Expanded Soundstaging and 3D-Imaging

Dear folks out there, I would like you to participate at one of the most interesting filter designs I ever tested on my Behringer. Some time ago a French gui called Thierry Martin mailed me some information about a new kind of filter design for speaker crossovers engineered my Mr. Le Cleac'h. The material was ONLY in French so it was quite hard for me to follow his approach. Finally I found a French person which translates the article to German (uuh, what an ugly German!). After that I started translating the article to real German and also to English for you. The whole material you'll find here:

Document and Speadsheet (doc, xls) Theory of operation (ppt) 

Well, in-between I tested the approach of Le Cleac'h with my DCX-2496 and got so astonishing results that I thought I had to let you know about his theory. Believe me or not: With his filter design you get a soundstaging and imaging you never heard before on your system!! 

So what has to be done? First adjust your DCX-2496 the way you have a flat frequency response and time aligned speakers which can be achieved by the auto align function of the DCX 2496 (yes, you need a microphone this is VERY important!). I guess you did it before ;-) 

Now read the paper (.doc-file) I submitted in the ZIP, open the spreadsheet and enter the values according to your current DCX-2496 configuration. Do not enter the current time delay of your DCX in the spreadsheet! Now in the spreadsheet modify the values as described in the paper. If you got a good result in the spreadsheet adjust your values in the DCX-2496 so they match the spreadsheet. 

A bit care has to be taken at the delay. The auto align function of the DCX calculates values for the delay. To these values the values from the spreadsheet have to be added. This means the distance between the chassis will become bigger. Le Cleac'h says the speakers (bass, mid) have to be moved towards the listener. With the DCX-2496 you have to move the mid and tweeter away from the listener which is the same!! The distance gets bigger. 


Measurements of the Le Cleac'h approach

The technical evaluation of the Le Cleac'h approach is really fascinating. The test signal used was a square wave of 1kHz which was injected by S/PDIF (24/96) to the DCX2496. Two outputs of the DCX2496 were taken and added via a resistor network. The result was displayed on an oscilloscope.

For the first measurement a Bessel 6db filter was taken with a x-over frequency of 2980Hz. As expected the output signal was a nearly perfect square wave (no phase distortion) with a bit ringing. The ringing results from the steep output filters behind the D/A converters of the DCX2496.

Ideales Rechteck 1kHz

After this the filters were switched to Butterworth 18 with the same corner frequency. The result shows a very strong phase distortion.

But18, LP 2980Hz, HP 2980Hz

Inverting one of the two channels improved the result but the rising edge of the square wave is very slow and there is a heavy peak at the falling edge.

But18, LP 2980Hz, HP 2980Hz, Inverted Polarity

Shifting the tweeter back (time delay) - the 24mm computed by the spreadsheet - a further improvement can be seen.

But18, LP 2980Hz, HP 2980Hz, Inverted Polarity, 24mm delay

Finally the corner frequencies were modified to the values of the low-pass to 2620Hz and the high pass 3390Hz. This leads to a further improvement of the signal.

But18, LP 2620Hz, HP 3390Hz, Inverted Polarity, 24mm delay

Over all Le Cleac'h's approach results in an x-over with nearly no phase distortions. This is the reason for improoved soundstaging and 3D-imaging.


Listening

Now save this adjustment under a new preset of your DCX, sit down and listen while switching between your old preset and the new one. 

What you will hear is really astonishing. The whole characteristic of the sound will stay the same (same frequency response) but with the new settings the soundstage expands and you will get a never heard 3D-imaging. 

A nice test for the new setup is the SACD "Scared Love" from Sting. In my opinion it is a bit over instrumented and it is sometimes difficult to differentiate between the voices and the instruments. With the new filter parameters the whole soundstage unfolds and ..... you know, I now really love this SACD. And best of all: The filter modification is for free just try :-)))