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Thread: B&W DM2A refurb's

  1. #131
    Join Date: Jan 2009

    Location: Essex

    Posts: 22,561
    I'm openingabottleofwine.

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    The inductors shown attached to the wooden (!) board are air-cored, so there is poor confinement of the magnetic flux around them, thus the need for an orthogonal disposition between the two.

    The inductors of the B&W crossover use ferrite cores, so there is much tighter flux confinement. You could rearrange them to be mutually orthogonal to one another, but I doubt it would make much difference to the SQ.


    I have a pair of the DM2a speakers as shown. No modifications have been made and they do not display the 'dark' 'cloudy' symptoms complained of.
    Barry

  2. #132
    Join Date: Apr 2012

    Location: Southall, West London

    Posts: 43,065
    I'm Geoff.

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    I did wonder about the influence of the ferrite cored items.
    "when common sense, logic and plausibility are excluded. All that remain are foolishness and lies"

  3. #133
    Join Date: May 2020

    Location: Northern Ireland

    Posts: 21
    I'm Emmett.

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    Thanks for all the advice so far. Its been amazing, if disputed. The prospect of building a cross-over is daunting for some-one who as only started to dip a toe in this world. However I'd be willing to give it go.
    I think the advice of Spendorman to measure the functionality of the Coles is a good place to begin. I have bought a multi-meter online (reflecting just what a noobie I am). Testing those should narrow down where the problem might lie.

    I wonder too if tweeter/woofers can be function but not be working at their best? Could there be a deterioration of their quality if previously driven too hard? I checked the rubber surrounds on the woofers and they seem to be fine.

  4. #134
    Join Date: Feb 2008

    Location: Middlesex, UK

    Posts: 4,149
    I'm Alex.

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    Quote Originally Posted by Barry View Post
    The inductors shown attached to the wooden (!) board are air-cored, so there is poor confinement of the magnetic flux around them, thus the need for an orthogonal disposition between the two.

    The inductors of the B&W crossover use ferrite cores, so there is much tighter flux confinement. You could rearrange them to be mutually orthogonal to one another, but I doubt it would make much difference to the SQ.


    I have a pair of the DM2a speakers as shown. No modifications have been made and they do not display the 'dark' 'cloudy' symptoms complained of.
    Good point Barry, I have three pairs of DM2/ DM2a, and none of them sound 'dark' 'cloudy', well, I'm exaggerating slightly, only three pairs as one pair is on permanent loan to a friend.
    Spendorman

  5. #135
    Join Date: Dec 2017

    Location: limerick

    Posts: 33
    I'm charles.

    Default B&W DM2A refurb's Your Message

    Barry, the inductors shown in my pics are not orthogonally disposed. You are looking at the coil windings, instead look at the axes. I could probably find the article I referred to in Sound Practices but I'm not going to bother. I made exhaustive tests with cored coils and air-cored coils and they both benefit from being orientated the way I demonstrated.

    Have you ever tried the test I described. Do it then report back.

    I am bowing out of this thread as I see no constructive advice being offered. What I see is, for some reason I do not understand, the desire to downplay my advice and experience.

    Good luck Emmett.

  6. #136
    Join Date: Apr 2012

    Location: Southall, West London

    Posts: 43,065
    I'm Geoff.

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    Quote Originally Posted by sailor View Post
    I am bowing out of this thread as I see no constructive advice being offered.
    Yet again. Dismissing the opinions of other members! Others are not precluded from expressing a view, just because you apparently think you know best!
    "when common sense, logic and plausibility are excluded. All that remain are foolishness and lies"

  7. #137
    Join Date: Jun 2015

    Location: London/Durham

    Posts: 3,865
    I'm Lawrence.

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    I've owned about 5 pairs of these over the years and I have noticed some differences in sound between them and one or two pairs tended towards the possible description of muddy. I'll admit though after reading up about the crossovers and that the caps didn't age that badly compared to Elcaps for example, I didn't try replacing the components. However is I was particularly attached to them I would probably have tried.

    Can I make a first suggestion which is that you put some choral music on quietly with boy trebles or sopranos (Tallis works quite well ) play one channel at a time if you have a balance control on your amp (or disconnect the other speaker). Cover the lower tweeter with your hand and put your ear near the supertweeter. You should hear some sound from them, it might be either hissing or sibilance, but if you hear it it's working.

    There's the chance as mentioned your hearing is no longer sensitive to the frequencies generated by the supertweeters. Therefore maybe don't assume they're broken if you can't hear. Maybe progress to the resistance check if so. Also this may not mean you don't need them as they apparently can contribute to dispersion of the lower frequencies and improve the audible frequencies. This idea is a little controversial I think (in the realm of genuine supertweeters >20khz) and I'm not qualified to have an opinion.

    The other potential issue is that the Coles may have been replaced at some point in the past with the incorrect type, they had at least 2 models with different resistance I'll say 8 and 16 ohms but that's a guess. If someone just dropped the wrong type in without checking (esp. if they replaced the lower resistance with the higher) then it might have the effect you noticed, even if they are working.

  8. #138
    Join Date: Apr 2012

    Location: Southall, West London

    Posts: 43,065
    I'm Geoff.

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    The HF1300 is a strange device, it can sound a bit hard, despite having a very flat response up to the slight 'ring' just before the upper end cut off. I think the hardness must be a colouration, possibly a reflection through the diaphragm. Nonetheless, it's a very fine tweeter with great transparency and transient response. I have several pairs of varying impedances, including the rare T718 variant with recessed front plate.
    "when common sense, logic and plausibility are excluded. All that remain are foolishness and lies"

  9. #139
    Join Date: Feb 2008

    Location: Middlesex, UK

    Posts: 4,149
    I'm Alex.

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    Quote Originally Posted by walpurgis View Post
    The HF1300 is a strange device, it can sound a bit hard, despite having a very flat response up to the slight 'ring' just before the upper end cut off. I think the hardness must be a colouration, possibly a reflection through the diaphragm. Nonetheless, it's a very fine tweeter with great transparency and transient response. I have several pairs of varying impedances, including the rare T718 variant with recessed front plate.
    I believe that Spendor ran the HF1300 out of phase with the Coles 4001G so as to partly nullify the "slight ring". Nerveless, the HF1300 is a fine unit. My almost fav speakers, LS3/6 use it with a HF2000 supertweeter.

    The Celestion HF1400, is interesting, basically a 1300 with a larger magnet, used in another BBC speaker and the B&W DM3, probably making it more efficient. I have a couple of pairs of these, one pair in DM3's
    Spendorman

  10. #140
    Join Date: Apr 2012

    Location: Southall, West London

    Posts: 43,065
    I'm Geoff.

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    Quote Originally Posted by spendorman View Post
    HF2000 supertweeter
    I have a late (UL10) set of those too.
    "when common sense, logic and plausibility are excluded. All that remain are foolishness and lies"

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