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Bose 901 Series VI Active Equalizer Measurements

Ah. Makes a lot of sense.

The 901’s are very much like listening to vinyl. Not accurate or detailed but enjoyable anytime you want music that sounds respectable in multiple listening positions. This is probably why it sounds good for classical music too. At the MLP, it’s also enjoyable for its spatial presentation.
My recollection I that Amar Bose came up with the design based on measurements of concert halls showing the majority of sound came from reflections in the concert hall with the driver location matching his measurements.
 
My recollection I that Amar Bose came up with the design based on measurements of concert halls showing the majority of sound came from reflections in the concert hall with the driver location matching his measurements.
Yes, and having recently gone to a John Williams / Anne Sophie Mutter concert in my post ASR era and being lucky enough to be in THX spec perfect seating distance, there’s no question that the sound presentation of the 901 more closely matches the perspective of being there. There is clear stereo separation but not quite as three dimensional as a hifi setup, making hifi hyper real while the Bose is a bit more similar to that experience.

What continues to impress me is the physical impact of the percussion instruments at the symphony which I attribute to a mix of acoustics and even something as simple as the seating.
 
Yes, and having recently gone to a John Williams / Anne Sophie Mutter concert in my post ASR era and being lucky enough to be in THX spec perfect seating distance, there’s no question that the sound presentation of the 901 more closely matches the perspective of being there. There is clear stereo separation but not quite as three dimensional as a hifi setup, making hifi hyper real while the Bose is a bit more similar to that experience.

A live concert, especially one with a lot of instruments, sounds nothing like a loudspeaker. A loudspeaker at its best captures the point of the microphone, or microphones mixed in a console. Unless you are 'up close and personal', a live concert ends up being mish-mash of sound--your seats will make the biggest difference in what you hear.

Imaging, front to back depth, and all the other stuff just isn't there. No one who is honest with themselves will ever confuse a living room loudspeaker with a live performance.

The entire idea of reproducing live sound in a living room via a stereo, which is what some people argue, is to me ridiculous. If you have a set of 901s, and like them, then that is enough. Or it should be enough.
 
We had a demo pair of 901 v? (cannot recall which version) on the sales floor were I worked 50 years ago. One of our competitors carried Bose. Bose was a difficult franchise to acquire. They had sales volume requirements, I think, or at least that was what I was told. Granted that under a sales floor environment they could not be optimized for room placement. Everyone's listening room is different. I suspect that they initially targeted Klipsch speakers as their primary market. Their advertising campaign (using "science") was novel for the time. I believe the target market was financially successful middle aged modern homeowners with a little scientific background and disposable cash. Science was all the rage with the Moon mission and pocket calculators.

The 901 sound had immediate sales appeal, they invariably created a very favorable first impression. Very wide and deep sound stage because of its iconoclastic design. But it was clobbered in A/B testing especially DBT. The shop was run by college students and DSOTM had recently been released and became the de facto test track when we demonstrated speakers. The 901s were absolutely crushed in the showroom by most EPI and large Advent models (OLA). Which were all more affordable for younger buyers (baby boomers). The opening track was recorded heartbeats that the 901s massively distorted when driven by a Phase Linear 700. The audible distortion immediately dissuaded many younger buyers (as well as positioning problems in smaller rooms).

In addition the sound stage seemed "smeared" and the imaging lacked the "realism" of other speakers. OTOH the sound stage was very wide and perceived from most locations in the room. For instance, the EPI M1000 and Ohm F, which were more expensive, ran circles around the 901. That is if you had a listening room large enough to accommodate those monsters. This must have sent alarm bells throughout Bose HQ and made a series of modifications and upgrades mandatory to maintain market share.

The Bose marketing department immediately realized that they had significant competition from lower priced products from Advent and EPI (also RTR, Rectilinear, Microacoustics and others) and rushed the Model 201 to market. Sound wise, it was a dawg and not competitive at the price point. The 301 fared much better and sonically was competitive with OLA and EPI. the improved versions of the Model 301 continued to close the gap.

After that, I left audio to pursue an unrelated career (read..after receiving a college diploma, I got a real job) but remained a hobbyist. The Bose 901 represented a novelty and iconoclastic product in the audio market and Amir's review seems to confirm that status.

Well that's my opinion.
 
