Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ.

---

[ Follow Ups ] Thread: [ Display  All  Email ] [ Tweakers' Asylum ]

---

[ Alert Moderator ] [ Edit ] [ Delete ]

---

Review - J. Risch room lens design (long)

203.12.171.18

Posted by David Aiken on March 20, 1999 at 01:01:38

I built a modified version of Jon Risch's Room Lens design today. It took me less than 2 hours to roughly assemle 4 three tube units - they aren't glued together yet, nor have I tried cleaning and polishing the tubes to help appearances.

My modifications were simple and concerned only with linking the tubes together and providing a base. I linked pairs of tubes together by using PVC saddles - these are clips shaped like the greek letter omega for holding pipes to walls. By bolting 2 saddles together with the feet facing each other, I created a simple clip. The middle tube therefore has 2 clips at each end - one for the tube on each side - and this arrangement is duplicated at each end. At the foot of each tube I used an 88 degree PVC radial bend fitting - the outside tubes have the foot of each bend facing out slightly and the centre tube has the foot facing directly back. The feet form a rudimentary tripod base and the unit is free standing. It's just a matter of bolting them together.

I used tap washers between some of the saddles to create the variation in spacing suggested by Jon. The closest pair of each unit is around 7/8 of an inch apart at the foot of the tube (prior to fitting the radius bend), and the top around 15/16 of an inch apart due to use of 1 tap washer on each side. The wider pair has 1 tap washer spacing between each side of the 2 saddle clip and the top has 2 washer spacing. Separation of tubes is around 15/16 of an inch at the bottom and 1 and 1/16 of an inch at the top. This is slightly wider than Jon's specification.

The tubes are 58 inches long each and the polyester batting is placed within as per Jon's instruction. The radius bends add about 4 inches in length to the bottom of the tube and this is additional to Jon's instructions for placing tha batting - I could remove the bends and fit them straight into wood bases and tops as per Jon's instructions if I chose. Currently I'm using panty hose pulled over the end of the radius bends as a gauze - it looks like they're wearing socks :-).

Because the tubes aren't glued into the clips as yet, they are a little unstable. The clips aren't real tight and the tubes can move in relation to each other. I've had 2 tubes collapse in a bit over 3 hours with normal traffic through the room. Stability should be much improved when I finally glue them together.

Room and equipment:

I have a room around 22 feet long by 11 wide, and just under 10 foot high ceilings. There is a partial wall on one long side half way along extending about 2 and a bit feet into the room, creating two 11 foot square areas. Facing the part wall the left area is the living room/listening area and the right area is set up for dining. Speakers are placed along the long wall, about 40 inches into the room and the left speaker is around 33 inches from the side wall. The right speaker is symetrically placed in relation to the false corner formed by the part wall. I sit midway between the speakers and around 30 inches from the back wall - kind of an AudioPhysic arrangement with near field listening to minimise the effect of no side wall next to the right speaker. That left/right asymmetry was one of my problems, as well as a lot of room nodes related to 10 and 11 foot distances. The equipment rack is against the wall between the speakers for minimum speaker cable runs. There are windows behind the speakers. The glass is "dimpled" which seems to help a little in terms of breaking up the worst of the reflections, and there are light gauze curtains covering them.

The floor is polished floor and the only floor covering is a rug about 6 foot by 4 foot placed between the speakers and the listening position. Walls and ceiling are plaster. There are lots of pictures on the wall and basic furniture. The room is much more lively since we had the carpets taken up and the floors polished. Sound has been improved tremendously prior to building the room lenses by paying extensive attention to vibration control at the equipment rack and speaker stands. Much of what I originally thought were room problems seems to have been due to vibration.

Equipment is as follows:

NAD 5440 cd player
NAD 312 integrated amp (25 w/ch)
KEF 104 aB speakers (now 20 years old).

Listening results:

My main problems were the effect of the asymmetry between L & R speakers due to the lack of a wall beside the right speaker and room nodes affecting mid/upper bass and lower mid range. I thought I had a reasonably wide sound stage but that depth was restricted and there was a sense that room acoustics "dominated" the recorded acoustic to a degree - that is I felt I could sense what the recording space was like, but that I was "looking into it" from my room, rather than being present in the recorded venue.

I placed a lens on each side of the equipment rack about a third of the way out from the wall to the speakers and one lens outside and forward of each speaker - much as the standard recommendation is apart from doubling up on the rear wall due to the need to flank the equipment rack. I haven't experimented much with placement and I've only done about 3 hours listening so far.

The primary impressions are:

- sound stage slightly wider;
- sound stage much deeper;
- improved imaging and sense of 3 dimensionality;
- the acoustic space of the recording now dominates and there is a sense of being present in that space - the feeling of the listening room itself as a presence has been drastically reduced. Recordings in large reverberant spaces like cathedrals can be positivley spooky with a sense of singers close to the mike and hall echoes from way back around them (and me);
- bass is tighter and cleaner and top end airier so mid range appears much enhanced and the overall sound balance more natural;
- on some recordings there's a sense of greater depth to the bass and my wife commented that it sounded "more punchy";
- overall things sound a little louder at the same volume setting.

Visually, given the small room area, it's a little like having 4 of the 2001 monoliths in the room with you - a slightly surreal affect, but they're easily removed when guests come (unless they're hi-fi addicts also).

Overall, I'm very impressed. All up it cost me under $150 Australian (equiv to around $225 US). Relying totally on plumbing components increased costs by about 30 percent but greatly simplified construction.

Jon, any comments on fine tuning - eg modified batting placement for increased tube length? I can also arrange the tubes so that the centre tube is not in the same plane as the outer 2 - sligtly behind them - to "fudge" the apparent distance between the tubes. This would probably improve stability slightly also by providing a deeper footprint.

If you want to use any of these comments in conjunction with your instructions, please do so. I can post further comments in a week or two if you're interested.

David Aiken

This post is made possible by the generous support of people like you and our sponsors:

Kimber Kable

---

[ Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2024, Audio Asylum, all rights reserved ]

---

[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]

---