Basics About Bass

By Bryan Geyer

I began my own DIY hi-fi hobby time in early 1954, after returning from draft duty in Korea. In that era, virtually all serious speaker systems were big, featuring 12” and 15” Ø woofers that were more efficient than most woofers in common use today. As a result, bass reproduction was always pretty solid; we moved a lot of air. And when more was needed we’d just sink 2 or 3 more Bozaks into a handy side wall. This was in the mono-era, so location and directionality aspects were of little concern. The trend to produce bookshelf-sized speakers came about soon enough, and generally curtailed bass output, but then Edgar Villchur (AR) announced his new “acoustic suspension” design, and those speakers could rival a floor-stander’s bass if you’d just sacrifice some efficiency. The new “AR size” speakers (and the competition that they inspired) materially eased the transition to stereo, and bass output never suffered because bigger power amps soon became pervasive. So sufficient and abundant bass was common until the mid-’80s, when the home theater craze came to market.

Cramming all of that “surround stuff” into a home theater room often caused decor problems, so some speaker systems got downsized, and subwoofers got popular. The “subs” were all highly optimized for bass below 100Hz, with cone suspensions having restricted range but long throw axial excursion (Xmax) capability. This tool was vital to deliver the separate low-frequency effects (LFE) channel of the movie media, otherwise known as the “boom track”. Bass accuracy was never the goal. The express intent was to simulate loud explosions, gunshots, and monster grunts. A single shared (blended) subwoofer was fully adequate.

The application of subwoofers for 2-channel stereo service has evolved more recently, partially in response to concerted efforts to render more realistic and authentic bass, but principally because collective advances in technology have now made that goal attainable. These developments include…

…the creation of Linkwitz-Riley 4th order (phase-coherent, non-inverting) active crossovers.
…the increased availability of multi-sourced low noise monolithic op-amp chips at low cost.
…the significantly improved response of “long throw” low bass subwoofers.
…consistent improvement in the performance of super-efficient Class D power amplifiers.

These assets now make it practical to produce more effective and reliable self-powered subwoofers, as well as the frequency-selectable active crossover controllers needed to define and isolate the deep bass passband that they serve. The possibility of providing accurate deep bass has never been more favorable, but the old mechanical constraints still apply. When the listening room is smaller than a public auditorium, it exhibits a Schroeder frequency* that’s too high to avoid the inevitable peaks and dips that arise due to resonant mode rebounds off the room’s planar surfaces. A traditional means of managing this problem is room treatment. Surface-mounted traps (padding) are added to absorb some of the excessive waveform bounce. The customary 2 inch thick broadband absorbers are ineffective at low bass frequencies, so it’s then necessary to use fatter 4 inch absorbers and/or large canister-style tuned bass traps to tame the low bass (< 100Hz) resonance. That decor is acceptable when the listening room is a dedicated “man cave”, but less tolerable in a shared condo living room.

When that’s the case, multiple subwoofers can be utilized to effectively achieve cancellation of the reflected modal bass over large portions of the listening area**. Two subwoofers will work well; more subs will work better. The subwoofers’ output will naturally be ~ 180˚ out-of-phase with the reflected modal bass, so effective partial cancellation will result when the opposing wavefronts converge.

The potential benefit conveyed by using a pair of widely spaced (along front wall) self-powered subwoofers can be appreciable. Their impact will always be advantageous, regardless of the bass capabilities of the main speakers. The variance implicit in room response will preclude full cancellation of low frequency resonance, but the audible improvement will be obvious. The use of wide-spaced subwoofers can dramatically upgrade the bass in any room—including rooms with big full range main speakers. In the latter instance, let the floor-standers handle all of the mid-to-upper bass, and assign the bottom 20Hz-80Hz passband to the more widely spaced subwoofers. (No matter how costly your top quality main woofers might be, good subs can handle the bottom better; it’s their specialty.) Set the external active crossover controller (e.g. Marchand’s XM66†) to split the passbands at 80Hz. (A lower frequency crossover is seldom beneficial; usually detrimental.) Then optimize the subwoofers’ phase angle and input gain control settings in the manner that’s described in our related white paper††. The critical bass octaves above 80Hz can then be reproduced without compromise, and the bottom bass can be programmed (in fixed ±1dB stepped increments, with ±5dB range on both channels) to provide an output level that best fits the genre of the selected source.


**Refer pp. 234-262 of Floyd Toole’s “Sound Reproduction”, 3rd edition (Routledge, 2018, ISBN 978-1-138-92136-8).


††Refer “On Optimizing Subwoofer Gain & Phase Angle…”

BG (January 2019)

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Meet the Staff

Meet the Staff
John J. Puccio, Editor, Publisher, Reviewer

Understand, I'm just an everyday guy reacting to something I love. And I've been doing it for a very long time, my appreciation for classical music starting with the musical excerpts on The Big John and Sparkie radio show in the early Fifties and the purchase of my first recording, The 101 Strings Play the Classics, around 1956. In the late Sixties I began teaching high school English and Film Studies as well as becoming interested in hi-fi, my audio ambitions graduating me from a pair of AR-3 speakers to the Fulton J's recommended by The Stereophile's J. Gordon Holt. In the early Seventies, I began writing for a number of audio magazines, including Audio Excellence, Audio Forum, The Boston Audio Society Speaker, The American Record Guide, and from 1976 until 2008, The $ensible Sound, for which I served as Classical Music Editor.

