BW150/M5 from B&W DM5 - diyAudio
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Old 26th June 2011, 09:16 AM   #1
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Default BW150/M5 from B&W DM5

Hello. . .I am playing with some DM5 this month . .
tossed the broken tweeter . . . .matched a ring radiator
to the crossover and 7 inch driver . . . .

Does anyone know about the construction of this driver.
I know it has real low Q, high flux, "acoustic suspension"
compliant suspension...

Does anyone know if these old B&W (bextrenes ? ? ) had
dope applied ? Or is the cone just over built . . .it is very thick (too thick)
stiff and some lower midrange timbre and reverb gets lost in the cone.


~erick~
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Old 26th June 2011, 11:11 AM   #2
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I just found quite a bit of material on the Net. Googled B&W DM5 and got old brochures etc. Being a black cone from that era my first thought was Bextrene but closer viewing suggests a woven appearance and as they were moving on from bextrene around that time e.g. with the non-bextrene mid-range for the DM6 I would guess that it was not.
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Old 26th June 2011, 09:24 PM   #3
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I have scene the B&W owners manual.. . It does not state the composition of the cone.
My drivers were made in may of '79 but the DM5 seems to be a '73 design judging by the silk screened date on the crossover mount (that is what the name plate is - a mount for the crossover. I think the DM6 was '74. They made the DM5 for many years and could have been tweeking them in the factory with no new model number though ? ? ? I was under the impression the DM6 midrange was of BBC heritage and Bextrene (perhaps not it has been a week since I casually looked at it). Someone out there stated how Bextrene is BBC developed (and a brand name) and the LS whatevers and variants where heavily doped ...The BW150/M5 is not woven. It is molded and or forged something- likely Bextrene. This driver has great bass, and the top most midrange is nice. But it is dull in the lower midrange. This sounds great on spoken voice (lending justification to BBC / Bextrene ). But it just does not have the depth and reverb resolution of say a P13WH. . . .I am considering an acetone wash to remove possible PVA doping if removing the stock inductor does not fix the resolution. I can also retire the thing to sub duty or toss it...the beauty of yard sale shopping for diamonds in the rough . . . have a nice day . . ~erick~
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Old 26th June 2011, 10:11 PM   #4
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Hi erick, I'm not an expert on these but I understood that Bextrene did need damping and my KEFs (several B110 and B200 over the yrs) all had it as does my Focal 8" from nearly 20 yrs ago. The bass unit (10") on the DM 6 was definitely Bextrene. Btw the preferred damping was a product called Plasitflex 1200, I think made by Bostick. I got some from a local Oz designer but have never even got a nibble when trying to Google it. Hard to track down.
If you are interested in cone materials Lyn Olsen (hope that's correct...poss' Olson) has an extended section discussing various types and there is a much more rigorous technical discussion from Alan Whatsisname who took over Harbeth. On their site there is an interesting interview and explanation of how they got to their new cone plastic.
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Old 27th June 2011, 12:09 AM   #5
sreten is online now sreten  United Kingdom
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Hi,

FWIW, damping applied or not, bextrene cones typically required some form
of midrange notch filter, and matching that to driver variation was an issue.

Bextrene is a plastic derived from turpentine, wood spirit, like bakelite.
In all respects polypropylene is better, and a notch filter is not needed.
(The latter actually developed for making cheap kitchen equipment.)

Paper cones can be better than both the above, but it is far more difficult
to maintain batch to batch consistency, and deal with humidity type issues ...

rgds, sreten.
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Old 16th July 2011, 05:03 PM   #6
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sreten you are reffering to some generalizations and experiences by olson. . .these drivers have no notch filters and do not need any. . . .paper is horrible for speakers...they usually have a resonance at 1k and broad break-up/ resonance 1k to 10k. . . some people liek break up and it's coloration. . . I cured my DM5 just fine. . . I used a Vifa ring radiator tweeter, and bypassed all the Polyester Caps with Polystyrene which cured some sizzle and opened up the depth n the woofer ( I bypassed the shunt ) I then measured it and saw that there is a 2db dip from 2.5k to 3.5k so I dialed in 2 db of gain at 3k on my parametric eq.....when I replace the 3rd order/2nd order crossover with 4th order crossover. I will use Cheybyscheff +1db filters and overlapping crossover points to reduce the dip by 1db, possibly it will be close to flat with excessive overlap . . .I am developing these as a third Studio monitor so I can't have any eq on them. . . .beware of olson's generalizations as there are a lot of drivers he has not heard. Such as K2 exponential 7"s (Kevlar) with 4th order crossovers. Which yield a very ntural smooth, break up free midrange. . . re-read stuff before quoteing dude. . . .
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Old 16th July 2011, 05:06 PM   #7
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this driver and system is pretty darn good for '73 (or 2011) . . .I bought mine for $20 and spent another $70 for a wicked system. . . that will get even better with another $80 for a new crossover . . .
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Old 22nd July 2014, 03:48 PM   #8
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update. came to figure out the drivers are Kevlar, they just happen to be black. B&W started using them a year or two before production date which was actually '79, not '73 silk screened on the crossover.
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