Design Notes The Columns

Design Notes 3: Sound Lab “The Complete White Paper”

Writer’s word: Every product comes with an Owner’s Guide to familiarize the client with its operations. These documents are often written in a dry type and to the purpose. But every now and then, we come throughout vast sections in Guide that reads like a clean presentation of ideas and juicy description of sensible technologies, and if we’re fortunate, even a narrative on the challenges confronted by the engineers and designers in bringing the idea to fruition. ‘Design Notes” is a new collection created to function the informative and properly written documentary inside these Manuals to the readership, to offer information and viewpoints that we consider will profit and even entertain us. All supplies are reprinted by permission.

Submit your Design Notes tips to [email protected]

Sound Lab Electrostatic Loudspeaker

“The Complete White Paper”

Thanks in your interest in Sound Lab. This paper is designed to introduce you to our technical philosophy, and it is our hope that it’ll reply any questions that you might have relating to our merchandise.

Sound Lab has been in enterprise since July 1, 1978. The founders of the corporate, Dr. Roger West and Dr. Dale Ream, shared a belief that electrostatic transduction was probably the optimum know-how for loudspeakers. Over the intervening years, the corporate has successfully addressed many main issues of electrostatic speaker know-how. As well as, our initial aim was, and stays, to get rid of as a lot as attainable anything that might detract from the purity of the reproduced sound. Particularly, it has been desired to develop a loudspeaker incorporating the following attributes:

1. Really full-range electrostatic know-how having excessive reliability, broad dynamic range, good sensitivity and wonderful bass response.
2. Single-membrane know-how from which the complete audio spectrum is radiated, offering good time-alignment.
3. Ultimate part response by eliminating using spatially separated a number of drivers to cowl the audio spectrum.
four. Dipole topology to get rid of enclosure coloration.
5. Line-source topology to offer uniform response over the complete listening area from wall to wall and from flooring to ceiling, and to scale back wave interference patterns by eliminating flooring and ceiling reflections.
6. State-of-the-art electronics using toroidal audio transformers to preserve delicate nuances inherent in music, high-grade polypropylene foil capacitors with low dielectric absorption and high-current functionality, army grade resistors, iron-core inductors, and a regulated bias provide for secure sensitivity.
7. Wide selection equalization controls to offer a flat response in nearly all listening rooms.
eight. Furniture grade esthetics that may grace nearly any room décor.

We really feel that we now have efficiently glad our initial objectives.

The electrostatic speaker art was in its infancy when Sound Lab started business again in 1978. Thus, by default Sound Lab is a analysis and improvement laboratory in addition to a manufacturing facility because of its formidable objectives, which require that the know-how base of the corporate essentially continues to grow. A robust patent and trademark base has resulted from this continued effort. From the attitude of a customer, nevertheless, this might trigger some uneasiness because the product they elect to buy may probably turn out to be out of date if its know-how is outmoded. To allay this worry we’ve established a policy that any product that we manufacture may be introduced up to the present technical degree at an inexpensive value.

Our products are meticulously handcrafted piece by piece. Every operation is rigorously completed and checked to make sure that it’s appropriately manufactured. Batch processing and mass production methods could not insure the person quality of each product that we manufacture.

The following sections present an in-depth consideration of the technical rules upon which our products are based mostly.

1. How Do Electrostatic Audio system Work And What Are Their Advantages?

This part describes the basics of electrostatic speaker know-how. The following materials is taken from a superb article written by Jacob Turner entitled: “Why Electrostatics?” The article offers a superb tutorial on electrostatic audio system and why they’ve decided advantages over other speaker technologies:

“Because the latter half of the nineteenth century (circa 1871) the copy of sound by way of electrostatic transducers has stirred the artistic vision of professional engineers and idle dreamers alike. It is an fascinating reality of historical past that no other single gadget within the audio gear hope chest has loved such an in depth and extended courtship between engineer and Audiophile as the electrostatic transducer.

Early makes an attempt to embody this means of sound copy have been solely marginally successful partially due to the shortage of suitable materials and processes.

What’s the glamour of the electrostatic principle that gained it such prolonged, devoted attention? Why has the electrostatic transducer remained the usual of excellence by which other acoustic units are so typically measured?

The answer to these questions lies in no less than three areas, which will probably be discussed within the following order:

1. Some peculiarities of the hearing process

2. The nature of the acoustic medium: air

3. The operational options of electrostatic acoustic units as associated to the above and to dynamic acoustic transducers

The current improve of exercise within the highly elusive area of psycho-acoustics promises to contribute significantly to a more profound grasp of the complexities of man’s perception of his sound setting. Several current research have been carried out in regards to the sensitivity of regular adults’ ears to totally different ranges of harmonic distortion. The outcomes recommend that relatively excessive levels of harmonic distortion (odd and even order) are imperceptible within the presence of normal musical program, while quite small modifications in amplitude and phasing are readily ascertained. Amplitude modifications have been described as altering the tonal high quality of the program, while part displacement e.g. bass and treble of not more than 5 levels degraded the readability and definition of musical transients and upset the homogeneity of the stereo image between two main frequency bands.

