A good tweeter to match 5" SB Acoustics Magnesium Woofers

[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]

Nice what are those in the background?

[dcibel]

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

[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]

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]

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.

[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]

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]

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

[dlr]

For those who may wonder why there's so little change below 500Hz, here's what the impedance magnitude is for the 2-element 2nd order crossover without the 6.2 ohm resistor.

dlr

[xmax]

Like I said the response in my graph below 500hz are not directly audible just an interesting result.
I think the change in transfer function shown in my test and the original design are doing what
the designer set out to do. Also the resistor is after the filter although I'm not sure it will it will
make much difference. I am most concerned about the distortion being 10dB higher at 1K.
and high in general. Perhaps you should measure it yourself before saying my results are
flawed.

[dcibel]

You'd think a recording engineer would be well versed on the topic of noise floor, and also what sort of output to expect from a tweeter at 150Hz...Also, who gates a distortion measurement? Also, a gated measurement wouldn't have any resolution at the lower frequencies, but that is not shown in the measurement, unless the gate is "Wide open" at something like 200ms+. All that looks like is greater background noise in one of the measurements, maybe some hum coming through haha better check those grounds!

On thing is true, per my first post in this thread, it has been entertaining as I predicted. ;)

[xmax]

Yes I do know a thing or 2 about noise, let's say there is noise in the system why is it louder with the resistor?

[xmax]

I can measure it to -120 dBu (I have 2 audio precision analyzers)

http://techtalk.parts-express.com/member/23426-xmax/media

[dlr]

To be fair, I ran it with the resistor after as you stated. In series with the driver, not parallel across it. The change is much closer to the change in yours with almost no change at 3K with about 5db drop and somewhat more drop as frequency drops. So on the part there is some agreement in results. For SPL that is.




But that provides significant reduction in output below Fs and should not create any sort of peaks as shown, so those must be due to some sort of measurement conditions.

You're pointing out two peaks at the low end in what appears to be a a level below them in a region that is rising with decreasing frequency when the output is decreasing rapidly (ref. the crossover transfer function), not increasing as your measurement seems to indicate, so the noise floor is almost certainly an issue. Those two points, from what I see, have no relevance. They're are likely measurement condition artifact, all of which highlight possible issues with the measurement conditions. It seems to me that everything below 400Hz should be ignored.

One thing I may have missed is what are the two distortion curves? Solid 2nd harmonic and dotted 3rd? What I see isn't consistent with what I would expect given the change in SPL between the two curves. If I'm reading it wrong, do explain. And I'm puzzled with that massive 4K drop in the curve without the resistor in the blue set.

dlr