The Legacy of Paul Voigt

Plus

Harman Kardon Citation X and Eico HFS-2 Speaker Systems
plus Hegeman, Lowther and Brociner

By Roger Russell

These pages are copyrighted
No portion of this site may be reproduced in whole or in part
without written permission of the author.

 

 

 

In the Beginning

 

Paul G. A. H. Voigt was born in London on December 9, 1901. He was educated at Dulwich College and University College, London, receiving a B Sc. degree in electrical engineering in 1922. Among many other audio contributions and 32 patents, he can be credited with the first high flux energized speaker drive unit and horns using the “Tractrix” contour. While with the Edison Bell Works in London, Voigt started work on his loudspeaker. When the company went under, in 1933, he set up his own company “Voigt Patents, Ltd.” based in Sydenham, London. Under agreement with Bell, he remained the owner the 19 patents that he received on his ideas. The domestic corner horn (at the right) was released in 1934 and set a new record for high quality sound reproduction. This unique design gave an extremely lifelike non-directional presentation with the sound entering the room at a height between 3 and 5 feet from the floor.

 

A unique feature of the Voigt designs is the use of a single driver that covers the entire frequency range. This is done using a mechanical crossover, commonly known as a whizzer. The driver then consists of a main cone and a short cone both of which are attached to the same voice coil. Bass frequencies are radiated by loading the rear of the driver with a folded horn enclosure. In addition, Paul took great pride in designing the drivers with very high efficiency and concentrating  very high flux density in the magnetic gap. This was accomplished using a very small gap making the centering of the voice coil very critical.

 

About this time Paul met O.P. Lowther from the Lowther Manufacturing Company and eventually this resulted in a merge between the two companies.. This became Lowther-Voigt Radio.

 

During the war, Paul was kept busy maintaining his horn speakers installed in cinemas. After the war, priority was given to the design of a new driver using new magnet materials and drive unit having a flux density of 18,000 gauss (1.8 tesla). It was released in 1949

 

Unfortunately, due to poor health and slow sales, Paul decided to move to Canada with his wife in 1950 and set up North American sales for his new designs. The company folded because of the Korean War. He taught electronics for a while and then moved to Ottawa and worked for the Canadian Government in Radio Regulations. He retired in 1969 and pursued other interests.

 

He died on February 9, 1981 leaving a legacy of his inventions. Geoffery L. Wilson wrote a glowing memoriam about him in the April 1981 issue of the Journal of the Audio Engineering Society. Paul Klipsch contributed and mentioned that Paul Voigt was one of the unsung pioneers in audio. Donald Aldous also write a nice memoriam in the June issue of Audio magazine. More information can be found at the Lowther Museum.

 

I did get a chance to speak with Paul Voigt following a 1974 Audio Engineering Society (AES) meeting in New York City. We talked about several things but I gathered that he had some reservations about how his invention was being used at Lowther and things were not as amicable as I was led to believe. The next day he was presented with an honorary membership in the AES. I also found it strange that neither memoriam mentioned his association with Lowther, although other companies were mentioned.

 

Meanwhile, Donald Chave, who was previously Lowther’s chief engineer, had bought the company after World War II. He finally developed the PM-1 driver using the Voigt cone assembly. Before Paul had left it was agreed that Lowther would produce the domestic corner horn under license. About 400 corner horns were produced between 1934 and the early 1950s. Chave later expanded the products and developed new drivers based on the early Voigt units.

 

Stewart Hegeman was also involved with Lowther in the early 1950s. In 1951 Lowther released the incredible "Lowther Hegeman" reproducer, which was three-times the price of a Lowther Voigt domestic corner horn. The enclosure was four feet wide, four feet tall and two feet deep.

 

The newly-developed PM4A drive unit was used inside a large horizontal plaster horn, giving an amazingly wide dispersion of mid and treble frequencies. It was a result of a collaboration between Stuart ( British spelling) Hegeman and Donald Chave of Lowther. Later in the 1950s, Hegeman and Chave also developed the Harman Kardon Citation X driver.

