Understanding Home Stereo
Basic Information for Stereo Shoppers
Home theater systems are extremely common these days. However there are a number of people who prefer to listen to music in its native, stereo format. This type of system is referred to in a number of ways; stereo, two channel, hi-fi and others. In the eyes of many, when you are listening to a two channel music source the only correct way to do it is in its native format. Good sources, good amplification and a couple of good speakers, possibly augmented by a high quality subwoofer, are all that is required.
We are constantly surprised by how many people have never heard a really good properly set up stereo. New visitors to the store often volunteer a disclaimer that they are not audiophiles and there’s no point in showing them a high performance system because they won’t be able to appreciate it. We very rarely find this to be the case. Perhaps they don’t know the language to describe it; in some respects we are as bad as wine connoisseurs in having developed a somewhat arcane language to describe what we hear. But the fundamental qualities of a good system are readily apparent and easy to enjoy.
For lack of a better description, well reproduced music simply sounds more real. In fact, the word stereo doesn’t mean two channel as opposed to monophonic, as most people think. Stereo is from Greek and means “solid”. A reviewer in a magazine a number of years ago was trying to describe the sound of a component in a system and finally resorted to saying “There’s just more there, there”. It sounds kind of ridiculous and yet makes sense. One of the easiest tests when listening to a system is the sound of the human voice. You may not hear a Stradivarius violin on a regular basis, nor a heavy metal rock band. But you hear the human voice every day. One of the attributes of a two channel system that surprises many people is imaging. A properly set up two speaker system can convincingly create the illusion that there is someone standing between your speakers singing. Or that a symphony is spread in a believable space in front of you. The impression is that you are seeing the orchestra as it is playing, including a sense of depth.
So, let’s take a look at the components that make up a stereo system and how to put them together.
The sources for music are more varied than ever. Some of the traditional analog sources are still in use. FM stereo, various tape devices, and vinyl lps via turntables are the most commonly found. Thankfully eight track stereo is no longer with us. Cassette has largely been supplanted by other portable devices. Vinyl is enjoying a huge resurgence. See our separate discussion of turntables and vinyl playback for more detailed information.
In today’s world, most of the playback is done from a digital source. For many years that was in the form of a CD player. CD’s are still very present but in recent years have lost ground to downloadable music played back on anything from a CD player to a computer to an iPod or other portable device.
Unfortunately the typical download is of questionable quality for higher levels of playback performance. MP3’s are a lossy, compressed format. Of the two attributes, lossy is the more egregious. Lossy storage of music means that you are literally discarding parts of the music signal, the parts that an algorithm has predicted you will miss less. Unfortunately it is this kind of low level detail that makes recorded music sound natural and involving. Many people don’t realize it but using a device like an iPod does not mean you have to seriously degrade your music. I use an iPod in my car’s glove compartment which provides non-lossy compressed music via a digital stream to a dash mounted playback system. Virtually all of the music was ripped from my own CD’s.
CD players are giving way today to small iPod type devices and, on the higher performance front, computer based digital playback. This is a near ideal way to combine the incredible ease of use of a music server with levels of performance associated with the very best digital has to offer. Music is ripped and stored on a hard drive on a PC or Mac, and is played back by streaming via USB to an external Digital to Analog Convertor (DAC). There is a wide range of playback and control options including using an iPhone, iTouch or iPad to control your music. There is enough involved to warrant a separate discussion so please see the Computer Based Music section for more in depth coverage.
Many listeners consider speakers to be the primary determinant of sound quality in a system. While speakers are certainly important, and are a transducer, meaning they change a signal from one form of energy to another, in this case electrical to acoustic, they inherently can’t be any better than the signal they are provided.
The tuner, of course, pulls in broadcast signals, either analog or digital. The preamplifier selects the desired source and either attenuates or amplifies the signal being fed to the power amp. Although some people feel the best sound is available going straight from the source to the power amp, with some means of attenuation built in, our experience is that a good preamp is a great benefit to a system. The power amplifier is fed the output of the preamp and amplifies it to drive your loudspeakers.
The most common form of electronics is a receiver. Receivers combine three separate functions on one chassis, with one power supply. These functions are a tuner, a preamplifier, and a power amplifier. The number of channels in a receiver can vary from two in a stereo piece to nine or more in a surround receiver.
Receivers are popular because they are cost effective, don’t take up as much space, and don’t require connecting cables between the units. However their nature does often, if not always, work against them in terms of performance. Moving upwards in performance, in two channel systems, there is an integrated amplifier. Integrated amps do what the name implies. They combine the preamp with the power amp on one chassis. If you want a tuner it is a separate piece.
