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RE: Room Lens Question

Posted by Jon Risch on May 26, 2010 at 20:15:13:
They tend to work a little better with more room to develop the diffusion, but that should be enough room to try them.

Realize also that placing the Room Lens in various positions MAY require that the speakers be moved to achieve the very best results. Thus, you may find that moving the speakers away from the wall a bit more might be helpful with the Lens placed between them and the wall.

Here is a repost of my original note:

Argent Room Lens Analysis/Clone Note
by Jon M. Risch, (old e-mail address deleted) 3-8-99

I thought it might be interesting to share a process of product analysis concerning the Argent Room Lens. Please note that I have not seen a pair in the flesh, have not seen any whitepapers on the product. I have visted the review at Soundstage (http://www.soundstage.com/noisy14.htm), and read the review in Stereophile. See also the Argent web page:
http://www.roomlens.com/index.html
and the StereoTimes website review:
http://stereotimes.com/acc112999.shtm
The Enjoy The Music review:
http://www.enjoythemusic.com/magazine/equipment/0503/argentroomlens.htm

Using dimensions and derived dimensions based on the photo's provided, I proceeded to analyze the acoustics of the product.

Over all dimensions: 58" long tubes/pipes, slightly less than 2" I.D. on the three pipes, probably 2.5" nominal PVC plumbing pipe with close to 1/4" walls, the HD pipes. The composite width at the tubes is approximately 8 1/2". The spacing between the tubes varies from top to bottom, with the wider spacing at the top, varying from about 1" to about 2/3".

Now what would this do to a sound wave that hit it broadside (parallel to the three tubes)?

First, ignoring the Helmholtz resonator aspect, it can only affect frequencies above a corner of about 1.6 kHz, the frequency where the wavelength equals the width. There will be some effect down to about 800 Hz, below which, it won't present any sort of significant obstacle acoustically. Any significant affect on a sound wave will occur above these frequencies, slight effects above about 800, and near total effects above about 3 kHz.

The spacing between the tubes will allow frequencies with wavelengths above the spacing distance to shine through in a straight line in the cracks between, and be almost totally blocked where the tubes are, so they act as diffractors (a form of diffusion) from a low corner of 1.6 kHz, up to about 16 kHz, where they will act as a picket fence shadow, mostly blocking the frequencies above 16 kHz. A significant amount of energy within this band will also be directly diffused off of the rounded tubes.

The recommended placement and orientation will essentially make the aforementioned frequency band for the nominal first side wall reflections and the front wall reflections (to a lesser degree) become diffused on the way toward the way reflection point, and diffracted before the remaining sound energy is reflected off the wall.

This would result in the side and front wall reflections effectively being diffused and broken-up up to a large degree, avoiding a coherent presentation of energy to the ear from the first reflection.

Unlike wall hung diffusers at the mirror points on the side walls and the front wall, these Argent Room Lens will actually re-radiate a diffuse field from their location in the room, as well as diffuse the side wall reflection like wall mounted diffusers. This re-radiated sound energy will not be readily apparent as a distinct source for two reasons: one, it has been dispersed in an almost 360 degree pattern, to bounce off of other room surfaces in most instances with an arrival time at the listener at a much later time, and second, the re-radiation will be at a minimum along the edge of the three tubes, which happens to be aimed at the listening position.

The tubes themselves will act like classic Helmholtz resonators, and if they were simply open tubes, they would resonate at approximately 117 Hz, and multiples and sub multiples of that frequency. However, they have some acoustic resistance at the bottom (a fine screen), and some stuffing somewhere inside the length of the tubes. Clever placement and density choices of this stuffing could effectively result in a bass absorption right where the typical 8 foot ceiling has it first resonance mode, effectively damping this first mode via the tubes. If all three are tuned slightly differently, not only could the first floor to ceiling mode be reduced, but several of the higher order modes as well. This 8 foot floor to ceiling mode would be fairly universal, and so would be a definite way to help reducing this floor to ceiling set of modes.

My conjecture would be that by reducing the floor to ceiling modes, and enhancing the amount of random and uncorrelated horizontal reflections, as wqell as delaying and reducing the first arrival times of the side and front wall reflections these devices would tend to enhace the apparent sound image, effectively reducing the negative effects of the room itself. I would guess that they would have less of an effect with planar or other highly directional speakers, and would be at maximum effect with a full omnidirectional sound source, and at a high amount of effect with most dynamic multi-way speaker systems.
Reducing the side wall, and to a lesser extent, the front wall first reflections without any absorption or radical room geometry is a new one on me.

For those interested in constructing there own, it should be easy to obtain the necessary materials from a hardware store. Use 2 1/2" heavy duty/high pressure PVC pipes, cut to 58 " lengths, spaced apart 1" at the top tapering to 7/8" at the bottom for the left pair of tubes, and spaced apart about 3/4" at the top tapering down to a little over 5/8" at the bottom for the right pair of tubes. Make a nice heavy non-resonant base, and a hardboard cap to hold them in place. Finish as desired.

Now for the educated guess part:
Roll up a wad of 3/4 to 1" thick loose/puffy polyester batting about 16" long by 12"for each tube, rolling up the 16" portion, and push it into the tubes using a long stick. From left to right tube, position the end of the wadded polyester 18" from the bottom, 23" from the bottom, and 18" from the top on the last one. A wad of fiberglass could be used as well, a piece of 6 1/2" by 4' by 12" long, or 3 1/2' by 8" by 12" long. Then place a piece of very fine mesh screen on the bottom of each tube. If you can't get a very fine mesh screen, wrap a layer of nylon stocking on each side of a regular piece of screen door metal screen, and wedge/glue it into place.

You might even make it one tube wider, just repeat the tube pair spacing (I would opt for the wider spaced pair) opposite the added tube. This would make it effective down to even lower frequencies.

This would be a minimal investment to see if they do anything for your room acoustics. I do not have the time to build them anytime soon, so if anyone else does, let us know how they work for you.

Jon Risch

***************************************

Posts on constructing a DIY Roomlens
Alternate construction:
http://www.AudioAsylum.com/audio/tweaks/messages/307.html
the base:
http://www.AudioAsylum.com/audio/tweaks/messages/8679.html
http://www.AudioAsylum.com/audio/tweaks/messages/13630.html

3D DIY Room Lens (David Aiken):
http://www.AudioAsylum.com/audio/tweaks/messages/99714.html
and
http://www.AudioAsylum.com/audio/tweaks/messages/102957.html

Original Room Lens reviews:
http://www.stereotimes.com/acc051199.shtml
http://www.soundstage.com/noisy14.htm
http://www.enjoythemusic.com/magazine/equipment/0503/argentroomlens.htm
(This one has the placement diagrams)

Hope this helps.