Crossover question(s)

[BoomieMCT]

I have a speaker I'm thinking of building and (as a learning experience) I want to make the crossover myself. However, before I embark on this journey I have some questions.

I am thinking of using an 8" Goldwood woofer in an open baffle with this tweeter. To cross this over, I was planning on using a second order Linkwitz-Riley circuit crossed at 2250 Hz. Because the woofer in an open baffle alignment can easily overexcurse itself below 80Hz, I was going to also put in a low order highpass.

Here are my questions:

1. The power handling of the woofer is 65 watts and the power handling of the tweeter is 40 watts. What can I assume is the total power handling? Do I use the lower value, sum them, or what?

2. The impedance of the woofer is 8 ohms and the tweeter is 6 ohms. What can I assume is the total speaker impedance? Is it calculated in the same way as resistors in parallel?

3. For the crossover capacitor and inductor values, do I calculate it using the "nominal impedance" (8 and 6 ohms) or do I use the DC resistance values?

4. Do I simply wire up the highpass circuit before the LR or will there be some sort of interation between the two? Perhaps should I only wire it up to the woofer's part of the circuit?

I apoligize if these seem real basic but I can't seem to find a good information resource that is more comprehensive then Wikipedia but more basic then the Loudspeaker Design Cookbook. Any additional comments are welcome.

[BoomieMCT]

The crossover I was thinking of is attached. C1, L1, C2 and L2 make up the LR circuit. C3 and R3 is the highpass.

[JCD]

NOthing related to crossover's is basic.. I wish I knew a lot more about this stuff so I could give you some answers. Big reason why my next project will be an active network -- I know I'm not smart enough to figure out the crossover bit.

Anyway, I've got some links that may help you.. use them as you see fit.

Link 1
Link 2
Link 3
Link 4
Link 5
Link 6 (Has a basic calculator in the middle area)

JCD

[F1 fan]

BoomieMCT wrote:

I have a speaker I'm thinking of building and (as a learning experience) I want to make the crossover myself. However, before I embark on this journey I have some questions.

I am thinking of using an 8" Goldwood woofer in an open baffle with this tweeter. To cross this over, I was planning on using a second order Linkwitz-Riley circuit crossed at 2250 Hz. Because the woofer in an open baffle alignment can easily overexcurse itself below 80Hz, I was going to also put in a low order highpass.

Here are my questions:

1. The power handling of the woofer is 65 watts and the power handling of the tweeter is 40 watts. What can I assume is the total power handling? Do I use the lower value, sum them, or what?

2. The impedance of the woofer is 8 ohms and the tweeter is 6 ohms. What can I assume is the total speaker impedance? Is it calculated in the same way as resistors in parallel?

3. For the crossover capacitor and inductor values, do I calculate it using the "nominal impedance" (8 and 6 ohms) or do I use the DC resistance values?

4. Do I simply wire up the highpass circuit before the LR or will there be some sort of interation between the two? Perhaps should I only wire it up to the woofer's part of the circuit?

I apoligize if these seem real basic but I can't seem to find a good information resource that is more comprehensive then Wikipedia but more basic then the Loudspeaker Design Cookbook. Any additional comments are welcome.

I can answer a few of the questions but you should read through the links that JCD listed.There is some great info in there.

1. The power handling will be that of each driver.But a poorly designed hi pass filter can reduce the tweeters power handling substantially .Also using the woofer on an open baffle will restrict the amount of power it can handle.

2.Generally the impedance will be that of the woofer below the crossover and the impedance of the tweeter above the crossover.Although the crossover will also have an effect on system impedance.

3.Honestly a crossover designed from a formula has very little chance of working well.Measurements and crossover CAD programs are really needed to get top notch results.But if you want to experiment then use the nominal values.

4. were you just going to use a large cap as a hipass filter?

[BoomieMCT]

Groan. I just finished reading most of those links. Let me see if I got this straight;

1. IF the crossover is designed right the speaker in question's power handling would be 105 (65+40) watts BUT if the crossover isn't designed right the tweeter will most likely suffer (melt) because of it.

2. The speaker's impedence depends on whether the tweeter or woofer is dominant - bouncing between 6 and 8 ohms in this case.

3. The impedance values for the rough formula is the impedence of each of the driver's at the crossover point.

4. It seems to me from the links that, yes, conjugate networks are the sum of their parts.

Is there any good free crossover design software? A crossover equivalent of Unibox or WinISD? I'm afraid of the number of capacitors and inductors I'll have to buy to do complete trial and error.

[F1 fan]

BoomieMCT wrote:

Is there any good free crossover design software? A crossover equivalent of Unibox or WinISD? I'm afraid of the number of capacitors and inductors I'll have to buy to do complete trial and error.

Heres one but it will take a while to learn http://www.audua.com/

[BoomieMCT]

F1 fan wrote:

4. were you just going to use a large cap as a hipass filter?

Oh, and yes, I was either going to simply use a cap in series or a cap in series and a resistor in parallel as my highpass.

[BoomieMCT]

I tried out the FRD Consortiums passive crossover designer. I like this a lot! I can even measure my parts when they come in and compare to the theoretical values. Here is the theoretical response from the crossover I have so far (highpass not yet added).

I've also included a plot using the "textbook" values for a 2nd order LR crossover for comparison.

[BoomieMCT]

I switched to a different woofer and crossover and I think I have my design licked now. I'm ready to start wiring stuff up but I got one more question - what do y'all anchor the parts of the crossover to? I assume they can't be flopping around as a bundle of wire and parts.

[brucek]

Honestly a crossover designed from a formula has very little chance of working well

I guess you could always use REW to check whether a filter worked properly as calculated.

If I loop a cable from output to input on my soundcard and then in REW clear C-weight and meter files, but leave the soundcard calibration file, then that loopback cable should measure a flat frequency response.

Then if I break that cable out so I can connect a passive circuit in series with the loop, I can plot its response.

I calculated a simple passive RC 1st order high pass filter with a C = 0.1uf and an R = 22K, I get a calculated -3dB down fc of 144Hz. So if I test at 75dB, the filter should show 72dB at 144Hz.

So I test it out (I tested 10Hz to 10KHz with a 512 sweep duration x4) and my results are 72.3Hz at 144Hz.

Pretty close...................

hpf.jpg

brucek

[F1 fan]

Bruce,the filter values calculated from formulas for passive crossovers will be accurate.It is when you hook them up to a driver with its varying frequency,phase and impedance responses that the end result is usually quite different than what would be expected from a pure 8 ohm resistor.

[brucek]

It is when you hook them up to a driver with its varying frequency,phase and impedance responses that the end result is usually quite different than what would be expected

Yep, I was aware of that. I thought you were indicating that his standalone crossover wouldn't be as calculated.....

brucek