The "FIX" is in.

[soundminded]

I said in another thread that I thought that the limitations of the original Bose 901 could be overcome. And now I am completely convinced that I was right. I dragged them downstairs from my bedroom where they were in a very unfavorable location, flanking a 9 foot dresser in an 18 x 22 bedroom with an expansion ceiling and slightly on the dead side acoustically. Now they are in a 14 x 14 sun room where the acoustics are live, the walls are half glass and there is nothing to prevent them from reflecting their sound as intended. I have been experimenting all morning with additional indirect firing tweeters, biamplificaton, and a little additional equalization. They sound teriffic. The bass is awesome, the highs are soaring now and the sound is as clear and balanced as I could ask for. I think that there are a lot of Bose bashers out there who would be very disappointed to hear this system. I forsee years and years of future enjoyment for me coming out of these speakers.

[soundminded]

After an order from Parts Express arrived last week, I installed 4 tweeters per channel by hanging them from the top plate overhang. Three face backwards (two 1/2" Dayton polys one one each side) and a third 3/8" Audax poly at the apex and another 3/8 Audax poly on the front just above the 4" driver. All are crossed over at about 9khz 6 db/octave with a 2.7 mf NPC on each one and all in parallel. They are being driven by an AR amplifier (talk about overkill.) The 901s are being driven by a Marantz receiver SR930 which seems to be about 60 to 100 wpc (anybody know anything about this receiver?) It has the advantage of a preamp output/amp input jumper which allows the Bose equalizer to be placed in this part of the circuit and the AR amplifier connected to the Bose equalizer tape output. This allows both amplifiers to be driven by one volume control so the AR amplifier gain and tone settings can remain untouched. The AR amp has a nice feature, a null L minus R function which allows you to adjust for mistracking of the tone and volume controls and there is a slight mistracking of the treble controls which was easily fixed. The SR 930 also has a 10 band equalizer built in and it was very useful for tweaking the overall response especially eliminating a broad 500 hz peak characteristic of the original Bose 901. I also added a slight bass boose and a treble rolloff.

The left Bose speaker did not seem to have quite the deep bass of the right speaker. I removed the back grill cloth and decided that the problem was that the speaker was no longer airtight. After a call to Bose, I went at the gasketing material with a caulking gun and some GE silicone clear caulking. I was extremely creful not to get any on the cones or the surrounds which appeared to be in perfect condition after 34 years of use and storage. It's easy stuff to work with because it has the consistancey and feel of vaseline so you can work it with your fingers and any kind of tool you want. This fixed the problem. The system now sounds as good as I could ever ask for. Only future improvements I can think of would be to swap amps for a Crown DC300 or 300A and get a second set of speakers. I'll play with the direct/reflecting ratio of the tweeters by adding a couple of resistors to the direct firing units but I don't think it will have a big effect.

[soundminded]

In early July, I added an 8 ohm resistor across each front firing tweeter and a 4 ohm resistor in series dropping their output by 3db and changing the direct to reflected ratio of the tweeters from 1:3 to 1:6 without changing the crossover frequency. This was done to reduce a slightly forward sound that couldn't be equalized out and to make the tweeter direct/reflected ratio closer to that of the main 4" drivers. It worked. That and continuing to tweek the speaker location, aiming, and equalization resulted in additional improvements. I am extremely satisfied with the sound which now has all of the character of a full range reasonably flat frequency response speaker system while retaining the advantages of the direct/reflecting concept inherent in the 901 design. I find myself listening to them more and more and liking what I hear very much.

How do they compare with the enhanced Teledyne AR9s? It's difficult to say. The effect of the direct/reflecting character makes them sound different and the presence of solo instruments and small ensembles in the room is unique. The treble is similar with a slight edge still going to the AR9s. The AR9s still have it in the deep bass but it's impossible to tell whether that is due to the speakers themselves or the limitations of the Marantz SR930 receiver. I don't have any figures for the receiver but the meters highest reading is 135 watts/ channel and I recall once reading that it is 180 wpc. I was skeptical until I noticed that the main fuse is 8 amps. With the additional bass boost of several decibels, I have to use the 40 hz cut switch on the Bose equalizer or the meters keep getting pegged (can you peg LED meters?) and I can clearly hear the distortion as the amplifier clips. On paper the 901s equal and even better the AR9s but c'mon, nine 4 inch drivers compared to two twelves in each of the AR9s, who am I kidding if not myself? Given the availability of these on the used market at very low prices and the low cost of very high power amplifiers such as the Crown CE-1000, I may just try a second pair and a new amplifier. But I'm in no rush.

