Even though do-it-yourself hi-fi for the home started with open baffle speakers, why is it that mainstream hi-fi loudspeaker designers frown upon the very concept of it?
By: Ringo Bones
D.I.Y. high fidelity loudspeaker design books whose “self-worth” is invested upon the mathematics behind the Thiel-Small Parameters often view open-baffle hi-fi loudspeakers as “a fish out of water” due to their low bass output being 100 times less in comparison to closed-baffle box hi-fi loudspeakers optimized via Thiel-Small Parameter based mathematics. But is this really so?
Believe it or not, home D.I.Y. or do-it-yourself hi-fi as a hobby started a few years or more before the “Golden Age of Stereo” got underway in the mid 1950s. Back then, the home constructors set-up consisted of a 15-inch Tannoy Dual Concentric loudspeaker mounted in an open baffle in the corner of the listening room – or some young hobbyist’s bedroom – driven by a home built zero negative feedback single-ended triode amplifier putting out 3-watts or so. Such open-baffle hi-fi loudspeaker set-up was known for their open and natural midrange qualities that made recorded singers sounds as if they are really singing in front of you. But the higher bass output – probably the inherent “boominess” of closed-boxed loudspeakers commercially designed and manufactured around the Golden Age of Stereo and the advent of Rock n’ Roll Music probably won out in the end, relegating the open-baffle hi-fi loudspeakers by the wayside.
Surprisingly almost out of nowhere, the 1990s came and the “Western World’s” single-ended triode amplifier revival, which again resurrected the charmed qualities of the open-baffle speakers. Given the “irresistible” mid-band qualities of open baffle speakers, why do mainstream hi-fi loudspeaker manufacturers view open-baffle hi-fi loudspeakers – bass volume aside - with such a “low opinion”?
Sadly, despite rigorous scrutiny of every annual convention of the Audio Engineering Society, adherents of the closed box design parameters based on the white papers of A.N. Thiel and Richard Small are not quite entirely truthful in telling the D.I.Y. hi-fi hobbyists about the shortcomings of closed-box hi-fi loudspeakers – ported or not. The cabinet that is placed around the rear of a “conventional” closed-box hi-fi loudspeaker drive unit to contain back radiation – and to boost low frequency bass response below 100-Hz or so – imposes a low-frequency limit upon bass reproduction. More often than not, closed-box hi-fi loudspeakers’ low frequency limits just roll-off too high or too early to allow low notes of properly recorded bass-based musical instruments like acoustic upright double bass and full-sized pipe organs to be played properly with convincing fidelity in a typical listening room.
Closed-box loudspeakers also compromises perceived bass quality by making it sound lumpy, boomy, uneven or just dry and anemic in comparison to the recorded acoustical music event. The panel resonance enclosing the rear of a typical closed-box hi-fi loudspeaker also adds mid-band coloration that makes singers’ voices sound “electronic”, whilst box echoes add whoomph, chestiness and a megaphone effect. Add in the cost of the woodwork, its weight and volume and you have a severely bad idea staring you in the face.
And believe it or not, it gets worse. In my years of actual usage of conventional closed-box hi-fi loudspeakers, the least understood but perhaps the most significant drawback of the closed-box hi-fi loudspeaker: it is a monopole (while open-baffle hi-fi loudspeakers are dipoles in its sound radiation) that cannot be properly matched into an enclosed space – i.e. your listening room / bedroom / hobby-room in other words. All that pulling and pushing of closed box hi-fi loudspeakers in the left and right corner of your listening room to get good – or just maybe “bearable” – bass performance from them is down to this property.
Believe it or not – according to first-hand acclaim to seasoned hi-fi hobbyists – the best hi-fi loudspeaker of all time to them is the Quad ESL-63 Electrostatic, which not surprisingly, is an open-baffle design. So does the naturalness and vocal qualities of the Quad ESL-63 be transferred to the “inherently uncouth” dynamic magnetic coil loudspeakers? In a word, yes, if you mount one in an open baffle and use zero negative feedback single-ended triode amplifier designs to drive them.