Given the small stereo perception below 150 Hz, the 3A Triphonic system proposes to mix the left and right channels in one cabinet. Of course the mid-high ways are not mixed, the separation of ways remaining identical to the traditional stereo system.
The advantage here again is to reduce the volume of the speaker. The « Satellite » in such a system no longer having to reproduce low frequencies, it may be of reasonable size.
Thus 3A invented the « subwoofer », principle widespread today.
To combine helpful with pleasure, this subwoofer will naturally take the form of a coffee table, equipped according to the models with 2 to 4 slaved 27 cm speakers (see Acoustic pressure feedback). This is the « Sub Bass » Triphonic table (30 Hz to 3 dB). This table can be incorporated into any existing stereo systems, however it comes with two types of stallites developed for the occasion, the Atom 2 (2 ways) and Atom 3 (3 ways).
Ten years later, 3A offers the « Stele Sub Bass » (SSB), of reduced dimensions, and once again innovative with the principle of « Push-pull » in symmetrical load (see Push-pull). This new Triphonic integrates two incredibly small satellites (see TR60 & TR100)...
• Input impedance : 8 Ω
• Rated power : 80 W
• Maximum power : 120 W
• Sensitivity (for 1 W at 1 m) : 90 dB
• Bandwidth (±3 dB) : 40 to 200 Hz
• Cutoff frequency : 200 Hz
- Boomer : 2 x 21 cm 3A
• Dimensions (H x W x D) : 38 + feet 4.5 cm x 30 x 30 cm
• Unit weight : 15 kg
Subwoofer in « Push-pull »
3A patent filed January 13, 1988 n° 88 00 317
Synthesis
This is a symmetric (or asymmetric) load wherein are mounted two speakers facing each other. The back side of the upper speaker looks at a fully enclosed load damped by some absorbent material while that of the lower speaker looks a bass-reflex load where the vent is located at the base of the enclosure. Each of the two speakers respectively receives the modulation from the right channel and the left channel. They are connected in parallel with crossed phases, so when one ahead the other back, and vice versa (push-pull) ... Thus they accept twice the power of a unique speaker with full compensation of non linearities.
This push-pull mount with shifted coupling allows to smooth the parasitic resonances and to down very low in frequency with excellent linearity for a reduced volume. By this principle of load, the cut is made acoustically and so there is no need of a lowpass filter, hence a better impulse response and a damping factor close to ideal.
Art & Acoustique Appliquée
3A patent filed April 13, 1977 n° 77 11 085
