There is off course flow in a horn. Otherwise you would not get any pressure, and therefore no sound. The direction of the flow is determined by the differences in pressure, and this is what the adapter adresses. One may off course use optics references, but in the end, this is simply a question of a pressure wave creating flow in an unwated direction, causing distortion to the shape of the wave front, which in turn causes interference that kills off high frequencies. I think the article you are linking to goes a long way in complicating explaining interference between multiple radial sources. The fresnell model gives us clues to understand how far the concentric rings can be apart for a certain frequency resolution. But I believe all who have built a few speakers, and off course all of us working in the field, knows about how interference between multiple sources work.
What you are refering to with the throat diameter is well known in the field of PWT-measurements. However, the use of diameter is not a precise method as this heavily depends on the angle of the outgoing wave from the driver. If you are interested in the energy response, one can say that a driver with a flat wave front will give a reliable result at any frequency, while a driver with a 2pi spherical wave would cause interference based on the wavelength model. This is also amplified down the tube. If a driver can maintain its wave shape coming out of the drivers exit, the difference between the exit angle and the tube cross section is what causes interference to happen. But the diameter is what tells us the lowest frequency where this can cause problems. So the actual issue is that there is a change in the angle that affects the frequency response. This is not an intrinsic problem with a certain throat diameter.
What the half wavelength model describes is the transition between what can be regarded as simple plumming and what has to be regarded as a waveguide. But that is not the same as saying that a waveguide can not work. My point is that if the cross section of the exit of the driver was an intrinsic cause of this type of separation as you describe, it would be the case in any horn, at any part of the horn, meaning that a 600mm horn would have this issue at 283Hz in its exit. Both theory, simulations and practical testing shows that this is not the case. We can distort the wave front of very high frequenies pretty far out in the horn. Understanding HOM really kills off this idea as any conical 50mm horn would measure the same as any other horn above 3,4kHz, and we know for a fact that this is not the case.
So the reason this works in a horn, and the reason why this adapter works, is that it prevents the pressure from leaking sideways. As I mentioned earlier, this could also have been done with the correct type of roundover. The entry of this horn is extremely abrupt, and there is no way you can get a sensible transition from a near flat wave to a spherical wave with this transition. The adapter simply contains the flow and pressure so that the wave does not collapse from the middle first, but instead from the edge and inwards. The same thing works on bass port tubes and is just as effective.
Like this?
Anyway, I think there are two mistakes made in this driver. The first is that they use a concentric phase plug. This will lead to uneven timing of the channels at high frequencies, which in turn distorts the shape of the wave front at high frequencies. This in turn prevents the horn from working as intended. This is especially true for horns like the K402 being a diffraction horn. I would never choose a diffraction horn myself but the issue would not completely disappear on other horns either.
The other issue is that their attempt to avoid the compression chamber modes, they made this "infinity suspension" which is a part of the diaphragm itself, and has an infinity coupling to the fixed parts of the driver. This may cause both HD, IMD and even potentially non harmonic distortion.
If they had gone for some type of radial phase plug they could have used a traditional suspension not having to fix the issue with uneven timing.
Really?...
Finally, a correct statement:
What hyperbole! I think most people that actually listen to and measure the Axi-2050 on a K-402 Horn (the only in-production horn that can actually use all of this driver's output effectively that I'm aware of) will have a dramatically different point of view than yours.
You can read about my observations, spread over a month's worth of listening side-by-side with a TAD TD-4002 on the left channel and Axi2050 on the right (K-402s on top of KPT-KHJ-LF bass bins, dialed-in carefully)--the second posted pdf file found here:
https://www.diyaudio.com/community/...heritage-jubilee-acoustic-performance.396074/
Chris
Distortion is high already in uppper midrange compared to a better driver. I think that may be more audible than the top treble though the latter also probably matters.
Sure it can sound good to people. But as long as they don't have a reference and do proper AB comparisons, it doesn't give much anwers.
I have listened to many drivers I thought sounded good in different speaker designs. But when I heard a driver that was better in direct comparison, the reference changes and the driver you thought sounded good doesn't hold the same value anymore.
It's basically the same with much the feedback regarding beryllium. People rave about the majore difference, but an AB test it will often be very subtle compared to a good alu diaphragm.
Peoples stories about their experiences are very hard for anyone else to quantify into something useful. Also, I would avoid the 402s without a fix for the throat. It is really not a tool for reviewing the top end quality of compression drivers. But, I do agree with Omholt that this driver does not have a great top end, even in more suitable horns.
