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mpmiller1980

Round horns VS, Rectangular horns "standing" waves?

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Okay I have had really good input about the square VS round when I meant to post Rectangular Vs ROund, I keep hearing about standing waves at the mouth of the round and square horns what does this mean? is it bad, I have done some research and it looks like in really high end systems people used round horns alot so is it bad or good, I love music and movies and I like hearing the tiniest details, does standing waves create distortion? let me know because Im going to spend a bunch of money on this project, I have an extra set of speakers at my house I am thinking about experimenting with round, rectangle,and oval shaped horns. Im using 2-8inch aluminim woofers- Parts express, and titanium 1.5 inch horn drivers. give me some input thanks

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The "standing wave" issue is typically reserved for horns with parallel sides or walls. Square-mouth horns would of couse be parallel all the mouth and since horns are a bandpass item, sub-multiples of the wavelength that corresponds to the parallel walls or mouth exit would tend to form a backwards reflection towards the throat or simply stay there as a standing wave.

A circular horn does not have parallel sides (its round) as it is a continuously curving form, so there is no real oportunity for a sub-multiple of the wave to find a point at which the wave sub-multiple width corresponds to the width of the horn as a parallel wall due to the horn walls continually changing in diameter... for this reason a circular horn is the best case, but again, the dispersion pattern is equal in spread from the horn mouth, i.e, vertical is the same dispersion as horizontal, diagonals are the same, too...

DM

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This is a complicated issue.

So call standing waves are the result of having two waves of the same frequency travelling in opposite directions in the same media and pretty much at the same strength. This is diffiult to visualize. However, The sum of the two waves will combine at one or more spots. The sum is a pattern which seems to stand still. That is to say a bunch of nodes and anti nodes

You can find this by playing a single tone through your stereo, and best if you use one speaker. The reflections off walls and the original source will create a mix. As you move your ear(s) around the room, you will find peaks. Interesting, you will find the nodes where there is no sound perceived at all.

This is an important way of gaining an appreciation of room effects. If you move from one wall to the other, you will find your are hearing an intensity (at that frequency) which goes up and down, like a wave. Hence standing wave.

To some extent this can happen in a bass horn, per DM, where two sides are parallel. Most treble horns are not like that.

- - - - -

.

The next issue is how reflections can occur. This complicated. The easiest example is when air meets wall, in the room.

However, this also happens in a tube, when confined air meets an opening at the end. There is a sudden open wall, or non-wall.. This is easier to explain in terms of electrical loads on a transimission line, but requires a good knowledge of that subject. I will not go into it.

None the less, if we have air in a confined tube (like a horn) we want to avoid a sudden change in area, we can do that by gradually increaesing the area to the mouth so that there is no sudden change.

However, at some frequency (large wavelength) a mouth is not "big" and there is a reflection or echo.

Here we have a standing wave not across the mouth, but rather back up the horn. It becomes an echo chamber, like the room described above. The only good thing is that maybe it will be absorbed by the driver.

(For those keeping track, this is why driver to throat impedance matching is important. A good match prevents a return echo. Just as the match allows for good transmission, it allows good absorption. So the driver is not a relector because it is not a hard wall, or a sudden openning)

- - -

A better issue about what is good or bad about horn geometry along the length ,or at the mouth is how much it beams sound. I think that round or square is not too different. Each share a common problem.

The problem is that there is beaming. Another difficult subject. This arises because of the geometry. So if there is common geomety on all axis, i.e. round, there is going to a gainging up at one frequency range. It might be better if we can play with that. and have two horns in one. A big one, and a small one. But how?

One thing we can do is to make a rectangular mouth. Then the vertical one is small and the horizontal is big. So we can play with both geometries and maybe even things out.

- - - -

The other solution is to make a horn which has constant beaming at all frequencies. A conical expansion does that. But you need a big cone and a big mouth. That makes the Klipsch tractrix horn work.

- - -

I'm sorry this got very complicated. And I didn't really answer the question.

Gil

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