3DsoundSurge Reviews: VideoLogic Systems' DigiTheatre DTS


	Mikael Hagén puts VideoLogic Systems' DigiTheatre DTS speaker system to the test

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DigiTheatre DTS - Mikael Hagén - August 1, 2000

Sound level tests:

With 220 watts RMS of power the DigiTheatre has specs that are clearly ahead of the other Dolby Digital systems we reviewed last fall (Cambridge SoundWorks DTT2500 and VideoLogic Systems’ DigiTheatre) and this spring (Altec Lansing’s ADA880). If we look at systems that don't include a Dolby Digital decoder it’s well behind Klipsch’s 4-speaker system, the Promedia, which has specs of 400 watts RMS.

Watts (RMS), however, doesn’t tell the true story about the loudness since the speaker cone efficiency can vary quite a bit between two systems, that is some cones requires more RMS to deliver the same dB to your ears than a more efficient speaker cone. In case of the DigiTheatre DTS we know that the Sirocco Crossfire with only 100 Watts RMS is clearly louder than the ProMedia so the DigiTheatre DTS should have no problem generating at least the same loudness if not more. As usual we used a sound level meter to be able to test their loudness with more than a simple "they are loud" or "they are not so loud" statement.

While using this sound level meter is better than just using ears and memory to compare the speaker system's loudness it's not 100% accurate and especially the 1 kHz tends to vary a bit between different tests. The results of these tests are given in Decibel (dB), which is a unit of measurement commonly used for intensities of sound or sound pressure. This is a logarithmic unit defined so that an increase of 1 dB represents multiplication in signal power (what the speaker produces) of 1.258 or sound pressure (what your ears hear) increase of 1.122. When you place both yourself and the speakers in air the logarithmic scale of sound intensity and sound pressure can be considered identical.

The sound pressure meter was positioned where my head would be positioned when I am at the PC watching DVD movies. This means 3 feet away from the front speakers and 3 feet from the rear speakers. I also did a test when the front speakers and subwoofer are 9 feet away and the rear speakers about 3 feet away, which is a more typical movie set-up. I used a 1 kHz test tone, which is generally accepted for testing sound pressure as well as some real world DVD tests using the Fifth Element and a real world music test using Rossini’s William Tell Overture. The results of those tests are summarized in the first and second tables below. All sound level tests were done using an original Sound Blaster Live! with the windows mixer wav output set to maximum and the master volume just one notch below maximum. The DVD tests are of course done in Dolby Digital 5.1 mode. For reference I compared the volume to the Cambridge Soundworks DTT2500 digital system, VideoLogic Systems’ DigiTheatre and Altec Lansing’s ADA880.

The DigiTheatre DTS put out a peak SPL of 108 dB using the 1 kHz test tone where as the DTT2500 put out a peak SPL of 98 dB, the original DigiTheatre 105 dB and the ADA880 104dB dB. In the music test the DigiTheatre DTS reached 105 dB while the ADA880 achieved 102 dB and the original DigiTheatre 101 dB. The music test was never used for the DTT2500 but Mark tried it in a different room with his DTT2500 and got 99 dB. In the DVD test the DigiTheatre DTS managed to reach an impressive 110 dB, clearly ahead of the DTT2500’s 102 dB but only slightly better than the DigiTheatre’s 108 dB and ADA880’s 107 dB

Looking back to the logarithmic nature of a dB this means that at full volume the DigiTheatre DTS has a sound level or signal power of 6 times stronger than the DTT2500 and twice as strong as the ADA880 when playing the DVD movie. This however does not correspond directly to the perception of loudness. We generally perceive loudness to be doubled when the intensity increases by a factor of 10. This corresponds to a 10 dB increase which for example means that DVD test is perceived to be 30% louder on the DigiTheatre DTS than on the ADA880. The obvious conclusion is of course that DigiTheatre DTS clearly but not significantly louder than the original DigiTheatre and ADA880.. One other interesting thing to note is that the ADA880 actually offered the same volume when I tested 9 feet away from the front channels and subwoofer as when I was 3 feet away from the front channels and subwoofer in the DVD test. I did an additional test that showed the reason was not the rear speaker volume. The only conclusion I can come up with is that it’s because the ADA880 shakes my room in a way none of the other speakers including the DigiTheatre DTS manage. Your results may be different and you will also notice a clear difference if you decrease the bass level.

When you try to push a speaker system to the maximum, distortion will usually become a problem. Distortion, when used in the context of sound, is defined as a change in the waveform of a signal during processing, often caused by the signal level being too high for the hardware or software that is processing it. Something to keep in mind is distortion is a fact of life when it comes to sound reproduction. The higher quality something is, the lower the distortion is going to be at normal operating levels. Pushing the system to its maximum will result in higher levels of distortion and it's at this stage where what is acceptable will depend for the most part on three factors. First, you don't want to push the system so hard that you damage it. The next two are personal as its your ears and your tolerance as distortion starts long before your system sounds like its going to blow up! With respect to the DigiTheatre DTS, when playing DVD movies I had to lower it about 3 dB for the DigiTheatre DTS which was about the same as for the DigiTheatre and ADA880, where as with the DTT2500 I had to decrease the volume about 5 dB.

1 kHz test tone - no subwoofer response at this frequency so this is a test of satellite output alone.

Distance to front (and sub)/rear speakers	DigiTheatre DTS	ADA880	DigiTheatre	DTT2500
3 feet	108 dB	104 dB	105 dB	98
9 feet and rear off	100 dB	96 dB	96 dB	90

Rossini William Tell Overture - this is a test of combined subwoofer and satellite response.

Distance to front (and sub)/rear speakers	DigiTheatre DTS	ADA880	DigiTheatre	DTT2500
3 feet	105 dB	102 dB	101 dB	99 dB
9 feet (DTT2500 7 feet) and rear off	101 dB	100 dB	96 dB	93 dB

DVD Scene in The Fifth Element - this is mostly a low-frequency test

Distance to front (and sub)/rear speakers	DigiTheatre DTS	ADA880	DigiTheatre	DTT2500
3 feet	110 dB	107 dB	108 dB	102 dB
9 feet and 3 feet	106 dB	106 dB	103 dB	98 dB

For a little more perspective, a typical conversation is 65 dB, a loud orchestra is 80 dB, unsafe levels start at 90 dB, thunder is around 109 dB, a rock concert is 110 dB and the pain threshold is around 130 dB. U.S. Department of Labor regulations set permissible noise exposure to 105 dB at no more than 1 hour per day! Can also be interesting to know that when I watched Star Wars: Episode 1 in a movie theater that featured Dolby Digital–Surround EXand THX the sound level meter rarely went above 100 dB even during the action scenes and never past 105 dB. I didn't check the meter the entire time but since it was the second time I saw the movie I checked at least most scenes with loud sound effects.

The loudness tests noted above, with the exception of the DVD tests, were done with the soundcard connected to the DigiTheatre DTS in analog stereo mode. Choosing Pro Logic, Hall or Theatre mode on a stereo source may change the volume with a couple dB but no major difference assuming you have all the speakers placed correctly. Using the digital connection gives almost the exact the same result and only significant difference is the noise level when no sound is playing. I used the Live for all tests other soundcards/devices may show a difference between analog and digital as the internal electrical "noise" level of a PC can vary quite significantly from PC to PC and even within a given PC! I would expect that every DVD player on the market will use a DAC with significantly better analog output than the Live.

Back to the installation

So on to the sound quality tests