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They haven't done the comparison I have. There are other people who have come to the same conlusion as me. Thirdly and most importantly; measurements comfirm the rise in distortion. If there wasn't a correlation between measurements and listening, I wouldn't trust my own experience. Perhaps TAD 4002 isn't that great either or doesn't match the K402 horn that well, I don't know.
In fairness, I can say that the Axi2050 probably suffers more from HF beaming above 6.8 kHz than the Radian 950BePB (Be dome diaphragm 2" compression driver). Put the "phasing plug adaptors" (throat diverging lenses) into the horn/compression driver interface and I think the story is going to change a bit. I know that this device used on my TAD TD-4002s did make an audible difference, and the effect is "not boring"... YMMV.
I didn't see that in my measurements. In fact, lowering the crossover point to 220 Hz (easy to do with the K-402 and the Axi2050, relative to the TAD TD-4002s crossed an octave higher) actually slightly decreased the harmonic distortion relative to the bass bin HD. I don't think this is a subjective factor that the trained listener could pick out. I listened for a month with a lot of test signals, measurement sweeps and a lot of different types of music (greater than 8 hrs/day, 7 days/wk) and didn't hear anything that I could attribute to HD,
Chris
It has a transition from round to square, with a significant change in angle. This transition is not long enough to avoid diffractions at any audio frequency. So yes, it is a diffraction horn, even if it does not have a vertical diffraction slot.
This is incorrect in my experience.
Different compression drivers have different polar coverage above 6.8 kHz (and approximately the same coverage below that frequency). If you choose a compression driver with a long snout, such as the Axi2050 and the TD-4002, you'll hear more difference. If you instead use drivers with much shorter distance from the acoustic center to the horn throat entrance, the difference isn't nearly as great IME.
I'm not sure who you actually are, or what your long-term experience is with K-402s, but my experience is extensive and is well documented since December 2007.
Chris
Yes I found that to be true as well. It is subtle they are different sounding but not smack in the face different. I am comparing the same driver with Aluminum JBL 435Al and Beryllium JBL 435Be so it's strictly material differences vs different drivers with different materials.
Rob
I think what you are really talking about here are differences in exit angle, differences in loading, and differences in wave front errors. With so many variables going on at the same time it is really hard to determine what is causing the differences you are experiencing.
K402 has an abrupt angle conversion followed by a conical section. This is known to cause HOM.
I cannot agree with even 10% of what you are saying about the K-402 or related compression drivers, and your attributions from where all subjective sound quality performance arise. It looks as if you are parroting a fair amount of misinformation that can be found on web forums. I would go further and say to others here that it's easy to write stuff down, but to back up what is being said with real-life subjective listening and measured differences is a much different matter.
Chris
You made me think of our discussion the other day in your thread. What I am referring to was your comment about the HF
The wide radiation only serves to distort the FR, where as narrow directivity serves to increase the clarity of it. While one approach may appear highly resolved in anechoic measurements, the other provides higher resolve in situ... The below are ~1m in a 12x16x8H room with no room treatment, hard floor/ceiling/walls positioned and 3/4 away from rear. Directivity is more potent towards increasing resolution, than Be is, as a diaphragm material, is my guess. In relevance to the current discussion, the HF of the K-402 is wide, the HF of my exponential horn is Narrow.
PM sent.
unfortnautely I don't have any outdoor measurements at these levels to share at this time. Its thd is clouded in these measurements
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The Ciare is a metal fabricated horn...any "ringing", or similar issues that you experienced?
If there were did you dampen the horn ?.
Thanks...
Hello camplo
Not to sure about that. Assuming they have been equalized to the same frequency response. The difference between say an exponential and a CD horn on the systems designed listening axis WRT first arrival, using the precedence effect, is going to be minimal.
In my experience different materials are different for example reverb tail offs and low level detail appear to be more resolved and transients sharper with Be. This is sighted so a grain of salt. Could it be expectation bias? Could be but I don't think so.
You would be able to hear this readily on either horn type especially listening near field.
Once you move away you still can hear the material differences listening on CD systems both on or off axis.
Something you would have to experiment with off axis with non CD systems where the HF response rolls off because of narrowing directivity.
Rob
Instead of playing tit-for-tat, why don't you relate your direct experience with matching exit/entrance angles on horns/compression drivers--and relating the varying distances of the driver's acoustic center (~midband) from the bolting surface...with subjective listening correlations...to start with.
We can go from there.
Chris
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Ok, I thought you were referring to a horn with diffraction slot.
I found the K402 sounding somewhat harsh, no matter what driver I used with it.