Canned Crossover Design - What Next?

[system7]

8" plus 1" is a very difficult combination, as I have said before.

When working with rigid-cone drivers, there are some hard choices to make: if you lower the crossover frequency to minimize driver coloration, tweeter IM distortion skyrockets, resulting in raspy, distorted high frequencies at mid-to-high listening levels.

If you raise the crossover frequency to improve the sound of the tweeter, the rigid-driver breakup creeps in, resulting in a forward, aggressive sound at moderate listening levels, and complete breakup at high levels. (Unlike paper cones, Kevlar, metal, and carbon fibers do not go into gradual breakup.)

With the drivers we have today, the best all-around compromise is a 2nd, 3rd, or 4th-order (12-24dB/Oct.) crossover with an additional NOTCH filter tuned to remove the most significant HF resonance of the midbass driver.

Lynn Olson

About the best you can do with an 8 ohm tweeter is something like this 4kHz notch. The bass filter has to be lower order than the tweeter filter at crossover. The red 8 ohm resistor is your tweeter level adjustment. The red LCR is impedance correction (optional with SS amp). I'd just wire 3.3R in series with the 3 ohm XT25 and hope for the best. The tweeter Zobel depends on circumstances.

 

[ODougbo]

Woops, wish I read this before I ordered second pair of the 8" woofers;
(W 17RC38-08)

I was going to follow the last speaker build (with the smaller mid-woofers) i.e. double/half everything and make a 16ohm MTM.

Also ordered Dayton RS28F Dayton Audio RS28F-4 1-1/8" Silk Dome Tweeter 275-140

Having a bast with the smaller 6.5's there just noooo-wayyy they can have so much bass, but they do and there's really not much cone movement.

 

[system7]

I'm getting confused. I thought the 8" woofer was the Silver Flute W20RC38-08...

4kHz notch/tank needed for sure. Easy calculation actually. 1mH plus 1uF and 22R tank is 5kHz. The resonance is an inverse square root, so 1.5mH plus 1uF gets 4kHz. Or you MIGHT do it as 7.5uF and 0.2mH and 1.2R as an LCR, except it plain don't work with 8" drivers, so faggedaboudid, go for the tank.

Monitor Audio used to make a speaker like this D'Appolito you are contemplating. Series wired bass is cool, because the undamped mutual resonance has the drivers IN PHASE, which I think is a good thing.

 

[ODougbo]

Typo yes of course - W20RC38-08

Tank sounds like the best and only choice, need help with interpretation though

So this a viable plan? (mock up pics)

The reason I wanted to go down this road, the 8" has better mid than the smaller 6.5. And the 6.5 has the deeper base (all backwards for some reason).

Hoping to fix the bass issue by doubling them up.

 

[ODougbo]

Was thinking now might be a good time to try a one chamber box (double size). Thinking 20L is about as large as can go for each, i.e. 40 box. Tuned to 50HZ

Checked with WinIsd, it just doubled the rectangle, with a slight length correction.

Might have to make a 1/2" MDF box to check for port chuffing.

 

[ODougbo]

Checked a few xo charts for the RS28F-4; well for one, they are all over the place.

The general idea for a 2300 second order xo point seems to be:
C1 = 9 (will use 8.2)
L1 = .35

Any suggestions?
http://www.parts-express.com/pdf/275-140s.pdf