This article is provided by Lenard Audio.

 
This article is a basic overview of crossovers.  Next time we’ll take an in-depth look at passive crossovers, followed by active crossovers and then time alignment.

Three octaves or 3.2 octaves (1 decade) is the optimum bandwidth for a speaker (a topic which we’ll touch on in a later article).

The crossovers function is to decrease power at a given rate from either or both sides of a given bandwidth.

The slopes rotate phase in opposite directions. In some passive crossovers this is adjusted for by reversing the polarity of adjacent speakers. Electronic active crossovers can have extra compensating circuitry.

Crossover Points & Order:
At the crossover point, power to each speaker is reduced -3dB (1/2) so total sound energy is 1. At the crossover point sound comes from 2 sources and on-axis directivity is increased.

Recent design trends are for power to be decreased to -6dB (1/4) to each speaker at the crossover point, and the slope rate can be selected.

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1. First order (-6dB /octave) reduces power to 1/4 per octave, adequate for cheap low power systems.

2. Second order (-12dB /octave) reduces power to 1/16 per octave. Provides the best technical accuracy with the least complications and harmonic distortion.

For mid and high speakers the cone or driver diaphragm movement is kept constant as the frequency decreases (constant excursion).

3. Third order (-18dB /octave) reduces power to 1/64 per octave. Is good for protecting speakers at higher power. Also helps reducing bass energy from harming compression drivers with truncated horns.

4. Fourth order (-24dB / octave) reduces power to 1/256 per octave. Is best for maximum control of speakers, but requires critical alignment which is rarely achieved.
Fourth order has become the standard crossover for professional systems.

3 Laws of Crossovers:

1. It is not possible to stitch 2 different speakers together, perfectly.
2. A crossover should have the minimalist complexity to achieve the desired outcome.
3. The more complex a crossover, the more difficult the system is to control.

Selecting Crossover Points
Our ears are most sensitive to detail between 300Hz to 3kHz. As a reference, the telephone system operates between these 2 points.

Sound system distortion between these points can easily be heard and therefore the worst position to cross speakers over, but we have no choice. The best crossover points for our ears do not line up with the physics of speakers.

For domestic use at low power crossing tweeters over between 2kHz - 3kHz is often done in 2 way systems. However the tweeter is easily destroyed at higher power particularly when having parties.

There has been many attempts to force speakers to be crossed over at 300Hz and 3kHz at higher power but with limited success.

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The sound spectrum is large 20Hz to 20kHz (3 Decades or 9 octaves). For home use a passive full range 3-way speaker system is cost effective and adequate for most people.

The best way to understand a 4-way speaker system is to approach it a 3-way, with an added active bass (sub-bass). Hopefully the explanations below will make this understandable.

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