Other research have pointed out that the inherent transient nature of musical and speech sounds dictates a high degree of transient constancy as a prerequisite of top of the range acoustical transducers. The importance of these observations insofar as electrostatic transducers are concerned can be pursued slightly later.

One other very important hyperlink within the chain is air, which has the following major traits of conduct which might be germane to our matter. Air is very compressible, that is, the quantity of air strain (variety of air molecules) in a given area might be increased or decreased past its regular situation. Air, then, might be stated to be like a spring, a way for storing power; a compliance. Air additionally has weight or mass. Ten kilos of air are just as heavy as ten pounds of potatoes. Air is, subsequently, like an inertance, which opposes an action or drive; an inductance. Air can be randomly excited, air molecules eat energy by producing warmth. Air can then be stated to be like a resistance. This acoustic impedance is generally very low, although at excessive audio frequencies it is considerably larger than at low audio frequencies. So as to insure that the transfer of diaphragm or cone motion to air motion occurs with the greatest effectivity, it is essential that the whole mechanical impedance of the gadget be as near the acoustic impedance of the body of air it is thrilling over as a lot of the audio range as attainable.

To narrate the previous dialogue to the topic of the electrostatic transducer, it is going to be mandatory to stipulate the operational options of the push-pull electrostatic system. The previous points shall be related on the similar time to the operational options of the dynamic transducer. As illustrated in Fig. 1, the electrostatic transducer consists of a skinny membrane (diaphragm) made from Mylar that’s stretched and contained between two acoustically open plates. The two plates are related to both end of a coupling transformer which offers the excessive voltage audio signal. The diaphragm is related to a high voltage, low current bias supply, which offers an electrostatic charge that becomes trapped in the diaphragm.

In recent times a way referred to as “electretification” has been developed whereby the bias cost is completely embedded in the diaphragm materials, in order that the diaphragm is self-energized without an external supply of bias voltage. The web end result is identical in each instances. The 2 plates present an electric subject that’s the voltage equal of the audio signal. In the presence of an audio sign, the electric subject exerts forces on the electrostatic charge that’s trapped in the diaphragm. These forces are transferred to the diaphragm, inflicting the diaphragm to move in synchronization with these forces.

Against this, Fig. 2 will illustrate the make-up of a dynamic driver, which consists of a frame housing, a magnet, and a voice coil hooked up to the apex of a cone which is suspended at its edge by a versatile material or other material. The voice coil is about into movement in synchronization with an audio signal that causes current move by means of the coil. As the coil is about into movement by this signal, it in turn sets the cone into movement.

Although each models achieve air excitation by means of diaphragm or cone movement, the way by which this is achieved includes radically totally different methods and outcomes. The electrostatic system employs using a shifting member for all its working frequencies that’s often solely zero.0004 inches thick (Observe: the fabric used in Sound Lab audio system is simply 0.00012 inches thick) and weighs solely as much as a physique of air 7mm thick (2mm thick in Sound Lab audio system) whose boundaries are equal to these of the shifting diaphragm.

The electrical subject, which acts to make the diaphragm transfer, exerts its actuating pressure uniformly over primarily the whole space of the diaphragm. A diaphragm of such extreme lightness, together with an actuating pressure that’s uniformly distributed over the whole floor of the diaphragm, leads to a transducer whose transient response intently duplicates the electrical enter. The web result is a diaphragm motion that may be a excellent duplicate of the electrical forces appearing upon it, with all sections of the diaphragm surface shifting with extremely accurate part and amplitude linearity all through its complete range of travel, at all frequencies within its area of operation.

The forces appearing to maneuver the dynamic transducer’s cone, nevertheless, produce totally different outcomes. The appliance of the driving pressure solely to the apex of the cone necessitates a sufficiently stiff cone to stop buckling and deformation of the cone structure. Such a stiff cone normally has considerable mass, which degrades its effectivity, its transient response capabilities, and its excessive frequency efficiency. As well as, the forces applied at the apex don’t act uniformly over the surface of the cone, inflicting the cone to “break-up” into an infinite number of vibrational modes, only one in every of which is actually representative of the unique signal. This mode of operation produces amplitude and part nonlinearity typically of considerable magnitude, and these tend to increase as the cone is pushed to higher excursions. Clearly, the discussion of dynamic driver operation relates fairly strongly to the earlier dialogue in regards to the unusual sensitivity of the human ear to the problems of transient response, amplitude linearity, and part linearity. The essential conclusion is that an electrostatic unit behaves with better composure in all the above areas.

