need help

[kevinbolen]

ok guys i'm new to the list but i need some help, ive recently built a bass guitar cab, its a horned sub cab, i was told i need a hi pass crossover at 100hz,my speaker that i'm using is an eminence 8 ohm, how do i know what size coil or cap i need ? thanks Kevin B

[Green Machine Mowing]

http://www.parts-express.com/resourc...tion-guide.cfm

theres alot to xo's so id post a plan on here and ask for questions before you order anything

[bobblickle]

This is a bit like asking "How hard do I have to press the accelerator to go 50 mph" If you were on a straight flat road for miles this would be pretty predictable. On the other hand, if you were in Colorado or West Virginia the question would suddenly get harder to answer.

Your speaker (any speaker) has a nominal (think 'average') impedance value. In your case it is 8 ohms. On average, Colorado is flat too! The difficulty is that the actual impedance varies with the frequency it is reproducing. This therefore effects the component value required.

Crossovers can also be built at various 'strengths' called Orders or Slopes. The most basic crossover is either a Capacitor or an Inductor (coil). This is known as a First Order Crossover and will reduce the output (in your case below the crossover frequency) by 6db per octave. A rule of thumb is it takes roughly double the amount of power (watts) to raise the volume 3dB. Very roughly, this means that when you play a note one octave below your 100Hz crossover frequency that the driver will be given that signal at approximately 1/4 the power it would if the note were at 100Hz. This means the sound is reduced but it's not a wall, it's a slope, and in this case a shallow one.

This is all without even considering the effect of the horn!

Here's the rub, you should ask the designer of the horn exactly what he recommends for the driver you're using. That would be best. Barring that, ask him what the slope of the crossover should be and provide us a model number for the driver.

I could have just said it's a 200 microfarad Capacitor but that is a crap answer and could potentially cause a problem for your amp. Try to get more info and we'll try to help.

bb

[rogoll]

I really appreciate the above response by Bob (I guess that's his name?). A nice way of taking one of us "apprentices" and teaching us some of the "master's" wisdom without making us feel dumb. Thank you! By the way, really good explanation of XOs and a good way to explain it (going 50 mph...you can add parts of Alabama to that analogy as well).

[spasticteapot]

The simple way to do this is to multi-amp and use an active crossover. Unlike passive crossovers, which are dependent on the frequency-specific impedance of the speaker they're connected to, active filters work the same way no matter what they're connected to.

[dotzs]

Go with an active X over hopefully with different slopes =steep thru shallow ,mmmmm wonder what the P.E. sub amp would do for a live bass rig with another cabinet running 8s and maybe a 3" mid/high driver ????????????????