- Introduction -
- The beauty of the Enclosure -
As mentioned below, a broadband driver reproduces a wide range of middle frequencies in an inimitable manner. As is the case with many musical instruments, we use the resonant properties of inner volume and walls in size and material to extend the frequency range towards the bass region. At the same time the enclosure is left open at the bottom and towards the back , so that the sound waves can radiate into the room. In this manner we have recreated the conditions for which these broadband drivers were originally constructed – an open baffle as dipole with an airy reproductive ability as well as resonant amplification.
|The increase in strength of the middle frequencies of broadband drivers caused by physics requires as additional step the broadening of the radiating baffle as well as the bending of the sides of the housing towards the front. This produces a light horn contour. Both measures enhance audibly the lower frequency range, as is also predicted by computer simulations.|
|In logical consequence of all these requirements the shape of the cabinet is dictated by functionality and not by other artificial considerations. The result is a charming design – Butterfly is no box but a wonderful resonance cabinet.|
|The material of the front and ceiling consists of 18 mm thick birch plywood, machined out of a single board and provides together with the tweeter chamber a very stable and vibration-reduced mounting for the speakers. These are fastened in a decoupled way so the four resonating side wings are only activated by sound waves.|
|The resonating side wings are manufactured purely by hand, stand under high tension and are glued to the front, top and the open hind part without adding heat or moisture. For optimal results they are made of triple-layered birch plywood with a solvent-free surface.|
|Depending on room size and furnishings, the best reproduction is achieved when the speaker distance from the back and side walls is at least ¾ m – more is better. At a distance of the listener from the speakers of more than about 2.50 m and an inner distance between the two cabinets of about 1.50 m the speakers need not be placed at an angle. In case the optimal position of Butterfly for maximal musical enjoyment does not harmonize with the living quarters, shifting the cabinets to the correct positions is no problem: they weigh only 9.9 kg. Butterfly has the following dimensions: height 112 cm, width 64 cm and depth 29.5 cm.|
- The wide-band Driver -
|In the last 10-20 years a dedicated group of enthusiasts had enough of the hi-fi norm propagated by diverse magazines. These freaks – often equipped with self-made valve amplifiers of low power – discovered that a flat frequency curve is only half the truth. . It was discovered – rediscovered – that the old radio chassis have a surprisingly broad frequency response.|
|The light-weight membranes made of paper, tightly fixed, stable but with inner dampening, lead to high acoustic resolution and surprising sound experiences.|
|The construction of the speakers with magnets usually made of Alnico, which focuses the magnetic flux into the narrow air gap surrounded by the paper voice coil, is predestined for open baffles or open cabinets. The efficiency of 95-97 dB lies far above the average of modern chassis. As a consequence not even the faintest sounds are lost by sluggishness or compression.|
|Butterfly also permits the fitting of speakers other than the round SABA types, for example oval ones, or those of Loewe-Opta, Siemens, Grundig, Philips, Isophon etc.. Even the larger types of up to 24 cm diameter can be used. The result will always tend towards the highly sensitive, and therefore finest, uncompressed sound unrestricted by encasements. This can already be reached by very small and simple amplifiers.|
- The Tweeter -
|The frequency range of different producers show large variations. They either encompass a range of up to about 20 kHz and consequently need a boost in the bass range, or they are already strong in the bass region, needing a boost in the higher frequency ranges. The combination we would like to recommend and which was successfully tested in the Butterfly design consists of a 20 cm wide-band driver with Alnico magnet and the well-known, open towards the back, 10 cm tweeter, also with Alnico magnet. Both from the SABA production lines of the 50ies and 60ies.|
|Both speakers ideally augment
each other, so that the transfer of music from the one to the other
happens smoothly. The tweeter is coupled only by a condenser,
which omits damping construction elements and avoids phase shifts. The
tweeter is housed in a container without parallel walls, so that no
standing waves occur. The volume of the chamber is chosen so that the
point of resonance coincides with the frequency depression region of
the wide-band driver, reducing the latter.
The condenser can easily be adapted to the requirements of the music room, since it can easily be accessed from the outside. This is often underestimated, since the speakers form a unit with the room – a bare room has a different acoustical behaviour from one with damping materials, a big one is different from a small one etc..
- The Amplifier -
Since the driving amplifier is electrically coupled to Butterfly, the choice of the final amplifier stage is very important. If the „match“ is good, the best fascinating sound experience which Butterfly can provide, is achieved. There are no definite rules for the choice. The best results are obtained by „trial and error“, i.e. listening sessions. The first choice are not necessarily the most expensive amplifiers, but rather the simpler constructions – e.g. two SE-triodes 6AS7G giving 2x10 Watt
shown here is an example of the famous „darling“, as SE-triode an old 1626 valve from US-Army stock and 0.7 Watt /Channel without feedback.
an SE-Amplifier, using the EL84 in triode mode
with 2x1.7 Watt without feedback and only three
influencing parts in
- Conclusion -
|Please make an appointment in
our auditorium in Karlsruhe or at
your home. Please bring
along your wife or partner,
women often have the better judgement! And women notice at once that Butterfly has
a charming shape. Bring along your favourite CDs or records. You will
hear music passages which were
hitherto unknown to you. The wooden
surfaces are available only in birch wood, because of acoustic reasons.
Staining in different colours is possible at a small extra charge.
Butterfly can be delivered with or without SABA speakers. In the latter case, we have to agree on the type, suitability and size of your own drivers. Butterfly is pure handwork and is carefully made in a professional studio according to our design and the quite complicated constructional details. Delivery: about 4 weeks after receipt of your order.
und Urheberrecht: Architekturbüro - archos
- Dipl.-Ing. Niels von der Osten-Sacken
Seboldstrasse 7 - D 76227 Karlsruhe
|Telefon: (+)49 (0)721 - 49 68 66||
Fax: (+)49 (0)721 - 47 626 74