Take a look at this one vs the T25B https://audioxpress.com/article/Test-Bench-Wavecor-TW030WA12-30-mm-Cloth-Waveguide-Loaded-Tweeter
Which resonance specifically?
And yes there will be modes in the diaphragm.
That is a complete hack review of the ND4015BE.
Hard to find a worse example actually.
Take notice of the text in the first picture, there is also a component missing in it.
Take notice that is a 1,5" exit compression driver yes?
It was tested on the 18S XR2064 2" exit horn.
What is missing is the throat adapter that is a gross mismatch to the compression driver exit..
If you want reliable data on the ND4015BE go to the website of : @docali
... and by page 10, more or less every product on the market will have been mentioned... as usual... ;-D Time for a 2025 version?
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Who is this?
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I have a background in live mixing during my time at university and study of sound engineering. Open air stages with great line arrays with a LOT of resolution (you identify mp3s easier with these as I ever had at home). I built a few PA tops and tested plenty of drivers, use the BMS coax 2" in my bigger speakers.
You can achieve very good resolution with compression drivers.
But not "T25B with Hypex in a dampened room at close distance" resolution. It's more detailed AND more natural/real. MOST compression drivers have some hickups under 20kHz - you her a difference, give it a try.
Of course not in 4m distance in a living room, you mush everything and directivity will help in such a situation (I use a DE360 in my living room, very smooth and HiFi like sound).
I have an AKG K812 and top and mid resolution can EASY keep up with the Bliesma drivers. I recently bought a Hifiman Ananda Nano - this will be an interesting comparison as soon as I finish my new version of the speaker.
Look at the measurements when you need objectivity. T25B has it's membrane resonance close to 50kHz and works as perfect piston far above the audio range. You destroy the driver before it get's 1% THD (I wanted to do the standard 1% Max SPL test, limiter kicked in and I got no results). Very even off axis radiation, up to higher frequencies as the wide surround 1" drivers.
Yes, a compression driver get's WAY louder and has "unlimited" dynamics. A good horn can help with a bad room. But that's not the topic here - they can't compete in terms of resolution and "natural"/"real" reproduction in the last octave.
Docali's measurement review of the ND4015BE: https://sphericalhorns.net/2023/07/15/drba-test-bench-eighteen-sound-nd4015be/
A very high frequency resonance (circled red) is still present in the free air as well as in horn impedance plot. Though at least it seems decently well damped in the frequency response and decay measurements.
Having now stumbled across Joseph Crowe's measurements of the TAD 2001 I mentioned earlier, this CD would seem to measure almost resonance (mode, breakup) free within the audible range - still some minor ripples in the impedance plot around ~15-20 kHz, which might be masked in the burst decay chart due to the dropoff in SPL above ~10 Khz.
So, as I alluded to, it's probably the best candidate to compare to a reference dome tweeter such as the Bliesma T25B-6 regarding signal reproduction quality.
Apart from decay measurements, I'd be looking at multitone distortion measurements, which would show both IMD as well as HD behavior. I'll cite JBL Technical Note Vol. 1, N8 - Characteristics of High-Frequency Compression Drivers for the reason:
In my comparison of one of the better measuring 1" dome tweeters vs. 1" compression drivers (in similar sized horn/WG) on the market, on average across the frequency spectrum, both came out about equal in that metric; but in the very high frequency (VHF) region, in this case 6 - 20 kHz, the dome tweeter showed clearly better distortion behavior. Compression drivers' inherent limitations, such as the large & heavy diaphragm, and the high pressures in the compression chamber, mostly affect the VHF region, so this needs to be looked at if someone would like to claim they can keep up with the best dome tweeters in signal reproduction.
Why? It leaves piston motion way before 20kHz, has bad off axis behaviour (these mini waveguides don't work - 100% wide radiation at 2kHz and narrow at high frequencies), not even better sensitivity as T25B! Here actual useful measurements:
https://hificompass.com/en/speakers/measurements/wavecor/wavecor-tw030wa11
https://hificompass.com/en/speakers/measurements/bliesma/bliesma-t25b-6
Even THD is lower with the T25B.
These are SO different.
