Surround Sound From Just Two Speakers?

The concept gained popularity during the 1990s as three-dimensional stereo or surround sound from two loudspeakers, but is it possible to have surround sound with just your front left and right speakers?


By: Ringo Bones


Older audiophiles would probably credit the 1957 EMI release called the SDDI stereo demonstration LP with its traffic noises, trains and an orchestra as the first two-channel surround sound capable recording. Yes, it has only left and right channels, but this EMI test LP record can project a soundfield behind you without the aid of rear speakers. By the late 1960s, probably by creative accident, Jimi Hendrix made his guitar fly around and behind the listeners head – something two-channel stereo supposedly can’t do – via creative flanging in the song Bold as Love from the album Axis Bold as Love. Unfortunately, no audio engineer during this time has reliably able to do the same with natural / field recordings – i.e. the sound of a bee buzzing in front then behind your head as it sounds in real life – using standard two-channel stereo.

Hence the hi-fi and record industry in the very tail end of the 1960s decided that since the multitudes already have stereo, maybe we’d introduce them to surround sound. And when 1970 came, everyone witnessed the birth of quadraphonic sound – it was called as such because educated people knew Latin in those days. Unfortunately, a format war resulted with many manufacturers introducing their own version of quadraphonic sound / four-channel surround-sound that the buying public became confused – and bought none. A surround-sound system based on a quad system patented by Peter Scheiber – i.e. Dolby Pro-Logic – which is very compatible to existing standard two-channel stereo was introduced too late, thus quadraphonic sound expired with barely a whimper in 1975.

Even though Dolby Pro-Logic eventually became the standard surround-sound format for home theatres of the 1980s, the prospect of getting surround-sound from just two front speakers is just too tempting a concept to ignore. A researcher from the Oxford Institute of Mathematics by the name of Michael Gerzon had been toying the idea at about the time when quadraphonic sound was on the wan that you don’t need four or more loudspeakers arranged around the listener for surround sound. Gerzon had uncovered during his research that it is possible to fool the brain into thinking that a sound lies behind you with just two front-placed speakers. That’s a lot of money and unnecessary boxes saved, thus various companies influenced by the data gathered in Michael Gerson’s research had released their version of two-channel surround-sound that are - fortunately for us audiophiles - compatible with each other. Thus came Thorn EMI Sensaura, OM 3D system and Roland’s RSS system – all three dimensional stereo surround-sound systems that works with just two channels at the beginning of the 1990s.

At around near the end of 1993, the Thorn EMI Sensaura two-channel compatible surround-sound system was announced to the unsuspecting audio world as a surround-sound system that uses your existing standard two-channel stereo. Developed by EMI in their Central Research labs by Dr. Alastair Sibbald and team, Sensaura is an ingenious and complex recording trick that relies on a comprehensive understanding of psychoacoustics to work properly. It processes acoustic positional cues into a recording, in order for the ear / brain system to hear sounds from all around the room. And the end result can work whether recorded on CD, LP or cassette tape – and Sensaura’s effects can only get better the better the recording format sounds. And it even enhances high-resolution digital audio formats like 24-bit 192-Khz sampled DVD-Audio.

Another system with an almost similar principle that had been first made commercially available to the public since 1991 is Perfect Pitch Music’s OM 3D system. Used in their Francinstein Stereo Enhancement System Plus, the OM 3D system uses psychoacoustic cues to position individual sonic images within a 360 degree arc anywhere about the listening position. The OM 3Dsystem has been successfully used on CDs, cassette tapes, and radio broadcasts, it has even been used by musicians and recording engineers to enhance musical styles as diverse as experimental jazz and children’s educational tapes.

Like Sensaura and Roland’s RSS system, OM 3D uses left-right channel time delays to make low frequency sounds appear to come from beyond the boundary of the loudspeakers. In fact low-frequency stereo 3D stereo is relatively easy to create. It is at high frequencies that the 3D system / two-channel surround-sound systems previously mentioned has to be really clever. Because our ear / brain system determines acoustic directions at high frequencies by analyzing the tonal spectrum of a sound as it enters the auditory canal.

Unfortunately, as all of these three-dimensional stereo systems became popular, competing discrete digital surround sound systems – like Dolby digital AC3 and DTS – were introduced during the mid 1990s. Though an overwhelming application of the two competing discrete digital-based surround-sound systems were for movie soundtracks, a majority of audio-store “cowboys” had the brilliant idea of demo-ing The Eagles’ Hell Freezes Over DTS surround encoded DVD to death. Thus making your 1990s era home theatre customer inextricably linking DTS surround-sound with The Eagles’ Hell Freezes Over DVDs.

Since 1990, the audiophile label Chesky had been featuring three-dimensional stereo demo tracks in their test CDs. Though it doesn’t say on the CD liner notes, but many “mainstream” CD recordings that had came my way since 1991 had demonstrated surround-sound capability in my standard two-channel stereo set-up. Like the studio version of Dead Skin Mask by Slayer from their Seasons in the Abyss album when the hapless victim of Ed Gein had been calling him from behind my back even though my stereo only has two front speakers. There are now probably a large number of CDs out there that has already been three-dimensionally encoded that only became apparent if your main front speakers are properly toed in.