bose 901 driver surround repair replacement

[Cal Weldon]

No we don't.

[Cal Weldon]

Originally posted by TICUL38
Re=7.0 ohms

Interesting. When did Bose switch to a more conventional motor? The only 901 drivers I have come across were 1 ohm, all wired in series.

EDIT: I am wondering if those drivers are from the 800 series, the ones used for small PA duty. IIRC those were 8 ohms and the boxes were very similar to the 901's

[TICUL38]

The pair of 901-II that I took apart are S/N 166414 (M.O. 2287) & 166510 (M.O. 2288).
The 7 ohm drivers were wired three parralleled series strings of three. I recall someone suggesting 1 ohm drivers...possibly adavancing a rumour without first checking.
The parameters mentioned earlier are per driver. I never bothered measuring the speaker's frequency/impedance signatures because that would not have been productive for me after the "disapointing" listening tests.
P.S. I dont recall "bashing" Bose in my first post, so please dont read into any post what's not there.

[Cal Weldon]

Hi Louis,

If you have a series II then you have 4 bolt hole, cloth surround, blue cone drivers correct?

They were last made in 1976. From then on (series III and up) they used foam surrounds and at one point reduced it to 3 bolt holes. No where can I find any bose 901 driver that is other than 1 ohm. I wonder if your drivers have been renewed. If so they must have used the 800 series drivers.

Cheers.

EDIT: I think I spoke too soon. I did a little research and found the series I & II drivers were in fact 8 ohms, wired as you have described. Sorry for the diversion. We now return to your regularly scheduled programming.

[TICUL38]

INDUCTOR ...you posted:

{{i'm interested in knowing the t/s parameters for one (of those) driver(s) only, and output/impedance in freq. (/graphs), for those people that want to find one to build a similar speaker. Thanks}}

I will go a distance with you on this, with a open baffle frequency/impedance graph for a "single" driver. I am curious though why you wish to duplicate a BOSE 901 design? Dont forget you would have to acquire a series of 18 duplicate drivers (+spares) for a stereo pair. I am all for the "ambiphonic" sound the 901 was designed for, and in fact I am concentrating design time with that approach of music/TV sound reproduction in mind, since IMO it provides the most natural rendition of music/sound in my space. Also, the focused in your face speaker boxes do not fit my listening/viewing room unless I forego peace of mind with my mate!

...and Cal, you posted:

{{If you have a series II then you have 4 bolt hole, cloth surround, blue cone drivers correct?}}

The drivers I have here are the 4-mounting hole vintage, with the Bose name printed on a blue paper cone. In passing, the frame vibrates like hell in vicinity of resonance, so will require damping with some mastic molded into the magnet-frame crease, and possibly onto the frame spiders. I still dont know if I will be passing these drivers onto the obsolete shelf....have to do a trial run somehow. Also, glad to read you cleared up the 1 Ohm dingy...could not imagine a driver manufacturer accepting to give birth to a 1 Ohm "runt"...

[Inductor]

Hi,
Just to make sure you have and/or use the BOSE processor for the boosted limit frequencies with your BOSE speakers (?).

I am not interested in building a copy physically -- that would be interesting but costs (a lot of) money -- but in the process and philosophie behind it's construction and it's quality of sound, and calibration. It's a long process for that speaker to the point where it arrived to the maket and played in discos at a very high SPL.

[TICUL38]

Hello Inductor,
Listening test was done without the BOSE Equalizer in play.
My first objective was to get around that "boxy sound" detected in the midrange, which from experience is mostly attributed to "paper cone transparency" to internal reflections escaping and muddying the resolution. I did not want to succumb to my usual enthusiastic way of proceeding with a vintage acquisition...and so decided to research/correct in steps, and then re-evaluate the midrange before checking how the equalizer impacts on sound quality. I kept in mind that driving the cones harder pulls them into a non-linear coil/field region...and that is what this equalizer will likely do. Loudness will bury distortion as the brain wants to shut off the ears. Soooo, I shall correct the cones/surrounds to make them as opake as possible, and then check out the midrange again.
Will report results later. I am currently overwhelmed in putting together a more accurate frequency counter ...need 0.1Hz resolution for more accurate Qe, Qm measurements.

[Inductor]

From what I understand, it can not work without the equalizer. Unless you use another similar equalizer, with stepped bass and treble, or, with passive xovers at the same critical frequencies, or, active amps with stepped curves. Also there is a dip for the ressonance, maybe similar as the one in the open baffle speakers. note I don't know them and I never tested them, just from the papers on the speakers. Also don't get confused, they were the best speakers in "small discos" around, for me, at the time.

[twistedsymphony]

this is an old thread but I wanted to bump it to say thanks!

I personally don't care for the 901s... but my father has always loved them, he talked about getting a set all the time and eventually bought a new pair several years ago... he recently lost his job and had to sell almost everything he owns to stay afloat including his 901s.

a member of my car club was cleaning out his garage and had an old set of series IV 901s up for sale for $20. I though it would be a great fathers day gift if I bought them and fixed them up a bit.

Of course upon pulling off the tweed grills the speaker foam was all rotted way.

I was searching for whole replacement drivers when good 'ol diyaudio came up with this thread... I never knew they made repair kits for the foam surrounds

I'm sure the $$ could be better spent building a nicer pair of speakers, but the 901s have some kind of sentimental value for my father so I figured it was worth it.

After fixing the drivers I'll probably sand down and paint the enclosures black and then work out some better looking grill material to replace the 70s tweed.

The speakers did come with the equalizer and it is much needed. If my memory serves you can use the speakers without the equalizer, Bose even sells them separate from the equalizer but they "require" that the equalizer be used at all times with the speakers. They sound like tin-can speakers with out it... but they do have a very warm and inviting (albeit horribly inaccurate) sound when the equalizer is in use.

[tomtt]

Originally posted by twistedsymphony


had to sell almost everything he owns to stay afloat including his 901s.

it would be a great fathers day gift, if I bought them and fixed them up a bit.

Certainly Would.



listening with BoSe, is better than not listening, at all ...