B&W DM2 Series II dull sound

[Dom123]

Hello Everyone,

I just picked up a pair on DM2 series II 3 way speakers manufactured in 1979 The cabinets & drivers all appear to be in good shape, and I really love the classic look of these speakers especially on their stands.

They sound good with voices sounding great, but the issue is that they are very slightly dull sounding on some types of music, so I feel the output of the tweeters (TW-26) isn't as good as it could be. Also the bass is a bit woolly. Both tweeters are definately working though, just the treble is not so present as on other speakers I have. Difficult to know if the tweeter output is low or the mid drivers are too prominent sounding. Adjusting the mid down & treble up on my amp (Sansui AU-7900) definately improves the sound balance though. The voice coils of both tweeters measure around 7 ohms.

I read on various forums about this issue, and appears to be a fairly common issue for these speakers to sound dull in their original unrestored condition. Some propose to re-dope the tweeter cone (material) with some pva or shellac, or to disassemble the tweeters (which I don't want to do) to clean the magnet gaps, or to recap the crossovers considering the change in ESR of capacitors over time.

I guess I should recap the crossovers first, but on checking the capacitors for the tweeter circuit, these appear to be film type, whereas the other caps for the mid & bass are electrolytics. My understanding is that film type capacitors don't age with time, so the ESR or characteristics of these caps is unlikely to have changed. Is my understanding right ?

Also if anyone has experience of a similar issue on B&W DM2ii speakers I would be interested in hearing.

Many thanks

 

[luxmaster]

I had a pair in black. I thought they looked really cool and kept them for awhile just based on that alone. They did sound very dull indeed. They were able to take a lot of power. The speakers had like no ambience or sonics. I eventually sold them.

 

[RossW]

Some film caps definitely don't age well, it's worth the few extra bucks to just replace all the caps.

Not sure if the DM2 uses ferrofluid in the tweeter, if it doesn't there's not much point to opening it up, if it does then cleaning out and replacing the ferrofluid can make a big difference. If you're not comfortable doing it yourself, see if you can find a speaker shop that will. Shouldn't be too pricey. I definitely wouldn't apply anything to the tweeter dome, it will just add mass and mess up the response.

British speakers tend to be a bit wooly, it's part of their signature sound. I've heard some that were almost unlistenable even after a full restore and others that are excellent, easy to listen to speakers. What speakers are you comparing them to?

 

[Dom123]

Thanks for the supply. I'm not sure if the tweeter uses ferrofluid. It's also the same tweeter (TW-26) used in some other models I believe, so for example the DM14, which aren't especially known for being dull. From what I read on one forum they do not have ferrofluid

I just have bunch of old vintage british speakers, Kef 104ab, B&W DM570, Celef Domestic III super , and all sound brighter than the DM2ii. I have recapped all of them. The Celefs sounded much better after recapping & are easily the best & most enjoyable sounding speakers I have. I just don't beleive the DM2ii are inherantly lifeless & dull and put this down to capacitors that are 43 years old.

I would just use some good quality electrolytic caps for the bass/mid, but any recommendation about the caps for the tweeter would be appreciated, especially as I am loooking for a brighter sound.

 

[ElliotJoseph]

Thanks for the supply. I'm not sure if the tweeter uses ferrofluid. It's also the same tweeter (TW-26) used in some other models I believe, so for example the DM14, which aren't especially known for being dull. From what I read on one forum they do not have ferrofluid

I just have bunch of old vintage british speakers, Kef 104ab, B&W DM570, Celef Domestic III super , and all sound brighter than the DM2ii. I have recapped all of them. The Celefs sounded much better after recapping & are easily the best & most enjoyable sounding speakers I have. I just don't beleive the DM2ii are inherantly lifeless & dull and put this down to capacitors that are 43 years old.

I would just use some good quality electrolytic caps for the bass/mid, but any recommendation about the caps for the tweeter would be appreciated, especially as I am loooking for a brighter sound.

View attachment 2619731

Hi Dom, did you managed to recap your B&W's? I'm currently facing the same issue as my B&W DM2 Series II sound rather dull compared to my DM4's. I'd like to know your progress and what you replaced so I can do it to mine too! (if there is an improvement).

