Hegeman’s second generation of speakers stand as yet another testament to his unrivaled creativity and willingness to question audio orthodoxy. They embody design ideas that, like many of Hegeman’s contributions to audio, were disregarded as “eccentric” in his lifetime, but have now been adopted and adapted by industry giants like KEF, Shure, and others.

The first in what I call the “H-Series” was the Hegeman Labs Model 1 (H1), released in 1971 and later revised as the Model 1A (H1A). The second was the Hegeman Labs Model 2 (H2), released in 1974. The third was the mysterious “Hegeman Subwoofer,” AKA: The HSW. 

The HSW will be covered separately.

Side Note: Hegeman 1 vs 1A

There are two versions of Hegeman's first model: the 1 and the 1A. I've never gotten my hands on an H1. But lucky for us, YouTuber and audio enthusiast Anthonyhfe6450 has! Best I can tell based on his videos, there are two major differences between the 1 and 1A:

1. The H1A's woofer has three more decoupling rings than the H1's

2. The interior dividers of the H1 cabinet are 1/4-inch thick, while the dividers in the 1A are 1/8-inch thick, meaning the tubes (more on this later) in the H1A have a 12% larger cross-sectional area than those in the H1. 

With that said, I will point out differences as I go. if I don't specifically call out the H1, then what I'm writing applies to both versions of the speaker. 

The Hegeman Model 1 and Model 2

The H-Series cabinets, unassuming boxes wrapped in teak-look vinyl (real walnut veneer was available for an upcharge), appear unremarkable from the outside. A basic acoustic suspension design, you might guess. But you’d be wrong. Behind the woofer is not an open box, but a plenum for a labyrinth of 6 tubes of varying length constructed of 1/8-inch (1/4-inch in the H1) Masonite (hardboard). The tubes open to the plenum: two entrances along the perimeter of the right cabinet wall, two along the perimeter of the left cabinet wall, and two parallel to each other located front-center directly under the woofer. The woofer is loaded by these tubes instead of a simple box. 

The reasoning and purpose behind these design choices is brilliant, in particular, the tubes. Keeping in mind Hegeman’s design objectives, we will start with the familiar and work toward the novel.

Outside the Box

Inside the Box

The cabinet’s aforementioned internal labyrinth is composed of quarter-wave stubs: tubes with one open and one closed end that are tuned to resonate at specific frequencies over specific bandwidths by adjusting their length (frequency) and cross-sectional area (bandwidth). The tubes in the H-Series speakers are tuned such that their summed response bandwidth overlaps with the woofer’s in-cabinet resonance over its operating range.

 The effect of this design is to:

1. critically damp the cone assembly’s movement across the entire range of the speaker’s resonance

2. dissipate the woofer's back-wave more completely and in a smaller enclosure that achievable with a standard sealed box

3. create a minimally reactive load for any amplifier.

For the listener, this means extended, clean, and exceptionally articulate bass in a relatively small cabinet.

An impedance plot showing an H1A driver in free-air (red), in a simple sealed box of the same volume as Hegeman's enclosure (green), and mounted in its actual cabinet (blue). 

Inside the Model 1A

Each of the 6 quarter-wave stubs in the Model 1A are 1.172 x 3.875 inches (2.98 x 9.84 cm) in cross-section. Their lengths (measured using the centerline method) are: 83.75, 67.0, 51.5, 41.625, 32.3, and 22.4 inches. 

Mathematically, these correspond to quarter-wavelengths of approximately 40, 50, 65, 81, 105, and 150 Hz. Their actual tunings, despite the folds and interactions between stubs that can affect their operation, closely match their calculated tunings. 

I am unable to tell whether the H1 shared the same stub tunings. I assume so. What I do know is that the stubs were each 1.0625 x 3.8125 inches in cross-section, smaller than the later H1A.

Inside the Model 2

The Woofers

The H-Series woofers are hand-made AlNiCo units. The H1/1A woofer is 8 inches (20.3cm). The H2's woofer is 10 inches (25.4cm). The process of making them took place at first in Hegeman's basement, then later in his "factory" in West Orange, NJ.

A sheet of aluminum was clamped over a cylindrical die/form. The form was essentially a bowl, the interior profile of which was the desired profile of the cone. The die was attached to a potter's wheel. As the die spun, a worker used a smooth blunt tool (Peter Hegeman described it as a "rolling ball tool")** to gently stretch/work/form the aluminum sheet from-the-outside-in and down-into the die until it had been formed into the desired shape. 

