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IDS-25
Frequently Asked Questions
Answers directly from the
Designer and Originator
Roger Russell
1. What do the letters IDS stand for?
2. Why does the IDS-25
have better imaging, depth and spaciousness ?
3. What is image distortion?
4. Is the IDS-25 a dipole
radiator?
5. Does the system have a “sweet spot” where you must sit for good
sound?
6. How does
the IDS-25 column avoid room reflections and resonances?
7. Why must the column be so tall and will a short column work just
as well?
8. The system is too tall for my living room ceiling height, what do
I do?
9. Can I use these
speakers in a smaller room?
10 Why is an equalizer
required?
11. Why doesn’t the equalizer have different frequency controls?
12. Why does
the equalizer have a mode IN-OUT switch?
13. Doesn’t the extra power demand from the bass boost hurt the small
drivers?
14. How can such little cones provide any bass, even with the
equalizer?
15. What is so
unique about these drivers?
16. What is the
power handling for the system?
17. Does
the system have protection from excessive power?
18. Is there a problem with IM distortion when covering a wide
frequency range?
19. What about Doppler distortion when the drivers handle lows and
highs?
20 What about comb-filter effects caused by the driver spacing?
21. Why is the sensitivity of the IDS-25 system higher than one of
the drivers?
22. How good
is the transient response of the system?
23.
What are the advantages of eliminating crossover networks?
24. How low does the
impedance get?
25. What
would it be like to hear the IDS-25?
26. What are the dimensions, how much floor space does the
system require?
27. What is
single, wide range, line source?
28. What is
coherence?
1. What do the letters IDS
stand for?
They describe the
outstanding features of the system: imaging, depth and spaciousness. The
goal was to create a system that would faithfully reveal these listening.
Imaging is the
ability of a speaker to accurately reproduce stereo information so that the
listener is able to locate instruments as they were positioned in the actual
performance or as they were mixed.
Depth is the
illusion that the instruments are located at various distances behind the
plane formed by the two speakers.
Spaciousness is the
illusion of size, either natural or artificial, giving the impression of a
very large room or enclosure having reflections with various amplitudes,
time delays or frequency shifts. The synthesized spaciousness used today in
popular and electronic music is extremely appealing.
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2. Why does the IDS-25
have better imaging, depth and spaciousness than other systems?
ALL of the
frequencies are radiated from the same wide-range drivers that are all in
the same vertical line. There is no image distortion. This offers greater
accuracy over multiple columns.
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3. What is image distortion?
An example of image
distortion is when the fundamental tone of a violin is in one place but the
harmonics of that note are in other places. The location and sound of the
complete instrument is indistinct. However, if all of the sound from the
violin comes from the same point in space, the sound is more realistic. When
all the instruments are playing it enables you to experience their total
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. The superior imaging of the IDS-25 lets you audibly locate the
entire characteristic sound of each instrument more accurately in space and
the details are incredibly realistic. The images remain stable, in your
listening environment, regardless of frequency or your position in that
environment.
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4. Is the IDS-25 a dipole
radiator?
No. 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.
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5. Does the system have a “sweet spot” where you must sit for good sound?
No. In the vertical
dimension, the sound will always appear to come from an area centered at the
region of your listening height. For many systems, the sound changes when
you are standing and then sit down. When you try this with the IDS-25, the
sound, whether it is stereo or monophonic, does not change at any listening
height.
In the horizontal
dimension, stereo sound can seem to come from almost anywhere but the
speakers. Sounds can be located in a wide horizontal area. Even if you are
listening way over to one side, you can still hear excellent stereo, depth
and spaciousness.
When listening to
monophonic material, the sound image will appear to be exactly in the center
between the speakers at all frequencies. However, a monophonic image will
follow you as you move from left to right and if you are directly in front
of one speaker, the sound will appear to come only from that speaker and not
the other one.
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.
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6. How does
the IDS-25 column avoid room reflections?
The IDS-25 column is
very directional vertically but it extends essentially from floor to
ceiling. It means that floor and ceiling reflections over most of the
frequency range that would normally interfere with the direct radiation are
effectively eliminated. At the same time, the horizontal dispersion provided
by the small drivers in the IDS-25 ensures a wide radiation angle over most
of the frequency range. This is a significant advantage over normal systems
that not only radiate sound as much vertically as horizontally but also
exhibit response changes with listening height. As a result, the IDS-25 is
able to fill the room with sound much more uniformly and at the same time
maintain better stereo listening further into your listening room.
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 a subwoofer or subwoofers located on the
floor may build up fewer resonances but at much higher amplitude.
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7. Why must the column be so tall? Will a short column work just as well?
