Posted by David Aiken (A) on August 28, 2006 at 14:19:35

In Reply to: Neophyte question(s) about Room Lens diffusion in the nearfield posted by Julien43 on August 28, 2006 at 06:31:14:

A room lens does 3 things:

1- sound striking the curved surfaces of the pipes is reflected over a wider angle than if it struck a flat surface. This effect reduces as frequency lowers—low frequencies will simply wrap around each pipe with little or no reflection.

2- sound passing through the gaps between pipes is difracted over a wider angle than if the pipes weren't there. This also is less effective as frequency lowers.

3- the hollow space within the pipe has some effect as a broadband Helmholtz resonator so it may help tame some room resonances slightly (depends a lot on the particular room resonances you have and how they relate to the frequency the pipes are tuned to).

Effects 1 and 2 provide diffusion. Both effects work in both directions. Effect 1, reflection from the surfaces of the pipes, will also block some reflections from the wall that would otherwise reach you and reflect them back to the wall where they are again reflected back into the room over a wider angle. Effect 2, the diffraction through the gap, also spreads wall reflections passing through the gap back into the room over a wider angle. The fact that the room lens works in both directions increases it's effectiveness quite a bit. Note, however, that it means you need a reflective wall behind the unit if it is going to work effectively. Put an absorptive surface behind the unit and you lose diffractive spread in both directions, leaving only the effect of reflection from the surface of the pipes. That's a large drop in effectiveness.

For the standard 2" pipes, Jon Risch suggests that the diffusion effects start at around 750 Hz and are in full play somewhere aroung 1500 Hz if I remember correctly. If those figures are wrong, it's much more likely to be my memory than Jon's calculation.

Place a room lens between speaker and wall and it will reflect some of the sound reaching it. If you're sitting somewhere where there will be a direct reflection from the room lens surface to you, you will still get an early reflection but it will be somewhat down in level compared to a wall reflection simply because the sound energy is being reflected over a wider angle than the wall would reflect it. The odds are that if the location of the room lens is along the line between the speaker and the early reflection point on the wall that it will generate an early reflection that you will hear, but it may do that also in some other locations because of the wider angle the reflections are spread over. The angle at which it is placed relative to the speaker will also play a part in determining whether or not a reflection is directed to you. You can play with angling to minimise this somewhat.

Wider pipe arrays (more than 3 pipes per unit) are going to be more effective. Pipe placements other than in a straight line may be more effective. I currently use 2 DIY units in the 'toe' area of my L-shaped room. One is an 8 pipe unit with pipes placed at varying depths determined by a quadratic residue formula. The other is a 4 pipe array with varying depths determined by a primitive root formula. I haven't done measurements but I prefer the results to what I got when I placed my original four 3 pipe units in the same area.

These 2 units are place in corners and their effects make me wonder whether what they do their is similar in some ways to what is claimed for the Shakti Hallograph devices and also for other devices like the Eighth Nerve products which claim to work by reducing the horn loading effects of corners. Argent, the manufacturers of the original Room Lens, don't make any mention of corner placement in their recommendations but I find some benefits with it and that's where I now use my units. One advantage of the room lens is that it lends itself to experimenting with placement and you're only limited by your imagination. Making your own room lens clones also gives you considerable freedom to play and experiment with unit size and design.

David Aiken

• Re: Neophyte question(s) about Room Lens diffusion in the nearfield - Ethan Winer 09:47:42 08/29/06 (8)
  In Reply to: Re: Neophyte question(s) about Room Lens diffusion in the nearfield posted by David Aiken on August 28, 2006 at 14:19:35:

  David and Bart,

  > sound striking the curved surfaces of the pipes is reflected over a wider angle than if it struck a flat surface <

  Doesn't this depend on where they're placed? I see these things in photos in many different places - right in front of the speakers, off to the side (where no sound will reach them), near the front wall (again where little sound gets to), and so forth.

  Has anyone measured their room's response and ringing with and without these things in place? Has the original manufacturer ever done this? I've looked in the past for such information and never found any.

