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[Jon Arneson]

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.

It says Measured Microphone Results, meaning real and not simulated.




Jon

[Tom Danley]

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

 Hi Merlijn, Art
HF absorption is certainly a real factor at larger distances but at small distances like you mentioned (200-300 feet) there are normally other (much more audible) things which cause the large changes in the subjective sound vs position and distance which drives the need for delay speakers.      Also keep in mind that when one has a constant directivity source with an appropriate pattern, that as one moves off axis, the spectrum does not change, only the SPL falls.  By using that single lobe, one can place that at an appropriate height and aim angle such that the SPL in the audience plane changes very little with distance and the spectral balance hardly changes at all. 
Here was an example I posted before which demonstrates that effect.  This is one not very large cabinet aimed at the 50 yard line and used for practice. The recording begins at the far end of the field (about 600 feet from the speakers) and stops at the other.   Here the effect of hf absorption is audible but the spectral balance and SPL is very constant being a near constant directivity source. Pop on some headphones;

https://www.dropbox.com/s/o0xlb17x8hhgekm/20140805120442.mts

As with this approach one can have far more directivity than a large array, the spl to the sides and rear is also reduced which is good for intelligibility.   It is not uncommon to have a maximum SPL variation of only a + - 2 or 3 dB over an entire space like a stadium and subjectively “sounds the same” everywhere.
 
That being said, it is also possible to make the vertical pattern narrow somewhat as the frequency climbs and so with the center of the pattern being aimed at the farthest seats, can offset some of the HF absorption related to distance.   For large distances like the stadiums, the far seats are 700 to 800+ feet away from the source and so J-4’s are often used in addition to add hf energy up high, usually limited to above 4Khz.

While each source covers a specific angle, the object is to have only one source covering any given seat which requires sources which can be arrayed horizontally without a seam. 
This way if an impulse is fed to the system, only a single arrival is heard at any listening position and not a train of arrivals from each source. 
While amplitude measurements are the norm, some music is actually quite “time variant” and so preserving time is an important factor in that use or if one needs a mono phantom image or stereo image.

Hi Art
The levitation sources were also a converging source but for what we are doing, that would not cover the end of a stadium 800 feet away with a constant SPL, that requires something around a 10 by 30 degree pattern and a large acoustic power / requires many compression drivers acting in unison.

Ivan, it’s probably time to stop posting on this here.  People judge something new based on what they already know and words don’t cut the mustard when describing an unknown.  This is a huge marketing mountain to climb, it’s not like demonstrating in a venue like a stadium side by side with a big array when the difference can be very clearly heard and as several explained earlier,  here sound quality can take a back seat to other concerns like portability etc.

Actually the X or house curve is a result of both explanations.   Going back to the origin in the mag stripe sound track, old style compression drivers and what makes it through a perf screen, one can see half of the reason the theater house curve was initially adopted.   
Part B is that even in a living room, a tilted response is chosen over flat. Floyd Toole’s testing verified that. 

On the other hand, as demonstrations at a large attraction in Florida illustrated, with wide bandwidth music, if you don’t have the theater’s rolled off curve and have more hf energy closer to flat, it is possible to make the source “sound like” the speaker system is floating in front of you 50 feet away even when it’s hidden 500+ feet away so it depends what one is trying to do.
Best,
Tom

[Hayden J. Nebus]

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.

Also, consider that standard practice for S202m (cinema B chain electroacoustic response -" xcurve" ) is for single channel FFT, measured beyond critical distance, I.e. inclusive of most reflective paths. I understand later incarnations have used multiple asymmetrically placed  mics summed for a poor-mans spatial average.

I understand there's a current working group addressing the antiquity of this process.

[Art Welter]

Hi Merlijn, Art
 Also keep in mind that when one has a constant directivity source with an appropriate pattern, that as one moves off axis, the spectrum does not change, only the SPL falls.  By using that single lobe, one can place that at an appropriate height and aim angle such that the SPL in the audience plane changes very little with distance and the spectral balance hardly changes at all. 

That being said, it is also possible to make the vertical pattern narrow somewhat as the frequency climbs and so with the center of the pattern being aimed at the farthest seats, can offset some of the HF absorption related to distance.

Tom,

Sorry to repeat myself, but as I mentioned in Post #13, a single source can only be built with one coverage pattern, which won't change to accommodate the wide range of temperature and humidity variations. If the system is set for a uniform flat (or whatever curve is deemed appropriate) coverage for one humidity and temperature, it will not be uniform for other humidity and temperature.

For instance, 25% RH is common here in the high desert of New Mexico, if a single point source was designed to cover the 43.8 dB 15kHz loss at 100 meters, when the RH would rise to 50% (as it did today after the rain) the spectral balance between near and far would experience a huge change, the near seats would be "fried" with HF sizzle.
If the system was designed appropriately for a 50% RH (-26 dB 15kHz @100m), and the weather "dried up" to 25%, the opposite would occur, the cheap seats become dull sounding. Nobody gets hurt, but the source no longer sounds like it is floating in front of you 50 feet away.