Today, I'm retired from teaching and use a pair of bi-amped VMPS RM40s loudspeakers for my listening. In addition to writing the Classical Candor blog, I served as the Movie Review Editor for the Web site Movie Metropolis (formerly DVDTown) from 1997-2013. Music and movies. Life couldn't be better.
Karl W. Nehring, Contributing Reviewer

For more than 20 years I was the editor ofThe $ensible Soundmagazine and a regular contributor to its classical review pages. I would not presume to present myself as some sort of expert on music, but I have a deep love for and appreciation of many types of music, "classical" especially, and have listened to thousands of recordings over the years, many of which still line the walls of my listening room (and occasionally spill onto the furniture and floor, much to the chagrin of my long-suffering wife). I have always taken the approach as a reviewer that what I am trying to do is simply to point out to readers that I have come across a recording that I have found of interest, a recording that I think they might appreciate my having pointed out to them. I suppose that sounds a bit simple-minded, but I know I appreciate reading reviews by others that do the same for me -- point out recordings that I think I might enjoy.

For readers who might be wondering about what kind of system I am using to do my listening, I should probably point out that I do a LOT of music listening and employ a variety of means to do so in a variety of environments, as I would imagine many music lovers also do. Starting at the more grandiose end of the scale, the system in which I do my most serious listening comprises an Onkyo C-7030 CD player, Legacy Audio StreamLine preamplifier, Legacy Audio PowerBloc2 amplifier, and a pair of Legacy Audio Focus SE speakers augmented by a Legacy Point One subwoofer. I also do a lot of listening while driving in my 2016 Acura RDX with its nice-sounding ELS Studio sound system through which I play CDs (the ones I especially like I rip to the Acura's hard drive so that I can listen to them whenever I want) or stream music through the system using my LG G7 ThinQ cell phone, which features surprisingly sophisticated audio circuitry. For more casual listening at home when I am not in my listening room, I often stream music through the phone into a Vizio soundbar system that has remarkably nice sound for such a diminutive physical presence. And finally, at the least grandiose end of the scale, I have an Ultimate Ears Wonderboom Bluetooth speaker for those occasions where I am somewhere by myself without a sound system but in desperate need of a musical fix. I just can't imagine life without music and I am humbly grateful for the technology that enables us to enjoy it in so many wonderful ways.
Bryan Geyer, Technical Analyst

I initially embraced classical music in 1954 when I mistuned my car radio and heard the Heifetz recording of Mendelssohn's Violin Concerto. That inspired me to board the new "hi-fi" DIY bandwagon. In 1957 I joined one of the pioneer semiconductor makers and spent the next 32 years marketing transistors and microcircuits to military contractors. Home audio DIY projects remained a personal passion until 1989 when we created our own new photography equipment company. I later (2012) revived my interest in two channel audio when we "downsized" our life and determined that mini-monitors + paired subwoofers were a great way to mate fine music with the space constraints of condo living.

Visitors that view my technical papers on this site may wonder why they appear here, rather than on a site that features audio equipment reviews. My reason is that I tried the latter, and prefer to publish for people who actually want to listen to music; not to equipment. My focus is in describing what's technically beneficial to assure that the sound of the system will accurately replicate the source input signal (i. e. exhibit high accuracy) without inordinate cost and complexity. Conversely, most of the audiophiles of today strive to achieve sound that's euphonic, i.e. be personally satisfying. In essence, audiophiles seek sound that's consistent with their desire; the music is simply a test signal.

Mission Statement

It is the goal of Classical Candor to promote the enjoyment of classical music. Other forms of music come and go--minuets, waltzes, ragtime, blues, jazz, bebop, country-western, rock-'n'-roll, heavy metal, rap, and the rest--but classical music has been around for hundreds of years and will continue to be around for hundreds more. It's no accident that every major city in the world has one or more symphony orchestras.

When I was young, I heard it said that only intellectuals could appreciate classical music, that it required dedicated concentration to appreciate. Nonsense. I'm no intellectual, and I've always loved classical music. Anyone who's ever seen and enjoyed Disney's Fantasia or a Looney Tunes cartoon playing Rossini's William Tell Overture or Liszt's Hungarian Rhapsody No. 2 can attest to the power and joy of classical music, and that's just about everybody.

So, if Classical Candor can expand one's awareness of classical music and bring more joy to one's life, more power to it. It's done its job. --John J. Puccio

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"Their Master's Voice" by Michael Sowa

"Their Master's Voice" by Michael Sowa