[Guest Bret]

>(can you peg LED meters?)<

If Obi-Wan Kenobi can have a light saber, then we can peg an LED meter.

All your work with the 901 is very interesting. You called the image "unique" in certain situations. I had/have several issues with the 901 and all direct-reflecting designs regardless of manufacturer (even the LST ). How's the image of a solo voice? Where's it coming from? Are the 901s hanging from a ceiling or on stands?

While you are subjectively comparing the bottom of the 9 with the bottom of a 901, isn't it true that your 12' x 12' room is really too small to allow for the full extension of either?

Bret

[soundminded]

Thank you for asking. My comments are completely unscientific. Just my personal reactions.

Because of what I have done to them meaning the way I use them, neither My Bose 901s, nor my AR9s probably sound anything like anybody elses. The 901s are on pedistals. I also "had issues" with Bose 901s. Perhaps that explains why I didn't listen to them for about 15 or 20 years even when they were sitting there ready to use.

The Imagaing of my 901s is also different. The stereophonic effect, which some people call imagaing is not nearly as pronounced as in speakers designed to create the illusion of a wide performing stage with the apparant source coming from beyond the speakers. The image is is about as wide as the speakers, and appears to be in the room, sometimes a little behind them but never deep. I don't care. That is not important to me. However, as with the AR9s, you will hear a stereophonic effect no matter where you are in the room. This is not surprising since the high frequencies give the cues for directionality and you are never really off axis with either of them in the usual sense.

Rather than give you an off the cuff answer about solo voices, I decided to do some careful listening first, just to refresh my memory and be sure of what I am saying. I used five handy discs of Kiri TeKanawa singing solo pop music; Kiri Sings Berlin, Kiri Sings Kern, Kiri Sings Porter, Kiri Sings Greshwin, and Kiri, Blue Skies with Nelson Riddle and his Orchestra. I thought a solo female voice would show up this aspect better than a male voice. Kiri is a great opera singer but as a pop vocalist, she leaves a lot to be desired. Frankly, "she ain't got that swing." Anyway, she does not sound 10 feet wide, she sounds like a normal voice right in front of you. If the volume is increased well above what is normal for a human voice, the size of the source gets a little bigger but not bad. As you move away from the center, the voice has a greater tendency to stay in the center until you are about in line with the left or right speaker at which point it shifts to that speaker. The AR9s have the voice shift a little sooner as you move off center. You should understand that the high end of the two systems as I have them are very similar. With the AR9's program controls set for the tweeter down to -6db and three indirect firing 3/8 inch polys firing straight up, much of the high end comes from the polys. With the 901, there is one front firing poly at -3db and three indirects firing at 0 db each. Not surprisingly there is a great deal of similarity.

As for other imaging differences, many people report Bose 901 makes a piano sound like it is 10 feet wide. Anyone who has ever seen a Steinway Type A or B Concert Grand knows that it IS 10 feet wide, even larger and depending on how it is miked, that's how it can sound. Listen to a grand piano with the top up in anybody's living room and you will get an idea of just how big a source of sound it is. Leon Bates' recording of Gershwin (Naxos 8.550341) is just such a recording and the 901s make the piano sound just like it is in the room. Yes it sounds BIG. OTOH, recordings where the piano is one instrument accompanied with by others will make it sound more confined, not quite a point but closer. A nice midway example is The Golden Touch of Frankie Carle (Good Music 108829) where he is accompanied by a string bass, drums, and an electric guitar playing music of Irving Berlin. Interestingly, the piano on this recording has a sound peculiar to some Steinways and is the closest I've ever heard on a recording to the sound of my own Steinway "M" 5 foot 7 inch parlor grand. It has what might be referred to as a peculiar midrange presence that is wonderful once you get over the surprise of it.

