Technical Description Jamo D 7 system
Technical Description Jamo D 7 System Contents: Page 1. General system description 3 2. The products: 2.1. D 7LCR 2.2. D 7SUR 2.3. D 7SUB 5 6 6 3. Driver explanation 3.1. Tweeter 3.2. Midrange 3.3. Woofer 3.4. (Sub) woofer 7 8 8 9 4. Electronics (D 7SUB) 9 5.
General description With the Jamo D 7 System, the goal was to create a THX certified system, where the famous qualities from our two predecessors are kept i.e. a wide and high listening window, design and compact size, but with an even more dynamic, open and detailed sound reproduction. This was done through the choice of very high quality in materials and development of completely new and very powerful driver units.
The most common listening distance is 2 – 4 metres, so we can quite accurately predict the contribution from floor reflections too. Wall mount: The rear wall “amplifies” low frequencies and the floor actually gives a dip in approximately the same range. With a carefully calculated compensation in the crossover we end up with a linear frequency response, down to 80 Hz (-3dB).
D 7LCR / D 7SUR / D 7SUB description D 7LCR D 7LCR is a 3-way speaker with two 5½”woofers, two 2½” midrange drivers and one 1” tweeter, see more details about the driver units below. The compact drivers improves the dynamics: As they weigh less they can move faster. Of course under the precondition that they are equipped with very powerful motors (magnet/voice coil) as is the case here.
D 7SUR The dipolar surround speaker D 7SUR, use the same drivers as the D 7LCR. This is done to achieve seamless timbre matching with D 7LCR and to obtain the same high level of detail in the sound reproduction. D 7SUR is equipped with one 5½” woofer, four 2½” midrange drivers and two 1” tweeters. At both ends of the speaker, there is a midrange/tweeter array with two midrange drivers, mounted close to each other D 7SUR with the tweeter above them - all in a vertical line.
However, under certain circumstances this can create a problem, which is why THX Ultra2 decoders feature a Boundary Gain Compensation filter. This filter compensates for the room influence at low frequencies, as any room amplifies the lowest frequencies. The magnitude of the room’s amplification depends on the room and where you are positioned – normally it increases the closer you get to a wall. This can result in too high bass level from approx. 60 Hz and increasing downwards.
The magnet features a vented pole piece leading into a chamber at the backside. The chamber and the “ventilation hole” in the pole piece are tuned in for achieving the very low resonance frequency at 600Hz (normal res. freq. for a tweeter is around 1.5k Hz). The voice coil former is made of aluminium for optimum heat disposal. The voice coil is made of cupper plated aluminium wire, because aluminium weighs less than cupper, but the copper plating is needed because of its conducting qualities.
The woofer operates without break-ups until 2k Hz, which is far beyond its working range as the x-over frequency is 400 Hz. Instead of a dust cap, the driver features a solid aluminium centre plug. This construction results in effective heat disposal and prevents airflow obstruction when the diaphragm moves. The result is clean, natural and detailed sound reproduction. (Sub)Woofer The 15” woofer features a vented double magnet system and a capton voice coil former, 65 mm in diameter and 40 mm long.
The MFB circuit is comparing the diaphragms movements with the input signal. The transducer at the back of the diaphragm monitors the movement of the diaphragm by measuring the acceleration of it. In the feedback circuitry the signal is converted to a signal proportional to the speed. The speed is highest at the resonance frequency and so is the negative feedback. Consequently, the woofer receives less power in this area, and combined with equalization the frequency response reaches 20 Hz (-6dB).
