Capacitor question

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Administrator
Joined 2004
Paid Member
Brain cramp.

I have an 8 ohm tweeter that I crossed over at 12K, 6 dB with a 1.5 mfd cap. It was a little strong so I added a 4ohm resistor to it. The output is fine but now there is an overlap with the mid. What do I have to add to it to get back to the 12K XO point? I'm thinking it's around 9K right now.

Thanks for the help ahead of time,
Cal

Edit: I don't have any 1.1 mfd here right now or this would be easy. I have lots of other assorted so I would like to add to it rather than replace.
 
Administrator
Joined 2004
Paid Member
Oops,
Sorry old boy, didn't know they had a number. I'll stamp that one on my heart :D Anyway I sure do appreciate the use of them. Now I can see what happens when you spend the time to do it right.

How 'bout we have a duel tomorrow, 7pm, your place, ten paces, turn and fire your remote at the amp and we'll see who comes out on top. Mind you, mines bigger.

Cal
 
Cal Weldon said:
Brain cramp.

I have an 8 ohm tweeter that I crossed over at 12K, 6 dB with a 1.5 mfd cap. It was a little strong so I added a 4 ohm resistor to it. The output is fine but now there is an overlap with the mid. What do I have to add to it to get back to the 12K XO point? I'm thinking it's around 9K right now.

Thanks for the help ahead of time,
Cal

Edit: I don't have any 1.1 mfd here right now or this would be easy. I have lots of other assorted so I would like to add to it rather than replace.


By inserting the 4 ohm resistor on its own you changed the tweeters effective impedance to 12 ohms and this has changed the timing cct of the capacitor hence shifting the crossover point.

To fix this you need to add a 2.2 resistor in series after the 1.5 uF capacitor and an 18 ohm in parallel with the tweeter. This will bring the tweeter level down by about 3dB and maintain 8 ohms for the crossover capacitor.

Cheers
 
Administrator
Joined 2004
Paid Member
Hi quasi,

Thanks a lot for your response.
I did what I could with what I had on hand for now. I added an 8.2 across after the 4.2 in line, dropping the dB's heavy and basically bringing my XO back to the separation I had before and it actually sounds OK. The tweeter is quite efficient so no big deal.

Man, I am such a hack. I'll have another go atter tomorrow before I head over to RAW

I'm going to bed.

Cal
 
planet10 said:
Cal,

the easy answer is to change the cap to 1 uF to get back the same nominal XO frequency (13,300 Hz). Nothing else required. If needed i'll teleport one over :)

dave


Hi Cal,

If he does that he will shift the crossover frequency back, but the level will be the same. I read that he wanted to bring the level down because it was too strong. Adding two resistors is still pretty easy.

Cheers
 
frugal-phile™
Joined 2001
Paid Member
quasi said:
If he does that he will shift the crossover frequency back, but the level will be the same. I read that he wanted to bring the level down because it was too strong. Adding two resistors is still pretty easy

No it won't, the level will come down, with ~ 2/3 the voltage across the driver there was before.

an L-pad is more appropriate with a more complex XO or when you want to be able to dynamically change the level, but this is better when it is a simple cap XO.

dave
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.