This process work-hardened the aluminum, producing a much stiffer and more durable cone than the common practice of metal stamping used to manufacture most metal cones today.

The profile of the cones was carefully designed by Hegeman**. The indented rings in the H1 and H2 cones are decoupling rings designed to reduce the radiating area of the cone as the frequency increases, thereby controlling the cone's breakup modes. Think of them as the cone's own built-in crossovers. Hegeman, remarkably, designed them iteratively (by trial and error). As you'll see below, he did a spectacular job.

Also impressive: the cone and coil of the H1A weigh 21.3 grams, with the cone contributing a mere 5.2 grams of that weight. A super light cone for an 8-inch metal-cone driver! Unfortunately, I have lost my notes containing the weight of the H2's cone assembly, but the cone and coil have a similar relationship, with the coil weighing about 4-5 times the cone. 

These super-light and very stiff cones offered, according to Hegeman, exceptional resolution that heavier cones cannot offer.  

** According to a post by Peter Hegeman, Stewart Hegeman's son, he designed the "rolling ball tool" used to form the aluminum cones.  He also claims Hegeman designed the cone in in conjunction with Frank Dickenson and/or Bob Burnet. All fellow residents (friends?) of Glen Ridge, NJ

The woofers in both models operated full range. No crossover at all. This fact might set off alarms in the minds of speaker builders. Aluminum cones typically have horrible break-up resonances that, if left untamed, would absolutely destroy the listener's ears. Not so with the H-Series. Each has one well controlled resonance peak and an otherwise smooth roll-off. Quite the astounding achievement considering how light the cones are, and that their design was arrived at entirely by trial and error by ear (without measurement).

Some marketing materials mention the use of special "finned voice coils" in the Model 1 woofer. I have no idea what this refers to. I have found nothing unusual about the H1A voice coil. And in images of the H1, I also saw nothing different. An early, discarded feature, perhaps?

Also interesting: the first mention of the Model 1 shows a different woofer! It has an octagonal basket. I strongly suspect this was Hegeman's prototype, and that he likely used a Philips woofer as the base for that prototype. 

I'm not aware of any other manufacturer operating at that time that offered octagonal baskets, and Hegeman had a history of using Philips products before (in the Hegeman Standard) and after (the Bookshelf series) the H1 was introduced. Not to mention the H1's tweeter was by Philips.

The Tweeters

The tweeters for the H-Series were off-the-shelf units; two highly regarded tweeters of the time. The Model 1 and 1A featured the Phillips AD 0160/T8, a one-inch mylar dome tweeter. The Model 2 featured an Audax/Polydax TW8B, a 2-inch aluminum-cone tweeter. Later production H1As also used the Audax tweeter. Both models used simple first-order Butterworth crossovers: 

The Model 1 used two 4.7uF tantalum capacitors in series whose summed capacitance was 2.35uF. Note: I have seen photos of some H1A that use as many as three capacitors in series. I can only assume they sum to the same value. 

The Model 2 used a 5.6uF film capacitor.

Troels Gravesen did a nice write-up of the Philips tweeter here.

Both tweeters are housed in a 4.75-inch diameter half-sphere diffuser made of rigid expanded urethane foam.  I painted mine black, but originally, only the flat part of the diffuser was painted. The four legs that attach the tweeter assembly to the baffle are designed in both speakers such that the bottom of the diffuser is 1/4 inch below the baffle in the H1A, and 1/4-inch above the baffle in the H2.

Their Sound

Having owned and heard several examples of H1A and H2, I can say they are like brothers. They're clearly related, but have different personalities. 

The H1A

The bass is extraordinarily controlled, articulate, and clear. Head-turningly so. It starts and stops on a dime. Yet it is not dry, as one might expect. In fact, the bass has a richness to it that usually comes at the expense of articulation. But with the H1A, those qualities coexist. 

As for the treble, I cannot better TAS's description. The H1A has a "translucent, silvery high end” that feels spacious, electric, and extended. That sort of treble often comes with a headache. But not here. The H1A’s treble is not all fatiguing.

The midrange is characterized by a ~5dB dip from 1.5-3kHz. Hegeman, apparently, just did not like that register. Maybe his work with Lowther drivers, which absolutely scream between 1-3kHz, made him hate it? Maybe he was especially sensitive to this range? Who knows! But for whatever reason, his speakers all have a dip there. And this adds some character to their reproduction of audio. 

