BIB

For me, the BIB was an effort to understand back horn loudspeakers. There was a mystique surrounding their design. Many at diyaudio.com decided to discuss the topic at what may be the ultimate BIB loudspeaker discussion. Years have passed and the BIB has been venerated as one of the easiest and best performing back horn designs.

The ‘group think’ was impressive on the diyaudio forum. I was proud to be a member of a community so willing to make time and provide input. BIB spreadsheets were developed and refined allowing builders to select any driver and calculate optimal cabinet dimensions.

I’d also like to mention that the late Terry Cain (pictured below) brought the BIB design back to life. He shared his sketches and built a prototype. He challenged us to revisit and listen to what was considered an old design.

Many thanks to all who contributed the the BIB. Your efforts allow music lovers and speaker builders to enjoy excellent sound for modest cost across the globe. Please read Scott Lindgren’s Introduction to BIB loudspeaker design below. Scott initiated the BIB discussion back in 2005.

Introduction

Welcome to a different paradigm.

These pages are dedicated to an unusual loudspeaker enclosure design that has somewhat wryly become known as the Bigger Is Better cabinet. I imagine that many readers won’t be too familiar with speakers of this nature, so this brief introduction will explain a little bit of the background to the enclosure.

Well for a start, what we are considering here is a real blast from the pre Thiel/Small days, an enclosure type which dates from a time when bigger was better, and the box volume was deliberately intended to swamp the driver’s Vas. Sounds simple? Well, to an extent it is. However, don’t be fooled into thinking that there was no solid scientific theory or engineering going on before Saint’s Thiel and Small came along to save us from the error of our ways – there was. But don’t believe me; just read some of Ted Jordan’s or Paul Taylor’s white papers, to name but two examples, and prepare to have your eyes pop out. T/S parameters are great.  I’d be the very last to deny it. As Greg Monfort (GM) observes, if you want to squeeze the last drop of performance out of a given bulk, or hit a target alignment, they’re vital, but when box size is no longer significantly restricted, they become much less important: it is almost impossible to have too large an enclosure, while the converse is seldom true.

Regarding the geometry, being a positive tapered pipe, the BIB is technically a horn, since its gain back-wave begins at ½ wavelength, and has both odd and even harmonics. In practice, this makes for a tall cabinet, with a single internal fold near the bottom, tuned to ½ wavelength of the design frequency. The top is left completely open, and this forms the terminus of the horn. The mouth is actually completed by the room, because these enclosures are specifically intended for corner placement (1/8 space loading), or, at least, for pushing as far back against a rear wall as possible (1/4 space loading), for they use the reflection boundary conditions these create to continue their expansion. You’ll find some drawings here on the site, which should make the layout of the enclosure clear.

For those with a historical interest, this idea for upward-firing corner horns actually pre-dates the modern concept of ‘hifi’ by a good fifteen to twenty years. The first patent was granted to the inevitable P.G.A.H. Voigt of Lowther fame in the 1930’s, though knowing I was interested in the background, GM advised me that both W.E. and Seimens had earlier experimented with extremely large floor or ceiling-loaded horn systems in the early days of cinema sound. They did not ultimately pursue them however, leaving the field open for Voigt a few years later.

Although quite an old idea then, this particular cabinet type remained relatively obscure, for home use at least, until cabinet-maker turned speaker-designer Terry Cain wrote a short article for the Single Driver Site about a pair he designed and constructed for the defunct Radio Shack RS 40-1354. It was Terry too who christened them the ‘Bigger Is Better’ enclosure. His article proved to be something of a catalyst, and thanks to the global reach of the internet, he brought the concept to a much wider audience. Several people, following Terry’s advice to experiment, built versions of this enclosure, and it gained something of a cult status due to the simplicity of construction, elegant geometry, and remarkable low-frequency heft. Subjectively, scale is another strong point of these big boxes, for they can easily fill the end of a room with a deep wall of sound.

One significant issue with these boxes is the difficulty of modelling their in room response. At present, the best option for the DIY audio enthusiast, Martin King’s seminal MathCad worksheets (www.quarter-wave.com) are effectively restricted to ½ space simulations with these enclosures due to the placement of their terminus at the top of the cabinet. As they are designed to use the room boundaries to complete their horn-mouth and loading, it is not surprising therefore that such simulations suggest a very ragged response. Fortunately, given that our listening conditions are anything but ½ space, we can rest easy. Don’t let the apparently poor predicted results put you off! The heavy ripple implied, and the suck-out in the mid-bass are considerably flattened when they are correctly designed and positioned, to a point where they equal or better many well-known and well-regarded horn designs. I gather that LspCad Pro should be able to model this in-room response with a fair degree of accuracy, but this is a rather expensive purchase for most DIY audio enthusiasts, myself included, and I have yet to try it.

None of this is to denigrate Martin’s superb work, or to suggest that his worksheets are of no use when designing these boxes however. They remain a mandatory purchase in my view for the DIY speaker designer, and despite their current limitations in regard to modelling this very specific type of enclosure (Martin regularly upgrades the sheets, so these will dwindle over time), they still do provide a good indication of the general response curve and low frequency extension you can expect. That’s why you’ll find a MathCad generated frequency response graph on these pages for each suggested driver / enclosure combination. Indeed, all of the suggested enclosures that I generated and that you’ll find on these pages were first sized roughly, then tweaked in MathCad.

And that’s quite enough from me. Many thanks to Jeff for generously offering to design and host these pages on his excellent site (All Hail Godzilla!). And in alphabetical order:

Terry Cain. Others might have built them before, but if anyone can be considered the father of the BIB, it’s Terry. I’d like to see some commercial Cain & Cain BIB’s soon –here’s hoping.

Martin J. King, as ever, for his technical advice and superb MathCad sheets.

Dan Mason –fellow BIB enthusiast and driver-rolling specialist.

Last but by no means least, Greg Monfort for so selflessly and patiently sharing his years of experience and knowledge with all who ask for it, and who assisted so much with this introduction and the designs.

Regards to all
Scott Lindgren (Scottmoose)

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Links to BIB articles:

BIB-Intro-by-Scottmoose

Fostex_FE-167E_BIB_Design

Links to the Voigt Pipe (which I believe provided the motivation for Terry to take the design a step further).

Voigt-Pipe-Straight-Pipe-loudspeaker-design