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Sorry, I do not share your sentiments with those 3 reasons. Below are my reasons.

jessie.dazzle wrote:

Three reasons: 1) To try high passing your upper-MF channel (S2 > 400Hz horn) above the 1250Hz secondary resonance assiciated with the plastic-suspended diaphragms of the S2 when used in wide bandwidth configuration. If I understand correctly, you currently use these diaphragms and run the driver from 10.5KHz down to 1KHz.

My MF channel is crossed well above secondary resonance – at  3200Hz

http://www.goodsoundclub.com/Site_Images/6-Chennal_Melquiades_DSET_Amplifier_Rev3.jpg

I get my 1000Hz by gliding the filter-declining slope of the secondary resonance

jessie.dazzle wrote:

2) To try unloading the lower end of that same channel which, again if I understand correctly, in your case is currently covering more than three octaves. Reducing that range may in practice not turn out to be desirable, but I would have thought you'd be curious.

 I do not feel a need to unload lower end from my MF channel. I did listen the naked MF channel extensively and in my view it does fine and do not need any crossover modification.

jessie.dazzle wrote:

3) To simply evaluate which driver/horn combination is best suited to reproduce the 1-1.5KHz range.

So we are taking about 500Hz that might be handled by ether MF of Fundamental channel. It might make sense mathematically and looking at graphs but in all practicality it unfortunately doesn’t works this way. In the 1-1.5KHz range I have pretty much 4 channels work together MF, Upperbass, Fundamentals and Insertions. Do not forget that with exception of upper knee of Fundamentals Channel they all are first order, with a lot of overlap and acoustic inner-modulations. Measurements-wise it if flat of course but in reality I never was able to set what I call proper sound by measurements. I do the following. I set the only Upperbass and MF flat by measurements and it will have a little dip of an octave wide around 800Hz. Then I run the Fundamentals all the way up until the peak of the Fundamentals response just touched and very slightly dent the bottom of the 800Hz dent. Then I begin to listen and set by hearing the level of Fundamentals in order to get the MF richness but not too prominent. The rule is that is that I need juts to recognize that Fundamentals channel is engaged but I shall not have it prominent in any auditable moment. A trombone sliding across it’s range and mantling the almost fixed vertical image is good indication that my Fundamentals are not too hot. I said “almost” because I personally feel that that in my old room the right amount of Fundamentals was when in the very top range the Fundamentals shall very-very-very little to shift the image up. It was very extreme nearfiled however and the degree to which it took place was not annoying in my view, particulary after I went DHT for MF.

jessie.dazzle wrote:

Concerning perception of the vertical center of the sound image; no, we do not want the perceived center to be located somewhere in heaven or hell, but the view of most people who practice audio is that it would be desirable to produce the entire audible spectrum from left and right points as close to ear-level (purgatory?) as possible. In answer to that, I would like to put forth the following idea or sort of hypothesis: First, what is the objective of audio? For me, ideally it is the selective recreation of an event according to and in reinforcement of the artist's original intention, as well as what I might myself decide to "keep" from that event, had I witnessed it live (the more the demonstration corresponds to my view of what life should be, the more I will keep). When reproducing live events witnessed in physical space, that space too must be taken into account. With the exception of small clubs where we might hear a jazz trio, when we listen to live music, we rarely find ourselves on the same plane with the musicians; we are usually looking down on them. This is not a chance occurrence; when seen and heard from this angle, the depth of the space, in both vision and sound, are more clearly revealed. Look at the image below showing the layout of an orchestra from the point of view of the listener; this is two dimensional data that successfully depicts a third dimension, that of depth. It does this by using both the horizontal and the vertical (if it were a more accurate drawing, it would make better use use of relative scale and relative intensity). Notice, there are instruments located at the top, middle and bottom of the image. I'm not trying to be silly; realize that sight (light) and sound (pressure) are first perceived as binary, two-dimensional sense data; from this, our brain extrapolates the third dimension; depth. Yes intensity (amplitude) and cast shadows (masking) play a part, but a really convincing illusion of depth is difficult without making use of the vertical axis. I think the depiction of depth in audio relies on the vertical; I think we are using it and I think we are not acknowledging it... It is what gives some mono recordings a semi-convincing illusion of depth. Absence of the vertical axis is the principal limitation and resulting frustration associated with headphones.

I personally prefer do not have center imaging as close to ear-level. I prefer to have center imaging elevated up and I like to listen with slightly raised my head. It makes discipline impact and put Sound in position of authority. The vertical axis is fine, I am not against it but I think that you are taking not about the vertical axis but rather about radiating surface. I wrote about it manse times – larger radiating surface when Sound comes not from a single point but from a large “cloud” is much interesting configuration. Unfortunately, due to the physics of our hearing (the position of ears) we can increase the size of the cloud only in vertical plane.

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