Phoenix Gold Phorum

can we set the crossover this way.....

my amp has a -18db/oct crossover ,
If i set my x-over point to 60Hz low-pass , the filter begins to attenuate the signal starting at 60Hz, so only anything lower gets pass , that's true so far rite...

And in this case, at two times the octave ( 120Hz ) the output power would be attenuated to -18db as to what i understand from a -18db/oct slope crossover.

So I tuned my crossover this way ,

1)The output voltage of the amp was set around 43v with 60Hz sine wave using DMM

2)Two times the octave ( 120Hz ) which would be -18db calculates to 43v halved 6 times because ;
-3db - 6db-19db-12db-15db-18db
Every -3db halves the output , so this happens 6 times for -18db.

giving us , 43/2/2/2/2/2/2 : 0.67V at 120Hz

3)Connected the amp's speaker terminal to DMM again, played a 120Hz sine wave , and adjusted the crossover till i reached 0.67V.

4) so thats - 18db at two times the octave of 60Hz meaning the x-over now, is precisely set to 60hz low-pass.

By theory i think this sounds logical rite, but can u guys pls reply if this method could actually work or am i not considering some other parameters.

Regards

In theory it should be correct but not always true, verify by reading the voltage again at 60hz, and at 40-50hz. The lower frequencies should be unaffected if all holds true.

it doesnt , around 40 to 45 its still ok but it starts to drop after that .
At 60hz, i noticed the voltage comes down to something like 33v from " the suppose to be " 43v.

Is this how it should be since its just passive signal processing or should it start dropping at exactly at 60Hz ?
meaning 60Hz is still 43v but 65hz shows something a little less....??

ahhh.... thought i had something working there....

As Tom said in another thread play 60hz and adjust the XO counterclockwise until you see the voltage dip a tiny bit and you are set.

do correct me if i'm wrong but,
shouldn't it be clockwise for low-pass.
starting at lowest frequency and going up till we see a dip...?

That's an interesting idea. I use my SA-3055 to verify crossover points, but I haven't used it on the amp outputs, because there's a circuit that I'm trying to find schematics of that would protect the input of the SA-3055. I use it mostly with the active and passiive crossovers, using the built in pink noise generator. I love my SA-3055.

eyesofra wrote:do correct me if i'm wrong but,
shouldn't it be clockwise for low-pass.
starting at lowest frequency and going up till we see a dip...?

No, you would start at the higher frequency, and then turn it "down" until you see the drop the drop in frequency, getting closer to the lower frequencies, for low pass anyway, high pass would in theory be the opposite direction.