PREOUT and SPEAKERS filters : type ? [solved: BESSEL filters]

[Alec_eiffel]

Hi all,
In the mid term, I plan to add 2 subwoofers to my setup, using the D200 PREOUTs.
The subs will have their own amp and filtering, incl. Linkwitz transform and low pass at approx.100 Hz, so I will send the full signal to the PREOUTs.
I'd like to filter my main speakers with a high pass at 100Hz using the D200 embedded filter, which is configurable (see attachment). The aim is to destress my bookshelves speakers where the subs will takeover, and prevent distorsion.
In the configurator one can choose :
- cutoff frequency
- filter type (high pass / low pass)
- filter order (1/2/3/4)
- delay
This is more than I need but there is no indication of the type of filter implemented : Bessel ? Butterworth ? Linkwitz-Riley ? Other ?
Anyone having this info or having measured it ? 
This important to me to understand the phase behaviour and configure the subs accordingly. 
Thx
   

[Pim]

Filter order stands for the slope; first order = 6 dB per octave, second order = 12 dB per octave etc.
So the higher the number, the steeper the slope.

[Alec_eiffel]

Thank you Pim, I understand well the relationship between order filter and slope. My question is more related to the phase behaviour of the filter. I have asked Devialet but no answer so far. Worst case i'll run some measurements.

[Waiski]

When you get an answer from Devialet, could you please send it here also.

[Vivialet]

I have stopped using the filter long ago as it is degrading the overall performance. But maybe the latest FW Version is better here...

[Alec_eiffel]

I think I'll run some measurements to be sure.
A side note regarding the Tone treble/bass : I was able to measure that the implementation is very good, no phase shift at all (at least above 500Hz, my room is too reverberant to allow for precise phase measurements in the low end of the spectrum).

EDIT: here are the SPL and phase curve with and without a +2dB treble boost @ 2.2kHz on the D200. No phase shift at all.
Measured on the left speaker using REW / Devialet Air / D200 / Athom EURUS 1.0 / UMIK-1

[Alec_eiffel]

I got today an answer from Devialet (Roger) : "we use Bessel filters for Speakers and Pre-Out filtering".
This is very good news for me as these filters preserve phase and group delay in the band, which is what I want !
   

[Waiski]

Thanks for the info!

[Waiski]

I have been scratching my head with the crossover... now I finally did measure the crossover and found out that you need to use little mathematics to get it working properly. My friend did help with the calculation.

Order
LP=>-6dB ... -6dB=>HP
HP=>-6dB ... -6dB=>LP
1st 1.733 ... 0.577
2nd 1.000 ... 1.000
3rd 0.765 ... 1.307
4th 0.643 ... 1.556

So for 2nd order crossover you can use this without adjustments. 1000hz is 1000hz crossover point.
But for example 1000hz 1st order crossover point are... low pass is 577hz and high pass is 1733hz.

Handy, isn't it? ...nope