Cross-over Help

[the727kid 10+ year member]

Sorry for all the threads... just a newb trying to learn and get help. But onto my question... I need to design a crossover for my center channel. These are the tweets I am using http://www.partsexpress.com/pe/showd...number=275-075

and these are the woofers http://www.partsexpress.com/pe/pshow...TOKEN=73621623 . I want to build a 2.5 xover crossed over at 2khz. Sound good? But I really have no idea how to piece together the crossover, that is where I need help.. As always any help/advice is much appreciated //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif.

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[BrianChia 10+ year member]

Some more crossover basics to get you started:

Acoustic order or slope is how fast the crossover attenuates the sound. It is measured in db/octave.

1st order = 6 db/oct

2nd order = 12 db/oct

3rd order = 18 db/oct

4th order = 24 db/oct

5th order = 30 db/oc

6th order = 36 db/oct

and so forth...

Electrical order is the usually the number of components strictly involved in the filter (not including notch filters, l-pads, impedance compensation, etc.)

Capacitors attenuate lower frequencies while inductor coils attenuate higher frequencies.

Capacitors are wired in series for high pass filters while inductors are wired in series for low pass filters. Capacitors are wired in parallel (as a "shunt") for low pass filters while inductors are wired in parallel for high pass filters.

The most basic crossover would be a "butterworth" 1st order that attenuates at 6db/octave. A 1st order lowpass is simply 1 coil in series with the woofer, the highpass is 1 capacitor in series with the tweeter.

Electrical order of crossovers:

High pass

1st - 1 cap in series

2nd - 1 cap in series, 1 coil in parallel (wrt driver)

3rd - 1 cap in series, 1 coil in parallel, 1 cap in series

4th - 1 cap in series, 1 coil in parallel, 1 cap in series, 1 coil in parallel

Low pass

1st - 1 coil in series

2nd - 1 coil in series, 1 cap in parallel

3rd - 1 coil in series, 1 cap in parallel, 1 coil in series

4th - 1 coil in series, 1 cap in parallel, 1 coil in series, 1 cap in parallel

The electrical orders of crossovers typically correspond to the acoustic slopes listed above (depending on the alignments used to determine component values). However, the total acoustic slope of the driver will be a summation of the attenuation by the electrical crossover and the natural rolloff slope or natural response curve of the driver itself. So a tweeter that rolls off at 12db/oct naturally will have a 4th order acoustic slope when a 2nd order filter is used where the natural rolloff occurs.

For your center channel, I recommended a 4th order acoustic slope (24 db/octave) for the crossover and a 1st order (6 db/octave) for the 0.5 channel. This will serve as baffle step compensation and the frequency is determined by the width of the baffle.

Baffle step compensation

In the most simplified explanation, soundwaves that are shorter than the width of the baffle are reflected forward while soundwaves that are longer tend to wrap around. Because they are not reflected forward, frequencies below the wavelength or the baffle width will not be as loud. The effect is a slope equivalent to -6db/octave centered at the baffle wavelength frequency. In reality the actual attenuation depends on how close you place the speaker to walls or corner since these surfaces reflect sound too. In a 2.5 way the 0.5 speaker compensates for this effect (hence the 1st order slope is utilized). If the speaker is placed close to a wall, then the effect is not as great (maybe only 1-3db of compensation is needed). Thus you use an L-Pad on the 0.5 to fine tune the BSC.

 

[JimJ 5,000+ posts]

Designing crossovers is a PITA.

Chances are, you need some pretty good equipment to know where to cross things over, depending on your room, cabinet design, drivers...etc. It's just so much easier when you're starting out to go active, that way you can play around with slopes and Xover points until you find what sounds best in your room.

Other than that, I'd go with a published design that you know has been testing and confirmed to work with the drivers in question. Zaphaudio, Parts Express, Madisound and others have kits or kit plans that have been tested and are known to be correct.

 

[Fast1one 10+ year member]

Or go full range

 

[the727kid 10+ year member]

Designing crossovers is a PITA.
Chances are, you need some pretty good equipment to know where to cross things over, depending on your room, cabinet design, drivers...etc. It's just so much easier when you're starting out to go active, that way you can play around with slopes and Xover points until you find what sounds best in your room.

Other than that, I'd go with a published design that you know has been testing and confirmed to work with the drivers in question. Zaphaudio, Parts Express, Madisound and others have kits or kit plans that have been tested and are known to be correct.

Where on Parts Express could I find this? I didn't find anything off Zaph and Madi wants $30.

 

[JimJ 5,000+ posts]

Their project page...full write-ups with construction diagrams, crossover schematics/parts lists...I don't know the URL off hand but it comes up with a Google search.

Or go full range

Would be the way I'd go, but I realize the true path to enlightenment isn't for everyone //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

 

[Fast1one 10+ year member]

Would be the way I'd go, but I realize the true path to enlightenment isn't for everyone //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

Amen brotha //content.invisioncic.com/y282845/emoticons/cool.gif.3bcaf8f141236c00f8044d07150e34f7.gif