Bose Model 901 Active Equalizer ('68 Edition) Measurements

[GXAlan]

Bose Model 901 Active Equalizer ('68 Edition) Measurements

I was able to source an original Bose Model 901 Active Equalizer (Series One). While there is no serial number on the equalizer, it was part of a set that had one Bose Model 901 speaker with a serial number BELOW #800. The matching speaker has a serial # over 1100 which had the more traditionally seen Bose label.

This unit has not been restored. No electrical performance specifications were provided at the time by Bose.

2.118V input
-51.3 dB
SINAD

1.0608V input
-55.1 dB
SINAD

We can keep driving the input signal down, but it doesn't get much better than ~58 dB SINAD.

Here is the 1968 equalizer in "flat" mode (blue) versus the modern Series VI model:

REW sweep showing distortion of the 1968 edition

vs the Series VI model under the same input voltage

Subjective Impressions? Not yet.
The original Model 901 speakers are a sealed design. The drivers are also different with cloth surrounds instead of foam surrounds of the Series III and newer.

It's interesting to see how the equalization differs but it’s unclear if the originals need less equalization because of the transducers and enclosure, or if the originals would have benefitted from the more complex equalization but the research or technology didn’t exist yet. Given the distortion performance of my vintage equalizer though, I probably do need to use a MiniDSP device to give the speakers a fair listen or consider recapping the original equalizer.

The speakers are actually still in transit, but given that I seem to fortuitously have a room where the 901 works really well, what I really intend to test is:

 

[GXAlan]

In Room Speaker Measurements

The original Bose Model 901 has a much worse frequency response in the critical 300 to 3 kHz range. Reports of the increased bass of the original sealed models (provided that you had enough power) seem to be untrue for musical content, although the sealed model is +5 dB at 20 Hz due to the slope.

Distortion is also higher with the vintage model, although this may be due to the vintage equalizer.

LEFT = Newer Model
RIGHT = Original Model

There was no real difference between the tube and solid state, except for the treble boost that was seen in our measurements of the specific 300B tube amplifier.

The use of solid state had decreased distortion, but not meaningfully so.

Subjective Impressions
The spatial effect is consistent from the 1968 Edition to the Series VI. That part is great.

Everything else? Not so much. The frequency irregularities are an issue to my ears. Although there are some who prefer the sound of the original Series I and Series II speakers, at least in my room and these un-restored vintage '68 Edition Bose Model 901's, the mid-range naturalness is gone, and the impressive bass is gone.

Had the '68 Edition Bose Model 901 been my first exposure to the Direct/Reflecting design, I don't think I would have been interested in trying the newer models. Starting with Series VI is thus a blessing.

I preferred the sound on the tubes as opposed to the solid state amplifier. While the swept frequency response tones are similar, the solid-state amplifier used, the Kenwood L-08M has an extremely high damping factor. It's possible that the looser control of the woofers with the tube amp improved the subjective sound.

Conclusion
It's possible that these un-restored original '68 Edition Bose Model 901's have suffered deterioration of the paper cones, or the cloth surrounds even if they do not have outright failure. I'll need to investigate more. Nevertheless, Bose prided itself on Better Sound through Research, and the measured improvement from the 1968 Bose Model 901 to the Bose 901 Series VI from the late 1990s is a clear demonstration of just how much better they improved the sound over the lifespan of this speaker.

Having now heard the first and second-to-last models of the 901, I think I have a better understanding of the Bose controversy. While I'm sure it was respectable against its 1968 peers, the Model 901 from 1968 simply cannot compete with any modern speaker except for the spatial effects. In contrast, the Bose 901 Series VI can easily compete with modern speakers. What these measurements suggest, at least for me as a listener, is the threshold between "improved spatial performance overcomes frequency response irregularities" versus the frequency response being too irregular to sound good.

I still encourage everyone to listen to a pair of Bose 901 Series VI's when you have a chance. The original Series? Probably best left as a museum piece.

What is interesting is Dr. Bose's lecture and approach to sound reproduction.

InfiniteMIT | Amar Bose: 6.312 Lecture 25

The InfiniteMIT site is a collection of videos that create a vivid portrait of an institution that is continually changing the way we live and work. Interviews with legendary change-makers, historic footage from the MIT Museum collection, unforgettable lectures, commencement speeches, and symposia.

infinite.mit.edu

 

[GXAlan]

Updated: In-Room Measurements

I realized that the equalizer was probably a big limitation of the test since it's a 55 year old product with no service.

