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Bose 901 Series VI Active Equalizer Measurements

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GXAlan

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i have to say they sound quite good. Quite happy with them so far, especially for the low budget involved.

My measured curve more or less stops at 8 khz, similar to the one above from GXAlan. I was thinking about adding a pair of ESS AMT Dipol Air Transformers, and a passive crossover 12db @7000Hz. Did anyone try such a setup yet, any dos/donts?

View attachment 333024

I added a JBL UT405 super tweeter which is crossed over way higher at 16 kHz. You just need Dirac to be convinced that you have some signals that are high enough to try to correct everything below. If you pull your curtains to the right as-is, it will still get you a bit extra correction. So getting a cheap Aperion audio super tweeter might work too

You can also use a Harman curve with the downsloping room curve which will still help you get a bit extra performance.
 
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teashea

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I had two pairs of 901's. There are remarkable. The spaciousness is quite something - that no other speakers can touch. Fun but not accurate.
 
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GXAlan

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I had two pairs of 901's. There are remarkable. The spaciousness is quite something - that no other speakers can touch. Fun but not accurate.
Once you start playing with Dirac, it really starts to become something special. I imagine someone running Acourate or Audiolense or RePhase could do something special.

I will be shipping my 901 Series VI ver 2 to Amir to characterize.
 

SpaceMonkey

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I gifted myself a pair of used but in excellent condition VIs for Xmas, this review was basically the tipping point (that is my excuse at least). After setting them up with a Minidsp Flex and Dirac (software crossover only) with the Dirac Autocurve (+4.0/-0.8db) i have to say they sound quite good. Quite happy with them so far, especially for the low budget involved.

My measured curve more or less stops at 8 khz, similar to the one above from GXAlan. I was thinking about adding a pair of ESS AMT Dipol Air Transformers, and a passive crossover 12db @7000Hz. Did anyone try such a setup yet, any dos/donts?

View attachment 333024
Pretty nice.
I am toying with an idea of installing a coax unit instead of the front driver...
 
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SCR

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I did it… and it works quite well! AMT via 12db Crossover @5000Hz, Dirac room
correction.

IMG_9133.jpeg
 

Mr. Widget

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Looks pretty cool too. I would love to hear this especially with the DIRAC DSP correction.
 
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Rmar

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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.
Using a higher powered tube amp (i.e. McIntosh, Cary, etc.) clears up any smear. Tube mono;s even more.
 

le bibi beige

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Thank you for the nice review !
True innovation is made by design and few speaker design is smarter or at least more creative than the one discussed.
IMHO those speakers are a work of art for at least 2 reasons:
  1. They are made to play with the room instead of against it ...
How often do you see people with poshy high-end audio gear in their raw living room, untreated spaces ?
95% to 98% of the time ?
What do these people think they are really listening to ? Hifi as a life style expression is very ok.. but it is a bit like driving a mc Laren in a mall parking.
You are basicly missing an essencial part of the high-fidelity concept.
Professional spaces cost more than the gear itself for good reason,
Acoustics are the price to pay for any high fidelity system, you can ignore it, but unfortunately there is no turn around this.
The 901's are made with this in mind at their root ... your sound will only be as good as your room ..
They made a design that embodies the room in the best way possible, using the wall and room structure
This is why placement is crucial, it has to be done considering the room structure even more than your listening position .. AH!
Might not be "the greatest speakers of all time" but how Great is that way of thinking ?

2. One way full range (multiple drivers)

They bet that correcting the response of an unique driver design via EQ would sound more natural and integrated than correcting the usual crossover/phase issues until it sounds like the sound is coming from a unique point ... and the way it's done is a nice try!
Nowadays the sound, like the image are all about "details" with HF informations to the point of excess leading to quick fatigue and volume turned down more often than up, at least it is my point of view.
The 901 are not "airy" (at all) but they are very musical to my ears and fun to listen to for sure.

Due to their design I would say they need an even better amplifier than other speakers .. They need super juice.
I use them with an MC300 and a very light touch of high end boost from a C712 preamp (one O'clock light)
Could listen to them all day and night loud or quiet with great enjoyment.
 
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EJ3

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Very nice effort on both fronts. I have only listened to them once many many years ago. They were suspended from a living room ceiling with thin chains.
That is the same setup when I listened to them, suspended from the ceiling by thin chains. Unfortunately it was a party environment in the home of these Bose 901's and I was much more interested in presenting myself to the opposite sex, Bose or no Bose.
 

EJ3

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But accurate enough to enjoy the music.

But accurate enough to enjoy the music.
I have one femail (yeah, I know, spelling) friend that has her 901's running on speaker A speaker out and her Cerwin Vega's on B speakers out & the Cerwin Vega's (which are on the same side of the room more or less under the 901's seems to fill some of what the 901's by themselves lack.
Is it accurate? No! Does it sound better than either set of speakers by themselves? Yes! Is it entertaining? Yes! (She lives in a home [not an apartment or condo]) and likes to crank up the the volume: says that she enjoys annoying the neighbors (they are all friendly, bringing each other home cooking, etc.).
I really don't think that she actually manages to annoy them.
 

kemmler3D

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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
View attachment 284625

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?

EDIT: I ran Dirac Live against an un-EQ'd Bose 901 with a Harman curve with +10 dB bass boost. Then I ran a sweep to see how Dirac's room correction compared to the Bose Active EQ.
View attachment 289023
Great test and writeup here.

Growing up, my dad actually had 901s in the living room. Eventually he got rid of them in favor of some Goldenears. As I recall the sound was big, enveloping, balanced. Granted, this was a long time ago, but given all the hate Bose got in the "knowledgeable" spaces, I assumed based on my experience that Bose had been good at some point in the past and "sold out".
 