Integrateds have been around for a long time but always seem to have more acceptance in Europe and Asia, possibly because of the space issues. Although the ultimate is total separates, modern integrateds can provide surprising good performance. They do have one design element working in their favor; rather than having no idea what amplifier the preamp section will be driving and therefore need to put a buffer circuit on the output, the integrated’s preamp section knows exactly what it will see. This enables a simpler circuit, which some consider to be beneficial to sound quality.
Last we have separates. This breaks out all of the pieces. You have a separate preamp, power amp, and tuner if desired. The ultimate separates are achieved when you break the two channels of a stereo amp apart. Each amplifier, or monoblock, drives one speaker.
There are many misconceptions about amplification’s importance in a system. For many years Stereo Review espoused the philosophy that all amplifiers with the same power sound alike. This is simply, and obviously, untrue. Interestingly, the technical editor, Julian Hirsch, who pushed this idea so hard, did a review of a high end amplifier just before he retired. He was shocked to find that there were substantial improvements in the sound. So, after decades of misleading people, he essentially said (think Gilda Radner’s voice) “Never mind”.
Preamps, power amps, and integrateds come in two basic flavors; tube and solid state/transistor. In the early 70’s solid state had become completely dominant for a variety of reasons: It typically cost less, it ran cool, it had better measured performance, it was easier to provide higher power amplifiers. One company bucked that trend, starting a manufacturing company that made all tube products at a time when the technology was officially dead. That company was Audio Research. They still make tube and solid state gear to this day, both to a very high standard.
Solid state has come a long ways since its early days. In fact the very best designs of either technology sound less and less like their chosen technologies and more like music. To paint with a wide brush, people tend to like tube gear for the sense of ease and slight warmth of the sound. The imaging can be very good. There are degrees of these qualities among the different manufacturers. More traditional tube sound has distinct warmth, less controlled bass and slightly rolled off highs. More modern designs tend to be more accurate yet still give a sense of palpability that is very appealing, particularly in the mids.
Solid state gear will typically give you more bass “slam” with good articulation and a slightly more open top end. Some solid state gear is also capable of delivering substantially more current into a 4 ohm load. See Loudspeaker section below. Solid state gear can sound a little analytical and sometimes seems to lack the midrange warmth and can be a little bright on top. Please note that these are all generalizations. One of my favorite ways to combine the best of both is to go with a tube preamp and a solid state power amp. Tube preamps are also easier to maintain. Their tubes tend to last longer than the output tubes in power amps and don’t require a periodic, once or twice a year, check of their bias current. (It’s actually very simple)
There are so many variants in loudspeaker design it’s hard to know where to start. But, start we must…
The most category of speaker is called a dynamic speaker. This basically means it uses cones and domes rather than ribbons or electrostatic panels. Because it is virtually impossible to cover the full frequency range with one driver, most speakers are multi-driver designs, often referred to as two way, three way, etc.
Having drivers cover specific parts of the frequency range requires crossover networks send to each driver the part of the spectrum that it is meant to handles. Crossover design is very complex and usually involves equalization of the drivers as well as the actual crossover function, to provide more linear frequency response. Crossover slopes generally range from first order to fourth order. First order means that the signal to the driver is attenuated by 6db per octave. Second order is 12 db per octave, third is 18, etc. First orders are a rather gradual rolloff, fourth is very steep. First order slopes, with drivers that are staggered so that their voice coils are aligned, is the only option that retains the phase relationship of the original signal. This means that all of the frequencies reach your ear at the same time, a desirable attribute. Like most areas of speaker designs, there are tradeoffs involved with every design decision.
Bass loading is most typically either a sealed box or a vented box. In general, sealed boxes roll off a little earlier and more gradually and vented do the opposite. Sealed boxes are typically less sensitive and vented boxes give you more sensitivity and lower bass, at the expense of the tightness and control of the bass. Transmissions lines are a very complex type of bass loading that have their own attributes. There is debate regarding their being a variant of vented boxes.
Free standing speakers are typically either so called bookshelf, although most are placed on stands, or floorstanding “towers”. Bookshelf speakers are most often two way designs. They tend to not go as low in frequency as floor standing designs and often don’t play as loud. Their advantages include simpler crossover design and less box resonance because of the smaller size.
Floor standing speakers tend to be at the upper ranges of a given brands designs. This does not mean that there aren’t incredibly good, very expensive bookshelf designs. They are just less common in the higher end price points. Floor standers have larger boxes and typically larger drivers which can allow the designer to increase the speaker’s sensitivity and/or provide more low bass extension.
We’ve mentioned sensitivity several times. Sensitivity is used to express the loudness when the speaker is driven by a test signal, typically 1 watt measured from a distance of 1 meter. Sensitivity is often confused with efficiency, which is a measure of how efficient the speaker is at converting the electrical signal into acoustic output. They are related but not the same.
