B&W DM2A refurb's

[spendorman]

Bear in mind that in revamping the crossovers, you may spend as much or more on components as the speakers are worth. And that there is no guarantee that you will like the end result.

I still think a good first move would be to use some contact cleaner on the rotary switch, the results may surprise you.

Above agreed, There is nothing really terribly wrong with the standard original crossover. B&W pretty well knew what they were doing. Just in case you did not realise, the rotary switch controls the level of only the Celestion HF1300 tweeter.

It's a bit personal, but your age matters, I'm 69 and my top end hearing is going a bit, I'm good for my age, my Dad at a similar age could not hear much above 8KHz, as other have said, what comes out of the supertweeter is pretty high, the crossover point is probably about 13KHz.

A good, but not infallible test of the supertweeter is to measure it's resistance with a multimeter. It does not have to be disconnected to do this. A good Coles 4001G should measure around 23 Ohms.

[Emmett123]

Bear in mind that in revamping the crossovers, you may spend as much or more on components as the speakers are worth. And that there is no guarantee that you will like the end result.

I still think a good first move would be to use some contact cleaner on the rotary switch, the results may surprise you.

It does require a good deal of force to move them at the moment. I dabbed a bit of WD40 on them today and left them to sit. i have not tried them on an amp since. I was reading too on a thread concerning B&W DM6 a problem with corrosion on the binding posts as they connected the back of the crossover board. A closer look at the binding posts external of mine shows that one is slightly bent out of line. But because the speakers worked at all I had dismissed that as a problem.

[walpurgis]

It does require a good deal of force to move them at the moment. I dabbed a bit of WD40 on them today and left them to sit..

The switches are supposed to have a reasonably stiff action. WD40 is not a good thing to use, as it leaves a residue. Something like Servisol would be better, preferably non-lubricating..

[spendorman]

The switches are supposed to have a reasonably stiff action. WD40 is not a good thing to use, as it leaves a residue. Something like Servisol would be better, preferably non-lubricating..

Agreed that WD40 is not the best thing to use, Servisol is ideal, Servisol Super 10 switch cleaner, does provide a lubricant as well, all to the good in my opinion, minimises wear on the cleaned contacts.

https://www.amazon.co.uk/Servisol-70.../dp/B000KEB6WW

https://www.amazon.co.uk/Servisol-Sw...WG4XX34MSSM7KR

[Pharos]

"Switch lubricant has become an embedded sloppy term often touted by Hi-Fi journalists.

There are two separate things to consider with a switch; mechanical functioning which should be treated with appropriated lubricants, and cleanliness and freedom from oxidation on contacts, needing a deoxidant, and possible preventer of further oxidation.

WD40 is not suitable for either purpose, it is a poor lubricant, which is partly why it is recommended for locks, to reduce the chances of easy opening, and the other reason being to displace water to prevent freezing and corrosion, as the name WD suggests, (Water Displacer).

[sailor]

Bear in mind that in revamping the crossovers, you may spend as much or more on components as the speakers are worth. And that there is no guarantee that you will like the end result.

Bear in mind that Emmett was considering buying a new amp to try and sort out his problem so I think it safe to assume he values the speakers and is prepared to spend some money to achieve this. Regarding the guarantee about him liking the sound, from my experience if done correctly I should think he will love the sound

The XO shown in the pics I posted were a substantial improvement over the original. The basic character remained but with cleaner highs, more detail and simply just more fun. I have rebuilt many XO's for many years and in every case the owners have been delighted. Some rebuilds have resulted in dramatic improvements.

Above agreed, There is nothing really terribly wrong with the standard original crossover. B&W pretty well knew what they were doing. Just in case you did not realise, the rotary switch controls the level of only the Celestion HF1300 tweeter.

It's a bit personal, but your age matters, I'm 69 and my top end hearing is going a bit, I'm good for my age, my Dad at a similar age could not hear much above 8KHz, as other have said, what comes out of the supertweeter is pretty high, the crossover point is probably about 13KHz.

A good, but not infallible test of the supertweeter is to measure it's resistance with a multimeter. It does not have to be disconnected to do this. A good Coles 4001G should measure around 23 Ohms.

