|I was thinking about the throat of my hypothetic midbass horn. This is complex, controversial and it has pretty much no answer, at least in the formeat I ask it. I will share my thoughts with you.
Let pretend that I went for exponential midbass profile, perhaps with a slight hyperbolic dent. Let look a very preliminary numbers for spherical horns. From the diameter of spherical it is simple to get area of circle and to convert it to any rectangular format. Also, if I would like to add to my exponential profile any hyperbolic depression (and most likely I would) then it would make the horn longer, let say 15% longer for a sane level of “hyperbolicizm”.
Throat diameter Type (Hz) Length Mouth diameter
4” , 10.2 cm, 81.7 sq cm 50 3m / 9' 10" 1.6m /5' 3"
4” , 10.2 cm, 81.7 sq cm 40 4.03 m / 13' 3" 1.95m / 6' 4.8"
6” , 15.2cm, 181 sq cm 50 2.5 m / 8' 2" 1.6m /5' 3"
6” , 15.2cm, 181 sq cm 40 3.5 m / 11' 6" 1.95m / 6' 4.8"
8” , 20.3cm, 324 sq cm 50 2.3 m / 7' 7" 1.6m /5' 3"
8” , 20.3cm, 324 sq cm 40 3.1 m / 10' 2" 1.95m / 6' 4.8"
10” , 25.4cm, 507 sq cm 50 1.98 m / 6' 6" 1.6m /5' 3"
10” , 25.4cm, 507 sq cm 40 2.8 m / 9' 2" 1.95m / 6' 4.8"
It would be very nice to have a good compression driver with 4” throat and to load it into 4m /13 foot horn. The biggest problem in here however is not the horn (that is a bitch itself) but the driver. Who the hell has a good driver with 4” throat that will be able to do 40Hz -50Hz and to sound “interesting”. The Japanese manufactures GOTO and ALE reportedly heavy and expensive bass drivers that might do the job but where is the assurance that they have interesting sound or even sound appropriately? I do not trust to those people (in fact I do not trust to anybody), their drivers are not available for experiments and whatever people do build with GOTO/ALE I do not like. What it important in this paragraph to memories that the biggest problem with GOTO/ALE drivers that they are the drivers with “predetermined” sonic quality and the quality of them unknown.
So, sanest solution would be to open up throat and look for larges driver. This would make the horn shorter that does not suck too much, but we I not want to go for too large throat as I will loss the horn gain at lower octave. The 6” is looks like fine throat but if I have my driver that I like is 15” then it will do too big front chamber. The 8” probable will do better with 3M 40Hz horn – almost manageable, isn’t it? Well, yes and not.
Remember I was bitching about the unknown sonic quality, the unpredictable TTH characteristic of GOTO/ALE bass drivers? I have a very high confidence in the TTH quality of my selected 15” drivers that is used as compression drivers in my hypothetic midbass but there is behind my confidence a very big slippery moment. Regardless what you heard from anyone and anywhere there are a few absolutely invariable rules on horns. They are not my own rules but they universal are the rules with what you can’t fuck with. I call them “Macondo's Axioms”, not particularly because they are implemented in Macondo bur because I discovered them while I was playing with Macondo (search for Macondo's Axioms if you wish more). So, one of unconditional postulates of the Macondo's Axioms is that it is absolutely impossible to predict how the sound of driver will be changed what the driver will be loaded into a horn. I know, I know, I know… I see a crowd of Morons armed HornResps, T/S characteristics, Earl Geddes’ assurances and other irrelevant craps scream in response that what I just said is not true. But trust me - they do not know anything about Sound - I do. The truth is that in driver-horn interaction besides the common algorithmable mass-reactance paradigm there are so many other satellites that the final TTH modification of a horn-loaded driver is absolutely non–predicable. Where does it leave me?
It leaves me with the fact that my beloved 151-10/40 driver of 15” sounds extraordinary but I know it when the driver is load into 15” throat. I have absolutely not idea how the Sound will change when it will be loaded to 8” or 6” throat. I might become even better but there is no way to know it, the very same as with GOTO/ALE bass drivers…
About my hunch. Generally I feel that the drivers that slightly compress sound at open air sound better in horns. My 15-inchers sound in open air or within a very low compression of 15” throat very nice and very full. This is not a good sign. However, I have no idea how big from the cone mass of the given driver the reactance of the 12” long horn would be and how the driver will be behave sonically when I begin to harden it with the back chamber. Some drivers bloom in this application and some loose colors, contacts and other “exoteric” characteristics. The point is that it is absolutely imposable to know what driver will do until you build the damn horn, put the driver in use and see what happen. An additional sad thing is that even among those few who have done something near-similar not one passes any constrictive critical feedback about the results.
So, in the environment of complete lack of clarity what would happen with the sound of a given loaded driver the decision to do for 4”, 6” or 8” throat become pure arbitrary and at this point I have no slightest idea what I would do it I go there.