How to build a speaker crossover?

Question

I would appreciate someone who is going to help me building a speaker crossover. If you E-mail me a schematic design would be great. I have two live speakers (woofers) 300 W 8 ohm 44 Hz-2kHz and two H F Drivers 30 W 16 ohm 1.2 kHz-20 kHz (horns).
Thanks Baskin.

Answer 1

Maniac's response is very good. I have just a few additional thoughts. As he says, you can find simple calculators that will spit out a crossover design from nominal impedance measures, but those rarely produce good real-world outcomes. You may end up with decent results by tinkering around with different crossover component values and listening to the results. Getting proper measurements and using them in crossover design software is usually a quicker and more reliable path to good outcomes.



I also use LspCAD as my primary speaker design tool, but since I got started with it, a wealth of excellent alternative tools have become available at low or no cost. One of the most popular is Jeff Bagby's Passive Crossover Designer (available here: http://audio.claub.net/software/jbabgy/jbagby.html). It is a free download, but will only run under Microsoft Excel.



With any of the software tools, there is a fair amount to learn before you'll have a decent understanding of what you're doing. There are hobbiest forums on the internet that can help you along the way. One of my favorites is the Tech Talk forum sponsored by Parts Express, http://techtalk.parts-express.com/forumdisplay.php?2-Tech-Talk-Forum. I recommend starting there with The Speaker Building Bible, http://techtalk.parts-express.com/showthread.php?219617-The-Speaker-Building-Bible.



After reading through the above link, feel free to ask for help on the forum. For example, you may find a nearby hobbiest willing to measure the impedance and frequency response curves of your drivers so you can get started using a good crossover design tool.

Answer 2

Maybe this will help you out...



http://www.apicsllc.com/apics/Misc/filter2.html



The link gives you a basic calculator, you just tell it the impedance of your drivers and what crossover frequency you want. You can do from 1st order ( -6 dB/oct) through 4th order (-24 dB/oct). It will tell you what inductor and capacitor values to use.



Now for the bad news... the results will be wrong. Simple calculators like this assume a flat frequency response from the drivers and they assume DC resistance from the speaker impedance. It may give you a starting point but if the results are good it will be due to shear luck.



The problem is that a speaker voice coil is not a resistor, it's a resistor in series with a capacitor in series with an inductor. Capacitors and inductors impedance vary with frequency. What's worse, the speaker inductor and capacitive elements are not constants. So, you have an element that varies with frequency even if it's value were constant and to make it worse it's value is not constant. They are variables within variables.



The other problem is that the speaker frequency response is not flat. Even if the impedance issue didn't exist you would still have the problem of such a simple crossover calculator not compensating for irregularity in the driver frequency response.



To do it right you need a measurement system to measure both the impedance curve (the impedance across frequency both magnitude and phase) and the frequency response. Then you need a real crossover software package like LspCAD http://www.ijdata.com/ (about $1,100.00) Once you have all that, you can do it right!



Baring having the proper equipment, being armed only with the simple calculator in the link above your only option is to do this by trial and error, mostly error. Start with what the calculator gives you and listen and adjust. If you download ARTA http://www.artalabs.hr/ and put a microphone with it you can at least get a look at frequency response. Then you can see what happens when you change values. With a simple inductor and capacitor for a 2nd order low pass filter on the woofer for example you might get a peak at the crossover frequency. ARTA would allow you to see this. In that case add some resistance (2 or 3 ohms to start) in series with the shunt leg (the capacitor in this case). Observe the peak go away.



In truth, with the ARTA measurement system and the simple calculator you will be better equipped than I was many years ago before going through many thousands of dollars in other measurement equipment far more expensive than LspCAD. It will be a bit of work trying different component values while watching the measurement result but in the end you can get good results.



You have your work cut out for you but it can be fun!



mk

Answer 3

To do this correctly, one needs to know the DC resistance of the drivers - the stated resistance figures are "average." Model numbers might allow me to look them up. There are also some other considerations; were I to do this, I would also want to see both a frequency and impedance curve for the drivers.