  Again, I'm not saying they make no change in a room. I just can't see how any change they'd make could be for the better. But if I'm wrong, please educate me! However, I'd much rather see hard dÏk than read subjective opinions.

  --Ethan
  
  

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  • Re: Neophyte question(s) about Room Lens diffusion in the nearfield - David Aiken 20:04:49 08/29/06 (6)
    In Reply to: Re: Neophyte question(s) about Room Lens diffusion in the nearfield posted by Ethan Winer on August 29, 2006 at 09:47:42:

    Ethan,

    "> sound striking the curved surfaces of the pipes is reflected over a wider angle than if it struck a flat surface <

    Doesn't this depend on where they're placed? I see these things in photos in many different places - right in front of the speakers, off to the side (where no sound will reach them), near the front wall (again where little sound gets to), and so forth."

    
    Does what depend on where they're placed? There are no soundwave free zones in a normal room. Wherever these things are placed in a room, some soundwaves will be falling on them, and those waves will be reflected over a wider angle. The only question is what soundwaves are falling on them. Yes, they are placement sensitive, both because distance from a reflective surface will have an impact on their effect and because where you place them determines what sound will fall on them. If you want them to reflect some of the early reflection path sound, you need to place them where that sound will strike them and you have to play with their angle in order to direct the reflections where you want them.

    
    "Has anyone measured their room's response and ringing with and without these things in place? Has the original manufacturer ever done this? I've looked in the past for such information and never found any."

    I said I hadn't measured them. I don't know of anyone who has. All I have to go on is my own experience and I said that up front. I'm not going to apologise for that fact.

    
    "Again, I'm not saying they make no change in a room. I just can't see how any change they'd make could be for the better. But if I'm wrong, please educate me! However, I'd much rather see hard dÏk than read subjective opinions."

    I can only say one more thing over what I've already said. You say "I just can't see how any change they'd make could be for the better…" I'm not certain what 'better' means here. We all know that people sometimes like things that measure worse—tube amps are a good example, and there's a hell of a lot of personal taste that flies in the face of measurement when it comes to speakers. I'm not saying that measurements are useless because they aren't. They do tell you what's going on. It's just that I don't think they're necessarily all that predictive of how we're going to feel about the sound. I've had DIY room lens units in one form or another for something like 5 to 6 years now. In fact, they were the first acoustic treatment I played with and they were chosen in part because of their relatively small size which was important in the smaller space I had back then. I wouldn't regard them as having as noticeable an effect as my bass traps or my 2 panels, and they wouldn't be the first thing I would recommend to someone wanting to treat their room, but their effect is noticeable. I've played with positioning and unit configurations and I've had them in my room and taken them out. They're in the room at the moment and I have no desire to remove them because I prefer the sound with them to without them. In fact, I probably won't remove them unless I need to stick some furniture into those corners or I decide to treat the 2 corners where they're currently located in some other way. I could use absorption and put bass traps there but there's already a fair bit of absorption in the room and I think a bit of diffusion is a positive.

    David Aiken
    
    

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    • Re: Neophyte question(s) about Room Lens diffusion in the nearfield - Ethan Winer 14:08:48 08/30/06 (5)
      In Reply to: Re: Neophyte question(s) about Room Lens diffusion in the nearfield posted by David Aiken on August 29, 2006 at 20:04:49:

      David,

      > I don't think they're [measurements] necessarily all that predictive of how we're going to feel about the sound. <

      Well okay, sure. But some things are worse even when someone believes they're better. A perfect example is an equalizer in the hands of a neophyte. We've all known people who goose the bass and treble, or scoop the midrange, or both, and proudly beam as they show off their terrific sounding system. I'm not saying you and Bart are like that! And there are things I might prefer in some cases but still wouldn't want to do.

      Sometimes comb filter artifacts can be perceived as pleasant sounding even when the response is made worse. If a comb filter null happens to fall on a boomy or honky or screechy frequency range, the sound could be deemed "better" with the filtering. My guess is the lenses do something more like that than true broadband diffusion which would be useful. Or maybe they add ringing at pleasing frequencies so the overall effect is pleasing.

