Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[Al Rettich]

As I've been taught over the years about how intensity shading is bad for line arrays, what about fixed angles? I've read how most manufactures created a "fixed" angle line array to take out the calculations (aka dumb-a-fy) of doing a proper line array. But two boxes doesn't make a line array, as well as fixed angles. So why have portable line array's that are fixed angles? Just so you can offer a line array?

Your thoughts?

[Jelmer de Jong]

Fixed angle is the way to go from a engineering standpoint. You can't build a box that has a 10 degree dispertion on one day and a 2 degree dispertion on the next day.
When you look at modern linearrays they are all used 90% of the time with lots of overlap between boxes, only the bottom few have enough tilt between them to not interfere to much with each other.

[Ivan Beaver]

Here are a couple of the "basics" for having something that actually "arrays well".

1: Look at the angle of the cabinet.  It should be 1/2 that of the rated coverage angle.

So if the rated coverage is 20*, then it has to be cut at 10* to be arrayable,

2: The size of the horn MATTERS!!

It takes SIZE to have control (so that one cabinet does not interfere with the others)

The problem is that the NARROWER the horn coverage, the LARGER the horn has to be to have the same control as a wider coverage horn.

Let's say you have a horn that is 16" tall and rated at 20*.

It will have pattern control down to just over 3KHz.  Below that the different cabinets will start to interfere with each other.

The same size for but rated for 40* would have control and octave lower or around 1.5Kz.  80* would get you down to 750Hzish

Of course if the horn is narrower and smaller-then that freq will be higher, which makes things worse.

Believe it or not (many people do NOT want to), loudspeakers DO NOT have the rated pattern across the freq range they are used at.

In many cases, the rated pattern is only for the top octave or 2 of the HF driver.  And in the usable range of the HF driver, it starts to lose pattern control. Forget about the mids, much less the lows. 

But at least the lows (in many cases) are close enough together (within 1/4 wavelength) that they couple (assuming the lows don't go to high)

So the loudspeaker just ends up "spewing sound" all over the place, bouncing off of things you don't want it to.

It takes SIZE to control wavelength, no way around that.  Unless you just want to believe what the marketing dept tells you.

BTW I have some ocean front property in Kansas if you are interested---------------------

[Jason Raboin]

It takes SIZE to have control (so that one cabinet does not interfere with the others)

The problem is that the NARROWER the horn coverage, the LARGER the horn has to be to have the same control as a wider coverage horn.

Let's say you have a horn that is 16" tall and rated at 20*.

It will have pattern control down to just over 3KHz.  Below that the different cabinets will start to interfere with each other.

The same size for but rated for 40* would have control and octave lower or around 1.5Kz.  80* would get you down to 750Hzish

Of course if the horn is narrower and smaller-then that freq will be higher, which makes things worse.

Believe it or not (many people do NOT want to), loudspeakers DO NOT have the rated pattern across the freq range they are used at.

Ivan, ren't there some exception to this rule?  I don't know the engineering behind it, but my Fulcrum Acoustic FA22AC have a fairly small horn but have pattern control down -12 @ 400hz.  That's based on their product specs but also based on my real world experience. 

I don't have the plots to back it up, but L'acoustics ARCS have very impressive pattern control with only a 22.5* rated horizontal dispersion and a fairly small horn.  How is this achieved?

[Ivan Beaver]

Ivan, ren't there some exception to this rule?  I don't know the engineering behind it, but my Fulcrum Acoustic FA22AC have a fairly small horn but have pattern control down -12 @ 400hz.  That's based on their product specs but also based on my real world experience. 

I don't have the plots to back it up, but L'acoustics ARCS have very impressive pattern control with only a 22.5* rated horizontal dispersion and a fairly small horn.  How is this achieved?

I am not aware of any exception.

Again, it is not only the size of the horn, but ALSO the pattern.

For two horns of the same size-the one with the wider pattern will have freq control down lower.

So a narrower horn HAS to be larger to maintain the same pattern as a wider horn.

The basic math is  Freq of control=1,000,000/(size of horn in inches x rated pattern in degrees)

This is a rough estimation.

If there is some way to control without size (relative to the wavelength involved), I would LOVE to hear about it.

There is no "magic" being done by anybody-that I am aware of.

[Peter Morris]

Ivan, ren't there some exception to this rule?  I don't know the engineering behind it, but my Fulcrum Acoustic FA22AC have a fairly small horn but have pattern control down -12 @ 400hz.  That's based on their product specs but also based on my real world experience. 

I don't have the plots to back it up, but L'acoustics ARCS have very impressive pattern control with only a 22.5* rated horizontal dispersion and a fairly small horn.  How is this achieved?

Vertically the horn starts to lose control at about 2KHz.  Below the crossover point of the horn (around 1000Hz) its the dipole action of the 2 x 12" drivers that help maintain some vertical pattern control down to around 400Hz.

