# Computer Speaker Basics



## vortmax

*Computer Speakers 101*

Computer speaker basics 

Why was I sent here?
There have been an uncanny number of posts concerning attaching speakers to sound cards.  This should answer any general questions you may have.

This thread is dedicated to informing the reader of two things

   1. Knowing how speaker systems work
   2. Knowing how to properly hook up said speakers to their computer


1. How Speakers Work 

*Basics *
Speakers are composed of a dome or cone of material such as cellulose (paper), rubber, Kevlar, ect.  This material is semi-rigid and is able to be flexed and still return to its original shape.  A voice coil, consisting of a coil of wire, is attached to the base of the cone which surrounds a solidly fixed magnet.  By passing current though the coil, a magnetic field is produced either attracting the coil to the magnet or repelling it away.  Signal is typically in the form of a sine wave, consisting of positive and negative voltage.  Passing this though the coil causes the coil to occilate at the frequency of the signal wave.  Moving the voice coil back and forth forces the cone to deflect outward and back inward, creating pulses of air known as sound waves.  How many times the cone moves in one complete cycle per second is the frequency of the sound.  The unit used it Hz (hertz) or cycles per second.  That is how a speaker works.

*Signal Power*
It is a speaker's job to move air.  For a high frequency wave (high pitch), the speaker cone doesn't not have to deflect very far.  It has to travel back and forth several thousand times per second, so it doesn't travel very far before being drawn back inward.  Since the coil isn't moving very much (thus not moving much air), it doesn't take a ton of power.

A woofer on the other hand has to move a great deal.  It needs to oscillate under 100 times per second.  Good woofers can hit below 50 Hz.  This means the cone has to travel a greater distance.  To allow it to travel this great distance, the diameter of the cone needs to be much larger then that of a tweeter.  This means the a woofer needs to move a heck of a lot of air, which requires more power.  

So the basic concept here is tweeters require less power then woofers.  So we can see that we can't just throw any signal at a speaker and expect it to play.

*Amplifiers and such *
All audio sources, such as your cd player, DVD player, sound card, ect... output these signals needed to drive the speakers.  These components are concerned with generating the signal in the proper channels and making them as crisp as possible.  One could make the output powerful enough to drive speakers, but this has some drawbacks:


Not all speakers require the same power or impedance, so you would have limited choices for speakers
Boosting the power to a useable level uses a lot of power.  Much more then you would want to pull though the Power Supply
The transistors used in amplification generate a lot of heat, not what you want in a case.

To simplify things, these audio components output a reference signal.  The reference signal is just a low power version of the signal passing through the speakers.  This signal must be passed through an amplifier to make it useable.  When you buy computer speakers that plug into your sound card, there is an amp built into the system somewhere (usually where all the inputs connect).

To attach external speakers to something that only puts out a reference signal requires an external amp.  Simple enough?


*So what about Digital sources?*

If you have a card with some sort of digital output (optical or coax) you can patch it into a device with digital inputs.  DUUHHH

However....It's not as simple as this.  We have to deal with how sound is digitally transmitted.

Transmitting signal digitally only really pays off when we get into 5.1 and above, essentially anything more then stereo.  Since we are dealing with 6 channels of audio (or more) they had to find a way to smash all that data together to allow for it to be transmitted at once.  There are three mainstream encoders that do this.  These are:


Dolby Digital
Digital Theater Systems (DTS)
Lucas Film THX

I'm not going to go into the differences, but they all do about the same thing.  Compress multiple channels into one data stream.

When you have something that outputs encoded audio, like a DVD player or a game, you have to decode the data before you can send it to the speakers.

**NOTE**  I have yet to encounter a set of computer speakers that have a built in decoder or digital jacks, so you will most likely use this for patching into a HT receiver.

If your card has a decoder on board, and you let it do the decoding, it will pass the audio to the receiver via digital cable in a format known as PCM (Pulse Code Modulation).   This is not the most accurate form of transmission as you get bit sync errors (sound doesn’t sync between channels or with video).  The better way to do it is to allow the receiver to do the encoding.  This is performed by forcing the audio card to output raw undecoded data, or bitstream.


One word of warning:  SB Audigy cards with optical ports lack that ability to pass raw bitstream data through the optical port.  They will also not send anything higher then 2 channels though the optical port, so the only way to get 5.1 sound out of one is though the component jacks.


2. Making it all work 

First off the cable types:


*1/8” mini-jack:*
Male:





Female:






*RCA cable (same as digital coax, except only one cable):*
Male:





Female:





*Optical:*
Male:





Female (with protective plug):




*Standard hook up*

Your sound card will undoubtedly contain female 1/8” mini jacks (aka head phone jacks) and you speakers will have the male versions.  Each jack is capable of carrying two channels worth of sound.  So a stereo set of speakers will have a single cable.  4.1 speakers will have 2 wires and 5.1 will have at least 3 wires.  I say at least because some systems split the center channel and the sub channel into 2 separate wires with the sub usually using an RCA cable.

