Front loaded and back loaded horn - diyAudio
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Old 3rd August 2007, 06:55 PM   #1
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Default Front loaded and back loaded horn

Does this make any sense?
Would it be of any benefit or would have lot of cancellations?
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Old 11th April 2016, 03:28 PM   #2
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The reasoning is that adding a front horn to the driver will increase the mids and highs, but the lows will be disproportionate to the intensity of the whole. Re the response plot. By adding a rear horn you can turn out of phase sound into reinforcing in phase sound by passing it through a quarter wave length passage where the sound appears in phase. Horns can use a fut off frequency pass filter In their design to eliminate other frequencies that will travel the same back loaded tunnel to emerge as out of phase distortions to the front wave. When all sound is added together from the front and rear horns you should get a new frequency plot that has more pressure for the lower frequencies which were lower when just the plot of the front horn were used, yet the rest of the frequencies hace the same pressure as before.
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Old 11th April 2016, 04:45 PM   #3
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Hornresp, TL.app and Akabak can all model a front and rear loaded horn load. In Hornresp it's called a compound horn.

Usually the front horn is much smaller so the rear horn is responsible for the lower frequencies and the front horn handles the higher frequencies. If you make the front and rear horn identical and the horn mouths are close together they will just cancel each other out to a large degree (theoretically perfect cancellation but not perfect in real life). So they have to be different to avoid cancelling each other.

There are many examples of compound horns, both diy and commercial. It was a fairly common thing a few decades ago.
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Old 11th April 2016, 04:48 PM   #4
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Click the image to open in full size.

It's not clear from this image whether the rear enclosure is sealed, ported or horn loaded but it doesn't matter, this is an example of a compound design and there's lots of examples of this kind of thing. As long as the front and rear are tuned differently they won't cancel each other (much).
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Old 11th April 2016, 04:56 PM   #5
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Another pic of this compound horn, this pic makes it more clear what's going on with the rear wave. Again, very small front horn. You can get up to 3 octaves of active horn loading from EACH side if it's designed properly.

Click the image to open in full size.

Click the image to open in full size.

Last edited by just a guy; 11th April 2016 at 04:59 PM.
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Old 11th April 2016, 09:38 PM   #6
Zero D is offline Zero D  United Kingdom
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Default !

OP posted this on 3rd August 2007

Still, good replies after All this time
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Old 11th April 2016, 10:13 PM   #7
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Yeah I didn't realize that until after when I realized the thread had 2000+ views. It was at the top so I replied ...
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Old 12th April 2016, 05:59 AM   #8
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Quote:
Originally Posted by just a guy View Post
Another pic of this compound horn, this pic makes it more clear what's going on with the rear wave. Again, very small front horn. You can get up to 3 octaves of active horn loading from EACH side if it's designed properly.
Example from the mid 1930's, developed by Olson and Massa.
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Old 12th April 2016, 05:38 PM   #9
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Hi Jag,

Usually for answers found, I have even more need.

In a Dinsdale article on horns (and he contributes Klipsch with coming to the same equations), he implies and I use the term advisedly because after it is stated his terminology changes and then I wonder if it meant the direct opposite. But in the two horn description, the front horn raises the mid and high with somehow causing the lows to be filtered out, while the back horn raise the lows and filters out the rest. He describes an equation that sets the volume of the pressure chamber behind the driver, the area of the throat entrance to the rear horn and the cut off frequency for the horn. Now he states that the cut off prevents frequencies above its level to enter the rear horn, and I parse the sentence to make sure that is what he means, and I find no alternate meaning. However I have later found gurus who claim the cut off frequency for the horn limits the low frequencies from enter the horn, exactly the opposite, yet quote the same equations.

However their may be other meaning when one uses a front and back horn. Does the front horn create extra pressure with the opening to the horn being the area of the driver, or do they make this front throat by enclosing a portion of the driver? After all, a horn needs pressure to work, or is the flare of the horn enough. Does the front horn then effect the pressure chamber for the back horn? I cannot find anyone who writes clearly and with any analogy other than electric circuits, not volumes, pressure throats inhibiting frequencies to escape the pressure chamber.

But my gut feeling is that if this equilibrium equation ( V=speed of sound x Throat area / 2 pi x Cut off frequency) for the rear pressure sets the volume larger for lower cut off frequencies, perhaps the larger volume prevents the shorter wave length to escape this pressure (aka air or coupling, depending on the romance of modern sages) and if you get a smaller volume for setting a higher cut off frequency, the shorter wave lengths can escape the chamber.

"Drinking deep may clarify the brain" or intoxicate you!

Dwight
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Old 12th April 2016, 05:50 PM   #10
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David,

Would you need to have a front horn if the full range driver has a fairly even response over the 100Hz to 18kHz range?

Where the response falls off from 93dB at 150Hz to 87dB at 50Hz, would not just a rear horn alone raise up the lows to achieve a flatter response across the usable spectrum?

Dwight
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