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Bose 901 Series VI ver 2 ("Final Edition") Measurements and Review

GXAlan

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Bose 901 Series VI ver 2 Active Equalizer (Final Edition)
Measurements and Review

1684637520812.png


Part 1: The Bose 901 Series VI:
Part 2: The Bose Model 901 '68 Edition:

In the very last article of this Bose 901 trilogy, I'll be looking at the Bose 901 Series VI ver 2. It was never clear why Bose chose not to call it a Series VII since it had a dramatic change in the drivers. Some hoped that there would be an 50th anniversary edition in 2018, but instead the Bose 901 was discontinued. Still, the Series VI ver 2 has a newer generation surround for the drivers as well as a new equalizer.

Series VI
1684637587577.png


Series VI ver 2
1684640722959.png


The Series VI equalizer has a well-dampened slider. The Series VI ver 2 has less resistance, physically, but there is a center "detent" or click. I used this position for the measurements. I ran it in the default Bass 1 mode which is the slightly boosted Bose house curve (which honestly is similar to Harman's house curve). The other difference is that my Series VI ver 2 equalizer has a green power LED whereas my original Series VI had a red power LED.

Electrical Measurement
80.6 dB

1 kHz SINAD

1684724668150.png

Same SINAD, but it's an improvement in both noise and THD. It's the 60 Hz AC mains noise that is worse in this unit. It may be variability, or the "electrical weather" at my home for the day. I was able to measure 81.0 dB SINAD once, but I just copy-pasted the image and the forum software lost my draft.

The Active Equalizer is also a slightly different slope with a seemingly greater treble boost relative to the bass. In the previous Series VI model, the peak bass and treble boosts matched.

1684712011451.png


Electrical Distortion (Equalizer)
Distortion is reasonable for the equalizer (shown here as %)
1684712084424.png



When comparing the Series VI vs Series VI ver 2, it looks generally similar, explaining why Bose chose not to call it a Series VII.
1684724866894.png


You can see the differences more clearly with more smoothing.
1684725036461.png


The ver 2 is slightly flatter in the midrange, but the bass is better in ver 1.

You can also look at distortion at Bose's 30 to 15 kHz and can see that the distortion on the Series VI ver 2 is slightly lower overall. In ver 2, most of the distortion is under 0.5% whereas the ver 1 seems to average 0.5%

Speaker-level Distortion
1684725994701.png
1684725948589.png



Subjective Impressions
The midrange/vocals do seem to be a bit cleaner with ver 2, but the reduced bass is noticeable. I didn't measure IMD, but my impression is that the Series VI ver 2 has improved IMD in that vocals are similarly good between both speakers when it's someone singing with minimal background music whereas the ver 2 has greater clarity of the vocals when there is a complex band playing as well. This difference in clarity is relatively subtle, but difference in bass extension is not subtle at all!

Running the JBL 708P in roughly the same position as the Bose 901's shows that the Series VI ver 2 more closely matches the the 708P's bass. You can also see how an un-corrected JBL 708P has a big dip in the bass (from the room) whereas the reverberations of the 901 help to fill that out (with the trade-off of comb filtering).

Swapping the equalizer units didn't change the sound beyond the different frequency response curve. No matter which equalizer unit I used, the drums were more convincing on the original Made-in-Canada Series VI while in complex passages, the vocals were slightly cleaner with the Made-in-Mexico Series VI ver 2.

1684725309701.png


Conclusion
Measurements help bust audiophile myths.

First, these measurements suggest that the phrase: "No highs, No lows, must be Bose" does not apply to the Bose 901 when used with the Active Equalizer. Maybe people assumed the equalizer offered a simple smiley face EQ boost and assumed that the speaker without the equalizer was the truest response. Maybe people assumed the Acoustimass 5 cubes reflected the sound of the Bose 901.

Second, there is misinformation about the original, sealed Bose 901's (Series I and II) offering better bass provided that you had enough amplification power and it was simply that the 901 came to market when tubes were still common. That's not true at all. The newer models provide deeper bass whether you use a tube or solid state amplifier. Advances in the full-range speaker driver also provide a cleaner frequency response, so the "sealed" original design is not inherently better. I did really enjoy the original when using advanced software EQ, and there's a possibility that I just need to restore my '68 Edition equalizer.