Sensitivity is one of the considerations when deciding how much power you need to adequately drive the speakers from your power amp. Speaker A at 87db sensitivity versus speaker B at 90 db sensitivity will require double the power of speaker B to achieve the same output. The difference in acoustic output of speakers as it relates to the power required is a logarithmic one; an increase of 3 db, what most consider a healthy “turn it up a bit” difference, requires double the power. So, the difference between 2W and 4W is 3db. The difference between 20W and 40W is 3db, as it is for 200W to 400W and 2000W to 4000W. The actual difference in sound level between two otherwise identical amplifiers, one rated at 100W the other at 120W is so small as to be insignificant.
Another factor to consider when matching speakers with amplifiers is the load the speaker presents to the amplifier. Part of this is the impedance rating. We’re all familiar with 4 ohm and 8 ohm speakers. 4 ohm speakers are much more common in today’s world of predominantly solid state amplifiers. You do need to be a little wary of the sensitivity rating of a 4 ohm speaker. 2.83V into an 8 ohm load is 1W. Manufacturers of 4 ohm speakers usually rate their speakers by that same 2.83V. However in a 4 ohm speaker there is half the resistance to current flow, meaning that, per Ohm’s law, you are actually delivering 2W of power to the speaker. Some high end amplifiers are capable of delivering twice their current into the 4 ohm load but most are not.
Speakers can also be a “difficult” load in ways not directly related to their sensitivity, or lack thereof. Even though we refer to ohms in describing a speaker’s load characteristics it is important to note that it is not actually resistance we are referring to but impedance. Resistance is a measurement that applies to DC voltages. Speaker impedance is AC and varies by frequency. Speakers that have low impedance can be hard for some amplifiers to drive, particularly when there is a large phase shift in the same frequency range as the low impedance. The technical word for this kind of speaker is a “pig”.
Another element of how difficult a speaker is to drive is how much back emf (electro motive force) it generates. A current flowing through a coil of wire immersed in a magnetic field is a motor and that is the way a loudspeaker works. However physically moving the coil through the magnetic field is just the opposite; a generator. That is exactly what happens when a bass signal has caused movement outwards in your woofer and the mechanical suspension of the driver pulls it back into place. It is actually generating its own voltage and pushing it back at the amplifier. You can attach a voltmeter to the terminals of a large woofer and move the cone in and out with your hand and watch the voltage rise and fall. Some speakers are much more difficult than others in this regard. See “pig” above. The ability to control the woofer motion in these circumstances is referred to as an amplifier’s damping factor.
There are a couple of alternative speaker designs that I will briefly mention. Horn loading is closely related to regular dynamic speakers but involves using a horn in front of the speaker diaphragm to raise the surface area controlled by the driver, thus raising sensitivity. Some or all of the drivers in a horn speaker are loaded in this manner. Horns typically require much less power than non-horn loaded speakers. They certainly have their adherents but many find the colorations that the horns cause to outweigh the increased sensitivity.
Many of you have probably seen planar type speakers, large flat thin panels. These incorporate one of two technologies, although they look very similar. These two technologies are ribbon and electrostatic. Without going into detail, they both radiate equally front and rear, both are “fast” sounding, and due to the large radiating surface, both have small optimum listening position, typically rolling off most of the highs when you stand up.
Again, a good dealer will be able to guide you to a good match between amplifier and speakers, keeping in mind your subjective tastes as well.
OK, this is a tough one. Some people simply don’t believe cables of any sort make a difference in a system. Some believe that to the point that a discussion about the possibility will raise their blood pressure. We don’t want to do that so if you fall into that category, it’s why we left this for last. If you feel your BP rising, consider not continuing.
We consider cabling to be a system component. It absolutely makes a difference. We demo this every day and often loan out cables so that you can make a comparison at home. Please don’t ask me to explain the technical elements of them beyond the basics, but I can describe the sound very easily.
An analogy that is often made is that cables, and other system components for that matter, are like looking through slightly opaque panes of glass. Replacing one pane with a more transparent one results in better sound. You can get close to having completely clear panes of glass but you can never improve on the quality of the object being viewed, in the case of our analogy, the original recording.
Better cables can remove a number of obstacles to music enjoyment. Subjectively it sounds like it is adding to the quality of the sound but realistically you’re just hearing less degradation. The qualities can include better bass, more natural high frequencies, more detail, more spacious, blacker silence, etc. Cables can be very moderate or very expensive. The investment you want to make is of course, up to you, but we make cables available for in home audition. This makes the process much more relaxing and increases the customer’s comfort level with what he is hearing.
Even though it seems counterintuitive, digital cable can also make a difference. Even though its 1’s and 0’s being passed along, the precise timing is essential and a good cable helps prevent timing errors (jitter). Timing errors as small as 100 picoseconds can be audible.
OK, that covers the basics. If you haven’t done so, feel free to see the section on evaluating audio systems for tips and thoughts about the listening experience and evaluation process.