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GXAlan

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Great test and writeup here.

Growing up, my dad actually had 901s in the living room. Eventually he got rid of them in favor of some Goldenears. As I recall the sound was big, enveloping, balanced. Granted, this was a long time ago, but given all the hate Bose got in the "knowledgeable" spaces, I assumed based on my experience that Bose had been good at some point in the past and "sold out".

I think they definitely sold out in that they make headphones and soundbars with MIT being the largest shareholder. They went into selling what makes the most money to support MIT’s academic mission as envisioned by Dr. Bose. Kind of cool in the grand scheme of things.


I think the problem was that for many, Bose really grew in fame with their cube satellite speakers which were great when size was a strict constraint but came at fidelity cost that anyone who *could* handle the larger speaker should have gone for. It’s no different than the actual market we see for audio today, but it was bad. I also think the whole Consumer Reports lawsuit had poor PR behind the whole thing.

Still, I think most people on ASR who have the opportunity to find a good pair of Bose 901’s would really enjoy listening to them on a modern system with modern electronics and advanced software DSP.

But accurate enough to enjoy the music.
Agreed. The biggest weakness of the Bose 901 for us young folks with better hearing is the high frequency roll off which can be addressed with a strategically placed set of super tweeters.

The second biggest weakness is that they *really* depend on having good amplification with low IMD so that your total system IMD is as low as possible.

But as I have said, I have a SOTA AV processor (Monolith HTP-1), SOTA speakers (Meyer Sound Amie), Audiophile approved non-SOTA speakers (Magnepan MG-III), and the Bose 901’s are one of my favorite speakers to listen to music on.

I use the example of headphones vs. speakers. It’s possible to enjoy both even though they clearly are not identical in representation. The 901’s offer a third aural experience perhaps replicated only by MBL speakers.
 

Rmar

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I think they definitely sold out in that they make headphones and soundbars with MIT being the largest shareholder. They went into selling what makes the most money to support MIT’s academic mission as envisioned by Dr. Bose. Kind of cool in the grand scheme of things.


I think the problem was that for many, Bose really grew in fame with their cube satellite speakers which were great when size was a strict constraint but came at fidelity cost that anyone who *could* handle the larger speaker should have gone for. It’s no different than the actual market we see for audio today, but it was bad. I also think the whole Consumer Reports lawsuit had poor PR behind the whole thing.

Still, I think most people on ASR who have the opportunity to find a good pair of Bose 901’s would really enjoy listening to them on a modern system with modern electronics and advanced software DSP.


Agreed. The biggest weakness of the Bose 901 for us young folks with better hearing is the high frequency roll off which can be addressed with a strategically placed set of super tweeters.

The second biggest weakness is that they *really* depend on having good amplification with low IMD so that your total system IMD is as low as possible.

But as I have said, I have a SOTA AV processor (Monolith HTP-1), SOTA speakers (Meyer Sound Amie), Audiophile approved non-SOTA speakers (Magnepan MG-III), and the Bose 901’s are one of my favorite speakers to listen to music on.

I use the example of headphones vs. speakers. It’s possible to enjoy both even though they clearly are not identical in representation. The 901’s offer a third aural experience perhaps replicated only by MBL speakers.
Well said!
 

Mr. Widget

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I think they definitely sold out ...
I don't think they sold out. I think they are a business and have done what is required to make a profit.

I have always been impressed with both Bose and Harman who have both invested in substantial original research. While I am not particularly interested in how Bose has often applied their research, I respect it. Further, I believe if Harman had remained a private company like Bose, they would likely be a much better company today, a bit smaller perhaps, but not the hot mess they have become.
 
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GXAlan

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I don't think they sold out. I think they are a business and have done what is required to make a profit.

I have always been impressed with both Bose and Harman who have both invested in substantial original research. While I am not particularly interested in how Bose has often applied their research, I respect it. Further, I believe if Harman had remained a private company like Bose, they would likely be a much better company today, a bit smaller perhaps, but not the hot mess they have become.

Lol. Yeah, I was using it as a figure of speech. “To sell out to academia”

The way Bose applied its research is smart and frustrating. It was early on that they determined that the difference between people feeling like they were hearing full range and not was NOT this 20 Hz to 20 kHz that was claimed. Even when testing young people, you only needed to get up to 15 kHz for symphonic music to sound like actual symphonic music. And then when going down to the bass, there was nothing that truly needed to go down to 20. It was 30 Hz to 15 kHz…

And based upon that science, that’s how the Bose 901 was designed.

This is the single best lecture in my mind from the series:

Based upon their science saying that you don’t “really” need to go to 20 kHz, they basically never bothered trying to reach to those high frequencies!

Backed by science, but contrary to anything we in the audiophile world would suggest.
 

Rmar

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Lol. Yeah, I was using it as a figure of speech. “To sell out to academia”

The way Bose applied its research is smart and frustrating. It was early on that they determined that the difference between people feeling like they were hearing full range and not was NOT this 20 Hz to 20 kHz that was claimed. Even when testing young people, you only needed to get up to 15 kHz for symphonic music to sound like actual symphonic music. And then when going down to the bass, there was nothing that truly needed to go down to 20. It was 30 Hz to 15 kHz…

And based upon that science, that’s how the Bose 901 was designed.

This is the single best lecture in my mind from the series:

Based upon their science saying that you don’t “really” need to go to 20 kHz, they basically never bothered trying to reach to those high frequencies!

Backed by science, but contrary to anything we in the audiophile world would sugges
 
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