The second main distinction involving electrostatic transducers deals with the considerable drawback of coupling to the air with affordable efficiency over the complete audio band. The electrostatic unit, due to its extremely low mass diaphragm and the uniform distribution of’ the driving forces over all the diaphragm floor, is inherently a unit with low mechanical impedance in any respect frequencies. As such, the coupling drawback at low frequencies (where the issue is biggest) for electrostatic models is significantly less than for dynamic models, that are encumbered by a high mechanical impedance. The results of these circumstances is that the electrostatic unit performs quite properly right down to its frequency limits and within its maximum excursibility with equal fidelity at all drive ranges.

The dynamic cone unit, because of its poorer coupling, have to be driven more durable to supply passable excitation of the air at low frequencies, and often encounters quite a lot of issues involving cone break-up, non-linear motion of the voice coil resulting from lack of magnetic coupling in the gap, suspension non-linearities, and so forth. In all equity, it have to be stated that the efficiency degree of immediately’s in style dynamic acoustic transducer is incredibly good given the economic and operational constraints of that sort of unit. However, the superiority of the electrostatic principle has been demonstrated by the good acceptance of the growing number of electrostatic headphones which have already emerged out there. In addition, in fact, a number of electrostatic speaker merchandise are extremely regarded by the audiophile group.”

We enormously recognize Jacob Turner’s capacity to elucidate some great benefits of electrostatic know-how over typical dynamic (magnetic) know-how. We might add that the comments relating to cone audio system apply to ribbon and different kinds of audio system also. In the case of ribbon speakers, they are planar in nature however the proportion of the world of the diaphragm that is instantly driven is on the order of 30% to 50% as an alternative of 100% as within the case of electrostatic audio system because the driving pressure comes from a thin piece of wire or foil that represents solely a fraction of the whole shifting area. Thus, as in the case of the cone speaker, a good portion of the diaphragm isn’t instantly driven and may inherit a number of the drawbacks of cones. Moreover, the wire or ribbon is often sandwiched between two plastic movies which adds to the shifting mass. Basically, the ribbon speaker is best than its cone counterpart when it comes to motional accuracy, nevertheless it has upwards of ten occasions the shifting mass of a properly designed electrostatic speaker.

2. What Is The Relationship Between Audio system And Microphones And How Is It Optimized?

The objective of high-end audio is to recreate a sonic efficiency with as much accuracy and realism as attainable. This demands near-perfect efficiency from every element within the copy system, including the traits of the sound room. Nevertheless it additionally requires a compatibility with sure circumstances involved within the recording course of which should do with the accuracy of the recreated stage (stereo picture, each measurement and site), ie: the spatial facet of the re-creation. Perhaps, the extra necessary of these has to do with the traits of the microphone(s) used to document the efficiency and their placement.

Not much might be executed to compensate for signal timing corruption as a consequence of mix-down procedures and bizarre microphone methods. These are in the arms of the recording engineer. But, one thing may be accomplished regarding an acoustical precept that we check with as microphone/speaker reciprocity. In the early days of stereophonic recording it was usually accepted that the “standard” microphone association was to put two microphones dealing with the orchestra which have been separated by eight ft. Reciprocally, the loudspeakers reproducing the recording would even be separated by eight ft. There have been many alterations to this easy geometry since then, corresponding to using more than two microphones to obtain particular results and sonic highlighting. Nevertheless, amid the fairly complicated science of recording, one generality persists. Most microphones utilized in recording employ a cardioid (directional) sample. A microphone having this characteristic readily accepts info from the front but attenuates sound waves approaching from the rear. Contemplating out there models, the bounds of the cardioid acceptance sample is such that pickup sensitivity is diminished by 6dB (half strain) varies from about 30 to 45 degrees both aspect of the central axis of the microphone.

The precept of reciprocity merely states that with a view to recreate a sound stage with good spatial accuracy, the dispersion angle of the loudspeaker and the acceptance angle of the microphone must be comparable. For instance, have been you to stroll around your sound room and examine the recreated sound area to walking across the auditorium through the actual performance, similarity of the stage picture can only be achieved if the principle of reciprocity is carried out. Because of this all Sound Lab speakers are rigorously designed to satisfy this essential precept. Extra concerning the requirements for correct staging will probably be discussed in a later section.