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Unless you are 'up close and personal', a live concert ends up being mish-mash of sound--your seats will make the biggest difference in what you hear.
Agree. I just happened to get lucky the last time I was at the symphony. I picked what was available, and ended up central to Anne Sophie Mutter (so just stage right of center) and at ear level matching the conductor, John Williams.

They weren’t the expensive seats— the Loge actually has a different sound profile.

Anyway, I agree that it’s impossible to fully replicate the symphony but that exact mishmash where the Stradivarius is clean, the horns and strings have some stereo separation is what the 901 does pretty well in my room.

I think the description is how I can explain when or why I prefer to listen to the 901 and when I prefer to listen to the JBL 708P in nearfield.

The Bose 901 represented a novelty and iconoclastic product in the audio market and Amir's review seems to confirm that status.

Well that's my opinion.
and just to clarify, this isn’t Amir’s review. He has promoted reader posts to the front page when he thinks it would be enjoyable to others as well. Sorry if that is not clear.

I think that’s a great description — novelty. But definitely not with a negative connotation but a positive Disneyland spin. You know the bad guys aren’t real on the rides but it’s still a thrill that brings a smile to your face.
 
... Ohm F, which were more expensive, ran circles around the 901. Well that's my opinion.

Your opinion is as good as anyone's in the matter of loudspeakers, which depend upon many different factors, mostly turning upon what one likes and what one does not.

However, in my own opinion, to compare the Ohm F (your example) with Bose 901, is less revealing. I don't know about running around in circles (we are not talking about stopwatching the Nurburgring, after all), however the Walsh design, while brilliant on paper, was quite limited in its real world application. Even so, many liked the Ohm, for what it did.

Probably the most 'personal' review of the Ohm F was written by Peter Aczel, who was a principal of the company (from 1971-74). Possibly because of that, he was honest enough to recognize its limitations. In 1977 he wrote:

Its sound is more highly colored ("canned" may be the better word) and less musical than that of any other speaker... [they were testing].

The Ohm F rings. It rings like a telephone. It isn't even possible to localize the ringing at specific frequencies; our test sample rang virtually everywhere. At 11kHz, where there was also a 6 dB peak in the amplitude response, our sample did worse things to a tone burst than we had ever seen in our laboratory. But then 11 kHz isn't in the most sensitive range of the ear. Maybe it was the 900 Hz ringing that was the real culprit. Maybe some other frequency. There were just too many bad spots to choose from. On top of it, the frame of the Walsh driver resonated at 118 Hz.

A single cone, mounted convex side out and apex up acts as a transmission line. ...the cone material must be extremely stiff (i.e., have a high Young's modulus) in order to have the proper sound propagation velocity. That means a high Q. At the same time, the cone material... must be well damped. Ohm... tries to get away with it with a mundane combination of titanium, aluminum, and paper, in tandem, which doesn't quite make it.

[the bass] is too loose and too boomy...


The point being, in the context of '70s loudspeakers, one cannot particularly overstate one's case against another's, without understanding inherant differences, and what any particular consumer was happy to take home. The Ohm, as an omni, certainly was competitive with the Bose, which also 'spread' the sound around. But to state that one was 'better' than the other, is a stretch. They both did things differently.
 
So isn't this just the early version of surround using very wide dispersion speakers? I am fond of wide dispersion since it somehow gives a more vivid and life-like sound. Pin-point details is not what I usually experience at concerts anyway.
 
So isn't this just the early version of surround using very wide dispersion speakers? I am fond of wide dispersion since it somehow gives a more vivid and life-like sound. Pin-point details is not what I usually experience at concerts anyway.

Some people would say that. But what Erin Hardisy mentioned (and his room wasn’t ideal) is that it isn’t just zero imaging or the same as your 360 degree Canon S50. There is still a nice left/phantom center/right where there is even some
In-between left and phantom center.

The height is tricky with the bass feeling closer to the floor while the treble is closer to the ceiling when the speaker is at 38” height.

The smiley face Eq is important for the effect where it feels more neutral with the measured treble boost which was explained as a FFT issue.

I have heard MBL’s which was great but I felt less precise than the 901 for *imaging* even though it’s more *transparent* by memory. That is, the 901 is neither direct/omnipolar/bipolar/dipolar but the whole 11/89% spread thing.

I bet achieving 11/89 with better transducers would be even better.
 
Some people would say that. But what Erin Hardisy mentioned (and his room wasn’t ideal) is that it isn’t just zero imaging or the same as your 360 degree Canon S50. There is still a nice left/phantom center/right where there is even some
In-between left and phantom center.