A column of half the
height has much less power handling and also has reduced acoustic gain,
making the efficiency of a short system much lower. These two factors work
against each other by requiring more power but having less power handling
ability. You lose the design benefits of the IDS-25 design. In addition, the
short column will exhibit vertical directionality and the sound will be
different for a standing versus a sitting position, requiring more power for
the same listening level.
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8. The system is too tall for my living room ceiling height. What do I
do?
The IDS-25 is a
custom made system. The cabinets can be made one or two drivers shorter with
no serious loss in performance. This will allow the user to fit them in
their home and still enjoy all the benefits of the IDS design.
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9. Can I use these
speakers in a smaller room?
The IDS-25 is ideal
for use even in smaller rooms. Close listening is not a problem because each
driver covers the entire frequency range and the sound level changes
relatively little as you get closer. You can walk right up to the column and
not be aware of any increase in loudness.
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10. Why is an equalizer required?
The response of the
drivers is unusually smooth and extended. However, they do not cover the
entire frequency range uniformly. The system by itself cannot deliver deep
bass. However, by boosting the bass using the equalizer, bass can be
extended to below 25 Hz. In the same way, the equalizer can extend the highs
to 20 kHz and compensate for losses when the drivers are arranged in a
column. The equalizer is carefully tailored to exactly complement the
drivers in the column arrangement.
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11. Why doesn’t the equalizer have different frequency controls?
The equalizer is
part of the speaker system design and is not intended to duplicate the
function of the tone controls that are in your preamplifier. Tone controls
are best suited to supplement the tonal balance of program material.
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12. Why does
the equalizer have a mode IN-OUT switch?
This switch provides
a bypass for the equalizer and response is flat in the OUT position. It
means that you can leave the equalizer connected between the preamplifier
and power amplifier when you temporarily use a speaker other than the
IDS-25. The switch must be at the IN position when playing the IDS-25.
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13. Doesn’t the extra power demand from the bass boost hurt the small
drivers?
At first glance,
your impression would be exactly right. However, when all the drivers are
used in a long column, there is a 10 dB acoustic gain over much of the
frequency range compared to a single driver, making the resulting efficiency
of the column much higher. Only one tenth of the power is needed for the
same listening level.
In addition, there
are 25 drivers, each of which will handle at least 10 watts. The entire
column will handle 250 watts and still not exceed the single driver power
handling.
The heat dissipation
capability at high power is outstanding with 25 voice coils per channel. A
single coil used in one large woofer is not able to dissipate heat as
effectively in comparison.
Also, since the
system will handle such high power over the entire frequency range, it means
that the mid and high frequency peaks can be handled effortlessly, far
better than a system having a single mid-range and tweeter.
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14. How can such little cones provide any bass, even with the equalizer?
It is true that
these 3-1/2” drivers are very small compared to the 12” or 15” woofers that
you are used to seeing in a system having good bass capability. You might
think of the IDS-25 as a woofer made of 25 individual diaphragms all working
together. Each one has an effective cone area of only 5.7 square inches.
However, when combined together, the effective cone area of 142.5 square
inches is equal to that of a sixteen-inch woofer and they couple to the
surrounding air very nicely. The equalizer then provides the means to
achieve a smooth and extended response for the deepest bass.
The large effective
cone area of the IDS-25 not only delivers excellent bass but also effortless
sound through the rest of the audio range and fills the room from top to
bottom.
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15. What is so unique
about these drivers?
This excellent
driver has a copper shorting cylinder around the pole piece. Unlike some
shorting ring designs, the ring extends through the entire height of the gap
and beyond. This is known to reduce distortion, particularly in the voice
range, by a factor of 10 or more. The ring also greatly reduces any
impedance rise at the higher frequencies that would otherwise reduce high
frequency output.
In addition, the
cone is made of a woven fiberglass material. This type of textile
construction has been used in various dome midranges and tweeters for many
years and has proven to furnish smoother response and without the peaks
sometimes found in rigid materials such as those having metal cone or dome
construction.
What's more, the
entire magnet assembly is shielded. The magnet structure is not only reverse
polarized but also has an external steel cover as well. It reduces stray
magnetic fields that could affect the picture of a television set or other
devices if placed in close proximity.
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 square
basket allows closer spacing between the drivers.
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16. What is the
power handling for the system?
The maximum peak
power for the IDS-25 is rated at 200 watts. However, because of the higher
efficiency over much of the frequency range, most of the time, you will need
no more than 2 watts.
However, at the
lowest frequencies, the bass boost from the equalizer increases power to the
column in order to maintain a constant low frequency output. As the
frequency goes lower, the power to the column gradually increases. At the
lowest frequency of 20 Hz, the power requirement can be up to 100 times
greater. It is very rare in music that frequencies this low will require
this much power. A power amplifier of 200 or even 250 watts is more than
adequate for the loudest of listening levels at the lowest frequencies.
