I have been running this blog since 2019 and have since examined a wide variety of horn types, reprogrammed historical design algorithms from scratch, developed innovative enhancements, and made them available to the community from time to time. In addition, completely new ground-breaking horn types have been developed.

In particular, I would like to mention the following milestones:

• Consistent modification of the spherical wave horn
• True Expansion Tractrix horn
• Hyperbolic spiral
• Cornu spiral
• Sici spiral
• Progressive Expansion T-Factor Horns (PETF)
• JMLC-inspired horn calculator with PETF and HVDiff
• William Neile Horn Series
• Acoustic Loading Optimized Horns (ALO and ALOV2)
• mk3b2 radial fin horn
• Coherent radial fin horn and the corresponding radial conical bell horn.
• Karlson Tube and DrBA K-Type

There were also various other projects that were not published yet. These included i.e. the so-called diffraction horns. Each research study has improved and extended my understanding of acoustic horns, shown me the strengths and weaknesses of the individual designs, and led to ideas for new solutions and algorithms that provide decisive improvements to acoustic loading and radiation control.

My vast experience has enabled me, at least, to assess which designs I would not be satisfied with for listening to music in the long term. And, above all, to rule out from the outset those designs that have obvious and serious flaws simply because of their construction. To cut a long story short, round horns, traditional fin horns, multi-cell horns (they are the worse of all), diffraction horns (use of diffraction slots), or horns with abrupt profile changes or other fancy profile shapes are a no-go for me. Most important, beaming horns and waveguides that do not provide sufficient acoustic loading are a no-go for me. Obstacles of any kind in the horn’s path, e.g., a small horn inside a larger horn, are also a no-go for me.

A side note to fin horns. Many people are not able to understand or don’t want to that the directivity control of the fin horn is essentially achieved by the basic horn profile and not by the fins! A horn without fins or without multiple cells will always sound more natural. This is simply because the wavefront at the exit of the fins or cells never combines coherently. I showed with the coherent fin horn how to mitigate this, but even then you still need to have the input wavefront shape to match the starting curvature of the fins, and that’s usually not the case. 

Finally, what main characteristics must an excellent acoustic horn have? This can be summarized relatively easily. The horn profile should not have any discontinuities or abrupt changes in profile. It must have very good acoustic loading down to the cut-off and an oversized mouth surface area as well. Excellent directivity control with a slightly increasing directivity index towards HF is important too.

After all this wealth of experience with various horn types, why on earth would the designer choose a semi-cubic parabola horn profile with natural dispersion? The answer is simple. The William Neile horn type delivers by far the most natural and coherent sound of all horn types. It combines all these characteristics that are important to me. And over the last few years, I have consistently refined the design, resulting in a rather complex algorithm. Everything I have learned over the years has been incorporated into this final generation design. Isn’t it a bit presumptuous to call the design #finalgeneration? I would say no because I am convinced that the current design cannot be significantly improved. From adapter to mouth, many different functions have been implemented, carefully optimized for each corresponding section of the horn. This is probably the most complex horn profile ever designed. All of this is based on the assumption of a coherent construction wavefront guided by the horn profile, and its surface area increases according to the specified expansion factor. This guarantees the design’s excellent acoustic loading down to the cut-off frequency. My rule of thumb for the acoustic loading of horns: “Horn length cannot be replaced by anything other than even more horn length.” Acoustic loading can be determined, for example, by comparing the open-air impedance of a compression driver to the combined impedance of the driver and horn together. By overlaying the two measured impedances, an estimate can be made of the influence of the horn on the acoustic loading of the driver. If the combined impedance of the driver/horn or driver/waveguide does not differ significantly from the open-air impedance, the corresponding horn can be disposed of without hesitation. This statement may seem radical, but it reflects my many years of experience. Ultimately, when measuring normalized distortions in the LF region of the horn’s passband, there will be a point in frequency where distortions increase substantially, like a knee. This is the point where the driver/horn combo should be out of the game. To make this more clear, here is comparison of the free-air impedance of TAD TD-4002 compared to when attached to my WN250RA prototype:

The free-air impedance peaks are completely eliminated, resulting in a uniform combined impedance curve. This will also result in low distortions and a more linear frequency response. The ultimate test is measuring the driver’s distortion attached to a horn. When the horn does not provide enough acoustic loading down to cut-off, then distortions increase way before the designated cut-off. My new design surpasses any expectation with respect to low distortions down to cut-off:

If you compare my design other designs that claim low cut-off values, you may recognize that distortion, especially k3, increases much earlier at higher frequencies. Therefore, my final generation horn series provides the capability to cross-over lower than other designs. Excellent acoustic loading is the key success factor for an excellent horn speaker, regardless what others might tell you.

