Bose 901 Modifications - Page 4 - diyAudio
Go Back   Home > Forums > Loudspeakers > Full Range

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 18th March 2012, 02:14 AM   #31
art64 is offline art64  United States
diyAudio Member
 
Join Date: Jul 2009
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.
  Reply With Quote
Old 22nd March 2012, 12:35 PM   #32
ctef is offline ctef  Bulgaria
diyAudio Member
 
Join Date: Nov 2011
Location: Bulgaria, Sofia
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

Last edited by ctef; 22nd March 2012 at 12:46 PM.
  Reply With Quote
Old 22nd March 2012, 12:48 PM   #33
diyAudio Member
 
Soldermizer's Avatar
 
Join Date: Feb 2012
Location: Tamper, FL, USA
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
  Reply With Quote
Old 22nd March 2012, 01:50 PM   #34
diyAudio Member
 
Join Date: Dec 2008
Location: Knoxville, TN
Quote:
Originally Posted by Soldermizer View Post
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.]
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.
  Reply With Quote
Old 22nd March 2012, 06:52 PM   #35
ctef is offline ctef  Bulgaria
diyAudio Member
 
Join Date: Nov 2011
Location: Bulgaria, Sofia
Quote:
Originally Posted by 901Fixer View Post
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
  Reply With Quote
Old 24th March 2012, 01:33 PM   #36
diyAudio Member
 
Join Date: Sep 2008
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.
  Reply With Quote
Old 1st January 2014, 11:03 AM   #37
ctef is offline ctef  Bulgaria
diyAudio Member
 
Join Date: Nov 2011
Location: Bulgaria, Sofia
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.
  Reply With Quote
Old 7th January 2014, 01:52 PM   #38
diyAudio Member
 
Soldermizer's Avatar
 
Join Date: Feb 2012
Location: Tamper, FL, USA
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.
  Reply With Quote
Old 8th January 2014, 01:18 PM   #39
ctef is offline ctef  Bulgaria
diyAudio Member
 
Join Date: Nov 2011
Location: Bulgaria, Sofia
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?
  Reply With Quote
Old 8th January 2014, 02:35 PM   #40
diyAudio Member
 
lanchile's Avatar
 
Join Date: Sep 2008
Location: AREA 51
My best modification that I did to my 901 long time ago was....I cleaned them very well using oil mineral cleaner and I sold them to a "washed brain" Bose fan.
I am very happy I did that
__________________
Make it simple...Make it better!
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
NHT 3.3 Modifications SY Multi-Way 22 22nd June 2008 05:12 AM
Hafler 120 modifications czarnolion Solid State 22 22nd December 2007 06:40 PM
DAC-in-the-Box modifications. Again. Aleksunder Digital Source 1 19th July 2007 03:10 AM
DAC modifications elaar Parts 5 29th May 2006 01:11 PM
Zen V4 modifications pro Pass Labs 2 31st August 2004 05:19 PM


New To Site? Need Help?

All times are GMT. The time now is 04:17 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2