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Old 15th May 2007, 04:26 PM   #1
freddi is offline freddi  United States
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Default Karlson - "equal amounts of energy"- what did he mean?

what was Karlson saying and can this condition be reached/calculated? (assuming possible)

a few excerpts from Karlson's first speaker patent

J.E. (John Edward) Karlson “Acoustic Transducers” US 2816619 filed Dec. 1951

"----Basically my invention consists of a pipe or elongated chamber closed at one end and open at the other. The size and shape of the opening are controlled to give the desired acoustic properties and differs from horns and similar devices in that the principal radiation occurs with a directiivity which is essentially normal or perpendicular to the axis of this pipe.

Stated differently, the sound comes out of the side of the pipe rather than out of the end. The advantages of this approach and the theory thereof are explained in the following paragraphs.

When sound waves are initiated in a pipe they travel towards the ends of the this pipe. At the closed end these waves are reflected back into the pipe and at the open end another reflection occurs due to the sudden rarefaction of the wave front of these waves. At certain wavelengths reinforcements of the incident waves occur due to these reflections which create the conditions for resonance. Therefore, a pipe open at one end and closed at the other end will resonate at a frequency whose wavelength is equal to four times the length of the pipe. The strengthness of this resonance is largely dependent upon the abruptness of the discontinuities at the ends of the pipe and the losses within the pipe. thus if only minor discontinuities exist at one end of this pipe, correspondingly weak reflections occur with the result that this pipe can only be weakly resonant. Also, if the energy within the pipe were gradually dissipated before it reached the end of the pipe, resonance would be further weakened. Then these conditions hold for a wide range of frequencies then we have the essentials for a non-resonate enclosures for use as an acoustic transducer for wide band applications.

This invention relates to a practical means of accomplishing these objectives. In order to present a minimum discontinuity at the open end of said pipe, a small opening is made in the pipe near the closed end of said pipe; said opening gradually being made wider until a maximum width of the aperture thus formed is realized at the other end of the pipe. The cross section of the pipe is also narrowed so that the energy being propagated toward the open end of said pipe is gradually forced through the opening formed by this tapered aperture.

This action continues until a minimum cross section at the widest end of the tapered aperture forces the remaining energy out of the enclosure. By this means, it is therefore possible to present a minimum discontinuity at any point in the opening in said pipe while at the same time providing a means of gradually dissipating the energy in said pipe in a useful fashion.

>>> (further down)


An elongated chamber is used in all thse designs in order to take advantage of the propagation effects inherent in a sound duct whose length is not small relative to the wavelengths transmitted, The parameters associated with these structures may then be regards as distributed constants and the ensuing acton may be analogous to electrical transmission lines and antennas.

The tapered apertures used in these figures although of different dimensions and shapes present a means for gradually varying the distributed constants of said chambers so that the high impedance driving sources may be adequately matched to the low impedance of the air.

The shape of the aperture largely determines the rate of release of the energy begin propagated toward the open end of any individual chamber. In order to have a minimum pressure gradient introduced at any point of efflux, it is necessary that equal amounts of energy be released for equal increments of distance along the aperture. This is done in several embodiments of my invention by varying the width of the aperture as the square of the distance along the axis of the elongated chamber.

Other rates of release of the included energy may be realized by changing the rate of taper.

>>>
An examination of Figs 1, 2, 3, 4 will show that all of said tapered aperture coupling chambers have be designed with a diminishing interior cross section starting near the apex of each aperture and narrowing down to a minimum at each base of said aperture.

The inclined planes thus present to the energy being propagated toward the the tapered apertures end of each coupling chamber deflects said energy over the entire length of said aperture. This action ensures a more uniform release of energy over the entire length of said aperture than would be normally experienced by a uniform cross sectional area. In addition to this feature a minimum discontinuity is also presented at the open ends of said coupling chamber by this structural design.

A less obvious result of the inclined plane so created in the path of the enclosed sound waves is in its influence of the radiation pattern of said coupling chamber. Properly designed relative to the rate of taper in the aperture, a uniform distribution of energy can be realized over the entire length of said aperture, especially for the high frequencies. When this occurs a roughly semi-cylindrical wave front results. This constitutes an ideal manner of propagation of these sound waves since the high frequencies will not be sharply beamed in any one direction.

If the angle of said inclined plane makes with the plane of said tapered aperture is greatly increased, several effects may be observed. Among these are (1) lower frequency limit (2) increased reverberation time (3) poorer transient response and (4) less uniformity in the radiation patter thoughout the frequency range. Obviously optimum results of any particular application would be subject to some trial and error tests...."
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Old 15th May 2007, 11:56 PM   #2
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A "k slot" horn? A cylindrical pipe with a speaker shoved in one end and an exponentially expanding slot cut into the side?

Edit: and it tries to solve the problem inherent in most horn designs: how to stop it from being extremely efficient (ie: resonant) at some frequencies but less efficient at neighbouring frequencies?

An ordinary pipe is resonant at just one frequency and a set of harmonics. Cut a little hole in the side and it adds another set of resonant frequencies to that pipe, just like a musical instrument. Keep adding more and more holes (and bias them towards the lower frequencies because the harmonics are already covered) and you eventually end up with a k slot.
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Old 21st May 2007, 06:20 PM   #3
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"and it tries to solve the problem inherent in most horn designs: how to stop it from being extremely efficient (ie: resonant) "

Horns achieve efficiency by impedance matching to the air, not by resonance.
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Old 21st May 2007, 11:54 PM   #4
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Hmmm, I think you misquoted me by omission, but I admit I probably wasn't very clear.

Yes both types work by impedance matching to the air. However, one way of describing that impedance matching is by a system that is equally resonant at a series of adjacent frequencies.
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Old 22nd May 2007, 08:47 AM   #5
sreten is offline sreten  United Kingdom
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Hi,

Note that you can patent anything by describing the method of creating it.
Whether it actually does what you claim it does is completely irrelevant.

/sreten.
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Old 24th May 2007, 03:59 PM   #6
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Measurements of a typical Karlson enclosure show a response that looks like a "too small" horn. That is one with numerous peaks and dips in the response, like a horn with a too small mouth.

I think he thought he'd manage to make a sort of "port" that resonated at different freqs proportional to the width of the front slot's taper - didn't happen that way.

There appear better ways to get the sort of results that Karlson was aiming for - aperiodic loading being one?

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Old 24th May 2007, 10:54 PM   #7
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"one way of describing that impedance matching is by a system that is equally resonant at a series of adjacent frequencies."

Because they both increase output doesn't mean the mechanism causing it is the same.

In particular, resonance is characterized by energy storage and ringing, whereas horn loading is not.
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Old 25th May 2007, 07:16 AM   #8
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All real sounds can be broken down into a set of continuous frequencies anyway, so it's just a question of semantics. Either of those two systems can be interpreted as having both a throat and a mouth, and an acoustic spring constant and mass, which varies with the distance from the speaker.
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Old 25th May 2007, 06:44 PM   #9
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"All real sounds can be broken down into a set of continuous frequencies anyway, so it's just a question of semantics. Either of those two systems can be interpreted as having both a throat and a mouth, and an acoustic spring constant and mass, which varies with the distance from the speaker."

No, it's not just semantics.

Just because springs and masses are present, and they always are since all materials have both these characteristics, doesn't mean resonance is a significant part in operation.
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