Third, there's a lot of misinformation on the 'net about there being no difference in sound quality beyond the Series V other than cosmetics. There are even reports that Bose themselves reported that there was no difference between VI and VII ver 2, although the internet discussion does talk about subtle differences. The forum posts I saw also fail to distinguish between Bose engineers and Bose retail store salespersons as the source for the claim that the VI and VII ver 2 were the same. With these measurements, we see that there is a clear difference in the equalization curve from "Series VI" versus "Series VI ver 2."

Fourth, in my previous Bose 901 threads, there have been comments "I heard these speakers in 1970 and hated them." By looking at these generations, it becomes clearer that this would be similar to saying that you drove a Mercedes S-class in 1972 and didn't like it, so you don't understand the point of an S-class today. While the Bose 901 kept the overall dimensions, the 11%/89% percent direct/reflecting ratio, and use of full-range speaker drivers, it's pretty clear that each generation was a bit different with measured electrical performance of the equalizer getting better between launch and final version as well.

I've had fun exploring these different Bose 901's and I'm done with the measurements. Now it's time to just sit back and enjoy the music.

That is, unless someone has the Bose 901P's which has a different driver complement as it appears to be 16 ohm impedance rather than 8 ohms, and utilized yet another variant of the equalizer. To my knowledge, this is the true "final flagship" of the Bose 901 concept.
 

pollock0424

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I think the measurements might improve if one uses a dsp to EQ?
Deercreek sells a miniDSP loaded with curves.
 
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GXAlan

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GXAlan

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IMG_7619.jpeg
I’m not sure how Japanese power handling ratings differ from the US but the 2004 Japanese Bose 901 specifications had a 700W peak power handling!

The US Series VI (presumably ver 1) stated
IMG_7621.jpeg

How many amplifiers do you know that can put out 700W into 8 ohms?!
 

audioresearch

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I believe that the accusation against the Bose 901 that it acts as a comb filter is totally irrelevant to its sound.

All you have to do is connect an audio signal generator to any loudspeaker in a typical listening room and vary the output frequency through the audible range, 20Hz to 20KHz while you are seated at any position in the room and what you hear is the volume constantly going up and down just like a comb filter. Don't take my word for this, try it yourself.

The effect is huge. I haven't done it myself in a long time, but I think it is roughly plus/minus at least 6db. Impossible to miss it.

What that means is that the room itself acts as a comb filter.

Now since essentially everyone who listens to music from a loudspeaker does so in a room, and I have never once seen anyone complain about the room acting as a comb filter, it becomes quite obvious that some rather severe comb filtering is totally inaudible when listening to music.

Therefor, who cares if the Bose 901 might also act as a comb filter???? Irrelevant.
 

beagleman

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I have heard the 901s numerous times, and like them in some important ways.

But while I find them a lot better than some "believe", they also have some built in limitations that make them unique and not comparable to most normal HI FI speakers overall.
My biggest impression of them, is for how small they truly are, they can create a "Lot of sound" and sound bigger than their small box would seem to dictate.
I admire your love of this speaker and your great write up and details.
 

audioresearch

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The limitations that I noticed were that due to the small size of the Bose 901 cabinets, they were limited in how much spl they could put out in the lower bass region without having audible distortion. This is true for all small speakers. I used to run four pairs of the 901 series IV and that did take care of that problem since together they acted as a large speaker. Then every single driver failed over a short period of time due to the foam surrounds rotting away.

So, I designed and built four of my own speakers. Each had an 18" woofer, 4 vertically stacked sealed midranges, and a tweeter. Each cabinet was 42" x 21" x11". I came up with a method to copy the frequency response of an original Bose 901 and "copy" it into my new equalized speaker system so mine had the same response at my listening position in my listening room that an original 901 had.

I also got a big sound like Bose, but I did it not by bouncing most of the sound off the back/side walls(my speakers have conventional front facing drivers), but by having 4 huge speakers spread across the front of my room. I used only a crude crossover to distribute the lows to the woofer, the mids to the midrange, and the highs to the tweeter and then I equalized the system too. My speakers are ported which greatly lowers distortion because at low frequencies, the air inside the speaker cabinet moves in the opposite direction as the driver cone and so the cone no longer has a high excursion and that eliminated or greatly reduces distortion due to the spider and surround stretching beyond where they are linear and also keeps the voice coil well away from the xmax limit where it would move outside of the motor's magnetic field which is another distortion disaster avoided.

