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[Lee Buckalew]

Hi Lee
The variation one hears when the wind blows across an interfering array is because of the interference pattern it produces.  A large number of separately radiating  sources if examined at any single frequency produces a spherical polar pattern resembling the rear of a porcupine, lots of peaks and nulls and when the wind blows that pattern moves around.  While it is thought one can’t hear that porcupine’s texture, it is audible when it changes or if you reproduce an impulse which arrives spread out in time according to the path length difference to each source.   

One can “fix it” with dsp by adjusting the time for each source BUT that correction only applies in one location (as everywhere else has a different path length).  If one can radiate as if one had a single source, then one has something approaching a bubble so when the wind blows, it has a much smaller effect. 


Best,
Tom Danley

Tom,
Yes, I understand each of these pressure phenomena I am just not doing a great job at describing them.
What MLA has done is create a phase coherent arrival from all sources at the listening plane as defined in the software.  This makes the interference patterns far less noticeable than in other multiple box systems or systems that have multiple drivers covering the same band passes. 
I can not say if Jericho achieves this better than MLA as I have not heard both.
Each is a different tool that can be used very successfully.  Both offer different approaches to their treatment of acoustical summation and both are unique when compared to other manufacturers.

Lee

[Ivan Beaver]

I would probably argue that many people  consider HF absorption.  For example EAW UX8800 processor has it, you just need enter the temperature and humidity and it has automatic compensation. It takes into account the speakers’ capability and applies a suitable HF EQ compromise.  Programs like Ease Focus also predict what the HF loss will be based on temperature and humidity.  Even some old processors like BSS’s Omni Drive could integrate automatic temperature and humidity compensation   http://bssaudio.com/en/products/fds-388-omnidrive.

EAW, Turbososund etc all allow zoning within the array to compensate for distance, tempreature and humitity.

Sure it is easy to simply "add HF" to help reduce the air absorbtion-HOWEVER you will QUICKLY run out of gas on the drivers themselves.

My first real experience with this was when I was doing the alignment at BYU.  I could not measure much above 4K at the back of  the stadium-even with a 10dB boost on the HF.  I did not want to do more than that.

That night at the hotel I did a little research and found that the air absorption ALONE (not counting distance) was on the order of 40dB!!!!!!!!!!  With the current elevation-humidity-temp etc.

You ARE NOT going to be able to put that sort of boost on some 2" drivers and get it back.

It is "cute" to simply say that some processors have "adjustments" in them-but when you start to look AT THE REAL WORLD and what it REALLY TAKES- the marketing quickly falls away-------------------

Of course closer distances require less boost (because of less loss) but the situations we are describing are REAL and that is the whole point behind some of the products that have what some people consider "extreme" HF.  Because there is A LOT to "push through".

I wonder how many people have actually listened to systems at 800' (with no delays) to have an idea.  Or do they even care at that distance. 

[Merlijn van Veen]

Unsurprisingly we agree on the very real consequences of absorption by air.

My apologies if I appeared to know little about VHF issues, by asking so many questions. For those of you who have played with my air absorption calculator you'll know that this is not the case. I'm aware of various prediction software and DSP processors as well, with build-in functionality to model and treat these phenomena up to a certain extend before resorting to brute force.

The reason I posed those apparent questions is because the OP in the thread that lead to this one asked a valid question about the high cost of line arrays. As an alternative the single box approach was suggested for evident reasons.

Numerous valid arguments and compliments, mind you, have been made for both approaches and IMHO each serves a specific purpose and application.

I was just curious what the sentiment is about the distance-dependent effect of air in a single point source approach, in contrast to a LA, in "regular" large scale situations (200-300 feet) without the ability to zone the audience area and yet try to minimize tonal variation by air in order of 12 dB without resorting to a second source/zone?


Regards,


Merlijn

[Art Welter]

I was just curious what the sentiment is about the distance-dependent effect of air in a single point source approach, in contrast to a LA, in "regular" large scale situations (200-300 feet) without the ability to zone the audience area and yet try to minimize tonal variation by air in order of 12 dB without resorting to a second source/zone?

Merlijn,

A single source can only be built with one coverage pattern, which can't be changed to accommodate the wide range of temperature and humidity variations that can range more than 10 dB.

Line array zoning can help address the problem, but unless the upper "long throw" HF units have a more narrow vertical dispersion than the lower units, the interference from a near flat front array will not result in a linear boost, even if the drivers can withstand 10 times the power.
This can clearly be seen in Meyers Leo System on pages 26 and 27:

http://www.meyersound.com/sites/default/files/leo_application_profile_marysville.pdf

Even with the benign 50% relative humidity (at 20% RH the loss would be approximately twice as bad) , when we compare 2 kHz from 30m to 120m level drops only about 7 dB, while at 12.5 kHz level drops around 22 dB, and 16 kHz is virtually non-existent at somewhere around 30 dB down, only 40 dB or so compared to 88 dB at 2 kHz.

To address a loss of 30 dB (or far more in lower humidity) requires devices built for the specific application, as well as the potential to steer the device output to account for  temperature/humidity gradient effects.

I think my Hyperboline concept, which has approximately 10 dB less attenuation over distance compared to standard horn devices (like DSL's J4, or any LA HF) coupled with electronic beam steering (or electronics solutions similar to those used in the Martin LA) has the best potential to solve the problem of HF air attenuation.

Art

[Ivan Beaver]

http://www.meyersound.com/sites/default/files/leo_application_profile_marysville.pdf

Even with the benign 50% relative humidity (at 20 % tHF loss would be approximately twice as bad) , when we compare 2 kHz from 30m to 120m level drops only about 7 dB, while at 12.5 kHz level drops around 22 dB, and 16 kHz is virtually non-existent at somewhere around 30 dB down, only 40 dB or so compared to 88 dB at 2 kHz.

