Bose 901
Everything said in this thread has some truth, however I had bought the guide you had mentioned and performed the modification.
The mod worked like a charm and if you read the guide it lead you through the entire steps on how to procure the drivers cheaply and recoup your money at the end of the project.
The guide is no longer available on Ebay it seems, but I found it at 5.1.cashkats and of course . com.
boseman
Everything said in this thread has some truth, however I had bought the guide you had mentioned and performed the modification.
The mod worked like a charm and if you read the guide it lead you through the entire steps on how to procure the drivers cheaply and recoup your money at the end of the project.
The guide is no longer available on Ebay it seems, but I found it at 5.1.cashkats and of course . com.
boseman
Did you replace the front mounted driver with a different full range driver or stick with all 9 Bose?
I'm guessing everyone has seen this:
Replacement Speaker Driver for Bose 901 4-1/2" 1 Ohm
Along with the measurements:
R901 LMS Impedance vs Frequency Graph
R901 T/S Parameters and Impedance Graph
Doesn't seem half bad to me. If it weren't for the 1 ohm impedance, I wouldn't mind having a pair to mess around with.
As for mounting 8 of them on the back of a box to splash all over the front and side walls..
Replacement Speaker Driver for Bose 901 4-1/2" 1 Ohm
Along with the measurements:
R901 LMS Impedance vs Frequency Graph
R901 T/S Parameters and Impedance Graph
Doesn't seem half bad to me. If it weren't for the 1 ohm impedance, I wouldn't mind having a pair to mess around with.
As for mounting 8 of them on the back of a box to splash all over the front and side walls..
Last edited:
You can replace the foam surround with this kit.
Surround Kit For Bose 901/802 Speakers 260-910
I used a kit like this for my old 301's that do shop duty. It worked great. The kit comes with everything you need, except some isopropyl alcohol. Some extra Q-tips are handy too.
Surround Kit For Bose 901/802 Speakers 260-910
I used a kit like this for my old 301's that do shop duty. It worked great. The kit comes with everything you need, except some isopropyl alcohol. Some extra Q-tips are handy too.
Perhaps I'm responding a bit late, but so what??? I speak from some experience, having owned a total of six pairs of 901s in the past several years. All of them used, ancient. Three pairs of series IV or V. Without exception, the surrounds were "dust" and I replaced them. Of three pair, I was able to get "almost" two pair near-perfect. This probably reflects a combination of my hit or miss re-coning skills and also the failure rate of the repaired drivers. I listened by ear and kept the best ones. In any case, I've sold off the 901 IV or V projects and/or given them to grateful friends.
What I would like to share is the following: I've also bought (1) 901-I and (2) 901-II. THEY WERE IN PERFECT PLAYING CONDITION (at least as far as many hours of listening could determine.) The 901-III and later were literally a different type of speaker (ported instead of acoustic suspension.) Some writers claim, and my experience agrees, that the original Bose 901 (I & II) were a better overall speaker.
Therefore, my advice is lose the newer stuff and get thee a pair of 901 I or II. No EQ? No problem. They are over-priced for what they do. Get a Behringer DEQ2496 or similar auto-EQ unit and you can equalize (or equalise in the UK) both speaker and room in one go. At least at US ebay prices, a pair of series I or II should cost you not more than $300. The EQs go for $50-100. Use it if included. If you really want to know, I will share my link(s) for 901 articles. Email me.
What I would like to share is the following: I've also bought (1) 901-I and (2) 901-II. THEY WERE IN PERFECT PLAYING CONDITION (at least as far as many hours of listening could determine.) The 901-III and later were literally a different type of speaker (ported instead of acoustic suspension.) Some writers claim, and my experience agrees, that the original Bose 901 (I & II) were a better overall speaker.
Therefore, my advice is lose the newer stuff and get thee a pair of 901 I or II. No EQ? No problem. They are over-priced for what they do. Get a Behringer DEQ2496 or similar auto-EQ unit and you can equalize (or equalise in the UK) both speaker and room in one go. At least at US ebay prices, a pair of series I or II should cost you not more than $300. The EQs go for $50-100. Use it if included. If you really want to know, I will share my link(s) for 901 articles. Email me.
Last edited:
I still have my Series IV 901's and in fact playing it right now. The only mods I did to them were replaced the back cloth with a nylon screen with bigger opening for less restriction on high frequencies, and I also turned them around much like the 802's. So far, still sound good. The amp that's driving these is a Sony HCD-H881 receiver. This receiver is a portable one with built-in cd and cassette players and detachable speakers. The original equalizer is in use. The speakers sound big due to its rich mid range and the bass is a killer also cause the amp has a built-in bass boost. The highs are ok too. I just have to watch out the volume. Don't wanna clip the amp. I was playing it side by side with the Infinity SM 152. SM 152 has thin mid range. With the 901's along side, the sound is much richer.