But sometimes I blow tweeters and so I've decided to integrate 2 pairs of original 901s(this avoids foam rot problem) that I bought on Craigslist into my system and they will bounce sound of the rear wall. The 901s will be directly behind my large speakers, one 901 behind of each my 4 speakers and so the front drivers of the 901 will be blocked by my speakers physically in the way. I will use the 4 sealed mids in each of my speakers to fire forward. I will also disable my tweeters and re-equalize the entire system to have the same frequency response as an original 901. That way, all my mid drivers will output both mid frequencies and high frequencies just like the 901 does and so the blown tweeter problem will be be eliminated. I will send only as much low bass to the 901s as they can handle without audible distortion (and this might even end up being no bass at all-won't know till I test this), and send the rest to my large speakers with 18" woofers.

I sold a few dozen of my large speakers and I demonstrated them to customers up against a Bose 901 series VI and everyone who listened agreed that my speakers sounded to their ears identical to the 901s but when the spl level was raised, the 901s just simply gave up and my speakers kept going in the bass region. My speakers also did not have the audible port tube air turbulence noise the 901s had. What I tried to do was to keep the best of Bose and fix up the worst of Bose. I used only drivers that had metal baskets. On many 901 series, Bose used plastic which cracked where the mounting screws went through. I used only cloth surrounds, no foam. At low sustained frequencies, the plug-shaped plastic piece inside the port tube of the 901 can be made to violently vibrate. It looks as if it is about to break off and go flying out into the room. I used much larger port tubes and did not need to use inner pieces to break up air turbulence. I could use larger port tubes and still keep them inside the cabinet because my cabinet was so much larger than the 901 cabinet.

I knew the engineer who had been the head of the loudspeaker design department at Bose, just underneath Bose himself, and he along with Dr. Joseph D'Appolito also helped with the design-at the time I had no computer based measurement or design hardware/software and they did.

By the way, that chief Bose speaker designer told me that he wanted to alter the 901 design to have a woofer(it was just simply far too obvious that the 901 could not move enough air and had too small a cabinet for loud low undistorted low bass in his and my opinions) but according to him, Dr. Bose said no. I've forgotten if the designer saide he wanted to make the 901 cabinet larger and put the woofer into it or wanted to use a separate subwoofer.

I notice though that Bose makes or made professional systems that know how to do low bass right-large cabinets, 18" woofers, high power, etc.

In my re-design, I plan to make use of Spinorama(which I'll have to do manually) and probably REW and the Dirac DSP system plus any other "modern" improvements I might be able to find that are priced right.

I had an acoustics professor design and build a bass reflex sub-woofer for me and his system started dying at about 30 Hz whereas my system started dying at about 40 Hz and so I plan to re-design my system to go lower in the low bass region to at least match what the professor's system can do. I'll most likely end up using different woofers and changing the port tube lengths/widths to properly match up. I originally selected the 18" woofer that I used because it was huge and would impress customers, it had a strong magnet, it used no foam, and I could buy it fairly cheap. But now I think I can likely do better by selecting another woofer that will match up better to the size of my cabinet and whatever port tube design works best with it. Leap 4.5 which I own can display all that in graphs so I can pick what looks like it will work best. I also have the ancient MLSSA measuring system and ancient computers that it will run in to measure all the parameters of my woofer so I can plug them into Leap to do the cabinet & port tube design.

I also avoid any possible problems introduced by subwoofers that might cause gaps in frequency response and/or be able to be localized by listeners by not using subwoofers at all in the system.

I power my system with an old Peavey PV-2000 amplifier which will probably output about 1400 watts into the system and if ever I designed the system to load it down with only 2 ohms per channel, can output 2000 watts. By the way, this amp simply murdered the class D Carver M1.5T amps I used to own. Not only would the Peavey keep playing continuously without shutting itself off to take a rest like the Carvers did, but it would output so much more power that it sounded to my ear far louder then two of the Carvers combined.

