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Xenon · 14th September 2009

I have a question about which QRD prime sequences would be best in my live room -- I'm just about to build several arrays ...

I read the Everest book, sorted through the math, read various threads, papers, saw videos, read specs.

The Room:
My live room is 5m (16'5")L x 3.45m (11'ish)W x 2.4m (7.8')H. It has a 'nook' for a drummer. Generally speaking the room is somewhat similar to that presented in "The Ultimate Home Studio" video at RealTraps (an impressive aid to me).

I plan to do bass trapping in all corners, and from the floor to 60cm (2') around the walls, and put a cloud esp. at the center of the ceiling and above the drummer.

My first step is building a diffusor along the 5m wall. I designed 94cm (3') x 94cm (3') frames. Four frames in a row, is about 3.8m (12'5"). Wells are mounted vertically. (Later, 94cm (3') x 45cm (1.5') horizontal QRDs will be above these).

QRD well dimensions:
My max. well depth is 13.5cm (5.32"), and well width is 3cm (1.18"). Well dividers are 25mm plywood.

Due to my mic positions, between 1.2m-2m (4'-6'6") from the wall, I fear building a deeper QRD.

Here is my main question:
I can build all 7-prime QRDs (16 periods), 4-per-frame (oriented in the sequence 1112212111, '2' being flipped). Or, I can build per-frame: "11-prime(well0=Left) + 7-prime + 11Prime(well0=Right)" -- making a total of eight 11-prime periods and four 7-prime periods, and the alternation: 11/7/11/11/7/11/11, etc.

Bandwidth of the 7-prime (LF/HF):
728 - 5746 Hz (= 5021Hz)

Bandwidth of the 11-prime (LF/HF):
1043 - 5746 Hz (= 4703Hz)

The RealTraps QRD seems a 13-prime (well depth @ 6"), so according to the math it is effective from about 1100Hz or higher. One period fits nicely into a 2' frame (is that why it was selected), or because 1100Hz+ is a reasonable LF? It seems rather high to me. (Gusstimate well width around 1.4"~1.5"?) So HF is less than my build I believe. Several periods are placed together in that room build. I follow the math, but "effective" concerning LF is something I read; mysterious...

I want the QRD to be as effective as possible, so bandwidth seems an issue.

On paper, the 7-prime looks best (bandwidth). The higher the prime the less the bandwidth-per-depth, and my QRD depth is not great. But, is there a problem with many repeating 7-primes? And with the 7-prime itself? If so, what? Should I scrap my frames and build 13, 17, 32, and sacrifice some LF?

Given the size of my room, and the repeating QRD periods, are there any suggestions or recommendations for a best or better approach? Thanks in advance for your thoughts.

14th September 2009	#1
Xenon Gear nut Join Date: Jul 2008 Location: Japan Posts: 77 Thread Starter	QRD Prime + Period Question (Live Room) I have a question about which QRD prime sequences would be best in my live room -- I'm just about to build several arrays ... I read the Everest book, sorted through the math, read various threads, papers, saw videos, read specs. The Room: My live room is 5m (16'5")L x 3.45m (11'ish)W x 2.4m (7.8')H. It has a 'nook' for a drummer. Generally speaking the room is somewhat similar to that presented in "The Ultimate Home Studio" video at RealTraps (an impressive aid to me). I plan to do bass trapping in all corners, and from the floor to 60cm (2') around the walls, and put a cloud esp. at the center of the ceiling and above the drummer. My first step is building a diffusor along the 5m wall. I designed 94cm (3') x 94cm (3') frames. Four frames in a row, is about 3.8m (12'5"). Wells are mounted vertically. (Later, 94cm (3') x 45cm (1.5') horizontal QRDs will be above these). QRD well dimensions: My max. well depth is 13.5cm (5.32"), and well width is 3cm (1.18"). Well dividers are 25mm plywood. Due to my mic positions, between 1.2m-2m (4'-6'6") from the wall, I fear building a deeper QRD. Here is my main question: I can build all 7-prime QRDs (16 periods), 4-per-frame (oriented in the sequence 1112212111, '2' being flipped). Or, I can build per-frame: "11-prime(well0=Left) + 7-prime + 11Prime(well0=Right)" -- making a total of eight 11-prime periods and four 7-prime periods, and the alternation: 11/7/11/11/7/11/11, etc. Bandwidth of the 7-prime (LF/HF): 728 - 5746 Hz (= 5021Hz) Bandwidth of the 11-prime (LF/HF): 1043 - 5746 Hz (= 4703Hz) The RealTraps QRD seems a 13-prime (well depth @ 6"), so according to the math it is effective from about 1100Hz or higher. One period fits nicely into a 2' frame (is that why it was selected), or because 1100Hz+ is a reasonable LF? It seems rather high to me. (Gusstimate well width around 1.4"~1.5"?) So HF is less than my build I believe. Several periods are placed together in that room build. I follow the math, but "effective" concerning LF is something I read; mysterious... I want the QRD to be as effective as possible, so bandwidth seems an issue. On paper, the 7-prime looks best (bandwidth). The higher the prime the less the bandwidth-per-depth, and my QRD depth is not great. But, is there a problem with many repeating 7-primes? And with the 7-prime itself? If so, what? Should I scrap my frames and build 13, 17, 32, and sacrifice some LF? Given the size of my room, and the repeating QRD periods, are there any suggestions or recommendations for a best or better approach? Thanks in advance for your thoughts.