Kef 104.2 mods for active amplification

[mbahi]

Hellow :

I am a owner of a pair KEF 104.2 full range speakers . I want use it with active amplification , with a digital crossover-DSP procesor ( Beheringer DCX2496 ) . In the first fase I want only use two way configuration with two power amplifers .

This Baffles in the LF section , if you don’t know his configuration , use a two 8 “ woofers in schema called by Kef “Coupled cavity bass loading” ( I am not shure , but i think that this configurarion are a enhaced variant of the basic 4th order bandpass system , with two speakers ( Model B200 of kef ) in push-pull configuration ) . Any knows if this is right ?

I read that this configuration have theorcally the best of two worlds of sealed systems and bass-reflex systems , without his defects .

I put a drawing the acustical configuration of the speakers



The bar of the drawing , are a solid iron bar that fix the two speakers , that teorically miniminze the vibration of the system and are more rigid .

Because the boxes are ready to bi-amplification, I project don’t touch the HF part ( the tree speakers and his passive filters ) by the moment , and eliminate the passive filters of the LF part . I need bypass the passive filters that the speakers have incorporated .

The drawing of the interconnection of the two woffers and his pasive filter .

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But I am not shure how interconect the speakers with the active filter . For example : eliminate all passive elements like the drawing of alternative configuration ? .

Any ideas ?

[sreten]

Hi,

first off you should really repost this in the normal speakers
forum, as this one is for speakers with full range drivers.

The coupled cavity system, so called "4th order bandpass",
is really two second order lowpass and high pass sections
in series. Low bass loading is equivalent to a sealed box,
the upper bass and low mid roll-off is not equivalent to the
reflex loading of low bass.

One feature off CCS loading is its inherent 2nd order low pass
rolloff, this combines with the 1st order filter (top inductor in
your diagram - the rest appears to be impedance compensation)
to give a third order low pass rolloff.

IMO active crossovers are not the way to go - I'd go for 1st order
passive bi-amping with the speakers as standard - with low bass
filtered to the mid/treble and highmid/treble filtered to the bass.
For the 1st case you could reduce the power amplifiers input
coupling capacitor, the second is only slightly more complicated.

/sreten.

[planet10]

A friend has these, and we have discussed the possibility of bi-amping. We also speculated about getting the woofers out of the bandpass box (i have an aversion to them).

I think the idea of biamping them is a good one. !st step would be to outboard the XO so that you can use or not use parts of it (ie in the lowpass remove the inductor and then compare with 7 without impedance comp.

dave