It is true that a 14 x 14 room will not give the same bass reinforcement as a 14 x 30 foot room. Also, because of the way the room is furnished, you have to sit fairly close to the speakers, I'say about 7 or 8 feet from them. Still, the bass is not the equal of the AR9s. I don't think that is too surprising. The AR9s have some of the deepest, most powerful, distortion free bass I have ever heard and just beg to be exploited in this regard. With proper placement, not only do they seem to really get going where most other woofers have petered out, they excite every room resonance node there is. I'll take it warts and all. I'm sure a 1/3 octave or parametric equalizer and some bass traps would clean it up considerably but I'm not too interested in that, I'm satisfied with them just the way they are. On paper, the 901s should go deeper than the AR9s. AR9 is supposed to have a useful output to 28 hz but it's hard to say if they really stop there. All I know is that for really deep bass, you can feel it. You can also hear and feel rumble on a surprising number of compact discs. If there is a sound on the disc, I want to be able to hear it and feel it. Bose doesn't publish its specs but independent lab reports of series I showed that they went down to 26 hz with strong output, and 23 at a lower volume level. I don't have enough amplifier power to say if the limiting factor is the speakers themselves or the amplifier (I suspect it's the amplifier) but don't get me wrong, by almost any standards, these speakers can produce lots of clean deep bass. You can feel it. You can also see the receivers LED meters kick way over to the right with power levels often approaching 100 watts per channel even at moderate levels. Remember, in addition to the 20 db of bass boost in the deep bass, I've added another 6. But I've also engaged the deep bass cut which has a 10 db shelf cut below 40 hz.

Being an uncompromising sort of person in many ways, what' I'd really like is a speaker which combines the best attributes of both. For that, I'll have to design and build it myself. In the meantime, It's wonderful to be able to enjoy either or both of them any time I want.

[Guest jbangelfish]

And I thought you were ready to throw those old 901's in the trash. Well, I still have 4 pair of the damn things and I still can't get over what they can do. I had two pair of series II's stacked and for a while added 4, 12 inch woofers. It was less than an ideal setup and position was the worst but was fun for a while. I powered everything with my two Parasound HCA2200II's which are now biamped to my AR9's. The system could easily reach deafening levels and my neighbors were not amused.

Definately get a bigger power amp, you won't believe the results. When I bought my first set of series II's new in 1975, I also bought a Crown IC150 preamp and DC300A power amp and never regretted it. For some reason, everyone seems to hate all of these components, especially the 901 but I also see much bashing of the old Crown stuff.

I can't, for the life of me, understand why. The bashers like to say that it had great specs and sounded awful, I completely disagree. At least one reviewer, many years ago, proclaimed the DC300A to be the best amplifier ever made. Probably not completely true but I still consider it to be a fine amplifier and certainly better than any receiver or integrated that I've ever heard. No, I haven't heard them all. My Crown stuff took a week or so longer than the rest of my system to come in so the store gave me a loaner integrated amp. It was a Yamaha with about 110wpc. The difference when the Crown came in was nothing short of amazing, the Yamaha just didn't have the gas. Everything came to life with bass, punch, better treble, it just became complete and I've been a power freak ever since.

I had sold my Crown amp and preamp to one of my brothers many years ago when I needed some cash, with the agreement that it would never leave the family. He sold it to my other brother after a time and my son eventually bought both of them for $75 with the amp needing repair. We had it fixed for alittle over $100 but alas, recently, it did crap out and I think it's fairly serious, probably burned up one of the main transformers, I think.

Anyway, I picked up an Accuphase integrated with 100wpc or a little over and it is OK driving the 901 but not really enough power.

My son is now using it to drive a pair of series I 901's and since he is living in northern Wisconsin, at our cabin, he is better off with it or he'd be pissing off everyone in the north woods.

The point to all this blather is that 100wpc is not enough for the 901 and especially that of a receiver, even a Marantz. My old Crown was bench tested at 188wpc, 8 ohms and was barely enough for the 901's. You could clip it but it would be very loud so in almost any situation, I would consider it enough. My suggestion to you would be to give one a try, as I know that you like them too, or if not, any decent amp of around 200wpc or even more. You can't seem to hurt those old 901's and mine have had plenty of power run through them over many years. Be sure and let us know your findings when you switch to a new amp.

