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"off duty" 1970 - 1997 - eine Werbezeitung für's US Militär

Die in diesem amerikanischen (Freizeit-) Shopping-Magazin angeprie- senen Produkte waren auschließlich amerikanischen und kanadischen Militärangehörigen ausserhalb der USA zugänglich - also zu kaufen - vor allem zu ganz ungewöhnlich (verblüffend) niedrigen US $ Military-Preisen. Zu der einführenden "off duty" Seite geht es hier lang.


Nach ein paar ersten einzelnen 901 Anzeigen - (advertisements) - jetzt voll zugeschlagen ...

In der 1972er Juni Ausgabe hatte der BOSE Military Vertrieb gnadenlos zugeschlagen und 5 große A4 Anzeigen geschaltet. Das war für dieses "off duty" Magazin, das sich ja nur an aktive Militärangehörige wenden durfte, schon außergewöhnlich.
Und weil auf diesen Seiten recht ehrlich beschrieben wurde, was diese Boxen wirklich für Vorteile - natürlich immer zur damaligen Zeit 1970/1972 - erwarten ließen, sehen Sie hier alle 5 Seiten.


What's behind the BOSE 901 Speaker System?

Off Duty / Europe / June 1972 - This article is one of a series explaining the features and benefits of the Bose 901 - the most highly reviewed speaker regardless of size or price.

  • If you have heard the BOSE 901 DIRECT/REFLECTING® speaker system, or if you have read the unprecedented series of rave reviews, you already know that the 901 is the longest step forward in speaker design in perhaps two decades. Since the performance of the 901, covered by U.S. and foreign patents issued and pending, derives from an interrelated group of advances, each depending on the others for its full potential, we hope you will be interested in a fuller explanation than is possible in a single issue.

In this issue (from Off Duty), we'd like to tell you what our research revealed about the roles of direct and reflected sound in the reproduction of music. The direct sound is what you would hear if the walls and roof of the concert hall were removed. If you have ever listened to an orchestra outside, without a reflecting shell, you know that it is very soft and dull compared to what you experience in the hall. The difference is the reflected sound.

The reflected sound comes to your ears from the walls of the concert hall in almost equal quantities from all directions whereas the direct sound comes to you from the direction of the instruments. The direct sound is responsible for your sense of localization while the reflected sound contributes to the fullness, presence and warmth of the concert hall performance. As the research indicates, "this spatial property of the sound incident upon a listener is a parameter ranking in importance with the frequency spectrum of the incident energy for the subjective apprecation of music". *)

*) From 'ON THE DESIGN, MEASUREMENT AND EVALUATION OF LOUDSPEAKERS', Dr. A. G. Bose, a paper presented at the 1968 convention of the Audio Engineering Society. Copies of the complete paper are available from the Bose Corp. for fifty cents.


The 901 has eight speakers on the back panels and one on the front. This accomplishes two objectives. First, it radiates the desired ratio of about 89% reflected sound to 11 % direct sound.

Secondly, by proper choice of the angles of the rear panels (see fig.) the 901 projects the image of a musical performance spread across a stage that is located about two feet behind the speaker. This image is established to the extent that it is possible to hear the full stereo spread from a wide range of listening positions including directly in front of one speaker - a feat that is not possible with conventional speakers.

This concept of direct and reflected sound would result in an improved speaker by itself but it would fall far short of providing the realism offered by the 901. There are three other essential advances that must be used in combination with the direct and reflected sound to obtain the full benefits offered by the 901. These will be the subjects of other issues.

AD no. 2 - How does the BOSE901 eliminate audible RESONANCES?

The best known feature of the BOSE 901 is its Direct/Reflecting® design, which copies the proportion of direct to reflected sound measured in me concert hall.

But aiming a speaker at a wall does not magically give it greatness. What is not yet so well known is that even in conventional terms the 901 is a better
speaker - a more precise instrument than other speakers for converting an electrical into an acoustic signal.

The primary source of this precision is the use of an array of 9 same-size, full-range, acoustically coupled speakers in each 901. In the research that led to the 901, a digital computer was used to simulate an ideal vibrating surface "having no resonances, phase shift, diffraction, or distortion of any kind."

