Thursday, August 22, 2013

Amiga, Makerbot and Line Arrays

Anyone remember trying to render graphics or print anything other than text from a computer in the mid 80's? I recall having to wait till sleep to hit the render button with a 50% probability that the computer will crash, only to end up with a crude version of the graphic that took another whole eternity to to create and when it finally came to printing it out after 20 false starts to get the layout formatting correct between lock ups and those darned reboots that required a reload of a shit ton of floppy disks because hard drives were not yet a common consumer item of affordability.

Well, the reason this comical now but frustrating then memory comes to mind is my adventures with 3D printing. Though nowhere near as archaic, the nuances of creating printable drawings and sit and wait adventure while the little nozzle moves around squirting hot plastic brings back those old memories. For those not familiar with how the most common 3D printers operate, basically all they are is a hot glue gun nozzle attached to a plastic wire feeder that can move around in the X and Y axis and a plate that moves up and down in the Z axis while it squirts hot plastic in hopefully all the right places to end up with what was on the computer screen.

Line Array Adventures!
(as promised to answer a twitter question)

OK, so how about taking a look at some aspects of line array HF design? One of the major challenges with designing a line array is getting the sound to radiate out of all places of the enclosure at the same time. This may sound more trivial than it is. Sound likes to radiate outward in circular waves like rings from a stone dropped in water. But line-arrays need sound to radiate more like a flat stick shape from each horn.  If you just use a horn that has a tall narrow opening, the sound will exit the shortest distance first which is the middle and still have an arc shape as it leaves the horn/waveguide.

To get around this, there are several methods that the various manufacturers employ with varying degrees of success. I will divide these up into the three basic types/approaches and gives a brief description of some assets and issues with each as well as a few links to patents from the manufacturers.

The Equal Path Length Waveguides

Three examples of companies that patented this type are L-Acoustics, Adamson and Turbosound.  The concept is to create a waveguide wherein the the shortest distance from the horn driver diaphragm to anywhere the sound can exit, is exactly the same (or of a predetermined minimal offset).

L-Acoustics does this by first determining the distance from the driver to the top/bottom of the waveguide exit, which is the longest distance.  Then designing the waveguide shape such that the sound travelling out of the middle area of the exit has to travel an equal distance. The patent explains it in depth.

Since L-Acoustics had already patented the most simple and direct design, indirect designs started being developed. Nexo came up with an interesting method. How about sending the sound from a compression driver down a horn and reflecting the sound off of a curved surface such that the reflected sound was correctly timed by the time it leaves the horn. 

Adamson came up with another work-around. I heard rumors that some potential infringement questions that arose but I guess the patents were differing enough that Adamson's held. Basically what the Adamson design does is it divides the process into two parts.  The first part over corrects the sound wave so it comes out the top and bottom of the initial waveguide first and the middle last.  Then the second part lets the sound wave expand naturally in the secondary waveguide.  The two waveguides are designed such that the over correction and natural expansion combine to have the sound exit the secondary waveguide at the same time.

Another way to try and solve the equal length conundrum is to divide the sound up into a multitude of smaller tubes of equal length and then rejoin them at the exit. This is the path that Meyer Sound and  Turbosound followed to develop their line array waveguides as shown in. 

You can almost feel the minds churning to create a solution to get in the line-array game. In general, my experience has been that the more complex the design is, the more room for error, resonance issues and unwanted reflections.

The Multi-Driver Designs

This concept goes back pretty far and I was able to find a patent by RCA from 1927. Basically it is simply using a higher quantity of smaller drivers instead of one, two or three larger 2" drivers.  This gets the sources close together and all radiating at the same time.

So with L-Acoustics having a patent on the simplest most direct solution in 1988 and the other 'equal length' concepts to get around the L-Acoustics intellectual property patent yet to be concocted, companies started coming up with various multi-driver contraptions that basically use a multitude of long narrow horns with on each.

Unlike the L-Acoustics and Adamson solutions, the Clair multi-driver approach does not fully create an output where all the sound radiates at the same time. Instead there are a bunch of smaller arcs, one from each horn/driver.  The more drivers the better but the drivers tend to be physically a bit of an issue limiting the maximum quantity. Though Clair did an admirable job by employing nine 1" drivers I believe in their I5 rig, every other driver offset to the left or right so the vertically fit in the box.

