design consid

8/2/2019 Design Consid

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Design Considerations

AXIS

seriesY-axis

A D A M S O N S Y S T E M S E N G I N E E R I N G

T O R O N T O C A N A D A

T e l : 9 0 5 6 8 3 2 2 3 0 - F a x : 9 0 5 6 8 3 5 4 1 4

w w w . a d a m s o n p r o a u d i o . c o m


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Y18


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Y10

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Adamson Y-axis Line Arrays offer the best possible solutions to the complex questions of line

array geometry. Sound chambers, waveguides, driver size and box angle are all critically

optimized in the integration process of array design. Each of these components plays a

significant role in the outcome.

It is simply not possible for every manufacturer to produce a top performing line array withonly a few years devoted to its development. This is reinforced by the fact that many key

technologies are defined by patents or patent applications that are in progress by

Adamson and others.

In the past fourteen years, Adamson has pioneered the use of waveguides based on the

work of Dr. Earl Geddes. In 1987, before the introduction of the line arrays of the 90s,

Geddes clearly described the geometries of the Cylindrical, Elliptical Cylindrical and the

Oblate and Prolate Spheroidal waveguides.

Since then, Adamson has developed many useful line array geometries founded on our

early use of waveguide technology. Adamson holds numerous patents, has new patents

allowed (but not yet published) and has new applications filed. . . . . . . All in the field of linearray technology.

Introduction to Y-axis


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The properties of a multi-way line array are complex and often misrepresented. We at

Adamson would like you to know that the Y-axis employs the very best of all possible line

array geometries and drivers and wed like to explain it clearly.

All line arrays contain closely spaced rows of acoustic transducers and associated

structures that comprise line array source geometry. Since not all types of

transducer/structure geometries couple optimally, it is important to examine them carefully.

There arefour basic types of line array source geometry:

- closely spaced row of direct radiators

- closely spaced row of horns- long flat radiator (ribbon tweeter)

- continuous row of iso-phase energized slots (curved or flat exit sound chamber)

All currently available line arrays employ a combination of at least two of these source

geometries. But whichmethodisbest?. . . First consideration: .size matters

Line Array Elements

Wavelengths and Coupling

Multiple sound sources in an array must be centered within a wavelength of the highestfrequency for coupling to occur. So the first thing we need to do is compare driver size to

wavelength.

It is simple to see that there is a problem with the driver/wavelength size relationship. The

ratio of large to small loudspeaker diameters is approximately 10:1 (15 woofer - 1.5 horn

throat). But the ratio of wavelengths of wide-band audio from low to high is 1000:1 (20Hz -

20,000Hz).

Simple observation indicates that woofers are much smaller than the operating

wavelengths (200Hz = 68). This is a good thing. Mid drivers range from smaller than, to

equal to, the wavelengths (2,000Hz = 6.8). But high drivers are equal to, or larger than, the

operating wavelengths (20,000Hz = .68). This small fact is a large problem.

Simply put: drivers dont exist that are small enough to couple at the highest frequencies

with sufficient output for professional use.


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It seems like a simple matter to place a horn throat section in front of a compression driver

with an exit in the shape of a vertical slot. But... the resulting slot is energized by a

wavefront that expands spherically. An array of these devices, by definition, contains

and delivers correspondingly poor far field

performance.

This type of horn throat dates from the 70s and was found in the Manta-Ray and Constant

Directivity Horns. It was not considered a solution to vertical arrayability at the time and

should not be considered a solution today.

Mid range devices may be chosen small enough (7) to be arrayed in the required

frequency range, but show serious limitation in SPL and distortion. They may be chosen a

little larger (10) with poorer upper-mid array response.

Horn loading with a typical mid driver (10 - 12) solves the power problem, but offers poor

upper-mid frequency array performance since the output is curved and the box to box

driver spacing is too large.

curved

too

much overlap to couple properly in a line array

The High Frequency Dilemma

High frequency

Mid-range

Low frequency

drivers are the most obvious problem. The exit of a compression driver is

likely small enough, but the magnetic structure of the driver is much larger and prevents the

correct spacing. Ribbon tweeters have limited output and thus, limited use.

direct radiators can be made small enough, but there will be a real limit

regarding distortion, SPL and crossover frequencies. This problem is not as great an

obstacle.

direct radiators can be arrayed with little difficulty, since typical wavelengths

in this frequency band are many times greater than driver diameters. (In another sense it is

thevery low directivity of the mid and low driversthat allows them to couple.)

Unworkable Solutions for the High and Mid


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AXIS

The exact same rules concerning apply to horizontal driver

placement within the enclosure.

far more serious effect because the

listener can move further off-axis in the horizontal plane.

serious

degradation of sound quality off-axis

coupling in the vertical array

Most line arrays are designed (and marketed)with two primary things in mind:

- Vertical driver spacing is minimized to reduce vertical lobing.

- The array is shaped and positioned so listeners face of the array at

nearly equal distance.

In other words, we have precise vertical control of the driver/array/audience position.However, in the horizontal plane it is not only much more difficult to comply with the spacing

rules, but it is actually, in some respects, more important.

So, in fact, violation of spacing rules has a

This critical fact is ignored in the design of many current line arrays resulting in

.

multiple elements

Why is it so much more difficult and how can it be more important?