I first measured the '68 edition speaker without EQ

Then I developed a 16-band EQ.

And threw it into Equalizer APO

Which results in this:

But the real test is how it sounds in multiple listening positions. This is a about an 8 foot spread, so the overall results are pretty similar at 1/6 octave smoothing.

Subjective Impressions with EQ
What a difference!

I was able to play with the bass boost to preference, and the '68 Edition can deliver a lot of bass with the right equalization. On the other hand, you pretty much cannot equalize the performance beyond 15 kHz. This is consistent with Dr. Bose's comments about the original Model 901's being a 30 Hz to 15 kHz but then having the "reviewers" insist that he publish 20Hz -20 kHz. Their science showed that no speaker of that time could reproduce 20 kHz but were forced to make the same marketing claims into order to sell their speakers.

My hearing still extends beyond 17 kHz and the loss of high frequency content on the Series VI was a limitation and the '68 Edition is even a bit worse. Nonetheless, this still results in a "warm" and pleasant roll-of.

Since the overall spatial effects of the Bose Model 901 '68 Edition are consistent with the Bose 901 Series VI, I can now recommend the Bose Model 901 '68 Edition provided that you have access to equalization.

 

[gnarly]

Hi, I've really enjoyed your enthusiastic posts about the 901s. Thx!

To refresh memory, I've owned the series 2, and still have a pair of series 6 running in the garage hung from the ceiling.
Was cool to see the old original processor....I'd forgot what it looked like.

Having now heard the first and second-to-last models of the 901, I think I have a better understanding of the Bose controversy. While I'm sure it was respectable against its 1968 peers, the Model 901 from 1968 simply cannot compete with any modern speaker except for the spatial effects.

I share that opinion. The early series had a huge omni-like sound, but lacked bass extension or resolving treble....probably helped seed the saying "no highs, no lows......."

In contrast, the Bose 901 Series VI can easily compete with modern speakers.

I don't share this opinion however. The 901 is a fun speaker, a party speaker, and one that can allow decent conversation over at festive SPL.
But imo it's not even close to a good modern speaker, (or even a good vintage speaker....good is good. )

By good, I mean one that doesn't have smeared HF/VHF that comes from a multitude of drivers (spaced too far apart for coherent summations)
The 901 has that problem in spades using nine 5.5" drivers for HF/VHF duty; not to mention eight of used as indirect wall bouncers.
Transients have no chance of not being smeared.

This is one of those this things that can measure well in terms of frequency response, but frequency response doesn't tell the whole story.
I mentioned in another of your 901 threads that 'Coherence', a measure of the statistical "sameness" between the signal stimulus and the device under test, will be very low for the 901's HF/VHF. That's because which of the multiple arrivals can the measurement try to correlate with?

A dual channel FFT like AARTA or the free OpenSound Meter makes coherence measurements.

Probably the best surrogate for coherence using REW is simply to look at the Impulse Response for multiple arrivals.
I don't remember seeing an IR in your measurement posts, apologies in advance if i missed it.
Do you have one of the in-room speaker response?

Another major issue with using single drivers full range (with substantial EQ, is simply a whole lot of modulation going on.

Anyway, that's all techno-babble stuff.
The major reason I think the 901's can't compete is simply from a long history with them,
and my personal list of speaker comparisons that make them sound like fun, but very lacking in a number of ways.
Just my personal take....don't mean to throw cold water on the 901's...just to say it helps to remember 'horses for courses' sometimes.

 

[GXAlan]

Hi, I've really enjoyed your enthusiastic posts about the 901s. Thx!

To refresh memory, I've owned the series 2, and still have a pair of series 6 running in the garage hung from the ceiling.

Thanks!

The 901 is a fun speaker, a party speaker, and one that can allow decent conversation over at festive SPL.
But imo it's not even close to a good modern speaker, (or even a good vintage speaker....good is good. )
...
Just my personal take....don't mean to throw cold water on the 901's...just to say it helps to remember 'horses for courses' sometimes.

