Hegeman's Design Vison

"It gets down to what kind of sound you want. There are two different approaches: one, that the orchestra should be brought into your living room; the other, that you should be taken out of the room and transported to the concert hall. I want the latter.” (2)

To accomplish this, Hegeman launched an all-out assault on the state-of-the-art, designing speakers that challenged the industry's notions of high-fidelity reproduction. The principles of their design were the fruit of Hegeman’s theoretical and experimental efforts to the bridge the gap between his scientific and subjective experience of audio, and led him to embrace certain design principles that, at the time, were considered highly eccentric. All of them were rooted in Hegeman’s belief that preserving the temporal relationship between all parts of an audio signal is key to realistic and lifelike sound. An idea Hegeman was nearly alone in championing. As Hegeman described it:

“If phase shift is excessive, or not linear… it causes transient distortion. Take, for example, the overtones of plucked strings or of timpani. In live sound, those overtones have a definite relationship in time to their fundamental tones. If, in reproduction, that relationship is changed, the resultant sound becomes unnatural, unlifelike sound that seems ‘canned’”(3)

In speakers specifically, it led him to omnidirectionality, because a speaker that faithfully reproduces the temporal relationships of sounds…

“...would also be inherently omnidirectional, something like a sphere of infinitely small size expanding and contracting. The same design techniques that make for linear phase shift do, at the same time, make for omnidirectionality… a problem largely restricted to mid-range and high frequencies. These tones tend to beam, resulting in unpleasantness and lack of naturalness in reproduction, caused by the loss of the spatial characteristics typical of live sound.”(5)

But that's not all... 

“On the other hand, a wider angle of dispersion…  gives you a greater sense of the music as played in a live environment.”(6) By reestablishing, “in a small room something of the natural ratio of reflected to direct sound (often as high as 4 to 1) that we hear in the concert hall (5). Furthermore, it helps make that environment acoustically part of your room.”(6)

On this last and key point, Don Morrison, to whom Hegeman passed his torch, explains:

“Thatʼs the advantage of the design [point source omnidirectional]. The reflected sound off any walls or ceiling has the same source [and therefore the frequency response, phase response, etc.] as on axis. The ear/brain quickly adjusts as it does in real life…You can accept the sound of someoneʼs voice in a reverberant room and easily understand him. If another person was talking to you at the same time from the side only a wee bit delayed it would be rather difficult to follow the conversation.”(7)

Finally, preserving the temporal relationship of the parts of audio signals also led to Hegeman's quest for wide bandwidth in his designs, not only to avoid phase distortion caused by response roll-off, but "because though he couldn't measure it, Hegeman recognized that the response limits of speakers and amps reflected distortion back into the audible range "somewhat as a sea wall throws back the surf."(4) This idea of Hegeman's, laughed off for nearly 20 years, was by the end of Hegeman's life, recognized as fact by the entire audio industry. 

Hegeman's attempt to "bring the listener to the concert hall" led him to create two generations of unique loudspeakers the likes of which were never seen before.

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The First Generation

Hegeman's first generation of loudspeakers is defined by two key elements: (1) Hegeman's Split Slot-Loaded Conical Horn bass design (2) Use of uniquely shaped radiators to achieve omnidirectional radiation patterns. Each section will describe in detail how Hegeman implemented these elements in each speaker starting with the Hegeman Professional, his flagship and concept speaker from which all the others were derived. 

The Second Generation

Hegeman's second generation of speakers are characterized by (1) the use of upward firing aluminum woofers with tweeters coaxially mounted in semi-hemispherical diffusers above them to achieve point-source omnidirectionality; and (2) use of quarter wave stub labyrinths to load the woofers for smooth roll-off and gradual phase shift.  

The Bookshelf Series

(1) Popular Electronics, June 1960, Page 55

(2) Hifi/Stereo Review, April 1963, Page 50

(3) High Fidelity, February 1961, Page 43

(4) New York Times, July 29, 1990, Section 2, Page 13

(5) Radio Electronics, September 1958, Page 42

(6) High Fidelity, February 1961, Page 109

(7) Rooms & Speakers — Morrison Audio