Introducing the IDS-25

 

Stereo Loudspeaker System

 

We hope you will be rewarded with a new and wonderful listening experience for all the music that you love to hear.

 

The IDS concept is specifically intended to recreate all of the stereo information as it was recorded. It brings to the listener accurate details of the artist's work, whether it is a recording of a traditional symphony orchestra or of electronic instruments. The design eliminates major problems that have plagued conventional systems for many years. There are no woofers, mid-ranges or tweeters and no crossovers. No subwoofers are needed. All frequencies are radiated from a single wide-range column.

 

If you are a true lover of music and you prefer a system that has greater accuracy and brings out all of the imaging, depth, spaciousness and coherence in the music, then you will appreciate what the IDS-25 can do for you.

 

This is definitely a connoisseur system intended to be like fine wine or fine art to be savored for what it can reveal. There are many people who still want honest-to-goodness stereo sound of the finest quality. Listening is also most enjoyable when you can have a dynamic range that matches a live classical music performance, big band sound, smooth jazz or your favorite vocalist. The sound from the IDS-25 remains completely faithful from the softest to the loudest passages.

 

 

 

 

 

 

 

 

 

 

 

Meet the Designer

 

Interest in sound, for Roger Russell, may have started as early as fourth grade when he was taking violin lessons. By ninth grade, he became a devoted listener to all kinds of classical music. In the early 1950's, good sound was hard to find and nothing seemed to accurately reproduce a violin. There were all kinds of speakers available and they were all lacking in one quality or another. There had to be something better and he was determined to find a way to improve speaker performance.

 

His first exposure to stereo recordings was in the early 1950’s when he heard Emory Cook’s binaural demonstrations and the AM-FM stereo broadcasts from WQXR in New York City. He was soon using a Viking stereo tape deck and two Telefunken dynamic microphones to make stereo recordings of a Wurlitzer pipe organ at the Lowes Theater in New Rochelle, NY. This was later followed with a Magnecord professional recorder that he used to record a few concerts, thunderstorms and even diesel trains at Harmon, NY.

 

After graduating in 1959 from Rensselaer Polytechnic Institute in Troy, NY with a degree in Electrical Engineering, he gained experience while working as a senior engineer in the Audio Products Section of the Sonotone Corporation in Elmsford, NY, a well known manufacturer of hearing aids and other audio products. He spent 8 years there designing a new line of loudspeakers and microphones. Russell also wrote his first two magazine articles about a stereo volume expander-compressor and sealed speaker system design.

 

Following this, he was Director of Acoustic Research at McIntosh Laboratory for 25 years. While there, he designed the C26 preamplifier, a wide variety of speaker systems, and was awarded several patents. He continued to write magazine articles as well as pursue other interests in photography, painting and music. He was also a member of the Audio Engineering Society and the International Society for General Semantics. Pictured at the left is the designer and one of his earlier creations.

 

Today, after devoting much of his life to designing loudspeakers, crossover networks and cabinets, veteran designer Roger Russell has arrived at the simplest and yet most effective of all of his creations. Compared to the complexity of many systems made over the years by a host of different manufacturers, straightforwardness and simplicity can still be found to be the best of all worlds. In his pursuit of stereo sound over the years, he became even more resolved to create a loudspeaker system that could dramatically advance accuracy for stereo sound. The result is the new IDS-25 stereo loudspeaker system.

In Search of True Stereo Sound

It is interesting to note that almost all recordings are made with a small, single diaphragm microphone that handles the entire frequency range; but when it comes to speakers, drivers are almost always divided into at least a woofer and a tweeter or even more. A woofer needs to be large in order to move a lot of air. A tweeter needs to be smaller, lighter, and maintain wide dispersion. Although a microphone can be used in reverse as a driver, as in headphones, a single small driver is only useful for low power and/or close listening. You certainly can't shake the room with concert hall sound. It handles very little power, and has practically no bass output.

 

The IDS-25 system is a single column of identical wide-range drivers that cover the entire frequency range. That's right, the entire frequency range radiates from the same line source. There are no crossovers, woofers, mids or tweeters. The concept is an extension of two of his patents. Patent number 4,267,405 Stereo Speaker System for Creating Stereo Images is for drivers arranged in a long column. Patent number 3,715,501 Loudspeaker System is for the use of equalization to compensate for the natural low frequency rolloff of a loudspeaker system.