I would love to see actual measured responses, instead of just predicted in a case study.

And then of course to compare the measured with the predicted-to see how they relate.

Very often the real world is very different than the predicted.

[Peter Morris]

I would probably argue that many people  consider HF absorption.  For example EAW UX8800 processor has it, you just need enter the temperature and humidity and it has automatic compensation. It takes into account the speakers’ capability and applies a suitable HF EQ compromise.  Programs like Ease Focus also predict what the HF loss will be based on temperature and humidity.  Even some old processors like BSS’s Omni Drive could integrate automatic temperature and humidity compensation   http://bssaudio.com/en/products/fds-388-omnidrive.

EAW, Turbososund etc all allow zoning within the array to compensate for distance, tempreature and humitity.

Just to add a bit more ...

I’m sure you are aware of the X-curve used for cinema.  It nominally rolls of the HF from 2KHz @ -3 dB per octave to 10K and then @ -6 dB per octave. (steady state measurement) For small rooms the curve is less dramatic.

While I think this is not quite appropriate (see link below), I believe it does indicate that some HF roll off is appropriate especially at a large distance.

I don’t think you have to completely compensate for atmospheric HF losses for it to sound correct at a distance.  Your ears / brain are expecting some loss of HF. And if you make it flat your system will sound bright and harsh.

The need to correct for atmospheric losses is not quite as bad as it first looks.

For relatively short throws – 10m – 20m, I would suggest about 1 dB per decade from around 1k – 2k sounds nice, further than that … not sure what I would suggest.

http://www.aes.org/technical/documentDownloads.cfm?docID=391

[Jon Arneson]

I would love to see actual measured responses, instead of just predicted in a case study.

The actual measured responses are on pages 26 and 27 of the LEO case study, although the effects of air absorption aren't as pronounced as in the MAPP predictions Art mentioned since they are only shown out to about 50m.



Jon Arneson

[Ivan Beaver]

Just to add a bit more ...

I’m sure you are aware of the X-curve used for cinema.  It nominally rolls of the HF from 2KHz @ -3 dB per octave to 10K and then @ -6 dB per octave. (steady state measurement) For small rooms the curve is less dramatic.

While I think this is not quite appropriate (see link below), I believe it does indicate that some HF roll off is appropriate especially at a large distance.

I don’t think you have to completely compensate for atmospheric HF losses for it to sound correct at a distance.  Your ears / brain are expecting some loss of HF. And if you make it flat your system will sound bright and harsh.

The need to correct for atmospheric losses is not quite as bad as it first looks.

For relatively short throws – 10m – 20m, I would suggest about 1 dB per decade from around 1k – 2k sounds nice, further than that … not sure what I would suggest.

http://www.aes.org/technical/documentDownloads.cfm?docID=391

The X curve has an interesting history.

The main reason for the rolloff is because that is the result of what happened when they put loudspeakers behind screens.

So basically over time they just kept the response the same and made it a "standard".  Since the mastering houses know this is the response that will be int ther cinemas, they "compensate" for it during the mastering process-so the end result in the theater is predictable.

I would NOT recommend anybody going out and putting the X curve on a live music sound system.  They will not be happy.  Fine if you like dull music (like some styles) but not for anything with any harmonics.

[Ivan Beaver]

The actual measured responses are on pages 27 and 28 of the LEO case study, although the effects of air absorption aren't as pronounced as in the MAPP predictions Art mentioned since they are only shown out to about 50m.



Jon Arneson

Meyer Sound

My comment was made based on the fact that it says VIRTUAL SIM freq response-which to me means "not real-but simulated".

Maybe I was reading it wrong.

[Peter Morris]

Sure it is easy to simply "add HF" to help reduce the air absorbtion-HOWEVER you will QUICKLY run out of gas on the drivers themselves.

My first real experience with this was when I was doing the alignment at BYU.  I could not measure much above 4K at the back of  the stadium-even with a 10dB boost on the HF.  I did not want to do more than that.

That night at the hotel I did a little research and found that the air absorption ALONE (not counting distance) was on the order of 40dB!!!!!!!!!!  With the current elevation-humidity-temp etc.

You ARE NOT going to be able to put that sort of boost on some 2" drivers and get it back.

It is "cute" to simply say that some processors have "adjustments" in them-but when you start to look AT THE REAL WORLD and what it REALLY TAKES- the marketing quickly falls away-------------------

Of course closer distances require less boost (because of less loss) but the situations we are describing are REAL and that is the whole point behind some of the products that have what some people consider "extreme" HF.  Because there is A LOT to "push through".

I wonder how many people have actually listened to systems at 800' (with no delays) to have an idea.  Or do they even care at that distance.

I agree - I certainly would not us the X-curve for live music, but it does point to some psychoacoustics effects that should be noted. i.e. even with live sound a flat system in a large space will sound too bright.

 http://georgiahilton.webs.com/apps/blog/show/2999266-x-curve-history-by-tomlinson-holman-a-history-of-the-x-curve

"The background behind this work began with Texas acousticians C. P. and C. R. Boner, who established in the 1960s that a "house curve" was a needed concept. They showed that a flat electroacoustic frequency response in a large room sounds too bright on well-balanced program material. This was subsequently found to be correct by other researchers, such as Robert Schulein and Henrik Staffeldt, as well. While Boner's practice was for speech reinforcement systems that did not require theater-to-theater uniformity in the same way that film does, nonetheless the concept of a house curve traces back to them."

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