 

[luxmaster]

I'm just wondering that so many of these speakers do sound dull that maybe they are suppose to sound this way? Maybe its just the wrong type of music being played with the DM2's. I heard they sound best with jazz.

 

[Dom123]

Hi Dom, did you managed to recap your B&W's? I'm currently facing the same issue as my B&W DM2 Series II sound rather dull compared to my DM4's. I'd like to know your progress and what you replaced so I can do it to mine too! (if there is an improvement).

Hi Joseph - no not yet recapped. I ordered 100V electrolytics from Falcon acoustics for the LF & MF, but they only just shipped them today after one week. Then for the HF I bought some Dayton DMPC polypropylene film caps for the HF which I have received. This weekend will be tricky, but am hoping to get this done by next weekend. Will give some feedback

About the Daytons, I brought 1% tolerance for the tweeter series cap as the original is 5uf, and the closest Dayton was 5.1uf, but regular 5% tolerance for the other caps. But when I measure them, they are all very close to nominal :

0.47uf - measure 0.46uf & 0.47uf
2.2uf - measure 2.22uf (both caps)
5.1uf - measure 5.14uf & 5.16uf

Moral of the story (if buying Daytons), just order the regular 5% caps.

About the electrolytics I will measure them when I get them. I guess there is always the possibility to put some low capacitance film caps in parallell with them. TBH if the sound of the highs don't improve after recapping, I will need to consider whether it will be worth investing more time & energy on them.

I'm just wondering that so many of these speakers do sound dull that maybe they are suppose to sound this way? Maybe its just the wrong type of music being played with the DM2's. I heard they sound best with jazz.

I was thinking the same but hard to tell whether it is an inherant characteristic or not. Maybe it needs someone who remembers these speakers when they were new. It is the identical tweeter (TW26) used on several vintage B&W though. Actually they do sound best on classical music, and not too bad on Jazz. For rock & other types of music the dullness does zap the musicality though. I've noticed the mid is very prominant indeed, so it could be a case of the mid driver unbalance drowing out some of the treble

 

[ElliotJoseph]

I was thinking the same but hard to tell whether it is an inherant characteristic or not. Maybe it needs someone who remembers these speakers when they were new. It is the identical tweeter (TW26) used on several vintage B&W though. Actually they do sound best on classical music, and not too bad on Jazz. For rock & other types of music the dullness does zap the musicality though. I've noticed the mid is very prominant indeed, so it could be a case of the mid driver unbalance drowing out some of the treble

Thanks for taking a dive into this, Dom. Very intrigued to see what the results are.

As for the characteristics for the speakers, I would agree but I find the opposite really. The high end is so dull it's such a stark difference to a pair of DM4's. There's definitely potential there because I prefer the bass and midrange but it's just that limited top-end which sounds rounded off. I have ended replaced one of my TW26 tweeters and it didn't make a difference and i dont want to rely on my amp EQ settings. It would be strange if this was a wide issue, surely we can't all have dull sounding DM2 S2?

 

[Dom123]

You're right. I'm just hoping it's those 42 year old ochre coloured 100V film caps on the tweeter section causing this. I can't beleive the speakers sounded like this when they were brand new.
Turning up the treble on the amp does bring more brightness yes, but it doesn't sound right or nice for some reason - hard to explain.
The tweeter coils measure fine. Concerning ferrofluid, this could be an obvious explanation, but tbh I don't think these tweeters used ferrofluid - I may be wrong though.

Once I take them apart I will also look for signs of any corrosion anywhere. On one speaker I already removed the bass driver & dislodged the plastic reflex bass tube - that was really a major struggle, requiring a lot of force, but is necessary if the cross over is to be removed.

There's also some threads on a French forum about these speakers and their dull sound. One mentionned re-doping the cone on the tweeters, and the other dissassembling the tweeters to clean the voice coil gap of the magnets (using wd40 !!). They both claim it brough some significant improvements, but I am not totally convinced about this. The fact you tried a different tweeter with no change in sound speaks for itself

 

[baco99]

replacing the caps is a relatively inexpensive potential solution. I would start there. inspect everything inside. there's not much you can do with the tweeters themselves unless they have ferrofluid. they are said to have a "high temperature coil assembly" according to the literature, but don't know what that means exactly.