I have no plans to sell this system, just use it personally. A huge problem with using DIY parts sources and trying to sell systems based on them is that every few years many or all such parts get discontinued. I'll probably start the re-design in about 2 years as I'm busy with other things I have to finish.
 

Rmar

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The most accurate and complete evaluation of the Bose 901's to date. Well done and thank you.
Bose 901 Series VI ver 2 Active Equalizer (Final Edition)
Measurements and Review

View attachment 286942

Part 1: The Bose 901 Series VI:
Part 2: The Bose Model 901 '68 Edition:

In the very last article of this Bose 901 trilogy, I'll be looking at the Bose 901 Series VI ver 2. It was never clear why Bose chose not to call it a Series VII since it had a dramatic change in the drivers. Some hoped that there would be an 50th anniversary edition in 2018, but instead the Bose 901 was discontinued. Still, the Series VI ver 2 has a newer generation surround for the drivers as well as a new equalizer.

Series VI
View attachment 286943

Series VI ver 2
View attachment 286949

The Series VI equalizer has a well-dampened slider. The Series VI ver 2 has less resistance, physically, but there is a center "detent" or click. I used this position for the measurements. I ran it in the default Bass 1 mode which is the slightly boosted Bose house curve (which honestly is similar to Harman's house curve). The other difference is that my Series VI ver 2 equalizer has a green power LED whereas my original Series VI had a red power LED.

Electrical Measurement
80.6 dB

1 kHz SINAD

View attachment 287241
Same SINAD, but it's an improvement in both noise and THD. It's the 60 Hz AC mains noise that is worse in this unit. It may be variability, or the "electrical weather" at my home for the day. I was able to measure 81.0 dB SINAD once, but I just copy-pasted the image and the forum software lost my draft.

The Active Equalizer is also a slightly different slope with a seemingly greater treble boost relative to the bass. In the previous Series VI model, the peak bass and treble boosts matched.

View attachment 287201

Electrical Distortion (Equalizer)
Distortion is reasonable for the equalizer (shown here as %)
View attachment 287204


When comparing the Series VI vs Series VI ver 2, it looks generally similar, explaining why Bose chose not to call it a Series VII.
View attachment 287242

You can see the differences more clearly with more smoothing.
View attachment 287243

The ver 2 is slightly flatter in the midrange, but the bass is better in ver 1.

You can also look at distortion at Bose's 30 to 15 kHz and can see that the distortion on the Series VI ver 2 is slightly lower overall. In ver 2, most of the distortion is under 0.5% whereas the ver 1 seems to average 0.5%

Speaker-level Distortion
View attachment 287250View attachment 287248


Subjective Impressions
The midrange/vocals do seem to be a bit cleaner with ver 2, but the reduced bass is noticeable. I didn't measure IMD, but my impression is that the Series VI ver 2 has improved IMD in that vocals are similarly good between both speakers when it's someone singing with minimal background music whereas the ver 2 has greater clarity of the vocals when there is a complex band playing as well. This difference in clarity is relatively subtle, but difference in bass extension is not subtle at all!

Running the JBL 708P in roughly the same position as the Bose 901's shows that the Series VI ver 2 more closely matches the the 708P's bass. You can also see how an un-corrected JBL 708P has a big dip in the bass (from the room) whereas the reverberations of the 901 help to fill that out (with the trade-off of comb filtering).

Swapping the equalizer units didn't change the sound beyond the different frequency response curve. No matter which equalizer unit I used, the drums were more convincing on the original Made-in-Canada Series VI while in complex passages, the vocals were slightly cleaner with the Made-in-Mexico Series VI ver 2.

View attachment 287244

Conclusion
Measurements help bust audiophile myths.

First, these measurements suggest that the phrase: "No highs, No lows, must be Bose" does not apply to the Bose 901 when used with the Active Equalizer. Maybe people assumed the equalizer offered a simple smiley face EQ boost and assumed that the speaker without the equalizer was the truest response. Maybe people assumed the Acoustimass 5 cubes reflected the sound of the Bose 901.

