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- Home cinema basics
- Home cinema setup
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Setting up a stereo system is a matter of simple geometry
A hi-fi system consists of an amplifier, a CD or record player and two identical loudspeakers for playing back stereo signals. Most people who invest in a high-end stereo system will position it so that the stereo image produced by the two speakers can be best appreciated (as opposed to arranging it so that the speakers merely look nice or are least in the way). The handiest trick for this is to imagine lines connecting the two speakers and the listening position. Ideally, each of these lines will have the same length and form an equilateral triangle. This will ensure that the sound from each speaker reaches the listening position at the same time.
Home cinema systems use up to ten loudspeakers
Setting up a home cinema system is a good deal more complicated than positiong a hi-fi system because there are many more variables. A typcial surround sound system always includes a subwoofer for the reproduction of the bass frequencies as well as additional loudspeakers that fulfill different roles in creating the overall surround sound image. In order to produce a sound stage that is harmonious and in which individual sounds are accurately positioned, it is important that the speakers are arranged properly with respect to each other and to the listening position.
This is no easy task. After all, even within a standard 3-way stereo speaker, getting the tweeter, midrange driver and bass driver in perfect alignment is a challenging task that only the best manufacturers master. Above all, the loudspeaker developers need to ensure that the bass driver’s volume and phase perfectly complement the volume and phase of the midrange driver and tweeter. Only then can a linear frequency response be assured.
With home cinema systems, the alignment of the bass driver in the form of a separate subwoofer is much more difficult. That’s because the bass not only has to be aligned with a single tweeter and midrange driver but with many tweeters and midrange drivers in a centre speaker, two front speakers and two rear effect speakers. Some systems even include two additional effect loudspeakers for the front.
All of these individual home cinema loudspeakers are powered from the A/V amplifier or receiver. That’s why it’s important that the amplifier is configuration for the individual loudspeakers used in a surround sound system.
For example: A loudspeaker manufacturer might separate the frequency range of its satellite/subwoofer system at 100 Hz with a slope of 18 dB. This creates a basis for a harmonious interplay of all speakers. However, if this set were to be connected to an amplifier with a subwoofer output that has a cut off frequency of 90 Hz and a slope of 24 dB, the incoming signal will not match. Since there are no norms when it comes to home cinema systems, every manufacturer can pretty much do what it wants which places the burden of ensuring a good match squarely on the shoulders of the consumer.
Differences of 80 to 90 Hz between a sub and an A/V receiver will still lead to an acceptable result, yet discrepancies of 200 to 80 Hz would cause major problems with the bass playback. And yet there are many manufacturers who do not give the cut off frequencies and slopes for their amplifiers, subwoofers and surround speakers.
The only standard that guarantees a way out of this chaos is THX. All devices and loudspeaker that carry this seal use the same standardized values so that all components are sure to be in perfect alignment.
Audio for stereo versus surround
There are still other differences to consider between hi-fi and surround sound systems. CDs, for instance, were mixed from the very beginning to play back in optimal sound quality in typcial living rooms and bedrooms. Movie sound tracks on DVDs or Blu-rays, on the other hand, contain the original soundtrack mixed for playback in large cinemas.
Whereas the viewer sits very far away from the speakers in a cinema, the distances in a home cinema are relatively small. In order for the same soundtrack to produce a similar result in two very different listening areas, it needs to be electronically processed by a decoder. When purchaseing an A/V receiver, it is therefore important to note that at least the two main home cinema codecs, Dolby and DTS, in their most up-to-date formats are supported.