David Lee Blog

February 7, 2022

David Lee Blog

February 7, 2022

Point sources aren’t line arrays

Stop using the AT312 as a line array.

Comb-filtering

Everything that makes the AT312 special is compromised when they are set up in arrays.

A drill costs more than a hammer, but no number of hammers can do the job that a drill can do.

David Lee

Comb Filtering from 1cm to 35cm

The AT312s, when set up side-by-side, leave a minimum of 50 degrees of overlap between them. Unfortunately everything that makes the AT312 special is compromised when they are set up in arrays. The AT312 is a point-source. It’s as close to the ideal point source as you can get. This means that the entire audio spectrum effectively emanates from a single point in space, the center of the 12” co-axial. This results in excellent imaging and intelligibility. Adding a second one defeats the purpose of having a point source. Basically, it’s the acoustical equivalent of using two video projectors on the same screen, but each projector’s image is centered at a different spot on the screen. This would make the image very blurry. On their own, AT312s are better than almost anything on the market. In arrays they are less good than they can be. Nevertheless, people will and do put them in arrays, and the world hasn’t ended. It’s just a compromise that’s best avoided.

It seems there’s a need for some improved explanations of our different boxes. Here’s some of the how and why the boxes are what they are…

The issues with the boxes and these applications are coverage angles and overlap. Wide coverage angles result in greater overlap when the boxes are adjacent to each other. Overlapping coverage of high frequencies causes what’s called comb-filtering because the arrival time from each loudspeaker is slightly offset. Comb-filtering is the acoustical equivalent of pulling down every other fader on a graphic equalizer. Suffice it to say, the sound quality is not improved.What could make things a lot worse would be overlapping them even more. They could be flown AS IF they were line arrays. This would result in even greater overlap and, acoustically, as in the video analogy, more image blurring. I really don’t like to see people spending good money on great loudspeakers and not getting the best results from them. What drives me crazy is that there is so much bad information and bad advice out there that if our customers listen to it, they may get results that aren’t anywhere near as good as they can be.

The AT212s can be arrayed. The horns should be rotated 90 degrees to make the 60 degrees horizontal by 80 degrees vertical. They should be set up with the sides of the cabinets touching each other, flat side to flat side. There are tricks to minimizing the negative effects, which is another conversation, but they can be used that way. In short, overlap is bad and there are 30 degrees of overlap when the AT212s are set up that way. Most people won’t notice. Many other boxes are way worse in that regard, so they will still provide better sound that most alternatives.

Line-array is a technology that is subject to the laws of physics, it’s not a method of hanging boxes one above the other. A well-executed line-array provides benefits well beyond just a vertical stack of boxes because the boxes are designed to interact constructively, in very specific ways, when they are stacked vertically. For one thing, they have extremely narrow vertical coverage angles to minimize overlap and the comb-filtering that results from overlap. Boxes that aren’t designed to interact in those very specific ways will not provide the benefits associated with the technology. Their interactions will almost certainly be destructive over critical ranges of the spectrum.

Try the applet yourself at falstad.com/interference/

Every loudspeaker and every combination of loudspeakers needs to be chosen and set up for a particular purpose. Even a set of purposes, but decisions, or compromises, have to be made when choosing gear. One has to prioritize something, whether that’s set-up or cost or coverage or power consumption or weight or marketability, something will place a limit on a systems’ uses. Once someone chooses a particular loudspeaker for a particular reason, then they are best served using it as it was engineered and intended to be used. It is what it is. It can’t be morphed into a different type of loudspeaker because that’s the fashion. If someone needs a particular loudspeaker but buys a different loudspeaker, they have bought the wrong one, and to some extent they have not invested their money wisely. They won’t get the benefits that the loudspeaker was designed to provide.

Perhaps someone doesn’t buy the most expensive loudspeaker, but they get the next most expensive one instead, thinking it would be a way to save money, and maybe they could make it look like something else. What they might have bought is a hammer when what they needed was a drill. A drill costs more than a hammer, but no number of hammers can do the job that a drill can do. As I said before, a Toyota Supra is a very nice car and makes a lot of horsepower, but welding a tow-hitch to the rear frame to pull a trailer doesn’t make it a suitable replacement for a pickup truck, SUV or van. Bolting flyware parts onto an AT312 or AT212 cabinets will not turn them into line-arrays.

The reality is, for most events, a line-array isn’t needed, but “line-array” is a buzz-word and people think they need one, or their customers think they need one, so they try to make some horrible compromise to make it look like they have one. This is actually worse than any of the other options. If you need a conventional array, buy a conventional array. (AT212) If you need a point-source, buy a point-source. (AT312) If someone needs a line-array, they should buy a line array. And they should buy a good one! (MFLA)

The unfortunate truth is that there are MANY cabinets sold as line-arrays that are not well executed. They are probably worse than a vertical stack of AT212s or AT312s. All in all, our customers will probably get better results using our boxes inappropriately than they will using some inappropriately designed boxes. Ideally we need to do our best to make sure our customers get the boxes that are appropriate for them whenever possible.

– David Lee
BASSBOSS Designer

Music Made Physical

Production Subs

Mobile Subs

Production Tops

Mobile Tops

Shop

Kraken

Quad 21" Subwoofer

BASSBOSS ZV28-MKII Powered Subwoofer

ZV28-MKII

Double 18" Subwoofer

BASSBOSS SSP218 Powered Subwoofer

SSP218

Double 18" Subwoofer

SSP215-MKII

Double 15" Subwoofer

VIEW ALL

VS21

Single 21" Subwoofer

SSP118-MKII

Single 18" Subwoofer

BASSBOSS DJ18S Powered Subwoofer

DJ18S

Single 18" Subwoofer

BASSBOSS BB15 Powered Subwoofer Hero

BB15

Single 15" Subwoofer

VIEW ALL

MFLA

Dual 12" Line Array

BASSBOSS AT312 Powered Top Loudspeaker

AT312

3-Way 12" Top

AT212-3K

2-Way 12" Top

VIEW ALL

DV12-MKII

Single 12" Top

DiaMon 112

Single 12" Coaxial Top

BASSBOSS SV9 Powered MicroMain Loudspeaker

SV9

Single 9" Top

VIEW ALL

LOUDSPEAKERS

APPAREL + ACCESSORIES