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[Ivan Beaver]

As usual Ivan phrases his response to support his companies products. No one expects a line array to exhibit good control at 35Hz.

OK.

In full "disclosure", it would take a seriously large horn to also "control" 35Hz.

It does not matter what approach is used-the lower the freq in question-the large the device (be it horn mouth size or line array length) has to be.

Therefore it is important to understand how the size of the device (be it horn or line array) affects the freq in question.

To be honest I was using the "opportunity" to simply point out a "general formula" for figuring out how the length of an array affects the "3dB rule".

Just to throw the general "horn pattern control" formula out there (for those that care about such things or would like to "play along at home).

The "general" formula for the freq that a horn has control  is    F(freq of "control")= 1,000,000/(pattern of horn in degrees x size of mouth of horn in inches)

If you plug in some "numbers to play around with" it will become quickly apparent that for a narrow horn to have the same control as a wider pattern horn-it has to be LARGER than the wider coverage horn.

On the other side-given 2 horns of the same size-the one with the wider pattern will control down lower.

There are physical limitations with everything associated with sound waves, and without a basic understanding of 'what is at play" it is hard to make "general statements".

OF course most people just want a "simple number" to describe everything about a loudspeaker-resulting in WRONG opinions and ideas.

[Ivan Beaver]

How big would a horn have to be to have a 3dB loss per doubling of distance at 35hz?  How big would a horn have to be to simply have adequate control of 35hz?

By the very nature of a horn-it will not have a 3dB/doubling of distance.

However this is not entirely true.  As you get close to a horn, the actual measurements can become a bit "skewed" due to the size of the horn.

THat is why it is important to measure at a distance (NOT 1M) to get an idea of what is really happening.

As far as the size of the horn to control 35hz, it will change vs the pattern.  So for a 90 degree horn it would have to be 317" in size.

But "controlling a freq" Is different than 3dB vs 6dB over distance

[Ivan Beaver]

OK.

In full "disclosure", it would take a seriously large horn to also "control" 35Hz.

It does not matter what approach is used-the lower the freq in question-the large the device (be it horn mouth size or line array length) has to be.

Therefore it is important to understand how the size of the device (be it horn or line array) affects the freq in question.

To be honest I was using the "opportunity" to simply point out a "general formula" for figuring out how the length of an array affects the "3dB rule".

Just to throw the general "horn pattern control" formula out there (for those that care about such things or would like to "play along at home).

The "general" formula for the freq that a horn has control  is    F(freq of "control")= 1,000,000/(pattern of horn in degrees x size of mouth of horn in inches)

If you plug in some "numbers to play around with" it will become quickly apparent that for a narrow horn to have the same control as a wider pattern horn-it has to be LARGER than the wider coverage horn.

On the other side-given 2 horns of the same size-the one with the wider pattern will control down lower.

There are physical limitations with everything associated with sound waves, and without a basic understanding of 'what is at play" it is hard to make "general statements".

OF course most people just want a "simple number" to describe everything about a loudspeaker-resulting in WRONG opinions and ideas.

And the same sort of "number playing" can be done with the "line array formulas".

What would be realized is that for a given length, the distance that the array "exhibits 3dB/doubling of distance will vary with freq.

The higher the freq, the  further away from the array the "3dB" will be exhibited.  So for lower freq the 3dB will not be very far from the array (unless it is large)

I HIGHLY SUGGEST people "play around with the formulas at different freq and patterns and see how they "react" to get a better understanding of what is really going on.

The more you know-the better equipped you will be to understand.

[TJ (Tom) Cornish]

  - unless you have a couple hundred feet of array length and one heck of a tall room to deploy that rig in.

Hi Tom, everything I've read says the source has to be large "compared to the wavelength being re-produced" to exert significant control over the directionality of the wave, sooo, since 30hz is about 36' wavelength, I'm curious what the advantage of going to "a couple hundred feet would be?
"you must be at least this tall to control this frequency" LOL
Chuck

Chuck, there are two ideas that are frequently confused - the idea of pattern control, and the "-3dB loss over distance".  These aren't the same thing at all.

Pattern control relates to the array's ability to put sound where you want it, or not put it where you don't want it.  For conventional arrays, this is largely done with horn size.  Vertical arrays accomplish this with the interactions of the various modules with each other.

Line arrays are often claimed to fall off slower over distance by the fact that sound radiates from a "line source" or cylindrical radiator, rather than a point source, which is a spherical radiator.  While this is theoretically true, you have to have a long enough array that at your observation distance it still appears to be a line.

Ivan mentioned the math.  Here is a JBL white paper that derives it: http://jblpro.com/ProductAttachments/AES_May_01_Ureda_Line_Arrays.pdf

Page seven of the above paper gives the formula for estimating the end of the near field (-3dB/doubling of distance land):

near field distance = array length ^2 * frequency/2300

The above formula is for feet.  For meters, use 700 as the constant instead of 2300.

