There are active and passive Speaker crossover networks that can be installed between the amp and drivers.
And there are units that can split the signal between multiple amps running separate drivers.
I have used setups in my band that send the signals to three different amps, the low goes to a giant set of amps running the bass scoops, then a smaller amp running the mids, and a much smaller amp running the horns.
Mainly because they are something we can easily make at home.
Once you understand the basics of crossover networks, you can also figure out if you would rather purchase active crossovers.
The basic job of the crossover is to discriminate low and high frequencies and send the right one to the right drivers.
First, it lets you hook up 2 or more drivers to an amplifier so that the two or three 8 ohm drivers are seen as one 8 ohm load by the amplifier.
Second, it lets you hook up two or more very different types of drivers without getting a large drop in sound pressure across the frequency ranges.
Third, it lets you smooth out the response of either the low end or high end frequencies that wouldn't be possible using the drivers without the network in place.
Unlike other electronics that went from electron tubes, to transistors, and then IC chips, the crossovers are still the same parts used 100 years ago.
The parts work perfectly so why use something else.
You have a resistor, a capacitor, and an open air coil inductor made out of wire, I have always heard people call it a choke coil.
With these 3 parts, we can send the high frequency signals to a tweeter’s while stopping the other frequencies, and do the same with the mid range and the woofers.
How fast it can store and drain power is measured in farads.
One farad equals one million micro-farads. uF is the electronic designation for micro-farads.
In a DC circuit, the restriction of electrical power is called resistance, but in an AC circuit, it is called impedance.
When a capacitor is wired in series with a resistor in an AC circuit, (where both are in line in the same circuit,) the lower the frequency is, the higher the impedance is.
So this becomes by default, a High pass filter.
At a point, determined by the size of the capacitor, at a higher frequency it lets the power pass as though it was just a wire. it acts like a short circuit for the friendly frequencies.
So it acts like a valve that only lets faster waves into the circuit.
A choke coil moves electrons along a path round and round like a merry-go-round, lazily across the diameter of the coil, moving up and down and round and round.
The higher the frequency, the more electrical force is required, so depending on the size of the coil, it chokes the higher frequencies.
It does exactly the opposite of the capacitor.
Putting a capacitor in a series circuit with a tweeter creates a high-pass filter.
At the crossover frequency, the reactance of the capacitor is the same as the impedance of the tweeter.
When choosing a capacitor for crossover duty, remember that audio is a type of alternating current, so you need to use non polarized capacitors.
For use as a crossover, Mylar or other film capacitors work better than electrolytic ones.
But electrolytic capacitors cost less.
This speaker crossover chart shows the crossover point for capacitors and choke coils.
First find the frequency that you want to put the crossover point at, along the bottom line.
Then move up to the line that matches the impedance ohms of the cabinet.
The lines going up and left indicate the capacitor size.
The lines going up and right indicate the choke coil size.
For an even more accurate value you can use these two formulas instead.
Capacitance uF = 159,000 / ( ohms x frequency )
Inductance mH = ( ohms x 1000 ) / ( 6.28 x frequency )
These answers are in micro-farads, or Milli-henries.
These formulas are for first order networks.
Normally, for low and high crossover points, you pick a point around an octave away from the driver limit.
For a woofer with a high end limit of 4,000 HZ, one octave below the maximum would be 2,000 Hz or 1/2 the maximum.
For a tweeter, you look at the low end limit, let’s call it 2,000 Hz.
This time, you would double it to move one octave.
So this will be 4,000 Hz.
These are as simple to use as capacitors for a high pass filter.
You wire them in series with a woofer, or a mid range driver.
These can be store bought, but they can be home made.
It is just a wound coil of wire.
The reactance to high frequency is stronger when there are more windings.
So the coils are often called inductors.
Inductance is measured in Henries, and for crossovers you are measuring Milli-Henry (mH).
A Milli-Henry is 1,000th of a Henry.
First is an open air coil made from magnet wire which is used to make electric motors.
Magnet wire is wire with a very thin layer of insulation on it to make the coils more compact.
You can find magnet wire at Parts Express.com, among other places.
Then there are iron core inductors.
The air cores are the ones you would rather use, but if you need a larger coil then the iron core will give you a stronger inductance with a lower resistance because they don't use as much wire.
Click the link below to go to Parts Express.com
Speaker Building - Build your perfect speaker with our parts and supplies from crossover components to full kits.
Follow the picture and the chart below for the size of the coil you need for your speaker crossover.
I have made this form out of scrap wood I've had around the house.
You can also use plastic, but wooden dowel pins are found in any hardware, lumber or hobby shop.
You can't use metal because it will affect the electrical properties of the coil.
You can use anything that is invisible to electro-magnetism.
You can drill a hole through the center to install a metal nut and bolt, to clamp the parts and mount it in a drill motor to make winding easier, but remember to remove the screw before using the coil.
This form only applies to 8 ohm cabinets.
You can also make the form removable and pull the wire coil off the form.
But you have to be careful not to disturb the coil while removing it, and tape it up to keep its tight profile.
Frequencies for 8 Ohm speakers.
Be sure to keep both ends exposed as a leader to make your connection.
From 4,000 to 10,000 Hz the form should be A = 1 inch, C = 1/4 inch and B = 1/2 inch dowel.
The wire is 24 gauge.
For 4000 Hz the number of turns wound around the dowel pin form is 141. this winding will need 28 feet of wire.
For 5000 Hz it is 125 turns of wire. 25 feet
For 6000 Hz it is 116 turns. 23 feet
For 7000 Hz it is 106 turns. 21 feet
For 8000 Hz it is 100 turns. 20 feet
For 9000 Hz it is 95 turns. 19 feet
For 10,000 Hz it is 89 turns. 18 feet
The next series is for 22 gauge wire, and the form is larger.
The form size is: A = 1-1/2 inches, C = 3/8 inches and B = a 3/4 inch dowel.
This covers 2500 to 3500 Hz.
For 2500 Hz 145 turns 43 feet
For 3000 Hz 132 turns 39 feet
for 3500 Hz 122 turns 36 feet
This series is 20 gauge wire, and the form size is:
A = 2 inches, C = 1/2 inch and B = a 1 inch dowel
This covers 1000 to 2000 Hz.
For 1000 Hz 200 Turns 78 feet
For 1500 Hz 162 Turns 64 feet
For 2000 Hz 141 Turns 56 feet
This series uses 18 gauge wire, and the form size is:
A = 4 inches, C = 3/4 inches and B = a 1-1/2 inch dowel.
This form covers 300 to 900 Hz.
300 Hz 296 turns 175 feet
500 Hz 230 turns 136 feet
700 Hz 194 turns 115 feet
900 Hz 171 turns 101 feet
In a three way speaker crossover system you would put them in series with your mid range driver.
Calculate the capacitor to crossover for the low end of the mid range driver.
Calculate the coil to crossover for the high end of the driver.
A first order speaker crossover fades the energy at a rate of 6 dB per octave beyond the crossover point.
First order networks are simple, and simple is good, these are usually the ones engineers like the best because they are very simple and economical.
A big drawback to a first order crossover is that signals well beyond the limits of the drivers range are still getting to the driver.
The tweeters for instance will blow apart, if they are overpowered by lower frequencies.
Small tweeters can be protected by crossing over sooner, or you can use a second order crossover on the tweeter.
First order crossovers can also cause phasing problems created when two drivers at different distances from the listener create the same sound which cancels the sound out.
Offset drivers are even more prone to this "lobing" effect.
The top drawing is a parallel circuit.
The bottom drawing is wired in series.