Soldermizer
So, if I understand You right, your opinion is, that the S I & II sounds best?
But, do You notice any difference between S IV and S V or especially S VI if You own them?
Did You open S V, and are they damped inside like S VI?
About DEQ, I have one. I'm not convinced, the sound will be the best possible for 901's, simply because their response with the original EQs is not flat. With DEQ must try to follow their original response or to keep close to it, with small changes for improvement.
art64
I also from time to time listen them turned at 180 dgr. And the sound is really not bad. More clean, with clear stereo, and instruments and voices are better positioned. The best for live acoustics and solos. But with 901s in right position, the bas is going more dipper, I think.
Well, Thanks for now
So, if I understand You right, your opinion is, that the S I & II sounds best?
But, do You notice any difference between S IV and S V or especially S VI if You own them?
Did You open S V, and are they damped inside like S VI?
About DEQ, I have one. I'm not convinced, the sound will be the best possible for 901's, simply because their response with the original EQs is not flat. With DEQ must try to follow their original response or to keep close to it, with small changes for improvement.
art64
I also from time to time listen them turned at 180 dgr. And the sound is really not bad. More clean, with clear stereo, and instruments and voices are better positioned. The best for live acoustics and solos. But with 901s in right position, the bas is going more dipper, I think.
Well, Thanks for now
Last edited:
Yes, I think the "original" (acoustic suspension or sealed box) Series I or II is best, mainly because the bass goes lower. With series III, the change to ported causes a loss of the lowest octave [this from an article, and listening seems to confirm it.]
I am not sure, but I did own S IV and V (but not VI) and I think there were few differences. See the article(s) that describe the different series.
You are correct about the DEQ not being exactly the Bose EQ. For example, at least for series III +, there is a roll-off of the lowest bass (perhaps below 40 Hz) since the speaker can't reproduce that. The 901 does not sound happy trying to produce 20 Hz
You can reproduce the original curve closely if you have a good graphic or parametric EQ and with auto-EQ you can make it flat for the room as well.
Here is a link describing the different Bose 901 speakers:
Will The Real Bose 901 Please Stand Up !??...A Guide To Buying Bose 901 Speakers - Important Speaker Characteristics - Epinions.com
I am not sure, but I did own S IV and V (but not VI) and I think there were few differences. See the article(s) that describe the different series.
You are correct about the DEQ not being exactly the Bose EQ. For example, at least for series III +, there is a roll-off of the lowest bass (perhaps below 40 Hz) since the speaker can't reproduce that. The 901 does not sound happy trying to produce 20 Hz
You can reproduce the original curve closely if you have a good graphic or parametric EQ and with auto-EQ you can make it flat for the room as well.
Here is a link describing the different Bose 901 speakers:
Will The Real Bose 901 Please Stand Up !??...A Guide To Buying Bose 901 Speakers - Important Speaker Characteristics - Epinions.com
OY! So what was Bose attempting to accomplish with going to a vented enclosure, less bass? Maybe he had to for the new drivers to have any extension. I guess I should try my Bose EQ and see what magic I have been missing without it.
Yes, I think by the same way. Why to make something for worst!? And S 3 III and the next aren't cheaper, with their acoustic matrix and more complicated EQ. I don't know how much they save from the drivers exchange with their own, or made specially for them. But I think, this are not usual drivers, taken from the first store on the way.
I'm very curious about the first series of 901. But, It's a pity, S I and II aren't very widespread in Europe. I have also and a little impressions from S VI, but have some reserves about them.
Soldermizer, thanks for the link, I had read a lot before to buy the mines
Among the many speaker systems I own are original Bose 901s I bought in 1970. They are among the few speakers I ever bought brand new. In their day and time they didn't seem particularly bad sounding but I was not nearly as critical a listener then and my expectations were much lower. For example their treble didn't seem much worse than AR3a, the other speaker I considered at the time. They produced excellent bass if there is enough LF amplifier power available and the source has LF in the signal. They got stored away for decades until I took them out and listened again. Not so good anymore they had a relatively dull muffled sound and their bass wasn't so great anymore especially in light of my new reference Teledyne AR9, one of the most potent bass producers I've encountered.
I tried twice to improve them. The first try was a failure, the second attempt was very satisfactory but took 4 years after I figured out was was wrong with them. That effort took from 2004 to 2008.
The first problem with them was massive air leaks. The putty used to seal the drivers to the wood cabinet had dried out and cracked. To repair that rather than try to remove all 18 drivers and reapply caulking I sealed the space where the speaker frame meets the wood and around the screw holes with GE silicone caulking being very careful not to get any on the cones or suspensions. It worked.
