Satellite Unit

The actual left and right speaker (satellite speakers when combined with a sub woofer) are matched to fit the subwoofer. The lowest frequencies around 40 Hz are therefore sligthly filtered. The satellites consists of a two way speaker system. Since the lowest bass is handled by the Sub, the Satellite can be designed as a relatively small box.

The speakers and enclosure

The mid-bass and tweeter are both from Focal. The mid bass is a 7" speaker with a neoglass cone and a special designed aluminium dust cap. This improves the directivity of the high frequephoto of satellite unit, click to see an enlarged viewncies. This is important to get a smooth frequency response towards the tweeter. The Focal speakers have very smooth repsonses, both on- and 300- off axis. To use the magnetic field and so the force factor of the system optimally, an edgewound voice coil is used.
Like the Sub woofer, the mid bass is in a closed box enclosure and uses the same mathematical model. The box is 95cm high, only the upper half of the box is used for the mid bass speaker. This small volume makes a Q = 0.7 possible with sufficient bass repsonse to be combined with the sub woofer. In the total calculation, this speaker is modelled as a second order acoustical system.

The tweeter is an inverted tioxid dome tweeter with phase plug. The phase plug improves the the directivity of the highest frequency range (around 20kHz). The 300- off axis response only differs from the on-axis repsonse at frequencies above 12kHz. The maximum difference is 3dB.

It must be noticed that in the modelling of the active filters the acoustical phase of the speakers/acoustical listening axis are not taken fully into account. Only the electrical parts are fully calculated. The acoustical phase is corrected mechanically, see below.

Speaker_back1.jpg (23336 bytes)The mid and high speaker are acoustically aligned for phase differences that arrive from a mismatch between the acoustical centres of mid-bass and high. To correct for this mismatch, the tweeter is placed 3 cm behind the front of the mid speaker. As a result the time differences in sound waves originating from both speakers around the crossover frequency, is compensated for. Electrically, the crossover was already in phase.
As such the acoustical listening axes is in a horizontal plane. With a mean point source height of 90cm the speaker is exactly at hearing level. The tweeter itself is placed in a separate housing. This is done to improve high frequency sound directivity and to minimize reflections on the front panel. In general, the box is made as small as possible, all to decrease front panel reflection and improve directivity. Additionally, the mid bass is placed at the top at hearing level. Tweeter and mid bass are only 2 cm apart. This is smaller than the wavelength of the cross frequency (17cm) of the filter. Then, the 2 kHz (crossover) frequency range is still projected to the listener as a single point source.


 

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