Another advantage that is accrued from a wider dispersion angle is that harsh direct reflections from partitions are enormously lowered, making speaker setup a lot easier since undesirable room modes are typically much less pronounced. Via experience we’ve found that horizontal dispersion angles from 45° to 90° work properly in the residence surroundings. The extra slender angle supplies higher speaker sensitivity and dynamic vary while the wider angle supplies a wider stage. Both angles are available in our products.

three. Sound Lab Audio system Don’t Seem To Sound Any Louder Up Shut Than They Do Far Away! How Is This Completed?

The secret behind this seemingly magical trait has to do with the characteristics of the acoustical line supply. All Sound Lab merchandise are categorically vertical acoustical line sources. My opinion is that the vertical line source is the optimum acoustical geometry for correct staging and acoustical power management within the residence listening surroundings, which I will now try and justify.

Theoretically speaking, a vertical acoustic line supply is a two-dimensional vertical line, having infinite size and 0 diameter, from which full-spectrum sound power emanates. It is perhaps helpful to ascertain an extended violin string, sufficiently long in an effort to produce decrease frequencies. In the actual world, where an infinitely long line is an abstraction, the size of this line needs to be giant compared to the all wave lengths that it radiates (there is a vital exception when utilized in an enclosed room, as can be mentioned later). If this criterion is met, the main characteristic of the vertical line supply is that it disperses power solely within the horizontal course and none within the vertical course. In different phrases, all sound rays emanate perpendicularly from a vertical line. Subsequently, the radiation subject could be compared to the shape of a slice of pie through which the highest and bottom surfaces are flat (no vertical radiation) and aspect radiation is confined to a prescribed angle (horizontal dispersion). In distinction, most speakers out there available on the market are more related to the “point source”, the attribute of which is a uniform radiation sample in all directions: up, down and sideways.

My justification of why I consider the line supply to be superior to the point source within the residence setting will now be thought-about. For many who don’t want to get entangled in arithmetic I will first give an evidence that appeals to the intuition. This can be adopted by a extra rigorous strategy.

In your mind’s eye, envision an infinitely lengthy vertical line from which perpendicular power rays are being radiated. A bottle brush held vertically can be a superb analogy whereby the backbone is vertical and the bristles radiate horizontally. It must be intuitively clear that If a skinny flat floor, that’s parallel to the power rays, is positioned on the road, it might not disturb the rays since there can be no reflections. Now, place a second flat surface, parallel to and above the first floor. Neither of the surfaces will intrude with the power rays. In different phrases, the sample of the rays between the plates wouldn’t be affected by the presence of the plates. Think about that the decrease and upper plates characterize the ground and ceiling of a listening room. The point being made is that if a line-source speaker is placed in a room, the sound it emits will protect the traits of an infinitely long line supply. One may ask what the advantages of this may be. First off, it eliminates flooring and ceiling reflections, since all sound rays are parallel with the floor and ceiling. The consequence of this is that the complexity of interference waves inside the room is minimized, offering a more pure sound subject. The horizontal dispersion of the speakers is designed to attenuate wall reflections. Secondly, because the line source has no vertical dispersion, all power is concentrated within the horizontal path. The theoretical effect of this, ignoring the reflective area resulting from wall reflections, is that sound drops off at solely 3dB per doubling of distance from the speaker fairly than 6dB per doubling of distance as in the case of the point source. Subsequently, as the listener walks towards or away from a line source, modifications in loudness are much less obvious. That’s the reason the sound degree of our speakers does not appear to drop as one walks away from them, nor does it appear to grow to be louder as one approaches them. Thus, the sound degree doesn’t range noticeably as one strikes toward or away the audio system, which makes the whole room the proverbial “sweet spot”.

One may marvel how a big speaker might probably perform as a skinny vertical line supply. As pragmatic proof, simply walk round to the rear of certainly one of our audio system whereas it is reproducing sound. Utilizing an ear as a detector, a dramatic improve in sound degree will probably be apparent on the middle of curvature of the speaker. The sound rays emanating from the horizontally curved radiating surface will converge at some extent about three ft behind the speaker, and past this level the rays will diverge. This focus is the virtual line source. Thus, as unimaginable as it might seem, the sound from our large speakers seems as if it is being radiated from a minuscule vibrating vertical line. The more close to the highest of the speaker is to the ceiling, the more precisely it performs as an infinite line supply.

The only requirement for a truncated vertical line supply (being trapped between a flooring and a ceiling) to carry out as if it’s an infinite line source, is for the floor and ceiling be acoustically reflective. It can be shown mathematically that the interaction between the ground and ceiling reflections create infinite phantom extensions of the road supply above and under the room. It really works in this method, the vertical element of any ceiling reflection shall be cancelled by a complementary reflection from the floor (and vice versa) leaving only the horizontal element. In the actual world the floor and ceiling will take up some sound power, but the effect is just not enough to change the line characteristics enough to be audible. The web result is that the listener can sit down, rise up, do deep-knee bends, walk forwards and backwards and the sound picture doesn’t appear to vary. Some extent supply can’t give this sort of efficiency.

