The Absolute Sound      August 2022

From The Editor
A Beautiful Bouquet
Robert Harley on why there are so many different types of loudspeakers — and why that's a good thing.
Editorial By Robert Harley

  In this special Directory to Loudspeakers and Cables you'll find lots of speakers — dynamic speakers, electrostatic models, ribbons, planar-magnetic designs, horns, Air-Motion Transformer tweeters, bending-wave drivers, hybrid dynamic/electrostatics, hybrid dynamic/ribbons, concentric drivers, and diaphragms made from paper, ceramic, carbon-fiber, beryllium, and graphene, to name a few.

And that's just the driver technologies.

Throw in woofer loading — sealed, ported, transmission-line, isobaric — along with box and boxless models and single-driver, two-way, three-way, four-way, point-source, bipolar, dipolar, and omni-directional speakers — the variations go on and on. Despite their vast differences, all these technologies are viable in today's marketplace.

But which approach is right? And why should as mature a technology as the loudspeaker be realized with so many wildly disparate materials, technologies, and methodologies?

With virtually all consumer products, a consensus emerges over time as to the best way to make that product. A Darwinian process ruthlessly eliminates inferior techniques, designs, and materials, eventually leading to the amazing performance, ease of use, and reliability we enjoy in today's products. Why are speakers so different?

Every one of the speaker technologies I mentioned has some advantages and disadvantages compared to the competing technologies. There is no single technology that delivers every advantage in every application. Consequently, the designer makes a series of technical and aesthetic choices as to which tradeoffs he is willing to make. The designer is guided by what he values most in reproduced sound, and how he perceives musical realism.

To use just one example, a ported speaker will extend lower in the bass before it starts rolling off than a speaker in a sealed enclosure, all things being equal. The ported speaker is also more sensitive, producing a higher sound-pressure level for a given amount of power. Finally, a ported speaker will play louder than a sealed speaker, again all other factors being equal. But a sealed enclosure has more accurate transient performance than a ported one; the woofer stops faster after the drive signal ends.

And although porting an enclosure lowers the woofer's bass extension, ported bass rolls off at a much steeper rate than the bass from a sealed enclosure (24dB/octave versus 12dB/octave). That is, although the ported speaker's –3dB point is lower, it doesn't deliver as much truly deep bass as a sealed speaker. In a nutshell, bass from a sealed speaker is tauter and leaner, with outstanding pitch and dynamic precision. Bass from a ported speaker has more punch and impact. That's a generalization of course, but largely accurate.

But that example still doesn't answer the fundamental question of why such different technologies — some of them diametrically opposed — proliferate and thrive in the marketplace. It's been 147 years since the invention of the dynamic driver; 99 years since the ribbon driver was patented; 93 years since the invention of the electrostatic speaker; and 91 years since the multi-way dynamic speaker, yet the loudspeaker industry has reached no consensus as to which is the best technology.

The reason is that there's no objective standard by which to quantify loudspeaker performance. Of course, we can all agree that linear frequency response, wide bandwidth, and low distortion are laudable attributes. But an attempt to definitively characterize every aspect of a speaker's performance with a series of mathematical symbols, apart from being impossible, excludes the speaker's raison d'ętre — the reaction the speaker produces in the human brain when listening to music. Theoretical advantages and disadvantages of certain technologies, along with measured performance, can only go so far.

These are two-dimensional approaches to a multi-dimensional phenomenon, not just in how the speaker behaves, which is incredibly complex in its own right, but in the interaction between the reproduced sound and the listener's musical perception. How do you measure and quantify the startling sense that a vocalist is crossing time and space to sing directly to you? Or that one speaker produces good sound, while another fosters a thrilling sense of contemporaneous music making? It takes the human mind to interpret the speaker's performance as greater or lesser musical realism, and greater or lesser musical involvement.

It is this interpretation, this translation from mere reproduced sound to glorious music, that varies from individual to individual. No single set of loudspeaker attributes triggers everyone in the same way. And that is why nearly a hundred and fifty years of loudspeaker development has failed to coalesce around a single technology for converting an electrical signal into air-pressure variations.

We should rejoice in the astounding variety of loudspeakers we can choose from. Many different flowers make a beautiful bouquet.

— Robert Harley

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