Crossover design
This is for reference only this is only. Use this information at your own risk.
In a perfect world, we would have a single speaker that would play the entire audio spectrum from 20 Hz (Hertz) to 20,000 Hz or cycles per second. Reality always deals us another picture.
Background Info: Audio Facts
A speaker playing 20,000 Hz or 20kHz changes direction over forty thousand times a second. To maintain the same amplitude, a speaker must move four times the amount of air every time the frequency is cut it half. (see table) To create a sound at the same amplitude as at 20kHz you wound need to displace more than one million times the amount of air! It's no wonder a single conventional speaker can do all this. Table 1
Our solution has been to develop drivers (speakers) that are optimized for different frequency ranges. Typically these ranges correspond as follows. These ranges also correspond to how we perceive location.
| Speaker | Range Name | Bandwidth | Localization Perception |
| Tweeter | Highs or high frequencies | 2,500 - 20kHz | Amplitude |
| Midrange | Midrange or mid-frequencies | 400Hz - 2,500 Hz | Amplitude & Phase |
| Midbass | Midbass or lower mid frequencies | 100Hz - 400Hz | Phase & Amplitude |
| Woofer | Bass or low-frequencies | 20Hz - 100Hz | Phase (Time arrival) |
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topCrossover Basics
Crossovers are acoustical devices or circuits that filter the signal to a speaker. Crossovers can be accomplished acoustically, passively, actively and digitally. There are three types of crossovers: high-pass, low-pass and bandpass.
High-pass crossovers allow high-frequency information
to pass to the speaker while preventing lower frequencies.
Low-pass crossovers allow low-frequency information to
the speaker while preventing higher frequencies.
A bandpass crossover allows a "band" of frequencies
to pass to a speaker while preventing higher and lower
frequencies outside the band.
Top 4 Crossover Myths
- High-pass crossovers are only used for tweeters:
It is commonly thought that high-pass crossovers are only used at the higher frequencies. This is not true. While high-pass crossovers are used for tweeters, the actual frequency does not matter. In fact, subsonic filters (used on subwoofers) are actually high-pass crossovers! - Low-pass crossovers are only used for subwoofers:
Like high-pass crossovers explained above, low-pass crossovers can be used at any frequency. Many amplifiers employ some sort of low-pass crossovers set to a high frequency (above 20kHz) to "filter" out noises generated by power supplies or other switching devices (digital crossovers for example) used in a signal chain. - Bandpass filters are some sort of quasi-filter
alignment:
Some audio companies would like you to believe so. Actually, bandpass filters are just a combination of a high-pass crossover (this determines the lower frequency limit) and a low-pass crossover (determine the high-frequency limit) - Passive
Crossovers rob 3dB of power for every "order":
When I was young an naive, I always believed what I was told. I believed that the above statement was gospel. Only when my friend Gary challenged me (he could not say which way either) did we decide to do a test. We used tweeter and measured the SPL (sound pressure level) with a audio control, we played frequencies well away from are agreed crossover frequency. And the results were interesting. Near the crossover frequency there was some perceptible loss but not 3dB and at higher frequencies, we had trouble measuring any difference. The difference made by slightly moving the tweeter or the microphone (less than an 1/8") made more difference than our simple crossover! I was devastated. All this time I had realized that I believe something just because that is what everyone said was true. Well no more. We did some more testing and my view point about this subject has changed.
There is some truth to this however it is not always true. (This is like saying that all blue cars are cars but not all cars are blue. (Confused?) In a perfect world, passive crossovers would create zero loss. In our world, there is internal loss through passive crossovers. The technical term is called "insertion loss" or the loss created by inserting the passive component between the amplifier and the speaker.
There are many factors that determine the efficiency of a passive crossover component: the ESR (equivalent series resistance) , circuit design and crossover frequency play significant roles. What you can generalize about passive crossover signal loss is this. The higher order the crossover slope high higher potential to lose power. The lower the crossover frequency, the higher potential for power loss. The poorer quality of components, the high potential for power loss. The operative word of these sentences is "potential".
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