To make this extra significant, I shall be somewhat rigorous mathematically. The acoustic depth (I) of a sound wave is outlined as the typical power transmitted per unit space in the course of wave propagation:

Where:

I = common power transmitted per unit space in the course of wave propagation

Prms = effective strain in nt/m2 (newtons/sq. meter)

c = velocity of sound in m/sec (meters per second)

ρ = density of air in okay/m2 (kilograms per square meter)

With the purpose supply, the world that power is distributed over is quadrupled every time the space from the source is doubled. Thus, in decibels, the intensity of a sound drops roughly 6.02dB for every doubling of distance:

Since doubling distance reduces (I) by a factor of 4:

As compared, with the road source space, the sound degree modifications solely by a factor of two for doubling the space toward the line supply, since doubling the space distributes the sound power over solely twice the world. Thus, doubling the space from a line source reduces the sound degree by only 3.01 dB. In other phrases, sound depth drops off with growing distance significantly slower with the line source than with the purpose supply.

For the mathematically inclined, a more rigorous remedy of the road supply will now be given. To start with, when comparing commonplace sensitivity measurements of point sources versus line sources, it’s common to misinterpret the results because it applies to sound strain ranges at normal measurement distances. The rationale for this controversy is because of the proximity impact of the line supply compared to that of the purpose source. Sound degree varies as the inverse of distance for the line source, whereas it varies because the inverse of the sq. of the space for the point source.

Because of the distinction in proximity characteristics, comparing the usual sensitivity measurement values of the line supply and level source (normally measured at one meter with one watt of enter energy into 8 ohms) to the sound strain degree measured at regular listening distances, the end result could be startling. Usually, the point source speaker has a better power density at the standard one-meter distance than that of the line source because of the power of the point source being concentrated right into a smaller space in comparison with the road supply, and thus sometimes has a better commonplace sensitivity score than that of the road source. Nevertheless, when the sound degree is measured at a typical listening distance from the speaker, say 25 ft, this distance compared to the usual 1 meter distance is about eight occasions higher, giving the road supply almost a 9 dB benefit over the purpose source. Since this benefit increases with distance, there comes some extent, we term because the “critical distance” the place the sound strain degree (SPL) of the road source equals that of the purpose source. Past this level, the road source continues to increase in loudness at a +3dB/(doubling of distance) price compared to the purpose source, as distance is further elevated.

Thus, when commonplace one meter sensitivity measurements of a line source and some extent source are in contrast the outcomes might be deceiving. It only is sensible to measure sensitivity at the listening distance fairly than at one meter when evaluating point-source and line-source speaker sensitivities.

Maybe, the easiest way to relate commonplace one-meter sensitivity values with the efficiency at typical listening distances is to calculate the space from the speaker at which the sound degree is identical as a perform of the difference of the one-meter sensitivity scores of the 2 audio system. Preserving in thoughts that the road source SPL drops off at a slower fee than that of the purpose supply and further, that the one-meter sensitivity score of the purpose supply is usually higher than that of the line source, there’s inevitably a distance from the supply the place the sound degree will be the similar, past which the line supply will all the time be louder than the point supply. In truth, the diploma that the road source is louder than the purpose source is proportional to this distance.

The components for this important distance (D), where the road source and point supply have the same SPL, is given by:

Where:

D = the space in ft where the point-source and the line supply have equal SPL

RP = Price of change of some extent supply SPL as a perform of doubling distance: -6dB/octave

RL = Fee of change of a line source SPL as a perform of doubling distance: -3dB/octave

SP = One-meter sensitivity of a point-source speaker: SPL in dB @ 1 meter

SL = One-meter sensitivity of a line-source speaker: SPL in dB @ 1 meter

SP and SL are obtained using the usual technique of measuring speaker sensitivity. This equation assumes that the point-source speaker sensitivity (SP) is bigger than that of the line-source speaker close to the speakers, which is a protected assumption typically.

This equation is derived from the fact that the theoretical infinite line-source obtains a three.01 dB advantage over the theoretical point source with every doubling of distance from the source in an anechoic surroundings. In apply, actual speakers will differ from the theoretical model by varying levels depending on how intently they emulate both some extent or a line supply, therefore one may anticipate that the results might range considerably from the perfect case. However a departure from the perfect, the precept holds true and may be fairly vital.

A remarkably accurate easy rule-of-thumb is:

“The critical distance D (in feet) is approximately equal (within 10%) of the difference between the one-meter sensitivity ratings (in decibels) of the point-source and the line-source.”