 

 

 

Lowther still exists today although similar drivers are now being sold by other companies as well/

 

 

 

Brociner Model 4

 

My first audition with the Voigt design was when I heard the Brociner Model 4 speaker system at the 1955 New Your Hi-Fi show. The system was used in the Tetrad diamond room. I was very impressed with the sound. The design was very similar to the Lowther TP-1 speaker system made in England. Although the Model 4 was only playing mono, it sounded very clean and smooth. It did require corner placement. I was only a student then and could not even afford one, let alone two.

 

Victor Brociner had a business in New York City and made amplifiers and preamplifiers plus the Model 4. He later went to work for University Loudspeakers in White Plains, NY. I was actually interested to get a job there since it was only a few miles from home but they were not hiring. After an evening session at the AES, Victor told me University was an ulcer factory. Then University moved to Oklahoma and soon Victor started his own speaker company called Avid, based in Rhode Island.

 

 

In 1952, the Brociner model 4 had been demonstrated in room 602 at the Fourth Audio Fair in the Hotel New Yorker from October 29 to November 1. Other Brociner equipment included the Brociner A100 preamp-equalizer, CA-2 control amplifier, UL-1 Ultra-Linear Williamson power amplifier, Model 250 Transcentent 3-way corner reproducer and the Ductflex coaxial speaker cabinet, In attendance were Victor Brociner and A. Stewart Hegeman. Right next door in room 606, McIntosh Engineering Laboratory , Water Street, Binghamton, NY was demonstrating their audio amplifiers. In attendance were Frank McIntosh and Gordon Gow. In attendance for Harvey Radio in room 631, among others, was James Carroll.

 

 

Harman Kardon Citation X Loudspeaker

 

Then, by 1959, I had graduated from RPI and had found a job in audio at the Sonotone Corporation in Elmsford, NY. About that time, stereo had begun to take root and by then the Harman Kardon Citation X came along. That was when I first met Stewart Hegeman, the designer, at the 1960 New York Hi-Fi show. The mids and highs sounded very smooth and reminded me very much of the Brociner Model 4. I was so enthusiastic about the sound of Lowther drivers that I ended up buying a pair. A full page ad for the Citation X describing the system was published in the December 1960 and March 1961 issues of Audio magazine

 

Today, the Citation X loudspeaker is relatively unknown and probably forgotten by audiophiles who even heard about it. Hegeman is better remembered for his other designs of tube equipment such as the Citation I preamplifier, Citation II power amplifier and Citation III tuner plus the multiplex adapter, and the Citation IV preamplifier and Citation V power amplifier. He was also relatively unknown concerning his Model 1a omni-directional speaker. A conversation with Hegeman and Norman Eisenberg was published in High Fidelity magazine in February, 1961.

 

 

Here is Stewart with the Citation I preamplifier and a Citation II amplifier in the background. This is from ads in the September 1960 and May 1961 issues of Audio Magazine. Note the slide rule in his right hand. What we engineers had to go through in those days. I assembled a Citation I kit back in 1960 during my stay at the Research and Development Labs at Ft. Monmouth, NJ.

 

 

The Citation X loudspeaker departed further from the Voigt and Lowther TP-1 designs. The new principle was aimed more at achieving omnidirectional sound. Although the driver faced upwards, it was not horn loaded the same as the TP-1 and radiated upwards as well as side to side and front. There was no rearward radiation and a board with acoustic material was used to absorb rear radiation. This may have been a practical consideration and it meant the system could be placed against a wall and not in the corner. Radiation was more like into a quarter of a sphere.

 

 

The Citation X CL-1 driver is a modified Lowther PM-6. The square, cast aluminum basket is 8” on a side. The rubber surround has the roll facing inward. The main cone and canoe shaped whizzer are both made of paper. The effective diameter of the driver is 6-1/2”. Three specially shaped pieces of aluminum foil are glued to the main cone. Stewart told me the aluminum increased the velocity of propagation along the cone. Apparently, it improved the high frequencies. The whizzer is attached directly to the voice coil and covers the range from 2 kHz to 7 kHz. The driver weighs about 6.2 pounds.