At high frequencies,
a boost from the equalizer also increases power to the column to accomplish
a constant output. As the frequency goes higher, the power to the column
gradually increases. At the highest frequency of 20 kHz, the power
requirement can be 10 times greater. This is not a problem for the IDS-25.
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17. Does
the system have protection from excessive power?
Yes. The IDS-25 will
easily handle short-term power peaks found in music. It is protected against
long term, high power levels but there is no guarantee that this circuitry
will protect against all types of program material. Care must be taken when
the sound becomes distorted at excessive levels, particularly at the lowest
bass frequencies. Turn the volume down and wait for ten seconds and then
play the system at a lower level for that particular passage. This will
allow time for the automatic protection circuit to reset.
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18. Isn’t there a problem with intermodulation distortion for a driver
covering such a wide frequency range?
No. 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 through the entire length of the voice coil
gap. This shorting cylinder is known to significantly reduce distortion
contributed by the magnet structure to one tenth of conventional driver
distortion. This improvement is particularly noticeable in the voice range.
The diameter of the cone is small compared to the voice coil diameter and
also contributes to lower distortion.
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19. What about Doppler distortion when the drivers handle lows as well as
highs?
Doppler distortion
occurs when the cone motion at low frequencies shifts the higher frequencies
up and down at the low frequency rate. The longer the low frequency cone
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.
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20. What about comb filter effects caused by the driver spacing?
The closer the
drivers are, the less perceptible any variation in sound is. A spacing of
one foot between drivers is obviously too large and if you put your ear six
inches from such a column and move up and down, you will be able to clearly
hear individual sources, even far back into the room. However, the
closely-spaced drivers used in the IDS-25 perform far better. With music,
you can come as close as one foot and the sound still appears to be
continuous.
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21. Why is the sensitivity of the IDS-25 system higher than only one of the
drivers.
There are two
reasons for greater effective sensitivity compared to a conventional system.
First, there is an inherent 10 dB increase in acoustic gain from this long
array over most of the frequency range. Second, the sound is radiated in a
cylindrical pattern from floor to ceiling. The sound level decreases at only
3 dB for each doubling of listening distance.
In a conventional
system, such as one having a single woofer, mid and tweeter, the sound is
radiated in a spherical pattern in each frequency range. The sound level
decreases 6 dB for each doubling of listening distance.
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22. How good
is the transient response of the system?
The transient
response of the system is excellent. Good transients or “fast speakers”
depend on a driver with a wide bandwidth and low moving mass. The drivers
are inherently wide bandwidth. The weight of the moving parts of each IDS
driver is very light, measuring only 2.5 grams or 0.088 ounces compared to
45 grams or more for a 12-inch woofer.
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23.
What are the advantages of eliminating crossover networks?
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. Conventional systems,
having a woofer, tweeter and perhaps a mid-range as well, require
crossovers, either passive or active. 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 eliminates the debate
about which passive components sound the best. Electronic crossovers require
extra amplifiers, adding a significant cost to a system.
Either method
involves common difficulties. In the area of the crossover frequency, both
drivers radiate the same frequencies and may interfere with each other
causing uneven response around the system. A different physical location for
each driver adds to the problems.
More importantly,
and perhaps not so obvious, is that a driver 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, all of this can be avoided and a
continuous coherent spectrum can be presented.
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24. How low does the impedance
get?
The impedance is
7.2 ohms or higher throughout the frequency range. The rated impedance is
8-ohms. The impedance of some systems using crossover networks can dip far
below the advertised impedance and cause a mismatch to the power amplifier.
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25. 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 would definitely need 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. The coherence, when
an entire orchestra is playing, is simply 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 the
performance and what the artist has created. Not only is the sound from the
IDS-25 effortless but it also 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.
Even if you have
been able to distinguish a few of these qualities 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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26. What are the dimensions and how much floor space does the system
require?
Many systems,
particularly when 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 7-1/2" wide (tapering to 5-1/2" in front) and 9-1/4"
deep. The height with the base is 88-3/4” and 87-1/4” without the base.
Because the IDS-25 is capable of significant output down to 20 Hz, no
subwoofer is needed.
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27. What is
single, wide range, line source?
This is our patented propagation system where all
frequencies radiate from a single plane, in other words, in a straight line.
By using full range drivers each center of effort, or cone position, is
perfectly aligned with all others creating a precise line source for the
sound. The uniqueness of this system is by using full range drivers we have
no phase shift distortion from placing the center of effort for the larger,
bass drivers behind those of mids or of tweeters. It becomes a perfect
aligned source for your listening pleasure.
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28. What is coherence?
Coherence is the ability of the speaker to recreate the original sound in
a faithful manner without inducing unnatural reflections and distortion
which is not found in the original composition.
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