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[Keith Broughton]

I have been searching for a calculation that would give a rough prediction of the loss of low frequency pattern control in a line array speaker system.
What I have is      1128/length x 4
So a 10 ft array would loose control at about 450 Htz.
Look about right?

[Russell Ault]

I have been searching for a calculation that would give a rough prediction of the loss of low frequency pattern control in a line array speaker system.
What I have is      1128/length x 4
So a 10 ft array would loose control at about 450 Htz.
Look about right?

If memory serves (I'm playing around with one of Magu's calculators to remind myself) without splay a line array will exhibit a 72° vertical dispersion angle at the frequency with a wavelength equal to the length of the array, with this angle narrowing by half for each doubling of frequency, so an unsplayed 10' array at normal room temperature would have a 72° vertical dispersion angle at ~113 Hz, a 36° dispersion angle at ~226 Hz, etc.

-Russ

[Dave Guilford]

If memory serves (I'm playing around with one of Magu's calculators to remind myself) without splay a line array will exhibit a 72° vertical dispersion angle at the frequency with a wavelength equal to the length of the array, with this angle narrowing by half for each doubling of frequency, so an unsplayed 10' array at normal room temperature would have a 72° vertical dispersion angle at ~113 Hz, a 36° dispersion angle at ~226 Hz, etc.

-Russ

So 450hz (OP mentioned) would be 18* with a 10ft array?

I’d say 18* counts as control.  Math seems to make sense with both of what you guys said.

[Bob Faulkner]

I have been searching for a calculation that would give a rough prediction of the loss of low frequency pattern control in a line array speaker system.
What I have is      1128/length x 4
So a 10 ft array would loose control at about 450 Htz.
Look about right?

hmmm... Seems I remember reading something about the height of the array dictates the lowest frequency it can control (direct?).  So, a 10ft high array (assuming the array is full-range?) could control down to around 100hz.  The height of the array is the lowest wavelength it can control -- sort of what Russell mentioned (above).

[Ivan Beaver]

I have been searching for a calculation that would give a rough prediction of the loss of low frequency pattern control in a line array speaker system.
What I have is      1128/length x 4
So a 10 ft array would loose control at about 450 Htz.
Look about right?

Here is the formula John Murray (RIP) published in the November 2004 issue of Live sound international.

CD = length (squared) x (Freq/2300)

CD is the point it starts to lose pattern control

 NOTE: 2300 is for units in feet, use 700 for meters

[Keith Broughton]

Here is the formula John Murray (RIP) published in the November 2004 issue of Live sound international.

CD = length (squared) x (Freq/2300)

CD is the point it starts to lose pattern control

 NOTE: 2300 is for units in feet, use 700 for meters

My math leaves something to be desired so let's see if I have this right.
When the term CD is related to "the point it starts to loose pattern control", is that point a distance or a frequency?
Also, how is the "freq" in the formula derived?
Please show an example of the math with my 10' flat array.
I looked at some array software plots and it looks like the formula I originally posted is not accurate and the 10' array should give some directivity down to 150.
Of course the question of what determines loss of directivity is rather loose as well.

[Mac Kerr]

My math leaves something to be desired so let's see if I have this right.
When the term CD is related to "the point it starts to loose pattern control", is that point a distance or a frequency?
Also, how is the "freq" in the formula derived?
Please show an example of the math with my 10' flat array.
I looked at some array software plots and it looks like the formula I originally posted is not accurate and the 10' array should give some directivity down to 150.
Of course the question of what determines loss of directivity is rather loose as well.

The formula is not for frequency, it’s for wavelength.

Mac

[Steve-White]

Here is the formula John Murray (RIP) published in the November 2004 issue of Live sound international.

CD = length (squared) x (Freq/2300)

CD is the point it starts to lose pattern control

 NOTE: 2300 is for units in feet, use 700 for meters

Like this?  CD = Controlled Distance?

[Ivan Beaver]

My math leaves something to be desired so let's see if I have this right.
When the term CD is related to "the point it starts to loose pattern control", is that point a distance or a frequency?
Also, how is the "freq" in the formula derived?
Please show an example of the math with my 10' flat array.
I looked at some array software plots and it looks like the formula I originally posted is not accurate and the 10' array should give some directivity down to 150.
Of course the question of what determines loss of directivity is rather loose as well.

The "CD" is the distance at which the "3dB/doubling of distance" changes to 6dB/doubling of distance.

The problem is that a line array of a fixed length, will have pattern control that differs with distance and freq.

For example: your 10' array length at 10KHz would have 3/dB/doubling of distance losses (not counting air absorption losses) to around 434'.

At 1Khz it would be around 43'.

At 100h it would be around 4.34'.

This is one reason the tonality balance is different at different seats.

[Keith Broughton]

I think I'm getting more info than I need. I understand the directivity changes with frequency.
Correct me if I am wrong but, the lowest frequency that an array (or driver) can exhibit some directivity is related to the size of the array (or driver); consequently the ability to properly combine with adjacent drivers.
So, just looking at low frequency directivity cut off,  a 10' array (10' aperture)  would have some directivity at a 10' wavelength, or about 115 Htz.
So when the boss makes me use a 4box, small array that is 3.5' long, I'm going to have problems with control of frequencies below 300Htz.
A reasonable approximation?

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