Why so few high end line arrays?

09-11-09: Tbg
If you ever look at the frequency response of line arrays, you will see what looks like a comb. Each driver interferes with the others at a regular interval throughout the frequency range.

Selah Audio Alexandrite - on-access Freq Response(200hz-20K), on-access Freq Response(10-200hz)

Selah Audio Symmetrica - on-access Freq Response(200hz-20K), on-access Freq Response(10-200hz)

You think a signal sweep disproves what I said?

Tbg,

This is audiogon. Laws of physics are very often suspended here. Our favorite products do everything perfectly with no drawbacks or compromises to our favored designs. ;-)

For those with line arrays, this explanation is one of the simplest I have seen:
A good graphical explanation about lobing or "comb filtering" - which are the same thing. It shows snapshots at different frequencies but if you imagine how it will sound at a particular listening position across all frequencies then you will realize that you progressively get multiple nulls as you go higher in frequency.

Tbg,

I've been researching line arrays for the last couple of weeks, but that only assures I have way more questions than answers or experience...

But, the website which you refer seems to be only concerned with is only concerned with farfield sound reproduction(stadium, club). Not that nearfield acoustic completely diverge from farfield, but the goals are significantly different.

The "lobing" and "Nulls" which you(and your link) refer to primarily become a problem for listening at the point/frequency where c-to-c spacing of the source(drivers) exceeds the distance of one-half to one full wavelength of the highest frequency produced by that particular array(low, mid, or high).

The "trick" is in designing a widerange(mid/bass) array which crosses over to the next higher frequency array below the threshold where lobing and comb filter effects become troublesome. Within the home audio industry there are a variety of drivers small enough in diameter to achieve those goals.

These issues really seem(to my inexperienced eye) to be no more difficult than the many design limitations and compromises which plague all speaker designs(including traditional 2 or 3-way "box").

Here's a far better, and more technical, analysis(besides Dr Griffin's link above) of the design parameters and limitations of array design in this ElectroVoice paper.

Darkmoebius,

You are correct. You have to design line arrays carefully to take into account lobbing and nulls. They work very well when properly designed and will ensure a higher SPL reaches further out into the audience at a sports or rock arena event.