 

[luxmaster]

Well I am very curious to hear what the results will be after a recap.

 

[Dom123]

Well I am very curious to hear what the results will be after a recap.

They should sound better after a few beers !

 

[Dom123]

I haven't got the electrolytics yet, but dismantled the cross over from one speaker today, lifted a leg on each cap & measured their values.
The electrolytics are way out of spec, but the film are close except for the smallest one (0.47uf) on the tweeter circuit. Not sure such a deviation in this cap could suppress the tweeter output

 

[Dom123]

I also measured the resistance of R5 in series with the tweeter (after lifting a leg of course) and measure 7.5ohm instead of 6.8ohm.
This is obviously restricting some output to the tweeter, but is this significant enough to be audible ?
Should I just go ahead and change the reisistor ?

Thanks

 

[baco99]

Definitely recap. And while you are in there change that resistor.

 

[Dom123]

Just a precision, the cap measuing 0.68uf is actually marked 0.68uf, so it's spot on. For some reason they used a different value that the drawing

I notice the old film caps in the tweeter circuit are ITT PMT/2R UK , which are actually metallized polypropylene & are known to be high quality caps.

 

[ElliotJoseph]

Any updates on the recapping, Dom? I'm probably going to sell off my pair of DM2 S2's but wondering if it's worth maybe even cleaning the tweeter to get a bit more brightness. You always wonder if it's something the buyers will complain about?

I got a pair of Celestion Ditton 25's last week and they're everything I wanted and expected from bigger vintage speakers. I definitely prefer the B&W looks but if they lack with the sound then It's obvious what I'm sticking with!

 

[CohibaJoe]

Just a precision, the cap measuing 0.68uf is actually marked 0.68uf, so it's spot on. For some reason they used a different value that the drawing

I notice the old film caps in the tweeter circuit are ITT PMT/2R UK , which are actually metallized polypropylene & are known to be high quality caps.

Any chance of a picture of the Crossovers? I would also change out the Caps, Films and Resistors...Fresh parts in the long run.

 

[Dom123]

Any updates on the recapping, Dom? I'm probably going to sell off my pair of DM2 S2's but wondering if it's worth maybe even cleaning the tweeter to get a bit more brightness. You always wonder if it's something the buyers will complain about?

I got a pair of Celestion Ditton 25's last week and they're everything I wanted and expected from bigger vintage speakers. I definitely prefer the B&W looks but if they lack with the sound then It's obvious what I'm sticking with!

It's taking time to get the electrolytics from Falcon (Thank you Brexit), but should be there tomorrow, and I will start with the job tomorrow evening after work. As mentioned before the electrolytics were way out, so whatever happens it will definately clear up the midrange. Will be interesting to see what effect a less hollow or "honky" midrange (if that makes sense) will have on the treble. For the treble section I am using Dayton Audio DMPC caps.

I also considering re-doping the tweeter cone with a very thin layer of PVA, as per the original coating used by B&W. Would use PVA glue watered down to a very thin liquid. I done some tests on a scrap tweeter and it seems to dry to a thin & shiny layer, although a little sticky.

Hopefully this will brighten the sound up. I am also contemplating changing the resitor in series with the tweeter from 6.8ohm to good quality ones (>10w) of 5.6ohm or 4.7ohm - basically a trial & error exercise.

 

[Dom123]

Any chance of a picture of the Crossovers? I would also change out the Caps, Films and Resistors...Fresh parts in the long run.

Sorry photos aren't great, but see attached. On the otherhand all components on my crossovers are identical to those shown on the drawing (attached) except C8, which is shown as a .47uf, but is actually a .68uf on the board, and the C9 which is 5.0uf on the drawing but actually a 4.7uf on the board. The .68uf measures spot on, but the 4.7uf measures 5.1uf. The 3 film caps (C7, C8, C9) are all 100V rating

Note : the original electrolytics have varying voltage rating: 8uf 50V, 30uf 50V, 75uf 50V, 80uf 25V, 15uf 25V & 20uf 70V