I've always said that the main failing of Bose 901 series one and two was their lack of a high end. Subsequent versions three through six also lack the lowest octave as the manufacturer went from an acoustic suspension design to a ported design. The main reason for this shortcoming in series 1 and 2 as I see it is the inability of a 4 inch driver, especially one designed to handle low frequencies to overcome its inertia to the degree necessary to fully reproduce high frequencies. And even if it could, the front firing driver would not have very good dispersion due strictly to its diameter. This may have been less than critical in the sixties and seventies when most loudspeakers did not have a very bright or extended high end response but in the eighties and nineties as brighter speakers became the vogue, this speaker was left in the dust and has been highly discredited by most audiophiles to the point where it's routinely derided and bashed mercilessly. For those wanting what is considered accurate by today's standard, Bose 901 our of the box would be a very poor choice indeed and so maybe the criticism is to a large extent justified except for those who would forgo its severe tonal imbalance shortcomings for the special attributes of the direct reflecting principle.

I'm the kind of person who wants to have his cake and eat it too and I don't give up easily. I've made half hearted attempts in the past to fix this problem but now I've made a real effort and the results have paid off beyond my best expectations. I've added four tweeters to each chanel mounted right on the speaker itself secured to the top molding except for the front tweeter which is secured with double sided tape. The front tweeter is similar to an Audax 3/8 poly without a shielded magnet and so is the one at the apex of the rear. This was done for mounting reasons due to their reduced depth. Two Dayton 1/2" polys are mounted on each of the angled rear panels and are similar to the Audax units. Each tweeter is crossed over with its own 2.7 mfd NPC which gives them a 6db per octave rolloff hinged (3db down) at about 9khz. They are connected in parallel and have a combined nominal impedence of 2 ohms. The system now consists of an Optimus 5 disc 1bit carousel cd player, a Marantz SR930 receiver and a separate AR amplifier to drive the tweeters. The Marantz receiver has the advantage of a 10 band equalizer and removable jumpers between the preamp and power amp. This allows the Bose equalizer to be placed in this circuit with the AR amp connected to its tape outputs. This means that the Marantz volume control controls the signal to the AR amp as well as its own power amp and the signal to the AR amp is unaffected by the Bose equalizer. The volume control on the AR amp serves as a "brilliance" control affecting the relative level of the tweeters to the main speakers. The AR amp has its bass control at full cut and its treble set flat. The bose equalizer is set to its indicated flat position. The Marantz equalizer actually is adjusted for additional bass boost, a cut to eliminate the known peak around 500 hz and a very gradual and slight rolloff above the midrange. The room is a 14 x 14 sunroom with a cathedral ceiling and the walls are over 50% glass so it is on the live side.

The results so far are outstanding which mean to me, wide flat response across the entire audio band, very clear highs which characteristically for a direct/indirect array are never shrill but exactly balanced, excellent stereo imaging everywhere in the room, and of course preservation of the direct reflecting basic character of the sound.

I may fiddle with the direct reflecting ratio of the array by inserting an 8 ohm resistor in series with the front firing tweeter ahead of the capacitor to alter the direct reflecting balance from 3 to 1 to 6 to 1 which is more in keeping with the rest of the system which is 8 to 1. I am also contemplating replacing the power amp section of the Marantz receiver with a Crown DC 300 or 300A as the Marantz does not have quite enough power for deep organ pedal notes at moderate to high levels. Other than that the sound is all I could ask for. Ultimately, I might even consider adding a second pair.

If you try something similar with a series 3 to 6, I'd opt for a pair of first class subwoofers as that version does not have much response below 40 hz.