First time I became aware of the name Heil was years ago when I reviewed then new Mark & Daniel loudspeakers with their AMT-tweeter. AMT stands for Air Motion Transformer. The AMT is a ribbon tweeter but not a conventional ribbon tweeter in that it moves air in a semi-perpendicular manner utilizing an accordion type of folded diaphragm (made of polyethylene, polyester or polyimide), the diaphragm featuring a series of aluminum struts positioned in a high-intensity magnetic field.
Since then I’ve heard AMT-transducers in Adam Audio, Martin Logan and some other loudspeakers. The AMT element was invented by Dr. Oskar Heil decades ago but, as far as I know, the modern AMT tweeters are further developed, eg. have more powerful magnet s (although construction itself does not require an extra large magnet).
The AMT techniques was first put into use in ESS Loudspeakers in the 1970s, the production continued until early 2000. For reasons or another Dr. Heil wanted to design and construct his own loudspeakers. Kithara is one such loudspeaker still in production made by Swiss Precide SA. In its current form Kithara has existed about ten years and according some sources it has been upgraded several times (the woofer, cabinet, crossover, wiring). The pair I tested was from the mid 2000.
Heil Kitahra (35kg) is easily explained. It’s 110cm tall 2-way speaker. The AMT/AVT element is in a wooden console radiating sound to both directions (dipole). Just below the Heil unit there’s a reflex loaded 10 inch woofer. The woofer looks straight at the ceiling and the port is at the bottom of the cabinet 180 degrees to the floor. The AMT element handles frequencies from 700Hz up, ie. five octaves. The bass part takes care of the band 28Hz – 700Hz. The sensitivity is said to be 94 desibels (W/m).
I drove the Kitharas with Brinkmann Marconi hybrid-preamp and Brinkmann 250/150W mono blocks. Irrespectively of Kithara’s high sensitivity I got the impression that such transistor amping would be the way to go with these speakers. The announced nominal impedance is 4 ohms but I’ve seen smaller figures too.
In a large slightly sonorous space Kithara’s tonal balance turned out to be quite well studied and considered, and that impression remained throughout my listenings. The sound is clearly not a result of the fantasy world of a yound speaker designer.
Something about the sound told me that the tone was occasionally darkish, from the 80s so to speak, but that this quality was not due to excessive bass but slightly rounded top end. This didn’t disturb me at all with eg. classic music but was more distinctive with certain studio material.
The HF department wasn’t subdued in a standard way – no frequencies were left out; the sound was just differently bright than with some other ribbon tweeters. To reproduce all hiss on the recording is not a preference of this speaker. The listening height somewhat affected the impression because the radiation pattern of the tall and narrow Heil unit is horizontally wider than vertically.
Would Kithara have benefitted from a super tweeter? Perhaps, perhaps not. Even without it the sound was spacious and airy.
Bass was generally fine. I personally might have taken away one two decibels here and there but no serious fault in the bass. Plus I was convinced that Kithara is more room friendly than speakers with forward shouting bass.
Intellectually the most interesting thing to hear was well Heil managed to integrate his element with the woofer’s output. To what extent the both coincide (or the opposite), and if such cancelation happens especially around the crossover frequency we know how that sounds. It all depends on the distance and placement of the drivers.
My feeling was that the integration isn’t perfect, what is, but that the speaker is capable of quite seamless performance after all. The most effective way to detect problems in this regard is to listen how logically music proceeds and if there are points of discontinuity.
But, but. With music the 700Hz - 7000Hz range showed absolute delicacy, simply great. Lutes and guitars were celebrating with precise attacks, purity of the sound, sumptuous timbres. Thanks to its AMT unit Kithara made many music very, very listenable. If the midrange and beautiful harmonics mean anything the Heil Kithara showed what a loudspeaker can do to support them in the best possible manner.
All in all, the Kithara accepted music with a wide margin, from Bach to Nightwish, always typifying certain level of quality and always remaining favourable to the music played.
To be able to try the Kithara was a highly positive experience. It’s a quality loudspeaker both technically and sonically and with the price of 5000 euro, I think, also competitive. With the money a man gets a speaker that deviates from the mainstream in many good ways, and one that shines most with big spacious acoustic music, but does not shy away heavier studio material either. The speaker never throws the music onto the listener's face.