The MODEL R

An I M FRIED "Signature Series" Loudspeaker

USER SPECIFICATIONS
Size: 28" high, 16" wide, 14 3/4" deep
Drive complement: 8" x 12" flat piston bass unit, visco elastic damped Bextrene
5" laminated plastic mid driver 3/4" melinex dome treble unit
Impulse and frequency response: Adjusted for optimum balance; frequency response, substantially flat 25Hz - 30 KHz Impulse response adjustable by "Impulse Perspective" Control
Crossovers: 200 Hz 3.5KHz, phase compensated and impulse damped
Efficiency: 25W. for 100db SPL (3 ft. on axis, noise, anechoic)
Impedance: Eight ohms
Supplied in matched, mirror image pairs only.
Weight: Sixty-six pounds each.
Accessory stands available.
Guarantee: Two years in "normal use".

Model R Series I I is the first loudspeaker in the I M FRIED "Signature Series". The "Signature Series" denotes loudspeakers designed and built to the most advanced specifications, the most modern performance standards for speakers of that type. On such loudspeakers are placed the name of the founder of the famous line of monitoring quality loudspeakers known as "I M F".

Model R Series II well deserves to be in that refined category, since it is an advance on previous designs, in some ways a dramatic improvement; bringing "monitoring quality" reproduction together with higher reproducing levels, for the first time. We want to explain how we managed to create a moderately priced loudspeaker of "monitoring quality", which also will play at loudness levels approximating the original program.

The predecessor of Model R Series II was the Model R, our first loudspeaker for the modern age of louder playback. Series I I is an improvement on that; a completely new crossover system, resulting from our continuous research program, permits high level playback with superior overall quality to any former loudspeaker done by us! Indeed, Model R Series II has more dynamic range and more sheer musical quality than any equally sized loudspeaker we know! We can assert the superiority of Model R Series II, because its materials, its technology, and its overall design represent better ways of making high quality loudspeakers.

Model R Series I I is by quality and design a true monitoring loudspeaker. Our former designs, such as the MONITOR and the STUDIO, established a world wide reputation for quality, provided that they were used under carefully controlled conditions, with the very finest input gear. Model R Series II is much less sensitive to input gear, much less touchy. Let us enumerate the technological innovations that make Model R Series I I unique.

I. The Drive System

Model R is a three way loudspeaker, with three drivers, each of which is produced under controlled lab conditions, of plastic formulations; rather than the now-obsolescent paper; for the purpose of high quality music reproduction. Illustration 1 shows the driver line up, in a "right hand" loudspeaker (see below for explanation on this). The BBC Researches, which we quoted in Newsletter 7, long ago established the superiority of plastic laminate cones, or diaphragms, over the traditional paper cones, where accuracy of reproduction was important-as in monitoring loudspeakers. We have been the prime exponents of plastic drive systems for home use, the world over, quoting the basic and essential superiorities, to wit:

Plastic laminate cones are essentially "dead", acoustically. Paper cones are resonant, and have coloration effects. The "sound" of plastic cones is more accurate and easier on the ears.
Plastic laminate cones are acoustically opaque, so that sounds from inside the speaker enclosure, caused by radiation from the back of the cone, and reflected back to it, are blocked. Paper cones are acoustically transparent, passing virtually all the sounds from inside, delayed in time, and thus smearing the reproduction.

3) Plastic cones have a predictable performance, built to very close tolerances. It has been said that the performance of a paper cone loudspeaker is statistically unpredictable; in addition to which, it changes with temperature, humidity, and age.

Plastic cones are the advanced cones. They do cost more than conventional paper cones, and, we assert, are well worth it. Using a paper cone in a loudspeaker is tantamount to saying that the speaker is not intended for critical applications just as in automobiles, if the manufacturer engineers fully independent suspensions, instead of "wagon axles", he is announcing his intention to make an automobile for the quality minded! Model R Series II, in our long tradition, employs only plastic laminate drivers, with the very latest refinements, permitting higher level operation.

II. The Enclosure

Model R Series I I has two totally separate systems inside its cabinet, a transmission line for the mid range, and a resistive line tunnel for the bass (see Illustration 2). Like all our previous monitor oriented loudspeakers, and for the same reasons, the mid line provides a better way of reproducing the vital mid frequencies, better than the usual closed back cone or dome configurations used in virtually all commercial loudspeakers. Model R's mid line contains a newly developed "corkscrew damping" technique, reducing backpressures on the driver, and damping the back waves more effectively, so that they are "lost" at the other end of the line. The new damping system improves mid range clarity, ambience, and overall "presence", since the driver is working under virtual free field conditions. Compared to the mid range of Model R Series II, sealed mid ranges produce pronounced "coloration" effects-as one British manufacturer says, makes everything "sound as if you are speaking into a bucket!"

