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jeffsg4mac : duff; DVD audio and SACD are mixed for direct firing speakers not bipoles or dipoles. Also, while Bipoles my be more forgiving than dipoles, dipoles need rear walls to reflect off of because they create a null in the listening area and the reflected sound is what is creating the ambiance. Cheers.
Not all loudspeaker designers that use bipolar drivers count on the rear wave for ambience or center-fill (though this is the most common situation). For example, take a look at the
InnerSound Q&A.
Quoted from the InnerSound Q&A:
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Quote </td></tr><tr><td id="QUOTE">I've always heard that speakers should have wide-dispersion and that InnerSound's speaker designer invented the wide-dispersion, curved electrostatic loudspeaker. So why does InnerSound produce narrow-dispersion speakers?
It's true that Roger Sanders, InnerSound's speaker designer, invented the free-standing, curved electrostatic panel in 1978. He published the technique in "Speaker Builder" magazine in 1980. He expected that his wide-dispersion, curved panels would perform better than narrow-dispersion, planar speakers. But he was stunned to discover that they were inferior to planer speakers with respect to transient response, imaging, frequency response, speaker placement, and output! Frustrated and disappointed, he spent several years studying these phenomena and eventually found that the laws of physics make it impossible for a wide-dispersion loudspeaker to have good transient response, imaging, etc. These topics are complex and technical, but the following explanation should help explain why this is true: To visualize what happens, imagine that you have a conventional wide-dispersion loudspeaker that is perfect in every way. Now play a short transient through it, like a drum rim-shot. The sound that comes directly from the speaker to your ear is flawless (because we said the speaker was "perfect"
. The transient is short, tight, and crisp. But because this hypothetical speaker has wide-dispersion, most of its sound goes out in the room where it reflects off various surfaces before reaching your ears. Because these reflected sounds must travel further than the direct sound to reach your ear, they arrive slightly later than the direct sound. The delay is not enough for your brain to perceive them as echos, instead you hear many rim-shots, over only a few milliseconds. So instead of hearing one crisp transient sound, you hear "pop corn" -- a group of transient sounds separated by tiny delays. Not knowing exactly what to do with this mess, your brain "averages" them all together into one, long, smeared transient sound. If you doubt this, just remember the last time you heard headphones. No doubt you were impressed that the sound was far more clean and crisp than what you have heard from any wide-dispersion loudspeaker. This was not because the headphones were so good, it is just that headphones do not introduce room acoustics into the sound. Since music is almost all transient information, wide-dispersion speakers must be avoided if you want accurate sound. Still another problem is frequency response. Because sound travels in waves, the out-of-phase room reflections will either augment or attenuate various frequencies when it mixes with the direct sound at your ear. This forms a "comb-filter", which seriously alters the accurate frequency response of our "perfect" speaker. Additionally, the room selectively absorbs the higher frequencies which tends to generally reduce the high frequency energy you hear in the overall sound when compared to the direct sound. The frequency response changes based on where the speaker is in the room, which is why speaker placement can be so difficult with wide-dispersion speakers. Finally, a wide-dispersion speaker expends most of its energy projecting its sound out in the room. A narrow-dispersion speaker directs most of its energy directly to you. Although both speakers may produce identical amounts of sound output, the narrow-dispersion one will sound much louder, and therefore subjectively seems more efficient. In summary, wide-dispersion speakers force you to listen to your ROOM. Narrow-dispersion speakers allow you to listen to your SPEAKERS. The benefits of narrow-dispersion speakers are superior frequency response, higher output, holographic image quality, precision imaging, much crisper transients, and ease of placement.</td></tr></table>
Note that Sanders goal is to minimize early reflections, even though he uses dipolar ESL panels in his speakers. With the narrow dispersion, proper toe, and reasonable placement, the back-wave simply isn't an issue, or so Sanders claims. I also use large panels to eliminate rather than create early reflections, because like Sanders, I like the clarity and imaging that the approach produces.
I agree with your comments as far as loudspeakers that are designed to use a reflected wave to create more (false) ambiance. Sanders, I, and a few others, use dipoles to achieve just the opposite result.</font>
