Types of Speakers
Coaxial
Coaxial speakers (or three-ways) are two (or more) speakers built-in the same frame. They are cheaper than separate woofer and tweeters and also easier to install. There is no need to worry about crossovers, since they are already built-in (you might still need to add a crossover to block bass if you are using high-power amplifiers). A disadvantage of coaxial is the lack of flexibility. For example, if the coaxial is all the way in the kick panel, or door panel aiming at your feet, not your ears. Some manufacturers try to compensate for this by making adjustable tweeters. You should usually consider coaxial speakers for the back of the car, in a car audio installation, and separates for the front, unless you only have one speaker hole and don't plan to cut any more holes in the car, for the audio installation.
Separates
Separates consist of a tweeter and woofer, and [most of the time] come with an external crossover. The woofer is usually mounted in the factory hole in the door or kick panel. The tweeters can be mounted in different places. The most common place to install tweeters is towards the top front corner of the door panel, aiming (if possible) between both front seat head rests. Another popular location for tweeters is in the dash, either surface mounted, or in factory dash holes. Yet another location where tweeters are commonly mounted is in the blank plastic piece on the top front side of the doors (where the mirror is on the outside). You would have to experiment with angle and location to achieve the best possible imaging and staging.
Midbass
Midbass are usually 5, 6 or 8 inch speakers that are designed to go lower in frequency and are part of a three way system with a mid and tweeter. The problem is that 3-way arrangements require more complicated crossovers. A well-balanced three-way set up will give you accurate imaging and staging. Midbass are most commonly mounted in the doors.
Subwoofers
Subwoofers add lower frequencies to the whole system. They have to be enclosed in a box, with the exception of free air subwoofers, which use the trunk as a box. There are many different types of boxes and implementations discussed in the subwoofers section.
Horns
A few high-end manufacturers are making horns for car audio use. Horns are very good at directing sound and have high efficiencies. Horns are usually mounted under the dash. By doing this, difference in distance from left and right speakers are greatly reduced over conventional mounting locations. Since horns play mids and highs, tweeters are not needed. Even though horns are mounted under the dash, they give great imaging. Horns cost more than conventional speakers and require customization. In many installations a good equalizer is required to compensate for their high sensitivity.
Center Channels
Center channels consist of a midrange speaker (3 or 4 inch) mounted in the middle of the dash (usually) on the top. Center channels play a mono (Left + Right) signal between 350 - 500 and 3500 Hertz (voice range). The purpose of the center channel is to raise the sound stage, by creating the sensation of the singers "being" in the front of the car, in a car audio installation, and not in the door panels. Center channels are hard to implement though: First, a band pass crossover is needed. Left and right channels have to be summed up. There are various commercially available center-channel processors (many with built-in amplification). The volume level of the center channel should be lower than the other speakers, since it is only supposed to make subtle changes to the total sound image.
Mounting Locations
Front Speakers
The best place to mount speakers in the front, in custom kick panels. By doing this, the path between the speakers and ears is minimized giving the best possible sound without having to add time delay circuitry. If this is not possible, try to point the speakers towards the center of the car, in a car audio installation, and try to minimize the distance between the right and left speakers to your ears. Custom kick panels are usually built from fiberglass or molded plastic, and are available from some manufacturers such as Ai Research.
Rear Speakers
Rear speakers should give a sense of space to the music, but not overpower the front speakers. If you are using rear speakers to add more bass to the system, at least use a crossover to cut off higher frequencies. You should be able to barely hear the rear speakers. A lot of hi-end systems don't even have any rear speakers. Separates are not necessary for the rear, a set of coaxials will work good for rear fill.
Sizes and Shapes
There are many speaker sizes ranging from 1-inch tweeters to 18-inch (or bigger) subwoofers. A smaller speaker will reproduce higher frequencies better than a bigger one. The wavelength of a 20,000 Hz signal is very small, while the length of a lower (bass) note moving in the air could be as big as 40 feet. That explains why a 4-inch speaker can't really put out bass (the lower the frequency, the more air mass that has to be moved by the speaker). Tweeters are designed to play frequencies from 3500, 4500 or even 6000 Hz, all the way up to 20,000 Hertz. Midranges (3, 4 or 5 inchs) play music from around 300, 500 Hz, to where the tweeters start in the upper level. Midbass (5, 6, 8 inches) play from around 50 Hz to 500 (and even 1000) Hz. Subs handle frequencies below 120 Hertz.
Do round speakers sound better than oval-shaped speakers (i.e. 6x9's)? The answer is yes for most practical purposes. A round cone is more rigid than an oval-shaped one, so at higher levels, an oval-shaped speaker will distort more. The reason why there are oval-shaped speakers is because of rear deck space considerations by manufacturers. An advantage of a 6x9 speaker over a 6-inch speaker is that it has a bigger area, so it will move higher air volume, producing more bass.
Power Considerations
Most people think that if they use a 50 watt per channel amplifier on their factory speakers, the speakers will be damaged. This may be true if the speakers do not have crossovers blocking off frequencies speakers were not designed to play. What destroys speakers is distortion. If you turn the volume all the way up on the radio, there will be distortion. If you start hearing distortion, turn the volume down. A high power amplifier allows the volume in the system to be higher, while the volume control on the radio is down in the range where no distortion is present. It is better to have more power than what you need to get cleaner sound.
So how much power do you really need? 30 to 50 Watts (each) would be OK for your front and rear speakers, while a little bit more (100-150 Watts) should be applied to each sub. If you are powering up your tweeters independently, they require less power (20 - 40 Watts). Example: A four-channel set-up with separates in the front and coaxials in the rear with two subs will need about 40 Watts on each channel (Total=160W), and 100W going into each sub (Total=200W). Notice that total power going to subs is more than total power going to the rest of the speakers. This is because our ears are less sensitive to bass.
Wiring
A trick that professional car audio installers use to get more power out of amplifiers is to wire up speakers in different ways, playing with resistances to achieve a desired total impedance "seen" by the amplifier. Even though speakers are active loads (resistance changes with frequency), it is accepted to treat speakers as resistors with a fixed resistance value (usually 4 ohms).
Parallel Resistance:
People commonly hook up two or more speakers to the same channel out of an amplifier in parallel. This is achieved by hooking up the negative wire from the amp to all the negative connections of the speakers, and the positive to all the positive connections of the speakers. By doing this, the load seen by the amplifier is lower. For example, if two 4-ohm speakers are wired-up in parallel, then their total resistance will be half, or 2 ohms. If three speakers are wired up in parallel, and they all have the same resistance value, then the total load would be a third of the value of each speaker's resistance. Here's a formula to calculate parallel total resistance for two speakers:
For more than two speakers, use the following formula:
So what are the advantages and disadvantages of this scheme? First, if one of the speakers burns out, then the other one (s) keep playing. If the amplifier is not designed to receive lower loads provided by hooking the speakers up in this fashion, you might end up destroying your amplifier. Check your manual or consult an expert.
Series Resistance:
Speakers are hooked up in series to decrease total load to an amplifier. To hook up speakers in series, connect the positive terminal of the amplifier to positive of one speaker, then hook up negative of that speaker to positive of next speaker, and so on. Then hook up negative of last speaker to negative of the amp. It is a lot easier to calculate total resistance for speakers hooked up in series. This is easily done by adding up all the individual resistances:
The disadvantage of hooking up speakers in series other than getting less power out of an amplifier, is that if one of the speakers burns up, the other one (s) stop working
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