 

 

Two black binding post terminals are provided to make connections to the terminal board at the rear of the system. The driver is mounted on a 1/8” thick fiber board to space the magnet further away from the round hole in the cabinet behind it. This allows the rear of the cone to couple better to the split, slot-loaded conical horn. Each folded section of the horn is 7-1/2 feet long. The slot at the end of the horn is said to reduce phase shift within the horn. The distance from the back of the mounting board to the back of the magnet structure is 4”. The enclosure is 20” wide, 14-3/4” deep and 36-1/2” high.

 

 

 

The design of the special CL-1 driver was a joint effort between Donald Chave at Lowther and Stewart Hegeman  Harman-Kardon.

 

 

When mounted in the system, the driver faces upwards and has a plaster mushroom-shaped stabilizer that places a damping load on the cone and acts as a diffuser and distributor of the very highs. The stabilizer is attached to the pole piece with a metal rod that is threaded into the pole piece. It is 6-3/8” high and 5-1/4” in diameter at the widest part. Being made of plaster, it weighs 1.8 pounds.

Warning! A giant stabilizer has suddenly appeared in Altamonte Springs, FL close to interstate 4. It is suspected to be of extraterrestrial origin. Scientists are investigating. This may be of particular concern for drivers that are passing by as it not only could cause damping, requiring windshield wipers and headlights, but could also affect the distributor at high speeds.

 

The Citations that I bought in 1960 have a beautiful mid-range and highs, but they don’t handle any deep bass at higher power. The Lowther drivers soon developed rubbing voice coils. The surrounds and spider centering material were flat closed-pore urethane foam that didn’t keep the voice coil centered very well. The coil gap is extremely small and provides 17,500 gauss flux density. The magnet is made of Ticonal G, which is very strong.

I took the drivers down to Harman-Kardon in Plainview, Long Island and Leon Kuby replaced them for me. The new ones came with thin rubber surrounds. This eliminated the rubbing, but they still didn't handle any power at low frequencies.

I am curious after all this time to listen to them again and hear if the sound of this system and the Brociner system are still as captivating as they were for me back in the 1950s and 1960s. The Citation X systems originally sold for $250.00 each.

 

 

 

 

 

On the back at the top of the system there is a terminal board made of masonite. It contains a barrier strip for connecting the system to the amplifier. There is also an acoustic balance control to adjust the amount of higher frequencies relative to the low frequencies. The serial number can barely be seen on the white label. The fuse is 1-1/2 amp fast blow and a spare is provided also. System impedance is 16 ohms.

 

On the other side of the board the acoustic balance control can be seen with a large coil. These two are connected in parallel and they are in series with the driver. The wire wound control can be varied in resistance from 20 ohms down to zero ohms. This in turn will vary the mids and highs.

 

 

Some systems ended up like this.

 

 

 

Recently I was contacted by a person in Canada who had found one but it was in very bad condition. Most of the top wooden frame was damaged or missing. The above picture shows the view at the top front. The early systems came with a plaster “mushroom” stabilizer but later versions came with a Styrofoam stabilizer that did not follow the mushroom contours as accurately. A rod through the center of the mushroom screwed into the driver pole piece and held it in place. On the board at the rear is a potentiometer and large air core coil. This is used to adjust the amount of high frequencies relative to the low frequencies.

 

Because the phasing plug is in the center, no dust cap can be used to keep dirt and magnetic particles from accumulating in the extremely strong magnetic gap. Harman Kardon did offer a bag made of crinoline, something like fine window screening, to cover the driver and plug assembly. It was acoustically transparent but it may not have stopped fine particles from getting in. On the other hand, it would at least keep roaches out!

 

 

The above picture shows a second board with a fiberglass absorbing material. This is used to absorb radiation to the rear of the system and prevent reflections from the coil board and a wall if the system is mounted against a wall. The grille cloth is woven plastic and acoustically transparent.