Agree 99%. In a different post somewhere, I mentioned the Bose 901 is like a 4 year old who can play basketball as well as the 14 year old. The best 14-year old basketball player cannot compete with a college athlete or pro, but you can imagine how *fun* it is to watch a 4 year old play as well as a 14-year old. Same is true for modern speakers being the college athlete/pro.

For the 901, a lot of the fun/party element is hearing how great something that price point can sound despite all of the technical issues.

Using your garage example, I bet those Series 6's still sound better than any equivalent speaker that you can hang in the same position in the same price point. You could wall mount Sonos Era 300's or something like that but they're not going to get the same bass that you get from the Series VI or the ability to be anywhere in your garage and not hate the sound. Or, if you could sell your Series VI for exactly what you bought it for, what garage speaker would you run instead?

 

[pollock0424]

Big sound is what 901s are for. Accuracy is out of question here! I never understood the phrase, "no highs, no lows". My 901s had plenty of highs and lows, although not accurate!

It is a matter of taste, for e.g., some people like being shouted at by horns (klipsch, altec, jbl) in small room.

 

[Shonver]

What a fun and revealing thread this is! Thank you, @GXAlan , for taking us on this adventure. I have heard the 901 sound very good in the sparsely decorated lounge of a "student" home and (probably) the 802 in my high school's hall. I was but a teen then, but that (802) still stands out as one of the best-sounding pro rigs I have heard. I was not hi-fi savvy back then, but... first impressions last!

 

[audioresearch]

Hi, I've really enjoyed your enthusiastic posts about the 901s. Thx!

To refresh memory, I've owned the series 2, and still have a pair of series 6 running in the garage hung from the ceiling.
Was cool to see the old original processor....I'd forgot what it looked like.


I share that opinion. The early series had a huge omni-like sound, but lacked bass extension or resolving treble....probably helped seed the saying "no highs, no lows......."



I don't share this opinion however. The 901 is a fun speaker, a party speaker, and one that can allow decent conversation over at festive SPL.
But imo it's not even close to a good modern speaker, (or even a good vintage speaker....good is good. )

By good, I mean one that doesn't have smeared HF/VHF that comes from a multitude of drivers (spaced too far apart for coherent summations)
The 901 has that problem in spades using nine 5.5" drivers for HF/VHF duty; not to mention eight of used as indirect wall bouncers.
Transients have no chance of not being smeared.

This is one of those this things that can measure well in terms of frequency response, but frequency response doesn't tell the whole story.
I mentioned in another of your 901 threads that 'Coherence', a measure of the statistical "sameness" between the signal stimulus and the device under test, will be very low for the 901's HF/VHF. That's because which of the multiple arrivals can the measurement try to correlate with?

A dual channel FFT like AARTA or the free OpenSound Meter makes coherence measurements.

Probably the best surrogate for coherence using REW is simply to look at the Impulse Response for multiple arrivals.
I don't remember seeing an IR in your measurement posts, apologies in advance if i missed it.
Do you have one of the in-room speaker response?

Another major issue with using single drivers full range (with substantial EQ, is simply a whole lot of modulation going on.

Anyway, that's all techno-babble stuff.
The major reason I think the 901's can't compete is simply from a long history with them,
and my personal list of speaker comparisons that make them sound like fun, but very lacking in a number of ways.
Just my personal take....don't mean to throw cold water on the 901's...just to say it helps to remember 'horses for courses' sometimes.

If I remember right, Dr. Floyd Toole said something to the effect that coherence is not known to have any positive effect but that it can't hurt. I trust what he says, so I'm not concerned about coherence. I think coherence is one of those things that seems like it ought to be very important, but in reality is not. I'm sure the 901 does what you claim in terms of coherence, I just don't think it is audible to humans. It is certainly not audible to me.

 

[Earl2120]

I found this article through the back door. I registered just to say thank you for this extensive measurement and analysis of the original 901 series. I still own a series II 901 bought when I was stationed in Germany back in the early 70's.
Yes, my issue with that equalizer has been a problem very early on with-it popping power amp fuses during power up. We had factory service staff on our base and analyzed the problem with my Sansui 8 popping amp fuses was the Bose EQ pushing out DC during power up.
I currently have a surround system and don't use the Bose EQ and I get by with my current Denon systems room EQ calculations with the calibration mic it supplies.