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jerishi 17th September 2006 12:27 AM

bose 901
Found a pair cheap- series 1 or2 , I think. Speakers have 4 mounting holes each. Any knowledge about the (obviously) series/parrallel hookups these have? I've taken out 'bad' speaker (one of nine) find it measures proper, re-install...and get nothing. Next step is to find how/why this can happen. Anyone repaired/ re-placed these drivers/ boxes?

FastEddy 17th September 2006 12:39 AM

you will probably need ...
... the Bose pre-amp & amp circuit that goes with the drivers & boxes ... If you have the original Bose boxes, so much the better. The Bose folks tweaked the amp/pre-amp & box quite a bit (using special, exotic equalization) to make up for the medium quality of the drivers ... to make them behave like a quality, relatively flat & responsive setup. It seem to me there are eight or nine drivers in each box ... yes? (You mention 9 drivers, that may imply that you only have one box = :( ... )

If you have the whole set with the circuits, etc. then these make a very good stage performance PA ... and a decent listening system, although modern technology (at least in speaker construction, etc.) has pretty much passed these by.

If you replace the busted drivers with alternate types, you may have to completely redo the eq section of the Bose pre-amp/amp as well.

:) ... :(

Cal Weldon 17th September 2006 12:52 AM

I thought the original drivers were three hole, 1 ohm drivers all in series.

jerishi 17th September 2006 01:00 AM

Hi, so did I...however, this set has 9 speakers per box... each appears to measure 7.5 ohms (more accurately, the 2 individual speakers out of one box I've tested thus far)...out of "bad" box. The other box total impedence is 7.2 ohms. I see no signs of speakers having been replaced/ repaired. Thus, was curious if anyone has schematic of (obviously) series/parralel connection the 'dr. bose' must have used in these. Thanks!

FastEddy 17th September 2006 01:01 AM

could be but ...
... I have only seen the Bose drivers that have 4 mount holes ...

One (1) Ohm per driver ? = could be, they were wired in series / parallel inside the boxes if memory serves ... four drivers in series times two arrays of four drivers in parallel plus one driver in series with the array (and aimed out the back of the box = ~~ 4 to 6 Ohms @ around 1K Htz., but there may have been some added components including resistors as I remember that the whole box was supposed to be rated at around 6 to 8 Ohms @ 1K Hrtz.... but the Bose equalization may have been playing with the response around the usual 1K Htz / input impedence rating on these boxes.


3-LockBox 17th September 2006 01:07 AM

Why do people meter drivers?
take the suspected bad driver, plug it into a music source, and see if it plays music. If it doesn't, its a bad driver. Otherwise, I'm not aware of any internal crossovers, since these units came with an outboard contour network/passive EQ. Could be internal wiring.

Parts Express sells a drop-in replacement model for a reasonable price.

FastEddy 17th September 2006 01:15 AM

Well, then I'm wrong ...
" ... each appears to measure 7.5 ohms (more accurately, the 2 individual speakers out of one box I've tested thus far) ..."

Is this a DC Ohms (resistance) reading from a volt/ohm meter ? ... in that case they might have been wired two by two in series, the two sets by two sets in parallel, then four by four in parallel plus the "extra" one in series with the array = ~~ 6 to 8 ohms ... or some combination.

If you have both sets, and one set "works", you should open the good one up and check, then try to build the "bad" one back up to the same configuration as the "good" one.

If you have a single bad driver (busted or bent voice coil, etc.), replacing that one driver with a very similar driver would be a good idea ... if several drivers are bad, then you may be spinning your wheels ... but that's the name of this game = DIY and DIY again until you reach Nervana or whatever ... :smash:

(It has been thirty years since I tried to duplicate what The Doctor was doing ... series / parallel of 8 Ohm drivers in a box plus tweaked response, etc. ... I managed to discover the original maker of the Bose drivers and got hold of some, stuffed 'em in a box and tried to make 'em sing ... but, no joy, as the speakers really need that special Bose EQ circuit to work well = get flat response, good brightness, etc.)

FastEddy 17th September 2006 01:20 AM

Yeap ...
" ... plug it into a music source, and see if it plays music. If it doesn't, its a bad driver. ..."

Yeap, works for me ... or you can just put 'em on a bench and drive 'em direct from a signal generator ...

Sometimes it is informative to use a meter for DC resistance measurement, especially on a completed box / driver / crossover assembly === ya don' wanna kill your amp with a 0.05 Ohm load, right?


jerishi 17th September 2006 02:36 AM

bose stuff
Hi, eddy, I think I got it... In any case , I use both a working amp w/signal to test as well as a DMM . I usually trust my ears first. (also, the individual speaker pulled from unit(s) do produce sound when given source) And, yes, I've got the 'bose' crossover here as well. My quandry ...was how can any one speaker in a set of nine sound wrong, yet test right? ... and then.. Anyway, it's the series/parralel problem, (I'm pretty sure) ... and I can use the good sounding box... to trace what might have gone sour in the other box. Thanks!

Willitwork 17th September 2006 05:29 AM

Re: could be but ...

Originally posted by FastEddy
... I have only seen the Bose drivers that have 4 mount holes ...
So have I, but I was only familiar with one 901 series out of 5 or 6...

Back in college we had 4 901's in the main student hall and these were used both for PA purposes and playing music over the closed-circuit "campus radio" as it was called. I was one of the student "techies" in charge of broadcasting, the only requirement for the job was knowing how to operate a reel-to-reel deck lol.

These speakers came with a dedicated 3-unit amp system which consisted of a preamp, EQ and power amp. The EQ had an input for preamp and an output to the power amp and as far as I remember the EQ's sole purpose was to attenuate bass response below 50Hz in an effort to deal with the LF resonance most Bose products are plagued with, among other problems. In my opinion at the time, these speakers did not sound very good for music but were okay for PA.

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