Free Line Array Angle Calculator

The Coupled Point Source or as it's called on the street the Line Array, is an interesting bit of engineering that uses constructive interference of sound to produce high SPL and cover large front to back distance ratios. In the high end, beam spreading will fill the audience area with plenty of level for excellent articulation even far away. A properly setup array can create an even sound field of minimal variance in level from the first seat to the last one. One note before we move on, a line array is not a line source because it has splay. It is only a line source if there was no splay and all the angles between boxes were at 0 degrees.

In this article I would like to cover a few of the first steps for finding the "coverage angle" of your audience, this would be the angle in degrees from your speakers to the top and bottom (or front and back) of your audience.

You cannot find this angle by measuring from the center or top of the array, it is based on a point behind the array that you could not ever get to physically. This will be shown graphically below.

With the help of a colleague Nathan Lively, I built a Microsoft Excel Calculator that will give you the coverage angle of your audience area and will start you out with an average splay for each box to fill that whole angle. Keep in mind this is only in the vertical plane. As far as what the appropriate distance is between array hangs to cover your audience horizontally, that is for another article.

Lets have a look at the first section of the calculator

To use this tool, fill in the grey fields and it will automatically do the math for you. The first field is asking for the number of boxes in the array. The second field is asking for trim height or how high the top of the uppermost box in the array will be off of the ground. The third field is asking for the height of a single box. This calculator will work with foot or meter measurements as long as you only use one or the other for each calculation. As for the single box height use a decimal if it is less or more than one foot or meter. The next two fields will populate automatically and you will have your approximate line height displayed.

This calculator will attempt to fill the audience coverage angle by using the available splay angles in the array. This is always 1 less than the amount of boxes in the array and it will calculate based on the fly bar being level. The angle of the box connected to the fly bar directly is included in the average calculation.

Above is the second section for user input and it is described with the graphic included in the calculator. Triangle one is the right side green triangle.

Side A for triangle one will already be filled out for you as trim height. This only applies to flat audience area so if you have a sloped seating you will have to determine 1A with measurements and manually enter it yourself. Side 1B is a measurement you will have to find and enter every time. Start under the front end of the array and measure to the last seat with a lazer or wheel. Angle AB is always 90 degrees.

Triangle 2 is the left one and it is blue. Side A will already be calculated for you as trim height minus line height. As before your job is to find 2B and put that distance into the calculator. You have now found all the information for the inner triangle shown below.

Your answers will appear here

In a real world example, I ran a stage at a local festival in a large parking lot for a few days and had two 4 box arrays of QSC Wideline 10 on Supertowers.

The box count was 4, trim height was 15 feet (4.57 m) and a single box was .9 feet (.27 m) high. The number of splay angles was 3. The front edge of the audience area was chalked out by the client and project manager since the performance was crowd sourced choreography and involved a static overhead camera shot. The edges of the audience area needed to be strictly defined for the videography so I needed to strictly define it for the array. The front edge was 15 feet (4.57 m) from the base of the array and the back edge was 110 feet (33.52 m) and was the fence enclosing the parking lot itself.

As you can see in the above screenshot, the audience coverage angle was 29 degrees and the calculator came up with 9.8 degrees of splay per box. The closest I could come to that on the hardware was 10 degrees. Each angle was therefore splayed 10 degrees.

This is only the beginning to a fully optimized line array. Future articles will go into detail but I will outline some additional considerations here.

If you are ever wondering how many boxes to ask for to cover a space it will be based on the distance ratio. In the above example 110 ft / 15 ft = 1:7.33. A non perfect but practical way to decide on box count is by this ratio. There will be 7 zones that you need to cover, it would have been nice to have 7 boxes for a little more overlap and liberty with splay angles.

This is not a hard and fast concept either since it might be valuable to have several boxes fill one zone for consistency sake especially in the high end at audience top position. Deciding how many boxes to use per zone is another important skill to have.

The next concept is the "line of minimum variance." As you approach the array from the back of the audience you are arriving more on axis to the lower speakers and between this and being less distance away it will be louder in this spot. We want it to be even from the front to the back. This will involve reducing level for lower boxes and may involve introducing delay. To verify these adjustments, you must use an audio analyzer and take strategic measurements at on axis and crossover points to confirm that you are not varying wildly in level.

In the above example, I did not have independent control over each box in the array, I only had control over the lows, mids and highs independently. In such cases you do the best you can and can fine tune splay and level to create as consistent coverage level from front to back as you can get.

The calculator is available for free here:

https://docs.zohopublic.com/file/p5s972e9e34da2b0c4bbfa23f4d2edb8d823e

It is stored on the ZOHO Document cloud and features a https connection. You must download it to use it. If you don't have MS Office, the calculator will work on OpenOffice (Freeware) and Google Sheets. Yes you can use it on your phone.

For more training visit sounddesignlive.com Nathan Lively's course was inspiration for this tool and his courses are great for the techs looking to take their engineering to the next level.

? 2018 Michael Reed

https://www.dhirubhai.net/company/marathonas

https://www.dhirubhai.net/in/michaelreedengineer