It was then proved (and demonstrated at a professional group meeting of the I.E.E.E. in Nov. 1964) that a multiplicity of closely spaced, acoustically coupled, full-range speakers "can produce music and speech signals in a normal listening environment that are subjectively indistinguishable from those that would be produced by an ideal pulsating sphere in the same environment." *)

Any speaker has many inherent resonances - frequencies where its response is irregular. Our research determined that when many similar speakers are closely spaced and acoustically coupled to a common chamber, the resonant frequencies of each speaker diverge from those of every other speaker. As a result, each resonance becomes inaudible, since it causes a change in the output of only one speaker of the many.

Anyone familiar with the problems of resonances in conventional speaker design will appreciate how important a discovery this is. In the case of the 901, it means that only one speaker out of 9 can be in resonance at a time - a proportion which is inaudible.

The resultant freedom from audible resonances and other forms of distortion helps to account for the utter clarity and honesty of musical performance for which the 901 has already become famous.

  • Anmerkung : Hier wird die Physik etwas zu einfach verdreht oder ausgeblendet, denn das mit dem vermittelnden Ausgleich der Resonanzfrequenzen von 9 einzelnen Tiefton-Chassis funktioniert nur, wenn die Qualitäten bzw. die Fertigungsstreuungen weit auseinander liegen. Liegen zum Beispiel die Eigenresonanzen von 9 hochpräzise gefertigten Chassis quasi übereinander, habe ich die gleiche Resonanzüberhöhung wie bei einem einzelnen Bass-Chassis.

For the present, if you would like to hear the difference that a multiplicity of full-range speakers can make (in combination with 3 other major advances), ask your franchised BOSE dealer for an A - B comparison of the 901 with the best conventional speakers - regardless of their size or price. Then, go back to your present speakers - if you can.

For complete reprints of the TECHNOLOGY BEHIND THE BOSE 901 write our European Rep: BRANDEX, 6 Frankfurt am Main, WiesenstraBe 34, Germany

AD no. 3 - BOSE on the reproduction of BASS

In other issues of this series (of ads) we have explained how a multiplicity of same-size, full-range, acoustically coupled speakers "eliminate(s) the sound coloration caused by resonances of speaker systems using only a small number of speakers and by irregularities in the 1 radiated energy spectrum of systems employing crossover networks." *)

Walnut grille modification extra. Can be added to any 901.

But how does the use of 4 inch, full-range speakers allow such spectacular
bass performance? It has always been assumed that large woofers in large enclosures are required to deliver full bass response.

The answer to this question lies in the fact that bass performance is purely a matter of how much air you can move and how well you can control its movement.

In the 901, this depends on four interrelated features.

  • A) The 'Array Effect', by which a group of proximate small speakers, moving in phase, acts like one large speaker with the area of the group.
  • B) The Special Design of the Drivers Used in the 901. These are special long-excursion, high compliance speakers with large magnets, which can move large amounts of air.
  • C) Use of the Well-Controlled "Frequency Region Below Fundamental Resonance". In conventional speaker design the fundamental resonance is pushed as low as possible and the region below this is discarded for music reproduction.

Contrary to convention, the fundamental resonance of the 901 is designed upward to about 200 Hz.

The reasons for this departure are:

  • 1) Below 200 Hz, phase irregularities are much more audible than above 200 Hz.
  • 2) Any speaker exhibits strong phase irregularities in the region of and above its fundamental resonance.
  • 3) Below fundamental resonance, these irregularities are absent. Both amplitude and phase characteristics are very smooth functions of frequency and are electronically equalizable.

Thus the 901, by having its fundamental resonance designed at 200 Hz, allows us to make use of this region of smooth response to reproduce bass instruments with unprecedented accuracy of timbre.

  • D) Active Equalization.
    Since phase and amplitude are very smooth below fundamental resonance, it is possible through active equalization to control the amplifier signal to maintain flat radiated power down to lower frequencies than even the largest conventional speakers can produce.

Ask your franchised BOSE dealer for an A-B comparison test with the best conventional speaker systems, regardless of their size or price. Listen especially for the deep accurate bass of the 901 in contrast to the artificial bass (excessive response between 80 Hz and 200 Hz) which is often mistaken in conventional speakers for good low frequency response, but whose thumping and droning cause listener fatigue.
For complete reprints of the TECHNOLOGY BEHIND THE BOSE 901 write our European Rep: BRANDEX, 6 Frankfurt am Main, WiesenstraBe 34, Germany

AD no. 4 - Why is the BOSE 901 designed for FLAT POWER RADIATION?

