B&W Concept 90 Crossover advice requested

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Bludsport

  • Jr. Member
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B&W Concept 90 Crossover advice requested
« on: 11 Jan 2019, 10:52 pm »
Last year I plucked a pair of these speakers that had been tossed to the curb for garbage pick up.
With the exception of the metal dome tweeters, the rest of the drivers look okay. After a closer look, I found that both the crossovers located in the bottoms of the low frequency cabs had caught fire at some point melting into the foam padding holding them in place. The crossovers for the midrange and tweeters in the upper cabs didn’t burn, but did trip the APOC circuit protection module. B&W’s parts website lists the mid and tweeter crossovers as still being available for $87 each, but the LF crossovers are no longer available.

I’d like to rebuild the HF crossovers sans the APOC circuitry and do a complete rebuild of the LF crossovers sticking as close as possible to the original specs and without spending a bunch of cash. I can salvage the inductors for the HF boards, but I want to replace all the resistors and capacitors with comparable or slightly better components.

I don’t think I’ll have a problem rebuilding the LF boards, but I was hoping someone could explain why B&W chose to include a MF crossover between the LF board and the existing MF board in the upper cabs as well as reversing its polarity. I’m a little bit concerned with the HF boards due to the APOC circuitry and I’m having trouble determining where the APOC stuff stops and the the primary crossover circuitry begins.

Any help and recommendations would be much appreciated.

The crossover schematics can be found here:

http://bwgroupsupport.com/downloads/techmanuals/bw/CM2%20Concept%2090-TM.pdf

http://bwgroupsupport.com/downloads/techmanuals/bw/CM1%20Concept%2090-TM.pdf

 

stonedeaf

Re: B&W Concept 90 Crossover advice requested
« Reply #1 on: 12 Jan 2019, 04:42 am »
I own something like 2 and 1/2 pairs of these speakers -these were pretty much the last product done on John Bower's watch. Couple of things to keep in mind:
1.) The tweeters in these speakers have Beryllium domes -these haven't been available as replacement drivers or dome voice/coil units in quit some time.
2.) Please handle these domes carefully - Beryllium is poisonous -oddly enough -very poisonous for some folks.  I have no idea how much of these domes is this material -could be  plated or ?
3.) Dispose of them carefully if it comes to that -handle with gloves and DON't either cut yourself or breathe even/especially  small pieces in.
4.) All these years later -these are still one of the best speakers I've ever heard.
5.) As someone who worked for the local B&W dealer -I was a big fan of the APOC -circuit -it protected  speakers really well and personally -I've never heard what was wrong with it ??
6.) I thought the woofers were also APOC protected -until I bought my second pair and found the scraping woofer -at which point I looked a little more carefully and realized the woofers were vulnerable to abuse. Oddly enough -I don't remember any of these failing under warranty.Of course -we didn't tend to sell them to head bangers.

Bludsport

  • Jr. Member
  • Posts: 4
Re: B&W Concept 90 Crossover advice requested
« Reply #2 on: 12 Jan 2019, 05:35 pm »
Thanks for warning regarding the tweeters, great info. Unfortunately, both the metal domes are crushed, so I'll need to find suitable replacements for them. The frequency response for the upper CM-1 cabinet is supposed to be around 55 Hz to 33 kHz and based on this, I'll have to try and locate a pair of suitable tweeters..."super tweeters"? There's a good article on these at:

http://www.nrpavs.co.nz/archive_2_10/Sold_2_10_htm/BandW_CM2.htm