Bill

[soundminded]

The DC300 and DC300A were great amps...for the 1970s but even Crown has come a long way. Crown is probably the number one choice of professional sound installers and audio engineers because it performs superbly and is virtually 100% bulletproof. It also now has the backing of Harman International which makes it financially secure forever. The CE-1000 is probably the steal of the century boasting incredible power output and as usual nearly unmeasurable noise and distortion and ruler flat frequency response right across the audio spectrum. You'd be hard pressed to find another amplifier manufacturer who will give you a three year no fault guarantee of performance. At $450 including shipping from Parts Express it's very enticing. Rated power output can push one or even two pairs of original Bose 901s to their theoretical power handling limit. They of course have even more powerful units in this series and other series including their studio standard I and II. These are claimed to have "the best transfer function in the business" and a damping factor of 20,000!!!! The prices are a comparative bargain stacked up against competition like Krell. The main criticism audiophiles have about them is that they say they sound too bright. They never consider that the problem may be their speakers. This seems to be the constant cry of may "audiophiles" today. CDs are too bright and harsh, solid state amplifiers are too bright and harsh, moving magnet cartridges are too ??? something or other. Then they look for exotic audio cables to cut the high end and are lucky if they don't send their amplifiers into spontaneous oscillation with highly capacitive loads.

The addition of the 4 tweeters per side, using a separate amplifier for the tweeters, and re-equalizing the overall system and the thing is "a whole different animal." If you have a spare amp lying around, 8 audax 3/8 inch polys, 8 capacitors, and 4 resistors will only set you back about 60 bucks. Worth a try? Let me know if you do. Nobody else I know of has yet. If you do try it, I'll send you my equalizer settings, you can use them as a start.

[Guest jbangelfish]

Long time no see. The splattering of sound myth of the 901 is tremendously exaggerated and perpetuated by people who have never heard them or at the very least, never heard them correctly. They require perfect placement in perfect corners and a reasonably powerful amplifier, somewhere around 200wpc. The AR9's have similar placement requirements and maybe even more power. Since I biamped mine, I like them better and I never have clipping issues.

The 901 does some things better than anything that I've ever heard and that is to create a life-like or live sounding image. The AR9 provides slightly deeper bass but not by much, very surprisingly. I only refer to the two oldest series of 901, I or II which had sealed enclosures. Any of the newer series have lost the deep bass but don't need as much power to drive them. A trade-off that I don't care to make and I never listen to my pair of series VI.

I don't remember your choice of music but if you like rock music, there are some amazing stereo effects created by rock bands that lend themselves to the 901 very well. Rush, Steve Miller, Nazareth, Joe Walsh and probably countless others did some very cool sound effects where the sounds would travel 360 degrees and completely surround you. I've never heard any other speaker do this like the 901. It does it completely seamlessly and you would have no idea that it's coming from the two small boxes in front of you. The 901 seemed to solve some great mystery and managed to bring a live performance to the home better than anything else I've heard.

I can't say that they are as accurate as many other speakers and they probably are not but the other things that they do make up for some of the things that they cannot do. Rock music fits well into what they are able to do. Soundminded took them a step further and is enjoying classical music on them. Attaboy, I knew someone could do it.

All the controversy about them making things sound too big or random sound all over the place is absolutely incorrect. A single voice will sound exactly like it is supposed to and you can easily envision the singer standing in front of you, nowhere near the speaker cabinets. Another consideration is to damp the wall behind you with something that will absorb reflected sound. I used a large Mexican blanket, hung on the wall. A small room will easily cause problems and Soundminded's 14x14 is probably at the lower limit. He could easily overload the room with sound. Anyway, it's interesting to see someone fiddling around with these old speakers. I've heard them in many different rooms with many different amps and set ups for 30 years and they still amaze me.

Bill

[soundminded]

My big problem with Bose 901 series I and II is the same problem to a much greater degree as I had with AR9....inadequate treble. In fact the original Bose 901 only had a measured response to 14 khz and frankly, I'm even skeptical of that. The 9's problem is the same as every other speaker I've heard with a single forward firing tweeter and that is inadequate dispersion. As good as it is compared to much of the competition, it's just not nearly good enough for me. I have discovered, at least IMO, that until the treble problem is solved, you really can't get anything else to work right. Once it's solved, many great things are possible. Both speakers now in my home have very similar perceived frequency response. And why wouldn't they, I've adjusted them both to be as close to my memory of the sound of live musical instruments as I can get them on as many recordings as I can. Frankly I think the balance on cds is more consistant than it is on vinyl and although I have a couple of theories about this, I can't say exactly why that should be. Perhaps the widespread use of B&W Matrix 801 and 802 as monitors for making critical decisions results in most engineers winding up with comparable tonal balance.