The height is tricky with the bass feeling closer to the floor while the treble is closer to the ceiling when the speaker is at 38” height.

The smiley face Eq is important for the effect where it feels more neutral with the measured treble boost which was explained as a FFT issue.

I have heard MBL’s which was great but I felt less precise than the 901 for *imaging* even though it’s more *transparent* by memory. That is, the 901 is neither direct/omnipolar/bipolar/dipolar but the whole 11/89% spread thing.

I bet achieving 11/89 with better transducers would be even better.
As the early Carlsson. They were also never omni but used walls for certain amount of reflections
 
As the early Carlsson. They were also never omni but used walls for certain amount of reflections

Great article for those who don’t know the history
 
My problem with 901s is the design. They blast sound all over the place. If there's any good effect from that, it highly depends on the room. Room problems are well known. The object is to reduce reflections from walls and floor to a point where the direct sound from the speaker is less affected. Producers sit close to the speaker to be able to reduce the output of the speakers, and still maintain a relatively reasonable listening level, and involve the room as little as possible. Who knows what kind of response a person would get in various rooms with 901s? It's a poor design regardless of how fun it might be. I should admit that in general I see Bose as an audio company who's main purpose is to generally produced low quality audio equipment and charge a premium price for it to unsuspecting consumers.
 
My problem with 901s is the design. They blast sound all over the place. If there's any good effect from that, it highly depends on the room.
Headphones eliminate the room effect, but speakers are more enjoyable to listen to even though it's not as transparent. Most of us end up having both a headphones and speakers and may choose different setups for different music/moods. The 901's, for me, add a third "effect" category though it is more subtle than the headphone/speaker comparison.

Who knows what kind of response a person would get in various rooms with 901s?
This is a great point. Still, audio science isn't restricted to the goal of identifying the best speaker for the biggest number consumers (though that is important). We still want to use science and understand the best speakers for our own room.

Take a look at my in-room measurements. The JBL 708P is setup in a small home recording studio. ~7 speaker width, ~8 ft listening position. The Bose 901's are in a large family room. I'll estimate ~14 ft speaker width, ~15 ft listening distance. Room is ~20 ft wide and I'd say 2 feet from the back wall.

First, the completely un-smoothed recording, showing how the comb filtering sort of gets filled in even though your phase will probably be wrong. I have adjusted the levels digitally to ensure that they are easily to overlap and compare.

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And then a Psychoacoustic smoothing to show what it may actually sound like:
1683958778524.png


It's a poor design regardless of how fun it might be. I should admit that in general I see Bose as an audio company who's main purpose is to generally produced low quality audio equipment and charge a premium price for it to unsuspecting consumers.

The point of the fun is not just that it presents the music spatially in a unique way, but that it actually can sound and measure great in the right room. That's the incredible science part. Maybe it's the equivalent of a broken clock that's correct twice a day, but we're still talking about a measurement-based comparison between one of the most state-of-the-art active studio monitors in production today, the JBL 708P, against a bunch of full-range drivers put into a box with a largely unchanged concept from 1968. Then with our science pointing out that stereo makes it harder to hear frequency flaws compared to mono, it's easy to understand how it is possible for 901 Direct/Reflecting to make it even harder to hear frequency response flaws compared to a standard stereo setup.

Like you, I had no real respect for Bose as a hi-fi product. It was just scientific curiosity that made me want to try them.

The 708P is vastly superior at high SPLs and vastly easier to room correct with DSP. Dream setup? JBL M2 with the SDP-75. I'm a super big JBL fan, having stuff from the Los Angeles, Northridge, and present era including products that were Japanese-market only. I've owned many of Allan Devantier's original designs including the HLS line as well as their sub/sats designed to compete with the Acoustimass 5 series. I've been a fan of Revel from the very first generation Revel F30 and B15 combo. I've owned a number of Infinity's including the original Modulus and dreamt of owning the Prelude MTS until the CMMD delamination issue popped up. I've had lots of Proceed electronics. My cars have Harman developed sound systems.

Still, the Bose 901 data is jaw dropping to me. Maybe it's pure luck that the 901's end up with this response at the listening position, or I won the lottery with the 901/room combo.
 
Headphones eliminate the room effect, but speakers are more enjoyable to listen to even though it's not as transparent. Most of us end up having both a headphones and speakers and may choose different setups for different music/moods. The 901's, for me, add a third "effect" category though it is more subtle than the headphone/speaker comparison.


