SB Acoustics monitors build

[DeZZar]

Images of the damping here: https://techtalk.parts-express.com/f...17#post1476317

[rpb]

For damping, I like about 70% wall coverage with thick fiberglass like this. I prefer 2" depth in about 50% of the box. The more the better.

[augerpro]

Are you sure it's the tweeter misbehaving? Try a resonance trap, some tweeters just really don't tolerate the Fs getting tickled. Try 2.0 mH, 22 uF, 2.0 ohm trap on one speaker and see if that makes a difference. Model it first, that is for a ScanSpeak 9130 but the Fs is similar to the SB29 you're using and should get you close.

Off axis modeling is essential, off axis flares in the 2khz area can really make for a hard/harsh sounding speaker.

[rpb]

Tweeter is a damped 3rd order. See the 1 ohm resistor? I forgot to round up values, so adjust as needed.

The woofer is damped 3rd order with a tank on the first larger coil. (.4mH, and 2.4uf) It's moved to line 55 in order to add the cap in parallel. That's why L2 is empty.

[DeZZar]

This is the second order that produced the above result (post #32).



And this was the elliptical (?) I tried out which produced the best result on the woofer (-50db on all breakup) but needs more work getting the tweeter aligned.

[DeZZar]

Thanks mate - I'm unfamiliar with the spreadsheet so forgive me. Tweeter starts with 3.5R, followed by third order 6.96uf, 0.27mh, 8.32uf with an 8ohm+2.4ohm Lpad?

The woofer has third order as well? What's the value for L2? 18uf & 0.1mh for the rest of the third order and then a series notch 1mh, 50uf and 3.5ohm?

[rpb]

Here's a lower xo version.

[rpb]

Here's what I came up with. Used .025 for z offset.

[DeZZar]

Hey mate, the entire cab has felt lining on all walls except baffle. Top section is fully stuffed with acoustic damping material (i.e. acrylic stuffing) and directly behind the woofer is a layer of the acoustic stuffing as well (it's about 2" thick). I attached out to 60 degrees for the woofer and tweeter below. It measures as you'd expect...nothing unusual from what I can see.

With the last crossover under test Impedance is min 3.4 at 200hz, and does peak at the xo point (30) and has a kind of rounded hump as it heads to 20k sitting around the 10ohm region.

[Wolf]

I think you need to go 3rd order on the woofer. This will bring up the dipping range as it can give you a better blend at the knee before rolloff without scooping out the FR.
Does the Elliptical include the tank as well? I would try with both present too. I consider -40dB to be important, and -25dB to be bare minimum.

Not saying the tweeter can't go to 1.8Khz, and I've seen several designs that do this. However, the rising HD that I experienced when Coop and I measured them got ugly pretty quick below there. It is just plausible that moderate outputs and using it lower, as in metal compositions, could likely make it shrill. That response below the tweeter being drooped might make the treble stick out like a sore thumb.

Wolf

[DeZZar]

This is the difference in breakup suppression between a 2nd order filter (with tank notch) and the elliptical. The latter suppresses the first breakup node to -50db. However even the second order simpler network gets that first breakup (4.5K) to -25db and the rest to under -38db.

[DeZZar]

And here's the 0-60 on the woofer. These have all been merged with the woofer+port combined nearfield.

[DeZZar]

Here's 0-60 on the tweeter. I have all the way to 90, but upload restrictions....

I usually cross this tweeter under 2K. In a two way with a 6inch plus woofer I just cant see it working any higher. 1.5K the tweeter has 1.3% THD (my noise floor isn't great BTW) @ 2.83v. 2.5K is only a little less at 1.1%. I agree Wolf, that it would be ideal to go a little higher as things do rapidly deteriorate under 1.5K.

[Wolf]

2.3-2.5K should be better than 2kHz, considering the HD spectrum of that tweeter.

I'm wondering if it's not the polar response of the tweeter. It's a ring-radiator, and off-axis suffers quite a bit. There might be a peak off-axis. However, the polar response of the same tweeter in the Missing Link application does not have a peaking response. It just rolls off in both vertical and horizontal. I really don't think it's the tweeter.

The question is whether the elliptical suppresses the breakup to -25dB or greater. If it is not suppressed enough, it can be the woofer and not the tweeter at all, even if both the tweeter and woofer breakup are seemingly well below the level of the bass range. The diameter is a 17cm, so as long as you're not xovering at 3k it shouldn't beam badly either.

Maybe I'll take a crack at this...
Wolf

[rpb]

Unless I messed up, the posted tweeter frd file is incorrect. I messed up ! File is fine.