Plugging in a few numbers, we see that for 250Hz, a 6' array's near field extends 3.9'.  A 25' array's near field extends 68' for 250Hz.  A 100' array's near field extends 152' at 35Hz.

Mac mentioned that "no one expects a line array to exhibit good control at 35Hz".  While I agree that we don't have that expectation based on practical experience, that is also in my mind the smoking gun proof that we should stop talking about line arrays' "-3dB thing", as at some point we inevitably transition back into -6dB land.  Unless we like our high and mid frequencies running away from our subs, it's far better to pursue good pattern control rather than sticking a few boxes on top of each other and hoping they magically give us an "acoustical line source".

[Ivan Beaver]

Mac mentioned that "no one expects a line array to exhibit good control at 35Hz".  While I agree that we don't have that expectation based on practical experience, that is also in my mind the smoking gun proof that we should stop talking about line arrays' "-3dB thing", as at some point we inevitably transition back into -6dB land.  Unless we like our high and mid frequencies running away from our subs, it's far better to pursue good pattern control rather than sticking a few boxes on top of each other and hoping they magically give us an "acoustical line source".

But for simple people who want the "simple answers" and believe that those answers "give them what they need to make a decision", then it works fine.

And the marketing departments love it.

Even more so for the people who "think" they have a line array with 2 boxes.

I hope they are really tall boxes filled with drivers that are spaced close enough to avoid interference-------------  Nah-----------.

What I find really funny is the trend towards "mini line arrays".

I don't recall anywhere in the formulas "number of boxes".  Is it all about the total height.  So to get the height, you need A LOT more boxes.

So now you have a bunch of stuff to hook up, that costs more than a conventional box.

But it has "the look" that some people seem to like.

I guess some people relate to it in terms of "male inadequacy" or desire.   People just seems to "lust" after tall line arrays---------  Just sayin'----

[Steve M Smith]

So now you have a bunch of stuff to hook up, that costs more than a conventional box.

And involves a lot more wood and woodworking.


Steve.

[Tim McCulloch]

What I find really funny is the trend towards "mini line arrays".

I don't recall anywhere in the formulas "number of boxes".  Is it all about the total height.  So to get the height, you need A LOT more boxes.

I've been preaching this for a long time.  It's about array length, not the number of boxes, that determines the pattern control and the transition point to far field coverage.  It's why, for a given coverage distance, that you can have more total SPL at the back, or your can have more even tonality (but trade off max SPL).

Everything is a tool, the designer's job is picking the right tool for the gig.

[TJ (Tom) Cornish]

But for simple people who want the "simple answers" and believe that those answers "give them what they need to make a decision", then it works fine.

And the marketing departments love it.

Even more so for the people who "think" they have a line array with 2 boxes.

I hope they are really tall boxes filled with drivers that are spaced close enough to avoid interference-------------  Nah-----------.

What I find really funny is the trend towards "mini line arrays".

I don't recall anywhere in the formulas "number of boxes".  Is it all about the total height.  So to get the height, you need A LOT more boxes.

So now you have a bunch of stuff to hook up, that costs more than a conventional box.

But it has "the look" that some people seem to like.

I guess some people relate to it in terms of "male inadequacy" or desire.   People just seems to "lust" after tall line arrays---------  Just sayin'----

I own a baby system (Vertec 4886/4883), and I love it. It has incredible flexibility, sound quality, output, and a cool look. It is the right choice for me and does things I would struggle doing with out an inventory of a number of different trap boxes. Not everyone buying a small rig is an idiot, but I'm sure some are. YMMV

[Ivan Beaver]

. Not everyone buying a small rig is an idiot, but I'm sure some are. YMMV

I never said they were.

But if you simply post a photo of a tall line array- you get all kinds of people "oohing" about it.

But what if it is the wrong tool for the job?

I see that all the time.  People install them, SIMPLY because it is a "line array".  And without any understanding of how they work, what the principals are etc.

You post a photo of a small well done "point source" and nobody gives it a second glance-even though it is doing a great job.

To me, line arrays are like "audio porn".  It may be something to look at-but how good of a job is it actually doing?

Do you ever see any videos of "in the room" recordings?  Or measurements at different seats showing how well they ACTUALLY cover (or not)

Not that I have seen.

How about recordings of line arrays outside when the wind is blowing?  Especially at a distance?

 My statements were based purely on how "turned on" many people get when seeing a line array.

To me it is more important how good the final result is. 

[Tim McCulloch]

Line arrays have a Freudian aspect of the 'manly' persuasion. /nudge, wink

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