lorcoll

Here is another more compact explanation: The 7-inch midrange drive unit operates in the region between 170 Hz to 2 kHz. Housed in a separate grey painted metal cylinder enclosure, there is no crossover for the midrange driver, in fact it is driven full range. Avantgarde designs the drive unit to have a mechanical filter – high frequencies are gradually filtered off via the moving mass of the cone (mechanical impedance) while the low end extension will be limited by the natural impedance rise of the driver when the frequencies drops to around the fs – the natural ‘resonance’ frequency of the drive unit.

This is what you can read on the Avantgarde web site about the absence of the filter: CDC stands for “Controlled Dispersion Characteristic“. It is a technology developed by Avantgarde Acoustic™ to precisely align the frequency response, the sensitivity of the driver, the geometry of the membrane and the air chamber at the horn throat to the response curve of the spherical midrange horn. This way we manage to avoid any passive filter components in the signal path – routing the music signal directly to the voice coil of the driver engine. Less components, less interactions, less friction ensuring more detail. This is how CDC works: the lower cut-off frequency of a horn loudspeaker is determined by the size of the horn. The larger the horn, the lower the response. Below the cut-off frequency of the horn, the response falls off steeply at 12 dB/octave. The midrange drivers 6 dB roll-off is set to exactly the same frequency thus achieving a total of 18 dB/octave bottom end attenuation. Avantgarde Acoustic™ speakers thus operate only down to their cut-off frequency limit and require no high pass filters. The upper frequency response is determined by the driver itself. However, it can as well be influenced acoustically by the horn. For this purpose, Avantgarde Acoustic™ places a small chamber between the driver’s membrane and the horn throat. The driver does not emit directly but via a small air chamber into the horn throat opening. This air volume operates as a low-pass filter and automatically filters frequencies above the resonance volume of the chamber (at 6 dB/oct.). Avantgarde Acoustic™ now matches the -6dB roll-off point of the midrange driver to exactly the same frequency of the CDC air chamber. Thus we obtain an acoustic attenuation of the frequency response of 12 dB without any passive frequency crossover. No further low pass filters are necessary! The CDC system thus causes the midrange to only operate within its operational band and steeply fall off at the transition points.

Thanks for all replies. The Avantgarde sub has a built-in power amplifier, it sound good but loses the velocity and immediacy of a true horn bass like the Khorn. The midbass horn of the AG has a mechanical cut-off (at 170hz) and doesn't use a crossover filter anymore. I have tried the active bi-amp and I have been never satisfied with the result. Chris, according to your scheme, can I add a series inductor of 0.64mh to the existing 4mh? Then I can add a parallel 47uf cap to the 140uf in the bass bin. Is it right?

I have tried the two mid-high horns of the Avantgarde Duo with the Klipschorn bass bin and the result is incredible: more natural bass with the same extension without any constraint. In a word: exceptional. But I notice an overlap in the mid-bass due to the frequency cut-off of the Khorn network (in the bass bin I have a 4mh inductor and a 140uf capacitor). I need help to modify those values to obtain a second order filter with a cut-off of 170hz (12db/octave). The round mid horn starts at 170hz. The mid-high was extremely good with the standard khorn, but now it reaches a level of purity I cannot imagine before. I use a passive bi-amp: Golden Tube Audio SE-300B monoblock in the mid-high and a CJ MV-50 for the bass bin (the preamp is a CJ PV-8). Thanks for your help Lorenzo

Hi, if you have to sell the AK2 crossovers I can buy them. Ciao from Italy.

I have sent a PM to you

Ok. I'll buy your AK-2's. I'm waiting for your news.

I have a pair of AK2 Khorn and I need another AK2 crossover for an ACR rear system. I have all ferrite components that are fine with the stock AK2 network.

Hi. I need a pair of complete AK2 Crossovers for my rear set of Klipschorn. Lorenzo

Bump... Nobody has a pair of AK2 to sell?

Frzninvt, I know they aren't the best xovers for the Khorns but I already have one pair with those and I need another pair for the rear system.

Thank you, but only now I have seen your reply. I have sent a PM to you.

Hi, I need a pair of complete AK2 crossovers (I live in Italy), for my second pair of Khorns. Lorenzo

Ok, I think I have understand now. I don't speak english well (I live in Italy) and I have misunderstand your explanation for sure. But for the mounting board and rails you screwed the woofer directly onto the motor board with positive effects; why don't have I to remove them? I thought this was fully clear for me. Thank you for the reply. Lorenzo

They use K33P in the 1973 Khorn and K33E (square magnet) in the 1984 speakers.