The resistive line tunnel used for the bass driver is a relatively recent development, refined as result of extensive lab and field experience with the Model R Series I loudspeakers. The entire rationale for this new approach to bass propagation is to preserve transient performance, while increasing power handling. The bass system used is a far cry from the conventional "piece of paper in a box" bass systems (known in U.S. as "Air suspension", in England as "Totally enclosed box")-and the performance on musical passages is overwhelmingly superior, both technically and audibly. So that we wish to go into detail, pointing out the specific areas of difference, and why:

The driver: Newest version of the world-famous KEF flat piston woofer, with high temperature voice coil. This woofer has its geometric propagating point in front of the propagating point of the mid driver, eliminating geometric time delay distortion. Conventional loudspeakers use deep dished paper cones, creating severe time delay problems (among others).
The enclosure damping: Behind the woofer, and stretching top to bottom, are edge on acoustic foam filters (see Illustration 2). These, developed and adapted from previous designs, permit controlled damping of the air flow from the rear of the driver, without hampering the air flow. Our previous work has shown that restricting air flow near a driver is a prime cause of "boxy" sound; technically, restrictive damping produces "early» reflections back at the cone (just as for a mid range), and resonant pockets. The conventional damping techniques, which we long ago termed "stuffed" damping, do just this, restrict air flow and produce "boxy", resonant upper bass.
The resistive tunnel itself: Were this tunnel open, we would have a classically tuned "reflex" system. Instead, we have developed a graded foam damping system, which acts as a resistance across the tuned system. This resistance reduces the "Q" of the upper resonant peak, which otherwise would cause problems with subsonic inputs. The resistive tunnel is, in effect, a simple "line" with the major defect of lines removed (i.e., the sensitivity to subsonic disturbances). The net effect is to smooth out the impedance curve, for better power transfer, to augment the very low bass (down to 22Hz), and minimize subsonic disturbances. Conventional practice is to close the box completely, producing violent impedance rises, and the "heavy", "mushy" characteristic distortions of stuffed, sealed boxes.

The bass system of Model R Series I I is a transient-capable assembly, capable of reproducing fast bass transients with enormous dynamic content, i.e., the nature of live musical bass passages. By comparison, the "sealed, stuffed box" approach lacks dynamic range, clarity, and "life". Recent research findings (see our Newsletter 9) explain the reason; the boxes produce an extreme distortion of transient inputs, termed "transient intermodulation" distortion; and that leads to a "time smear" of transient data! The only justification for sealed boxes, in the light of modern research findings, is cost-they are easier to design, and can work with cheaper drivers, and are adequate for "commercial" results.

III. The Crossover System:

Crossover design is now the subject of intense investigation all over the world, occasioned by the new criteria of impulse performance as the most important measurement of a loudspeaker (cf. Newsletter 10). Model R Series I I is most startlingly advanced over Series I, as well as our earlier designs, by its new crossover system! (which can be fitted to earlier Series Is). We have been leaders in applying these new techniques to loudspeakers, are thankful for the research done on our Model H and all to-be-issued "Signature Series" loudspeakers.

The crossover from woofer to mid is the most critical region in any high quality system. Indeed, it is because this is so critical that we are on record against sub woofer add ons (see Newsletter 11).

The point of transition should be as low as possible (dependent on drivers, cost of crossover parts, space), and as smooth as possible. I n Model R, Series II, we have developed, in cooperation with authorities in England, a new woofer to mid system for this vital area, with an inflection point approximately a full octave below that of our previous loudspeakers. Since the human hearing apparatus is less phase sensitive at lower frequencies, since wavelengths of sound are longer at 200 Hz than at 400 Hz, the transition region is smoother than in our previous designs. Thus is removed another source of transient distortion from the midrange. Indeed, by comparison, loudspeakers with higher bass to mid transition points must be "jumbled". You can hear the result of higher transition points quite easily on continuous passages, such as orchestral strings; you can hear a fluctuation, or wavering, from "transient burp" effect; which is just another kind of pernicious speaker distortion we would be better without. Why do other manufacturers use higher crossover points? To save money!

The mid to treble dome is phase and step compensated, and is at 3.5KHz, well out of the region of ear sensitivity. The result is that Model R Series I I is more integrated in sound image, and retains its listening integrity better at high levels, than any of our previous designs. One old timer commented to us that Model R Series I I reminded him of nothing so much, in this "all together" sense, as the single cone horn drivers of another day! He commented that many listeners would not like a loudspeaker that hung together, so accustomed had they become to unintegrated designs. Be that as it may, the crossover system of Model R Series II is responsible for the sound integrity of the speaker, and that we will not prejudice.

There is only one control adjustment, which we have called the "Impulse-Perspective" Control. A three position toggle switch is marked "Plus", "Neutral", and "Minus". "Plus" is maximum rise time; "Neutral" is recommended for most quality program; and "Minus" is recommended for distorted program.