Firstly the horizontal dimension of the geometry needed (such as horn flares) for wide

horizontal coverage is so much greater than the size needed for 1 or 2 degrees of vertical

coverage. This makes it difficult to keep the drivers closely spaced horizontally, within the

enclosure.

Secondly, the horizontal listening window is up to 100 degrees, which far exceeds the

vertical window.

So, if you are listening on-axis, the horizontal space between drivers is not an issue. But when

you are listening off-axis, the time delay error is magnified as you move further from the

center of the array.

horizontal

Horizontal Spacing: A Different Kind of Trouble


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Multiple sources, mis-aligned in time, are no fun to listen to. The time smear that results as

the listener moves off-axis, takes two common forms:

- double rows of mid-range drivers (or slot sources)

spaced more than a few inches apart - Off-axis, you are listening to two identical sources

arriving at different times, causing interference in the time domain. This time smear results

in deep notches in frequency response and a remarkable reduction in transient response

through the entire frequency band.

- rows of mid and high divers separated by several

inches - This time offset between two different sources affects frequencies in the crossoverregion. The off-axis frequency response, the impulse response and the polar response are

all degraded. The horizontal lobing error generated by offset mids and highs is the same as

the vertical lobing error seen in studio monitors. You wouldnt listen to a monitor 45 degrees

below-axis, so why would you want to listen to a poorly spaced line array 45 degrees off-

axis?

Unlike conventional arrays, the line array system

With improper horizontal driver placement, the off-axis audience is short-

changed.

operating in the same frequency band

operating in different frequency bands

depends on the off-axis sound to cover the

audience.

What does this mean to line array performance?

Time smear and Cancellations


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Each driver element of the mid and low section of a typical three-way array can act fully

coupled, vertically, to the next driver in the array. These drivers are small, relative to the

frequency of operation and therefore very low in directivity. Coupling, as a result, is

complete. But the high frequency element is a very different matter.

The HF element in an array is likely equal in size to a wavelength at the lower end of its range

and perhaps equal to 15 wavelengths at the upper end, due to the physical size of the

average compression driver. Since the HF element is so long, it in fact, must be considered

as a miniature line array in its own right, possessing its own directivity characteristics.

It is important to realize that in a correctly designed line array, the direct radiators operate asa coupled array. But the HF elements should operate as independent highly directional

elements, since they are too large, compared to operating wavelengths, to couple.

So lets look at how this little line array ought to behave and how we should integrate it into

the bigger line array. If the line array is to be straight and we want it to produce cylindrical

waves, then the wavefront from the HF element ought to be flat. (As stated earlier, ribbon

tweeter will not be considered due to limited SPL.) If we want a curved array, then the

wavefront we are looking for will be curved.

How do we form a long flat wavefront from the exit of a compression driver?

AXISThe necessity of Sound Chambers

In the early 70s a JBL Engineer named Bart Locanthi designed a fascinating little tweeter. It

became known as the JBL slot tweeter and is still available now. The JBL device has some

interesting f eatures. First is t he combination of an and an that formed

a passageway for the transmission of a sound wave to the . But the next

part is more interesting.

The paths that the sound wave would naturally travel, from the diaphragm to the exit, is

shaped so that . The result of this innovation is a very flat iso-

phase wavefront. The directional characteristic of this transducer is about 22 degreesvertical ( by about 120 degrees horizontal.

inner body outer shell

rectangular exit

the paths are equal in length

as a result of diffraction)

The First Sound Chamber


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Sound chamber principles have been advanced by Adamson as by no other

manufacturer. In a significant advancement, he benefits of an energized iso-phase slot

source are introduced to the mid range.

The heart of the ystem is the proprietary Co-Linear rive Module. Adamsons unique

sound chamber within a sound chamber presents a radical new way to produce a

curved, iso-phase, co-linear sound source.

Y-axis S D

.

The Co-Linear Drive Module allows the mid and high frequency wavefronts to bepropagated co-axially, while separated by the walls of the high frequency sound chamber.

Both wavefronts are allowed to change shape until they emerge from three parallel slots at

the Co-Linear exit of the sound chamber. The high frequency slot is centered, with the mid

balanced on both sides, at the entrance to the ninety-degree waveguide.

- the system is completely symmetrical with an absence of lobing error

- the midsas wellas the highs are capable of very long throw

- phenomenal headroom in the mids from Adamsons Kevlar compression mid driver

The result: seamless mid/high-frequency energy in the same linear waveguide. Only the

wave-shaping properties of Adamsons new technology produces this result.

Each Y18 enclosure contains two complete Drive Modules. Each module is powered by

one Adamson 9 Kevlar mid driver and one JBL 2451 high frequency driver. (Numerous

recent Patent Applications are the result of this ground breaking work.)

This new technology resolves all the design conflicts inherent in line array design.

AXISThe Y-axis Drive module


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8 x 8 Y10 at Olympia Theatre (Paris)Toronto Canadar

www.adamsonproaudio.com

Werchter 2001

Set UpY10 Centre Fill

8 x 8 Y10 at olympia Theater (Paris)

Werchter 2001

Rigging the Main Stage

24 x Y18


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Werchter 2001 Y18 x 24 Stage Left


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T O R O N T O C A N A D A T e l : 9 0 5 6 8 3 2 2 3 0 - F a x : 9 0 5 6 8 3

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