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Author Topic: The science of line arrays...  (Read 6876 times)

John L Nobile

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Re: The science of line arrays...
« Reply #10 on: October 11, 2015, 02:38:52 pm »

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


JR

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

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Re: The science of line arrays...
« Reply #11 on: October 12, 2015, 02:56:35 am »

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

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Ivan Beaver

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Re: The science of line arrays...
« Reply #12 on: October 12, 2015, 07:36:57 am »

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. 
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Steve M Smith

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Re: The science of line arrays...
« Reply #13 on: October 12, 2015, 07:59:21 am »

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.
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David Morison

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Re: The science of line arrays...
« Reply #14 on: October 12, 2015, 08:05:39 am »

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.
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Re: The science of line arrays...
« Reply #15 on: October 12, 2015, 08:13:14 am »

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'.
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Dave Pluke

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Re: The science of line arrays...
« Reply #16 on: October 12, 2015, 08:49:09 am »

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
« Last Edit: October 12, 2015, 05:04:36 pm by Dave Pluke »
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Steve M Smith

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Re: The science of line arrays...
« Reply #17 on: October 12, 2015, 09:56:38 am »

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.
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Re: The science of line arrays...
« Reply #18 on: October 12, 2015, 10:12:43 am »

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...
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drew gandy

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Re: The science of line arrays...
« Reply #19 on: October 12, 2015, 12:43:50 pm »

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...
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Re: The science of line arrays...
« Reply #19 on: October 12, 2015, 12:43:50 pm »


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