Have you ever listened to a "Voice of the Theatre"?
Have you heard it with Kilimanjaro-Series field-coil speakers?

Altec Lansing 288

Most of us who’ve listened to a VOTT have shrugged our shoulders. I believe this has to do with the enormous model and cabinet variations in the marketplace. And with the drivers...

The Alnico 5 type permanent magnet, which was perfected during the war, was the most important driver feature in the loudspeaker industry at that time. Cooler operation, no need for separate field supplies, and one-third the weight of ferrite magnets were the advantages. But was there something earlier, something before the much sought after Alnico 5?

I assert that many of the audiophiles and connoisseurs don’t have the faintest idea how good a VOTT can sound. Years ago I was invited to Vienna Vibes, and decided to build a VOTT 825 enclosure precisely to the original drawings using spruce ply instead of pine (because of the disposability). I bought a pair of Altec 1505-B horns and outfitted everything with special designed field-coil drive units. For a network I used my universal model (available) dividing the spectrum at about 1500 Hz. The result was more than impressive; and it was instructional for everybody. The last night, a friend of mine and I listened to the complete Studio album "Nothing Lasts... But Nothing Is Lost" (2005) by Shpongle, an English psychedelic music project. The music was truly "like nothing you've ever heard before", and was real magic!

Voice of the Theatre 825 with Kilimanjaro-Series A515 and A285

Voice of the Theatre 825 with Kilimanjaro-Series A515 and A285
successors are available: A1500 and A3000

The A515 and the A285 (successors A1500/A3000) walk on air in the 825 enclosure. These drivers feel so comfortable in a VOTT that I go into a state of rhapsody when I hear them. Naturally I'm committed to my drive units. 

But what is so thrilling about these 'worn' enclosures? 

Lansing Monitor 500, Shearer Horn

The "Shearer Horn", with drivers from the Lansing Manufacturing Company, had become the movie standard in the late thirties. Virtually every loudspeaker manufacturer in the industry was offering a similar concept. But John K. Hilliard published design papers on the "Shearer Horn" system; and by 1945 the problem of time delays between several drive units was addressed. It was then that John K. Hilliard and Jim Lansing introduced their "Voice of the Theatre" speaker system. 

The principal deficiency identified by Jim Lansing and John K. Hilliard was referred to as a lack of presence. This was attributed to a dip in the mid-bass response between 250 and 500 Hz, radiation from the rear of the speaker system, phase discrepancies due to a long, folded horn path, and cabinet resonance.

VOTT A4, single 210
Altec Lansing Voice of the Theatre, VOTT, A5

The model A5 was for Deluxe Presentation Theaters

The primary solution to these problems lay in the design of a radically new bass horn enclosure. For the first time, a bass cabinet was developed that fully enclosed the drivers and eliminated rear radiation. The enclosure front loaded the bass drivers in a direct, flared horn as opposed to the previous folded designs. This eliminated the mid-bass dip caused by dissipation of higher frequencies in the horn folds. However, the front horn was not large enough to propagate bass frequencies below 100 Hz. The solution was to port the cabinet to allow it to act as a vented enclosure down to 50 Hz. The Academy of Motion Picture Arts and Sciences immediately began tests of the new system that confirmed the sonic improvements, and by 1955 the Academy adopted the VOTT as the industry standard for motion picture playback. 

VOTT A5 (825) and A7 (828)
Seiteneinsicht VOTT 825

Voice of the Theatre 825 cabinet partly opened. You can see the braces and you can also see that the bass driver’s voice coil is located in the same vertical plane as that of the high frequency unit. No phase problems, no delay.

Vertical plane of bass and hf unit means in phase

Such big systems normally have the acoustical centers of their different drivers far apart and the units are often not mounted in a vertical plane. Thus making it impossible to listen to music sitting relatively close to the speakers. This is completely different here and makes the concept unique and precious.  

