Can someone have a look at my XO ?

[rukkes]

Can someone of you tell me if i am on the right track with this XO
(Crossoverpoint ~2300) or are my values of the components åt helvete?

[Tim Moorman]

rukkes,
Not sure what you are doing here, but if you go by the usual textbook values yours are off considerably. Is this a recommended design? Looks like way to much series resistance.

First off, a crossover type like Butterworth, Linkwitz-Riley, or Bessel is usually chosen, unless you are working from someone else's schematic.

Anyway, if you want to try an ordinary Butterworth 2nd order(12 dB) filter, both drivers 8 ohm, then you would use about 6uf for the series cap on the tweeter, and around .75 mH coil across the tweeter.

The woofer would use the same values, but reversed:
coil of .75 on the series leg to + terminal, capacitor across the woofer to -.

Attenuation is needed because of the increased efficiency of the tweeter. Try a 3 ohm resistor after the capacitor on the + tweeter leg, and your 12 ohm on the shunt leg to -.

Because this is a 2nd order filter, you will need to reverse the leads to the tweeter and listen. Usually there is a big suck-out if not reversed.

Lastly, we have not attended to any baffle step losses. That requires another set of components and is based on the point at which your particular baffle transitions from omnidirectional to directional propagation. This usually occurs in the 300 - 500 Hz region, and frequencies above these should be attenuated a few dB to compensate.

Give it a try, but remember that this is just to get you close, and not a xover tailored for the drivers in use. That comes from measurements.

Tim Moorman

[Cal Weldon]

Hi rukkes,

I agree with Tim. I can't see where you got your figures from. The only unit I see that matches your XO point is the .58 mH choke on the tweeter. The rest don't seem to jive.

Here's what I see:

Woofer roll off: 6dB at 700 Hz and 12 dB at 1200 Hz.

The tweeters hard to tell but if you remove the resistance load it appears you have a 5100 Hz cut off at 6dB but the coil lets anything below 2300 Hz across.

Where did you get the figures from?

Cal

[gazzamongo]

let your p.c do the maths

http://lalena.com/audio/calculator/xover/

gary

[Tim Moorman]

rukkes,

I checked on the woofer. Is this it?
http://www.partsexpress.com/pdf/297-324.pdf

Also, this is made in a 4 ohm version. Which is it?

If so, you might want to try a lower crossover point to avoid the roughness above 3000 Hz.

This would depend on the resonance (Fs) of the tweeter, and if your willing to go to a sharper slope, like 18 dB (3rd order).


Cal, you rascal. How goes it up in the great and glorious NW?

Tim Moorman

[rukkes]

This is the original x-over scheme with a xo-point at 1750, it came second place at madisound DIY2000 contest.
It uses Vifa plwo18 8ohm and seas T-25-001 6ohm tweeter.
I wanted it to crossover at 2300 so i recalculated the values and
obvious i got it all om bakfoten.

[Ron E]

The only good way to design crossovers is to model them. Once you get a model that sums relatively flat, you listen and tweek.

People who use bafflestep compensation circuits - or textbook values for more than just a starting point - are in a rowboat with only one oar, IMO.

If you are talking the DIY2000 stuff, I think there is no need to redesign the crossover. IF you want to use a different tweeter (so it appears) you need to measure and model the setup, or just guess and live with the consequences.

[Tim Moorman]

rukkes,
OK, there must be something going on with the woofer's response which does not show up on the data sheet (big surprise) like a major rise in response, although it does show up later on.

If you reverse calculate the values, you have the equivalent of just under 800 Hz on the woofer for those components, which must smooth response an octave later to match up with the tweeter at the xover point of 1650 Hz. Curious, but not all that uncommon.

Kinda hard to guess what may happen at 2300 Hz, but if you follow the same logic and set the woofer up for an octave lower than the actual 2300 Hz crossover:
Inductor(coil)=1.57mH on leg to + terminal. Capacitor from + to - of 12.23 uf.

Tweeter: Capacitor of 8.15 on leg to + terminal. Inductor of .59mH from + to -.

You may still need to add attenuation to the tweeter, as discussed, and reverse the polarity of the leads.

Tim Moorman

[Tim Moorman]

Agree, Ron E, but that was pretty much understood. I don't think the poster has advanced to that stage yet.

Rukkes,
Sorry, but those values were for the 6 ohm Seas tweeter, not the Vifa.

Use the previous 6 uf capacitor; the .78 mH coil for an 8 ohm Vifa.

Tim

[sreten]

TM,

I really wish you knew what you talking about, honestly,
it only riles me because you seem to be good at making
out that you do, does it not ever occur to you you may
have missed something rather fundamental ?

sreten.