Second, there is misinformation about the original, sealed Bose 901's (Series I and II) offering better bass provided that you had enough amplification power and it was simply that the 901 came to market when tubes were still common. That's not true at all. The newer models provide deeper bass whether you use a tube or solid state amplifier. Advances in the full-range speaker driver also provide a cleaner frequency response, so the "sealed" original design is not inherently better. I did really enjoy the original when using advanced software EQ, and there's a possibility that I just need to restore my '68 Edition equalizer.

Third, there's a lot of misinformation on the 'net about there being no difference in sound quality beyond the Series V other than cosmetics. There are even reports that Bose themselves reported that there was no difference between VI and VII ver 2, although the internet discussion does talk about subtle differences. The forum posts I saw also fail to distinguish between Bose engineers and Bose retail store salespersons as the source for the claim that the VI and VII ver 2 were the same. With these measurements, we see that there is a clear difference in the equalization curve from "Series VI" versus "Series VI ver 2."

Fourth, in my previous Bose 901 threads, there have been comments "I heard these speakers in 1970 and hated them." By looking at these generations, it becomes clearer that this would be similar to saying that you drove a Mercedes S-class in 1972 and didn't like it, so you don't understand the point of an S-class today. While the Bose 901 kept the overall dimensions, the 11%/89% percent direct/reflecting ratio, and use of full-range speaker drivers, it's pretty clear that each generation was a bit different with measured electrical performance of the equalizer getting better between launch and final version as well.

I've had fun exploring these different Bose 901's and I'm done with the measurements. Now it's time to just sit back and enjoy the music.

That is, unless someone has the Bose 901P's which has a different driver complement as it appears to be 16 ohm impedance rather than 8 ohms, and utilized yet another variant of the equalizer. To my knowledge, this is the true "final flagship" of the Bose 901 concept.
An accurate and complete evaluation of the 901's worth reading. Great work. Thank you for sharing.
 
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GXAlan

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The most accurate and complete evaluation of the Bose 901's to date. Well done and thank you.

Thanks!

The other great graph was from my Series VI (version 1) post.

Dirac Live with 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


Obviously Dirac, being state of the art can correct some of the frequency response wiggles, but the fact that the stock EQ overlaps so nicely and we know that stereo playback reduces the impact of frequency response “wiggles” and the Bose 901 has super stereo tells you that actual in-home performance of the 901 was well ahead of its time *as a lifestyle speaker* where the smaller size matters.
 
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GXAlan

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The "Harman curve" (which actually isn't a fixed target for loudspeakers but depends on several factors) doesn't have a treble boost nor it is +10 dB at the bass si I don't see such as a confirmation for anything.

The Dirac target is this curve.

Which is flat but has a 10 dB bass boost. It does not have a falling treble.

The treble boost is to correct the naturally weak treble of the un-eq’d 901 drivers to flat.

The bass boost in the default middle position is also to correct the naturally weak bass of the uneq’d 901 drivers to a hefty amount of bass.

Un corrected 901 and telling Dirac to use the curve described = correction filter seen.

Factory EQ box’s correction filter is similar.

Remember that the Bose 901 was released decades before Toole’s work was published, and my measurements show that the response is largely similar minus the bass and distortion improvements.
 

steve59

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I had a pair of 901VI I bought from a big box store in the late 80's that sounded like a bust until I hung them from the ceiling 2' in and 2'out from the corners and their bass potential came thru. With a simple Realistic 55 wpc receiver the system sounded great. Many liked to poke fun at them, but for the longest time I ignored the noise and enjoyed the music.
 

thewas

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The Dirac target is this curve.
https://youthmanreviews.com/harman-target-curves-for-dirac-live/
Which is flat but has a 10 dB bass boost. It does not have a falling treble.
Than its just a bass target.

The treble boost is to correct the naturally weak treble of the un-eq’d 901 drivers to flat.
So your above plot is not a mic measurement but an "electric" of the EQ?

Remember that the Bose 901 was released decades before Toole’s work was published, and my measurements show that the response is largely similar minus the bass and distortion improvements.
Toole correctly says that there is no generic target for loudspeakers at the listening position but the only target is flat direct sound and smooth directivity, anything else can be a result of coincidence and doesn't mean anything.
 
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GXAlan

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Than its just a bass target.
Yes, fair statement.

