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In Reply to: RE: AGAIN Why no rear and front HORN loaded MIDRANGE drivers in Pro sound ? posted by Rafaro on December 12, 2014 at 19:48:13
Rafaro
In your original post you were proposing a theoretical double loaded horn design, and you asked why this type of configuration was not being used in PA designs. Maintaining the format of a vertical array of 4 8" drivers in a double loaded application presents several design challenges (sorry for going off in another direction with my suggestion to face the drivers towards each other on a horn wall).
_Front horn(s) on the array.
You could use a separate horn on each of the drivers as used in some compression driver PA arrays, but this would add to the size and complexity of the array. The alternative would be to use one large rectangular horn on the front of the drivers, which would tend to require separate phase plugs and/or a sectoral type of design. If the 4 drivers are coupled together on one air chamber (Fhc), this will limit/dictate the high frequency extension (see my post down page here about the Jensen BLH).
_Rear Horns on the array.
You would need to design a manifold to couple the 4 drivers to the rear horn throat (with another Fhc factor), making the array even larger and more complex. The usual formula for designing an optimum throat area (Sr) is based on the T.S. perameters for one driver, and determining this for 4 drivers will involve some estimation plus probable adjustment in the finished design.
In a front loaded horn, the (typically) closed chamber on the rear of the driver is not "wasted", rather it's tuned to resonated to resist the tendency of the mass of air in the horn to move back and forth as a unit (instead of the sound moving through it) and thus limit the bass response near the low frequency theoretical cut off of the horn. This is called reactance annulling. With a double loaded design there is no place for a reactance annulling chamber, so low end performance will be limited by the Fs of the driver (plus horn dimensions), or drivers in the present theoretical design. BTW Dinsdale makes a good suggestion to make sure that the combined horn lengths of the two horns in a double loaded design to be made equal to an odd number of half wave lengths at the acoustical crossover. Due to the muffler effect of the folded horn, this is more likely to be below 200 Hz. than above.
BTW the center to center distance between two 8" drivers is 8" assuming they are on the same flat plane and not a curved array.
These are some things to consider while attempting a design like you propose. Hopefully you will try an experimental prototype and let us know how it goes.
Good Luck!
Paul
Follow Ups:
Thanks Paul for your courteous patience in reality I just used the well known JBL Vertex as an imaginary example to ilustrate the idea. In reality the design is much simpler. Just one driver 8-10" in each side of a V type "horn" for the front wave and a minimally folded rear horn laterally expanding with a rear space chamber (plus folds) to limit HF output past the front horn LF output. The midline diffraction HF horn in the middle of the V. Please note that time differences between the HF diffraction horn and front horn of the MR drivers is almost nothing (2")and that the rear horn output is only two ms behind the front MR horns output which goes below 200Hz !!Again thanks
Rafaro
Edits: 12/14/14
Rafaro
Hopefully you can build this theoretical design and test it. I should have looked up the JBL VerTec in the beginning to understand what you were suggesting, I would'nt have gone off on some other tangents. Just make sure to follow the Dinsdale rule: total of both HF and LF horn lengths should be an odd number of half wave lengths at the acoustical crossover of the horns.
Paul
Very perceptive of you Paul I have done functional designs along these lines earlier but the latest version is indeed theoretical and pushing the imaginary limits. I been thinking about 1/4 wavelength(WL)reinforcement same as in Tapped horns (TH) but in independent and separate horns! Interestingly the first draft met the necessary criteria so on to sawdust and will see what happens. All my other "crazy" ideas have worked but this one is extreme.
Rafaro
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