Bose 901 loudspeaker Page 3

This is what the Bose 901 does, on a small scale. Fig.2 shows the paths of sound waves coming from a left-channel 901. A listener hears not only the front-facing speaker A, but also the right-rear reflection B and the left-rear reflection C which, bouncing from the side wall, effectively spreads the source of reflections beyond the limit of the rear wall and partway around the side wall. The reduced output from the front speaker (11% of the total) prevents it from dominating the entire sound "stage" and thus contracting the apparent radiating area to a small point. And since the distance between the front speaker and the listener is shorter than any other path, sounds from there reach him first, and his ear responds by localizing the unified wavefronts of direct sounds at about the center of the speaker. (This is known as the Precedence Effect.)

Fig.2 How reflections from the rear of a Bose 901 broaden the apparent source.

As for the rear-radiated sounds, these behave as do the reflected ones in a concert hall. Their time of arrival at the listener varies according to the distance they travel, phase interference takes place, and the comb filter effect chops holes in the response of the reflected sounds.

This broadens the apparent soundsource, and in that sense it does add spaciousness to the sound, but this alone can't account for the 901's remarkably spacious sound. What is needed to do this is the reverberant information from the second channel. It gets the same reflective treatment as that from the first channel, but now, along with the phase interference in each set of reflected signals, there is additional interference between them. Since this causes combing of similarities in the two reverberant fields more than it affects their differences, the effect is to increase the differences between the two reverberant signals, and our ears perceive the increased difference as enhanced spaciousness.

It is probably fair to say that the 901 actually exaggerates spaciousness from recordings, rather than reproducing it as it is contained in the recording. But since two-channel stereo reproduction is inherently deficient in spatial qualities anyway, it must also be said that the net result is an improvement in realism. The 901 does not synthesize the added spaciousness, though; it merely enhances what is already on the recording. Thus, a recording made outdoors will not be imbued with concert-hall spaciousness, but is instead made to sound even more convincingly outdoorsy. And a recording with no spatial information on it at all, like a mono one, will sound somewhat diffuse but will have virtually no more spaciousness than it would through any other speaker system.

This tremendous gain in spatial effect is not, however, achieved without some sacrifices. Even though Precedence Effect helps to localize the discrete wavefronts from direct sounds in their proper places across the stereo stage, there is enough repetitive (cyclical) signal content in even the direct sounds for them to be subject to some combing as a result of the multiple reflections, and this causes some loss of imaging specificity. There is no increase in "wandering" tendency—indeed, the 901 yields as stable a stereo image as any speaker we have tested. But there is a perceptible widening of the apparent source of any given sound, making it possible (by spacing the speakers too far apart) to create such monstrosities as 2'-wide singers and 8' guitars.

Even with optimal spacing, some purists will cavil at this loss of specificity, even though we point out that instrumental localization is not all that pinpointed under live listening conditions. On the other hand, at a live concert, our aural localization is abetted by visual localization, so there is something to be said for having more-specific aural localization when we must depend entirely on our ears, as when listening at home.

What is, we feel, a more serious shortcoming of the 901 principle is that it subjects the direct sounds in a recording to the same reflective process that enhances the recorded spatial material. The first of the rear-reflected waves reaches us a relatively long time after the front-radiated wave has passed, and while this is of no consequence as far as spatial information is concerned—and may actually enhance it—it cannot help but impair the detail of those signals which represent direct sound in the recording. Precedence effect can retain the localization of the direct sounds, but it cannot prevent the rear-reflected sounds from being audible a fraction of a second later. And since each rear-radiated wave reaches us from an infinite number of distances, it arrives not as a single delayed impulse, but as a smear. There is no perceptible echo—the delay is too short for the ear to perceive as a gap. Instead, there is what appears to be a marked softening of detail, as though every sound is being followed by a rapid decay rather than a sharp cessation of sound. It sounds, in fact, like short-lived hangover, which is just what it is. The only difference between this and the hangover we associate with resonating loudspeakers is that this involves a wider range of frequencies and is acoustically rather than mechanically induced.

