his in the PDF attached to the first post here.
Thanks for pointing that out - the diffuser and corner traps along the back wall are a reasonable representation of what John recommended for my room. The same goes for the slatted traps along the side walls.
In John's linked example room, the listener would be about 12 feet in front of the back wall diffuser so it's consistent with Stuart's recommendation.
Interestingly, John *did* specify flush-mounted speakers for the room in his speaker placement example. He is also asked for his recommendation for a Focal Twin or Solo 6" (which is what I have). I'm not sure I followed his response, but he seemed to feel that some room dimensions would benefit from flush mounting whereas others would call for "free standing" speakers that should not be too close to the wall.
The width of John's example room (13'5") is not dissimilar to my room (12') or Jason Baliban's room, so from a width standpoint John's flush mount example might work in my room. However, the specific configuration shown would put the listening position around 6' from the front wall. This is dead centre in my room (along both horizontal axes!), which I gather is the worst possible spot in terms of room modes.
I mentioned Jason Baliban's studio above. In Jason's video, at 8'57" for a few seconds, here, we can see that John's hangers do not hang; they are fixed top and bottom. I wonder if that is why he does not call them hangers.
You are right that the vertical vanes in John's corner bass traps are rigidly fixed at both ends, so "hanger" is not the first name that would come to mind (as it does for the other free swinging designs mentioned earlier).
I don't think Jason used any of the "waveguide" traps that John specified for my room and which he also shows in the rear corners in the GS thread on speaker placement. Jason's seem rather to be membrane traps (there is no membrane in the waveguide trap and the front face presents a PRD profile). I have seen the term "waveguide" used to describe ports designed to allow passage of fibre optic cables or non-conductive tubing through a Faraday cage while blocking EM waves in a certain frequency range (eg
https://hollandshielding.com/Waveguide); the name applies since these are short waveguide tubes tuned to act as an absorber. I still can't quite see the connection with John's corner trap though - would be nice if there was a reference somewhere.
As my studio has been designed by John I will be making a Prime 523 PRD this year.
You probably have the same plan I was provided - I'll be interested in seeing how you make it!
My studio is 6.2m (12'4") long and I will be making the smallest (shallowest) of the Prime 523 diffusors, so it would seem you are right, they are for larger (longer) rooms.
I will certainly hold off until I understand the physics better... I'm not too concerned about the physical incursion into the room, but would want to be sure there is an acoustic benefit before building something with so many precise cuts.
btw are you close to the Tatras? My wife is from Poland and until the pandemic we used to vacation in Zakopane every few years. It is a really beautiful region!