As a monitoring quality loudspeaker, Model R Series II should be used free standing, i.e., preferably on a pedestal, and away from walls, floors, and corners. This loudspeaker produces true bass fundamentals in such room position; whereas we have long asserted that speakers requiring "reinforcement" from walls and corners, in effect trigger room resonances, producing "room coloration". Aside from the unpleasant, boomy, or hollow characteristic of "room coloration", it tends to cover over the original characteristics of the room where the recording is made-and that a high quality reproducer should not do.

Therefore, like our previous designs, Model R Series II is built in "mirror image" pairs, Illustration 1 being of a right hand speaker; a left hand speaker has the mid and dome at the right edge. This technique, adapted from monitoring practice, helps to control diffraction effects; secondary radiation, the step in response, etc. It also bends the sound image toward the center of the listening area, toward the listener and away from the walls, which are sound distorting. This comprises our now famous system of "inward dispersion", part of the reason for the startlingly accurate stereo image from Model R Series II.

Cumulatively, you can see that Model R Series I I is a high quality, advanced loudspeaker. It is not a hastily assembled "miracle" speaker, pretending to repeal the laws of physics and acoustics. Rather, it is a loudspeaker which bears witness to our long time involvement with advanced, monitoring quality loudspeakers; and shows how the art is still progressing. Let us summarize what it can do, compared to our own best design efforts of a short time ago:

Reproducing level. It will play safely at higher levels. Actually, it will play at peak levels over those one encounters in the concert hall, and with the same transient linearity (or better) as our earlier loudspeakers. It can reproduce high level program even with less than ideal input gear-turntables, tone arms, amplifiers.
Dynamic range. We define dynamic range as the alternation of level, usually almost instantaneous, between pp and ff (very soft and very' loud). Model Rs from the beginning have had this quality, very impressive to first time listeners. The new crossover in Series I I increases the dynamic power handling-which also is a function of plastic drivers (no buckling pieces of paper), and transient proper enclosure (no distortion from sealed boxes and mills). The first time listener, unaccustomed to loudspeakers with dynamic range, invariably sets program level on the low passages too loud-he doesn't expect the incredible increase in loudness when the crescendi arrive. It takes a bit of time to readjust one's listening patterns to dynamic linearity)
Resolution of musical passages. "Resolution" is a technical phrase denoting that fundamentals and harmonics arrive in proper time sequence. It does contribute to greater instantaneous pressures (dynamic range). Next, one notices more accurate reproduction of the original timbres of various instruments (including that most difficult of all instruments, the singing human voice). Voice and piano are most different from their sound on ordinary loudspeakers. Next, woodwinds have an entirely different sound.
One doesn't have to guess whether it is an oboe, a clarinet, or a bassoon-you can hear the differences; indeed, you can hear whether it is an English or a French oboe! Percussion is vivid; a bass drum does not get confused with a tuba (as in so many speakers -try it!).
Spatial accuracy. Monitoring loudspeakers are intended to portray actual microphone placements, and actual source sizes. Model R does this better than any of our previous loudspeakers, mostly by eliminating "Venetian blind" effect, and improving smoothness of dispersion. Model R Series II avoids any semblance of six foot tall soprano voices, thirty foot piano keyboards, or wandering violin soloists playing "ghost image" duets or trios-all of these obnoxious effects from "source wander" or "phase bloat".
Bass propagation. Model R Series II continues our tradition of providing real bass propagation, rather, than "box boom". It has a smoother impedance characteristic (i.e., better damping) than former designs; thus avoiding any tendency toward bass heaviness in heavily furnished rooms (a proper criticism of some of our earlier loudspeakers). Piano in particular seems to benefit, along with any rapid, deep percussive.

Model R Series II is a modern, high definition transducer. Some people, first hearing it, may think it "too clear", "too bright", or "lacking warmth". We suggest they keep listening; for we have heard the self-same comments for decades, each time we introduced more accurate loudspeakers. People do tend to like what they know-and most of them are conditioned to conventional loudspeakers with the "time smear" distortions so effectively removed from Model R Series II. Interestingly, as in the past, the first listeners who always respond immediately are those involved in live music-orchestral soloists, singers, et al. Indeed, for all of you, we do suggest that you compare Model R Series II to live instruments-and not to old style loudspeakers.

Model R is a highly revealing loudspeaker, a true monitoring loudspeaker. As such, it operates from any stable, reliable amplifier (suggested 25 to 100W. per channel). It is not a touchy loudspeaker. It has inbuilt fusing protection against gross overdriving or amplifier failure. An instruction sheet with each loudspeaker gives advice on proper installation and use of the Model R Series II loudspeaker. We recommend Model R Series II for use wherever the most advanced standards of accuracy are required or wanted.

Like all I M FRIED "Signature Series" loudspeakers, Model R Series II is warranted in normal use (two years for Model R), to provide monitoring quality reproduction of any program source. Model R Series II is sold and serviced by franchised dealers, selected for their ability to satisfy the needs of perfectionist music lovers. Model R Series II is one of a new range of loudspeakers for such people.

I M FRIED PRODUCTS CO.
7616 City Line Ave.
Phila., Pa. 19151