Surround emulation: How does it work?

Surround emulation: How does it work?

The GT5051’s systems isn’t entirely new. In 1999, Altec Lansing already introduced speakers to emulate 4.1 sound with the ADA310, which had two speakers and one subwoofer. The GT5051 satellites share the same architecture. On the lower part of the satellite is a 3” speaker which reproduces frontal voices pointing towards the listener. On top is another 3” speaker pointing to the side and back. These two Side-Firing Dipole speakers emulate the surround channels found on 5.1 systems.


How does it work ?
To explain the functioning of this speaker set Altec Lansing sent us a rather simple diagram. We can see that the frontal and central voices work in the normal way sending sound directly to the user. It gets trickier with the Side-Firing speakers, which emulate the surround voices. Sound is supposed to bounce off the side and/or back walls and come back to the listener in what is called the principle of sound reflection. This only works if your walls are located in a certain position, which isn’t necessarily the case for everyone. As you can see the red arrows point to the front and also to the back of the satellite bouncing back on a rear wall.

5.1 sound emulation is based on two principles. First of all, speakers need to be placed with their back to walls with a high reflective capacity (like stone, concrete or metal). And the listener should be right in the middle of the two walls. This may already pose a problem for some people as their office or home environment may differ. The second principle is that sound must be resituated by the Side-Firing Dipole speakers.

Depending on the frequency, sound dispersion of standard speakers has the shape of a globe or flat ellipse (the angle increases with the frequency, the higher the frequency the more elliptic the globe is). In theory it is then possible to rely on high frequency sound directivity at some point. This is the reason why some speakers include diffraction grids for tweeters dedicated to treble. With the GT5051, Altec Lansing uses dipole speakers to reduce sound dispersion and increase directivity. A dipole speaker emits sound to the front and back of the speaker and uses the phase to reduce sound emitted to the side. You may notice that the top satellite, the one for surround sound, has a grid in the back to let sound through.

So with this type of speaker, surround voices don’t point directly to the user but bounce off the walls and come back on the side.

In order to have a surround effect with dipole speakers you need to be meticulous in their positioning. They need to be placed at least 1.2 meters apart and the frontal speakers need to point directly towards the listeners.

Sound quality and our impressions

Sound quality and our impressions

From a purely musical point of view, the GT5051 has a good overall sound quality. Mediums and lower mediums remind us of the CS21, with good presence and a slight but rather agreeable coloration. This is their strong side, even if we would have preferred a less dry sound that is a little more round. Trebles aren’t as good as mediums, but are still of good quality. We noticed a slight twinkling sound typical of Altec speakers, which reduces clarity but brings an unusual if not unpleasant touch. Saturation was immediately noticed beyond 65% of speaker volume. Basses are nicely reproduced, rather taut and sufficiently deep.


We tested the 5.1 emulation capacity, with RightMark 3D Sound 1.24. This software is able to locate any sound source in a 3D environment and lets us know how easily speakers are able to project sounds around the listening position. It also helps us to appreciate how front/rear, left/right transitions are made. We compared results to the Creative Labs 5.1 Inspire T5900.

To activate the 5.1 mode you need to turn a switch located on the back of the GT5051 subwoofer (6 channels instead of 2 or 4) and connect all three sound outputs (an Audigy 2 ZS) to the speaker inputs.

First off, the 3D audio positioning is quite good, and ambient sounds seem to be coming from the side of the listening position. It’s difficult, however, to ignore a significant part of sound dedicated to ambiophonic channels coming from the satellites placed in the front position. We noticed that the trebles actually seemed to disperse in a rather convincing way and create the best illusion. Mediums on the other hand always seemed to come from the front speakers. Front/rear transitions are well perceived but not as good as our 5.1 system of reference.

In games and movies, things were a little different as you aren’t entirely focussed on 5.1 sound emulation. With a movie like the “Return of the King” sound is better than with a simple stereo system. Accuracy, however, isn’t as good as with a 5.1 system. The real advantage of the GT5051 compared to stereo speakers is sound immersion more than the positioning. With games the result is noticeably better thanks to the singularity and isolation of sounds in 3D. With GTA III Vice City, for example, it’s easy to perceive if a car or character sound is coming from the back or the front.

Altec Lansing partly reached their goal even if it’s still below a real 5.1 system with separated surround speakers placed in the back of the listening position. If you concentrate on listening the surround effect fades, and you may notice that sound is coming from the front speakers. All in all, you need have faith in the GT5051’s 5.1 sound emulation to really hear it…

Conclusion

Direct comparison with 5.1 speakers sets like the Altec VS3151 or the Creative Inspire T5900 shows that the GT5051 isn’t a real 5.1 speaker set. It does show, however, that 5.1 sound emulation works. We feel that the GT5051 sound is a good compromise between a standard stereo and a real 5.1 system. On the one hand you don’t have to deal with the back speakers and cables, but on the other, positioning and sound immersion is reduced.

The GT5051’s recommended price for the US market is $149.95. This is higher than 5.1 systems like the 5.1 Inspire T5900, which provides an approximate equivalent sound quality (without the infrared remote control). We hope that recommended prices will soon fall as they usually do with Altec. Overall, the GT5051 is an interesting but rather expensive solution for those who want to have partial surround sound without the bulky 5.1 speaker set. For real 5.1 sound, you might want to look elsewhere.