That’s: D ≅ SP – SL (inside 10% accuracy)

For instance, our Model Majestic 745 speaker has a one-meter sensitivity score of 89 dB. Let’s examine that to a hypothetical “Brand X” point-source speaker having a better sensitivity score of 96 dB. The essential distance calculates to be 7.63 ft (the rule-of-thumb provides 7 ft). Beyond this distance, the Majestic 745 shall be louder for the same input voltage (this calculation assumes an anechoic setting). Acoustical environments which are only partially absorptive, similar to the typical residence listening room, will trigger some variation in precise measurements, however the basic precept still applies. The ethical to the story is:

“To properly compare the sensitivities of line-source versus point-source speakers, measurements should be taken at normal listening distances rather than at the standard 1 meter.”

Now, from a practical viewpoint, let’s interpret the above conclusions when it comes to advantages in the listening room. First, think about the consequences on the perceived sound subject brought on by walking to-and-fro in entrance of a reside orchestra in a symphony corridor. As one stands close to a aspect wall, the more close to musical instruments appear louder than those additional away, however they won’t mask (override) them. As one walks to the other aspect of the hall, an analogous effect is obtained. In different phrases, the acoustical sound stage is skewed as one stands to the aspect, however a three-dimensional picture of all the orchestra remains. This is exactly the impact of listening to music reproduced via stereophonic vertical line sources. More specifically, as a listener walks to at least one aspect of the listening room, the speaker nearest him doesn’t turn into considerably louder and, hence, does not masks the sound of the opposite speaker. The truth is, as the listener moves across the listening room the spatial picture of the reproduced orchestra responds very equally to that of an actual orchestra enjoying in a music hall. In distinction, the point-source speaker becomes considerably louder as one approaches it, and is thus capable of masking the sound of the extra distant speaker. Subsequently, one must stay equidistant from the two audio system to acquire correct staging.

The road source has additional advantages. As mentioned previously, sound rays emanating from a line supply radiate perpendicularly from the road. Thus, the sound that reaches the ear comes from sound rays which might be on the similar degree because the ear. Subsequently, because the listener stands or sits the sound is identical. Thus, one never listens “up to” or “down to” the sound source. The point-source, to the contrary, has a very distinct vertical position that may be simply localized, which may give music a man-made vertical localization effect. Opposite to some widespread beliefs, stereophonic music does not include any vertical localization cues and, subsequently, a true vertical image does not exist. To create a real vertical picture it might require an upper and a decrease set of speakers (with the corresponding four-channel microphone/recording setup with which to make such a recording) to simultaneously reproduce the vertical and horizontal pictures. Thus, the line-source speaker does not create synthetic vertical localization similar to a number of driver point-source audio system can do.

4. How Does Sound Lab Obtain Profound Bass Response With Dipole Panel Audio system?

If a compliant material, corresponding to a drumhead, is stretched over a frame and the drumhead is tapped with a mallet it should produce a sound having a distinct frequency, which is known as the drumhead resonance. It requires less power to cause the membrane to vibrate at this frequency than another frequency. Thus, if a vibrator is coupled to the drumhead and the frequency of vibration is diversified, when the drumhead frequency is approached the vibration of the membrane will turn out to be much higher than at different frequencies. That is the case with the electrostatic speaker as properly, since a membrane is equally stretched over a frame. As with the drumhead, the membrane of an electrostatic speaker will exhibit a robust resonant sound with comparatively low input power. This can be a drawback since when the audio sign hits the resonant frequency the membrane will amplify that exact frequency extra so than all others. If not tamed, the resonant power will create a coloration to the sound. Furthermore, because the membrane vibrates larger at resonance for a given enter signal degree, the membrane can easily be pushed into the stators, which limits the usable dynamic vary of the speaker. This resonant peak may be 20dB or larger and often happens on the lowest frequency of the membrane’s move band.

Numerous methods have been employed to remove this resonance. Some designers have used acoustical damping, resembling stretching a nice mesh, just like that utilized in nylon stockings, throughout the speaker. This strategy indeed damps the resonance, nevertheless it additionally reduces membrane movement at different frequencies to a lesser degree, reducing the vitality of the sound. Other approaches have been used to remove this nasty peak of power, but all have exhibited adverse uncomfortable side effects.

