The Calipso Line Arrayhttp://pub48.bravenet.com/photocente...31&album=48032
The Calipso Array has been developed on a model that includes the following essential characteristics:
Two 12 inch 15mm Xmax GoldSOund Woofers
34 Sammi 3.3mm X-max, Copper coils, composite paper/fab cone, mid woofers
60 Dayton ND20FA tweeters with flanges cut to a .9 inch Center-to-center distance
Rane Ac-23 Analog Electronic Crossovers, at 165 & 2600
Tri-amplification: 60 w/ch for tweeter array, 150 w/ch mid/woofer array, 350 w/ch woofers
1. Three-Way design.
In point source speaker systems, a two way design is often considered to be an inadequate compromise. Much of audio has gone to two way designs with a single sub woofer. Vance Dickason in his 6th Edition of The Loudspeaker Cookbook has indicated that the use of dual woofers that are capable of subwoofer frequencies produces a significantly better sound image than a subwoofer. In this design a large 12 inch, high mm Xmax woofer is used with each side, and it crosses to the mid ranges at about 165hz. While mine are not currently in the correct size box, the correct size is a 6-8 cu ft vented box.
2. No Crossover in the most sensitive areas of human hearing.
Rod Elliot at Southwest Audio( http://sound.westhost.com/bi-amp2.htm
) makes the case better than I:
It is not at all uncommon to see systems where the crossover frequency is set right in the middle of what I call the "intelligence band". This is the range of frequencies from 300Hz to 3600Hz, and is extremely important from a psycho-acoustic point of view.
It is no accident that this is the range of the telephone system (and has been for many years). If we are only to hear a limited range, then this band of frequencies is by far the most important. Just from this we can recognize a person's voice, which musical instrument is being played (even bass instruments!), and - more importantly - what is being said. It contains nearly all the "intelligence" of the sound, which is to say that if this band is "corrupted", intelligibility is greatly reduced.
So why do speaker manufacturers insist on placing their crossover frequencies within this band of frequencies? The public address (PA) systems used by many rock bands are a case in point - how often does one find that the vocals are completely unintelligible? Mind you, it may also be the case that the band's lyrics just don't make sense, but that's another story altogether.
Often this occurs because the system is so loud that the amplifiers are clipping badly, but even at lower levels it is quite common. Place a common-or-garden crossover filter right in the middle of the "intelligence band" and this is exactly what will (and does) happen. With phase aberrations and cancellations, this most important frequency range becomes muddied and indistinct causing loss of intelligibility - not only on voice, but instruments as well.
The effect is also noticeable with some hi-fi speaker systems, except that it usually less pronounced, and it is far less likely that the amplifier will be driven to clipping. Reviewers will often say of a speaker that the vocals seem veiled, or that there is noticeable coloration of either male or female vocals. These effects are often caused by the effects of phase shift around the crossover frequency, coupled with the fact that the crossover frequency falls right in the middle of the intelligence band.
This very hard to do with point source speakers, but with line arrays, the midrange speakers are often loafing along, and if they have the range, pulling the wagon as a group of horses, they can do the job admirably.
3. Use Electrical Crossovers.
Again, passive crossovers are, IMO, a DATED TECHNOLOGY. Passive's introduce so much negative into the sound that they should not be there. And the cost of a top of the line passive cross(with the increased cost of copper) and a electronic is almost the same. Read Rod Elliot's papers on Bi-Amplification and electronic crossovers at http://sound.westhost.com
The only reason for not using them is that you've spent years learning how to design them and you aren't giving that up, or you are in the business of selling speakers and you aren't willing to sell amps and crossovers too.
4. Separate the midrange speakers from all other influences.
Bad coloration of sound, in my opinion, is caused by other sound that the direct radiation coming through the speakers. This means that you have to eliminate ANYTHING that goes out the back of the speaker, and anything that might be in the box behind the speaker from coming forward through the speaker again and muddying the sound clarity. (Some people don't believe that this is impactive.)
To do this, this design uses SEALED separate 4 inch PVC tubes for each of the 34 midrange/mid bass speakers. Each tube is physically separates from its peers by ¾ inch of open air space.
On page 35 of the Dickason 6th Edition Loudspeaker Cookbook, there is an empirical study on the efficiency of various stuffing materials. The greatest attenuation was determined to be at the 4 lb/cu ft density level. Frequencies within the range of the mid/midbass speaker are right within the range of attenuation. Only by using tubes can the appropriate density be achieved, since the insulation can be stuff tightly against the walls of the tube and not push up against the speaker itself. The part closest to the speaker is protected by a layer of sheet pillowfill from the fiberglass threads that might otherwise get into the voice coil.
A recent study by Rod Elliot showed that the smaller the diameter of the fiber the more effective the attenuation. Pillow fill= .01 in, regualr fiberglass=.005 in, Acoustical fiberglass= .001 inch
Additionally there are some benefits of the tube's inability to make even ordered harmonics, or even ordered harmonic distortion, but that will not be addressed here.
This design is labor intense but it helps make the 3 inch midrange speaker process viable.
5. Keep the cost down below $1400 for the speakers, and the required electronics.
6. Keep Comb distortion in the mid and high frequency drivers below Griffin minimums, and use dome tweeter SOUND rather than ribbons or planars, for their flatter frequency response.
The only dome tweeters that I know which have a center to center distance small enough, and at the same time can be crossed low enough, are Dayton Neo ND20FA's. These have their flanges cut so that the c-to-c is .9 inch, and the comb filter distortion doesn't start until more than half way into the last octave, or more than 15,000Khz.
All statements except for referred to studies or references are my opinion.