 

 

The bottom portion of the system is finished in oiled walnut. Because of all the internal paneling, the system weight is about 90 pounds.

 

 

 

Courtesy of Rodrigues

 

 

My solution in 1962

 

 

Because the Citation X bass handling was inadequate for my use, in May 1962, I imported a pair of Lowther PM4 drivers directly from Donald Chave at Lowther in England. Flux density for the PM4 was 22,000 gauss, about the strongest magnetic gap ever used for a speaker. The design followed the original design of Paul Voigt. The PM4 drivers came with a short stabilizer shown below. It appears to be made of Bakelite. I decided to purchase two mushrooms from Harman-Kardon but by then they had changed them from plaster, which was used in the early Citation X, to Styrofoam. I didn't know if this would be as good because the shape had changed slightly but I decided to use them anyway. The driver and mushroom face upwards as in the Citation X and I sealed around the edges of the driver basket and the enclosure with Mortite. I decided to supplement the bass using an AR3 woofer and the system is further described on my History Page.

 

Hegeman 1a Speaker System

 

These are the only pictures I have found and were copied with permission from the owner who has since parted with them. He said the imaging was unsurpassed. By coincidence, Hegeman Labs was in East orange, NJ, the same town as United Speaker Systems that was making speaker systems for Fisher and McIntosh.

 

This system pursued the idea of omnidirectional sound even further and radiated a hemishphere. Of course, it meant that the system needed to be placed out in the middle of the room for best performance.

 

 

 

 

 

 

 

Morrison Audio

 

The legacy of the Hegeman 1a speaker system continued at Morrison Audio in Toronto, Canada. By 1977, due to health and financial problems, Hegeman transferred the remains of his company to Don Morrison, who continued with the 1a concept. The latest version is the smaller Model 7, a two-way omnidirectional design. The 4.5” woofer faces upward into a hemispherical reflector. Mounted in the top of the reflector is a small tweeter that also faces upward into a smaller spherical reflector. Crossover frequency is 8 kHz. A subwoofer is also available for this system. Other larger models have been available using the same design principles.

 

 

Eico HFS-2

 

 

 

The HFS-2 may have been a predecessor to the Citation X. They were both designed by Stewart Hegeman. The HFS-2 made the front cover of the September 1958 issue of Radio-Electronics magazine. A 3-page article was written about the system by Stewart Hegeman and Norman Eisenberg.

 

The system was smaller but had the same dual slot loaded horn for the bass. However, there were two drivers, a woofer and a tweeter. They both faced upward and the same ideas were used  to approximate a hemispherical radiation pattern with minimum phase changes.

 

In this design, the edge of the tweeter cone is cut to provide a constantly varying distance between  the cone’s edge and the voice coil. This is claimed to broadband the tweeter response while smoothing it.

 

It is further claimed that to enhance response further for mid-range and highs, a rigid and non-moving acoustical loading cone or plug is inserted concentrically within the radiating cone. This plug forms an air gap between itself and the inner surface of the radiating cone. The gap acts as a ring radiator.

 

An additional benefit from this plug is that it obviates any effects of response peaks or instability which might be caused by radiation diametrically opposite points on the inner surface of the radiating cone.

 

One of the advantages of this design and the Citation X is that since the drivers face upwards, response can remain uniform 180 degrees around the system.

 

The HFS-2 was advertised in a July 1958 Eico brochure. It includes many technical specifications.

 

It was available in mahogany or walnut for $139.95 or in a blond finish for $144.95

 

 

 

 

 

The HFS-2 also made the cover of the April 1960 issue of Audio magazine. Note the Citation I preamp and Citation II power amplifier in the cabinet.

 

 

Realistic Nova T-1 Tweeter

Radio Shack

 

 

Here is a relatively unknown tweeter designed by Stewart Hegeman for Radio Shack. The date of manufacture is unknown but may have been in the late 1950’s. The design is similar to the tweeter used in the Eico HFS-2. The cabinet measures 6-1/4” high, 10-1/4” wide and 6” deep.