In previous articles (in this magazine) we have explained that when you attend a concert, the reverberant field is dominant over the direct field at your seat. In order to create a similar situation in your living room, the speaker must use one wall of your room in the same way that the orchestra uses the back wall of the stage - to reflect sound.

A fundamental property of the reverberant field is that its distribution of power vs. frequency is related, not to the radiation of a musical instrument along any one axis, but rather to the total power it radiates in all directions.

Therefore, in order to more accurately simulate the live performance in your home, the loudspeaker must be designed for a flat power radiation into the room rather than flat frequency response on axis.

The need for flat power radiation was first recognized in the research that led to the BOSE 901, and the 901 is the only speaker that uses this principle. The result - you can now listen to an ensemble of violins or other instruments playing in the higher registers of the musical scale and enjoy all the overtones and proper attacks without suffering from the annoying shrillness so characteristic of Hi Fi.

(Musicians and many women are very sensitive to shrill and screechy sounds - they will instantly recognize the unique properties of the BOSE 901 in this respect. In fact, many owners have commented that their wives can enjoy the 901 at a much higher volume level than they could tolerate with conventional speakers.)


Figure 1 shows the measured directional radiation of one of the better conventional speakers at 50Hz and 15KHz. The fact that the two solid curves coincide on the speaker axis indicates that the speaker has the same response on-axis at the two frequencies.

However the much smaller radiation pattern at 15KHz (both horizontally and vertically) shows that the total power radiated in all directions at 15KHz is only a fraction of the power radiated at 50Hz. This is why you notice that the high frequencies drop off as you move off axis with a conventional speaker.

If this speaker were to be equalized to radiate flat power, the on-axis response at high frequencies would be so intense (indicated by the dotted line) that you could not sit in front of the speaker. This problem is fundamental in conventional speakers.

(We leave it as an interesting exercise for the technically inclined reader to show that even a cylindrically shaped speaker cannot employ flat power radiation without excessive high frequency radiation toward the listening area.)


- By directing the greater percentage of the radiation at precisely selected angles to the rear wall, the 901 achieves flat power radiation without high frequency beaming toward the listening area.

Ask your franchised BOSE dealer for an A-B comparison test with the best conventional speaker systems, regardless of their size or price. Note especially the absence of the 'Hi Fi edge' on the violins and the uniform distribution of the highs throughout the room.

For complete reprints of the TECHNOLOGY BEHIND THE BOSE 901 write our European Rep: BRANDEX, 6 Frankfurt am Main, WiesenstraBe 34, Germany

AD no. 5 - Technology must be confirmed by performance.

Here are the judgements of the most respected critics and reviewers. (- in amerikanischen - stateside - Magazinen)

"... I must say that I have never heard a speaker system in my own home which could surpass, or even equal, the Bose 901 for overall 'realism' of sound."
Hirsch-Houk Laboratories, STEREO REVIEW

"It is our opinion that this is the speaker system to own, regardless of price if one wants the ultimate in listening pleasure."
HIGH FIDELITY (gemeint ist aber die US-HIGH FIDELITY !)

"I urge that you listen for yourself. I think you will have to agree that Bose has, in a single giant step, produced one of the finest speaker systems ever made."

"To hear a thunderous "low C" organ pedal..., or a clean, weighty impact of a bass drum is truly impressive ... There is no doubt that the much abused and overworked term "breakthrough"
applies to the Bose 901 and its bold new concepts."
Bert Whyte - AUDIO (gemeint ist aber die US-AUDIO !)

"The 901 is very possibly the only speaker to date to actually pour forth in true concert hall fashion."

"But these speakers provide a quality which is not to be . matched."

"... if your response to it is like ours, you'll be reluctant to turn it off and go to bed."
Norman Eisenberg, HI FIDELITY

"After a time trial measured in months rather than weeks, this one can definitely proclaim Bose is best, big or small, high or low."

"The Bose have replaced forever our bulky studio speakers with compact, handsome units. The only trouble is - our studio is beginning to look like a living room!"

For free copy of the Rave Review Booklet write: BRANDEX, - 6 Frankfurt am Main, WiesenstraBe 34, Germany

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