Re: This Forum Needs A Sticky
Originally Posted by squeak9798
I have lurked here for a while. I figure the least I can do is toss out some info. Most of this is pretty basic, but for the sake of completeness I will try and provide some info about each of those terms.
Originally Posted by Bigrick31
Crossover Points I am sure you have heard the term 20 to 20 in refering to audio. Sound is just pulses of air pressure our ears can pick up. Frequencies are measured in cycles per second (Hz) which is just the number of pulses which happen each second. If your speaker moves back and forth 80 times in a second it is playing an 80Hz tone. It is generally acepted that the range of human hearing is 20Hz to 20KHz. KHZ is KiloHertz or 1000Hz. If you know piano, the fundamental tone for middle C on a Piano is about 263 Hz. You will not find any speaker anywhere which can produce 20Hz all the way up to 20KHz (that will fit in your car or that you can afford). That is why you use some combination of tweeters and woofers to reproduce sound. A typical 2 way component set will have the tweets covering notes from 3KHz-20KHz and the midbass covering from 80Hz-3KHz. The sub covers 20Hz-80Hz. In the system I just described the crossover points would be 80Hz (where the sub gives way to the midbass) and 3KHz ( where the midbass gives way to the tweeters)
Crossover Slopes In the above example I listed a midbass/tweeter crossover point of 3KHz. If I were to unplug my midbass speaker and play a 1.5 KHz tone I should not hear anything, right? Wrong. The hand off between two speakers is very gradual. If you take two speakers playing the exact same note at the exact same db, the result would be 3db higher than one speaker. Since the falloff of a speaker is gradual, the crossover point is the tone where both speakers are down 3db. There are a few common crossover slopes: 6db, 12db, 18db and 24db. These are know respectively as 1st order, 2nd order, 3rd order and 4th order. What does this mean? In my example from above, if the crossover slope was 3rd order (18db) it means that for every octave below the crossover frequency the sound fades off at 18db. So if we were to unplug our midbass and play a 1500Hz tone (one octave below 3KHz) it would be 18db below a 3KHz tone played into the tweeter.
tweeter attenuation In most car audio environments the tweeters end up very close to your ears while the mids end up further away. Since the tweeters and mids are playing at the same level it would make the tweeters sound louder than the mids since they are closer. This is why many crossovers will have tweeter connections for 0db, -3db, -6db etc... This allows you to lower the power to your tweets so you can match them to the volume of your mids. This is known as tweeter attenuation. FYI since every 3db drop is half power if you have your tweets set to -6db and running off a 100watt RMS amplifier you are actually only sending 25watts to your tweeters.
tweeter protection Like any speaker, if you stress them too much they will break. Some crossovers will have fuses installed between your amp and tweeters that will blow at a predetermined wattage to prevent you from blowing a tweeter.
impedence compensation [zobel network] This one is a bit harder to explain without getting into crossover design theory. Basically in order to design a crossover you need to know what the impedance of the speaker is. The components for a 3Khz, 6db slope crossover are totally different if you are using a 4ohm speaker rather than an 8ohm speaker. The problem comes into play near the resonant frequency of the speaker. As a speaker aproaches it's resonant frequency it tend to resist electricity more. For example, in a common 6ohm tweeter with a resonant frequency of 1Khz, the amplifier may see a 12 ohm load at 1Khz rather than a 6ohm load. This REALLY messes with crossovers because they suddenly see a 12ohm load and their crossoover point changes for that moment!!! A zobel network is normally used when you are driving tweeters down to a point near their resonant frequency. It is a set of components which divert power through a resistor near a particualr frequency (normally tuned to the resonant frequency of the tweeter) so as to show the crossover and amplifier a more consistant resistance.
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