Difference b/w RPG Skyline and GIK QRD diffusors

The RPG skylines performed WAY better than the QRD in my room.

I did ask Rives, and he was not offended at all. An explanation ( my understanding) is that I have three in-wall
speakers in the front wall, which effectively prevents hemi-cylindr. diffusor to be placed in the center.
With respect to Skyline vs. QRD, his explanation is that Skyline performance is just better.
I've also seen Rives designs with two hemi-cylindrical diffusors behind the speakers, but I didn't insist on having those included in my design.
I suspect, they do choose treatments, based on the level of service one orders. Level 1, which I did, presumes less expensive solutions, and levels 2 and 3 would implement more sofisticated, hence more expensive design elements.

Maril555,
Out of curiosity,did you ask RIVES why they suggested the Skylines for the centre of the front wall, or would that feel like you were challenging their expertise?! RiVES typically recommends a hemi-cylindrical (polyfuser) diffuser for front wall centre, not Skylines . . .

Given than Skylines will on average diffuse 50% of specular reflections horizontally and 50% vertically, whereas QRD's or hemi-cyclindricals will diffuse 100% horizontally, I would expect that you'll hear less ASW (apparent source width) with a 2D (i.e.Skyline) than with a 1D (QRD/Hemi)diffuser. ASW is associated with a wider soundstage. Given the listening distance from your chair to the front wall and given the propogation loss of reflections making their way to the front wall afer colliding with side and rear walls, in reality I doubt you'd hear any significant difference between Skylines and QRD on the front wall. You will hear more of a difference contrasting diffusion with broadband absorption on the front wall . . .

If cost is a concern, then I'd recommend building a DIY Skyline (see my system pics) or a hemi-cylindrical, both of which I've build several of and will gladly share my 'learnings.' Building your own will allow you to easily outperform the performance of mass produced Skylines and QRDs; RPG Skylines with its 7" depth will diffuse effectively to about 1kHz (50% of 965Hz wavelength is 7"). Diffusion should be broadband enough to work effectively (meaning cell/well depth should be a significant fraction of the wavelength, normally 50%) to 300Hz requiring a depth of 22.6" and a sitting distance of about 135" (3X the wavelength). Would your room accommodate these diffusion dimensions or slightly more conservative versions thereof?

The hemi-diffusers are great specular diffusers worth considering which can have their concave interiors stuffed with fiberglass to act as a bass trap - a two-in-one produce hard enough for MF/HF diffusion and LF absorption.

Some things to think about . . .

I did look on line and there seems to be very small to no discount on Skylines, more so on LP version, that I don't need.
If you could post a link, it would be much appreciated.

Look on line. You can buy RPG skylines for A LOT less on line. Paint them yourself for next to nothing if you want colors. There is online discussion on how to do so. Just google it. - Jim

RPG does make QRD panels as well, but Skylines are NOT QRD design.
I will try to ask Rives about it.

Maril,

The term QRD means quadratic root diffusor and refers to the math behind the calculation of these. I understand the Skyline is a QRD, but I realize it's confusing when there are commercially available products called QRD, like the GIK you asked about. Sorry my thread was ambiguous.

Diffusion in 1st reflection points on the side walls and on the ceiling (likely another 1st reflection point), is not uncommon. I would still be interested in understanding why Rives recommended diffusion on the front wall.

Horacio

Actually Rives specified Skylines on the front wall, and nor QRD. There also some diffusion on the ceiling and side walls at first refl..points. And , of course, a lot of bass trapping.

Maril,

I fully understand your point and if I were in your shoes I would probably do the same. Can you ask Rives what the difference would be?

Nevertheless I agree with Shadorne. To me that's an unusual spot for QRD diffusion and Shadorne is telling you how these are usually implemented, including the recommendations in Everest's and in Toole's books.

Come to think about it, maybe you can do us a favor and ask Rives why they chose QRD in that spot and post what they answer. Rives knows their stuff and maybe we learn something.

BTW: good move contracting Rives. Which level did you select? I'd be interested in the results.

Thanks,
I know about the DIY RPG project, but can't really picture myself going through the tedious process of cutting 156 pieces of wood for each panel,and then gluing them to the board, and I need four of them.
Lewinskih01, thanks a lot for your explanation, very helpful.
I suspected it to be similar. Here is the question: since the listening position is at the fixed height, the limited vertical dispersion of the QRD panel should not be that critical. I wonder, what I would actually hear with QRD panels vs. Skylines???
Shadorne,
I understand your point, but I'm not an author of this design, Rives Audio is, and since I decided to use them, I would like to follow their design to a letter. I doubt, I know more about room acoustics, then Rives does.

Of course, you can easily go overboard with RPG as Elizabeth points out. This studio used TONS of wood and not even ONE piece of wood is the same length.

I would recommend RPG above the listener (in a low ceiling) and on rear wall behind the listener. I would not recommend RPG on the front wall between the speakers unless you are using Bose or other rearward radiating speakers.

Frankly the majority of frequencies radiating backwards from conventional speakers are the LF - below about 300 Hz and some up to perhaps 600 HZ. So absorption panels or bass traps are most likely the best option there.

An RPG on the front wall may look good and many listeners will be more impressed when they can see and are looking at the RPG skyline but honestly it will be more effective nearer the listener or on the back wall behind the listener where parasitic reflections can muck up your imaging and collapse the sound stage.

Two cents...

RPG Skyline diffuse in two directions, so you get a hemispheric soundfield around one of these, as opposed to the vertical OR horizontal diffusion, whereby you get a hemicilyndrical soundfield.

As Elizabeth mentioned, the math is publicly available, and you could make this yourself, maybe using wood of a square section close to the RPG section, and cut it to the required lenght. Is not difficult, but it will be time consuming as you'll need a lot of pieces. For the math you can check out the Master Handbook of Acoustics by Alton Everest (I've seen links online to the pdf version, but I do have the book), which is highly recommendable reading anyway if you are getting into acoustics.

Horacio

GIK also has the D1 diffuser as well which would be a less costly option as well.

Here's another alternative for you. The Alphasorb panel from www.acousticalsolutions.com. As I recall they are about 470.00 per pair delivered. These panels are not as visually challenged as other diffusors.

I can't comment on how they would compare with your other contenders. I will say that these are very powerful tools and 2 or 3 on the wall makes a profound difference. It is easy to over do it in a room my size. I own 4 panels and with my current setup only use 2 on my back wall.