      That's why I asked about measurements. This is the only way to know if the sound truly is made better or if it's purely psychological. I never expected you to provide test data! But what does it tell you when the manufacturer doesn't even have that?

      --Ethan
      
      

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      • Re: Neophyte question(s) about Room Lens diffusion in the nearfield - David Aiken 16:19:34 08/30/06 (4)
        In Reply to: Re: Neophyte question(s) about Room Lens diffusion in the nearfield posted by Ethan Winer on August 30, 2006 at 14:08:48:

        Ethan,

        I accept that things can seem better when they are, in fact, worse and your example of the neophyte with the equaliser just happens to have been me some 30 or so years ago :-)

        I do think that we need to distinguish between things seeming better when they are, in fact, worse when the cause for this is simple ignorance and an unskilled ear and cases such as the comb filter artifact examples you mention. There's 2 very different things going on in these examples and we need to avoid confusing them.

        Whatever the mechanism for the room lens' effects, it is most definitely sensitive to placement and orientation. In that sense, they are 'tuning devices' just like an antenna is a tuning device—stick them in the wrong place and/or point them the wrong way and both will give you bad results. Put them in a right place pointed the right way and you get good results. One thing that variability in results with the room lens suggests to me is that they are genuinely doing something. If they weren't and we were simply fooling ourselves, one would probably expect the results to be more consistent regardless of placement.

        I don't think I accept your view that measurements will distinguish whether the sound is made 'truly better' or whether it's psychological. We're in this hobby for pleasure and to some degree I tend to equate 'truly better', which is after all a value judgement and a different assessment than 'truly accurate', with the consistent provision of increased enjoyment. The psychoacoustic aspects can't be separated out from the rest of what we hear. What we measure is not what we hear, only the parameters of the soundfield falling on our ears. If we interpret the measurements in the light of what we know about psychoacoustics and we have sufficient knowledge of the relevant aspects of psychoacoustics affecting our perception in a particular case, then the measurements and our experience should correlate. If they don't, then something has been left out of the equation and that something could be missing knowledge, an ignorant or uneducated ear (your neophyte with the equaliser), a personal preference, or it could even be one of those nasty psychological mechanisms which occasionally fool us into believing that black is white.

        I don't think this is one of those cases often, and erroneously, called a placebo effect. There are simple and well established mechanisms like reflection, difraction, and the Helmholtz resonance mechanism which should lead us to expect physical acoustical effects from the room lens, and their sensitivity to placement and orientation is consistent with those mechanisms. I'm satisfied that we can reasonably assume the existence of audible physical acoustic effects so the only question remaining about the value judgement people make about the favourability of those effects is whether that judgement is due to ignorance or not. Explaining why the effect is perceived as 'better' or 'worse' is a different matter and firmly in the realm of psychoacoustics rather than physical acoustics.

        David Aiken
        
        

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        • Re: Neophyte question(s) about Room Lens diffusion in the nearfield - Ethan Winer 14:12:14 08/31/06 (3)
          In Reply to: Re: Neophyte question(s) about Room Lens diffusion in the nearfield posted by David Aiken on August 30, 2006 at 16:19:34:

          David,

          > Explaining why the effect is perceived as 'better' or 'worse' is a different matter and firmly in the realm of psychoacoustics rather than physical acoustics. <

          Agreed. I guess my real objection is when people pursue that sort of acoustic treatment rather than the staples like bass trapping and first reflectin control, which are far more useful. (By your own admission.)

          --Ethan
          
          

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          • Re: Neophyte question(s) about Room Lens diffusion in the nearfield - bartc 17:17:36 08/31/06 (0)
            In Reply to: Re: Neophyte question(s) about Room Lens diffusion in the nearfield posted by Ethan Winer on August 31, 2006 at 14:12:14:

            Ethan, I'm going to second David's experience, because they were also my first foray into acoustical treatments and they have had the most profound and pleasing effect.

            By the way, my own experience with these DIYed versions was illustrative of the potentially bad effects if improperly implemented, so I don't disagree with either you or David there. Mine are behind my speakers and alongside my upright piano. When I first built them before I got Thorsten's stuffing instructions they were open bare pipes - perfect for resonating. Well, that was OK for the stereo speakers sort of, but the minute my daughter played the piano they resonated tooooooooooo much and it was detrimental to the sound. They picked up almost precisely the majority of the freq range of her music, resonated and amplified that and it sounded like pure crap!

            So as soon as I stuffed them to the specs close to the Argent originals, the whole thing tamed down to perfection. They do not interfere with the piano at all anymore and the stuffing changed the stereo picture for even better results. I don't credit the absorption properties of the lenses for that, because they're pitifully small to do much absorption; what happened was that the frequencies to which they were tuned as resonators was profoundly altered.

            So I'd like to say that Argent did a masterful job on their design, even if I don't own their originals.

            But you can get the diffusion effect with closed pipes, pipes of varying diameters, pipe arrays of different diameter pipes, or even swimming pool noodles on dowels! That tells you just how profound the curved diffusors can be if so many disparate designs will have similar effects in many different room setups.

            Honestly, dummy up a set for kicks (costs less than $25) of any of the prevalent designs and move them around your room (without your panel absorbers in place, or it won't work) and see what you hear.

            And David and I have traded speculation that the vaunted hallographs are really just corner diffusors of another feasible design.
            
            

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          • Re: Neophyte question(s) about Room Lens diffusion in the nearfield - David Aiken 16:51:13 08/31/06 (1)
            In Reply to: Re: Neophyte question(s) about Room Lens diffusion in the nearfield posted by Ethan Winer on August 31, 2006 at 14:12:14:

            I'm not certain how much I'd object. After all, the room lens was my first foray into acoustic treatments simply because it had a small footprint, was easily moveable, and could be moved in and out of the small, 11' square living room area of a combined living/dining room. Size and portability were the deciding factors. Eventually I got around to adding a couple of DIY bass traps based loosely on Jon Risch's quick and dirty design but they really pushed the limit in that room. I really only got the opportunity to play around with bass trapping and panels when we shifted house and I finally got a dedicated room.

            I think it's great whenever someone is prepared to start doing something with their room. Where they start is less of an issue to me in some ways than the fact that they have started, and once they start and begin to hear differences and start to discern room effects they often move on to more effective treatment anyway.

            Interestingly, you made a comment on one of the other boards about WAF and other factors being the limiting factors when it came to bass trapping, and people stopping before they had reached the optimum level. When I finally got around to trying the bass traps I went and bought 2 bags of polyester insulation batts and packed them into the back of my small hatchback car. With the back seats folded down, the insulation completely filled the rear of the car behind the back seats. I drove home wondering about how great the standard car radio/cassette player sounded with that much absorption in the car. I would hazard a rough guess that the insulation took up around 25-33% of the interior volume of the car and the sound improved amazingly. I've never heard sound that good in a car since :-)

            David Aiken
            
            

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            • Re: Neophyte question(s) about Room Lens diffusion in the nearfield - Ethan Winer 09:26:18 09/01/06 (0)
              In Reply to: Re: Neophyte question(s) about Room Lens diffusion in the nearfield posted by David Aiken on August 31, 2006 at 16:51:13:

              David,

              > I would hazard a rough guess that the insulation took up around 25-33% of the interior volume of the car and the sound improved amazingly. I've never heard sound that good in a car since :-) <

              I know a fellow who built a control room in his single car garage. He ended up filling about 1/3 of the room's total volume (not surface) with mineral wool. The bass response he achieved was remarkable.

              --Ethan
              
              

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  • Re: Neophyte question(s) about Room Lens diffusion in the nearfield - Ethan Winer 09:48:42 08/29/06 (0)
    In Reply to: Re: Neophyte question(s) about Room Lens diffusion in the nearfield posted by Ethan Winer on August 29, 2006 at 09:47:42:

    Posting glitch. I wrote:

    I'd much rather see hard evidence than read subjective opinions.
    
    

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