A Primer on the Popular Lowther Horn Loudspeaker
There were no high-powered amplifiers in the early 1930s when P.G.A.H. Voigt (Paul Voigt) designed his first loudspeaker with a permanent magnet. As a result, a speaker with very high sensitivity---the legendary Voigt Corner Horn---was born. Powered with the low-output tube amplifiers of the day, a horn speaker could push enough air to fill theaters with sound. Mr. Voigt soon joined up with gramophone manufacturer Peter Lowther; since then, the basic concept of a Lowther speaker has not changed much. The principles of horn loading are still the same, and the return of tubes (especially single-ended designs) completes the picture. Sometimes when I listen to my Lowther system, I am reminded that this design can compete with all kinds of modern, expensive stuff. Tell me, what did we gain in all those years?
Reproducing live concerts in the home isn't really possible. With the help of electronics, one can only hope to get an impression. Though the differences between the acoustical environments of the listening room and the concert will remain, once in a while, depending on the equipment used and the reliability of the recording, we get an impression that gives us the idea (or the feeling) of being present at that concert.
Live recordings often take place with microphones in specific places to record a stereo "image" of the performance at a certain distance. This explains why symmetrical positioning of speakers is important for playback, and also why you have to sit centered in front of them to experience the acoustical environment of the recorded space correctly. A microphone is a point source that records the whole sonic spectrum with only one diaphragm. However, conventional speakers are multiway systems with woofers, squawkers, and tweeters each producing a limited range of frequencies. To reproduce sound correctly, they also require a crossover filter that divides the signal into the ranges needed by each driver, which introduces phase shift. Because a multiway speaker uses more diaphragms than a microphone, it can't reproduce the music accurately.
Using a wideband loudspeaker gives the desired point source without the need of a crossover. Adding an amplifier with a simple wire diagram and just a few components, instead of the complicated high-powered designs of today, will gain even more detail, more music, more reality. Most simplified amplifiers (single-ended, or SE) suffer from a minor problem: their power is often limited to 3-10 watts. If you like to hear the dynamics accurately, you'll need an efficient speaker such as a Lowther horn with a very high sensitivity (greater than 100dB).
There are, however, some disadvantages. One is the lack of spherical dispersion above 12kHz. However, this is not really a problem if we are sitting between both speakers---just point them in the right direction! If you desire to have deep low frequencies, you'll need a rather large (and expensive) horn design like the TP1 or the Opus One. Properly placed in the corner, they will give a nice response (greater than 30Hz with only one speaker!). If you do not have the money or space for these, then you have to live with less bass (nothing below 50Hz). Luckily there are several great-sounding horn-loaded designs for free-standing use. The bass will be slim, but more then enough for the most recorded music. Purists will remind you that there are not many instruments producing frequencies below 50Hz, however.
Personally, I like bass that lifts the music, giving a real foundation to the sound. Therefore I designed the Oris sub, a huge horn (21-175Hz) that really kicks, and gives the music a realistic bottom end. (I do like House or Rock now and then, especially after an argument with the boss.) With this sub I do not need a back-loaded horn for the Lowthers, and so designed several front horns for the range above 150Hz. The latest design is described on my website. A crossover in this range (150Hz) doesn't have that nasty impact that a crossover point in the midrange (250Hz-10kHz) imparts. The advantage of using a front horn is the absence of the somewhat delayed lower mids that occurs in back-loaded designs. The range from 150Hz now comes from one spot (with great dynamics in the lower mids due to the size of the 78cm-overall-diameter horn mouth!).
Every horn is a kind of transformer that controls the excursion of the unit (not flapping around like cones!) and increases the sensitivity with a superb impulse behavior. The bass frequencies gained are detailed and palpable. The upper bass has strength, with drums being very present and realistic. Conventional speakers can't compete with this unless they have very large diaphragms---with the Oris system, musicians are almost present in the room when you close your eyes!
The sound output of Lowther units depends on the strength of the magnet and the moving mass of the diaphragm. The more flux, the louder the unit goes with gained control and detail. The most powerful Lowther, the PM4, has a flux of 24,000 Gauss and a cone with just 6.5 grams of moving mass. This unit has speed (!), and sounds as detailed as an electrostatic speaker. The price for this 10kg unit is rather high due to the costs for materials (AlNiCo/cobalt) and the effort needed to create one. Other Lowther units also have a very high magnet strength/moving-mass ratio, but are optimized for different horn designs. The PM4 is usable only in the larger (or front-loaded) cabinets for a proper balance in sound. Other models could be used in more domestic horn designs.
Due to the high ratio between the magnet/moving mass, the speed of all Lowthers is very high, with great impulse behavior, and they sound very dynamic compared to conventional speakers. Their speed, high sensitivity, detailed reproduction, dynamics, and transparency (even at low levels) give you the feeling that the musicians are more present when playing your favorite music. This clear, open, and lifelike character will steal your heart away, and is why there are many Lowther enthusiasts all over the world, with more entering the fold every day.
Because many Lowther fans build their own cabinets for the Lowther driver and like to share their experiences with other enthusiasts, Lowther England, with the help of their distributors, decided to establish Lowther Clubs worldwide. The clubs communicate with each other to learn or teach about developments regarding Lowther and share cabinet designs and building tips, and are an excellent place for the novice to get started. More information about the location of the Lowther clubs and distributors can be found at Lowther Loudspeakers' own website.
Lowther units aren't cheap, but when you listen to them you may agree that they're worth the money. You don't need extra woofers, tweeters, or (luckily) crossover filters. If you're able to build your own cabinets, you can save even more. Several drawings for all kinds of horn-based speaker designs (using Lowther units) are available, along with the Lowther units, from the nearest Lowther club, or directly from Lowther Loudspeakers England.
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More extensive information about the history and characteristics of Lowther speakers can be found at the Lowther Club of Norway Home Page.
Plans, cabinet kits, and completely built cabinets are also available from the US importer, Lowther-America. Contact Tony Glynn by e-mail for more information.