Although I am a fan of single point source sound, without multiple devices covering discreet portions of the audience, the variation in air absorption due to changes in humidity and temperature can not be addressed.

Art

[Peter Morris]

Actually the X or house curve is a result of both explanations.   Going back to the origin in the mag stripe sound track, old style compression drivers and what makes it through a perf screen, one can see half of the reason the theater house curve was initially adopted.   
Part B is that even in a living room, a tilted response is chosen over flat. Floyd Toole’s testing verified that. 

On the other hand, as demonstrations at a large attraction in Florida illustrated, with wide bandwidth music, if you don’t have the theater’s rolled off curve and have more hf energy closer to flat, it is possible to make the source “sound like” the speaker system is floating in front of you 50 feet away even when it’s hidden 500+ feet away so it depends what one is trying to do.
Best,
Tom

Exactly, if you maintain the HF flat and you close your eyes, the performer will sound like they are right in front of you.  My argument for not requiring quite as much HF boost at a distance is psychoacoustic. 
   
When there disagreement s between the visually perceived movement and the vestibular system's sense of movement (inner ear) we get motion sick.  I don’t think it unreasonable to expect when watching a performance that what we hear and see should more or less match. If they don’t, it will sound wrong, too bright or harsh.

Having said that, I think we should aim to be acoustically as close as reasonably possible to the performance. If we use the calculator in Art’s example (80 degress 50% humidity); at a mix position about 150 feet from stage we would need about 10dB - 11dB boost at 12KHz to have a flat response to 12KHz. http://www.sengpielaudio.com/calculator-air.htm.  My GUESS - it would probably sound best with about 3 dB less HF at 12KHz. i.e we would need about 7- 8 dB boost at FOH for it to sound about right.  That’s easily possible with what ever part of the speaker array focused at rear of the perfomance space. Without adding any more HF boost probably still acceptable up to 200 feet.

In your situation, where you are trying to throw across a football  …  good luck with those distances.

[Tom Danley]

Tom,

Sorry to repeat myself, but as I mentioned in Post #13, a single source can only be built with one coverage pattern, which won't change to accommodate the wide range of temperature and humidity variations. If the system is set for a uniform flat (or whatever curve is deemed appropriate) coverage for one humidity and temperature, it will not be uniform for other humidity and temperature.

For instance, 25% RH is common here in the high desert of New Mexico, if a single point source was designed to cover the 43.8 dB 15kHz loss at 100 meters, when the RH would rise to 50% (as it did today after the rain) the spectral balance between near and far would experience a huge change, the near seats would be "fried" with HF sizzle.
If the system was designed appropriately for a 50% RH (-26 dB 15kHz @100m), and the weather "dried up" to 25%, the opposite would occur, the cheap seats become dull sounding. Nobody gets hurt, but the source no longer sounds like it is floating in front of you 50 feet away.

Although I am a fan of single point source sound, without multiple devices covering discreet portions of the audience, the variation in air absorption due to changes in humidity and temperature can not be addressed.

Art

Hi Art
I guess I didn’t describe the situation very well, none of the largest stadiums use just one box but each box radiates as if it only had a single driver and ideally, no one is in the pattern of more than one box unless very far away from the system (where one is in the pattern of a full range and hf projector). 
   
Since most of them can be arrayed horizontally and some vertically without an audible seam and the hf projectors only cover the farthest seats and are independently adjustable, the result is quite satisfactory, enough to justify replacing the larger arrays that were used in all of them previously.   
On the other hand, to be clear, it is very hard to get even 10K out to 800 feet.   
Listen to the last video I linked which shows the effect of hf air absorption on one box (no extra hf) over a range of distances.
 Best,
Tom

[Art Welter]

Hi Art
I guess I didn’t describe the situation very well, none of the largest stadiums use just one box but each box radiates as if it only had a single driver and ideally, no one is in the pattern of more than one box unless very far away from the system (where one is in the pattern of a full range and hf projector)....On the other hand, to be clear, it is very hard to get even 10K out to 800 feet.   
Listen to the last video I linked which shows the effect of hf air absorption on one box (no extra hf) over a range of distances.
 Best,
Tom

Tom,

Yes, using conventional horns (even with 64 drivers per horn!), it is indeed difficult to get 10kHz out to 800 feet. Using a hyperbolic device, which has half the attenuation per distance doubling as a conventional horn, the variation over distance can be reduced by around 10 dB, a huge improvement.
This can be seen below in the comparison of a 13x13 degree conical horn compared to a hyperbolic device over a distance from 8 meters (26 feet) to 128 meters (416 feet). The conical horn "M" HF level falls into the noise floor just above 4kHz at 128 meters, while the pair of  Hyperboline "HX16pr" maintain level above the noise floor almost an octave higher at that distance, in spite of an initial SPL around 10 dB less in the near field as the conical horn.

The combination of your layered (driver) combiner with the Hyperboline approach could make 16 kHz at 800 feet quite possible,  potentially with considerably fewer drivers and power needed.

Art

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