 

 

The driver is 5 inches in diameter. Hegeman made several modifications to the original driver. Three aluminum foil piesces have been attached to the cone plus three strips of foam damping. The foam pieces may have been very soft originally but today are very stiff. As in other of his designs, the aluminum foil is said to increase the propagation velocity across the surface of the cone.

 

In addition, a thin ice cream cone-shaped tweeter is attached directly to the driver voice coil. It is extremely fragile. The edge is folded over to reduce resonances in the foil. A center aluminum foil cone is filled with expanded urethane foam that is rigid when cured. It remains stationary and is attached to the driver pole piece. Both pieces are cut at an angle so that the lower portion faces the front. In addition, a narrow piece of black tape has been added to the outside of the aluminum cone.

 

 

The driver is held face-up by three threaded stand-off rods. A recess is cut in the bottom of the cabinet to accommodate the depth of the magnet. The driver basket was originally the open frame type but black tape has been used to cover the open portions of the frame. The connecting terminals are towards the rear of the system. The driver is made by R&A in England. It is type 860P Mk. II. Flux density is 10,000 gauss. Several patent numbers are listed on the magnet structure for Britain, USA and Netherlands. In the late 1950s, R&A drivers were sold in the USA by the Ercona Corporation, 16 W 46 St, New York 36, NY

 

 

Two of the system input terminals are connected to the tweeter through two 8 mfd capacitors in parallel and then to a 30 ohm series wirewound control. The second pair of terminals goes to an external woofer through a series 1.3 mH coil. The control is used to adjust the amount of high frequencies. The system impedance is 8 ohms. The crossover component values indicate a crossover frequency of about 1 kHz. As in the Eico HFS-2, radiation from the rear of the tweeter reflects from the masonite back of the enclosure that contains the crossover network and terminals.

 

 

 

 

Harman Kardon Citation Thirteen

 

Harman Kardon continued with the omni sound and wide response approach. No mention was made that Hegeman was involved with this design but it may well have been.

 

The system contains three 7-inch woofers, one 1-1/2” dome mid-range and two 1” tweeters all mounted on a board tipped forward at an angle of 14 degrees. Response is claimed to be30 t0 20kHz. Dispersoin is essentially non-directional. Size is 29-1/2” high, 20-5/8”” wide and 14-3/4” deep. Weight is 75 lbs. Original selling price is $295.00

 

The three 7” woofers drive a dual chamber reflex system which terminates in two unequal length tuning tubes, one for each chamber, thus staggering the system and extending aas well as smoothing low frequency response. The crossover slopes are 6dB per octave, causing minimum phase distortion.

 

Mid-range and tweeter controls are provided to adjust for the amount of middles and highs. In large rooms, the controls can be used at maximum or flat response but in smaller rooms the controls need to be reduced to some degree. At some frequencies impedance drops to about 4 ohms.

 

The Citation Thirteen was reviewed in the May 1972 issue of Audio magazine and the February 1972 issue of High Fidelity magazine.

 

 

 

 

 

Harman Kardon HK-50 Omnidirectional Loudspeaker System

 

 

This is an interesting but small speaker system marketed in 1969. It is 11-3/4” by 11-3/4” and 18-1/4” high and weighs 22-1/2 pounds. This little gem radiates all reflected sound. The 8” woofer and 2-1/2” cone tweeter face upwards into a specially contoured Styrofoam cone shape. The sound radiates from all four sides. The top, although appearing to have a round grille in the center, is actually solid wood, perhaps for decorative purposes.

 

 

 

The Styrofoam reflector is held in place with two pieces of wood stapled to two wooden blocks. Note the extra contour in the right rear of the Styrofoam. This is located above the tweeter. The apex of the cone is about 4-1/2” above the base. Although the 8” driver is located off center in the cabinet, the apex of the cone is in the center of the cabinet.

 

 

Each side of the wood-frame grille has four large openings of equal size. The material is made of multiple-layer plywood and over the years has separated.