Mountain Road
Framingham, MA
(800) WWW-BOSE

dalethorn's picture

So far I haven't been able to find the original Bose 901 review on the Internet - the review which contained the phrase "Bose is best, big or small, high or low."  I've always wanted the 901, just like I always wanted a set of Klipschorns.  But getting the best that either of those systems are capable of (and the only reason to have them) requires a listening room the likes of which I've never had.

GKearny's picture

I've had some BOSE 901s since 1999, and they ROCK when set up in my front yard. With the complete ABSENCE of room resonance, and connected to an ACURUS linear power amplifier, they SOUND LIKE WE ARE ATTENDING A LIVE CONCERT! I have rocked my entire neighborhood with Wagner's Ride of the Valkyrie, and the original BOSTON album! I think that the BOSE 901s are, with the addition of a LOT of horsepower ala a linear power amp, sound WONDERFUL. Our house is made of concrete blocks, and we have a solid rock veneer wall, and when we set up the BOSE 901s to reflect off of this heavy, rock-hard surface, the amount of sound that is projected is worth WHATEVER it costs! WE LOVE OUR BOSE 901s ! Gerry K in Arizona

drblank's picture

I know a lot of people want to get their audio system sound like they are at a concert. The problem is that concerts don't have really good room acoustics or sound systems.  Obviously, if the recording is a live recording, we hope that it sounds like we are at the concert, but having the speakers basically rely on bouncing audio from the back as the main source is actually bad.   Some people like omni directional speakers like MBL, or others that are simlar in design, but they don't rely mostly on bouncing the sound from the rear.   With the 901's, you are actually listening to what you want less of, reflected sound.

I had an acoustic engineer come to my home to take some measurements and give me his recommondations for room treatment as my room measurements were probably the worst you could have.  a square room with a pitched vaulted cieling with a drastic slope to it.  He explained to me that it's good to have reflected sound, but you don't want too much as it removes detail and coherancy from the music.

When companies like ASC and others work with a client to measure room acoustics, they work with Articulation measurements of the room and they measure the direct sound compared to the reflections and they want to create a natural room sound rather than having it too dead, too live where the reflected sound is as loud as the direct sound coming from the speakers.

The 901's just simply do it wrong.  If the front had a bunch of drivers and the rear sides had only one driver, that might be better.

One thing to note.  When you walk into a Bose dealership or Bose Store, don't let them use those CDs that are produced by BOSE.  I talked to a dealer that carried BOSE for a short period of time and they explained to me that BOSE produced demo CDs that were mastered to sound good on BOSE systems, but when you listened to the same CD on another, they sounded like crap so those demos they use to sell the speakers mislead the consumer because most of the recordings you listen to weren't mastered specifically for BOSE speakers.  The local dealership that told me this doesn't carry BOSE anymore and the only reason why they carried the line is they got a lot of people asking for BOSE because of BOSE marketing and they seccumbed under the pressure of customers, and in the process, they got ribbed by their higher end customers like myself, but in the end, they dropped the line as people would actually walk into a higher end store and once they started listening to companies like Paradigm and others, they became disinterested in BOSE and then sales started to wain.

Best advice I can give someone is use your own CDs, and go to a variety of audio stores (not the big box stores) and start REALLY listening to a variety of speakers, there are plenty of really good products on the market that walk all over BOSE.  Paradigm is just one of many, there are Martin Logan, and many other small companies that make nice affordable products these days.  If I wanted the omni directional sound, but couldn't afford MBLs or something in that price range, I would be looking at Martin Logan, Magnapan and a few others that sound so much better than 901's.

machelp's picture
smileday's picture

I do not understand the claim in the review that single small woofer system results in flatter response than multi-woofer system.

Contrary to that claim, we can achieve flatter in room response by increasing the bass radiating area. That is because we can make the dip (cancellation null) in bass in the frequency response curve less deep. Some designers utilize large bass radiation area. Real world product examples include PSB T3 that was reviewed in Stereophile. PSB T3 has multiple woofers for frequencies below 450Hz. Moreover, the woofers are placed apart, not as close to each other as possible.