Jessie, at the home page, in the left, within the GoodSoundClub Section there is the “Announcements” item of menu, which will bring you to the thread with the instruction how to upload the images to the site.

Regarding the issues that you are trying to address. You are absolutely right and the throat’s side thickness is a commonly avoided acknowledgment subject. Ironically the throat’s side thickness is not only silent problem with the upper bass horn but also with compression drives. I have seen many of then that have internally a perpendicular surfaces that I personally believe shouldn’t be there. So, what to do with that Red Area?

I do not know. It is possible to make it as a contra-horn introducing a little bell in the opposite direction and making the deriver act as almost a compression driver. However it would essentially minimize the effective diameter of the cone. Sound derives from the perimeter of the driver diaphragm and by masking the outskirt of the driver you will change the driver characteristic. In which direction would it be? I do not think anyone knows… I do not think that there is anyone out there who was able to assess how different drivers with the different diaphragm profile, loaded into the different throat’s holes would sound. theoretically, purely theoretically the slightly larger  driver loaded into a throat create unavoidable front chamber. This front chamber acts as a first order low pass filter and as a resonator chamber with own completely unpredictable sonic qualities. If we add to the mix the reflections from the Red Area then we have a completely erratic behavior. The good part that all of it has to do only for higher frequencies and in your case when the horn will not be doing a lot of HF it might be irrelevant.

If you try to make the horn with 100Hz then the Fs of that driver should be around 1/3 octave below. For such a driver 1000Hz is handle-able but it might already that the driver might have a cone too heavy for 1000Hz. You have to listen it and see how it does. To make the Red Area as right and accusatorily abrasive as probably would be a good idea. Still it would have purely intellectual-logical purpose as I down that the stricture of this surface will be auditable at 500Hz. I ma very much be wrong and I look forward to learn form someone who has data regarding the subject.

Rgs,
Romy the Cat

JD,

In the case of the mid-bass horn, the throat transition does not affect the sound enough to worry about IMO. Due to the narrow bandwidth (100Hz - 1000Hz) the step transition between the woofer cone and horn throat is acoustically invisible. In order to have cancellation you need a reflection that is half a wavelength away from the source (i.e. the cone). The longest distance from the cone to horn throat is about 2-1/2 inches. This corresponds to half a wavelength at 2700Hz. So, our upper range of 1000Hz is in no danger of being screwed up by the throat of the horn. The 1000Hz wave is too long to "see" the throat transition. About the only thing one might wonder about is whether the upper harmonics that help to develop our tone are being affected?

Rgs, JLH

Posted on behave  jessie.dazzle as his Mac has problems to upload the images, The images and text are his:
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Here are some illustrations of a proposal using a removable transitioning spacer (fist shown without the spacer):

This will allow experimentation with a veriety of transition profiles.
Jd.

Remember that at the cone the wave front is not spherical, it is a flat plane. It only becomes spherical after transversing down the horn. This happens because the distance along the sides of the horn is longer than straight through the center axis of the horn. Of course I am talking about a round horn and not a square horn here.

Rgs, JLH

Jessie,

Perhaps if you search something in the throat jungle you might fish some interesting results. You see, optimizing the driver to throat transition you might get some HF out of upper bass driver. But besides getting more HF there is something else in there. Let me to explain.

Pretend that you have a perfect upperbass driver with very light cone, no excursion and with an ability to do OK higher frequencies. Then still to get HF out of that upper bass horn might be complicated. The upperbass horn has LF equalization that from my perspective screw up transient response at HF no mater what we do. I am not talking about the fool what make bent horns. Even in context of a straight spherical horn that for instance does 100Hz and the driver could be pushed up to 4000Hz the sound at 4000Hz is not necessary good. The horn is just too deep for highest frequencies: the radiation pattern suffers and the transients of the HF suffer… not to mention that the 100Hz horn would be with dumped diaphragm that is optimized for lower knee. I feel that for better result at higher knee other horns would be more suitable.  So, it is not about getting out of the upperbass horn more HF but rather to see HOW GOOD those HF would be. Most of the upper bass horns do not do HF well.

Perhaps a solution might be found in the optimization of a driver to throat transition. I personally do not think so as the premises that   “the upperbass horn is too deep for given HF”, the basis horn geometry will not be changed even if you make the very good throat transition. Perhaps a solution might be found in use of compression drivers for upper bass horns.  There is only one know to me driver that would be suitable for the task: ALE P1260, the one that Johan Dreyer used in his “Fundamentals Channel”. Another solution might be truing to inject into upperbass channel another overlapping channel with correct (or excessive) transition characteristics at higher frequencies. It is what I will be trying to do and I do not know yet if it will be working…

Anyhow, prior to any experiment with driver to throat transition we need to clearly identify what we are looking for. It is not about out intellectual satisfaction that one solution would be more “kosher” then other. We need to hear a specific horn. Then to identify what it dissatisfy us if any and then, ONLY THEN try to address this specific problem of sound. If it will be addressable by the driver to throat transition then it would be it….

Rgs,
Romy the Cat