What's very interesting is the difference in the curves from 75-80 db (moderately loud) vs. 90 db+(getting very loud). One of the other factors - as mentioned here already - is the level of loudness a given recording needs to achieve decent dynamic range in the 'ears" of the listener.
This last point about listening distance (and with that goes speaker separation) is important, as how will one's evaluation of a given pair of speakers change with variations in distance - within a given real room one has at home? The impact of room reflection changes and the speakers can be played at lower levels when you're closer.How can we EQ out baffle diffraction (other than on a single axis)? From what I've seen it creates an uneven response on or off axis. EQ one and the other will get worse. Once you remove the diffraction ripple (for instance with a smooth shaped baffle or proper mouth termination on a horn) the on and off axis curves will start to track each other (look similar/the same shape). To me this means one cannot EQ baffle diffraction and one should deal with it in another way. I guess that was the reason this thread was started. EQ-ing away ripple induced by diffraction would work in 2D only. At a single point in space. Not very useful.
To me, the above depends on timing. In a large enough room the reflections (now arriving later) may not be that harmful and even pleasing. Take an open baffle speaker, where the nulls avoid early side wall reflections, but that back wave is going to come back. It there is a proper time difference, it can sound very pleasing. Believe it or not, it can actually enhance the front stage if the timing is right. Due to the larger distance that reflection has travelled, it's SPL level will be lower too and it will be largely decorrelated from the direct sound if it reflects off of distant walls and furniture (making it more diffuse). Same goes for that HF driver firing backwards, timing (and level) will dictate how pleasing the end result will or can be. A room void of reflections will show the flaws of Stereo. Ideally we'd have some level of reflections (timed right) to enhance the Stereo illusion.
We almost always have reflections though, even in a reasonably large room it will be tough to avoid the vertical reflections anyway.
Have you guys seen how tight the vertical pattern needs to be to really avoid floor and ceiling reflections? And do we even want to avoid all of them? Some level of reflections is quite welcome and we will still be able to listen "trough" it easily with our brain trained to do so. I take it when someone talks to you in a room you can still follow what he/she said... There's bound to be reflections during that conversation.
Take away all the reflections and a lot of things change. Stereo cross talk will become much more obvious (*), you'd hear the balance change with little head movements because the nulls caused by cross talk (right speaker heard by left ear and vice versa) will shift. Slightly off axis the balance might even be better, as in the exact sweet spot both ears have these dips at exactly the same spots while off axis each ear gets them at slightly different places. Luckily reflection present in a normal room hide these anomalies. There are bound to be reflections with most type of speakers in a normal room. Even with horns we'd still have floor and ceiling reflections, though at lower levels than with most direct radiators.
A measurement at the ear position in a very well treated room (not my room, think above studio grade room treatment):
In the exact sweet spot, you'd be getting something close to this curve at both ears, if the room is void of reflections. The green trace is without reflections, the other two colors show a Hass Kicker (orange) and Haas Kicker with ambient channels (red). Original link.
This room is painstakingly engineered to remove all direct reflections, including floor and ceiling. It doesn't even look like a normal room. It was build for one purpose only: as listening room. Here's a link with a description of that room, with a bit of luck there's still some links to the measurements he made inside that room at the listening position. I had never seen anything like it (except semi anechoic measurements but never at the listening spot).
The FR of one channel measured at a time, both channels shown:
So be careful what you wish for... you might be surprised what happens if you do get it...
Even though I quoted @profiguy a couple of times, I wrote this reply as a more informal information piece. A part that get's almost no thought on this forum, even though it does have a huge influence on what we perceive. What does our room do for us? Can it enhance our listening pleasure? I can recommend reading the many papers of Griesinger for what a room can do (even if most of his work is about larger spaces, the information he gives still is an eye opener).
(*) = if one listens much closer to the speakers, like in nearfield, the direct sound will hide the effects of this cross talk effect. there probably will be more shading from the head too.
Here's a question - if audio engineers and speaker designers can objectively measure pretty much everything, than why has the speaker market not coalesced into a more narrow range of "solutions" for bringing the ultimate fidelity to the listener? If we look at the websites and /or literature of dozens of different speaker companies (talking high end), there are huge differences in the designs and components and the rationale as to why "our speakers are the best..."?
Because there are so many compromises in any loudspeaker design there is latitude for preference. The Doc, IIRC, has suggestted speakers ar eup to 80% of their potential, i think it ia more like 20%.
You can take a dozen of the best loudspeakers in the world, all of valid design, and they will sound quite different.
dave
This doesn't always happen. Some speakers are quite consistent regardless of distance.
I probably should have added that when things sound different at different levels, there might be diffraction.
A sphere does distribute diffraction to potentially render it less offensive but diffraction often represents widening directivity nonetheless. At mid and higher frequencies where it is more of a problem you might try holding the flat baffle out longer or using a large enough sphere.. or even a waveguide.
A sphere does distribute diffraction to potentially render it less offensive but diffraction often represents widening directivity nonetheless. At mid and higher frequencies where it is more of a problem you might try holding the flat baffle out longer or using a large enough sphere.. or even a waveguide.
The next logical step to the wide baffle design ethos might be to make the entire wall the baffle and mount the drivers flush in the wall.
What does that do to diffraction and imaging?
How about building speakers that are placed on the wall then. With contours to minimise diffraction. Curved to allow drivers to fire at the listening position, with a cross section like this:
You may find there's a limited window where such a contour helps. At lower frequencies it won't be necessary and when high enough to reflect, the inner curve won't guide so much as focus.
William Cowan did similar-ish maybe 15ya as I heard them in late 08 IIRC and they weren't new then. One of my plans is also similar but freestanding as my new house only really allows placement upon a very long wall.
Well, improved focus seems good. I'm no expert. Is better focus from improved diffraction from the wall boundary effect, by any chance?
In terms of lower frequencies being on the wall, might be beneficial with improved efficiency? Hornresp indicates
Thanks.
I was referring to physical splaying of the radiation, not stereo focus.. unfortunately 
As it turns out walls are an opportunity to multiply anything nearby, and while that can be used to advantage, I brought it up because it also multiplies mistakes. While not everything is a problem, whenever the source doesn't cooperate with the wall from the beginning you won't be able to undo that by simple blending. You could use phase plug type techniques, which are pretty involved considering... or you could provide some independent waveguiding that does properly coincide with the source, before letting the result free to meet the wall.
As it turns out walls are an opportunity to multiply anything nearby, and while that can be used to advantage, I brought it up because it also multiplies mistakes. While not everything is a problem, whenever the source doesn't cooperate with the wall from the beginning you won't be able to undo that by simple blending. You could use phase plug type techniques, which are pretty involved considering... or you could provide some independent waveguiding that does properly coincide with the source, before letting the result free to meet the wall.
It would be safe to assume infinite baffle speakers are the large scale equivalent to open back headphones... sort of. Some of the higher end phones tilt the drivers in towards the ears in an effort to produce a more natural sound stage that doesn't appear to originate between the ears as much. Of course with headphones comes a whole new set of challenges to overcome, making then sound as neutral as possible... well at least thats the ideal situation. Of all 15 pairs I own, I always go back to the old simple, but hard to drive HD560 ovations that follow the basic inter aural resonance curve. No speaker I've heard to date can touch their midrange resoluton. They are my yard stick by which I judge any other speaker.