So your above plot is not a mic measurement but an "electric" of the EQ?

Yes, electric of the EQ box vs electric of a Dirac EQ

The mic measurement at MLP is
1704135971544.png


Toole correctly says that there is no generic target for loudspeakers at the listening position but the only target is flat direct sound and smooth directivity, anything else can be a result of coincidence and doesn't mean anything.

Sort of. Coincidence, yes. But the sweep was in part to point out that the common phrase “no highs, no lows, must be Bose” has no validity when looking at objective measurements.

Professor Amar Bose, has just as much credibility as Dr. Toole, although his commercial approach and design goals are different.


Early on, Dr. Bose’s research showed that once you had about 15 kHz or so, people felt that it was high fidelity and you didn’t need to go much higher than that. That makes sense given the age he probably used as the sample. What he also found was that people value stereo and stereo effects greater than frequency response smoothness. This is also consistent with Dr Toole’s research indicating that listening in stereo masks frequency response flaws. We also know that bass is a big component of preference and the 901 achieves a lot of bass from a small enclosure.

So the 901 was designed around this idea of masking, maximizing the spatial effect and keeping it attractive/small. Again in the 1960’s when Boston was still debating public school desegregation…

Now, you could rightfully say that Dr Bose is like Newton where his research is accurate only under specific constraints/conditions and Dr Toole is like Einstein, and that our understanding of acoustics has improved a lot. But just as headphones are enjoyable as an alternative to speakers, the Bose 901 in room is enjoyable as an alternative to the classic flat direct sound with smooth directivity

The biggest issue was Bose suing Consumer Reports magazine for a bad review. That’s a business not science issue. The details make the issue less clear.

The writer of the Bose 901 review was also a speaker designer who had patented an electrostatic speaker and was trying to commercialize it. Bose argued that there were factually inaccurate statements that could “only” be explained by this conflict of interest.

1) “Complaints that the instruments wandered around the room”, they argued was factually inaccurate. It would be like saying that a mono speaker caused instruments to wander around the room
2) Complaints that the listening panel was asked what sounded like a reference direct radiating speaker as opposed to what was preferred by the audience and it was the reviewer who designed the panel evaluation.
3) Complaints that you needed a gigantic 50 watts of power which was factually inaccurate. (the 901 sounds fine with a 7W 300B SET. It can handle more power).


Back then we didn’t have the FTC disclosure for reviewers and financial conflicts of interest
 

mjgraves

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I power my system with an old Peavey PV-2000 amplifier which will probably output about 1400 watts into the system and if ever I designed the system to load it down with only 2 ohms per channel, can output 2000 watts. By the way, this amp simply murdered the class D Carver M1.5T amps I used to own. Not only would the Peavey keep playing continuously without shutting itself off to take a rest like the Carvers did, but it would output so much more power that it sounded to my ear far louder then two of the Carvers combined.
AFAIK, Carver never made any Class D amps. His trick was amps with "tracking power supplies." The power supply was a kind of switched mode. The audio path was traditional.
 

Chris Chagros

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Great article. Only thing I found incorrect was the power LED color depiction on the EQ. All version 2 EQs have a green LED. Not all Version 1 EQs have a red LED. They made the switch to green late in the Version 1 run . I have both versions. They are both equipped with green LEDs. The two EQs are definitely different as noted by the markings on the underbelly of the EQs. I also made the assumption the different colored LED were specific to the two versions.
 

skyfly

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Questions to those with 901 experience. (I have no 901s on hand now, but I have a friend owning 901 Series IV (blue drivers, not version 2))

How did you adjust tonal balance by ear? It was somewhat difficult (or different from conventional front firing speakers, or the particular pair of 901s was defective or counterfeit, or the particular room was exceptially bad. . . . )

some music tonally balanced -> dialog has hard to tolerate ess (not merely 4k-10k quantity issue I guess)

dialog in the evening news of big broadcast channels tonally balanced -> muffled incomprehensible dialog in movie channels

make dialog in movie channels intelligible -> the fight scenes are unbearable
(the same movie sounded intelligible while fight scenes were bearable on non-hi-end non-hi-fi speakers integrated to the TV chassis)
 
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