modifying crossover from tb28-8473 to Vifta xt25

[jaste]

Hi!
As stated above I want to go from the tangband 28-847s tweeter I'm currently using to the more soffisticated (?) vifa xt25sc30-04. Since I'm a total rookie in constructing crossovers I'm hoping for some help from this place!
The current crossover looks like this:

Specs for the vifa:

VIFA XT25SC30-04 SHIELDED DUAL CONCENTRIC DOME TWEETER $80 ea.
SPECS: 100 watts RMS/140 watts max, Znom: 4 ohms, Re: 3.0 ohms, Freq. range: 1,500-40,000 Hz, Magnet weight: 8.5 oz,
Fs: 500 Hz, SPL: 91.5 dB 2.83V/1m


And for the TB:

http://www.tb-speaker.com/detail/1208_03/28-847se.htm

Glad if you can help me!

 

[Jay_WJ]

Where did you get the crossover schematic?

 

[jaste]

I forgot to tell you in the first post that I alrady have a pair of speakers up and running with that crossover which I got from a memeber at a swedeish DIY audio forum. The reason why I'm changing the tweeters is simply because I got them very very cheap and they are waiting for another project.

From my rookie point of view the things I have to deal with is that the vifa is 4 ohm and a bit more sensetive. The xo point at 3 khz chould work and more compensations in the filter I don't think I need right now.

 

[sreten]

Hi,

That is a near bog standard "textbook" crossover that does not
consider the drivers used (much, only the zobel if it matches).

Consequently changing the drivers will not matter much.

Its not a 2nd order L/R crossover as c/o's are acoustic.
It is near L/R electrical but electrical is not acoustic.

/sreten.


http://www.rjbaudio.com/Audiofiles/FRDtools.html
http://www.geocities.com/woove99/Spkrbldg/DesigningXO.htm

http://www.zaphaudio.com/
http://www.rjbaudio.com/projects.html
http://www.troelsgravesen.dk/Diy_Loudspeaker_Projects.htm
http://htguide.com/forum/forumdisplay.php4?f=39
http://www.humblehomemadehifi.com/

http://www.linkwitzlab.com/
http://www.geocities.com/kreskovs/John1.html

 

[jaste]

So it doesent matter that they differ in impedans? If I would like to damp the tweeter a bit moore what value would you recommend (instead of the R2 1,5 ohm resistor right?)?

 

[sreten]

Hi,

Yes it does matter they are different impedances, though
where 16ohm "Zo" for the TB comes from I'm not sure.

The fact is the "8ohm" L/R network might work just as well
as changing it to be "4ohm" L/R, you do not really know.

The crossover for a start has no baffle step compensation.
Your bass/mid might have breakup modes glossed over
by the writing speed of TB's frequency response plot.

Look at this design, c/o is 4th order L/R acoustic.
http://www.zaphaudio.com/audio-speaker17.html


/sreten.

 

[Jay_WJ]

I wouldn't bother to swap the tweeters. According to my rough simulation, the actual xover point is around 3.5 k - 4 kHz. The Tang Band tweeter should be adequate for this task. You won't hear much difference by replacing it.