JAMO D 8ADD, Owner'S Manual

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Design, D 8CEN
Jamo D 8CEN was developed especially for the enthusiast who makes equally heavy demands on supreme and uncompromising
reproduction of surround sound as for hi-fi listening. As the main job of the centre speaker is to reproduce the dialogue and the action
taking place at the centre of the screen, we have given a high priority to obtaining optimum intelligibility of speech as well as powerful
reproduction of the full frequency range in the Jamo D 8CEN. This means that all the sound reproduced by the centre loudspeaker will
be clear and easy to understand - even at high sound pressures and when the dialogue is accompanied by loud explosions and other
impressive sound effects in the film sound track.
Cabinet
To obtain a “dry” reproduction of dialogue, a low resonance frequency is required - and usually a loudspeaker cabinet will do just the
opposite - which is to increase the resonance frequency !
The effect of the cabinet on the resonance frequency
We therefore used a special cabinet technology called
Aperiodic Chamber for the Jamo D 8CEN.
Other than the “dry” reproduction, this technology also permits using large woofers in a relative small cabinet, resulting in the desired
authoritative sound. Normally, using large woofers in small cabinets will result in a frequency overshoot immediately before the woofers’
low-frequency roll-off point. The consequence of this overshoot is very often perceived as a rumbling bass reproduction.
The effect of the cabinet on the bass reproduction
Therefore, the rear panel of an Aperiodic Chamber (cabinet)
is ventilated through holes constituting around 20% of the
woofer’s total diaphragm area. The ventilation results in an
acoustic short-circuit of the lowest frequencies (it becomes
effective around 200 Hz).
Ventilating the cabinet dampens the overshoot, partly because of the acoustical short-circuit, and partly because of the mechanical
dampening applied to the woofers.
In an Aperiodic Chamber, the diaphragm displacement will increase in the area below the resonance frequency - this means that
although there is a “low frequency short-circuit” the frequency response will extend way below what is required of a centre loudspeaker.
Of course the larger diaphragm displacement calls for customised woofers with well-controlled limits of displacement.
Controlling the ventilation of an Aperiodic Chamber requires critical dampening with a large amount of acoustic absorption foam. This
in combination with the reduced rear panel area minimises the formation of standing sound waves and thereby eliminates coloration/
distortion of the sound reproduction.
The cabinet for the Jamo D 8CEN is manufactured in 25 mm MDF board with genuine veneer. The front baffle is a sandwich construction
consisting of a strong die-cast synthetic shell and 22 mm MDF board.
Tweeter and Midrange
For the Jamo D 8CEN we have chosen a 1" and a 1½” soft dome to reproduce the treble and midrange areas, respectively. Both units are
equipped with coated textile diaphragms and highly efficient neodymium magnets. The advantage of the compact size of the extremely
powerful neodymium magnets is that they can be placed inside the voice coil. This ensures that a highly concentrated magnetic field is
created exactly where it is needed. An additional advantage of this design is that the magnetic stray field is minimal, which eliminates the
need for further magnetic shielding of these units.
Low freq. response in a normal
cabinet (overshoot)
Low freq. response in an Aperiodic Chamber
(natural roll off)
Impedance curve for
a normal cabinet
Impedance curve for
an Aperiodic Chamber
High resonance frequency
Low resonance frequency
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