 

Some designs depend on drivers that face in different directions or have radiation from the rear as well as the front. This approach uses the room environment to provide multiple reflections that are supposed to be like what happens in a concert hall. However, in the real world, the reflections and absorption of the listening environment control this “room sound” and each listening room is different. This is hardly the way to convey what is in the recording by adding extra room sound to the concert hall sound already in the recording. In addition, a dipole speaker must be placed out in the room. The IDS-25 was designed to be used within a few inches of the wall. The IDS 25 preserves the recording and minimizes the room sound. It does this using only a single column that radiates only from the front and distributes all frequencies throughout the height of the room.

 

Drivers in a Column

The IDS-25 Stereo Loudspeaker System incorporates twenty five 3-1/2" drivers arranged in an 88-3/4" high column. The advertised driver size is deceiving because that is not the size of the actual moving part. The effective diameter is only 2-11/16". So how can a few small drivers shake the room? First, if you add up the area of all the cones, the combined effective area is equal to a 16" woofer—impressive! Because the effective cone area is very large, very little excursion is needed to efficiently couple to the air. A smaller cone area with a longer excursion will not couple to the air nearly as effectively. Despite the large effective area, however, these drivers are in a relatively small enclosure and by themselves cannot provide significant output at the lowest frequencies. That is where the equalizer comes into play and is described further on.

 

Radiation Characteristics

Column systems have been used successfully for many years as a public address loudspeaker. It was valuable for its high power handling ability and directional properties. The narrow vertical beam eliminates sound being radiated above or below the audience where it is not wanted and that could cause acoustical feedback to the microphone. At the same time, it radiates over a wide horizontal angle to give adequate coverage where it is wanted.

The IDS-25 is very directional vertically but the column extends from floor to ceiling. It means that floor and ceiling reflections that would normally interfere with the direct radiation are effectively eliminated over most of the frequency range. At the same time, horizontal dispersion provided by the very small drivers, ensures a wide radiation angle, even at higher frequencies. This enables you to always be directly in front of the coverage area, whether you are standing or sitting. It is a significant advantage over many systems that radiate as much vertically as horizontally.

The IDS-25 has another unique feature. All frequencies are radiated as a cylindrical surface. The sound level decreases only by 3 dB for every doubling of distance. It means that you can listen closer without being overwhelmed with loud sound and makes the system ideal for use even in smaller rooms.

Normally, for a single speaker, whether it is a woofer, mid or tweeter, the sound level decreases by 6 dB for every doubling of distance. This is because each frequency is radiated as a spherical surface.

Elimination of unwanted floor and ceiling reflections, as well as less attenuation with distance, extends the useful listening area further into the room than many other systems. This is sometimes referred to as the near field, where most of the sound comes directly from the speakers and not from room reflections. When the sound is mostly from reflections, this is referred to as the far field and is room dependent. The IDS-25 can project direct sound further and extend the useful near field of your listening room from top to bottom.

In addition, low frequency room resonances are greatly reduced. This is because the lows are being radiated all along the height of each column, exciting room resonances at low amplitude. In comparison, subwoofers located on the floor can build up some resonances at very high amplitude.

The IDS-25, being a single column, has a unique sonic advantage over other column systems because ALL frequencies are being radiated from the same vertical line. This provides additional sonic clues contained in recordings that would be otherwise lost to the listener. Systems that have adjacent columns of drivers, each radiating the same or different frequency ranges can cause various degrees of image distortion and incoherence.

The Equalizer

Normally, a woofer or subwoofer must be used to extend the low frequency range. Rather than accept this as the limit for low frequencies, Russell’s earlier patent of electronic equalization is used to extend the response. The equalizer is designed to precisely complement the unique response of the drivers and is connected between the preamplifier and power amplifier. It can be used with both separate preamplifiers and power amplifiers or with receivers or integrated amplifiers that have jacks for preamp out and power amp in. Balanced and unbalanced connections are provided.

The mode switch can be used to bypass equalization. This way, you can leave the equalizer hooked up to your system but play a different speaker that does not need equalization. The equalizer can be left with the power switch at the on position and it can be powered from a switched outlet at the preamp or power amplifier.

High frequency response of the drivers is very smooth. However, a small amount of equalization is also used to maintain output at the highest frequencies.

