narrow and wide baffles and imaging
According to all the "professional" audio reviews that I've read over the last several years, narrow baffles are crucial to creating that so-desired pin-point imaging.
However, over the last few weeks, I've had the opportunity to audition Harbeth 40.2, Spendor Classic 100, Audio Note AN-E, and Devore O/93. None of these had deficient imaging; indeed I would go so far as to say that it was good to very good.
So, what gives? I'm forced to conclude that modern designs, 95% of which espouse the narrow baffle, are driven by aesthetic/cosmetic considerations, rather than acoustical ones, and the baffle~imaging canard is just an ex post facto justification.
I can understand the desire to build speakers that fit into small rooms, are relatively unobtrusive, and might pass the SAF test, but it seems a bit much to add on the idea that they're essentially the only ones that will do imaging correctly.
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Here's an interesting design. http://www.troelsgravesen.dk/PMS.htm Notice that there's no attempt to take advantage of what could be the total internal volume; the enclosure remains a box, and the front and rear baffles, as far as I can see, don't even join up at the sides. |
Yes, the IRS V had a very large baffle. But Arnie Nudell, physicist that he was, curved it back to minimize the effects of diffraction.It was also to re-enforce the bottom of the midrange so it could be xover (mated up) to the bass towers without a big hole in the upper bass/lowermids. as they were yet to bring out the much larger LEMIM low mid/bass driver that’s use in the IRS Beta a far better imaging speaker, with no baffle. Cheers George |
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 |
