The proposal is to compose a series of articles based on projects to hand which may be of interest and assistance to others in their quest, it is further intended to pass on engineering information of a more general nature to advantage this aspect.
When the desire to produce, or rather to reproduce sound artificially first rises within the individual. It grow slowly in most as the awareness of the potential unfolds, partially it may be or is hypothesized, as the ear becomes educated to timber and subtleties of the artificial medium and consequently the ability to hear into the sound reproduction chain with greater discrimination based on the advancement of discrimination as a direct result of the listening process..
Normally the motivation comes from the listening experience where equipment or a particular mood instigates the desire to have, for use as occasioned, equipment of the highest caliber, this was my case as was but is currently at variance with the initial premise and is now somewhat different.
I have sought, from the outset, to reproduce artificially sound to the highest possible quality, not based solely on subjective opinion and the ability to define the end result within the imposed limitations of my and others ability to determine any such advancements.
I must confess - I cheated - I have used my wife as the ultimate committee, who, as a result of accumulating thousands of hours of listening, has developed a most formidable set of educated ears.
Ladies, for you less well informed gentlemen out there, are made somewhat smaller in the most important factor of construction size, this has made us rumbustious males, to an extent, consequently the losers since the feminine mechanisms for the determination of sound is also smaller which has the quite substantial advantage of the feminine auditory systems ability of both response and the ability to detect the smaller subtleties contained within the sound picture this is one are where the larger male lacks, due to the increased mass of the "Active components".
Why electrostatics - well in the authors opinion they are capable of realizing vastly superior detail which almost any other driver is incapable of achieving, I suspect that, from the purely theoretical aspect, ionic devices, if investigated and developed to the fullest potential would achieve a further advancement, although it must be said the levels of voltages and potential energy levels required are to say the least frightening, a full blown "Insetocutor" working away in my listening room causes psychologically unacceptable levels of discumforture.
There is this massive "Hole" in the LF point capability of commercially available electrostatic drivers due, in part, to the imposed Electro mechanical limitations, diaphragm movement, arcing, or simply area constraints imposed by the normal domestic envior, in addition the phenomenon where the LF excited air has the capability to reduce the affective excitation of the forward room air mass due to self cancellation by passage of the LF air mass around the edge extremities of the diaphragm, mounting Quad 63's into a wall or large panel is quite revealing as to quite how much LF IS present.
How to solve the dilemma without recourse to moving coil drivers for the bottom end - simple! build very large electrostatic drivers into a wall and have four of them working as a split, left, and right channel pair.
Why go down this rout? well, there is a family sound with ESL drivers which is very distinctive and wishing to achieve the tonal balance allied with transparency, detail and realism that these device are capable of without the whopping great holes in the reproduced sound field, that almost every commercial assembly appears to be unaware of currently, or stoically chooses to disregard in moving coil systems as various drivers and parameters interact to disadvantage the reproduced end result.
The idea is to take advantage of corner affect and move suitable masses of air by running each driver in phase with it's twin, the rear radiation being dumped into a free void thus avoiding secondary reflected waves passing back through the membrane as an energy pulse, the imposed limit of upper frequency for the large units is to be of the order of 500 HZ with the initially intention to run them off a high voltage amplifier with special transformer coupling, in this way I can achieve an active system which shall enable the basis for a further development of drivers which also advances the design of the driver to enable a high voltage, directly coupled amplifier to be applied upon the driver design being finalized.
The intention is that the cross over will be based on solid state Gyrators with all of the advantages possible from this technology.
The size of each of the LF drivers shall be some 2 meters by 1 ( 6 foot by 3 foot, for the imperial brigade) times two plus the same again for the other channel - thus giving an effective area of 72 square feet per side, with corner affect.
Reproduced bass will not require the driver to move to any great extent, consequently it will remain solidly within its design parameters, consequently have an extended life and be capable of coping with demanding situations when the occasion requires.
I am constructing a special room for this exercise where the room is almost completely floored, so in the very near future the mounting wall will be installed and work on assembling the drivers into the walls commenced - then the fun really begins with all of the specialized electronics requiring action.
Phase two and the path to Endor found
During the setting out of the words, sections of explanatory additional notes will be added, the intent is to enable a quasi structured approach to be achieved both for the project and the non involved third party, as the project assembles in the minds eye so the various aspects of the Engineering limitations will be explored and resolved, I hope, said he, optimistically.
The size of the drivers imposes sever constructional problems of reaction of the driver to the air mass involved, this allied with the rapidity of direction change imposed on the assembly as they follow the variations in frequency makes the structural aspect critical in the extreme.
Core requirements for the sub assembly are :-
Integrity of structure capable of absorbing without propagation of secondary responses within the structural affixing. Integrity of air void separation front to rear or at least represent a very high load to the air mass front to rear. Dust exclusion from the charged element to avoid leakage paths from the charged diaphragm to the fixed elements of the drivers. Duplicity of the envelope of the drivers sonic substance to avoid dissimilarity left to right in the reproduced sound.
Other aspects which have to be resolved as a compromise, as are all Engineering works subject to, the variation in affective impedance seen by the driving amplifier which would give rise to variations in the effective driven energy levels to the diaphragm - the intention is to nullify this aspect during the design of the primary driving transducer, without resorting to corrections via impressed electronic methods.
All good stuff, I hear you say, but where to begin?
With the very first step.
Having set out the basis and a somewhat brief expose on the overall, a short revisitation in order to elucidate on the reasons for the the project concept.
One overall aspect to be clearly defined at the outset is that it has to be "Right first time" the levels of money and sheer time involved are substantial, the driving axiom is therefor it is much easier to address during the conceptual phase rather than the revisitation needed in order to rectify blatant Engineering, or whatever cock ups.
Attention to detail will enable the project to gain an element of success
Should the need arise the assemblies should have the capability of being easily stripped in order to rectify components that have failed in service.
One problem to resolve is the capacitive coupling of the materials used in the surround of the drive units since they represent a leakage path and consequently robb the drive of the drive so costly gained.
A variety of materials are under investigation in cluding "Captye"(sic) a hard plastic formed material, similar in appearance to nylon, which reputedly has a very high dielectric strength, will investigate and report.
The problem we face is the fequncey shunt affect caused by the capacitor we are attempting to drive, this shunt will become affective at a particular frequency and strip off the power we are trying to drive the thing with.
I am also considering the use of lead free glass for the spacers and since I intend to use this material for another project my source would provide the material for both, in fact for possibly three projects.
The norm for plate to diaphragm spacing appears to be of the order of 1mm per thousand volts, the knee point of reliability of HT power supply for ELS drivers is 5K so will limit the basic unit to this voltage level which could impose limits of LF capability but this is circumvented by the units being huge, and since the drivers are room and free field loaded on each of the two sides the driver will not require large diaphragm excursion to reproduce deep bass.
Glass however enables massive, relatively speaking, capacitors to be constructed once more we are faced with that hated word compromise - glass however shall enable a higher value than that achieved by using air.
Regards, Bill Baird