Power Handling and Protection

How can the little drivers handle any kind of power? Not only are they small, but then the bass is being boosted as well. This seems very contradictory to good design. In fact, it seems totally unreasonable! If we look at the maximum power handling for each driver, it can handle 10 watts. If we multiply by 25, we come out with 250 watts and that's through the entire audio range! True, boosting the lows increases the power to the drivers at low frequencies, but even for very loud listening levels, much less power is needed than would be expected. This is because the IDS-25 has an inherent 10 dB of acoustic gain over most of the frequency range compared to a single diver. It means that only one tenth of the power is needed for the same listening level. As a result, typical listening levels require only one or two watts.

However, there are occasional deep bass notes, such as a bass drum, pipe organ or even the 25 Hz heartbeats in Pink Floyd's Dark Side of the Moon  that do require much higher power. To safely handle the greatest low frequency peaks, an amplifier of 200 to 250 watts is recommended. Under these conditions, the system will play all types of music as loud or as soft as desired. This is all within the peak power handling ability of the system. The quality of bass peaks is very surprising, but then, what would you expect from a pair of 16” woofers?

The IDS-25 is protected against long-term, high power music levels. If an amplifier greater than 250 watts is used for even louder listening, the protection circuit may trip but there is no guarantee that this circuitry will protect the system against all kinds of program material. In the unlikely event that the system is driven at excessive levels and the sound becomes limited or distorted, it means the protection circuit has been activated. Turn the volume down and wait for ten seconds and then play the system at lower levels for that particular passage. This will allow time for the automatic protection circuit to reset.

Of course, a lower power amplifier can be used if all listening is done at a relatively low level. However, if a low power amplifier is used for listening at high levels, the amplifier may occasionally go into clipping and sound distorted.

Technical Information

Many systems, particularly where a subwoofer is needed, take up valuable floor space. The IDS-25 has a footprint for the base that is only 14" wide and 12" deep. The column itself is only 7" wide (tapering to 6" in front) and 9-1/4" deep. Because the system is capable of significant output down to 20 Hz, no subwoofer is needed.

The IDS-25 has exceptionally low distortion. When an ordinary driver is used to cover the entire frequency range, you can expect the harmonic and intermodulation distortion to be relatively high. However, the IDS-25 drivers have the same low distortion construction used in design of soft dome mids and tweeters. The cone is actually made of woven fiberglass and dissipates energy over its entire surface, reducing edge reflections and drastically lowering distortion.

In addition, the magnet assembly employs the latest technology consisting of a copper cylinder in the voice coil gap. This shorting cylinder is known to significantly reduce distortion contributed by the magnet structure to 1/10th of conventional driver distortion. The improvement is particularly noticeable in the voice range. The copper cylinder also reduces the impedance rise normally encountered with most drivers at higher frequencies. What's more, the entire magnet assembly is shielded to eliminate any stray magnetic field that would otherwise affect the picture in some television sets or other devices.

Related to this distortion is another quantity called Doppler Distortion that is similar to intermodulation distortion. This is encountered when the same driver diaphragm radiates both low and high frequencies. The diaphragm motion at low frequencies shifts the higher frequencies up and down at the low frequency rate. The longer the low frequency excursion, the more distortion is generated. If a single driver is used, distortion would probably be audible at high levels. However, the IDS-25 is unusual because the diaphragm motion of the combined 25 drivers at low frequencies is extremely small and modulation distortion is far below audibility.

Each driver diaphragm assembly is very light, weighing only 2.5 grams. Use of a flat spider, which is the major centering device for the voice coil, assures the same linear cone travel in each direction while keeping the coil exactly centered in the magnetic gap. A thin rubber surround eliminates the possibility of deterioration often found with foam surrounds.

The heat dissipation capability at high power is incredible with 25 voice coils per channel. A single coil used in a 16" woofer is not able to dissipate heat as efficiently in comparison. Heat buildup in a voice coil can increase voice coil electrical resistance and cause the driver impedance to change.

Speaker system sensitivity today is often referenced to a driving voltage of 2.83 volts instead of 1 watt. It means a 4 ohm system will play 3 dB louder than an 8 ohm system for the same voltage. However, the 4 ohm system is actually drawing 2 watts of power from the amplifier to accomplish this while the 8 ohm system only draws one watt. This is confusing for the buyer and allows the manufacturer of the 4 ohm system to advertise what can be mistaken for higher sensitivity. The IDS-25 is 8 ohms.

