B&W DM2 fettling

[Reffc]

As a (relatively) satisfied owner of a pair of second hand DM2s, I would echo this comment. I suspect that you could spend a lot of time and money replacing crossover components and replacing the internal wiring and notice no difference.

However, IF you do decide to go ahead and refurb your crossover, I would suggest you contact Jerry Bloomfield at Falcon Acoustics (sales@falconacoustics.co.uk>), he is INCREDIBLY helpful.

Good luck and I would love to hear what you do decide to do and how it works out.

Checking crossovers doesn't take long and is a good thing to do with any speaker older than 15 years or so old. Capacitors such as Solens or Ansars are relatively cheap and usually can be had in tighter tolrances (certainly to 5%) than many older capacitors, and it makes a heck of a positive difference bringing performance back by re-establishing the correct crossover points. Anything using electrolytics of that age has to be considered as requiring capacitor replacements IME (usually) PLUS some designs can be bettered very easily. For example, the DM2 used a well designed crossover but one which was badly laid out. By that I mean that the air cored inductors were all placed on the same axis, some very close to each other, which is inexcusably poor practice. By simply rotating selected inductors so that axis are all perpendicular can markedly improve performance.

Jerry is a very helpful chap and knows his stuff, but lets not forget that there are a few of us on AoS who are also happy to offer advice freely (Speaker refurbishments are also part of my own business)

[surv1v0r]

<snip>
The DM2 used a well designed crossover but one which was badly laid out. By that I mean that the air cored inductors were all placed on the same axis, some very close to each other, which is inexcusably poor practice. By simply rotating selected inductors so that axis are all perpendicular can markedly improve performance.
<snip>

How easy would this be to do? I attach a .JPG of my crossover.

B&W DM2 x-over.jpg

It shows that there are two black, one green, two white and one blue component. I take it that they are all inductors? Are ALL of them air cored or just the black and green ones to the left? As I understand it, the six green cylindrical and five brownish jobs should be OK?

Sorry if this is all a bit basic and do please feel free not to answer if you think my questions are too stupid to justify a response.


As to the "heck of a positive difference", I have to admit that I am expressing a personal opinion; I have no doubt that others will have much more sensitive hearing than I can now lay claim to

[istari_knight]

You may find this interesting http://www.troelsgravesen.dk/coils.htm

The black & green one's are air core, the blue one is ferrite core but I'm not sure about the 2 large one's ? They look to have some epoxy or resin in the core... A ohms test would reveal all...

[The Barbarian]

I don't understand the need to swap out the inductors?

[istari_knight]

I don't think there is. I posted that link as it visualizes what Paul was saying about the less than ideal inductor layout.

[The Barbarian]

Ok, however i do hear of a lot of people ripping out old inductors to replace with modern jobbies, ok some old designs do really have poor quality Inductors but these old B&W, the Dittons, early Castle etc really are good quality even though the bobbins look a bit gammy coloured..

In all honesty i do feel a lot of people go a bit mad sometimes.. Do you think these going a bit mad people loose sleep because they can't rewind the unit coils for modern wire

[istari_knight]

I just hope any prospective modders are honest with buyers if/when they sell up - I've had a few speakers now with completely bodged up crossovers

Power of the internet I suppose ? Speaking for myself, in the past if I didn't know sufficient amount to p*ss around with somethings inner workings I'd leave it well alone but now...

[surv1v0r]

In my youth I used to ride a motorcycle to work five days a week. At the weekends I would completely strip down some major component and rebuild it - just to make sure it was working better. After a year or two I could probably have completely stripped down and rebuilt the engine blindfolded.

I guess the good news was that it kept me off drugs, the bad news was that it wasn't so great for my sex life; I doubt that I could have coped without Rock and Roll.

I often wondered why I was never approached by a Japanese race team keen to capitalise on my experience . . . perhaps because they weren't as convinced of the improvements as I was

[Reffc]

Sorry for late response:

How easy or difficult the inductors in the photo above (Aaron's photo) would be to re-orientate depends on how they're held onto the circuit board. Some ferrites were attached using nylon bolts, some were epoxy glued in place whilst some were fixed with silicone or similar. If you can establish which might be the easiest to lift off the base, then those are the ideal candidates for moving. Air cores generally put out a stronger radiation field but by the same token are also more easily influenced by other magnetic fields and moving metal parts (such as vibrating conductive panels). By crossing their axis at 90 degrees to one another, you can get them fairly close (within 4 or 5 inches) without much impact on the signal. Ferrite cored inductors can be even closer as long as their axis are perpendicular. Tip: don't attempt to lift ferrite cored inductors that have been glued. The ferrite core and bobbin bases are surprisingly soft and fragile and will likely crack. Air cores are easier moved unless ferrites haven't been glued down. ..just be careful not to scrape any insulation varnish of coils when attempting to move either. If in doubt, leave well alone. If not confident on your DIY skills, leave well alone

Re-examining the photo, a couple of the large ferrites (LHS) appear to be glued to base plates and these riveted in place. First thing is to de-solder the connections (other side of the board) then the rivets can be drilled out and rotating the inductors should be easy. you may need to solder additional lengths of copper wire in place to reach the connection points when done. Silicone into place and add a cable tie if needed.

[surv1v0r]

Many thanks for the reply Paul and in my turn, I apologise for my delay in replying - decorating the living room has had to take priority!

I get the impression that the air cored inductors are glued to the PCB, they are certainly VERY snug. I can't see any practical way of reorienting them and I certainly couldn't move them four to five inches apart without utilising some other form of mounting which really is most unlikely to happen. The two larger inductors are ferrite cored (I think?) and are as you suggest, attached to metal mounting plates.


I have recently been listening to the DM2s (which are not my main speakers) and I have to say that they do produce a very good sound. My only criticism would have to be that they aren't as clear on speech or vocals as my Kef Concertos are. I suspect that good as it is, the Celestion HF1300 is not as good in the mid-range as the Kef B110? I hadn't realised for ages that the DM2s are transmission line speakers although they do weigh an absolute ton so perhaps I should have guessed.