Then there was the FR problem. In my present room, about 14' x 14' with a cathedral ceiling the speakers have a broad peak of around 8 db at 500 hz and fall below that at 6db per octave even with the equalizer. It reaches the 1 khz output at about 95 hz and continues to fall linearly. Simple equalization fixed that. The hard part is the top octave, it can't reproduce it. I agree with Gordon Holt's assessment in Stereophile magazine that the inertial mass of a 4" midwoofer, that's what these CTS drivers would be called today is too great to make for any kind of tweeter. The solution was to engineer a complimentary tweeter array which was not at all simple (it wasn't expensive though) that compliments the rest of the system. Right now each speaker system has 6 tweeters 5 of which fire indirectly (2 at the ceiling) and their FRs are not the same. Nor is their outputs, about 95% of which is indirect. The system is of course bi-amplified, the Bose equalized signal does not go to the tweeters.
When properly positioned and carefully equalized for each recording this is as accurate a speaker for reproducing the sound of acoustic instruments and voices as I've encountered. AR9 still beats it in bass capability but only because it can move more air and because the real power requirement for lowest bass for this speaker is closer to 600 to 1000 watts per channel and you'd need at least 3 pairs to equal one pair of AR9s. Each 9 driver enclosure is only rated to handle 270 watts. I know that sounds hard for anyone familiar with this speaker to believe, there's been so much bashing of it. Considering its shortcomings some of that was justified but so is bashing all other speakers I've heard. I'm a DIYer because I don't think much of what the industry produces on its own.
BTW, equalization is a perfectly valid engineering concept that has been used extensively.Among the technologies that would not have been possible without it are LP recordings, analog magnetic tape recording, analog color television, and FM radio broadcasting. Dolby noise reduction also depends heavily on it.
I tried twice to improve them. The first try was a failure, the second attempt was very satisfactory but took 4 years after I figured out was was wrong with them. That effort took from 2004 to 2008.
The first problem with them was massive air leaks. The putty used to seal the drivers to the wood cabinet had dried out and cracked. To repair that rather than try to remove all 18 drivers and reapply caulking I sealed the space where the speaker frame meets the wood and around the screw holes with GE silicone caulking being very careful not to get any on the cones or suspensions. It worked.
Then there was the FR problem. In my present room, about 14' x 14' with a cathedral ceiling the speakers have a broad peak of around 8 db at 500 hz and fall below that at 6db per octave even with the equalizer. It reaches the 1 khz output at about 95 hz and continues to fall linearly. Simple equalization fixed that. The hard part is the top octave, it can't reproduce it. I agree with Gordon Holt's assessment in Stereophile magazine that the inertial mass of a 4" midwoofer, that's what these CTS drivers would be called today is too great to make for any kind of tweeter. The solution was to engineer a complimentary tweeter array which was not at all simple (it wasn't expensive though) that compliments the rest of the system. Right now each speaker system has 6 tweeters 5 of which fire indirectly (2 at the ceiling) and their FRs are not the same. Nor is their outputs, about 95% of which is indirect. The system is of course bi-amplified, the Bose equalized signal does not go to the tweeters.
When properly positioned and carefully equalized for each recording this is as accurate a speaker for reproducing the sound of acoustic instruments and voices as I've encountered. AR9 still beats it in bass capability but only because it can move more air and because the real power requirement for lowest bass for this speaker is closer to 600 to 1000 watts per channel and you'd need at least 3 pairs to equal one pair of AR9s. Each 9 driver enclosure is only rated to handle 270 watts. I know that sounds hard for anyone familiar with this speaker to believe, there's been so much bashing of it. Considering its shortcomings some of that was justified but so is bashing all other speakers I've heard. I'm a DIYer because I don't think much of what the industry produces on its own.
BTW, equalization is a perfectly valid engineering concept that has been used extensively.Among the technologies that would not have been possible without it are LP recordings, analog magnetic tape recording, analog color television, and FM radio broadcasting. Dolby noise reduction also depends heavily on it.
Well, time is going fast.
Now, more than a year later, I'm a proud owner and of S2 speakers with S1 EQ.
Yes, they sound a little different than S4. Bass is not deeper, but is better controlled and clean. Seems. Just for information, this speakers didn't sound well with S4 EQ, to sharp High-middles.
And just to remind, it's good to exchange the old electrolytic capacitors with fresh contemporary electrolyticis, or where is possible with quality film caps.
Now, more than a year later, I'm a proud owner and of S2 speakers with S1 EQ.
Yes, they sound a little different than S4. Bass is not deeper, but is better controlled and clean. Seems. Just for information, this speakers didn't sound well with S4 EQ, to sharp High-middles.
And just to remind, it's good to exchange the old electrolytic capacitors with fresh contemporary electrolyticis, or where is possible with quality film caps.
