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Bose 800 rebuild

Dananton485

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Joined
Oct 15, 2023
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I recently rebuilt a pair of Bose 800 PA speakers. I removed all the drivers, tested them with an voltmeter and did a listening test on each driver. That’s 16 drivers by the way. I want to say these were similar to the series ll era of the Bose 901. Each driver had cloth surrounds and blue paper cones. The results my testing revealed about four bad drivers.

My simple test process was
  1. Physical visual inspection.
  2. Continuity test using a voltmeter.
  3. Ohm reading using a volt meter.
  4. Individual listening test for each driver.

Results: Four bad speakers found. One failed the voice coil continuity test, two had elevated ohm reading around 11 ohms. The fourth speaker past all tests except the listening test which the driver had a reduced output and distorted sound. The remaining drivers passed all inspections well. Though some units had a faded paper cone with the blue more like a very light blue. I was able to find four of the proper identical used replacement drivers online and ordered them. I also ordered four foam speaker gaskets. Each gasket provides a seal for four drivers so there are only four gaskets required for a the pair of cabinets.

Restoration process: I dyed the paper cones of each driver by had using a hand brush and blue dye that I acquired at a local hobby store. There was not blue spray dye available locally. Many may frown on this process, but the results were successful in my assessment with no damage to the paper cones. The key is limiting the amount of moisture and using a limiting amount of the dye in the mix (You have to dilute the dye it with water). I also masked the cones and spray dyed black fabric dye on the dust covers that were faded. I also elected to paint the silver driver baskets black to give the units an updated look. This was also done by brush using some basic flat black paint I had on hand.

Next, I removed all the internal wiring. The factory wiring was solid core wire and appeared to be 20 gauge. I replaced it with 14 gauge stranded and soldered all the wires to each terminal. Wiring was a little complicated. Each speaker has 8 x 8 Ohm drivers and and a 10 ohm resister. This requires cleaver wiring using a combination of series and parallel technics. The solution was to group the speaker s into groups of three A, B and C. The third group (C group) had two speakers and the 10 ohm resistor. Each group of three was wired in series resulting in 24 ohms for group A and B, while group C had a 26 ohms due to the 10 ohm resistor. Finally group A, B and C were then wired in parallel resulting in a net impedance of 8.2 ohms. This value was verified using my voltmeter.

I also had to rebuild the grills. I used a similar technique to the original grills. I made new 1/8” grill brackets using 1/8" thick MDF board while using one of the OEM grills as a pattern template. I went to the fabric store and located some suitable black fabric. I also ordered and installed a pair of OEM aluminum Bose speaker logos on each grill. I added a personal touch by sourcing some aluminum right angle trim pieces from my local hardware store and I installed the trim on the upper and lower edges of each wedge. I elected to remove the handles and some of the hardware since in my case these units will not be used a portable items. The original hardware was in poor condition/rusted as well. I also used a permanent marker to paint all the silver metal upholstery pins black. There’s a better name for them but I can’t seem to think of it at the moment. Final steps included replacing the 1/4” speaker connections with gold binding post terminals.

In addition, I also sourced a used Bose 800 EQ in fully working order. I do have a set of replacement caps on hand if a future repair is needed and I did take the unit apart and installed/soldiered in a new power cable.

Informal testing: I also did some informal testing with and without the EQ as well as an RTA test using a proper measuring microphone and some RTA software. Using pink noise, I found the response to be fairly even with some minor peeks in the 200 to 300hz range and to my surprise a general slightly stronger response on the lower frequency spectrum. The upper frequencies fade somewhat after 10 k but a little two click turn of the treble control on my integrated amp seemed to help as an improvement. I will state that at my age my upper frequency hearing does not extend beyond 14 kHz and I think a lot of people have similar hearing if they ever actually got their hearing tested. I did feel that the addition of using the Bose EQ made a positive difference. I'm not sure exactly how the circuitry works though from what I understand it is a Bass and Treble boost. I'm not sure why it's called active as I'm pretty sure it is a EQ with fixed point values. I guess you could say its active because its on the preamp level and not a passive EQ but using the word active I think implies that there is some sort of dynamic circuitry that changes based on input signal frequency. I doubt that is the case but my point is I think using the term like they did in the product name is a little misleading especially to the general public so that would be my main criticism of this product.

Conclusion: In the final phase I have been listening to these in my garage for a few months listening to various music. All of my favorites such as Esteban, Diana Krall, Chicago, and Albert Collins all sound great on this system. I’m very happy with the results. I am listening to them with the added use of a 8” Klipsch powered subwoofer set at a reasonable level which is really a nice complement to the 800’s. For amplification I am using an old school Onkyo Integra 8190 A integrated amp. One of it’s unique features is a variable loudness control called “Contra Bass” which provides up to 20 dB of mid-range attenuation though the hardware is not labeled this way this is what the Contra Bass essentially does. In most cases, I have it mildly set at 4 Db while my Treble is set at +2 Db. Overall, I would have to disagree with those critics of the Bose at least when it comes to the 901 and 800 speakers. I know this 800 is a slightly different system as all the drivers are forward firing and none are reflecting. Perhaps that solves some of the controversy. I think it's amazing that there are not passive crossovers in the design at all and yet it does produce a very nice full range sound using the small 4" drivers that all work together to reproduce lower bass and midrange at the same time. There could possibly be some additional improvements made in the design such as adding a tweeter with a passive 12db high-pass crossover. I was originally planning on doing this but after extensive listening I concluded it's not necessary. I do feel, as I mentioned previously that the powered subwoofer really brings this speaker system up to date as a nice improvement. It's not so much making up for anything as the speakers on their own have good extension on the low end. I see it more like a subtle bass enhancement at least in the way I have my levels set at. I generally feel a subwoofer is a good addition to any a sound system especially if its set properly. In general, I feel most people set the level too high on their subwoofer that often clouds the presence of the beautiful midrange.
 
Last edited:

Rmar

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Joined
May 25, 2023
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Danville, Kentucky
The only set of speakers I ever missed after selling them was my Bose 901 Series 1. They were magical. If you like vocals or instrumentals...nothing comes close. Once you have heard them...you will always remember their signature sound. Nothing comes close. Not bad for a speaker that people love to trash.
 
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