Home-Theater Sound: Amplifier Setup Basics
When it comes to amplification, what you need for the best possible home-theater sound quality is:
A/V receivers force you to use long speaker cables. Avoid this if possible. Using short speaker cables implies getting the amplifier(s) very close to the loudspeaker. You cant do that if all five amplifiers are in one box. Yet there may be reasons that you really need to set your home theater up with a single five-channel amp or A/V receiver.
Im going to list most of the practical ways to amplify a home-theater system and rank them with ultimate sonic performance as the goal. Convenience, ease of use and décor will count for nothing in these rankings so they may move around considerably when you apply your own personal needs to the mix. Just bear in mind that this ranking considers only ultimate sound quality and nothing else. Cost is a big consideration in building a home theater, but cost is not a factor in the ratings for this table. Since the front three channels carry the most information, they are given more weight. The home-theater subwoofer is not part of this table, but it is an important element of the home-theater sound package. All amps are assumed to be of similar performance, quality, and cost. I am not considering combining expensive amps with low cost amps in this table.
This table could be misleading. You can buy mono amplifiers for under $400 each. That would amount to something under $2000 for all five channels. You can also easily spend $2000 each (or more) on mono amplifiers. Thats a large spread in cost and sound quality.
Would five mono amps costing a total of $2000 perform better than a $3000 three-channel amp and a $2000 two-channel amp? Probably not, even considering the longer speaker cables you might need. You can overwhelm some of the performance concerns with money! How about a $2000 five-channel amp versus five mono amps costing a total of $2000? The nod might go to the five-channel amp, as there might be less money spent on one chassis, than five separate chassis. This leaves more money for better parts in the amplifier circuits. For example, single-chassis amplifiers like the outstanding $1399 Anthem MCA5 is a perfect example of high-value engineering. On the other hand, spend $2500 on five mono amps and theres a pretty fair chance youll out-do what a $2000 five-channel amp can do. The "best" options will tend to cost more than "good" or "better" options even though the specifications may seem similar on the surface. The exception might be powered loudspeakers where there is little money tied up in a fancy chassis.
That said, money alone is not the only consideration. Sometimes specific products perform so well that they break out of the mold. The Belles 150A Hot Rod amp ($1499 stereo, $1999 three-channel) is an example youd be hard pressed to find five mono amps for anywhere close to $3500 that sound as good as a 3+2 Belles Hot Rod setup. Because of all of these issues, dont consider this chart a bible for amplification selection in your home theater. There will always be exceptions to the rules laid out here. You might want to use the chart as a sounding board for potential choices you might need to make when designing or refitting your own home theater.
Speaker cables themselves can be a considerable expense. Dont underestimate the value of speaker cables for fine home-theater sound. Better cables are easy to hear in every channel. The surround channels are less obvious than the other channels. If you have to economize somewhere, do it on the surround channels. Interconnects matter too and should also be selected carefully.
Importance of matching
Good home-theater sound requires well-matched components in each of the five speaker positions. The speakers must match each other and the amplifiers must match each other. The cables must match each other as well. Sure you can build an unmatched home-theater system and it will still be amusing. But when you are trying to get the system to be something special, keep all the components as closely matched as possible. All amps should come from the same manufacturer and all should be "family members" so they sound similar. Amp manufacturers sometimes change their sound radically from model to model or year to year. Just having two Thrombosis amps does not mean that they will sound similar. You want amps of relatively similar manufacture date and amps, which use the same general circuit. If you use a five-channel amp or A/V receiver, this is not an issue.
Cables not silly and definitely not inconsequential
Care in selecting speaker cables is important. Some manufacturers have "families" of cables and you could easily take a cable in the middle of a family and combine it with a lower cost family member. But some cable companies make very different sounding wires at different price points. This is a tricky area for many home-theater enthusiasts and a knowledgeable dealer can help you avoid problems. If you are hell bent on doing the whole thing yourself, contacting wire manufacturers directly and finding out which of their wires are intended to work well together in a home theater could be a big time and money saver.
Hidden problems with mixing and matching amplifiers
Lets say you have an amplifier now and you decide to purchase another amplifier to run the other channels in your home theater. If the two amplifiers are not identical, there can be serious mismatches in sensitivity. One amp may play much louder for a given input volume setting than another. This mismatch could be so severe that there is not enough compensation available in your surround decoder to compensate for the difference in sensitivity. If that happens, two or three speakers in your home theater may always play too loudly.
You can also get different sound from two different amps. The original amp may be mellow and laid back while the new amp sounds bright and in-your-face. This is not a marriage made in home-theater heaven. You cant just mix and match amplifiers and expect the best possible performance. Someone who knows all the pitfalls and how to get around them can do this.
Setup for good sound
I dont think you can do a home-theater volume/balance setup by ear, and get a very good result. You should seriously consider getting a sound pressure level (SPL) meter. Radio Shack is a good source. They have two models to choose from. An older, less flexible analog model for under $35 (last time I looked) or a newer digital model that is easier to use for a little over $60 (also the last time I looked). Either one will be good enough for this job. Set the SPL meter to "C" weighting and "slow" response. Hold the SPL meter at the listening position, at ear height, and tilt it towards the ceiling at about a 45-degree angle. Aim it straight ahead when measuring all the front speakers. Turn the meter to the rear (maintaining the 45-degree angle) when measuring the rear speakers sound pressure level. Dont aim the SPL meter at each speaker in succession as you move the test tone around the room. Use the built-in test/setup tone in the A/V receiver or surround processor. Set one of the front speakers to produce 70 dB on the SPL meter. Then set all of the other speakers to also produce 70 dB using the setup menu in the A/V receiver or surround processor. Recheck the settings periodically to make sure no one changed anything by accident.
Even slightly more precise is to use the surround tones on a DVD like Joe Kanes Video Essentials. This bypasses a couple of variables and insures that you have the most accurate speaker volume balance you can achieve without spending a whole lot more money.
Subwoofer setup can be made to seem far more complicated than it really is. The objectives are to set the polarity and phase to get the output of the subwoofer as loud as possible at the listening position. The SPL meter can help with this also. Using a CD with bass test tones (like one of the Stereophile test CDs), select a tone in the 40Hz to 60Hz range and play it continuously. The level should be around 70 dB for this also. If the subwoofer has a polarity control and phase control, set phase to "0" and check both polarity positions. Use whichever one produces louder bass (refer to the SPL meter if you have one). Next, adjust the phase control until you get the loudest bass possible. When this is done, the subwoofer is set up correctly. Adjust the playback level for the subwoofer while viewing movies. After watching two or three different movies, which have significant bass content, youll know if you have the level correct. The SPL meter setting is not gospel in this case, you really need to listen to some movies and decide whether the final adjustment point needs to be a little louder or a little softer.
With the right amplification, the right setup, and the subwoofer set to the right level, youre ready to get into movie sound so good youll be wondering why real theaters dont sound as good as your home theater.
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