The Bose 901s enhanced as I have done are among the best speakers I have heard. The monstrous bass possible with AR9 notwithstanding, the sense of the presence of live musicians in my room is unequaled by any other speaker I know of. Not at all piercing, the high end is all I could wish for with balance and clarity second to none. (Same for the AR9s) The upper bass/lower midrange peak in the 200 to 500 hz region is also gone. I attribute this live presence to the fact that the 901 spatial radiation pattern is much closer to that of real musical instruments than AR9 or comparable forward firing speakers. Needless to say, I am very happy with them.

[Guest jbangelfish]

By golly, I think you've got it. Their main fault was always the high treble. Their bass far surpasses many or even most high end speakers and even many subs. It does require power however and when you replace the Marantz with something substantial, I know that you will be pleased with the results. You would still have to add some sort of bass module to do what the AR9's do (I think) but a bigger amp will produce surprising bass from the 901 and they have dispersion which is equal to nothing I've ever heard anyway.

As for adding another pair, I wouldn't rush into it, unless your room was exceptionally large or tall, I don't think that there is much benefit to it. I've listened to as many as 3 pair and the experience was no better than with 1 pair. All it seems to do is make the image taller, if that makes any sense. From the normal sitting, listening position, it just isn't warranted and you can save money not buying more amps or save your amp by not overworking it. If you were trying to fill a very large room or hall for a concert of sorts, you might want another pair, otherwise I would not do it myself and as I said, I have 4 pair.

I think that they get their unique sound from the direct reflection principle. I've said it before and I'll say it again that this causes a delay in some of the sounds reaching your ear which causes a new depth or dimension to appear in the music. Like it or not, this is what happens in a concert hall and was the reason for their invention. There may be other ways to create this effect but this is a simple one and it works very well.

I'm glad that you are enjoying your new toy. It's something that I've thought about for 30 years or so and am anxious to try it myself.

Bill

[roundhome]

Hello soundminded

I ask for some help I have a pair of 9s and a pair of 9ls both have the same problem low high end output. I reworked my AR3s with solon and silver wire they came to life i was vary happy now if I could do the same with the 9s I can't down load the stuff on the 9ls from the sight. I have the parts to put the AR9 crossovers into the 9ls without the switches.

also I have a pair of LST IIs that I could not find tweeters for so put in some seas h78s that bought them back to life i'm vary happy with them. as far as the AR9 Bose 901 mix I made my own that have electronic crossovers DBX drive rack pa. and seperate pioneer spec 4 amps. if I could only get the AR 9s to sound this good.

A picture would help. I have only sent these to Ken Kantor no ones els has seen them.

but here goes on top is the LST IIs with seas h78 tweeters, next LST .next I call it LST IIIs the have a AR9 woofer crossover in them the rest is electronic crossovers at the LST specs. to compensate for the 200 to 850 gap I use the 8 inch in the bottom speaker.

The bottom one has no name maybe AR9 LST ? It is crossed over with all the AR9 specs the AR15 inch goes to 100 and then the two 12s in the cabinet above takes over then to the 8 inch and the mids and tweeters. Its a mess but basically I have four diferent speakers top three old style, bottom rock your socks. and clarity you only dream of. still working on them with the spectrom in the dbx I'm making a room to do all the test in.

I can't get the pic to load I will have to email it to you

Jim

[soundminded]

I am really glad other people aren't just accepting what comes out of the box from the factory. I don't know if an AR9 crossover will work well with an AR9LS, my hunch is probably not but that would not be the first time I would be wrong.

