FAQ

Speakers

Why build monopole electrostatic speakers?

Monopole means that sound only comes out the front of the speaker. Most electrostatic speakers are dipole and therefore emit sound out both the front and back of the speaker. The sound coming out of the rear of these speakers is the opposite polarity of the sound coming out of the front. The high frequencies are directional and so they bounce off the back wall of the room and give a distributed sound. The bass frequencies are not directional and so they will come around to the front of the speaker and cancel with the bass coming out the front. As a result it is hard to get any large amount of bass out of a dipole speaker. It is also hard to obtain good speaker placement since the sound coming out of the rear of the speaker has to be precisely oriented and absorbed to give a balanced acoustic effect.

With monopole speakers the sound is much better controlled. There is little cancelling of the sound and the speaker placement is much less critical. With the correct equalization these speakers can be placed almost anywhere including up against and even inside walls.

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Why build line source speakers?

Most speaker drivers are point, or spherical sources of sound. The different drivers each emit their frequencies in a spherical fashion. Depending on the positioning of the drivers they will add and subtract their output depending on ther placement and the listening position in the room. Each driver generally has different dispersion, or angle of emission. Again, as one changes their position in the room the overall sound and coloration can change.

A line source is one that for all intents and purposes emits a perfect cylindrical wavefront from the speaker. Since the sound is coming from a virtual “line” of a very narrow width, there is very little change in the sound as one moves around the room. Also, a line source fills the room with sound differently. As one moves around the room the difference in loudness increases and decreases proportionally with respect to ones’ distance from the speaker. Most speakers act like point sources whose loudness changes inversely as the square of the distance from them. Line sources actually seem louder than their measured spl loudness specification would indicate.

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Why are the cabinets so large? The speakers must get loud.

The size of the cabinets are constrained by physics. Most speakers have small heavier diaphrams with large magnetic motors to make them respond quickly. Electrostatic speakers have very light diaphrams and large openings in the cabinets. The relatively smaller, heavier cones of dynamic loudspeakers effectivly lower the resonance of the speaker cabinet. Electrostatic speakers influence the cabinets much less. As a result the cabinets need to be larger to get the same resonant frequency. In addition electrostatic speakers have small displacements so they need large diaphrams. This takes up much more space.

Superlative Audio has carefully designed the speakers and cabinets to work well with relativly small cabinets. There have been very few electrostatic bass speakers made. We belive we have found many unique solutions to the traditional dilemmas mentioned above. The SAS-1LF has excellent performance with moderate sized cabinets

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Why are the cabinets so heavy?

There are three components to their weight. The primary issue is the physical size of the cabinets. It is very hard to make a large rigid cabinet light. Second, the actual components of Superlative Audio’s speakers are incredibly heavy. This is the result of building rigid, non resonant acoustic devices. The third aspect to the weight is the massive transformers built into the speakers. In order to achieve the very low distortion over large frequency ranges, large heavy transformers are used. This has enabled us to make a truly full range, high performance electrostatic loudspeaker.

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I have a large room. Will they be able to fill the room?

There are a number of unique features available with Superlative Audio’s loudspeakers that enable them to be used in large rooms. In general, electrostatic speakers can easily produce a large amount of high frequencies. As tthe sound gets lower in frequency it takes more air movement to create the same SPL sound level measurement. Electrostatic speakers are more efficient if the diaphram does not move as far. As a result the natural tendency is for electrostatic speakers to be only used for high frequencies. With Superlative Audio speakers the bass cabinet design produces moderate SPL levels over a wide frequency range. By using multiple cabinets and tri-amping the system multiple bass cabinets can be seamlessly merged to move as much air as is needed while maintaining a virtual line source. Also remember that the sound diminishes by only the inverse of the distance with line sources, so the sound propagates more evenly around a room.

Sometimes it is prudent to use a fast, low distortion dynamic subwoofer in larger rooms. to help manage costs. In general they can be integrated with crossovers below 60Hz. The response time of the faster dynamic subs can have minimal degredation at these frequencies. Since these subwoofers are virtual point sources a number of them can be stacked to create a bass line source. This gives more even sound distribution in larger rooms.

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Will SAS-1 speakers work in a home theater?

