Avantgarde Duo mid-high horns with Klipschorn bass bin: How to modify cut-off frequency

[lorcoll]

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

[Chris A]

Assuming that your Duo midbass/midrange input impedance is about 4 ohms at 170 Hz (which is probably not going to be a good assumption--as it could be almost anything between 2 and 100 ohms), here is a second order passive crossover circuit for the Khorn bass bin (5 ohms assumed for the input impedance) and your Duo midbass horn:

 

 

Chris

[Panelhead]

  The passive biamp might match up better if you were using the same amps top and bottom. The current setup is running both amplifiers full range into bandpass limited speaker load. 

  If you can, look into a software crossover to bandpass filter the amplifier and not the drivers. I use one that allows adjusting; frequency, slopes, levels, and overlap. All done with 64 bit precision. 

  The Duo may require a little padding down to match the output of the bass cabinet. 

[JohnA]

Since you're biamping, I'd recommend an electronic crossover.  The AK Series crossovers have built-in eq.  I think it's mostly in the 200 to 400 Hz range so you may not need any thing special, but an electronic xover could supply any that would be needed either to blend with the mid horn or for the room.  I would LOVE to hear a set of AvantGarde speakers! 

[lorcoll]

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?

[glens]

11 minutes ago, lorcoll said:

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?

 

That would net you the values given.  Whether they're actually correct for what you need is another question in itself.

 

14 minutes ago, lorcoll said:

The midbass horn of the AG has a mechanical cut-off (at 170hz) and doesn't use a crossover filter anymore.

 

What?

[lorcoll]

1 hour ago, glens said:

 

The midbass horn of the AG has a mechanical cut-off (at 170hz) and doesn't use a crossover filter anymore.

 

What?

 

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.

[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.

[Chris A]

3 hours ago, lorcoll said:

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?

Yes, inductors in series, capacitors in parallel for simple addition of their combined values. 

 

Remember that there are at least two assumptions being made in the above circuit diagram: input impedance of the loudspeaker drivers/horns (5 ohms for the Khorn bass bin @ 170 Hz, 4 ohms for the midbass horn/driver at 170 Hz--which probably is way too low since you say that it naturally rolls off on the low end--not using an electrical crossover).  

 

In order to get closer to flat response, some form of measurement of the output vs. frequency is needed.  I recommend a calibrated USB microphone, then all the guesswork is eliminated. 

 

Chris

[Chris A]

Note that the second order filter will introduce 180 degrees of phase shift on the Khorn bass bins so you might need to reverse the polarity of the leads if you can't move the midbass horn and treble horn farther back... about 1 metre.

 

Chris

[Bosco-d-gama]

I would love to see photos of this rig...........

[glens]

7 hours ago, lorcoll said:

This is what you can read on the Avantgarde web site about the absence of the filter:

 

...

 

Thank you for providing that information.  It's really interesting and totally new to me.  I'm going to research further - I like the idea very much.