Under Construction
The job of any transducer is deceptively simple; convert signals in one form of energy into another. Unfortunately the laws of thermodynamics intervene, and the process is anything but simple. In the case of a loudspeaker, sound waves captured during the performance of music are converted into acoustical pressure in a given space for one or more listeners to experience.
While the configuration of recording and playback for live music seems obvious, it has a miriad of factors that it appears many people ignore. Lets look at it closely as a chain:
Human Composer
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Human Performer
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Musical Instrument
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Acoustical Space
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Microphone
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Cable
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Mic Preamp
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Cable
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Mixing
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Cable
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Processing
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Cable
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Recording
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Mastering
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Duplicating
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Playback
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Cable
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Preamp
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Cable
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Power Amp
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Cable
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Loudspeaker
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Acoustical Space
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Human Listener
While some steps may be modified or omitted, it is hard to condense much from this sequence of events in the creation of a recorded piece of music. There are many feedback loops in this scenario which have been left out to avoid distraction from the main point; EVEN A PRISTINE RECORDING IS A VERY COMPLICATED PROCESS TO DELIVER THE EXPERIENCE OF MUSIC TO THE LISTENER AT A LATER TIME.
The very last step prior to the interaction with the local space the Listener is occupying, is through the Loudspeaker. Many approaches have been analyzed to CREATE sound, but few are truly successful at REPRODUCING the sound experience of being present in the original acoustic space with the musicians actually performing music.
One fairly effective way to approach good fidelity to the original, is by listening through headphones. While the critical local sound field is completely eliminated, let us analyze the part of headphone construction that DOES make them successful. When looking carefully at the sound-capturing element of a decent dynamic microphone, and then looking at the reproducing element in a nice pair of headphones, one is immediately struck by the verisimilitude of the two. It is as if a mirror image of capture and release mechanisms is employed in this case. The problem is one of scale. The job of the microphone is to capture small variations in sound pressure at a distance, and convert it into tiny signals. If we move a few feet from the headphones sitting on the back of a chair, we might still detect some audible output, but it would not make for a satisfying experience. Here is a first hand demonstration of the basic inefficiency of the conversion of mechanical motion into sound waves. In the case of a Human-played instrument, the mechanical equivalent of an air conditioner compressor or sawing wood is the energy a human must expend to make room-filling sound.
So how do we increase the scale of effort, in the form of a loudspeaker system, and not introduce gross errors in the process? At this point an understanding of the non-linearity of free-space acoustical coupling comes into play. At low frequencies, a VERY LARGE amount of mechanical motion is needed to match the pressure gradients in sea-level atmospheric pressure, in comparison to the mechanical motion needed to modulate the same gases at the upper limit of Human hearing. A nice way to show this is with a two dimensional figure that is the analogue of a graph, but visually portrays the surface emitting area needed for both good sound dispersion with angle of incidence as well as the acoustical coupling needs in free space.
“Pyramid”
