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Bose 901 Series VI Active Equalizer Measurements

GXAlan

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Bose 901 Series VI Active Equalizer Measurements
1683697970080.png


1683697931766.png



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


1683695401561.png



I decided to analyze my 901 Series VI Active Equalizer.

Manufacturer's Specifications:
1683695246409.png



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)
1683695834270.png


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.
1683696354403.png



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.
1683696841725.png

1683699986950.png


Running it at 0 dB (2.118V) shows clipping in the treble, where the EQ boost is particularly high.
1683697017932.png

1683700166821.png


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)
1683701792562.png


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.
1685379576613.png
 
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dougi

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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.
 

AlexanderM

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We had 901 knock offs when I was a kid, and we loved them. I noticed that Erin seemed to really enjoy his time with the speakers, pretty much saying they are just different. I also used to love the sound of my 301s, even though I now know they didn't produce accurate sound reproduction. When the time comes I won't be looking to purchase another set of Bose speakers but I do suspect that I would like the Definitive Technology towers, say the 9040 or the 9060, given they have the bipolar sound, with some speakers pointing to the back. Every time I look at them I think, that just looks like direct reflecting sound, just not using a single full range driver.
 

FrankW

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Nice. Maybe someone could recommend these in all those "end game" speakers threads.:)
 

krabapple

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It's unfortunately hard to access the original report about it, but circa 2010 there was a blind shoot out between Linkwitz Orions, Behringer monitors, and a home-made Bose 901-inspired (but better) speaker by hobbyist Gary Eickmeier that he called the "IMP"...and the Bose-inspired speakers won.

Here's a secondary reference to it, in the first post of a diyaudio thread:


Addendum: found a more detailed source of info, featuring Eickmeier himself.
 
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GXAlan

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Nice. Maybe someone could recommend these in all those "end game" speakers threads.:)

Yeah, and one of the rarest 901's is the VI ver 2 which has the different foam surround.
balzity8fvi7fa0ujik9.jpg


The advantage of the 901 as "end game" speaker is that you stop looking for something new. If you're happy with something that objectively measures poorly, it is "end game" since you probably won't be able to find something to upgrade to. If you're looking for end-game high performance, that's where the extra 0.1dB of smoothness or noise can be tempting when cost is taken out of the equation.
 

FrankW

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balzity8fvi7fa0ujik9.jpg


The advantage of the 901 as "end game" speaker is that you stop looking for something new.
Yeah but apparently the grill has trouble staying on so you might have to look for that on the floor or thereabouts. MKR should add to list. I'm thinking Ali's palace might not be a great fit but who knows?
 
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GXAlan

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Yeah but apparently the grill has trouble staying on so you might have to look for that on the floor or thereabouts. MKR should add to list. I'm thinking Ali's palace might not be a great fit but who knows?
+1, and for those who aren’t frequent visitors to ASR

MKR:

Ali:

Mark my words though, and this post can be the reference/proof. I am going to spend some time doing some research and homebrew one next year and send it to Amir for measurements :)
 

FrankW

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I am going to spend some time doing some research and homebrew one next year and send it to Amir for measurements :)
With or without the Velcro? What if it's the secret sauce and the sound "falls apart" without?
 

NiagaraPete

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I sold these and there was a certain amount of people that said “WOW”. The rest like me were horrified with how bad they sound.
 
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AdamG

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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?
To this day. I give full credit to the 901’s completely blowing my mind (without any drug influence) when I heard them. They were in a VFW Hall that was sponsoring a USO Dance. My first exposure to what began as my Audiophile journey. For their time they were head turners. Talking late 70’s. Bose may have a well earned reputation. But the 901’s were the exception in my book. Great review thanks for the work!
 

PierreV

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I still have my pair of 901 Type VI: I had a lot of _fun_ with them over the years.

But to be honest, they are hilariously poor as HiFi speakers when compared to my other boxes.


IMG_20230511_014713 (Small).jpg
 

phoenixdogfan

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I owned the OG 901s when I was a student in college and used them in the dorm. Had them for around 5 years. They were my step up from KLH 17s. Ran them on a Heathkit AR 1500 receiver. They were a great party speaker, but obviously distorted something fierce. Problem was the Equalizer added a 15 db bass boost which of course meant they speakers required 2^5 times as much amplifier power to play without clipping. Considering the AR 1500 put out 70-80 watts on a good day, it's not hard to see how the 901s got in trouble reproducing bass all the time. But still I played them loud. Ultimately were replaced with Rogers LS 3/5as, and I was not a bit sorry to do that. I lived with them for a very long time, and I don't see them as a high end, let alone an end game speaker.
 
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GXAlan

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I owned the OG 901s when I was a student in college and used them in the dorm. Had them for around 5 years. They were my step up from KLH 17s. Ran them on a Heathkit AR 1500 receiver. They were a great party speaker, but obviously distorted something fierce. Problem was the Equalizer added a 15 db bass boost which of course meant they speakers required 2^5 times as much amplifier power to play without clipping. Considering the AR 1500 put out 70-80 watts on a good day, it's not hard to see how the 901s got in trouble reproducing bass all the time. But still I played them loud. Ultimately were replace with Rogers LS 3/5as, and I was not a bit sorry to do that.

What’s impressive is that even the Series II Bose was rated for 400 watts as long as it was less than 5 seconds.

Continuous was 50 watts.
Where are the IMD test results?

Sure, I will run some tests tonight.
 

pseudoid

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There was an album by Peter Frampton (I think) and there was this song in the album, where the Bose901s would make a whooshing sound with a bit of fluttering. Each time we would play that song, the owner's parrot would do a head-cock and squawk back at the speaker!
 

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.
Yes, I agree.
As to the hanging from the ceiling, that was my 1 experience also. At a party in some point 1975-ish
 

damage

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My only complaint is the lack of crisp clear highs and the amount of power required to really make them sing. I didn't have the active equalizer before but was using an AudioSource EQ to mimmick it. I have the EQ now but haven't tried them with that. I'll have to give them a whirl.
 
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