Mark K's Speaker Pages
...when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind; it may be the beginning of knowledge, but you have scarcely in your thoughts advanced to the state of Science...Lord Kelvin
Midrange Group 4 test data- Scan Speak 10F 4424G
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Midrange test data
I was fortunate enough to have a pair of Scan Speak 10F midrange drivers sent to me to evaluate. Comparisons to the Scan Speak Revelator 12m and the Zaph Audio ZA14 were made.
Above, from left to right, the SS10F, the SS12m and the ZA14. Will the real 4" driver please step forward?
Impedance
Magnified impedance curve.
TS parameters
Nearfield frequency response
Note the 12m in red and the ZA14 in aqua.
FR open frame(dipole) at 0.25m.
FR unbaffled, dipole 180 degrees off axis (i.e. BEHIND the driver).
On axis, 0 degree curve in black and 180 degree curve in red, directly behind the unbaffled driver.
How about the FR front and rear for the ZA14 and 12m for comparison?
The ZA14 might be usable dipole. The 12m has some more prominent FR irregularities...
FR on wide baffle, enclosed.
I tossed the driver on my standard baffle and enclosed the back. The black curve is the FR 60 degree off axis. The hole for the baffle was not a great fit, so there is some ripple from the mounting. I thought about smoothing it but I let it go. It's very smooth, and probably smoother if you take better care with the baffle cutout.
Of note, the driver is very sensitive to the enclosure volume, backwave reflection and chamfering of the cutout. Care should be taken in mounting and choosing an enclosure.
ETC curves at 1k, 2k, 3k, 4k.
If you go for this sort of thing, the first 30 dB drops are quite excellent at all levels.
Waterfall 3ms, -30dB, 20-20k. Standard plot.
Again, if you're into this sort of thing.
Nonlinear distortion at 0.25m.
A couple different sets of curves were done.
Initially, I did 3 tone distortion bursts unbaffled and in a dipole configuration. This is good for a comparison to other drivers, but it is difficult to interpret the absolute meaningfulness of the distortion.
What do I mean? Well look for a minute at the curve below. You see a standard 3 tone stimulus at 350 Hz, measured at 92dB SPL at 0.25m.
I've overlaid in red the dipole FR. Given the falloff below 2k, the driver has to be driven much harder at 350 hz to get to the same spl level as a monopole. (See the same curve with a monopole wide baffle box way below. ) So the level has to be interpreted with caution. Since you would not use it in a dipole configuration to 350 hz, it's only relevant when compared to a different driver under the same conditions, with roughly the same frame diameter and FR response.
For example, the SS 12 m below compared to the 10F. Under roughly the same conditions (i.e. SPL and similar FR curves).
But it doesn't really tell us about the absolute SPL level. That is, the real question is how low can I use this driver on a baffle in a box.
I'm going to defer answering that for now and just show you the comparison graphs in the dipole unbaffled condition.
Here is a curve comparing the ZA14 and the 10F at 500 Hz. The spl level was limited by the sound card output at this point. The ZA14 is the winner.
What about 800 Hz? The gap closes.
At 1500 the gap is even smaller.
I've been tinkering with other ways of presenting the data, so I decided I would run the distortion tests unbaffled in a dipole configuration until the dominant distortion product hit -20dB, which would roughly correspond with xmax.
Above 350 hz, I had to run the system with max gain (the sound card output is a bit low even at max) and I still couldn't get to -20dB.
Is your mind numb yet with graphs. Well forget all that stuff.
Look again at the 350 dipole distortion graph, repasted below.
Now, let's do the exact same thing, except the driver is now on my wide baffle and chambered. Again, the frequency response is overlaid so you see what the drive level would be. You can see that, to get the same spl level out of the dipole, you have to drive it 20dB or so harder. That's why you can get 110dB at 0.25m and have a better looking distortion graph than the dipole setup, where the on axis spl is only 92db.
And this leads to the real question, "how low can the 10F be crossed over?" For nonlinear distortion, below a certain threshold, further reductions in nonlinear distortion are not audible. In my opinion, a driver should be able to generate a fairly clean signal, somewhere in the range of 100-105dB at 1m. Which means that the 2nd and third order distortion products should be below ~-30 and -40dB, respectively, and higher order distortion ~60dB down or below. The reality is that the 10F is remarkably linear, and if the distortion is still below the threshold of audibility at these spl levels, then that would make it a excellent choice.
As an aside, you might be skeptically thinking that "nonlinear distortion isn't important, "Dr. Geddes said so." Well, he's also said that he wouldn't operate a driver anywhere near xmax, to paraphrase. So you might not consider nonlinear distortion important, but you still want to steer clear of -20dB, right. Nonlinear distortion is inaudible, until it's audible. Right? I'm picking reasonably conservative numbers in the preceding paragraph that would steer clear of xmax.
So, since I still didn't have a great idea about the absolute level, I put the 10F on a baffle and in a box, and, well, cranked up the amp. As much as I could...fasten your seatbelts...
Still, the driver looks usable to 350, since it get's to 98dB spl at 1m still well under xmax and the profile looks good, if a bit undistinguished. Two drivers crossed at 350 hz LR4 should get you 104-107dB spl without hitting xmax.
Conclusion
The SS10F is a very wideband driver with a very, very flat passband and could be used 350-4k. It's very open in the back and could be used on a wide baffle in an open back configuration, though attention would have to be closely paid to excursion at the lower end. I consider it a better performer overall than the 12m based on the numbers. If you are planning to lowpass lower than 3k, I'm not sure the improvement in linear distortion makes up for the average nonlinear distortion below 800 hz and somthing like Zaph's ZA14, a w15 or, well, lots of other choices abound. If you plan on using a lower order crossover topology, and plan to cross at 3k or above, this becomes a very viable choice. It also is an outstanding choice for an upper midrange in a dipole configuration due to it's very extended FR and open back, extended rear FR.
As a bit of subjectivism, so take this with a grain of salt-I really hammered this driver. Although it seems only to have "middle of the road" distortion numbers, there were no circumstances where the driver really seemed to be straining and was never on the verge of falling apart. Many drivers look good and hit a brick wall when doing the nonlinear distortion measurements-they just fall apart. So I would rank this slightly better than the actual numbers-which aren't bad, but not class leading. There, end of my "consensus" statement.
Note-sorry I made fun of the waterfall and etc curves. I think that they are actually a bit interesting, but really, the waterfall, FR and ETC are all different sides of the same coin. I tossed them out because they are easy to do and some folks like them.