For five years I listened to my AR9s and was not particularly thrilled with them. I only bought them bacause a very unuaual opportunity came along as I described in the thread about what have you done to own AR products. (Other AR products I own came to me much more easily.) Then about 1989 I went to a trade show and heard Snell AIIIi. I have a close friend who owned AII and it is a speaker I liked very much. I noticed that the new version was even better and used an indirect firing tweeter. So I decided to experiment. Sometimes you just hit is lucky. When one pair worked well, I tried a second and then a third. I found out that a lot of other people were using this idea. It took me several year of thinking about it to understand why this idea works so well. I also found out that rebalancing the system using the program controls on the speaker and an equalizer, I could get what sounded to me like a much clearer and more accurate sound. The purchase of a cd player, in this case the Denon 1520 which had AB repeat made life much easier for me than using a turntable because I could get a very high quality signal and repeat any arbitrary musical passage over and over again easily. This made instant comparisons of different adjustments much simpler. I quickly found out that the most important assets anyone who experiments with high fidelity loudpeakers can have and has a specific goal as I did is a good set of ears, a good memory, lots of familiarity with the sound of live unamplified musical instruments, and infinite patience. This is far more important than all of the theories and lab equipment IMO, not to dismiss them as worthless, far from it but they need to be put into perspective. It should also be appreciated as I think most engineers sooner or later find out that there is usually more than one path to the same end result.

As I have said elsewhere, It takes me normally two years to tweak a 10 band equalizer to get it right to my satisfaction. Progress is made in minute degrees and sometimes you take a step backwards. I have found the pink noise generators, calibrated microphones, and spectrum analyzers worthless at least at a consumer grade of product. I have no idea if I had the equipment professionals use and were trained and experienced in using it whether my results would be better or achieved more quickly. And unfortunately, every time I have to replace an amplifier, cd player, move, or even replace the equalizer itself (my ADC 315 fried its power transformer), I have to start again. I don't have to be convinced that these devices including equalizers don't sound the same. Frankly, considering the trouble it causes me, I wish they didn't.

I've considered building another direct/reflecting speaker on a different model. This time using a pair of pre-engineered subwoofers (I think each speaker system should have its own subwoofer as AR9 does) and three full range two way or three way systems per channel, possibly pre-engineered or maybe from scratch. They would of course provide the same 8 to 1 reflected to direct radiation, possibly adjustable, posiibly bi or tri amplified (each full range system having its own amplifier) and of course adjustable frequency contouring of the reflected sound allowing for compensation of the absorption characteristics of the room boundaries behind the speaker. I belive that speaker radiating pattern, the way in which speakers radiate their sound into a room is possibly the most neglected area of loudspeaker research, some audiophiles intuitively knowing that the two or three driver direct firing paradyme is seriously flawed and limited. They express this through the popularity of alternaive designs such as bi-polar panels and speakers, direct/reflecting (Bose 901 would not be a very popular speaker as a direct radiator-many people are willing to put up with its awful frequency response to get the advantages of the direct/indirect design, to the chagrin of audiophiles who hate it.)

I'm going to have to get a digital camera. Too many people are asking for pictures and with 3 megapix models available for around $100, I don't think I can hold out much longer. (It's just that I have so many other cameras already.)

[soundminded]

Now that I've gotten excited about this project again, I decided to try something that was in the back of my mind for a while but I hadn't gotten around to. And that was to switch the relative phasing between the Bose 901s and the tweeters. In the 1960s when the AR amplifier was designed, I don't think people gave much thought to absolute phasing so having lost the schematic a long time ago, I don't know whether this amplifier inverts phase or not. I don't know if the Marantz receiver does either. I started with both bose speakers and tweeters connected in positive phase according to each amplifier's and speaker's designated + markings. So what did reversing the relative phase of the tweeters do to the sound. It's hard to say. If they did something, the change wasn't drastic. If it's not an illusion, it's subtle. My initial reaction listening to some recordings I am familiar with is that the frequency response is slightly flatter and the stereophonic imaging is slightly different with the different instruments spread out a little more as though channel separation had improved and maybe a little further back. Perhaps that is what some people refer to as imaging. As I said I don't know if this is an illusion or reality and I will have to switch it back and forth several times to decide. The front tweeter is about 3 inches above the Bose mid/woofer and about an inch forward of it. This first arrival wave establishes directional precidence and so it is important. The rear tweeters are not symetrical with respect to all 8 bose drivers and are several inches away from some of them. At 9khz, the approximate crossover frequency, a full wavelength is about 1 1/2 inches if I did my calculations right so any difference would be a little surprising since they can't really be consistantly phase coherent with each other. Anybody want to comment about the phase relationship between mid and tweeter? I know this was discussed relative to mid and woofer regarding AR3 some months back.

[soundminded]

The obvious way to compare if the outputs of two amplifiers have the same relative phase to each other is to take two small full range drivers, connect one to the same chanel of each amplifier in phase according to the phase markings on each amplifier and try them as headphones. That will tell immediately if the two amplifiers have the same or opposite phase relative to their inputs. This was probably obvious to the rest of you, but I just thought of it.