It might not be shocking if we have been asked how we get rid of the membrane’s drumhead resonance. An historic philosopher as soon as said: “Asking the proper question leads to the answer”. Applying this wisdom, we asked ourselves: “Instead of permitting the entire diaphragm to contribute to one resonant peak, why not set up a situation where different sections of the diaphragm resonate at different frequencies in a graded fashion, which would break up the drumhead resonance into a series of manageable resonances? The resulting set of resonant frequencies could be distributed over the pass band of lower frequencies and would have no effect on higher frequencies. And, by judiciously selecting the individual frequencies the bass response of the speaker could be equalized”. We tried it. Two fantastic results have been realized: the “drum-head” resonance was eliminated and the effectivity of decrease frequencies was dramatically increased since all was functioning on very responsive resonant power. The resulting bass response was flat, fast, dynamic and unrestrained. Because it seems, the “nasty” membrane drumhead resonance is a free supply of power that may be distributed to equalize the bass response of the speaker.

The distributed resonance principle also solves a nasty drawback related to dipole radiators: dipole cancellation. An acoustic dipole radiator is principally a vibrating membrane during which the acoustic power emanating from each of its sides is permitted to radiate freely. Dipole radiation has vanishing acoustic “coloration” since it’s devoid of enclosure resonances. Nevertheless, because the two waves radiating from opposite sides of the diaphragm are mutually out of part, they begin to cancel one another at lower frequencies, which leads to a prematurely rolled-off bass response, often occurring just above drumhead resonance. By judiciously choosing the “law” by which the resonant power sectors are distributed, the consequences of dipole cancellation could be nearly eliminated. Determine three exhibits the standard response of an unequalized dipole radiator taken axially to at least one aspect. Figure 4 exhibits certainly one of a number of strategies of sectoring a membrane to distribute resonant power. fl, f2, and so forth., characterize the resonant frequencies of every of the sectors. Figure 5 exhibits how the bass equalizing response contour is generated by dividing the membrane right into a distribution of resonant sectors.

It ought to be readily obvious from learning these figures that the lowest frequency sectors are placed on the excessive ends (prime and bottom) of the panel. This causes the apparent measurement of the radiator to seem equal to the peak of the speaker. The consequence of that is to scale back the vertical dispersion of decrease frequency power (ie: greater directivity), thus growing power density. In audio phrases, this represents a rise in bass dynamics. We seek advice from this as our “Bass-Focus” know-how. This is just like the work of Joseph D’Apolito, who employed this principle with dynamic speakers.


Within the “near-field” (that’s, when one could be very near the speaker) the bass response of the speaker has a rising effect as frequency is lowered. This occurs as a result of up near the speaker the consequences of dipole cancellation will not be as apparent. Nevertheless, within the far-field (which means normal listening distances and beyond) the rising attribute seen on the “near-field” disappears and as a result of resonant power distribution simply the correct quantity of power is provided at each frequency to provide the power misplaced as a consequence of dipole cancellation.

The ensuing frequency response is flat and extended. In other phrases, the “law” of the distribution of frequencies is such that it supplies the complement of the membrane’s unaltered pure frequency response curve. Obviously, an electronic equalizer could possibly be used to acquire the same impact, however it will scale back the efficient dynamic range of a given amplifier by 15 dB or more. Through the use of “distributed-resonance equalization” the dynamic range of the amplifier isn’t compromised. That is how the nasty drumhead resonance power is put to good use. That is about as shut as one can come to “having your cake while eating it”.

5. The Electron: The Spine of the Electrostatic Speaker:

In a standard (dynamic) loudspeaker magnets are used to create a drive area. Electrical cost is employed to do the same in the case of the electrostatic speaker. The standard of the efficiency of the electrostatic speaker is immediately related to how dense and the way uniformly the charge area is distributed upon the membrane. Sound Lab employs a pure copper charge diffusion ring across the outer boundary of the membrane to feed cost into the center of the membrane from all instructions. The low impedance of this ring insures that leakage paths, brought on by things like moisture condensing onto the membrane from humidity, has no impact on the efficiency of the speaker. The cost on the membrane is thus exceptionally uniform and dense. The membrane floor have to be electrically conductive to permit the charge emigrate, however the resistivity of the conduction must not be too excessive nor too low, and it must not burn off or deteriorate with time. Such is the conductive membrane floor of Sound Lab’s audio system.

Furthermore, because the cost is fed from all factors around the periphery of the membrane, the speaker “charges up” shortly. Subsequently, the speaker might be disconnected from the mains if desired with out requiring time to recharge when it is desired to take heed to them.

6. Geometrical and Development Issues:

The excessive efficiency capability of our audio system has much to do with the interior geometry of the electrostatic panels. First, the spacing between the stators and the membrane is extraordinarily crucial with a view to acquire the right electrostatic area depth plus having sufficient room for the membrane to maneuver. Moreover, the spacing have to be precisely the same for each the front and back stators with a view to have optimum push-pull motion and low distortion.