To hook up your system you need to find which color cable corresponds to which set of channels and match that to your sound card.  Documentation is your friend.

*Hook up through a receiver *

When patching into a HT receiver, you can either run digital cable (optical or coax) from the appropriate port on the sound card to the appropriate port on the receiver, or by running component audio (if the receiver supports it). To do this you will need cables with male mini jacks on one end that split into two separate cords with male RCA plugs on the other end.  These are available at most stores.  You then match the channels again.  You may have to play with it to figure out which RCA jack corresponds to the right and left channels.


*Running independent speakers*

Remember from the previous section I mentioned that you need to amplify the reference signal from the card to make it work?  When passing the signal into a receiver, it is passed through an internal amp before being sent to the speakers.

You can do this the hard way, but you will need to find a separate amplifier.  You will need as many channels of amplification as you have speakers to hook up.  So for 2 speakers (standard stereo) you will need a two channel amp, or two one channel amps.  5.1 will require 6 channels of amplification.  

When selecting an amp, you will need to get one that matches your speakers, or get speakers to match your amp.  As a general rule of thumb you need to match the RMS power of the speaker to the RMS power of the amp.  This is not 100% accurate, but when you get to the point of needing this info, you will have moved into the realm of Home Theater which has it’s own discussion boards.  The more important thing to match is the impedience of the speakers to the amp.  Most home theater speakers (except for high end woofers) are rated at 8 ohms.  Most amps will handle anything from 2 to 10 ohms, but check the spec sheet to make sure before you start hooking things up.  You can easily overheat the amp or the voice coil if you don’t.

This approach is more complicated and more expensive, but has potential to produce amazing sound.  This is why all super high end home theater systems use separately amplified components.

*Receiver VS Amps*

So for high quality sound, you need to ask: Do I want a receiver or separate amps?

Lets look at pros and cons


*Receiver *

*Pros *

Multiple inputs: Can hook more then one component into the system, yielding greater flexibility
Internal Amp: clean and space saving design.  Everything is contained in one package
Built in crossover:  Crossovers limit frequencies sent to speakers.  This keeps base notes from going to tweeters and high notes from going to the sub.  Not a concern with component audio, but can be a concern with some sub configurations
 Built in DSP:  May receivers make use of matrixing algorithms such as Dolby PrologicII that will convert 2 channels of audio into 4, so you can turn stereo into halfway decent surround sound.  This is not always available on sound cards, and passing decoded matrixed sound can cause sync issues.

*Cons*

Thermal issues:  Enclosed amps within receivers generate a lot of heat.  The “all in one” design isn’t great at heat dissipation.  Some receivers are worse then others
Power limitations:  Because of power, thermal and space limitations, an internal amp will never produce the power a system with independent amps will
Frequency range:  Receivers usually run a single multi channel amp.  This limits the amount of signal processing that can be performed.  This does limit the sound quality, but not by much
The number of speakers used in the system is limited by the internal amp’s characteristics.

*Amps *

*Pros *

By using separate amps for each channel (or even sets of speakers on the same channel) you can effectively use combinations of speakers instead of just a few.  Large tower speakers that consist of a sub, midrange and some tweeters are usually separately amped
Easier use of crossovers:  Again, you have more control of the signal and how it’s split and when it’s amped, so it’s easier to get very specific bands of frequencies to specifid speakers.
Higher power:  You can use much larger speakers that require much more power, as you are no longer trying to split power 5 ways.  You can run a single sub with a single amp and put several thousand watts through it if you want.

*Cons*

Cost: Adding extra amps costs money, and amps are not cheap.
Complexity:  The more you add to the system, the more complex it becomes.  You will soon find yourself a master at tweaking settings, soldiering wire and hiding cable.
Did I mention expense?  A good system like this will run $10,000 and up.

So in a nutshell:

Running separate speakers will be more expensive, but offers you greater flexibility and much better sound quality.  Using a standard receiver is the simplest and most cost effective means of getting the job done.  It does limit flexibility somewhat.  If flexibility is what you want, then running separate amps is for you.  Note:  you can run separate amps and have it run like a normal HT system with a preprocessor, which is just a receiver with no internal amps.  I should add I'm running a 6.1 system through an Onkyo reciever and it is more sound then I need.  Like I said earlier, playing with seperate amps is pretty complex and takes some know how to do properly.  Unless you have very specific needs, or are a serious audiophile, you could run a reciever based system all your life and not be unhappy.


mods:  can you make this a sticky and tell me of any alterations I need to make to it?


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## Praetor

Sticked for now, will go over in the near future; a very nice start.


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