When a mixed system for two-channel stereo and multi-channel soundtracks is to be used in a single room, there are quite a few different options to choose from. In another article, we discussed optimizing speaker selection (link). This time we're going to focus on electronics setup.
Let's start with the fact that most of us don't need to combine stereo and home theater equipment. Salespeople sometimes try to get buyers to invest in overly complicated and expensive solutions, but let's not be persuaded to spend unnecessarily.
People who have moderate requirements for sound quality can buy a stereo or KD system and use it for all kinds of material. In such circumstances the choice between a two-channel or multi-channel system is more a matter of practicality than sound quality. As a basic option, we advise you to choose two channels, even if you will be using them for movies or TV work. This is simpler, cheaper and easier to install.
You can play two-channel music through your home theater system and vice versa, you can play movie tracks on two channels. If someone is definitely focused on one type of material and treats the other as negligible, there is no point in trying to be universal. It is enough to buy equipment specialized for your needs. An audiophile will buy a stereo, while a videophile will buy a home theater.
Suppose you have a good quality stereo system and want to supplement it with a center speaker and rear sets. In multichannel mode, the speakers and stereo amplifier will be used as front channels (FL - front left, FR - front right). To achieve this functionality two conditions must be met. First, ensure that the volume control section of the stereo amplifier is bypassed in multichannel operation - all channels should have their volume controlled by a multichannel amplifier/amplifier. Secondly, to equalize the mutual volume level for all channels.
Let's start with the issue of equalizing the mutual level of the channels. You need to consider the gain of the individual channels and the effectiveness of the speakers. Some power amplifiers have adjustable gain. In active subwoofers, level adjustment is found routinely. Generally, we make relative channel level adjustments in the AV electronics settings.
The volume control workaround (diagram in the figure opposite) is most conveniently done using devices that have this feature. Many integrated amplifiers and preamplifiers have bypass option, which also applies to strictly audiophile models. Sometimes a separate input is installed, connected directly to the power amplifier output, without volume control. Sometimes it is possible to change the input modes and set them separately in bypass mode (Home Theater Bypass).
If you are using a separate preamp and power amp, you can simply bypass the preamp. The same applies to integrated amplifiers with PRE OUT and power amp section input. In principle it is enough to connect the cables differently so that the signal from the AV equipment goes to the power amplifier without the mediation of the stereo preamplifier. Frequent switching of cables would be inconvenient. However, you can buy an additional passive switch with which you can select whether the signal to the power amplifier should come from the stereo preamplifier or from the AV equipment.
A conventional integrated amplifier without the functions described above is in principle not suitable for integration with a home cinema, but some possibilities exist even in this case. First of all, it is about using the stereo system speakers themselves for multi-channel sound. You can install a switch on the speaker cables, which will allow you to select whether the signal from the stereo amplifier or the AV amplifier will be fed to the speakers.
Although we do not recommend this, as a last resort you can connect the output from the AV preamplifier to a regular stereo amplifier input, but this has two serious drawbacks. First, you will lose quality because the signal to the main speakers will go through two volume controls. Second, you will need to find a position on the stereo amplifier's volume control that will give the same signal level as if you had omitted the preamplifier - which can be quite inconvenient.
Check also: Rubicon Hi-Fi loudspeakers
The configurations discussed above did not take into account the presence of a subwoofer, and after all, it is a very popular element in home cinema. We'll start with two variants where accepting some compromises allows you to simplify how to add a subwoofer to a mixed stereo/AV system.
One option is that the subwoofer is connected to the output of the AV equipment and works only in home theater and remains unused at all in stereo. The requirement described above (bypassing stereo volume control, adjusting channel gain) remains in effect. This simple option will be satisfactory for many people, especially when the main speakers provide sufficient amount and extension of bass when working in stereo.
In the second variant we can connect the subwoofer together with stereo speakers so that they always work together and are controlled from the stereo amplifier. Appropriate filters will constantly share the bandwidth in the same way, serving as a crossover. Such filters are often found in active subwoofers, and may also be included with the amplifier. Note, however, that in this case, the subwoofer is tightly and permanently connected to a pair of stereo speakers. From an AV standpoint, the subwoofer is not present at all, and the subwoofer+columns combination is treated as a pair of full-range front speakers. In the multichannel sound processor settings, you have to select the subwoofer-less mode setting. Formally speaking, your multi-channel system will be classified as 5.0 or 7.0 (zero after the dot means no subwoofer). In the KD equipment settings you should then select the option with full-range LR front speakers, and set the types of the other speakers according to their capabilities.
Fully optimizing the subwoofer application means that in addition to the already mentioned need for common volume control for all channels and gain matching, there is an additional requirement for filtering. To properly utilize a subwoofer in both home theater and stereo you need to provide different types of filtering depending on the mode of operation.
In a two-channel stereo system, the filtering serves the same function as a crossover in speakers, splitting the bandwidth into an upper portion for the stereo speakers and a lower portion for the subwoofer. The filters work the same way all the time and should be chosen to provide a flat response for the entire system.
The LFE (low frequency effects) channel in a home theater is something different. It is the processor in AV electronics that decides how to reproduce low tones depending on the equipment configuration. So the way of filtering is not always the same and generally different than in stereo variant. In this case the filtering used in stereo should be turned off so as not to distort the filtering done by the AV electronics.
The most convenient option is to use an advanced AV preamplifier-processor to handle all sources, whether for stereo or KD. A well-equipped processor can adequately handle the various sets of connected speakers and provide both appropriate volume control and filtering as needed for the current configuration. Unfortunately, such preamplifiers are usually not the audiophiles' favorite devices. In addition, models that combine good quality with extensive features are quite expensive.
There are also analog preamps that have bass management capabilities (i.e., they will provide crossover filtering for stereo operation) and bypass functionality in an extended version that includes both a regular input and a subwoofer input.
Other configurations can be created to ensure proper subwoofer operation in stereo and home theater. These can be accomplished with a variety of filter arrangements (built-in or external) and switches. In this article, however, we have limited ourselves to discussing the simplest, most conventional and typical solutions.