Yes, I assumed that you had found the spec sheet; I only included the link for the convenience of others following the thread.
Klaus wrote :
"...whats wrong with 9,9"? its rougly 55% of sd? you think, 43" is too short for a 62hz horn?..."
About a year ago, in discussing the design of a 45Hz mid bass horn using a 15 inch driver, Guy Sergeant asked how I arrived at the ratio of throat to diaphragm area... At 16", the driver you are using is slightly larger, but here is what I answered ("ø" = Diameter) :
"...The ratio I used for the 45Hz horn is about 65% of the ø of the diaphragm when measured WITHOUT THE SUSPENSION.
ø of diaphragm WITHOUT suspension (AK151) : 11.25 inches
ø throat (45Hz horn in the illustrations) : 7 inches
Ratio : About 65%
I arrived at this ratio via the following logic :
This is a bass horn, and, based on all information I have been able to gather, it needs to be long to be effective... I will be using it down to about 60Hz ; a 60Hz wave measures about 18 ft in length... I targeted a half wavelength dimension at 55Hz (though I'm not sure this is anything to go by). I also looked at other horns which don't simply use the diameter of the driver as a throat diameter, taking info from horns in a local audio shop and also from various postings on the web.
If you take Romy's Upper-Bass horn for example :
ø of diaphragm less suspension (Fane 8M) : 6 inches
ø throat : 4 inches
Ratio : About 65%
Space considerations aside (just move), if you are going to all the trouble of building a large horn, in the end you will expect performance; I feel that you will be doing nearly the same work as would be the case with a smaller throat, while getting only some of the performance.
Klaus wrote :
"...will try 2nd order at 500, but also 700 1st order..."
As far as the driver is concerned, you should be OK with either.
"...i would like to try different diaphragmas (especially the real metals, my instinct tells me they would sound very good with my poweramps)..."
Going by your latest info on diaphragms, I'm not sure what you currently have :Try to post a good image.
Romy wrote :
"...When you will be doing your 60Hz horn include into your design a perspective lower midrange channel from approximately 300-to 1000Hz. I know, you not doing it but if your consider it architecturally while you do your midbass horn then it will be much ease for you when you decide to try it..."
"...I would like do not screw you up implanting in your head the idea of a dedicated channel between your midbass horn and MF. At this point it does not matter to you but sine you told that you are planning to go for 250hz Lecleach later then you would need to think about it. The biggest question you would need to answer is what Lecleach horn to get for your S2: 180Hz, 250Hz, 330Hz, or 400Hz. That would all depend from where and how you will be intending to cross your S2 driver and that would be all depend from how good your upper know of your midbass and how deep are you willing to load your S2 into the depth of your MF horn (lower horn rate = longer horn = more HF attenuation + more beaming + less transients + less LF lower knee equalization). Soon or later you need to take all of it for considerations..."
In my original reply, I also started to suggest leaving room for additional horns, but stopped myself. If you can conceive your project such that you are able to start to use the system, and progress in such a way as to allow growth without waste (wasted effort, wasted cash), you will be doing the right thing; for that, Romy's comments above are extremely good advice. To that I would only add the following : Start saving up now for a second pair of S2s.
How to short-circuit evolution: Enshrine mediocrity.