Part1: Tech talk about SoloAmp vs. other small line array systems

[aboutjack]

I had a question in another thread that deserves its own topic here.

Originally Posted by Cayoot

... So as far as "spreading the love" around the room evenly, how does this measure up?

Maybe I'm not articulating this question properly, but hopefully you understand what I'm asking.

Hi Cayoot,

Thank you for this question, as it goes to the heart of why I've put 40 years into tinkering with small speakers, and 13 years specifically into tackling this small portable line array challenge — and exactly what actually happens with these things that impact the sound heard by the player on stage and by the audience at various distances.

A line source sound generator is a theoretical thing... math on paper... not a real thing in real life, as it presumes a source with zero width and infinite length. So, the moment somebody start referring to a product as a "line array," the topic is already technically incorrect. All we as product developers can do is try to get as close to that hypothetical ideal as possible using actual components and designs.

A theoretical line array is an amazing concept. It propagates sound into one plane (vertical or horizontal) as a "slice" or "pie wedge" pattern, evenly sending waves of sound out into that plane of space. A theoretical line array is an amazing thing. Only it does't exist.

I put together my first "line array" of 20 Radio Shack 5-inch full range drivers when I was 14 or 15 years old, and have been playing around with the things ever since. And, in 2002 I realized there was a market for a portable product that used the technology to be small, light, and give working musicians a great sounding hand-carryable sound source. So, I began investing time and money to make it happen.

I started by identifying the characteristics of a "line array" that I wanted to manifest in my product, and set these as my engineering goals. How close could I get to the theoretical line array with a real product as small as I wanted?

So, while I was on maybe my 20th hand assembled prototype in Nashville, in 2003, Bose popped up with a product and a big ad campaign for a product claiming all of the theoretical line array benefits — which kinda blew my mind, as what they were saying, and have been saying since, simply is not possible. You can get "fairly close" to some of those traits, but certainly not to the degree they claimed.

So, I kept working. The reason I chose then to ramp up my commitment to that product, which I had named SoloAmp, was that a few years earlier I had finally solved one of the big physical limitations that kept such a small vertical array from "sounding the same" on stage as it sounded back in the audience. I had gotten into a couple of anechoic chambers a few times with good test gear and had done very precise near field and far field spectrum analyzer measurements and had found the frequency response, linearity, and dynamic response of my small arrays differed in a consistent way when measured very close to and very far away from the product. And, I found that these two behaviors abruptly changed at a very specific distance from the face of the array.

I found that there was a very specific distance at which the behavior shifted from one set of values to another. Closer than this distance and the values looked like a traditional point source emitter (again, an imprecise use of the term, as "point source" is also only a theoretical thing, not a real thing). Farther than this distance and the values looked more like what a line source emitter would produce. And, I also explored the second break point that occurs at a far distance when that same line array effect falls apart and the sound basically devolves into a jumbled mess.

Here's what I realized: Up close, any attempt at a line array using traditional loudspeakers behaves like individual conventional loudspeakers — more like a point source: 6dB per doubling of distance, spherical dispersion pattern, nonlinear frequency and dynamic response, and a falling off of SPL toward the periphery of that spherical pattern (louder in the center). Then, at this "transition distance," the behavior abruptly shifts to be more like a line source: 3dB per doubling of distance, planar dispersion pattern, linear frequency and dynamic response, and a very linear SPL across a planar dispersion pattern, including at the periphery — all the cool stuff that horizontal line array theory predicts.

I also realized the reason: IN the real world, when conventional speaker drivers are used. all neatly lined up in a row, only a portion of that line of objects is producing sound: the speaker diaphragm in the center of the driver. The flexible support around that diaphragm emits little sound, and certainly no in-phase sound. And, of course, the speaker frame around that produces no sound. So, when you line up a bunch of normal speakers into an “array,” what you get is some portion of that array producing sound, and some portion not producing sound. And, that is what was causing that “transition distance” effect from about point source behavior to about line source behavior, and was making the products sound different on stage the in the audience.

That was sometime in 1998-1999, and it was the turning point in my work toward getting to a real product. It gave me the problem I needed to be solving. And, obviously, it was a problem nobody else in the world was even aware existed, and where nobody else was investing effort.

So, the challenge was to maximize the portion of the array length that was producing in-phase sound. More emission. Less dead space. More diaphragm. Less non sound producing mechanical stuff. And, I found two ways to tackle the problem.

My first approach was to adopt rectangular or “oval” shaped drivers, instead of round ones. And, this was the main development strategy I chased in the 2002 to 2005 period, working with a smart driver OEM to iterate through dozens of designs for such a full range driver to get to one that worked like I needed for an 80Hz to 16Khz response small array, for guitar-vocal performances. And, this is the work that led to the intellectual property bundle I licensed to Fishman in November of 2005.

I also realized that there was a second, superior method to maximize the emitter portion of the array, but was one that would take enormous time, effort, and money: design an all-new driver that had no non-emitting structure around the diaphragm, so that 100% of the driver face emitted in-phase sound.

So, while Fishman’s team began item by item deconstruction of the design I licensed to them and evolving it into the thing they launched to market in 2008 (and that I see in their NAMM booth today, unchanged 7-years later), I worked on this new hypothetical driver. I will note here, since in the context of this explanation it would make the most sense, that the one magical thing inside that IP bundle Fishman licensed — the use of the rectangular drivers to radically reduce the transition distance problem — is the very first thing their engineering guys changed. They moved back to conventional round drivers. Of course.

Here is an image showing the product I licensed to Fishman in 2005, and the one they eventually pretty much totally redesigned and took to market in 2008 with my name on it.



So, Cayoot, if you are still here :-) … Starting from 2003 I began working on this non-existent new driver. I brought in a couple of the most respected driver engineers in the world, and partnered with a hugely talented driver OEM, and together, we did design after design after design for five years of what I back then called the AudioPiston driver: a speaker with all of its support mechanism moved around the back, complete behind the diaphragm, so that 100% of its face emitted in-phase sound.

Here is an image showing the difference in centerline emission area between a typical 5-inch conventional driver and my 3-inch SoloDriver™.



In 2008 we got to an Audio Piston driver that met the design goals. Full face emitter. Hi fi quality sound performance. Crisp, tight transient response. Beautiful. We worked on optimization for manufacturability, to reduce costs and complexity. And, we finalized the design the end of that year. Here is a free air frequency response plot of the Audio Piston driver development unit that was close enough to what I needed to tell me, “Yes! This is actually going to work!,” measured on February 13th, 2008.



Behind the scenes I was then a year into a licensing dispute with Fishman, and my SoloAmp name was not available to me. So, I implemented a set of other strongly held technology ideas, designed a product around that first generation AudioPiston driver, partnered with another China OEM that was willing to invest into the project, and tried to bring a product I called the BagAmp to market, within a broad group of active partners and investors.

That story is documented elsewhere, so isn’t needed here. It was tragic.

In the 6 years since then I have continued to evolve the driver design, which is now called the SoloDriver™, and is used on the new 2016 SoloAmp. The current driver is notably better than the 2008 units, with improvements in everything from the adhesives that hold it together, to the materials for the diaphragm, frame, voice coil, the magnet composition, and more. And, along with similarly broad improvements made in that time to the enclosure design, materials, construction methods, electronics, and more, the result of that effort is the new SoloAmp.

(continued in a second thread: http://www.acousticguitarforum.com/f...26#post4798726 )