I know this is probably a dumb question. I know the 901s are getting very old by now. Has you friend taken off the grills and checked to make sure the driver surrounds are all ok and working well? Also you can check to make sure each individual driver is working by just touching it. If any are not really 100% it would mess with the sound. I just had this thought and wanted to pass it on. I used to repair a bunch of them 30+ years ago.
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Bose 901 Series VI Active Equalizer Measurements
- Thread starter GXAlan
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Bose 901 Series VI Active Equalizer Measurements
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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.
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
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I decided to analyze my 901 Series VI Active Equalizer.
Manufacturer's Specifications:
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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)
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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.
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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.
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Running it at 0 dB (2.118V) shows clipping in the treble, where the EQ boost is particularly high.
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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)
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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.
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Bose 901 Series VI owner. My EQ has gone bad. Looking for a cheap solution. Others have described using a graphic equalizer to replace the Bose EQ, with good results.
Would I move the sliders to replicate the 'smiley face' on this chart?
Would I move the sliders to replicate the 'smiley face' on this chart?
Dennis_FL
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What do the Bose haters say about Dolby Atmos?
Dennis_FL
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I saw one on eBay for $190
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What's the connection?
Petrushka
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I have a series I purchased in 1968, delivered in January 1969. Still working, one driver replaced.
I have a Series II and IV, purchased at garage sales. The drivers in the II were replaced by Bose when foam rot became an issue. The warranty was extended for a number of years.
I have mini-DSP replacements for the equializers.
The biggest problem is finding a place where they work. That’s a problem for all speakers, but problem squared for the 901s.
I have a Series II and IV, purchased at garage sales. The drivers in the II were replaced by Bose when foam rot became an issue. The warranty was extended for a number of years.
I have mini-DSP replacements for the equializers.
The biggest problem is finding a place where they work. That’s a problem for all speakers, but problem squared for the 901s.
Petrushka
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All 9 are in series parallel in the I and II. I believe the later ones are 1 ohm each and connected in series. Bose wrote a lot of ad copy regarding their proprietary design and the fact that they made them in their own factory.
Bose switched from sealed enclosure to ported without changing the size or shape. Possibly the only case where the two designs can be directly compared.
- Thread Starter
- #150
You could use a software EQ to do this and you are pretty close.
Most graphic EQ’s cannot boost the bass enough, but you can attenuate the midrange to get as close as possible following the electrical curve I measured.
Petrushka
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How cheap?
Petrushka
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I’m pretty sure graphic equalizers are not going to sound great. I’ve tried.
I had a pair of Bose 901's and thought they were stunning. I still have a very high opinion of them in terms of the enjoyment that they produced. The experience was dynamic, clear, full and immersive. (All of the kinds of adjective's I generally deplore and dismiss now).
- Thread Starter
- #154
I really enjoy the Bose 901 for classical music. The only caveat I would say is that it is very enjoyable, in direct comparison to something like a Meyer Sound X40 you give up clarity for the dynamics and immersion.
I really do think modern DSP with the Bose 901 is better than the external EQ.
I can't imagine this is controversial in the least.
Bose knew what they were doing. One can agree or disagree with their design goals, but the original design was certainly hampered by limitations imposed by analog filters and real world cost considerations.
SCR
Member
Not a cheap solution but an alternative approach i did with my VIs and would recommend, get a miniDSP Flex with Dirac and let the room correction handle the linearity.
Dirac supports four different profiles which you can adapt to your taste, as example with a +2 or 4 db bass boost as additional profiles.
Dennis_FL
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Direct/Reflected
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