how do you find the optimum x-over point?

I have a tweeter and a midwoofer. Is it possible to find a good cross-over point with only the t/s parameters for each of the 2 drivers? Do I need the frequency response graphs? Is there a good program available that can do this? I have made graphs with a program called loudspeaker LAB 2, but the graphs seem to be a very rough estimate and my woofer has a flat freq. response up to 10 Khz, which I don't think is actuate.
 

CHRIS8

Disabled Account
2001-12-12 8:47 am
VA, USA
"Is it possible to find a good cross-over point with only the t/s parameters for each of the 2 drivers? "

No.

"Is there a good program available that can do this? I have made graphs with a program called loudspeaker LAB 2, "

Yes, their are good programs for measuring this. The one you specify is one of them. Other choices are Speaker Workshop, CLIO, Etc. However LLAB is shareware, Speaker Workshop is freeware and CLIO is stricly commercial software that requires a special isa/pci card that is included with the product when purchased.

"but the graphs seem to be a very rough estimate and my woofer has a flat freq. response up to 10 Khz, which I don't think is actuate"

Are you using shareware version? Or registered version? I think that the shareware version(I think) only gives like 1/3 or 1/4 octave resolution measurements. You can download SpeakerWorkshop for free(www.speakerworkshop.com). It is not crippled and gives you full, unsmoothed responses.

As far as measurements being accurate, that is depedant on your mic, soundcard, gating time, etc. I find both LLAB and SpeakerWorkshop to very accurate measurement tools, when of course a calibrated mic and mic preamp is used along with them. However, dependant on your particular soundcard, you can get good measurements without a mic preamp.

-Chris
 
I didn't use a mic to aproxiamate the freq. response. All I did was punch in the t/s parameters into the program and it gave me a freq. response graph. I don't know how to use a mic to record freq. response. I have a little computer mic and a soundblaster PCI 512 sound card. But I don't know if the mic is of the proper quality, since it came with the sound card. And I don't know what frequencies and at what volume to put through the speaker when I'm recording the sound from it. Maybe I will figure it out when using the program. Thanks for all your help.
 
If you do have the graphs that the manufacturere supplied and it shows a nice curve at the upper end of the woofer's range you can do a 6db high pass at about 1 k below where the woofer starts to roll off. A bit off overlap is ok and a 6 db high pass is the simplest cross you can make. You can let the woofer run free and crossing high protects your tweet. Be sure and run your drivers a few days before you start making any adjustments as there is definatly a break in period for the motors of the drivers. Building a complicated cross for a two way won't necessarily sound better but you can always go to that later. I actually prefere a single 6 db high pass because it doesn't suck up as much power. I use low wattage tube gear and a cross can use up a lot off power.