Help please for a real beginner. I would like to add super tweeters to my 2-way active monitors. I have a pair or Cole’s 4001 16ohm drivers, and I am hoping I can get away with just adding a capacitor. The nominal impedance of the driver is 16ohms and the DC resistance is 23ohms. I am planning on a crossover frequency of 12500Hz. I presume the output impedance will be in the range 16 to 23ohms(?). I do not know how to find the input impedance if that is even necessary. So far I think I need a 0.8uF capacitor, but this may be completely wrong. If by some miracle I am right, what type of capacitor should I use. I think 0.8uF is an odd size as well. This is my first venture into diy and my first post on this forum. Any advice would be welcome.
Mitch
Mitch
I will start with the 0.68uF and try that. For future reference should I be using the nominal impedance or the DC resistance in the calculation? Does it matter if the capacitor is close to the magnet of the driver. If I was using an inductor I can see tat this might matter, but a capacitor? Thank you guys.
Neither. If you must use a single value, then begin with the value at the frequency of the cross.
Nitpicking, but he should use dats v3 to do impedance sweep.
Personally i believe, any calculation is useless, what matter is final listening tests with various caps. He is using just one cap, so first order, very shallow slope, lots of overlap between original tweeter and super tweeter. Interaction between these two can not be calculated, because for such a high frequencies the position of supertweeter matter a lot. Moving it inch or two will result in adding or subtracting at around crossover frequencies. Swithing polarity too. Only listening and experimentation is the way to go.
Btw, when it comes to odd cap values, you can create pretty much any value just by paralleling the caps.
Good luck.
Personally i believe, any calculation is useless, what matter is final listening tests with various caps. He is using just one cap, so first order, very shallow slope, lots of overlap between original tweeter and super tweeter. Interaction between these two can not be calculated, because for such a high frequencies the position of supertweeter matter a lot. Moving it inch or two will result in adding or subtracting at around crossover frequencies. Swithing polarity too. Only listening and experimentation is the way to go.
Btw, when it comes to odd cap values, you can create pretty much any value just by paralleling the caps.
Good luck.
If you will compensate an already full-range system, often is enough a partially compensation (for example series resistance or L-pad and smaller cap for virtually higher crossover point). A very-very small proportion of near-ultrasonic compensation provides remarkable change of full spectrum. It's good fun!
This is where I have to ask the ‘stupid’ question. The inputs to the calculation I am using are 2 of: the capacitor value, the impedance (that of the speaker I presume), and the desired crossover frequency. If I input the crossover frequency (12500Hz in my case), to get the capacitor value for that frequency I have to enter an impedance value - what should that be if not 16ohms nominal or 23ohms DC resistance?
It sounds like you do not think a single capacitor is the best solution - what would you suggest please?
Even that is nitpicking, adason, and I'm not targeting that at you 
I suggest that tuning by ear is a big shortcut with adding a supertweeter specifically, for the following reason.
While the factory impedance curve would be fine for simulating, crossing this will more a matter of power. Measuring power is more complicated, and since it's going to come down to one value of capacitor it makes less sense to go down that road. In any case, any simple calculation will be no more than a guess.
I suggest that tuning by ear is a big shortcut with adding a supertweeter specifically, for the following reason.While the factory impedance curve would be fine for simulating, crossing this will more a matter of power. Measuring power is more complicated, and since it's going to come down to one value of capacitor it makes less sense to go down that road. In any case, any simple calculation will be no more than a guess.
First read my above reply.
A simple capacitor probably is the best way to begin with this. It may also be sufficient. A supertweeter is adding some air, not necessarily crossing in the simplest sense.
Therefore bigger means more and smaller means less. If that doesn't sound right, try a resistor. If that doesn't sound right, try something else.
OK thanks. I have ordered 0.68 and 0.82uF caps and I will experiment with those to start with.
I understand adason’s point about the positioning of the super tweeter to be critical. I will design the enclosure so that I can have the super tweeter either facing forwards or directly up. As I am looking for an ‘ambient’ improvement (more air) I thought that if the tweeter was pointed upwards the signal I would hear would be a reflection that would be so far out of phase with the direct signal that my ears would interpreted it as a reflection and not a dip or boost to the direct signal - just more ‘ambient’?
I understand adason’s point about the positioning of the super tweeter to be critical. I will design the enclosure so that I can have the super tweeter either facing forwards or directly up. As I am looking for an ‘ambient’ improvement (more air) I thought that if the tweeter was pointed upwards the signal I would hear would be a reflection that would be so far out of phase with the direct signal that my ears would interpreted it as a reflection and not a dip or boost to the direct signal - just more ‘ambient’?
Almost every tweeter beams. Even those expensive scanspeak be domes. Seems like more expensive, more it beams.
Big change in directivity between mid and tweeter is no good.
Supertweeter most of the time just spreds highs wider.
I preffer $14 foster supertweeter which does not beam up to 40kHz.
Big change in directivity between mid and tweeter is no good.
Supertweeter most of the time just spreds highs wider.
I preffer $14 foster supertweeter which does not beam up to 40kHz.
Attachments
Forgive my ignorance, does this driver have a higher DC resistance than its nominal impedance?
I disagree. If anything some meters are consistent with frequencies across the band, and some aren't. DATS is not necessary, these days many just sweep through their computer.