Atelier Rullit Aero 9"
We would like to illustrate an important job commissioned to us by a customer who owns a pair of Atelier Rullit Aero 9 Field Coils loudspeaker. We won’t comment on the speakers; they are outstanding products. Oleg Rullit builds according to the principles of the past, he uses field exciting reels with high tension and low current (on the contrary of all modern producers who use low tensions and high currents). In its top of the range models Oleg handcrafts the membrane, which is beautiful to look at. The spyder is made of Bakelite and it has a four point connection and a leather suspension. Oleg uses vintage materials on every part, from the clamps to the cable used to wrap the reel, even the baskets; at least this is true for all the products we’ve seen in our workshops. Our customer commissioned us the pair of speakers and the power supply for the field coil.
We decided to solve some issues that we think Rullit left unsolved, such as the fastening of the speaker and the cantilever support of the heavy magnet. The use of vintage frames prevents us from fixing them to the front using screws; therefore we realized a 5mm counter flange made of AISI 304 which, pulled towards the front panel, holds the speaker for 360 degrees.
The magnet is then suspended by an adjustable cradle-shaped ‘supporter’, which glides on two M8 stainless steel threaded bars tied to a thick mahogany crossbeam. The latter also reinforces the side panels, pretty much doubling the resonance frequency.
The cabinet’s countertops are supplied directly by Rullit. The cabinet is not tuned and based on our experience it is a dipole. This choice allows to build speakers of manageable size without significantly jeopardizing the quality of the musical performance.
The parameters of the speaker are well matched with the dipole charge; indeed the Qts varies from 0.6 to 0.45 in the field of variation of excitement tension. The sensitivity settles around 95 dB/W/m. The linearity is extraordinary; we are impressed by the response extended to almost 20 KHz and most of all for the absence of destructive interference, usually 3-4 KHz between main cone and whizzer and here completely absent.
The power supply is extremely neat. It offers an adjustable tension with 15 volt steps, between 120 and 165 volts. The adjustment can be made by commuting, through a PALAZZO professional commuter, the secondary of the power supply transformer. The power supply is completely dual, starting from the secondary sides of the transformer. The filtering uses polypropylene condensers and the filtering is inductive.
The internal and external wiring is extremely well made, with silver plated copper wires and Teflon insulation.