Woofer/Tweeter frequency response curve bad crossover design?

[mycity_33]

I have installed Vifa XT-25 tweeter with Fountek FW-146 and crossed it at 3500 Hz. Tweeter roll off appears OK at around 3K however woofer continues to play where it should roll off past 3K ( tweeter in blue and woofer in red). Where to start, is this normal behavior for woofer or is crossover not filtering where it should?

I include 2-nd image with both drivers measured at same time

 

[elnaldo]

What is the woofer crossover? I think with woofer impedance data and xover values, somebody can help you....

Also a xover schematic would be helpful...

 

[Elfasto]

Looks to me that the Low Pass filter (coil) of your crossover is not working. Even if the Woofer is not the same impedance as the tweeter, the rolloff should be really obvious, and I'm not seeing this on the graphs.

 

[GordonW]

Is there a Zobel across the woofer? If not, the woofer inductance may be negating the low-pass crossover effect.

Regards,
Gordon.

 

[mycity_33]

Reply: next step

Actually this is a simple 2nd order with 4uf cap and 0.50 Mh coil, no zobel. To avoid using crossover that I build I did solder another one this time for low pass section only (to avoid any high pass interaction if any) however I am getting same result. It makes me think that my measurements are bad but it makes little sense considering that tweeter measurements look OK. Since I was going to get new microphone I will order one and see if measurements look better. Trying new microphone because I am running out of ideas. Thanks all for replying

 

[michiganpat]

observations from this hack....

looking at the small FR & impedance graph on madisound's website, it looks like at ~3500hz, the actual woofer's impedance is more like 12 ohm...

https://www.madisound.com/catalog/images/userimages/fw146_t1.jpg

also, looking at this graph, looks like it's relatively flat to about 5khz, then has a 10-13db peak centered between 8&9khz.....

because the impedance is not 8ohm at the desired xover frequency, your low pass filter is not behaving as expected, I'm not good enough to have a feel as to the shape the crossover slope will have, but the .5mH coil would normally filter higher with a 12ohm vs. 8 ohm load (I think that's what gordon was alluding to)...with a simple 1st order butterworth, a .5mH coil crosses at 2500hz w/an 8 ohm load, but 3800 hz with a 12ohm load, using an online calculator...


using a standard 2nd order (12db/octave) filter at 3500, you should be down ~12db at ~7khz & ~24db@14khz, etc electrically, but you don't have a nice mechanical woofer roll off...typically the electrical component of the filter is combined with the mechanical roll-off of the woofer to get a higher than 2nd order slope (more like 4th order)....since your driver doesn't do this, but actually peaks in the higher frequency range, I'd think you'd want some sort of notch filter to kill that bump, and probably use a higher order (4th order?) low pass filter

 

[RayW]

Yeah, what they said.

If you really want a picture of what's going on, measure the woofer by itself and then with the filter and compare. You'll get a much better idea of what to fix.

 

[mycity_33]

Update- corrected impedance

Well, michiganpat correctly pointed out that impedance was 12 ohm, I guess I missed that and now got a 0.75mh coil and 2.2uf cap installed. Unfortunately I did not have axial cap and had to buy a radial cap that was only type available in the store. Now I did measure woofer without crossover, please look at image, peak looks better but there is still no rolloff like crossover wasn't there. Red is woofer connected straight to speaker terminals and green with low pass filter.

 

[RayW]

Looks like it's acting just like it's supposed to. At 5kHz they're 3 or 4dB apart and at 10kHz they're about 15, that would be right around 12dB/octave. With the steep slope it's hard to estimate 20kHz but it looks like almost 30dB...15dB + 12dB would be 27 so a guess of 30 is in the neighborhood.

Like Pat said though, you're looking at a peak that's almost 20dB so you're going to need a notch filter or a higher order slope on your crossover to bury that.

 

[Nat]

This isn't by any chance a metal cone woofer is it? Its common for them to have big peaks in the upper frequencies, a result of the stiff cone having a very narrow, therefore strong resonance peak.
To me, it seems like a woofer that isn't worth the hassle of designing around such a big problem. The complexity of the crossover would defeat me, and the more parts in a crossover, the more the potential negative effect on the sound, and the greater the expense.
I recognize this isn't actually helping you..

 

[ken kantor]

Well, michiganpat correctly pointed out that impedance was 12 ohm, I guess I missed that and now got a 0.75mh coil and 2.2uf cap installed. Unfortunately I did not have axial cap and had to buy a radial cap that was only type available in the store. Now I did measure woofer without crossover, please look at image, peak looks better but there is still no rolloff like crossover wasn't there. Red is woofer connected straight to speaker terminals and green with low pass filter.

Crossover design is complicated, and it never works to think about the woofer as a fixed impedance. Best to either use a circuit simulator, or to copy a design you like the sound of. Trial and error is fine, too, but that requires a lot of time and huge supply of parts.

From what I can see, that large peak at the top end of the woofer is going to require either:

- A lower xover than 3.5K.

- A higher order xover than 2nd-order.

- A tank circuit to target the offending freqs.

- Learning to love, "clear, detailed" sound....

 

[RayW]

From what I can see, that large peak at the top end of the woofer is going to require either:

- A lower xover than 3.5K.

- A higher order xover than 2nd-order.

- A tank circuit to target the offending freqs.

or d) all of the above.

- Learning to love, "clear, detailed" sound....

:lmao:

 

[ken kantor]

or d) all of the above.



:lmao:

Uh oh... are you really a minor?