This is a great point. Still, audio science isn't restricted to the goal of identifying the best speaker for the biggest number consumers (though that is important). We still want to use science and understand the best speakers for our own room.

Take a look at my in-room measurements. The JBL 708P is setup in a small home recording studio. ~7 speaker width, ~8 ft listening position. The Bose 901's are in a large family room. I'll estimate ~14 ft speaker width, ~15 ft listening distance. Room is ~20 ft wide and I'd say 2 feet from the back wall.

First, the completely un-smoothed recording, showing how the comb filtering sort of gets filled in even though your phase will probably be wrong. I have adjusted the levels digitally to ensure that they are easily to overlap and compare.

View attachment 285238 View attachment 285240

And then a Psychoacoustic smoothing to show what it may actually sound like:
View attachment 285241



The point of the fun is not just that it presents the music spatially in a unique way, but that it actually can sound and measure great in the right room. That's the incredible science part. Maybe it's the equivalent of a broken clock that's correct twice a day, but we're still talking about a measurement-based comparison between one of the most state-of-the-art active studio monitors in production today, the JBL 708P, against a bunch of full-range drivers put into a box with a largely unchanged concept from 1968. Then with our science pointing out that stereo makes it harder to hear frequency flaws compared to mono, it's easy to understand how it is possible for 901 Direct/Reflecting to make it even harder to hear frequency response flaws compared to a standard stereo setup.

Like you, I had no real respect for Bose as a hi-fi product. It was just scientific curiosity that made me want to try them.

The 708P is vastly superior at high SPLs and vastly easier to room correct with DSP. Dream setup? JBL M2 with the SDP-75. I'm a super big JBL fan, having stuff from the Los Angeles, Northridge, and present era including products that were Japanese-market only. I've owned many of Allan Devantier's original designs including the HLS line as well as their sub/sats designed to compete with the Acoustimass 5 series. I've been a fan of Revel from the very first generation Revel F30 and B15 combo. I've owned a number of Infinity's including the original Modulus and dreamt of owning the Prelude MTS until the CMMD delamination issue popped up. I've had lots of Proceed electronics. My cars have Harman developed sound systems.

Still, the Bose 901 data is jaw dropping to me. Maybe it's pure luck that the 901's end up with this response at the listening position, or I won the lottery with the 901/room combo.


I mentioned earlier in the thread about having a friend with 901s.
Jaw dropping would not be my description, but would agree, so much better than some/many claim.

In fact I would conjecture, some may not have even heard them in actuality OR heard them set up completely wrong or without the required EQ and so on.

The sheer size/amount of sound they create from what is quite a small box can not be believed in some ways.
While I greatly value "High fidelity", at times I often value an "enjoyable type of sound" more so.

These fall into the fun/interesting/amazing sound type of speaker but to me not the last word in fidelity, which is fine!
 
I mentioned earlier in the thread about having a friend with 901s.
Jaw dropping would not be my description, but would agree, so much better than some/many claim.

In fact I would conjecture, some may not have even heard them in actuality OR heard them set up completely wrong or without the required EQ and so on.

The sheer size/amount of sound they create from what is quite a small box can not be believed in some ways.
While I greatly value "High fidelity", at times I often value an "enjoyable type of sound" more so.

These fall into the fun/interesting/amazing sound type of speaker but to me not the last word in fidelity, which is fine!
Agree.

I think the jaw dropping is the spread between how bad I expected it to sound and how it actually sounded. Since my expectations and bias were soooo low, when it sounded enjoyable, the shock was higher. It would be like a 4-year-old that can play basketball as well as a 14-year-old. The kid still isn’t as good as a college or NBA athlete by objective measurements, but you’d probably be stunned in that scenario.

That is a reflection of how strong the “no highs, no lows, must be Bose” perspective was for my generation who were introduced to Bose via the Acoustimass 5.

I assumed the 901 was going to be an no highs, no lows, but amazing soundstage. What I got was great lows, great midrange, respectable highs, and amazing sound stage. The FR is not at all amazing but great + amazing sound stage?

What I would say is that when it was discontinued in 2016, I believe it was a Made in North America speaker for $1500 a pair including stands.

Taking this price point into context, I do think it was a competitive product as long as you had an in home trial to see how it worked in your room.