[Ivan Beaver]

Vertically the horn starts to lose control at about 2KHz.  Below the crossover point of the horn (around 1000Hz) its the dipole action of the 2 x 12" drivers that help maintain some vertical pattern control down to around 400Hz.

And therein lies the whole size thing.

Drivers that are properly spaced can change the pattern being radiated.

But to go lower and lower the spacing has to be larger and larger.

So the "size" is larger with lowering freq.

Just like waves in the ocean.  You cannot "control" large waves with small barriers.  It takes large barriers for large (low freq) waves.

[Keith Broughton]

So the "size" is larger with lowering freq.

Just like waves in the ocean.  You cannot "control" large waves with small barriers.  It takes large barriers for large (low freq) waves.

Good one!
I have to remember that whey trying to explain pattern control.

[Ivan Beaver]

Good one!
I have to remember that whey trying to explain pattern control.

Here is another way to "look" at it.

Go to the ocean and find a pier.

Notice how there are basically 2 sizes of waves.  The obvious large ones (caused by the tide), and the smaller ripples (caused by the wind).

The large ones are low freq and the small ones high freq.

Now look at the area around one of the pilings on the pier.

Notice how on the opposite side that the wind is blowing, there is a calm area (in respect to the small waves) behind the piling, where it is being shadowed.

The piling is large in respect to the size of the wind waves.

But ALSO notice that the large wave is completely unaffected by the piling.  It is still the same size and shape

It takes something MUCH larger to control or affect the larger wave.  A large barrier -in respect to the size of the wave.

As it is in audio, the larger the wave (lower the freq) the more "stuff" it takes to either control or affect it.

This goes for either pattern control or acoustic treatment.

DO NOT expect to put some fuzz on the wall and control low freq.

It takes SIZE.  So the best you can hope to do is to "break it up" rather than absorb it.

Once you start to think about sound in terms of wavelength SIZE, all sorts of things start to "come together".

Don't think freq, think SIZE OF THE WAVEFORM.

Go out in your drive wave and draw a single cycle of a 50Hz (or better yet a 20Hz) wave to get an idea of how LARGE we are talking about.

For those who don't want to do the simple math, 50Hz is roughly 22 feet for a single cycle and 20Hz is roughly 56 feet-for a single cycle.

And 10 Khz is less than an inch   That is easy to draw and control

YES SIZE MATTERS

[John Roberts {JR}]

Reflecting on the topic title, isn't "the science of line arrays" an oxymoron? 

Sorry just trying to make a joke about the compromises involved....

Of course they behave as defined by physics just like all speakers.

JR

[John L Nobile]

Reflecting on the topic title, isn't "the science of line arrays" an oxymoron? 


JR

It's mislabeled. Should read the "The Marketing of Line Arrays"

[Scott Holtzman]

Here is another way to "look" at it.

Go to the ocean and find a pier.

Notice how there are basically 2 sizes of waves.  The obvious large ones (caused by the tide), and the smaller ripples (caused by the wind).

The large ones are low freq and the small ones high freq.

Now look at the area around one of the pilings on the pier.

Notice how on the opposite side that the wind is blowing, there is a calm area (in respect to the small waves) behind the piling, where it is being shadowed.

The piling is large in respect to the size of the wind waves.

But ALSO notice that the large wave is completely unaffected by the piling.  It is still the same size and shape

It takes something MUCH larger to control or affect the larger wave.  A large barrier -in respect to the size of the wave.

As it is in audio, the larger the wave (lower the freq) the more "stuff" it takes to either control or affect it.

This goes for either pattern control or acoustic treatment.

DO NOT expect to put some fuzz on the wall and control low freq.

It takes SIZE.  So the best you can hope to do is to "break it up" rather than absorb it.

Once you start to think about sound in terms of wavelength SIZE, all sorts of things start to "come together".

Don't think freq, think SIZE OF THE WAVEFORM.

Go out in your drive wave and draw a single cycle of a 50Hz (or better yet a 20Hz) wave to get an idea of how LARGE we are talking about.

For those who don't want to do the simple math, 50Hz is roughly 22 feet for a single cycle and 20Hz is roughly 56 feet-for a single cycle.

And 10 Khz is less than an inch   That is easy to draw and control

YES SIZE MATTERS

Ivan I always that was intuitively obvious, I guess not.  When I was a kid building inverted V antenna for my ham radio the lower the frequency the longer the wire.  if the length did not match the frequency the wave could not leap off the wire so it got reflected back to the radio and  blew shit up.

Simplistic but worked for an 11 year old.

Sent from my SM-T800 using Tapatalk

[Ivan Beaver]

Ivan I always that was intuitively obvious, I guess not.  When I was a kid building inverted V antenna for my ham radio the lower the frequency the longer the wire.  if the length did not match the frequency the wave could not leap off the wire so it got reflected back to the radio and  blew shit up.

Simplistic but worked for an 11 year old.

Sent from my SM-T800 using Tapatalk

But I bet if you asked most of the peopl in audio how large (approximate) a 100Hz wave is-you would get a blank stare.

