Trap Boxes?

John Chiara

John Chiara

Senior
Jan 11, 2011
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Troy, NY
Maybe it's because I am unable to afford a line array but if I see one more small stage in a 30-40 ft deep room with 4-5 small...expensive...line array boxes stacked up on each side I think I might hurl.
I have found myself at many a show the last year and left scratching my head. The systems probably cost 3-5 times what a similar quality trap system would and just never seems to sound good to me.
I just too old and broke to grok the concept here?
 
With all the attention on things that look like line arrays, I think many people just don't realize just how good the top line traps have gotten.

I also prefer the fewest boxes necessary for coverage which is often a good trap system instead of a bad(deployment) line system.
 
Re: Trap Boxes?

To play a bit of devils advocate....

If you are going to invest heavily in one or two modular PA's... why wouldn't you do a line array for the performance increase when you HAVE to throw much farther and punt on the short throw gigs?

This, of course, has nothing to do with the stupidity of the install market currently.

:razz:
 
Re: Trap Boxes?

Mike Brown said:
To play a bit of devils advocate....

If you are going to invest heavily in one or two modular PA's... why wouldn't you do a line array for the performance increase when you HAVE to throw much farther and punt on the short throw gigs?

This, of course, has nothing to do with the stupidity of the install market currently.

:razz:
Click to expand...

This question falls into my category of the season. I see all kinds if stuff happening in all kinds of markets with the result being less than optimal. My answer to the obvious mismatch is that nOone buys audio service based on sound as the primary concern.
 
Re: Trap Boxes?

John Chiara said:
Maybe it's because I am unable to afford a line array but if I see one more small stage in a 30-40 ft deep room with 4-5 small...expensive...line array boxes stacked up on each side I think I might hurl.
I have found myself at many a show the last year and left scratching my head. The systems probably cost 3-5 times what a similar quality trap system would and just never seems to sound good to me.
I just too old and broke to grok the concept here?
Click to expand...

It's probably what the provider had in stock and they're trying to maximize their earnings on what they already have. Maybe changes in the market has forced them to do gigs in smaller rooms then they normally would and they're trying to make the best of it...

That being said. I have seen similar and though "one of our stacked trap systems would rock this place and look good doing it....that right there: Not so much".
 
Re: Trap Boxes?

Mike Brown said:
To play a bit of devils advocate....
why wouldn't you do a line array for the performance increase when you HAVE to throw much farther and punt on the short throw gigs?


:razz:
Click to expand...
That is one of the "fantasies" goes around-that is pretty much false.

I have done quite a number of demos/shootouts that totally disprove the "3dB/doubling distance vs 6dB/doubling" theory.

If that were true, and the levels were matched up close-how come the line arrays ARE NOT waayyyy louder at a distance? In fact-very often the complete opposite is true. The point source (a good one anyway-not one that calls itself a "point source" yet has lots of interference) is at least equal in loudness (sometimes louder) and waaay clearer.

When you are talking about "perfect sources"-yes the theory will apply. HOWEVER nobody is making perfect sources (of either type), so in reality the products AVAILABLE (both point source and line array) are NOT behaving as the theory states.

Side by side tests can be VERY reveling.
 
Re: Trap Boxes?

John Chiara said:
Maybe it's because I am unable to afford a line array but if I see one more small stage in a 30-40 ft deep room with 4-5 small...expensive...line array boxes stacked up on each side I think I might hurl.
I have found myself at many a show the last year and left scratching my head. The systems probably cost 3-5 times what a similar quality trap system would and just never seems to sound good to me.
I just too old and broke to grok the concept here?
Click to expand...
At the extreme low end that you're talking about, it does seem a little silly, especially if they're stacked as I often see them - firing at my belly button rather than over people's heads. That being said, I would argue that a big piled up trap system is just as silly, and just as likely to be set up too low. A nice pair of SOS boxes would be great, but lack the visual panache some people want.

As someone shopping for a small line array, I will comment that while Ivan's Genesis and Jericho horns can outrun many line array systems, they're totally impractical for someone like me who needs a flexible, lightweight, flyable, adjustable coverage system for portable use. For that matter, any trap box with sufficient output to do what I want to do - SRX725, KF650, SH64, or whatever is too cumbersome for setup by one person. My current constant curve system has 50lb elements that I can lift myself and is both pole mountable and flyable. The system I'm looking at has 36lb elements, more output, variable coverage, and still pole mountable when I need it to be, but scales to do bigger events than I'll ever be able to handle by myself. Horses for courses...
 