We are 180 degrees out of phase here Spendorman B&W may know what they are doing now but back then I would have to disagree, looking at the XO they built. They did not take cognisance of proper orientation of inductors, whether by choice or because this phenomenon was at that time not widely known, if at all. The pics I posted illustrate the correct orientation. I was made aware of this important fact from articles published in Sound Practices. Simple to try for yourself. Hook up a coil to a signal genny and drive it at 1Khz. Hook up a second coil to an oscilloscope and watch the display as you move it towards the driven coil. A dual O'scope would be better and show almost full coupling if you placed one coil on top of the other. That's how transformers work. As you move the coils apart it will show the amplitude of waveform diminish. It will be seen that if they remain orientated as per B&W they need to be well apart. It will also be seen that orientated as per my pics there is very little coupling even when close to each other and zero coupling at the distance I have them. This is not whim or guesswork it is provable sobering fact. The B&W XO has a bunch of coils all closely coupled. So it should be apparent that coils for the bass driver are influencing the tweeter coils and the tweeter coil are effecting neighboring coils etc. They are all in a little huddle arguing, just like us I have upgraded XO's on modern B&W speakers that are properly done. I am not having a dig at B&W here.

The age of the listener is not important. As I mentioned previously, the tweeter response is responsible for providing the higher order harmonics, which regardless of whether or not they can be heard individually, when overlaid on the fundamental, give you the timbre of voice or instument and provide directional clues. If you take a saxophone, piano and guitar and they all play middle C, but robbed totally of all harmonics then you would not be able to tell them apart. All you would hear is a 261.6Hz sine wave. It is the harmonic structure overlaid on the fundamental that provides the clue to the instrument playing. This is the tweeters job. Provide it with a clean pure signal, which is the XO's job. Provide these conditions then for example a piano will sound more like a piano Read up on Max Townshend's super-tweeter for the psychoacoustics or Leo Beranek (a true acoustician)

You are correct that measuring a tweeter in place is fallible, in fact pointless. Tweeter attenuation is usually done after the last series cap so any shunt resistance would give a reading. In this case, 45 years grand old age, the adhesives will be suspect, the voice coil could have separated from the former yet still give a reading. Establishing continuity is a wasted exercise, that's why I didn't mention it. Ears are best.

Emmett: build a new XO along the lines I have suggested, avoid the level-control switch which is unnecessary and you will hear a vastly improved, top to bottom performance. The missing sparkle will be back along with previously unheard detail and imaging. This need not be that expensive. All the coils can be reused and probably the resistors unless out of spec. although replacing them is advisable. Mill are a safe bet at about 5 pounds a pop. The series caps to the 2 high frequency drivers is where the bulk of you budget should go. Feel free to PM me for specifics.

[walpurgis]

That seems pretty dismissive of the foregoing posts by others.

[spendorman]

That seems pretty dismissive of the foregoing posts by others.

I hope it does not put Emmett on a long unnecessary road of actions.

Just for example in the DM2a one can accurately measure the resistance on the Coles whilst still in circuit. It is a good start to checking the unit, however there is a chance (smallish) that the coil measures around 23 Ohms and the unit does not work. For example if the coil has separated from the diaphragm former.

In an ideal world we would space the inductors differently. I am aware of these things having worked the major part of my working life as an electronic engineer. Admittedly, I don't know everything.

[sailor]

Well I'm surprised Geoff and Alex.

Please excuse me for intruding into your exalted domain. I was not dissing anybody but saw little of value being offered. None of the responses to his cry for help were actually steering him in the right direction. Basically he was told, B&W knew what they were doing, all looks fine, clean the switch and you're good to go.

Post 97, when Emmett joined this thread he declared that his speaker sounded cloudy/dark with a lack of detail and transparency and would love to know what could be done. He so wanted to get his speakers to perform that he was prepared to by a more powerful amp.

So, in the spirit, ethos and intent of this forum, I tried to assist the poor fellow by offering a proven solution. My post was not only to provide the necessary information but also why it was necessary, and why the correct functioning of the tweeter is vitally important.

And You're criticising me for trying to be helpfull. Really?

I hope it does not put Emmett on a long unnecessary road of actions.

In an ideal world we would space the inductors differently. I am aware of these things having worked the major part of my working life as an electronic engineer. Admittedly, I don't know everything.

In what way do you find anything I recommended unnecessary, if as you say "In an ideal world we would space the inductors differently? It was precisely this point I was addressing by providing the means for anyone to test this for themselves. Would it not be sensible to optimise the correct mounting of the inductors if he were to opt for a full rebuild? Correct orientation is something you claim you were aware of yet did did not suggest this vital aspect of optimising XO component layout, which is the 'heart' of any speaker.

I, too, admit I don't know everything but I have spent a lifetime specifically targeting speaker design and measurement with hands-on application in this field. It is my accumulated, tried, tested and proven with measurement experience that I tried to impart to Emmett.

We are all big boys here and surely the man can decide for himself the road he wants to take!

[walpurgis]

Try addressing the subject, without having a dig at other members.








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