By dividing the horn into a major and minor radiation plane, it is possible to achieve almost constant radiation in both radiation planes. For the vertical radiation plane, the goal is a narrower radiation because reflections from the horn to the listening position via the floor or ceiling must be avoided. And furthermore, we don’t need broad radiation in the vertical because the corridor where our ears are located is quite small. This allows us to make the horizontal radiation very comfortable and wide and even. The resulting natural soundstage is astonishing, extending far behind the speakers and very stable while walking through the room.

Many guests have been completely thrilled by the excellent sound quality of my acoustic horns. Personally, I think that I have now reached a point where most probably no further significant improvements can be made using natural dispersion, and I have therefore decided to give the design the descriptive name “final generation.”

• Polynomial optimized Semi Cubic Parabola algorithm Version 2 (SQPV2).
• Acoustic Loading Optimized Version 2 (ALOV2).
• Absence of any discontinuities or diffraction slots in the horn profile using natural dispersion. These are the best conditions for a very natural sound.
• Overs-sized mouth surface area and mouth circumference wrt to cut-off frequency.
• No integration waste due to the use of excessive and unnecessary rollback elements. The generous mouth surface is shaped to fit the outer shell of the horn as gently as necessary.
• Slight edge rounding in order to mitigate the sharp edges inherited of the rectangular base shape by preserving the pre-defined expansion rate.
• No fake cut-off numbers. Full acoustic loading will reach down to the designated model number. This provides the ideal conditions for the driver to operate with low distortion right down to the lowest frequencies of the horn’s pass band.
• Excellent directivity control for major and minor radiation planes with a slightly. increasing directivity index towards higher frequencies.
• Removable adapter optimized as an integral part of the horn function. Provides maximum flexibility to mount drivers with different throat exits with a custom version.
• Unique horn speaker design that combines the first time perfect acoustic loading and excellent directivity control.
• Natural sound stage, perfect sound reproduction, unique listening experience.

The first part of this series is about the 2 inch final generation version. Some time ago, there was a request whether it would be possible to adapt my new design for larger drivers with a 2-inch exit, especially TAD TD-4001 and TD-4002. Until now, I had focused on 1.4-inch and 1.5-inch horns, as the smaller throat diameter tends to offer better opportunities to optimize the horn for higher frequencies. If the wavelength becomes larger than the throat diameter, the horn designer has very few options for influencing the radiation at high frequencies. After looking at the results of the initial 2-inch designs, I was very surprised at how well the design could be transferred to 2-inch drivers, and from then on I focused on developing a prototype for these specific TAD drivers first.

I would now like to let a few pictures speak for themselves. From production to integration into my existing system and the final sound check:

This is my test method for flexibly assembling turnout components. Individual cross-over branches can be quickly and easily adjusted or replaced. The final version will of course be soldered:

Of course, you will do all this much better and create a digital crossover with the help of DSP. For my part, I have a fully analog playback chain, and for me, a passive crossover fits better into the concept. In terms of sound, this approach has proven itself completely, and the guest who listened to the prototypes in my setup immediately decided to purchase them:

The WN250RA defined a new level of natural and distortion free sound. The sound stage opens up far behind the speakers and at the same time seems fixed in place when you move around the room. A sound full of dynamics, timbre, tone, depth of image. Voices and musical instruments sound so beautiful. Electronic music sounds so spectacular that it’s hard to believe. This horn series truly deserves the designation “final generation.”

Since decades people only blindly copy old and obsolete designs or use stupidly simple horn functions . These final generation horns are brand new extremely complex design, high-tech, high performances devices to surpass all existing designs and build to last without any compromise.

Stay tuned for more articles about my final generation William Neile Acoustic Loading horn series, especially when they a treated with triple cocked linseed oil. Please don’t hesitate to contact me via E-mail if you are interested in acquiring a pair of these horns. In addition to the 2-inch horn, a 1.5-inch version is also planned, which can then be used with all 1.4-inch and 1.5-inch drivers. Please note that no plans will be provided. Any inquiries in this regard are futile.

p.s.: here is a small video of the prototypes fresh from the CNC made by Mr. Cluse: