Optimum Horn Mouth Size

[dragonfyr]

Keele - Optimum Horn Mouth Size

KeeleOptimumHornMouthSize.pdf

[WMcD]

I've read this many times. It as referred to by Dr. Edgar in his works in SpeakerBuilder.

There are a couple of interesting things.

ONE: I think Harry Olson was holding out on us in a way.

Keele reprints Olson's data on throat impedance. Olson shows results as Kc Am gets larger and larger, all the way to 0.93 in half space (all in the diagram are half space). The next diagram by Olson is for an infinite horn with an infinite mouth.

Keele wrote he was surpized that very large mouths were showing poorer results. That is to say he had never read of an optimum. I've never seen anything to that effect except what Keele wrote, here.

So Keele did the analysis to find the optimum in various space conditions at the mouth. The optimum in half space was 0.935. That is to say, just 0.005 away from the condition where Olson showed the largest before infinite size.

From that I like to think that Olson somehow had determined this was the optimum; there was no reason to go larger. But he never said so.

Olson didn't have digital computers. Maybe he just lined up the diagrams for normalized impedances and overlayed them to see where the less light showed through. I.e. the most overlap. Just guesswork on my part. He was a very smart cookie.

TWO:

Table 1 tells us something about corner loading. Please note that there are optimums for Fc 1 to 10, 2 to 10, and 1 to 2. The last is probably best for bass.

Note that in all load conditions (two of them anyway), you need a bigger mouth to optimize Fc 1 to 2. The exception is the corner. The mouth size gets smaller, rather than larger!

Best,

Gil

[WMcD]

People may need some help with the concept of the Kc Am product. It is basically a matter of "how big is the mouth compared to the Fc of the horn.

The horns have a certain Fc. You have to convert that to a cut off wavelengh, which comes out to be some length. Let me call that Lc. (PWK points out this is 18.1 times the length in which the horn cross section doubles.)

Then you have the mouth of the horn which has some circumfrence. Another length.

Just wrap the Lc around the circumfrence of a round mouth. If they are the same, Kc Am = 1.0. If the mouth is bigger, and you can only wrap Lc around halfway, then Kc Am is 2.0.

Therefore you can see how the number is a handy way of comparing mouth size to Fc.

- - -

The other tough math part of the article is finding the optimum in a corner. Keele gives all fractional space in terms of steradians. If anyone is interested I can help with that.

Gil

Gil

[JJkizak]

PWK wrote in one of his early papers that the theoretical horn size for a 15" driver would be 66 feet. It was impractical then but now?

JJK

[Nklipsch]

JJK : The physics constants which control this universe havent changed in the last few years. That horn length will also have a certain mouth size. The optimal St and Vrc will be dependant on the driver itself.

[JJkizak]

Way back when I had big ideas and no money (still have no money) I designed my dream home with a humongous living room shaped like dual exponential horns with K-horns as drivers. Mucho glass windows and chairs carved into solid rock, and a whole tree slabed sideways for the bar with branches and chairs for same. So I added up the price and in 1976 it was 3 million, 3 million more than was in the bank. It sure would have been kool though with those 66 foot throats. The chairs would have to have seat belts.

JJK

[boom3]

I think Paul was talking about a horn in infinite space, in other words, without baffling effects from any walls or the ground, in the case of an outdoor installation.

The 66 figure also shows up in his Eight Cardinal Points of Sound Reproduction paper, where he says that a direct radiator, to have the same bass extension AND efficiency as the Klipschorn, would have to be 66 inches in diameter.

[Nklipsch]

BIG horns,that probably are only just CIR=1 IE largely resistive but still not ideal.

http://www.geocities.com/xobt/

[JJkizak]

Is that kool or what? Big horns for big people.

JJK

[jacksonbart]

I think your horn should be 4 times your wifes mouth.