Home  |  Audio Reviews  Audiophile Shows Partner Mags  News     



August 2012

Distributed Bass
A simple execution for the distributed bass concept.

Article By Jeff Poth

Difficulty Level


  As I mentioned in my Kaboominator article, I destroyed one of the woofers that would have made my project more complete (two kaboominators rather than one).

Distributed bass is one way of saying that the bass loading in the room is intentionally varied in order to reduce the influence of the room. The room is the dominant factor in low frequency performance for most loudspeaker systems, in most rooms, below some 200 Hz or so. By distributing where the bass sources are the distances to various boundaries are also varied. Note the sine waves below.

If you were to sum this first set, the waves which are exactly 180 degrees out of phase will cancel and there will be no net SPL, or sound. If the first wave were the sound coming from your woofer, and the second were a reflection within the room, you can see how this frequency would be dramatically reduced compared to the "correct" sound coming directly from the subwoofer. This sort of cancellation causes a notch in the frequency response and is very common in typical rooms. In other words, your woofer is working against the room, and the room is winning. Likewise, where the waves are closer to equal phase, they will sum and you can have peaks, instead of notches, in the frequency response.

These cancellations and reinforcements from standing waves and other room/boundary effects are a major hurdle to good frequency response in the bass. There are a number of ways that modal behavior in rooms can be limited, all of which are intended to reduce the influence of the room. One is to use bass horns. When true basshorns are used, the sound is directed into a specific beam which is focused towards the listener. A significant reduction in energy to the sides and rear takes place, and thus the room plays less of a role. Basshorns reduce the influence of the room by increasing the ratio of direct to reflected energy. The drawbacks with bass horns are that they are extremely large -- a proper bass horn needs to be large relative to the wavelengths produced. With approximately a 10 foot wavelength @ 100 Hz and 20 feet @ 50 Hz, proper deep basshorns are bigger than cars.

Dipoles are another method, which have a narrower beamwidth than the omnidirectional behavior of typical sealed or vented box subwoofers. Dipoles radiate equally (ideally) to the front and rear, and dramatically less to the sides (or above). Instead of one directional beam, we have two. The room is excited, but still to a much lesser extent than with a normal monopole subwoofer, which sends bass frequencies equally in all directions. With dipoles, however, the system requires a lot of woofer to make up for the lost SPL from dipole cancellation. This can mean large systems with multiple 15" or 18" woofers and lots of amp power, though more modest systems can be made at the sacrifice of either max SPL or bass extension. Larger baffles (and again, large relative to bass wavelengths) can reduce the influence of the cancellation, but they also give up the desirable directional characteristics and limited room involvement of a smaller dipole frame/baffle.

Line arrays can control bass, and used carefully can help control sidewall reflections via directionality and minimize the involvement of boundaries by loading the room from many locations. This distributes the phase relationships of the reflections very similar to our last, and possibly best, choice. Line arrays, like dipoles and bass horns, can be quite large and expensive, and their ability to spread modal behavior in the room is lessened as bass wavelengths get longer.

The final choice is distributed bass. This is a method with many proponents, including Earl Geddes, and Duke LeJeune, both of whom sell subwoofers for "Swarm" subwoofer systems, another way of describing distributed bass. Below is Dr. Geddes whitepaper on these. He favors bandpass subwoofers for their high power handling and low distortion



Where Mr. LeJeune utilizes more conventional sealed or vented systems.


The idea is simple, using multiple subwoofers to spread the distances to room boundaries around. In doing this, there will be an averaging effect, wherein the peaks and notches associated with the room are reduced. Imagine if the output from the first graph above (which results in no sound at the listening position) were combined with a third wave, representing the output from a second subwoofer, with a different phase relationship, and a fourth representing the reflected energy from the second location.

This four wave model is grossly simplified, but serves the purpose of explanation- the more different sources one has, the larger the variety of frequency and phase responses that will manifest themselves at a given listening position. The complex sum of these will tend to average to minimize the influence of the room, and thus give smooth bass response. People may wonder "Doesn’t this averaging make for less clean bass since the timing is all different?" In the bass, time behavior is not as readily discernible, and is dominated by standing waves in the room- that is unless you manage those standing waves. A multi-source bass system reduces the influence of standing waves and thus can achieve better, "Faster" sounding bass.

Typically distributed bass is achieved with multiple active subwoofers, each with variable phase, allowing for the use of the phase control along with the placement variation to minimize the influence of the room. Distribution of the subwoofers in this manner is ideal for minimizing the influence of the room, but doesn’t work with every setup. The need for wiring to each sub, both power and line-level, can be a major challenge in some rooms, as can the multiple locations.

Such is the case in my room so I had to create the best solution I could, and that was by stacking the subwoofers so as to spread the driver locations over a wider area. The kaboominators have two large dimensions and one short, making them perfect for stacking on their sides. I rotated one sub 180 degrees from the other, placing one manifold on the rear, top, left of the enclosure, and one on the bottom right front. While this is not the ideal case for distribution, it still creates some significant amount of variation in the interaction with the room. The acoustic sources are arranged over a 30" range vertically, out of a 96" typical ceiling, this is enough variation to reduce the consistency of standing waves between the floor and ceiling, and thus reduce the depth of the notches and amplitude of the peaks. There is a similar amount of distribution in the other dimensions, and while it’s not enough to fully distribute bass down to the lowest octaves, the high-q resonances in room response may still be compensated for even in frequencies where 30" would seem to be minor.

This is a fairly simple execution for the distributed bass concept. Wish I could squeeze more locations into my room, but even audio reviewers sometimes have to sacrifice performance for livability. With a dedicated room, one would likely use a variety of locations with infinite baffle manifolds.








































Quick Links

Audiophile Review Magazine
High-End Audio Equipment Reviews


Equipment Review Archives
Turntables, Cartridges, Etc
Digital Source
Do It Yourself (DIY)
Cables, Wires, Etc
Loudspeakers/ Monitors
Headphones, IEMs, Tweaks, Etc
Ultra High-End Audio Reviews


Enjoy the Music.TV


Editorials By Tom Lyle
Viewpoint By Roger Skoff
Viewpoint By Steven R. Rochlin
Various Think Pieces
Manufacturer Articles

Show Reports
Pacific Audio Fest 2023 Report
T.H.E. Show 2023 Report
HIGH END Munich 2023
Australian Hi-Fi Show 2023 Report
AXPONA 2023 Show Report
Salon Audio Montréal Audiofest 2023
CanJam Singapore 2023 Report
Florida Intl. Audio Expo 2023
Capital Audiofest Show 2022
KL International AV Show 2022
Toronto Audiofest Show 2022
CanJam SoCal 2022 Show Report
...More Show Reports


Audiophile Contests
Cool Free Stuff For You
Tweaks For Your System
Vinyl Logos For LP Lovers
Lust Pages Visual Beauty


Resources & Information
Music Definitions
Hi-Fi Definitions


Daily Industry News

High-End Audio News & Information


Partner Print Magazines
Australian Hi-Fi Magazine
hi-fi+ Magazine
HiFi Media
Sound Practices
The Absolute Sound
VALVE Magazine


For The Press & Industry
About Us
Press Releases
Official Site Graphics


Contests & Our Mailing List

Our free newsletter for monthly updates & enter our contests!




Home   |   Industry News   |   Equipment Reviews   |   Press Releases   |   About Us   |   Contact Us


All contents copyright©  1995 - 2023  HighEndAudio.com and Enjoy the Music.com®
May not be copied or reproduced without permission.  All rights reserved.