|Intolerance seems hardwired into human behavior. Its resultant wars plague human history as perhaps nothing else. So it's a relief to see tolerance practiced in whatever walk of life we get to meet it. For an excellent example in audio, consider Siegfried Linkwitz. He is the famous co-architect of the ubiquitous crossover that bears his name. He's also the former president of Audio Artistry, a loudspeaker company that was dedicated to dipolar designs which he has always championed. Since his retirement from HP and with the speaker company long folded, the very much active Linkwitz Lab website supports DIYers interested in resurrecting Audio Artistry by way of a cost-effective, down-scaled Beethoven called the Orion, a full-range open-baffle speaker with electronic compensation.
This bit of history is well known. Newer is the Pluto model, a small omnipolar twin column. The really interesting part about it (relative to our opener) is Siegfried's commentary: "Now that I have lived with Pluto for some time, have compared it to the Orion often, had other people listen to it when they visited to hear the Orion and then noting their observations, I have come to the conclusion that uniformity of the polar response is even more important than I had thought previously.
"When comparing Pluto to Orion the thought immediately arises, how can they sound so similar when one is essentially a closed box and the other an open baffle speaker, and both operate in a fairly live room? The drivers in Pluto cost a fraction of those in the Orion, and though they are exceptionally well suited to this application, they are not equivalent. Both speakers share a uniform on-axis and off-axis frequency response from the very lowest frequency up into the low kilohertz range. One is figure-of-eight, the other is circular, both horizontally and to different degrees of uniformity also vertically. The typical box speaker has a transition region from circular (4p) radiation to increasingly forward radiation (2p and less), the so called "baffle step", which occurs in the 300Hz to 800Hz range depending on front baffle and driver size.
"The smaller the box, the higher in frequency this transition occurs. For Pluto it is above 3kHz. Now, if we listened in an anechoic chamber or outdoors, then none of this would matter, but since speakers are used in rooms we also hear the sound that is radiated off-axis. It merely arrives at our ears with slight delay, attenuated and possibly changed in timbre by objects and reflecting/diffusing surfaces in the room, and often reinforced at specific low frequencies. Listening to Pluto or Orion highlights the importance of illuminating the room uniformly over a very wide frequency range. The strength of illumination from Orion is 1/3rd (-4.8 dB) of that of Pluto, thus the room is less of a factor with Orion. This can be completely compensated for by listening to Pluto from a closer distance. Regardless of listening distance, Pluto elicits a significantly more neutral response from the room than the vast majority of box speakers is capable of.
"A few days ago I had the opportunity to set up the Pluto at a friend's house -- electro-acoustic consultant Brian Elliott -- and to compare it there to the most sophisticated and lowest distortion open baffle system that I am aware of. A day later I compared Pluto to the Quad ESL 989 at a local high-end audio store. Using immediate A-B switching and also longer uninterrupted listening we were all amazed by the similarity of sound from such dissimilar sources. Actually more so when listening from a greater distance than I had suggested below and with the Plutos at least as far apart as the comparison speakers... the addition of the subwoofer to Pluto had somewhat surprising results. Not only does it extend and increase the low frequency output capability as expected, but it also extends the tonal similarity to the Orion into the low bass region. Orion goes subjectively a little deeper but the overall character is almost identical, yet one is a monopole and the other a dipole. Listening to either speaker system in the setup that I described for Pluto, I can easily get confused as to which speaker I am listening to and that on a wide range of program material."
Naturally, you should read this in its entirety on the Linkwitz Lab site. However, for the focus of today's column, the relevant matter has already been stated. Namely, that a designer long committed to one particular way of doing things -- dipolar open baffle speakers -- was open-minded and curious enough to try something different and then honest enough to express his surprise over how similar the results were - in public. The upshot of this -- that different roads lead not only to Rome but can end up at the same table in the same piazza -- is something most of us in audio always suspected. However, it's a lot rarer to see a designer noted for commitment to one particular approach try another one, arrive at more or less the same destination and then tell the tale. Next time our excitement about a particularly brilliant implementation of any given audio solution becomes evangelical and then preaches superiority, we might do well to remember Siegfried Linkwitz' celestial friends Orion and Pluto. After all, Mirage and mbl at first glance don't seem to share more than a first letter...
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