Needless to say, the elimination of crossover networks takes away many of the compromises involved in juggling components, drivers and crossover frequencies to try to make the best sound using this older technology. Passive crossovers often involve losses and can cause unwanted changes to the system impedance in order to gain an improvement in response. Having no crossover in combination with the controlled impedance from use of the copper ring avoids presenting complex load impedances to the power amplifier. Having no crossover eliminates the debate about which passive components sound the best. Electronic crossovers require extra amplifiers, adding a significant cost to a system.

The Enclosure and Wiring

 

The enclosure is made of high density non-resonant panels. Cross bracing is utilized at intervals of every two drivers to ensure rigid construction. The braces are integrally locked to the front, back and side panels. The angled sides not only benefit by skewing any acoustic resonances but also provide a more attractive appearance. Acoustic material is used throughout the enclosure to effectively absorb internal sound reflections. The metal grille is designed to give protection to the drivers and at the same time be completely transparent to the sound.

 

Eighty one feet of high grade Cardas chassis wire is used in each system to interconnect all of the drivers. Cardas is one of the leaders in manufacturing high quality parts for the audio industry. All connections are wrapped and soldered to eliminate any contact resistance or corrosion problems. Cardas terminals are used to connect wires that go to the power amplifier. They are solid copper and plated with gold.

Listening Impressions

What would it be like to hear a system like this? It is overwhelming. Perhaps your first impression will be the unusually good bass response. When you first see the system, your eyes and past listening experience with small speakers may tell you that this system definitely needs a woofer or two. Common sense may tell you that you can’t possibly get any deep bass from a bunch of 3-inch drivers. But, the bass is not only impressive; it is free from ringing and “boominess” that is found in some systems.

After making an adjustment for what you see versus what you hear, more benefits can be discovered. The response of the IDS-25 is very smooth. It is free from any resonances, peaks or dips. However, this is not enough to explain the instant reaction you get when you first hear the system. I found the coherence, when an entire orchestra is playing, to be amazing. You may realize, perhaps for the first time, that the stereo image, depth and spaciousness provided by this system is totally mesmerizing and you are only aware of what the artist has created.

There are several qualities that explain how all of this comes together. First, the superior imaging of the IDS-25 lets you locate the entire characteristic sound of each instrument more accurately in space. For instance, if the fundamental tone of a violin is in one place but the harmonics of that note are in other places, the location and overall sound of the instrument is indistinct. However, if all of the sound from the violin comes from the same place, the sound appears more realistic. Then, when all the instruments are playing it enables you to experience their complete sound at their individual locations without getting all muddied up with each other. This is true whether you are listening to the softest or loudest passages. Details are incredibly realistic.

A second, and perhaps not so obvious feature, is the complete freedom from crossover networks. A driver (or drivers) used to cover one part of the frequency range does not have the same construction, tonal characteristics or dispersion characteristics as a driver covering another part of the frequency range. In the area of the crossover frequency, these differences between drivers cause sudden discontinuities in the overall sound balance. It results in a loss of valuable stereo information. By using the same driver to cover the whole frequency range, a continuous coherent spectrum can be presented and transients do not suffer.

Third, you will also experience a completely effortless sound throughout the entire frequency range. The reason is the large effective cone area that couples so well to the air. Normally, the area available for mids and highs in most systems is very small and single drivers are easily driven into distortion at higher levels. Not only is the sound from the IDS-25 effortless but it fills the room from top to bottom and appears to play louder than a typical point source system. When you combine all of these impressions it goes beyond overwhelming.

How many times have you heard about the “sweet spot” which is the only spot between the speakers where best listening can be found. This is easily revealed when you are standing and then sit down. The sound changes. When you try this with the IDS-25, the sound does not change at any listening height. When you play spacious recordings, the sound can seem to come from almost anywhere but the speakers. Sounds can be located in a wide horizontal area and centered in the region of the listening height. You can even listen as close as 2 or 3 feet from the wall that they are against and still get excellent stereo sound including spaciousness.

In addition, even if you are not listening in the center position but way over on one side, you still hear stereo, depth and spaciousness. The only exception is when listening to monophonic program material. This could be a monophonic recording or a combination of stereo sound with mono mixed as a solo at center stage. The monophonic image will follow you as you move from center to left or right.

No matter how the recordings are made, the sound images will be revealed with razor sharp accuracy when heard with a pair of the IDS-25 Stereo Loudspeaker Systems. Even if you have been able to distinguish a few of these sounds when listening to your existing speakers, the IDS-25 system can do this better because it has inherent design advantages that other systems do not have. You will most likely want to play your entire music collection over again to discover the many details and enjoyable sounds that you did not hear before.

 

 

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