Designing, Building, and Testing Your Own Speaker System
How a Speaker Works
There are many factors that go into selecting speakers for a speaker system. The first thing to take into consideration would be the frequency response. The biggest thing to remember about frequency response is that a system with a smoother response within a smaller range is better than one that has a larger range but peaks at certain frequency within its range. If you want to get good performance about 10,000 hertz, the cone has to be light. You don't want the mass to be greater than 5 grams, but as you get lower in the frequency range, the cone will bend. The key is that the cone needs to be big enough to produce good bass sound at lower frequencies, but it must be small for good dispersion at high frequencies. A heavier cone will have poorer tansient response and won't perform as well as the range gets higher. However, you can add a secondary cone to help solve this problem, and it is called a whizzer. It is driven by the same magnet and voice coil as the main cone.
Another factor to take into consideration is the speakers transient response. Transient response is a speakers ability to start moving right when it receives the signal from the amplifier, and then stop right when the signal ends. The extra movement of a speaker after the signal ends is called hangover.
"A speaker is omnidirectional only up to the frequency at which the effective cone diameter is equal to the wavelength of the sound. A speaker that is fully omnidirectional when: For a 12 inch speaker, to about 1,300 hertz, for an 8 inch speaker, to about 2,000 hertz, and for a 4 inch speaker, to about 4,000 hertz. If you want your speaker to perform at higher frequencies, you can use a whizzer cone. Sound is more directional at the upper end of their range of frequency.
The opposition of the voice coil to the current flow is called impedance. The restistance of a speakers voice coil is generally about 75% of it's impedance.
A speaker's efficiency is its ability to convert electrical energy into sound energy. Efficiency is sound power output (acousticl watts)/electrical power input(electrical watts). If youw ant to increase the efficiency of a speaker, you can reduce the cones resistance to movement, or you can increase the force of the voice coil. To make a cone less resistant to movement, the best thing to do is to make it lighter. If you divide it's mass in two, the speaker will be 4 times more efficent.
You will also want to take into consideration the power rating assigned to your speakers. Power rating is the amount of power the speaker can take without being damaged. Power ratings rise as the voice coils diameter rises. An amp or receiver with a high power rating is often safer because they can handle more power without being damaged. You have to be very considerate of it's power rating because if you biuld the speakers wrong and exceed the power they can handle, you will damage the speakers, and no one wants that.
Next is speaker polarity. If you are only using one speaker, it doesn't matter which lead goes to which terminal. However, if you have two speakers in the same room that cover the same frequencey range, they can cancel each other's sound. You want to make sure that the leads from the positive terminal go to the positive reciever, and the negative to the negative. You may have the problem of two speakers cancelling each other out. You will want to reverse the leads to one speaker and then test them by facing them. You only have to change the leads on one of the speakers.
A speaker system is made up of direct radiator speakers called drivers. Because single cone drivers struggle to cover large frequency ranges, a good speaker system often consists of two drivers, a woofer and a tweeter. The woofer is for lower frequencies and the tweeter is for higher frequencies. A woofer generally has a limited high frequency response, so the tweeter is added to cover the higher range, making a better quality speaker system. However, there is not a simple cut off line where it will switch from the woofer to the tweeter, there are mid-range frequencies that require a combination of both, so a crossover system is need. Crossover systems are very important because you don't want a driver to recieve the wrong frequencies and fail. If you want a good quality system, a crossover system is used with a woofer and a tweeter.
Kinds of Speaker Enclosures
There are really two types of speaker enclosures that are generally used for most stereo speaker systems, closed-box enclosures and ported-box enclosures. A closed-box speaker is when the speaker is installed and inclosed inside of a closed box. This type of enclosure is generally easy to build. The air in the box acts as a type of air spring. The air, because it is enclosed, acts like a spring against the cone. Closed box systems tend to have poor efficiency, but they do have a a higher bass range. Ported box enclosures are similar to closed-box enclosures, but they have a hole in the back of them. This hole provides somewhat of an air piston which reinforces and increases the range and sound of the bass output. There are other types of speaker enclosures you can make (labyrinths, horns, flat baffle), but considering the cost to build many of them, the complexity of them, and my limited knowledge/budget, closed-box enclosures and ported-box enclosures are the most appealing to me. I think that the closed-box enclosure would be easier for me to make, I think that the ported-box enclosure is the right one for me. It is easy enough for me to make but challenging enough that I will really have to think about what I am doing. The ported-box enclosure, in some cases, costs the same or less to build, and I think with less pressure in the box, the speakers will last longer.