Some of the thin laminates were rattling around inside when I received the system. There is no indication of which side is the front but judging from the terminal location under the cabinet, the bottom of the above picture is the rear of the cabinet. The system is a sealed type and the drivers are sealed in place with Mortite that is now as hard as a rock. Even the mounting screws are covered.

 

 

The terminal plate is located in a corner of the bottom of the cabinet. The speaker terminals are either screws or an RCA phono type socket. System impedance is 8-ohms. An adjustable brilliance control is for the tweeter level.

 

Unlike the Eico HFS-2 and Citation X that have a closed back to allow placement against a wall, this system must be placed away from the wall or other reflecting surfaces. However, it is this very requirement that creates an advantage of better sound distribution. First listening to the system revealed a very spacious sound but the low frequencies were very limited by today’s standards. A review of the HK-50 was published in the June 1969 issue of Audio magazine.

 

 

Reflections on Reflections

 

The design of the Citation X, HFS-2 and 1A systems advance the theory that much of the sound that we hear in a concert hall is reflected sound. Both Hegeman and Bose have concluded that the speaker system should also accomplish the same thing in the living room. Their discussion also acknowledges that a point source and therefore radiation from a pulsating sphere is ideal. So then, the sound radiated from the speaker should have a wide dispersion radiating both vertically and horizontally all around the room. There are fatal flaws in this reasoning. A living room is not a concert hall! What a surprise. I have been in concert halls and they are nothing like my living room. For one thing, the concert hall is much larger with longer arrival times and has longer reverberation times. There are many seats in the concert hall filled with people. Hopefully, there is no one coughing behind you, rattling papers or talking during the concert at home.

 

Recordings usually contain information of the concert hall environment whether it is natural or artificial. Even if the recordings were recorded in and an anechoic chamber having no reflections at all, the living room acoustics do not duplicate any concert hall acoustics that I know of. By adding the living room acoustics to the recorded concert hall acoustics yields double acoustics and is then partly dependent on individual living room furnishings, surfaces, room construction and dimensions. Different rooms produce different sounds for the same speakers. Of course, there is the silly example of trying to fit all the symphony orchestra musicians and their instruments into your living room.

 

Going to the extremes, if a pair of speakers was placed in a large anechoic chamber, there would be no reflections at all. This gives the impression that you are listening to something more like headphones. Despite any influence from stereo crosstalk, almost all of what is in the recording can be heard.

 

The other side of the story is that when listening directly to a loudspeaker system, when it is facing you, the directional characteristics play a very important part. If the directionality is not smooth and uniform around a loudspeaker throughout the audio spectrum, errors can be heard. This is where the ideal point source of sound might come in handy. Despite the negative criticism, indirect (reflected) sound does present a pleasing quality with less harshness sort of like when you are listening in the next room. In a similar way, a full range system mounted in the rear deck of a car produces reflected sound from a slanted rear window and also has a pleasing sound. The price paid is accuracy in coherence and imaging compared to the original performance or at least the way it sounded to the recording engineer and producer in the recording studio. If a system that is designed to face forward is directed towards a reflecting surface instead, such as a wall, it can cause an indistinct and blended sound. In addition, if the power response of this system is not uniform, the overall sound balance can be altered compared to the sound of a system with good dispersion that is facing forward..

 

On the other hand, many of the Voigt systems including the Brociner Model 4 and Lowther TP-1 were different and did not intend to produce spherical or hemispherical radiation. They had the advantage of using horn loading and indirect sound within the enclosure but then directing it in a controlled fashion. For instance, the Brociner Model 4 has a driver facing upward into a horn loaded reflector that then projects the sound forward at about ear height when you are sitting. Not only are the imperfections blended or averaged but also the room influence is reduced.

 

If the same dual cone driver were mounted in a baffle facing forward, such as the PM6 in the Lowther Acousta, the sound would not be the same at all. First, there is no mid-range horn loading, except between the phasing plug and whizzer. Second, the mid-range dispersion tends to be not uniform. Third, radiation would also be directed towards the floor and ceiling causing reflections that could create interference with the direct sound.