[roundhome]

Hello soundminded

this is the stack I was trying to show you

Jim

[Guest Bret]

>and try them as headphones<

If they are out-of-phase headphones, be sure to listen to Black Sabbath at 78rpm.

I did once and "saw God."

Bret

[soundminded]

Wow!

That's quite a stack you've got there!

(Last time I said that to a woman I got my face slapped.--guess she wasn't an audiophile. :-) )

[soundminded]

Hard to believe, two different systems, two different rooms, two different everything and ths speakers are so different in design...BUT....the enhanced Bose 901s are now within a gnat's eyelash of the enhanced AR9s. They sound nearly identical now. It's taken a year and a half to get them that way and I often had my doubts if it could be done. If I had to say where the differences still are, I'd say that the AR9s still have the edge in deep bass but the 901s have better stereo effect (what some might call imaging.) They seem slightly clearer than the AR9s but that might be due to either the imaging resulting from the way the tweeters are aimed or the fact that they are biamplified. Part of the imaging difference may be due to the fact that the AR9 tweeters all point up at the ceiling while the 901 tweeters are aimed horizontally. Either way, they are remarkably similar. The 901 might benefit from a more powerful amplifier and a second set placed on top of them to increase their power handling capacity before the drivers reach their limit on deep bass. It should be understood that neither pair sound much like what the manufacturer intended as returning everything to their factory default settings including eliminating the added equalization makes them very different from each other and from what I wanted to hear.

[soundminded]

Results with the 901 have been so pleasing that I had to go back and tweak the AR9 system to come closer to where the 901 system landed. This involved a slight increase of about 3db at 8 khz. The two continue to converge in timbre but their so called imagaging is different due to the difference in geometrical radiating pattern between 200hz and 7 khz. The subjective difference is that sound sources appear to be further forward and slightly more in the same distance plane or flatter with the AR9 while the so called soundstage remains wide for both but I'm not sure I can say which is better, only that they are slightly different in this one regard and this should hardly be a surprise.

Another queston is whether the original Bose 901 can ever give AR9 a run for its money in bass response. Each AR9 has a total bass radiating area of about 32 pi sq inches while Bose 901 only has about 20 pi sq inches of radiating area and of course, the Bose's nine 4 inch drivers can't move nearly as much air in agregate as the AR9's woofers due to their more limited maximum excursion. The AR9s system f3 is 28 hz but is easily equalizable to 20 hz while the 901 has an unequalized system resonance of 180 hz but a usable equalized output to 23 hz (requiring enormous power to produce moderate sound levels.) After careful listening, I would say however that within its loudness limitations the answer is yes (published measurements reveal about twice the harmonic distortion level in deep bass 10% for the bose, 5% for the AR both of which are inaudible.) How many Bose 901s and how much power would it take them to equal an AR9's bass? Right now my best guess is four pairs and about seven to ten times as much power. So wiring two pairs per channel presenting a 4 ohm load to two Crown CE-1000 amplifiers would equal a pair of AR9s driven by a 100 to 200 wpc amplifier. Interestingly for such a setup, no additional tweeters or other amplifiers would be necessary to maintain the current timbral balance and the only equalization changes would be necessitated by any differences the Crown units have from the current Marantz amplifier.

[soundminded]

I'd been toying with the idea for awhile of somehow changing the relative spectral balance of the front firing tweeter to the indirect firing tweeters but I didn't want to add yet another amplifier. So I put a 1 mfd non polarized capacitor across the voice coil of each front firing tweeter. The intention was to roll off the high end of this driver requiring an additional treble boost to flatten its response and in so doing, add sufficient hf energy to the rear firing tweeters to overcome the differential absorption of the walls it reflected off of. Exactly the opposite happened, it was necessary to cut a moderate treble boost back to only a very slight one and increase the volume of the tweeters relative to the main Bose drivers. I have no logical explanation for this. The improvement is noticable removing any last trace of hardness from the treble. It did require slight re-equalization of the main equalizer too...here we go again. The sound is getting closer to the AR9 set up timbre wise in the other room. I cut that system back 1 db at 16 khz as well. These slight changes make a surprising degree of difference.