I would put these head to head against the Revel M106 and basically say it’s a trade off between imaging vs soundstage and neutrality vs taut/clean bass. The Revel is the better system to grow into (with a subwoofer), but if you just had two speakers on stands? I think reasonable audiophiles with “luckily compatible rooms” might find the 901 a better option from an aesthetics standpoint or desire for multiple listeners to enjoy the music simultaneously.
 
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What I would say is that when it was discontinued in 2016, I believe it was a Made in North America speaker for $1500 a pair including stands.
First, thank you for the measurements, review, and commentary. I found this very interesting.

I remember a Klipsch magazine advertisement from back in the '70s with silhouettes of a Klipschorn, of a Bose 901 and a couple of other distinctive but unnamed speakers from the era. The Ad line was something to the effect of, "Klipsch has been around since the late forties, which of these speakers will still be around in ten years." Or something like that.

I have thought of that ad many times over the years and as the decades rolled by and both Paul Klipsch's legacy and Amar Bose's lived on far longer than most others. Now in 2023, it appears Klipsch was finally proved the winner in speakers, but Bose built a bigger and healthier company. It'll be interesting to see where this shakes out in another 20 years.
 
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Bose 901 Series VI Active Equalizer Measurements
View attachment 284620

View attachment 284619


The Bose 901 Series V has been measured on the Klippel NFS. In Erin's measurements, he noted that the equalizer added an extreme level of distortion.

I recently tried a Series VI in my own home and came around incredibly impressed with the audio. For all the harassment that Bose received from audiophiles, especially in the era of the Acoustimass 5, the actual in-room sound quality of the Bose 901 can best described with a simple "Wow." Maybe it was because my expectations were so low going into my listening tests, or I've simply lost my audiophile credibility card or suffer from early dementia, but I thoroughly enjoyed the in-room experience from the 901. When appropriately compared to a lifestyle speaker peer, I can confidently state that I prefer the 901's sound presentation over a Sonos speaker or Devialet Phantom. When compared to a traditional audiophile system, I would describe the Bose as a third spatial presentations beyond headphones or dynamic speakers. In a way, it sounds like a Magnepan without a true ribbon with less transparency and much more bass.

Science has shown us that listening in stereo can make it harder to hear differences between speakers (as compared to mono). It's likely that the Bose 901's spatial performance, in a well configured environment, is also enhancing the perceived sound quality despite the frequency response irregularities.
UvF7rx5.png

A REW sweep at my listening position playing stereo sweep through ASR's record holder for worst 5W SINAD was actually quite impressive given that this technology was fundamentally available in 1968. The original 901's apparently have even better bass response as they were sealed, but required more amplification power than was available at the time. The 901 Series III and newer are ported designs. The 901 Series VI is officially rated at 450W per channel or 250W IEC.

What immediately caught my attention was the overall low distortion at the speaker level. After all, this sweep was done with a 300B SET that will add its own distortion as well. The high frequency roll off can be the effect of comb filtering.

In-room BOSE 901 measurement (stereo)
Speaker System Performance


View attachment 284614


I decided to analyze my 901 Series VI Active Equalizer.

Manufacturer's Specifications:
View attachment 284612


Test Setup
Bose 901 Series VI Mid-Bass and Treble sliders, roughly centered
Topping D90 MQA as tone generator
@pkane MultiTone
@JohnPM REW

BOSE 901 Series VI Active Equalizer
Electrical Performance

80.5 dB

1 kHz SINAD


Bose advertised <0.09% THD, or 61 dB. Our THD+N is 80.5 dB or 0.009%, a full order of magnitude better. This is at 0 dB (2.118V from the Topping D90)
View attachment 284615

Decreasing the volume on the Topping to -6 dB (1.0608V) shows a big drop in the distortion products, although SINAD is worse due to the increase in noise.
Apologies for the change in X-axis scaling.
View attachment 284616


A REW sweep at -20 dB from the Topping D90 gives a very nice distortion profile. I have shown both the dBFS as well as % THD.
View attachment 284617
View attachment 284622

Running it at 0 dB (2.118V) shows clipping in the treble, where the EQ boost is particularly high.
View attachment 284618
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Commentary
The Absolute Sound was founded after Harry Pearson was unhappy with the sound quality of the Bose 901's he purchased. Today, the Absolute Sound offers 6 recommended digital interconnects $1000 and higher.