DE360 is resonance free up to 20kHz but goes down short above it. A very relaxed sound like a good HiFi ring radiator with all the information there in the upper octave. But it's still a soft membrane, it's great for everyday listening but I might repeat myself - not the resolution of ...
Yes that is unavoidable due to the diaphragm size.
WIll find it in any 4" diaphragm.
And it is one of the better ones.
Might also notice where the phase plug ends, it's a "throatless design ala JBL 1,5".
It is actually very well behaved if you look at the spectogram for having a 4" diaphragm.
And Truextent Be foil is generally well damped, due to it's ductility vs a TAD CVD dia.
The TD 4001/4002's have a 'flatter' extended response due to the secondary resonance from the half roll Be surround. And a much lighter and stiffer diaphragm. Look up the old JBL tech notes for a explanation.
It has issues in its lower range, the TD-2002 is better.
The TD-2001 has a cavity resonance ca 1,7 khz, due to the voice coil gap. As ilustrated by the picture below, from the 1978 AES paper by Kinoshita and Locanthi.
The TD-4001 had a similar quirk just less pronounced.
While the TD-4002 has a plastic/rubber ring in the VC gap to counter the effect.
Just look close on the cutout, besides the red colored magnet.
TD-2002 :
Actually a interesting little 1" Be compression driver that i never saw measured, or even mentioned by anyone else:
As for the DE360 it struggles with rising distortion below 2k.
So the normal advantage of a comp driver extending low with grace is kind of lost.
For that range JBL's D2415K is a interesting option, but no commonly available horns/waveguides.
And if you want a 'tweeter' the JBL 045be, and the recently released TAD ET-703A are clean in theyre useable range, but requires a high xo.
But all of this has been extensively covered in the 2022 thread with a similar subject.
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The last musical octave contains almost no spatial musical information. "Resolution" of the system is fully described by the midrange octaves. So, I don't quite understand the logic of how the frequency of breakup mode is related to the "resolution" o the driver. With a high-quality compression driver and horn, the size of virtual images and spatial localization are excellent; with ordinary domes without a horn, such resolution cannot be obtained.
"This compression driver is available in two versions, a 1.5" throat and a 2" throat. For this review, I tested the ND4015BE, which has a 2" throat. "
And it is not.
And from his picture you see it is a 1,5", with a 'zero degree' exit, the phaseplug ends at the driver exit.
The adapters i guess are 29 degrees so it fits most of the 18S drivers.
The "2" version is one of they're 1,5-2" throat adapters, the throat adapters have a exit angle, and the flare rate does not match the compression driver in question. That is why you see the large anomaly in the review from 10-ca 13k, a gross mismatch in the throat.
You can read the same here too, from @docali .
https://sphericalhorns.net/category/drba-test-bench/
This is the ND4020 which is the 2" exit ND4015 version.
Do you see the difference ? a externally mounted throat adapter.
Look up the dimensions in the specsheet etc. and it is very obvious.
and here is the picture of the said adapters you mount on the ND4015 to make it a 2" exit..
If you look at this one you can see it is not zero degrees, and there is no way for the phaseplug to end at the drivers face/exit.
Another example from they're webpage:
The difference between ND32ST and ND3ST is the externally mounted throat adapter in this case 1,4" - 2".
Again it is obvious when you look at the mechanical drawing in the specsheet, and the dimensions.
And on the product picture you can even see the bolts that mounts onto the ND3.
https://www.eighteensound.it/en/products/hf-driver/2-0/8/nd32st
https://www.eighteensound.it/en/products/hf-driver/1-4/8/ND3ST
https://en.toutlehautparleur.com/lo...on-driver-1-4-inch-to-2-0-inch-for-nd3st.html
Compare this to the product picture of the ND32ST, and it will be obvious?
Pretty obvious by now i would think, and Vance D. made a mess out of his review of this driver, was not a good one.
And certainly not the first time these reviews have inconsistencies.
And this subject was also elaborated in the old "best compression driver" thread quite extensively, you might not have seen it although you participated 🙂
And if you don't believe me, find the drawing of both products depth dimensions and add them for the exact same result as the 2 separate parts.