JAMO D 400 Description technique - Page 8

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Drivers

Tweeter

The tweeter in the D 4 range, has already been well acclaimed

in Jamo products, as it is used in the Jamo D 7 THX Ultra2

system, winner of the EISA award as "High-end Home Theatre

2002/2003".

However, to suit the exact purpose in D 4, we developed a

new, asymmetric front baffle.

The tweeter was chosen for 3 main reasons:

1. Extremely low distortion

2. Totally freedom of accentuation of "s" sounds.

3. The low range extension

The 1" tweeter features a completely new design of the diaphragm/dome called Dual

Concentric Diaphragm.

The coated textile diaphragm looks like two rings, one on the "inner" and one on the

"outer" side of the voice coil – hence the name "Dual Concentric".

The quite eye-catching centre plug has two

purposes: It is a wave-guide and it clamps the

diaphragm.

The purpose of clamping the middle of the dome is

to eliminate out phasing of the treble at high

frequencies. At high frequencies only the cone area

just around the voice coil is able to follow the voice

coil whereas the middle of the dome typically

breaks up and actually is in opposite phase –

resulting in zero, or very limited output from the tweeter. By clamping the

middle of the dome and only using a ring of the cone area on each side of the voice coil,

the tweeter is able to reproduce frequencies up to 40kHz.

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 resonance frequency for a tweeter is around

1.5k Hz).

cupper, but the copper plating is needed because of its conducting qualities.

The "wire" from the driver's terminal to the voice coil is a thin litz wire. Usually, the voice

coil wire continues to the terminals. However, litz wire features much higher compliance

and therefore it has less influence of the movements of the voice coil.

Furthermore the pole piece is copper plated in the

magnet gap in order to reduce eddy currents. The

purpose of this is to obtain linear impedance throughout

the full frequency range and thus a linear treble

reproduction.

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

D 4 asymmetrical tweeter design