It's hard to design out that mess above 10khz but if it breaks up in a downward fashion it's not as bad. The new 18s look like they do that. My current favorite, the JBL 2431 which breaks up downward too.
Here's the polar response of a $80 Eminence ring radiator on a $20 waveguide. It can definitely be achieved:
There only exists one version of the 4015. That has a 1,5" exit, and different diaphragm materials hence ND 4015BE , N and Ti2.
Check the brochure i added,it used to say the ND4015 was available with 1,4" and 2,0" throats, by fitting throat adapters again.
The picture you linked from voice coil clearly shows the 1,5"exit ND4015 besides the 2" exit 2064 wether you see it or not
And yes i should read more closely sometimes
But still the review is pretty much a hack review of a ND4015BE making it look a lot worse in performance then the driver itself is.2" version would be a ND4020BE in 18S webpage these days.
What was reviewed was a ND4015be 1,5". Hopefully with the 18sound adapter i linked below attached. But clearly the Combination of ND4015BE, 2" throat adapter and XR2064C is not a good solution for the upper octave. Not that it is something shocking for a 2" exit compression driver from 10-12k and up. But the measurements clearly shows the is a mismatch in geometry somewhere along the exit path or similar, it drops 15db! 9-10k, along with clear traces in the impedance curves that are not there in the mfg. datasheets, or other measurements, that also occurs around 5khz, where you can also see the THD increase.
Go to Eighteensounds webpage, look up the ND4020Ti2 and ND4015Ti2. see if you can spot the difference. Hint: look at the link below.
https://en.toutlehautparleur.com/adaptor-for-compression-driver-1-5-inch-to-2-0-inch.html
While there go look up the ND3ST and the ND32ST, see if you can spot the difference. a hint : https://en.toutlehautparleur.com/adaptor-for-compression-driver-1-4-inch-to-2-0-inch-for-nd3st.html
Again while there, go look up a ND1460/80, and compare them with the Different ND2080 and 2060 versions. See if you can spot the difference. Hint : https://en.toutlehautparleur.com/ad...4-inch-to-2-0-inch-for-nd1480-and-nd1460.html
Now i will leave it up to you to guess what the difference between the HD2000 and the HD2020 is
Maybe more obvious here as the 2" exit HD2020 has a 2,4" voice coil.
And if you ever want to experiment with a 1,4" exit ND4015 this one will do that, just as described in the 'vintage' specsheet i added, just don't expect greatness and be disappointed.
https://en.toutlehautparleur.com/adaptor-for-compression-driver-1-5-inch-to-1-4-inch.html
You achieve a wide range of transducer models in a very economical way with throat adapters, but the results are not always ideal as can be seen in that review. The same can be said for diaphragms in 4 different versions on the same driver. One compression driver can give you 8 different models to sell. But there are compromises and tradeoffs for that choice too, but it is highly beneficial for the manufacturer in terms of economy, efficiency in production, stock, spare parts etc.
They're 2" drivers mentioned above does not have the phasepulg at the driver exit as shown in the picture below, of the ND4015BE stolen from @docali webpage. That is actually a important thing to consider when looking for a driver, and a horn /waveguide to match it to.
You also never see the throats of the drivers in the mfg. webpage.
Straight from 18S's website, in the drawing of the 4020 you can clearly see where the ND4015 driver ends and the throat adapter begins.
Separated by the line. Also easily visible in the 18S webpage of the mentioned 2" models.
That Voice coil mag, have'nt got the details specified or shown is not my fault or yours
Now this is no different then a Radian 950 vs 951. The 950 version has some anomalies in the 9-10 khz range with alu diaphragms likely due to the same reasons.
Or the classic example a JBL 2450H and 2451JH.
Or he Tad TD-4002 that is 39mm exit, coming with a 2" throat adapter so it could be used both ways.
Or ordered as 4002Z as used in the TSC series, simply without the adapter.
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Another view of the ND1480 and ND2080 if anyone is not convinced, from both sides, easily showing the difference and the fact that it is a throat adapter, not a different driver. Meaning that of 18sounds selection of 2" compression dirvers only 2 out of 9 are anything close to 'unique' drivers.
If you look at the HD3020T and HD2080T you can easily see what drivers they dripped down from, in the 1,4" exit range.
But they have shorter throats with faster flare rate, being that the throat is contained in the depth of the Ferrite magnet motor structure. So there is some difference beyond the simple throat adapters.
Now for the next exercise:
Look at the picture below of the 2080. You see the phaseplug exits into a seemingly straight circular / conical? adapter.
Also keep in mind the exit angle of the ND4015 is close to zero.
Compare the drawings of the ND4015Ti2 and the ND4020Ti2.
The driver depth of the ND4015 is 56 mm, the depth of the 4020 is 90,1 mm. a difference of 34,1 millimeters
There is a sharp discontinuity from the exit of the ND4015 into the circular/conical 34mm long 2" throat adapter, which pretty much explains the issues as viewed in the review in Voice coil mag.
If you look at the HD3020T and HD2080T you can easily see what drivers they dripped down from, in the 1,4" exit range.
But they have shorter throats with faster flare rate, being that the throat is contained in the depth of the Ferrite magnet motor structure. So there is some difference beyond the simple throat adapters.
Now for the next exercise:
Look at the picture below of the 2080. You see the phaseplug exits into a seemingly straight circular / conical? adapter.
Also keep in mind the exit angle of the ND4015 is close to zero.
Compare the drawings of the ND4015Ti2 and the ND4020Ti2.
The driver depth of the ND4015 is 56 mm, the depth of the 4020 is 90,1 mm. a difference of 34,1 millimeters
There is a sharp discontinuity from the exit of the ND4015 into the circular/conical 34mm long 2" throat adapter, which pretty much explains the issues as viewed in the review in Voice coil mag.
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Thanks @Arez for the detailed descriptions of the 18s drivers. And I can confirm once and forever that there is only one 1.5 version ND4015Be! Additionally,there exist two adapters. The 2" adapter has a quite fast flare rate and is almost useless imo for traditional horns. I will never understand why 18 approved such a strange setup like in VC. You can easily see the true potential in my review.
I'd be very interested in your comments on these drivers and how they were reviewed here
https://audioxpress.com/article/the-745neobe-compression-driver-from-radian-audio
https://josephcrowe.com/blogs/news/18sound-nd1480be-beryllium-1-40-compression-driver-test-review
Properly EQed, would you suspect their performance to be nearly identical?
If not, how would they differ, and by how much?
Yes that's right. Although Vance writes that the driver is 2 inches))
The driver is in production range, so there is no need to close the thread.