A good tweeter to match 5" SB Acoustics Magnesium Woofers

[dlr]

I used the SB26STAC-C000-4 in my Chameleon design, though it started out with the original SB25. That full design is posted at zaph's web site. The electrical and acoustic characteristics of the STAC version and the STCN version aren't all that different, especially given the measured response of mine with an Fs close to 900Hz with the exception that the impedance peak at Fs is higher in the STAC. Even so, I took my measured design and created a second order highpass with the values you provided. Then I added a 6.2 ohm resistor in series before the cap. The transfer functions are shown below. I can't at the moment export the filter responses for overlay, but it can be seen that there's practically no change in transfer function below 500Hz. The largest change is above Fs with the drop in level maybe 8db at the top and that part is similar to your measurements. It does not in any way alter any response below 500Hz in a way that would create the dramatic peaks at 150Hz and 300Hz. Your SPL measurements show up about a 6db change from around 450Hz up to more then 1.5K. This will not be the case for either driver. The change is less than 3db at 2K for the STAC and is likely to be nearly the same for the STCN since they both have very similar electrical curves above Fs.

The dramatic changes in your measurements as shown are not in any way accurately reflecting the change from adding a 6.2 ohm resistor in series. In fact you state that you intended to show the electrical characteristics of adding the resistor when in fact it does not show that at all. The distortion measurements shown are inaccurate and flawed. As others pointed out, it may very be the noise floor at issue or the gating. You state that reflections are gated out. What is the time scale of the gate in msec?

The first graph shows the transfer function without the resistor, the second with a 6.2 ohm resistor in series.




dlr

[xmax]

It is a 8.2 uF cap with a .35 mH choke, the baffle is very similar size to the speaker from the design discussed.
There are no serious reflection anomalies, (they are gated out) regardless the test was mainly to show the
electrical characteristics of the filter with and without the resistor.
This is the tweeter it has a Fs of 960hz; SB26STCN-C000-4

[dlr]

Show the filter circuit.

And a question. What are the boundary conditions? That is, what's the mic position from the floor or nearest reflective surface (you provided the distance to the mic only) and what windowing do you use, type and window stop time?

dlr

[xmax]

I can see that in the pics and a cards against humanity set! I build studio monitors so of course
I am familiar with ATC everything although now it seems the components are no longer available,
so I am using the Volt 3" mid instead of ATC which I used in the past. My current project is the
Volt Mid, SB tweet, Magnum (hopefully) 12" with 18" Ultimax with custom Hypex amps.
2 pairs. They move some air.

[dcibel]

I designed all the speakers I've built, with the exception of one "DIY kit" which is the Stentorian. While those look like a mobile PA speaker, they are extraordinarily heavy, and employ BSC, not like a PA monitor tuned for maximum SPL.

The old ATCs unfortunately are no longer 100% original, when I got them they were not in the best shape, dented dustcaps and the surround was dry, hard, and one had a small tear. But the price was right so these got new surrounds installed and the dustcaps replaced, and much improved T/S as a result, back to original factory spec.

[xmax]

ATC huh? WOW. what XO design does it use? does diy sound group sell a kit? I'm working with their "Magnum" 12" today.

[dcibel]

In the background is a B&C DE250 in a SEOS12 waveguide. The woofer is an ATC PA75.

[xmax]

Nice what are those in the background?

[dcibel]

Let's not miss the fact that with the resistor the tweeter has 10dB greater output at 20Hz! This is some subwoofer technology right there!

I'd prefer not to pull a tweeter from a perfectly good finished speaker for such a silly argument. On the topic of moving on, this is one thing we can agree on, xmax. ;)

[xmax]

Even if it is (how would a resistor increase noise), distortion is 10dB higher at 1K with the resistor.
Moving on...

[philthien]

Agree that looks like the noise floor.

It is -60db.

[xmax]

And I'm not saying that very low level information is audible, (directly) I'm saying it is a clue to
why the tweeter might sound a little "pokey".

[xmax]

[email protected] is only about [email protected], hardly torturing that tweeter at all.

You see how the slope of the roll off flattens out below 400Hz and gets all wiggly, that's how you know you've hit the noise floor. The slope of the response here should be very predictable by the filter applied and the natural slope of the driver.

Again it's only there with the resistor. It would be interesting if you did the same test. And again I am very familiar with the small
SB tweeters I have tried to use a similar filter and pad and noticed this happening. It really looks to me there is some aggressive
baffle step compensation plus less energy in the 2-3K region (like all SB tweeters) resulting in the use of the resistor to tilt the
transfer function. A slightly dirty fix.

It is more like 105dB now that I double checked.

[xmax]

Interesting, is that resistor after the crossover network?

Yes.

[Billet]

Interesting, is that resistor after the crossover network?