The framework of the panel can also be important. The whole function of the framework is to take care of the right geometrical relationship between the stators and the membrane. It have to be very inflexible, precisely constructed and non-resonant. Furthermore, the material used have to be moisture resistant and not degrade with time and environmental circumstances. We subsequently fabricate the interior members of the construction from a plastic that could be very robust, dense, non-resonant, non-hygroscopic and resistant to environmental elements. Thus, the integrity of the panel is preserved beneath all affordable circumstances.

The greatest basic criticism of electrostatic speakers has been that they easily “arc over” and are thereby broken. Some early design attempts have resulted in panels that break down easily which has created a nasty identify for electrostatics. Understandably, this could trigger individuals to draw back from them. Sound Lab engineers have nearly eradicated this problem by employing state-of-the-art cross-linked insulating materials. This can be very uncommon for a Sound Lab speaker to experience a voltage breakdown, even beneath excessive overload. This eliminates the best concern of those that want electrostatic sound. To insure the integrity of the speakers we manufacture, each panel is examined at the maximum rated energy before it’s shipped.

Yet one more essential geometrical consideration must be talked about. Some designers have attempted to offer horizontal dispersion of sound power through the use of a curved geometry, whereby the membrane is suspended such that it assumes a very curved surface. It is intuitively apparent that such a shape offers a non-symmetrical transduction characteristic, because the membrane rigidity will increase because the membrane expands outwards and it loses pressure because it strikes inwards. This unsymmetrical characteristic creates extreme mechanical limitations and thus prevents the speaker from performing as a very full-range speaker. Actually, for a given membrane width, because the radius of curvature is increased the severity of the issue increases proportionately for a given membrane displacement. Because of this the horizontal dispersion angle of a very curved membrane have to be limited to a fairly small angle.

In distinction, Sound Lab employs a piecewise approximation of a curved floor utilizing flat surfaces (sides). The flat surface offers a symmetrical attribute that allows giant linear displacements. Subsequently, the flat membrane strategy is the only means a very full-range membrane speaker might be realized. By judiciously choosing the right angle between adjoining flat sides, the dispersion of the sound subject might be as clean as the curved membrane however without the extreme displacement restrictions of the curved membrane. One other benefit is that there isn’t any limit to the amount of horizontal dispersion that can be used because the membrane dynamics aren’t affected by the angle of dispersion as is the case of a curved membrane. Audio system have been manufactured having up to 360 levels of horizontal dispersion, however we use an angle in our speakers that we have now discovered to be the perfect angle for common listing rooms. We offer 90 degree dispersion panels for extensive rooms in order for the sound to embody the room, and 45 diploma dispersion for extra slender rooms to attenuate side-wall reflections. We’ll customized construct panels for other angles upon request, up to 360 levels.

The membrane is another crucial a part of the speaker panel that ought to be talked about. Low mass and resistance to environmental elements are crucial necessities. Sound Lab uses a polyester material that is solely 120 millionths of an inch thick, which supplies the excessive compliance vital for giant, linear membrane excursions. Also, the shifting mass is so low that it represents only a fraction of the mass of the air volume it moves. Moreover, Sound Lab makes use of a singular mechanical/adhesive system to insure that the membrane never slips and loses its proper rigidity. Finally, the membrane is coated with a particularly thin proprietary substance to provide it precisely the right electrical conductivity. This coating is nearly indestructible and will not vaporize when the speaker is performed loudly.

7. Last Remarks

Sound Lab gives fifteen models, all of which make use of the applied sciences defined on this paper. Why so many models? We offer three types, the Ultimate collection with its steel space-age body, the Audiophile collection with its beautiful wrap-around furniture-grade wood body, and the Majestic collection having a extra easy trendy touch with furniture-grade wooden trim.

5 panel sizes are available for each of the above talked about types. The sizes vary from our just lately launched compact collection, standing solely fifty inches tall, to our largest panels standing at a monumental nine ft peak. In other phrases, there’s a measurement to satisfy all installations. The panels used on all models of a given measurement are similar. Further, the similar electronics are employed on all models. In consequence, there are not any choices to be provided aside from panel measurement and elegance. Our electrostatic sub-woofers and our hybrid fashions have not been thought-about in this paper in an effort to absolutely give attention to our really full-range electrostatic audio system. We invite you to contact us if you need to know more about these.

Congratulations! It understandably requires a bit of effort to work via the small print of this paper. Far more might be introduced to discover our know-how in additional element, however the actual check is within the sound. We’re pleased with our know-how, and we really feel that our audio system are based mostly on crucial acoustical rules that apply to sound copy within the house. If this presentation has not answered your whole questions, we invite you to contact us for the solutions. We also welcome any options that you’ll have.

Sound Lab Electrostatic Loudspeakers
P.O. Box 409, Gunnison, Utah 84634 USA Ph. 435-528-7218
www.soundlab-speakers.com           [email protected]