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A825 with Altec 811-B  horn and Kilimanjaro-Series A801 drive unit…
…maybe the most natural  composition – for sure the smallest

VOTT with A3000 and 1005B horn

Wolf von Langa VOTT 825 enclosure w/white lining and 1005B horn,
A3000 and A1500 field-coil drive unit

Altec 1505-B, 30166 bronze adaptor, Kilimanjaro-Series A285, VOT 825, Kilimanjaro-Series A515, and Altec N-500C

Altec 1505-B multicell horn w/30166 bronze adaptor, Kilimanjaro-Series A285 drive unit (precursor of A3000), VOT 825 enclosure made of fir ply, Kilimanjaro-Series A515 (precursor of A1500C), and Altec N-500C network and others

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Horn braces and glue blocks

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…adjusting the height of the drive unit to have the correct imaging in listening position…

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Comparison of A284 and A285 on an Altec 1505-B horn

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A825 battens and horn curve


Batten position



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Kilimanjaro-Series A285 center pole, pure iron

Kilimanjaro-Series A3000, pure iron, medium current field-coil, aluminum diaphragm 8 Ohms

Kilimanjaro-Series A3000, pure iron, medium current field-coil, aluminum diaphragm 8 Ohms


The first two loudspeakers I ever paid for in my life were Lowther PM2 units. I calculated a rear horn loading and reviewed almost every other similar kind of home construction. Among them of course were the original plans from Lowther UK; but also plans from J. B. Lansing, Jensen, Schmacks, Tannoy, Wireless World, and others. I decided to mount the full range unit on a marble soundboard and succeeded. However the enclosure was modified several times to get matching low frequency response and time behavior. In the end the performance was comparable to that of the large JBL 4333B Studio Monitor; and, in fact, they stood side by side in a recording studio for several weeks, but mine didn’t have the bass overhang and was more detailed and native in its presentation. 

Lowther units accompanied me for years. Over these years I got real treasures as well as garbage. I owned originals-- speaker systems like the early Acousta, the model Audiovector, the Mini-Acousta, the TP1 'D', the Audiovector Auditorium, and built several other systems, like 115, 124, Bicor 200 and 2000, Delphic 500, and horns for use exclusively as mid-high frequency units. The main thing affecting performance, however, turned out to be the cone assemblies. Recently, in developing a drive unit for existing cone assemblies, I made it a point to listen to assemblies from other manufacturers, like AER or Stefan Stamm, who worked for Loth-X years ago. Lowther UK can do a very good job, but they also failed for a long period and delivered awful sounding stuff. Today there is a cone assembly made in the UK which is excellent and based on my experience, very consistent in quality.

Voigt Loudspeaker name plate

Voigt Loudspeaker (high resistive field-coil)

Paul Voigt Mains Energised Drive twin cone (shellac treated)

Paul Voigt Mains Energised Drive twin cone (shellac treated). Look at the centering, isn't it fancy?

Lowther Mini-Acousta PM6Mk1, Acousta 109

The best vintage Lowther „chain“ I listened to in 1992
Turntable "The Source" equipped with a tangential tonearm "Airtangent"
Clearaudio "Insider" moving-coil cartridge
Preamplifier Mark Levinson "ML-7A"
Power amp L'Audiophile "300B Polypropylene"
Lowther "Mini-Acousta" with PM6Mk1

Not only do paper and the glue affect sound quality; the drive unit of course plays a major role. A lot of research and development around the world has gone into the geometry of the cone and twin cone, voice coils, and their electrical dampening; but the magnet assemblies have for the most part remained constant. Of course new lighter magnet materials, far better for commercial applications, have been released.

Lowther Acousta and Acousta De Luxe

Acousta 109

My job was to develop a drive unit that sounded better than permanent magnet devices. In March 2010 I released the AL2. This unit was designed for direct radiating applications and has a maximum flux density of 1.925 Tesla. The motor is comparable in its dimensions to a PM4, so it unfortunately won't fit in a lot of standard enclosures. But if you’ve ever heard what is possible in terms of detail, resolution, timing, and color, you’d accept the burden and partly reconstruct an existing cabinet or build something new. 

prototyp AL2

Prototype AL2
To achieve even higher flux I tested also the theoretical best material (50% CoFe) for very high flux density pole-shoes  (Vacoflux 50), which is extremely expensive and really hard to machine – but pure iron, which also is not a real joy to cut, lathe, and drill, did sound more native, more detailed, and transient speed and purity were retrieved.  

AL2 and AER cone assembly

AL2 with AER (Keller) cone assembly

A5000 drive unit in horn enclosure

Back loaded horn enclosure with perfect cutouts for A5000 drive unit

Christine von Langa - Roedlas 54 - D - 91077 Neunkirchen a. Br. - Phone +49 (0)9192 996926 - E-Mail: listen(at) -
WOLFVONLANGA produces unique field coil loudspeakers and drive units. As a manufacturer we solely use the highest quality materials.
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