Electrostatic loudspeakers make great theater speakers. They can literally “disappear” acoustically. The voices and sounds are natural and help enable the illusion of realism. Most people do not consider electrostatic speakers for home theaters because they have a reputation for not producing bass well enough. As mentioned above it is possible to build a full range, full loudness system with Superlative Audio speakers. As also mentioned above, it is sometimes prudent to use fast dynamic subwoofers for the very lowest bass frequencies.

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Amplifiers

What is a “floating bridge” topology?

The “floating bridge” is a patented technique that enables independant “floating” differential amplifiers to be used to produce arbirary performance amplifiers. In this case multiple low voltage, high speed, high performance amplifiers are wired to produce the desired number of channels, the voltage and the current that is needed for a particular application.

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Why is there no negative feedback loop on the output stage?

Traditional negative feedback loops provide continual correction to an amplifier’s output by comparing the input signal to the output of the amplifier. If there is any error a correcting signal is sent through the amplifier to eliminate the error. In theory this is a fine way to do things if the amplifier is infinitely fast. It takes time, however, for the signal to get from the input to the output. This delay produces continual overcorrection of any errors. This “hunting” for the correct signal injects a correlated noise into the output signal. Our ears are very good at detecting correlated noise. Correlated noise is a somewhat random signal that is related to the audio one is listening to. In this case it generates a masking of the inner detail of the music, the tonal nuance. This might be heard in the strident sound of a clave or the lack of an extended ring of a bell.

Many amplifiers rate their distortion at full level. The constant hunting can be the major component of the THD+N measurement quoted. Most music is played at 1 watt rather than 100 watts. Listening at this level effectively raises the distortion voltage by 10 times. A distortion rated at 0.01% can now become 0.1%. This is quite audible but is generally not consciously identifiable. It is most noted in the lack of musicality and detail.

Low and no feedback output stages do not use feedback loops to correct for errors in the output stage. Many techniques are possible, but the desire is for an instant response to errors with no overshoot and to the correct value. Superlative audio amplifiers have this type of output stage. Through the use of very low impedance highly biased Class AB amplifiers it is possible to produce necessary high speed and high damping factor performance. With no output feedback loop, massive power supply regulation, high output currents and 100MHz bandwidth, the Superlative Audio output stage gives open transparent sound with no hardness, impeccable musical nuance and startling dynamics.

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Why are there so many output devices and power supplies?

Large output devices that can safely handle the output current needs of a power amplifier have many undisireable attributes. This can include everything from changing base-collectors capacitances to heat induced transient gain changes. High frequency safe operation is very hard to achieve with a few large output devices. Superlative uses many low power almost “perfect” devices to achieve the performance needed for open loop output stage operation.

The abundance of line conditioners sold today indicate that power sourcing and power supply stability are a big factor in many amplifiers. Through the use of distributed regulation and bypass capacitance right at the output devices there is little deterioration of the output stage performance created by series impedances in components or wiring. The dynamics and solid base of Superlative amplifiers are the result.

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Why is the input and output bandwidths so high?

Any amplifier when pushed to its characteristic speed limit begins to introduce artifacts into the sound. This can include slew rate limited distortion, asymetric rise times, overshoot, undershoot and various forms of intermodulation distortion. In general it is best to have each stage of an amplifier be ten times faster than the previous stage. With most amplifiers the opposite is true. The input stage is the fastest component, the output stage is the slowest and the feed back has a low pass filter integrated into it. The fast correction of the input stage overshoots to correct for the errors caused by a slow output stage and the slowed down feedback tries to correct for the errors and the overshoot.

In the Superlative Audio SAA-250 amplifier the bandwidth is limited by a simple filter before the first stage with the first stages open loop full signal bandwidth being ten times higher. The output stage has a bandwidh of over ten times higher than the first stage. Bandwidth limited effects are nonexistent.

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Why can these amplifiers drive difficult loads?

Through the use of a large number of smaller output devices it is possible to run the devices completely in their safe operating areas. Each output device has its own protection circuit that keeps it in its safe operating area. When there is a short circuit the input stage is automatically and instantly limited so it cannot overdrive the output stage. Superlative amplifiers are designed to drive difficult loads so they can run at full performance into an almost short circuit. As long as the total current needed is less than the maximum drive current the amplifier can provide a pristine output with no hangover from traditional current limiting circuits interacting with the negative feedback loop of the amplifier.

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