Another version of the multi-driver as implemented in the JBL Vertec systems was just to use 3 drivers and not really be too concerned that the sound all leaves the horns at very close to the same time. Though this was consistant with the JBL design in that the Vertec system allowed for much more drastic angles between boxes as well.  I huge asset in versatility and a detriment in sound quality.

Also there are some other designs that utilize diamond or other shaped 'obstructions'  in the horn that assist in aligning the timing of the sound leaving the differing parts of the horn

Here is another multi-driver patent that I am not familiar with any large format systems employing but is interesting as well,

The No Waveguide Solution

Hey, why not just use a ribbon driver? That's what we want, right? All the sound to radiate at the same time in the vertical domain. I do feel that ribbons logically are the best solution, practically though, there are some challenges. Conventional drivers are most efficient when centered in the gap and as you drive them harder, there is both a mechanical limitation can be a decrease efficiency. This parallels other components in the system to a degree. Most ribbon designs have a perforated magnet in front and behind the ribbon, not only are there artifact from sound passing through the perforation, the harder you drive the ribbon the closer it gets to the magnets creating almost a sonic expander.  Yes, electronics can correct for this perhaps. I do believe major headway has been made in increasing the efficiency and frequency response of ribbons but in my opinion, they are just not yet fully on par with the top level voice coil driven systems, yet.

Other Stuff

A couple other older patents where we can see designs that control the distance sound travels to leave a horn

An older form of line arrays were products like the Shure Vocal Master

A few advantages of the equal path length designs is simplicity and that conventional drivers that are readily available can be used.

Multi-Driver Minimal Waveguide

The multi-driver designs can get costly very quickly but they do allow for separate amplification and processing of each driver. Which brings me to what I believe to be the best version of the multi-driver design is currently what EAW has implemented in the new ANYA system, just as I believe that L-Acoustics has the best version of the equal path length design, Anya has the best multi-driver design.

EAW's solution was to develop a very compact, high power 1" dome driver and use 14 of them on very short waveguides, therefore minimizing the timing errors to the lowes of the multi-driver designs to date, almost forming a perfect ribbon.  Except unlike using a ribbon, each segment of the ribbon can be independently processed and new levels of control realized that no other system has capabilities of accomplishing.

Here is a link to a video that explains more

If it sounds like I am a fan of the L-Acoustics design and EAW designs, you are correct. If you think that I am a fan because Rat Sound owns both those systems, you are incorrect.  The reverse is true. Rat owns those systems for many reasons and one of which is that I believe that the HF waveguide design is a core and critical aspect of line-array design, and also I have a special affinity for the early innovators with the most finessefull solutions. Yeah, 'finessefull' is not a real word but it should be as it is so useful.

Ok, enough brain dump.  How about a few pics to lighten the load.?

So we make the products at Rat and Bryant orders some new tube samples and normally this would be just a simple misprint but....

Ha! Rock and roll.... Off to the big rock show.... I bet you cant come up with any other one-liners. 

One of the wheels broke on the Midas Script Scroller 

Here is what the good wheels look like 

So I printed a new pair of wheels on my Makerbot2 3D printer, and back to good again.

I just had to share this. Left to right, my mom, Mark Schoenfield (former step brother), Me, Steve Schoenfield (other former step brother), my sister Tiffany and my brother Phil. And this was only a tiny smidge glimpse of the oddity of my previous life as David Levine before I somehow was renamed Dave Rat by my pals and peers.

Oh yeah! Did a 9 day train trip in Europe with Daughter Sammy.  It was her turn as Maddie and I did a solo pair run 2 years back. I would not trade those adventures for five worlds!

Not disturbing enough to make you want to poke out your mental eye but a fashion statement none the less

And just a pic that makes me smile from the the trip up to Anchorage for a few Peppers gigs.

Ok, that's enough.  And tomorrow one daughter moves out into an apartment with roommates and saturday the other is off to college in New York. Could not be more proud and filled with apprehension of a major life shift at the same time than I feel right now.

Dave Rat