Re: Trap Boxes?

Shane Presley said:
I know this is the consensus , but can you explain why in a couple thoughts... I've been curious to know why.
I mean I know it's preferred to fly , but why is stacked frowned upon? Does that include on scaffolding?

Just curious and hoping to be ejumacated. Lol
Click to expand...

It is difficult to get even front-to-back coverage with *any* ground-stacked system. That's simply a matter of the angles involved.

As far as ground-stacked line arrays, it's simply not possible to stack a long enough line in most cases. This manifests itself as a changing frequency response over distance culminating in no lows or low mids (but plenty of highs and subs) at the back of the listening area. Plus, modern line and curvilinear arrays are designed to be able to shape the vertical coverage pattern, which doesn't do you any good if the array just needs to blast forward.
 
Re: Trap Boxes?

kristianjohnsen said:
It's probably what the provider had in stock and they're trying to maximize their earnings on what they already have. Maybe changes in the market has forced them to do gigs in smaller rooms then they normally would and they're trying to make the best of it...

That being said. I have seen similar and though "one of our stacked trap systems would rock this place and look good doing it....that right there: Not so much".
Click to expand...

One local situation is where the provider has a great trap system yet sends out 4-5 small line array boxes and both fidelity and coverage suffer. My first remark to my assistant was.."this is a good example of 5 expensive array boxes sounding like a crapped out trap box.My SLS 960's would kill that 5 box array... And the KF 850's would be stellar.
 
Re: Trap Boxes?

I don't understand why a "line array" as commonly deployed would be expected to produce sound level that drops off like 1/R rather than 1/Rsquared. Sure the electromagnetic fields of a wire and a point source do drop off like 1/R and 1/Rsquared respectively, but to derive that result in physics you must make the assumption that the distant observation point receives field from every point on the linear wire, not just from one point on the wire. Mathematically, when you calculate the EM field at a point R meters from the wire you have to do the integral over the entire length of the wire so you are adding on some EM field from each point along the wire. A line array is set up to avoid interference of sound from multiple boxes (comb filtering) by having very narrow vertical coverage for each box. This means that a listener in the audience hears sound from primarily one box, not from all boxes in the line. So the fundamental assumption in deriving the 1/R drop off is violated. Avoiding interference among boxes and creating a sound field that drops off in SPL as 1/R seem mutually incompatible. Can anyone explain why we would expect the drop off of SPL from a line array to even approximate 1/R?

Being a pragmatic guy and accepting even not-very-good approximations, I am willing to ignore that the line array is not infinitely long, but I don't see how you can ignore the added complexity of vertical pattern control in each box. It just looks to me like the physics of a line array properly deployed to avoid comb filtering seems like a set of point sources only one of which is heard by any individual in the audience. So it should drop off like 1/Rsquared as Ivan has empirically observed.

Is it Marketing guys 1, fools like us 0? Or am I missing something important here?
 
Re: Trap Boxes?

George Friedman-Jimenez said:
I don't understand why a "line array" as commonly deployed would be expected to produce sound level that drops off like 1/R rather than 1/Rsquared. Sure the electromagnetic fields of a wire and a point source do drop off like 1/R and 1/Rsquared respectively, but to derive that result in physics you must make the assumption that the distant observation point receives field from every point on the linear wire, not just from one point on the wire. Mathematically, when you calculate the EM field at a point R meters from the wire you have to do the integral over the entire length of the wire so you are adding on some EM field from each point along the wire. A line array is set up to avoid interference of sound from multiple boxes (comb filtering) by having very narrow vertical coverage for each box. This means that a listener in the audience hears sound from primarily one box, not from all boxes in the line. So the fundamental assumption in deriving the 1/R drop off is violated. Avoiding interference among boxes and creating a sound field that drops off in SPL as 1/R seem mutually incompatible. Can anyone explain why we would expect the drop off of SPL from a line array to even approximate 1/R?

Being a pragmatic guy and accepting even not-very-good approximations, I am willing to ignore that the line array is not infinitely long, but I don't see how you can ignore the added complexity of vertical pattern control in each box. It just looks to me like the physics of a line array properly deployed to avoid comb filtering seems like a set of point sources only one of which is heard by any individual in the audience. So it should drop off like 1/Rsquared as Ivan has empirically observed.