In some recordings, the dip can make voices sound a little distant or give instruments like horns a slightly sweet sound. In other recordings, everything sounds perfect. Equalizing the dip reveals the opposite effect. Maybe Hegeman liked a dip here because audio engineers get a little too zealous in their mastering of this range and a 5dB dip seemed like a happy medium? Whatever the case, whether you notice the dip is highly recording-dependent, and whether you like it or not is a matter of taste. Many speakers have much larger variations in response.   

The H2

The Model 2 has the same mid-range character as its older, smaller brother. See that description above. The bass and treble, on the other hand, are very different.

The H2 reaches lower and does so with significantly less measured distortion than the Model 1.**  Like the Model 1, that bass is super articulate, super clean. Fleet and quick. Remarkably, head-turningly “fast.” But unlike the Model 1, I would not call it rich. The H2’s bass has a more analytical quality. It’s dryer. Not "dry", just drier. 

If you were to switch from the Model 1 to the Model 2 mid-recording, you would think someone had simultaneously turned down the volume on a hidden subwoofer in the room. But if you continued listening, you would soon realize the bass is still there. In fact, you'd hear that it’s deeper, but also more transparent sounding than you were probably used to. That, I think, is the best way to describe it.

Of course, one man's analytical bass is another man's honest bass. I suspect Hegeman would characterize the H2's bass that way: as more honest than the colored, muddy bass I and most people are used to. And he would probably be right.  

As for the treble. I've got to say, I am not a huge fan of the Audax tweeter. For me, it’s a little too bright, a little too sharp, and lacks the “air” of the Philips unit. But I may be in a minority. Some listening companions consider them, and therefore the H2's treble quality, superior to the Model 1 in every way. Hegeman apparently did, or at least I assume that’s why he started using the same tweeters in the H1A as well. 

And here it’s worth noting an important caveat. My reservations about the tweeters may have less to do their intrinsic qualities and more to do with their age. I have gone through at least 6 pairs of these tweeters trying to find a good one. Even NOS pairs are in bad shape with bad surrounds and floppy spiders. Some even have glue failures in their magnets, causing their voice coils to become clamped in place. 

The pair installed in my H2 are the best I have found to date, but they are still not close to their original specifications (in terms of Fs and other parameters), which makes me think I'm not hearing them as Hegeman would have. My last effort to restore them will be to have his pair re-magnetized, as it seems their magnets might not be as strong as they should be (this was apparently a known factory-issue with some of these tweeters). I will report back if that changes anything.

In the meantime, I’ll have a complicated relationship with these tweeters.

** The H1, to be clear, never had any audible distortion in the bass. Or at least nothing perceived as distortion, but perhaps its higher 2nd order distortion is what gives it that richness compared to the H2? 

Contemporaneous Reviews

Posthumous Development of Hegeman's Ideas

Don Morrison and Morrison Audio

Before he passed away in 1886, Hegeman handed his speaker business over to Don Morrison, who continued building loudspeakers using Hegeman's principles under his own brand, Morrison Audio. He is currently on Model 29. New developments and changes to the design include use of four quarter wave stubs instead of six, and the use of stuffing to control the bandwidth and damping of the stubs. You'll also notice the baffle is no longer slanted.

Below is Morrison's most recent iteration of the Hegeman H-Series speakers, the Model 29, and their matching subwoofers.

KEF and its "Metamaterial"

KEF recently announced to great fanfare the creation of what it calls a "metamaterial" that it will use to absorb the back wave generated by its tweeters. 

The term "metamaterial" conjures up images of a new state of matter, or a mysterious synthetic substance that absorbs sound like a black hole absorbs, well, everything. Nice marketing. But what it actually is, is a series of tuned quarter wave stubs attached to the back of their tweeter. The array of stubs, 30 of them, cancel out the sound radiating from the back of KEFs tweeters, just like Hegeman's enclosures did for his woofers 54 years ago, and with all the same benefits.

Shure: Hegeman for Headphones?

Shure has patented what they're calling a "low frequency extension filter" that they plan to use to enhance the bass response of, presumably, their headphones. What is it? It's a series of tuned quarter wave stubs that load the driver. In this case, the engineers at Shure created an 8 stub enclosure.

You can read the patent and/or an article describing it and its relationship (it’s a copy) to Hegeman's concept below after the excerpt.

What Next?

It will be interesting to see which large audio firm invents Hegeman's ideas next. Stay tuned!