Hi-Fi 101
If I'm going to follow up on my promise to start posting more stuff about my interests, you're all going to have to learn a bit about hi-fi. I'll try to make this as painless as possible.
Let's start with a CD. You all know CDs, right? Shiny little things that used to be all the rage ten years ago? So CDs store a bunch of songs in digital form. Let's go through the process of turning those bits on the CD into music, and in doing so take a tour of hi-fi equipment.
So, the CD has to go into something, right? You think immediately of a CD player, of course, but a CD player actually consists of a couple parts that can be purchased sepparately.
The first is the transport. It's the mechanical part, including the motor and the laser, that pulls the data from the CD.
A transport can output the digital signal straight to a digital to analog converter (DAC), which produces the corresponding analog signal.
This is electrical current that rises and falls with the peaks and dips of the sound wave it represents. Actually, you have two signals, one for the left channel and one for the right channel. They go out over interconnects, often called RCA cables because of the most popular type of connector, those round thingies with a little metal tip sticking out that are usually color coded red and white, with red representing the right channel and white representing the left.
The interconnects carry this line-level signal to a pre-amp. A pre-amp usually has a bunch of sources besides a CD player hooked up to it, and allows you to pick which one you want to listen to without haveing to unplug and replug the interconnects for different sources when you want to listen to a different piece of equipment.
The pre-amp takes the analog signal from the selected source (still the DAC of the CD player), and does something else useful, which is to allow you to change the volume of the signal, by amplifying or reducing the volume of the signal.
But the electrical signal at this point is still very low power. It takes quite a bit of energy to make enough sound to fill up a room, so the pre-amp outputs this volume adjusted signal, using another set of our old friend, the interconnect, to send the signal on to a power amplifier.
The power amplifier ups the energy of the signal significantly. Exactly how much depends on the particular amp you're using, but we'll assume here it's, well, enough.
Enough for what? Follow the electrical signal along 2 wires (speaker cables) to a pair of loudspeakers. The electrical signal hits a magnet, which makes the speaker cone vibrate at the frequency and amplitude (pitch and volume) conveyed by the signal.
Now the tricky thing with speakers is that small speakers don't handle bass well, and large speakers don't handle treble well. So what you see most of the time (unless your speakers are cheap or you're into the really weird shit) is a speaker incorporating multiple drivers of varying sizes that cover different frequency ranges. To make sure each one only produces the frequencies in the appropriate range, you use a crossover to apply a high pass filter (high frequencies "pass" through) to the smaller speaker and a low pass filter (you can figure that one out) to the larger speaker.
Generally the smaller speaker is called a "tweeter" and the larger speaker is a "woofer", a perhaps overly clever bit of onomatopoeia . A speaker with one tweeter (.75-1" in diameter is pretty normal) and one woofer (4-6.5" diameter) is called a 2-way speaker, one with a tweeter, a "mid woofer", and a subwoofer (8, 10, or 12", commonly) is a 3-way speaker, as is a design that uses a tweeter, a "mid-treble driver", and a woofer. If you have one tweeter and two woofers of the same size, it's called a 2.5-way speaker, and so forth.
So we've covered the following parts so far:
For example, it's almost univeral, particularly in what you'd find at, say, Best Buy to see the CD transport and the DAC in one box, and the whole thing is your typical CD player. Actually, it's even more unviersal to just see a DVD player instead of a CD player, but the principle is the same.
It's also quite common to combine the pre-amp and the power amp into one box, which is called an integrated amp or integrated. Add a radio tuner to an integrated amp and you get a receiver, which is the most common for of amplification you'll see.
If a receiver can do more than 2 channels of amplification, and has a DAC which can decode surround sound, it's a home theater receiver. It's also common for an HTR to be able to switch video sources in addition to audio sources and pass the video on to a TV or monitor, so you don't have to change inputs on both the TV and the receiver.
