SIDE FIRING DRIVERS:
Hi, this is Bob Carver checking in. There was a question asked that I found very intriguing - intriguing because the problems that arose from my side firing drivers were very challenging to solve. They were so difficult that at one point in the design, I swore that it was a big blunder and that if ever I wanted to do it again and if I were a dictator, I'd hang myself by my toes and give myself a zillion lashes with an expensive interconnect.
Here's my thinking:
The side firing drivers began with a conversation I had long ago with Henry Kloss up in Boston one winter while I was visiting good friends. He taught me that our sense of acoustic space lives in about an octave on each side of the octave centered on about 400 Hz. These have become known as the Henry Kloss psyciacoustic octaves. 200 to 800 Hz. He said if we get these octaves right, we will have a beautiful and believable sound stage.Then I read Harry Pearson's treatise on the making of a great sound stage, and I knew I wanted mine to follow HIS teachings. Now Harry did not know how to do it to make it happen in terms of speaker design, though he could describe its beauty like no other journalist in the world. I read what he wrote and could hear it in my head as plain as day. I was hooked forever on a sound stage that had front-to-back depth and emotional envelopment. Just like Harry described. From Henry Kloss's teachings and the sound-picture in my head, I suddenly knew how to do it.
Enter side firing drivers:
Use side firing drivers to engage the room, bounce sound off the walls of the room and deliver time-delayed reflections and allow the room to become part of the speakers.
All the while keeping their output centered on The Henry Kloss Psychoacoustic Octave. This makes a big space, a large acoustic within which to fit pin-point imaging provided by my ribbon. The ribbon puts the sound images inside the larger acoustic that has been built by the side firing drivers.
So far so good, but a problem came up that was so intractable I thought I'd never solve it short of asking the universe's help. Or at least not solvable by any rational method. The problem was with the time delay associated with the delay of the sound getting around the cabinet to meet the ribbon wave launch, causing a phase-shift related "comb-filter" effect. A phase correction filter done passively turns out to be huge, fully four times as big as the speaker itself! Not practical. I worked on the problem for about a year
and finally hit on the solution so simple I could not believe I did not think of it before. It turns out that the interarual time delay of our heads is about 800 usecs, the same as the time delay from the acoustic center of the side firing drivers to the ribbon wave launch surface. 800 usecs. At this point the solution fell into my lap. Design the crossover to have a large overlap and to allow the natural delays in the music to help generate a larger acoustic by allowing our brain to use those delays and build a big acoustic space. And no combing! What luck! I felt really lucky. That's why I use side firing drivers. Bob Carver
http://www.audiokarma.org/forums/showth ... p?t=391704