Julian Hirsch, an objectivist audiophile, emphasized measured performance of audio gear from the earliest days of this hobby, and loved the Bose 901

He had this to say about the Bose equalizer: "The active equalizer introduces no perceptible distortion. We measured its distortion at less than 0.13 percent for any output under 3 volts, which is greater than would be required with any amplifier we know of. The output signal is of approximately the same level as the input signal."

and this to say about the system as a whole:
"I am convinced that it ranks with a handful of the finest home speaker systems of all time. Because of its unconventional mode of operation, I rather doubted that any frequency-response measurements I could make would account for the remarkable realism of its sound... The Bose 901 had an utterly clean, transparent, and effortless sound. Its clarity and definition when reproducing complex orchestral passages were, in the writer’s opinion, unsurpassed by any other speaker he has heard. This impression was confirmed by its tone-burst response, which was uniformly excellent across the frequency spectrum. Its low-bass response was difficult to credit to such a compact system. It had all the room-filling potency of the best acoustic-suspension systems, combined with the tautness and clarity of a full-range electrostatic speaker. The spatial distribution, which brings an entire wall alive with sound, contributes greatly to the sense of realism.

There is, unfortunately, a serious obstacle to the universal acceptance of a speaker such as the Bose 901. The 12-inch gap necessary between the apex of the speaker and the wall places the front of the speaker about 30 inches from the wall. Bookshelf mounting is generally impractical, and it may be difficult to install the 901 in the correct location without disturbing room decor. Many potential users will be forced to decide between style and sound."


Conclusion
I grew up with the belief "no highs, no lows, must be Bose." The only Bose 901's I ever listened to were the ones in Bose retail stores where the 901's were spaced 2 or 3 feet apart. Today, after hearing the 901 in my own home, I realize that my belief that the 901 were a horrible speaker was based upon the same kind of experts who hyped up green markers for CDs. Was it simply that in 1968, the active equalizer was considered a gimmick or too hard to set-up? Today we don't think twice about the JBL M2 or any number of speakers which are dependent on active crossovers. But back then? Did the company's infomercials and aggressive legal threats to reviewers negatively bias the impression of the speakers? Was there too much attempt to market "halo" or "trickle down" technologies where the true gem of the Bose product line never had a chance to shine?

Estimated In-Room Response from Spinorama.org
Revel F328Be = ASR-v1-20201110 (lower bass measurement, no EQ)
901 Series V = EAC with software EQ (best case)
View attachment 284630

1. The Bose 901 is better than you'd expect given its reputation among audiophiles. Given how affordable the 901 can be in the present day, it's actually a very competitive product given its in-room bass response and attractive mid-century modern appearance with the tulip stands. The Series I and II products do not have deteriorating foam while the Series VI uses a modern foam which does not appear to be as fragile.

2. The Bose Series VI active equalizer works best with lower input voltages as long as you don't run into the noise floor. When using a Bose 901 in a modern setup, consider attenuating your source. If this is not an option, Deer Creek Audio offers MiniDSP based replacement 901 equalizer solutions with their custom EQs.

3. With perfect EQ, that a Bose 901 Series V is closer to an un-EQ'd Revel F328 Be according to Spinorama.org than anyone would have imagined in the absence of measurements. Now that all of the patents behind the 901 have expired, what happens if you put together a similar speaker leveraging all of the advances in full-range transducers, contemporary DSP technology, and the benefit of oodles of clean Class D amplifier power on demand?
Excellent review and information. Thankyou

I owned two pairs of 901's and always enjoyed them. They seemed to me to be open, dynamic and very clear.
 
Here is Erin's review, including with DIRAC. The most interesting thing to me is, at the end, he talks about what if it wasn't all full range drivers but instead used drivers that could perform the way they should. I have often thought about keeping the direct reflecting design but using drivers that can hit the highs and lows the way they should. It's a thought.


It was these comments from his review I was particularly interested in.

"I wonder how a design like this could be made to sound if you just replace the front full range speaker with a modern 5-inch midrange and tweeter."

"Because if this speaker’s performance could be improved tonally and its SPL limits increased, I believe there would be a lot of people interested. Myself included. "
 
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Here is Erin's review, including with DIRAC.
I linked his review in the very first post. :)

His review is of the Series V.

Each version is a little different but Bose never really published detailed info.


The Series V has early and late versions with different foam.

The Series VI has different equalization and early/late versions, but the aftermarket MiniDSP setups do not differ.

There is also a Series VI version 2 with the fancy surrounds:

1684039553744.jpeg
 

Posted some data on the original 1968 model.
 
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