Amplifiers that only amplify one channel of audio and are designed to be used in pairs (or more for a home theater system) are called monoblock amps. If two of these go in the same box, it's called a "dual-mono" design. If a stereo amplifier can be used as a monoblock amp, it's "bridgeable".
It's also pretty common to see CD players with digital audio outputs that let you bypass the built-in DAC and use a standalone one or one built into an HTR. This is because the DAC is usually the most expensive element in a nice CD player.
Some high-end CD players also acept digital inputs so that you can use their DACs for other sources. Some even have volume control so you don't need a pre-amp and can hook straight into a power amp.
If the amplifier is built into the speaker, the speaker is an active loudspeaker. Sometimes these even have their own source switching and volume control, as is common with computer speakers.
Another possibility is that you want to add a sepparate subwoofer to take over the bass duties normally handled by your main speakers. In this case you have an additional crossover which sends the very lowest frequencies to the amplifier that powers the subwoofer, and the higher frequencies to the speaker's own crossover. Subwoofer crossovers can be built in to an HTR (often referred to as bass management), an external box, or part of the subwoofer itself. Same for the amplifier, although you see it in the receiver only in cheap home-theater-in-a-box setups, and usually see it bolted to the back of the sub (a plate amp), or, occasionally, in its own box.
Now, imagine that instead of pulling bits off a CD using a transport, you pull them off a hard drive, and then send them on to a DAC. What you have is a digital music player that plays CD audio that just so happens to not be stored on CD. Essentially, you can do this running iTunes (or whatever software it is the infidels are using these days). Or instead of pulling the bits directly off a hard drive, the music player could even grab them off the network. Maybe you could even compress the CD audio using mp3 or something even better so it takes up less space on a hard drive. Wouldn't that be fancy...
So that gives you an overview of the basic parts of a stereo system, so the terminology won't be completely alien to you when I start throwing it around in future blog entries. Next time I'll talk about the equipment I have, and where my system stuff fits in to the schema described above, why I chose the gear I did, and what gear I ultimately aspire to own.
Source
Let's start with a CD. You all know CDs, right? Shiny little things that used to be all the rage ten years ago? So CDs store a bunch of songs in digital form. Let's go through the process of turning those bits on the CD into music, and in doing so take a tour of hi-fi equipment.
So, the CD has to go into something, right? You think immediately of a CD player, of course, but a CD player actually consists of a couple parts that can be purchased sepparately.
The first is the transport. It's the mechanical part, including the motor and the laser, that pulls the data from the CD.
A transport can output the digital signal straight to a digital to analog converter (DAC), which produces the corresponding analog signal.
This is electrical current that rises and falls with the peaks and dips of the sound wave it represents. Actually, you have two signals, one for the left channel and one for the right channel. They go out over interconnects, often called RCA cables because of the most popular type of connector, those round thingies with a little metal tip sticking out that are usually color coded red and white, with red representing the right channel and white representing the left.
Amplification
The interconnects carry this line-level signal to a pre-amp. A pre-amp usually has a bunch of sources besides a CD player hooked up to it, and allows you to pick which one you want to listen to without haveing to unplug and replug the interconnects for different sources when you want to listen to a different piece of equipment.
The pre-amp takes the analog signal from the selected source (still the DAC of the CD player), and does something else useful, which is to allow you to change the volume of the signal, by amplifying or reducing the volume of the signal.
But the electrical signal at this point is still very low power. It takes quite a bit of energy to make enough sound to fill up a room, so the pre-amp outputs this volume adjusted signal, using another set of our old friend, the interconnect, to send the signal on to a power amplifier.
The power amplifier ups the energy of the signal significantly. Exactly how much depends on the particular amp you're using, but we'll assume here it's, well, enough.
Speakers
Enough for what? Follow the electrical signal along 2 wires (speaker cables) to a pair of loudspeakers. The electrical signal hits a magnet, which makes the speaker cone vibrate at the frequency and amplitude (pitch and volume) conveyed by the signal.
