Mid-side stereo techniques

[Pano]

I tried playing pink noise panned hard L or hard R, and could never get it to sound like it was coming from where it was supposed to. It was always centre + some wall splash if you increase the "side" levels.

That's certainly an important - and telling - test.
Makes me wonder what Soundbloke's delay suggestion would do for you. Certainly worth a try.

 

[soundbloke]

That's certainly an important - and telling - test.
Makes me wonder what Soundbloke's delay suggestion would do for you. Certainly worth a try.

My suggestions derive from a basic understanding of the principles involved. I suggest politely that would be a better place to start

 

[chris661]

Removing the obvious compromises in your set-up would have been a good start. How did you compensate for the directivity of the dipole drivers? How did you implement the "levels"? I would guess not via the single pole filters that are necessary? Why did you not try the HF compensation and delay correction? Your sigh of relief returning to wide angle stereo is a sign that your method failed to remove the stereo combing. What you do with your own time is your own business, but I would suggested that you conclusions are somewhat premature.

Some answers to your questions:
- I tried angling the dipole speakers anywhere from 45 degrees forwards to 45 degrees backwards. No magic settings there - 45 degrees forwards was as good as it got.
- Professional mixing desks (that you'd see at a live event or in a studio) make it easy to duplicate channels and apply arbitrary delays, EQ, and gain to any of the mid, side, left or right channels.


The absolute best result I've had did the previously-mentioned "halo of sound" thing, and while it was obvious that instruments were panned in the stereo field, where they were supposed to be was a mystery. Here's how I did it:

Side: +10dB gain (although the smaller speakers will have lower sensitivity and take some of that away), +10dB low-shelf boost below 200Hz, +2dB high-shelf boost at 8kHz. Speakers pointing forwards and out at 45 degrees. Front edge of the cabinet aligned with the mid speaker, acoustic centres each about a foot away from the main speaker.
Mid: 0dB gain, +1dB high-shelf at 8kHz, 4.0ms delay.

I tried applying delay to the side speakers, but didn't find anything useful there. Delaying the mid got the closest to a stereo image, but it's still a long way behind traditional stereo.


You're welcome to make suggestions, but at this point it feels like we're going around in circles. I try something, you mention a few things ("HF compensation", "delay correction", "stereo combing", without any real explanation), then I guess at what you mean and try something else.


It seems to me that a fully-functioning mid/side speaker ought to be able to "throw" sound accurately within a 180-degree field, which is neat. However, that isn't of interest to me: I think sound should be kept away from the listening room walls as much as possible. I want to hear the recording, not the acoustics of my own room.


In conclusion, I've taken this as far as I'd like to. I've spent more time and effort on it than I had originally intended, and the results have been a little interesting, but nowhere near the revolutionary results that were suggested in the first few pages.


If someone else would like to follow on and carry on experimenting, my data is above.

Chris

 

[Pano]

Thanks Chris. It's been thought provoking.

 

[soundbloke]

Some answers to your questions:
- I tried angling the dipole speakers anywhere from 45 degrees forwards to 45 degrees backwards. No magic settings there - 45 degrees forwards was as good as it got.
- Professional mixing desks (that you'd see at a live event or in a studio) make it easy to duplicate channels and apply arbitrary delays, EQ, and gain to any of the mid, side, left or right channels.


The absolute best result I've had did the previously-mentioned "halo of sound" thing, and while it was obvious that instruments were panned in the stereo field, where they were supposed to be was a mystery. Here's how I did it:

Side: +10dB gain (although the smaller speakers will have lower sensitivity and take some of that away), +10dB low-shelf boost below 200Hz, +2dB high-shelf boost at 8kHz. Speakers pointing forwards and out at 45 degrees. Front edge of the cabinet aligned with the mid speaker, acoustic centres each about a foot away from the main speaker.
Mid: 0dB gain, +1dB high-shelf at 8kHz, 4.0ms delay.

I tried applying delay to the side speakers, but didn't find anything useful there. Delaying the mid got the closest to a stereo image, but it's still a long way behind traditional stereo.


You're welcome to make suggestions, but at this point it feels like we're going around in circles. I try something, you mention a few things ("HF compensation", "delay correction", "stereo combing", without any real explanation), then I guess at what you mean and try something else.


It seems to me that a fully-functioning mid/side speaker ought to be able to "throw" sound accurately within a 180-degree field, which is neat. However, that isn't of interest to me: I think sound should be kept away from the listening room walls as much as possible. I want to hear the recording, not the acoustics of my own room.


In conclusion, I've taken this as far as I'd like to. I've spent more time and effort on it than I had originally intended, and the results have been a little interesting, but nowhere near the revolutionary results that were suggested in the first few pages.


If someone else would like to follow on and carry on experimenting, my data is above.

Chris

I will try in the next week or so to put the theory up here and the design equations that result. Please stay tuned...

But I would suggest once again that the task in building loudspeakers is to "throw" sound preferentially at the listener, not the side walls. Issues regarding directivity and departures from a monotonic roll-off in the power response are another matter. But try turning all the loudspeakers to face the listener and I hope both the realisation of what you have made and the listening experience will prove very enlightening