narrow and wide baffles and imaging

Imo the Precedence Effect explains many observations made about correlations between imaging precision and baffle width, in particular those posted by @shadorne on the previous page.

The Precedence Effect kicks in at about .68 milliseconds, which corresponds to the time it takes for a sound wave to travel about 9 inches, which in turn correlates with the distance around the head from one ear to the other.  We get our primary directional cues from that first .68 milliseconds, after which the ear/brain system suppresses directional cues from reflections.

So any reflections occurring within those first .68 milliseconds will degrade imaging, and in general the closer to that .68 millisecond threshold, the worse the degradation.  This is because as we approach .68 milliseconds, we are approaching the interaural time delay that would correspond to a sound coming from one side or the other. 

So, the wider the baffle the worse the imaging (ignoring the potential improvement from round-overs) until the baffle edge is more than 9 inches away from the driver's edge.  Then imaging abruptly improves. 

A round-over can mitigate edge diffraction, but it must have a large enough radius to be effective, at least 1/2 wavelength and preferably 1 wavelength.  The ear is most sensitive to diffraction at about 4 kHz, and at 4 kHz a wavelength is about 3.4 inches.  That's a pretty big round-over!  Point being, small round-overs probably don't do much.

Driver directivity can reduce the amount of energy that sees the cabinet edge in the first place, but care must be taken to not do more harm than good in the pursuit of increased directivity. 

Duke

dealer/manufacturer

@twoleftears wrote:

"So what we need is a 19" front baffle?"

Maybe even wider, depending on driver diameters and crossover points!

That being said, I think a small baffle with large round-overs would image extremely well, assuming all of its other ducks are in a row.

The venerable and magnificent Snell Acoustics Type A used a wide baffle that was virtually one big round-over on both sides and on the top (of the front baffle), and its imaging was superb.

I think large-diaphragm panel speakers avoid significant edge diffraction by virtue of their inherent directivity.

The approach I embrace is to use a compression driver on a low-diffraction waveguide whose radiation is fairly narrow in the horizontal plane (-6 dB at 45 degrees to either side of the centerline, falling to about -20 dB at 90 degrees, or towards the cabinet edge). The woofer has a large enough diameter that its radiation pattern is essentially the same as the waveguide in the crossover region. I don’t claim that this is necessarily the best-imaging format, but I believe it does enough other things well to be competitive overall.

I have NOTHING against superb imaging, and I think I know how to get it (time coherence and application of the principles I described above), but it is not my top priority. Imo loudspeaker design is a juggling of compromises, and anyone who says differently is in marketing.

@tomic601 wrote:

"the big baffle also honks up frequency response....period..."

How so?

@tomic601 wrote: "reflected wave off baffle creates constructive and destructive interference, seen as amplitude....."

A wave travelling along a surface, parallel to that surface, does not reflect off of it. However it can diffract at the edge. The amplitude disturbance caused by diffraction, in and of itself, is imo not a big deal. It is only present in the first-arrival sound so its subjective impact is relatively minor in most cases. However what IS a big deal is, the time delay. The ear is often pretty good at overlooking a distortion that occurs at the exact same time as the signal, but usually quite poor at ignoring a distortion that occurs even slightly later in time. This has to do with a psychoacoustic phenomenon called "masking" which I can come back to if you are interested.

Tomic601 also said, "IF we are interested in moving forward instead of creating new flavors, perhaps we can agree that lower distortion is better?"

I think we should try to figure out which distortions matter the most to the ears and prioritize accordingly. "Lower measured distortion" does not necessarily correspond to "lower perceived distortion". The latter is what matters in my opinion.

Duke

@tomic601 said, "much harder to figure out with reliability psychoacoustics than the more or less well understood physics... "

Psychoacoustics is fascinating, in my opinion, in part because much of it is counter-intuitive.

Sounds like you already have a good background in acoustics (you are absolutely correct that the front baffle is a 180 degree horn!!). You might enjoy Floyd Toole’s book "Sound Reproduction: The Acoustics and Psychoacoustics of Loudspeakers and Rooms."   His book is basically all about answering the question, "what really matters?"

Best wishes,

Duke