Some might say that 1000Hz is about 1 foot, but have NO IDEA how to get to how large 100Hz is quickly. 

[Steve M Smith]

Two ways I can think of.  If the frequency is divided by ten, the length is multiplied by ten. e.g. about ten feet.

Or pretend it's the length of organ pipes (or strings) and go down in octaves:

1000Hz = 1'
500Hz = 2'
250Hz = 4'
125Hz = 8'

So guess 100Hz to be about 10'


Steve.

[David Morison]

But I bet if you asked most of the peopl in audio how large (approximate) a 100Hz wave is-you would get a blank stare.

Some might say that 1000Hz is about 1 foot, but have NO IDEA how to get to how large 100Hz is quickly.

Basic relationships between Freq/Wavelength & Speed were part of my high school physics when i was around 14 or 15 years old, but clearly not everyone goes to the same school or takes the same subjects.

For anyone still not sure, Wavelength = Speed divided by Frequency, so 344m/s divided by 100Hz = 3.44m (approx, depending on atmospheric conditions varying the speed of sound a few percent).

Simple as that.

[g'bye, Dick Rees]

Two ways I can think of.  If the frequency is divided by ten, the length is multiplied by ten. e.g. about ten feet.

Or pretend it's the length of organ pipes (or strings) and go down in octaves:

1000Hz = 1'
500Hz = 2'
250Hz = 4'
125Hz = 8'

So guess 100Hz to be about 10'


Steve.

That's how I guesstimate.  Knock off 10% after that and you come close to the actual wave length which is about 9.2'.

[Dave Pluke]

That's how I guesstimate.  Knock off 10% after that and you come close to the actual wave length which is about 9.2'.

I'm still trying to figure out the wave length FREQUENCY of my driveway (as per Ivan's exercise)...

Dave

[Steve M Smith]

That's how I guesstimate.  Knock off 10% after that and you come close to the actual wave length which is about 9.2'.

Add 10% and you get even closer.  100Hz is 11.25'


Steve.

[g'bye, Dick Rees]

Add 10% and you get even closer.  100Hz is 11.25'


Steve.

Chalk that up to an 18 hour day yesterday.

Hey!  I'm not 65 anymore...

[drew gandy]

Chalk that up to an 18 hour day yesterday.

Hey!  I'm not 65 anymore...

An 18 hour day pushed you over the limit?  I'll have to remember to watch out for that;) 

A different thought but along those lines; I worked a corporate show recently where they talked about smokers in terms of pack years.  It makes me wonder if there is a way to think about human age in terms of awake hours vs sleeping hours.   
And then in terms of wavelength:  You can't get deep sleep from 5 minute naps.  It takes a much larger waveguide...

[John Roberts {JR}]

  You can't get deep sleep from 5 minute naps.  It takes a much larger waveguide...

There are at least two different things occurring while we sleep.

#1 the brain recharges sugar stores. This occurs whenever the brain can take in more than it is burning so brief cat naps can be very helpful.

#2 the brain organizes (re-organizes?) new data. This is when daily lessons get burned into memory like students learning new topics. Extraneous data also gets discarded while sleeping. The brain's attempt to make sense of random discarded data is the raw material for dreams.

Surely more than just these two but dream sleep requires longer uninterrupted rest periods to properly process (at least a couple hours). Inability to clear the decks of discarded data could clog the cognition machinery.

JR

[Ivan Beaver]

Two ways I can think of.  If the frequency is divided by ten, the length is multiplied by ten. e.g. about ten feet.

Or pretend it's the length of organ pipes (or strings) and go down in octaves:

1000Hz = 1'
500Hz = 2'
250Hz = 4'
125Hz = 8'

So guess 100Hz to be about 10'


Steve.

Yeah- you just remember 1 number and then divide or multiply as needed to get "close enough".

[Scott.Sugden]

As I've been taught over the years about how intensity shading is bad for line arrays, what about fixed angles? I've read how most manufactures created a "fixed" angle line array to take out the calculations (aka dumb-a-fy) of doing a proper line array. But two boxes doesn't make a line array, as well as fixed angles. So why have portable line array's that are fixed angles? Just so you can offer a line array?

Your thoughts?

Great question Al,

There are several reasons that inter array gain shading is a bad idea. In no particular order.

The stability of the cancellation off axis (generally above and below) of the array. Generally speaking one of the significant advantages to a line source array is the stability in the coverage zone and the consistent rejection in the non-coverage zone.

The way a line source array works is that the further you move away the more of the line you get to hear. By gain shading the array you reduce the total potential of the array when you need it the most. This difference in potential offsets some of the local advantages (reduction in SPL) experienced in the targeted reduction zone. 

These two trade offs (and a few more) need to be considered when choosing to shade the array. With any speaker the difference between the short and long throw is always of significant concern.

Like fire if you get to close it gets hot.

Scott Sugden
Head of Applications, Touring
USA + CANADA

L-Acoustics

[ProSoundWeb Community]