Hi ctef, I think you will be happy with the series I with Active EQ (series I or II -- they are almost identical). As you already discovered, the early 901 (series I, II) are not compatible with the EQ for series III and later. Based on what other Europeans have said, your Bose 901 (I or II series) are comparatively rare compared to the later series. Almost certainly they were owned by a USA military person when they were new [Bose was, maybe still is, a huge seller to the US military in the PX's overseas]. Also recommended: check for air leaks around each driver, if present, seal with caulk. Leaks will dramatically reduce the bass the 901 is capable of. Perhaps that is why you don't hear deeper bass? I still think that the one you have "original" = sealed box is better than the later, ported (series III - VI) version.
[Bose was, maybe still is, a huge seller to the US military in the PX's overseas]. Also recommended: check for air leaks around each driver, if present, seal with caulk. Leaks will dramatically reduce the bass the 901 is capable of. Perhaps that is why you don't hear deeper bass? I still think that the one you have "original" = sealed box is better than the later, ported (series III - VI) version.Hi,
Mine are from Switzerland, so, I don't know about USA military persons there. But who knows? The EQ I got from US. The main problem with this big and heavy things is the shipment. I was lucky to by and a Spatial Receiver from US, before increasing of USPS prices. Any how.
As I mentioned, my EQ is S1. Watching the service manual, we see, S2 is with a few Dbls bigger gain for in the lower and higher ends. But this is not so important.
This thread is about possible 901 Modifications.
I don't see many options for cabinet mod. Probably for drivers, too. If you exchange them with other, it will not be 901, anymore. Lately, I see in Ebay some no genuine drivers for Bose 901, and I'm curious how they perform, but I'm not ready to spent money for them
Also, adding tweeters, like You, Soldermizer, is changing the system. It is no more a typical 901.
What I try to do, is to improve the things, as they are. To get more clear sound, better sound stage and so on.
For now I success to make not bad sound stage. The speakers disappeared, and I get the sound in front of me, in the middle. This took me a time, to place the speakers correctly.
Other we can do, is with EQ.
S1&2 is no so much. Just change the electrolytic capacitors with fresh new. Also, Bose uses 2 el. caps directly in the signal path. One is in the feedback, and other in output. They are the 4 grey axial caps 5uF/25V, close to thee RCA. You may exchange them with quality film caps over 2.2uF. It is tested and works.
Of course you may exchange and all other film caps in all RC groups, with better but with the same value! Exchange and nasty Bose RCA with better ones. Throw away and front lamp. Usually it is reason to hum, like in mine S4 EQ right channel. Place a LED.
A little bit difficult is the question of improving S4 EQ. For now I'm just thinking. Of course changed caps with fresh, but seems, it's not enough. Why don't change TL072 with some better ICs? And even more. Why don't try to null the offset, and throwaway all decoupling el. caps from the signal path? "The best cap, is the missing cap!" Isn't it?
Mine are from Switzerland, so, I don't know about USA military persons there. But who knows?
The EQ I got from US. The main problem with this big and heavy things is the shipment. I was lucky to by and a Spatial Receiver from US, before increasing of USPS prices. Any how.As I mentioned, my EQ is S1. Watching the service manual, we see, S2 is with a few Dbls bigger gain for in the lower and higher ends. But this is not so important.
This thread is about possible 901 Modifications.
I don't see many options for cabinet mod. Probably for drivers, too. If you exchange them with other, it will not be 901, anymore. Lately, I see in Ebay some no genuine drivers for Bose 901, and I'm curious how they perform, but I'm not ready to spent money for them
Also, adding tweeters, like You, Soldermizer, is changing the system. It is no more a typical 901.
What I try to do, is to improve the things, as they are. To get more clear sound, better sound stage and so on.
For now I success to make not bad sound stage. The speakers disappeared, and I get the sound in front of me, in the middle. This took me a time, to place the speakers correctly.
Other we can do, is with EQ.
S1&2 is no so much. Just change the electrolytic capacitors with fresh new. Also, Bose uses 2 el. caps directly in the signal path. One is in the feedback, and other in output. They are the 4 grey axial caps 5uF/25V, close to thee RCA. You may exchange them with quality film caps over 2.2uF. It is tested and works.
Of course you may exchange and all other film caps in all RC groups, with better but with the same value! Exchange and nasty Bose RCA with better ones.
Throw away and front lamp. Usually it is reason to hum, like in mine S4 EQ right channel. Place a LED.A little bit difficult is the question of improving S4 EQ. For now I'm just thinking. Of course changed caps with fresh, but seems, it's not enough. Why don't change TL072 with some better ICs? And even more. Why don't try to null the offset, and throwaway all decoupling el. caps from the signal path? "The best cap, is the missing cap!" Isn't it?
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.