What's the scoop on different horn geometries?
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Posted on Aug 24, 2008 10:36 pm
ted01
Member Since: Aug 24, 2008
As I'm scoping out various components should I decide to build my own PA speakers, I have noticed that there are many differences in horns.
What effect does the horizontal and vertical angle have? For example, what are the differences between a 90X40 horn and a 55X50 horn?
What effect does the material the horn is made of have?
What effect does the geometry of the throat have? I've seen some horns that have a smooth circular throat and others that are effectively square or rectangular. What's up with that!?!
Now, the million dollar question: If this hypothetical horn were destined for use in a cabinet that had a couple of 12 or 15 inch drivers rated in the 600 watt RMS range, and the horns were loaded with a compression driver that had a power rating appropriate for the low freq. drivers with the intention of entertaining from 300 to 500 people, which geometry should I consider? Oh yeah, I'd have four of such cabinets, two on each side of the stage, and a pair of 18" subs, one on each side of the stage. Generally speaking, I would be using these for the rock genre.
Hopefully that's enough info... Probably too much!
Ted
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Aug 24, 2008 10:55 pm The numbers that are given for the vertical and horizontal are degree patterns.
The first number is always the vertical, and the second is horizontal.
So 90 x 40 is 90 degrees of vertical coverage by 40 degrees of horizontal coverage.
The different throat length and diameter play a large role in the physics of the box.
A wide open throat will give a more natural sound. But it will diminish the throw of the horn. So, lets say you are trying to cover a room with the dimensions of 80' x 100'. This type of throat will only cover about 60' of the 100'. (Obviously depending upon the driver behind it.) So this may not be the best choice of lens for your design.
You also have what is called reentry horns. Reentry horn force the sound to return back to the horn before leaving out to the crowd.
This has advantages and disadvantages. The advantage would be more concentrated sound. Which translates into a farther throw. Also, it acts as if the box that it is in, was bigger. Meaning that your fs could change by using this design.
The disadvantage could be late arrival times, over riding the mids and lows. And a beam pattern in the near field.
ted01Member
Since: Aug 24, 2008
Aug 24, 2008 11:10 pm So, if I've got this right, a 90X40 horn will have a shorter throw but a wider pattern than a 55X50 horn. Is that right?
Aug 24, 2008 11:13 pm No. It will be the difference of coverage. A 55 x 50 will not be as high as a 90 x 40. But it will be wider then the 90 x 40.
Aug 24, 2008 11:25 pm One thing I think I should clear up is the fact that throat diameter, and lens pattern are two separate things.
The lens pattern is the degrees that it will produce. Throat diameter is the size of the hole that leads the driver.
ted01Member
Since: Aug 24, 2008
Aug 24, 2008 11:38 pm Ahh. So it is the length of the throat that determines the throw distance?
I'm looking at two (randomely selected) horns they've got at US Speaker:
The first, the Eminence LT250 has a 1 inch throat, is 60X40 and has a depth of 4.2 inches. The second is the P-Audio PH-4427, which also has a 1 inch throat, is 60X40, but has a depth of 8.74 inches. One obvious difference is the depth of the throat. (Another is the actual shape of the horn. One has a smooth flair while the other flairs for a while then has an aprupt angle and then flares some more). Would the horn that is longer also have a longer throw? Sorry for being dense, just getting going on this learning thing.
ted
Aug 25, 2008 11:25 am Yeah, now your starting to get it. The distance and diameter of the throat, will determine the resident frequency, throw, and delay of the horn.
One thing that I should point out, is that you can help lobing by lengthening or shortening the throat of the horn. This will help the time alignment of the box itself.
This is also how we can manipulate the pressure in the throat. By placing a 2" driver, on a 1" throat. We can increase the pressure. That will give a farther throw overall to the high end. Now this effects the tonality of the sound as well. Too much, can cause a tinny sound. Too little can cause a honking sound, somewhere around 2k, or 2.5k.
Sorry to say that I can not remember the equation for this off the top of my head. I will have to look up the book that has all of this for you.
But wait! There is more! Not only do you have the pressure to worry about. Now you have the issue of long and short waves that the driver produces. A long throat will expand the issue. Short waves will take longer to leave the throat. So, if you have two boxes side by side. both with a long throat. You will increase what is called "Comb Filtering."
Comb Filtering is when the long and short waves interact with each other from another box. What happens is phase cancellation. And a lose of sound in that region.
Just more of the fun issues that arrive when designing your own system. I will do some searches for the books that contain the equations that you will need.
