Most recordings have the important parts (lead vocals, solo instrument) in the center of the mix, but ordinary stereo speakers have trouble creating a central, mono sound-image without comb filtering and image instability (Lynn Olson says as much on his webpage). So, why not design and build a system based on sum/difference playback?
Here’s how I’m imagining it: a normal recording is processed by a preamp to create a "sum" signal (L + R) and a "difference" signal (L - R). The “sum” signal is fed into an amplifier and then into a single speaker that is positioned directly in front of the listener, facing the listener. The “difference” signal is amplified and sent to two speakers positioned directly behind the forward-facing speaker, wired in opposite phase, with one speaker facing left and one facing fight. I’d send everything below 100Hz to a subwoofer, to ease the burden on these speakers. In the room, these sounds should combine into a ghostly stereo image, even though the speaker array would be in front of the listener.
Has this been tried before? Would it sound/image better than a stereo pair? Apologies if this has been discussed before, I searched diyAudio and couldn’t find anything.
It seems to me that most recordings would sound better and more present with this setup. It'd be fun to try, anyway.
Here’s how I’m imagining it: a normal recording is processed by a preamp to create a "sum" signal (L + R) and a "difference" signal (L - R). The “sum” signal is fed into an amplifier and then into a single speaker that is positioned directly in front of the listener, facing the listener. The “difference” signal is amplified and sent to two speakers positioned directly behind the forward-facing speaker, wired in opposite phase, with one speaker facing left and one facing fight. I’d send everything below 100Hz to a subwoofer, to ease the burden on these speakers. In the room, these sounds should combine into a ghostly stereo image, even though the speaker array would be in front of the listener.
Has this been tried before? Would it sound/image better than a stereo pair? Apologies if this has been discussed before, I searched diyAudio and couldn’t find anything.
It seems to me that most recordings would sound better and more present with this setup. It'd be fun to try, anyway.
Jensen did this many years ago. The positive was that you got stereo in one box. In reality, though, you are making the opposite of a mid-side microphone. It will fire the right channel sound off in the right direction and the left channel sound off in the left direction, much like putting a pair of bookshelf speakers together but aiming 90 degrees apart from each other.
Whether you hear any stereo from such an array depends on what the sound bounces off of and comes back as. Firing sound in a left and right direction is not the same as it arriving at your ears from a left and right direction.
Several manufacturers are making TV sound bar arrays that use left and right fired sound to create stereo (as opposed to simple speakers at the left and right end of the bar). This can work quite well if the walls are well placed and the arrayed beams are wide, tight, and with little forward leakage.
David
Whether you hear any stereo from such an array depends on what the sound bounces off of and comes back as. Firing sound in a left and right direction is not the same as it arriving at your ears from a left and right direction.
Several manufacturers are making TV sound bar arrays that use left and right fired sound to create stereo (as opposed to simple speakers at the left and right end of the bar). This can work quite well if the walls are well placed and the arrayed beams are wide, tight, and with little forward leakage.
David
Search "Single speaker stereo" here.
Polk ran with the jensen idea and produced the SDA (stereo deminsional array) series back in the early 80's which used pairs of drivers side by side to improve IACC. Will say that doing it this way doesn't have the room size / shape constraints of the single speaker design.
I did alot of testing on these back in the day and depending on setup and confguration can either be setup for additional ambience enhancement or image enhancement passively.
Polk ran with the jensen idea and produced the SDA (stereo deminsional array) series back in the early 80's which used pairs of drivers side by side to improve IACC. Will say that doing it this way doesn't have the room size / shape constraints of the single speaker design.
I did alot of testing on these back in the day and depending on setup and confguration can either be setup for additional ambience enhancement or image enhancement passively.
I think this one might incorporate this technique commercially
Parrot Zikmu SOLO design by Starck l - Specifications
Parrot Zikmu SOLO design by Starck l - Specifications
Yes - it's called a synthetic 3.1 with Pro Logic II or DTS NEO:6--by setting the center loudspeaker channel to maximum setting--i.e., panorama is "off", or center width is set to narrow.
It actually works fairly well if you get all three front loudspeakers and sub time aligned and EQed within a couple of dB full range.
Chris
Hi,
It will work but will be very poor compared to a stereo pair of speakers.
By definition a well set up pair of stereo speakers provide a very well
deliniated "phantom" centre mono image, if they can't they are crap.*
If they can, they will be miles better at stereo than the above.
rgds, sreten.
Lynn Olson says a lot of things, without really being rigourous
about the context, use him as a reference for ideas at your peril.
* FWIW stuff like Dolby Surround on VHS created the situation
where you needed multichannel, because undecoded it does
sound very poor in raw stereo, stereo compatible my butt.
Lots of DS videos were effectively stereo, but the ones
that tried to use DS a lot sound terrrible in stereo.
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Comb filtering from stereo speakers is only an issue for mono microphones, people who only have one functioning ear, or for frequencies where the wavelength exceeds the width of a head and the listener is positioned considerably closer (imbalance>20cm) to one speaker than the other. In most stereo listening setup this means sitting at least half a meter away from the dead center position. If you time align, you can sit where ever you want (within reason).
If the above conditions are not met, the only perceivable effect is that one speaker sounds slightly closer/further than the other one due to HRTF, which they are.
The reason center speakers exist in home theater applications are because where there are multiple listeners, not everyone can be seated equidistant from the two front speakers.
For a single listener system, there is no reason to have a center speaker.
If the above conditions are not met, the only perceivable effect is that one speaker sounds slightly closer/further than the other one due to HRTF, which they are.
The reason center speakers exist in home theater applications are because where there are multiple listeners, not everyone can be seated equidistant from the two front speakers.
For a single listener system, there is no reason to have a center speaker.
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I agree 100%. IMHO, a rock-solid, well defined center image is perfectly achievable with a (proper) pair of speakers. Mine are dipoles.
A while ago I was curious to see if other approaches are better (for stereo signal). I've tried a matrixed 3-speaker approach (there's a thread here around that, basically center gets sum and L/R get a weighted difference). The only improvement I've got was that the center image was somewhat more stable with (large) lateral movements out of the hot spot. Other than that, from the center, the standard stereo setup did a significantly better job at rendering a realistic soundstage. The matrixed approach always sounded kind of flat and spatially flawed.
EDIT: what I've tried was an analog trinaural approach, see this thread: http://www.diyaudio.com/forums/mult...coding-equations-3-speaker-stereo-matrix.html
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The Jensen version of this was a large bookshelf system. The cabinet behind had a sealed box woofer. Just in front of it was a sideways dipole with two full range units on the baffle that bisected the woofer behind. Sum signal went to the back woofer and difference signal went to the two dipole elements (in theory only one was needed).
Just like an M-S microphone you end up with 90 degree crossed cardioids (45 and 45).
Again, though, there is no stereo width without relying on the wall bounces.
David
Just like an M-S microphone you end up with 90 degree crossed cardioids (45 and 45).
Again, though, there is no stereo width without relying on the wall bounces.
David
Thanks for the replies! I found the right search terms and I'm reading up on this stuff. Pretty interesting! I'm especially interested in the plans for a speaker box that generates the matrixes signals purely at the speaker level:
https://dl.dropboxusercontent.com/u/2400456/html/Elias_Pekonen/SingleSpeakerStereo.html
Seeing as how room-dependent this sort of system is, I'll relegate it to "curiosity" for the time being.
https://dl.dropboxusercontent.com/u/2400456/html/Elias_Pekonen/SingleSpeakerStereo.html
Seeing as how room-dependent this sort of system is, I'll relegate it to "curiosity" for the time being.
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