Monday, February 11, 2013

Evolution of the High End - Part 7

Most people think of first reflections as occurring from a nearby surface and reflecting sound back to the listener. All listening room tuning is geared toward eliminating these nearby surface reflections and controlling other resonant room modes.

Listening Room First Reflections

However, the first surfaces encountered by sound emitted from a speaker driver are those from nearby protruding surfaces on the speaker itself. First reflections come from many places such as protruding screws, driver baskets, speaker grills, cabinet edges, mounting hardware, actually anything that is not completely smooth and reasonably non-reflective. Real first reflections occur much closer to a speaker than a wall, floor, or ceiling and designers realized this after building the first high fidelity speakers.

Early on in speaker manufacturing, drivers were stuffed into holes that were the same size as the basket. Rear mounting was popular at first since everything could be assembled from inside of the cabinet. Front mounting became more popular to permit quick removal and replacement of blown drivers without having to remove the back of the cabinet. All was initially designed for ease of repair with no consideration of how the physical positioning impacted the sound.

Early Front-Mount Baffle Board

Cabinet edges were used to hold in grill frames and deliberately designed to protrude into the path of the oncoming sound.

One day, someone had a great idea: countersinking drivers so the front of the baffle board was smoother. This fantastic idea reduced the number of first reflections and all quality speaker manufacturers of the time jumped on the bandwagon.  What improves with lower first reflections is spaciousness and the width of the soundstage.  So speakers with countersunk drivers immediately "opened up" and exposed details that were always there, it was just that the first reflections prohibited them from being revealed.

Early Attempts at Lowering First Reflections

Recessing drivers was a great step forward in reducing first reflections but attention to detail did not come into the picture until much later. Today, drivers in high-end systems are mounted in a near-invisible way with little or no first reflections appearing anywhere on the front of the cabinets.

First Reflection Elimination Designs on Baffle Boards

Smooth surface transitions from driver to baffle board and even different basket designs to eliminate holes in gaskets soon appeared and the search was on to find more ways to eliminate these nasty little parasitic reflections.

Seamless Driver Mounting
Designers understood by now that anything protruding from the surface of a speaker contributes to first-reflection problems. More effort was made to understand what reflections on the sides and the rear of the cabinet had to the sound emitted from the front. Lo and behold, even these seemingly innocent indentations for attaching speaker wires and balancing tweeter or midrange volume levels again caused problems. The sound as it wrapped around the edges of a cabinet created reflections that appeared on the front. Once more designers stepped up to the challenge and highly exotic designs appeared that combined art with the goal of controlling all cabinet first reflections.
Exotic Cabinet Shapes Appeared

During this first-reflection revolution, other discoveries were made involving the coupling of the driver to the baffle board, time-aligned drivers, better crossover approaches, and properly coupling the loudspeaker to the floor. With all of these little tweaks, a synergy appeared that now considered the total impact of a driver on its surroundings that brought to sonic reproduction what Thiele and Small brought to understanding software modeling of loudspeaker design. Not only was it important to properly load the cabinet to the driver, it was important to eliminate first reflections that influenced the propagation of sound from that cabinet AND to control the interactions of the loudspeaker with itself.

Assumptions from first designs by the brightest minds in the industry were now dwarfed by the research and findings of subsequent scientists who explored the details of sound reproduction on a level never before imagined. And so it is with all of human understanding of any subject. Until more is known, all one can do is to regurgitate what someone else told you. Until you investigate other options and either fail or succeed, you will never know if what you hypothesize is fancy or fact.  Without an open mind, no progress can be made, only iterations of the same. This is not only a valuable lesson in loudspeaker design, it is a valuable life lesson too.

Change is inevitable and those who fear it are like those who prefer building speakers by stuffing drivers into boxes. Mistakes are how humans learn best and if we never try, we never make mistakes. It is just as important to understand what does not work as it is to understand what does.  If you never try something different, you will never know which category your idea will fall into.

To keep the leading edge moving forward, I encourage all of you to think out of the box (pun intended). Take what you have been told as a guideline and look at these guidelines from a different perspective or point of view.  Like overacting in movies, eventually humans learn what works best and what doesn't.  Change is a process, not an event and once the synergy is found between what works in this situation combined with what works best in that situation, the real truth is elusive. Until all effects of speaker wires, crossover component quality, amplifier design, and room acoustic treatment are unified into one system design, all you will get is what you have always got - compromise.  All aspects of all influences must be considered to squeeze more sonic truth out of any system.

Swapping interconnects and amplifiers, adding sonic treatment here and there, moving this over there and that to behind this all contributes to the quality of sonic reproduction.  Yet there is stil more to understand even though you may have run out of ideas at the moment. Remember change is inevitable and what you think of as a possibility may prove to be as profound as was the design of a dynamic or a planar driver. Keep thinking about details and question conventional wisdom. For it is when you remove the barriers of your mind that new discoveries are made.

Yours for higher fidelity,
Philip Rastocny

Copyright © 2015 by Philip Rastocny. All rights reserved.

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