Is it Marketing guys 1, fools like us 0? Or am I missing something important here?
Click to expand...

Each element in an array is only directional down to some (relatively high) frequency. So lows and mids can be treated as omnidirectional sources. Additionally, the listener will be in the pattern of (or outside the pattern but getting some output from) multiple boxes, so it is proper to include those boxes in the calculation.

Of course, it's also worth noting that none of these sources are infinitesimal, so they need to be treated as area sources up to a certain distance.
 
Re: Trap Boxes?

George Friedman-Jimenez said:
I don't understand why a "line array" as commonly deployed would be expected to produce sound level that drops off like 1/R rather than 1/Rsquared. Sure the electromagnetic fields of a wire and a point source do drop off like 1/R and 1/Rsquared respectively, but to derive that result in physics you must make the assumption that the distant observation point receives field from every point on the linear wire, not just from one point on the wire. Mathematically, when you calculate the EM field at a point R meters from the wire you have to do the integral over the entire length of the wire so you are adding on some EM field from each point along the wire. A line array is set up to avoid interference of sound from multiple boxes (comb filtering) by having very narrow vertical coverage for each box. This means that a listener in the audience hears sound from primarily one box, not from all boxes in the line. So the fundamental assumption in deriving the 1/R drop off is violated. Avoiding interference among boxes and creating a sound field that drops off in SPL as 1/R seem mutually incompatible. Can anyone explain why we would expect the drop off of SPL from a line array to even approximate 1/R?

Being a pragmatic guy and accepting even not-very-good approximations, I am willing to ignore that the line array is not infinitely long, but I don't see how you can ignore the added complexity of vertical pattern control in each box. It just looks to me like the physics of a line array properly deployed to avoid comb filtering seems like a set of point sources only one of which is heard by any individual in the audience. So it should drop off like 1/Rsquared as Ivan has empirically observed.

Is it Marketing guys 1, fools like us 0? Or am I missing something important here?
Click to expand...

Yes, you are missing alot,
so I recommend that you read in following order:
Mr McCarthys book
Mr Uredas papers on line arrays
Mr Heils original AES paper on line arrays

and there is no way that one could sum up this knowledge in a forum post without creating more misconception.

Nethertheless I will point out three things:
a) interference is not equal to comb filter, destructive interference is
b) a single line array element does not have very narrow vertical coverage, actually the vertical coverage is narrowing with rising frequency, how much is a design decision and will define the maximum possible splay angle between two elements.
c) how many elements of a line array interfere at a given listening point is a result of the directivity and the splay angle of the elements, the phase difference defines if interference is constructive or destructive


Uwe
 
Re: Trap Boxes?

Ivan Beaver said:
That is one of the "fantasies" goes around-that is pretty much false.

I have done quite a number of demos/shootouts that totally disprove the "3dB/doubling distance vs 6dB/doubling" theory.

If that were true, and the levels were matched up close-how come the line arrays ARE NOT waayyyy louder at a distance? In fact-very often the complete opposite is true. The point source (a good one anyway-not one that calls itself a "point source" yet has lots of interference) is at least equal in loudness (sometimes louder) and waaay clearer.

When you are talking about "perfect sources"-yes the theory will apply. HOWEVER nobody is making perfect sources (of either type), so in reality the products AVAILABLE (both point source and line array) are NOT behaving as the theory states.

Side by side tests can be VERY reveling.
Click to expand...

Ivan, I certainly don't disagree with you on that point.I have been involved in side by side tests and in terms of wide and long coverage there ARE situations where line arrays ARE preferable over (most) trap rigs. IMHO of course. :)~:)~:smile:

My point is essentially what Kristian said.
 
Re: Trap Boxes?

Shane Presley said:
I know this is the consensus , but can you explain why in a couple thoughts... I've been curious to know why.
I mean I know it's preferred to fly , but why is stacked frowned upon? Does that include on scaffolding?
Click to expand...

The problem isn't that the array is stacked, but that when it is the angles used are often set to 0 degrees, or whatever. When using a small number of boxes, the splay must be set so the pattern of the HF approximates that of the MF/LF. Any array stacked close to audience head height is going to suck anyway, everyone up front is just getting nailed.
 
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