Vifa XT25 Peerless 850122

[sinus]

Hello,
has anybody realised a project with an Vifa XT25 and an Peerless CSX176H (850122) or CSX176T and can give me a help for the Crossover?
i realised a paire with XT25 and CSX176H in 17l baffeled and a center speaker with XT25 and CSX176T in 11l CB. The crossover that i used for both is this on


calculated CO-frequency is at 2kHz.

with a simple program i measured now the SPL and i saw that there is a leak between 3-4 kHz of -6dB.

now i would like to change the XO-freuqeuncy to 2,4 kHz.

Have anybody a suggestion for the XO

cheers
Chris

[DcibeL]

What this crossover realy needs is a zobel to normalize the impedance of the drivers. I have re-calculated your crossover for 2.4Khz Linkwitz-Riley, using a zobel on both tweeter and driver. The L-pad on the tweeter was changed because you have too much attenuation IMO. I did not compensate for the resonance of the tweeter, however.

Using the picture you've provided, crossover is as follows:
R11 & R12 removed
C4 = 11 uF
L1 = 0.4mH
L4 = 0.8mH
C3 = 5.4uF
R6 = 0.9 Ohm
R7 = 7.3 Ohm

A zobel is a capacitor in series with a resistor. It is placed in parallel with the driver.
For the woofer:
C = 35uF
R = 6.1 Ohm
For the tweeter:
C = 3uF
R = 3 Ohm

For this crossover the tweeter must be wired with reverse polarity from the woofer.

Hope that helps you out. Additional information on crossover design can be found here.

[sinus]

Hello dcibel,
THX for the help. the resistors Rl1 ad Rl2 are the DC-resistance of the inductance.
its really necessary to compensate the inductance of the tweeter? i didnt see it before...

did you simulate the XO with the paramter for the speakers or did your experience give you this values?

Chris

[DcibeL]

If you look on the page I have linked to above, to compensate for the resonance of the tweeter, hence letting the tweeter appear purely resistive, is only really neccisary when the crossover point is less than 2.5 times the resonant frequency. The impedance spike at the resonant frequency will lift the crossover curve, making a non-uniform crossover.

To make the tweeter appear purely resistive, an inductor is added into the zobel for the tweeter. The link above to Elliot Sound Products will give you the calculation neccisary for this value.

[sinus]

hello dcibel,
i know this page its really good explaned.

I simulated now the values that you gave me and it looks really nice. the phase is also perfect

But the damping for the tweeter is only -3dB.

the Peerless (8 Ohm) have a sensitivity of 90dB/W/m between 1.5 kHz and 3 kHz. Under 1Khz he have only 88dB.
the XT25 (3.2 Ohm) have 91.5dB between 1.5 kHz and 3 kHz

to respect the difference of impedance and the difference in sensitivity i have to dampe the tweeter 5dB or more, what do you think?


Chris

[DcibeL]

I calculated the lpad using the sensitivity from the spec sheet. By all means, feel free to try out your values. Since resistors are cheap, it's not going to rip a hole in your pocket to try out a few different values and see what you like best.

Good luck with your project. FYI I am running a bookshelf system with the peerless 850122 driver, and the peerless 811815 tweeter. Sometime down the line I plan to upgrade to the Vifa tweeter you are using. From what I've heard it is an excellent tweeter. But who knows, in a year when I am out done schooling maybe I'll be making enough money that I can build an entirely new set of speakers.

[sinus]

hi,
that couple that you use is a commercial kit called SPUTNIK 17/2 from "Intertechnik.de"
17,5l baffled. they use a first order XO with an notch filter for the CSC and an 3 order XO for the tweeter. The Z-compensation is an 8,2uF cap with 0,82 Ohm in serie. I think the nothfilter is to make a better roll-off for the CSC

Chris

[DcibeL]

Interesting, if only I could speak German . I have used a 2nd order crossover on both woofer and tweeter, designed in the same fashion that I did to design your crossover. It is crossed over at 2600Hz, and sounds more than good enough for my needs at the moment.

[sinus]

Hi decibel,
you was right with the L-PAD. I modified the XO and the best result is for:

Lowpass:
Cp = 5.6 uF
Ls = 0.56 mH
zobel
6,8Ohm, 33 uF

Highpass:
Ls = 0.33mH
Cp = 10uF
R6 = 1,5 Ohm (alternative for more highs 1,2. i prefer 1,5)
R7 = 6,8 Ohm
no Zobel for tweeter needed

The result is really good!! Not to compare with the XO before. The voices are really natural.

new box

Chris

[DcibeL]

Wow, that's some nice speakers you built there! I wish I could speak German though

I'm glad I could help with the crossover.