Now the tricky thing with speakers is that small speakers don't handle bass well, and large speakers don't handle treble well. So what you see most of the time (unless your speakers are cheap or you're into the really weird shit) is a speaker incorporating multiple drivers of varying sizes that cover different frequency ranges. To make sure each one only produces the frequencies in the appropriate range, you use a crossover to apply a high pass filter (high frequencies "pass" through) to the smaller speaker and a low pass filter (you can figure that one out) to the larger speaker.
Generally the smaller speaker is called a "tweeter" and the larger speaker is a "woofer", a perhaps overly clever bit of onomatopoeia . A speaker with one tweeter (.75-1" in diameter is pretty normal) and one woofer (4-6.5" diameter) is called a 2-way speaker, one with a tweeter, a "mid woofer", and a subwoofer (8, 10, or 12", commonly) is a 3-way speaker, as is a design that uses a tweeter, a "mid-treble driver", and a woofer. If you have one tweeter and two woofers of the same size, it's called a 2.5-way speaker, and so forth.
Combinations
So we've covered the following parts so far:
- CD transport
- DAC
- Pre-amp
- Power amp
- Crossover
- Loudspeaker
For example, it's almost univeral, particularly in what you'd find at, say, Best Buy to see the CD transport and the DAC in one box, and the whole thing is your typical CD player. Actually, it's even more unviersal to just see a DVD player instead of a CD player, but the principle is the same.
It's also quite common to combine the pre-amp and the power amp into one box, which is called an integrated amp or integrated. Add a radio tuner to an integrated amp and you get a receiver, which is the most common for of amplification you'll see.
If a receiver can do more than 2 channels of amplification, and has a DAC which can decode surround sound, it's a home theater receiver. It's also common for an HTR to be able to switch video sources in addition to audio sources and pass the video on to a TV or monitor, so you don't have to change inputs on both the TV and the receiver.
Amplifiers that only amplify one channel of audio and are designed to be used in pairs (or more for a home theater system) are called monoblock amps. If two of these go in the same box, it's called a "dual-mono" design. If a stereo amplifier can be used as a monoblock amp, it's "bridgeable".
It's also pretty common to see CD players with digital audio outputs that let you bypass the built-in DAC and use a standalone one or one built into an HTR. This is because the DAC is usually the most expensive element in a nice CD player.
Some high-end CD players also acept digital inputs so that you can use their DACs for other sources. Some even have volume control so you don't need a pre-amp and can hook straight into a power amp.
If the amplifier is built into the speaker, the speaker is an active loudspeaker. Sometimes these even have their own source switching and volume control, as is common with computer speakers.
Another possibility is that you want to add a sepparate subwoofer to take over the bass duties normally handled by your main speakers. In this case you have an additional crossover which sends the very lowest frequencies to the amplifier that powers the subwoofer, and the higher frequencies to the speaker's own crossover. Subwoofer crossovers can be built in to an HTR (often referred to as bass management), an external box, or part of the subwoofer itself. Same for the amplifier, although you see it in the receiver only in cheap home-theater-in-a-box setups, and usually see it bolted to the back of the sub (a plate amp), or, occasionally, in its own box.
Now, imagine that instead of pulling bits off a CD using a transport, you pull them off a hard drive, and then send them on to a DAC. What you have is a digital music player that plays CD audio that just so happens to not be stored on CD. Essentially, you can do this running iTunes (or whatever software it is the infidels are using these days). Or instead of pulling the bits directly off a hard drive, the music player could even grab them off the network. Maybe you could even compress the CD audio using mp3 or something even better so it takes up less space on a hard drive. Wouldn't that be fancy...
So that gives you an overview of the basic parts of a stereo system, so the terminology won't be completely alien to you when I start throwing it around in future blog entries. Next time I'll talk about the equipment I have, and where my system stuff fits in to the schema described above, why I chose the gear I did, and what gear I ultimately aspire to own.
Labels: electronics, hi-fi, music, technology
posted by L. Maxwell Ward at 11:51 PM
