Yeah,, those ferrite core inductors sound like crap when they saturate. This happens at about 75-100w on the larger one (LP series with woofers). Having both woofers parallel makes this situation worse having twice the current load as with one driver alone.The sound when this happens can be a popping noise just like a voice coil bottoming out. Sometimes its just lower midrange fuzz. I would switch this inductor and the smaller one only for steel laminate and compensate with appropriate series R if needed. Stay far away from powdered iron or ferrite cores... they SUCK.
DM640s are a poor man's 802. B&W runs their mids up pretty high compared to other manufacturers, sometimes past 3k. This is alot of the character you hear. Many will say its not good to do so for off axis FR or power response, but keeping the tweeter out of the sub-3k area opens up the treble in terms of HF dynamic capability (again, much of the character). The kevlar mid in your speaker does pretty well at upper rolloff and not having a crossover in the 500 to 3k area is better for midrange coherence if the mid driver can pull it off (which it can). Vocals on a B&W like yours with the small kevlar mid can sound bewitching and life like.
So redesigning your crossover will certainly change the sound signature and character of your speaker. I wouldn't do that if they were my speakers. I'd just stick to the original design as close as possible by adhering to inductor DCR and insert.0.5 - 1 ohm when switching from electrolytics to film caps. I use 0.5 on anything that was smaller than 10uf, but most of the time it wont make much of a difference if the caps have aged well and haven't increased much in DF. The series cap to the mid has to be PP for sure. Won't be cheap but will be worth it - trust me on this one. If you do go PP, that one needs about 0.5 ohm extra series R (I would bump up R1 or R2 to 10 ohms and call it a day). If the mids are still a little too hot then make both R1 and R2 10ohms. A tiny bit more mid level will compensate for the mid bass heaviness found in the typical B&W speaker voicing.
Nevermind the comment regarding the terminal cup - your crossover is mounted inside, not on the terminal cup like most other DM series. Just ripping out those nasty inductors and replacing the series caps with PP (I prefer Solens for this speaker) along with freshening the other parallel electrolytics will transform these things into a giant killer. I've used this recipe on alot of older B&Ws of this vintage with similar results. Its worth the extra cost for the recommended parts. Don't skimp on the inductors and series caps.
DM640s are a poor man's 802. B&W runs their mids up pretty high compared to other manufacturers, sometimes past 3k. This is alot of the character you hear. Many will say its not good to do so for off axis FR or power response, but keeping the tweeter out of the sub-3k area opens up the treble in terms of HF dynamic capability (again, much of the character). The kevlar mid in your speaker does pretty well at upper rolloff and not having a crossover in the 500 to 3k area is better for midrange coherence if the mid driver can pull it off (which it can). Vocals on a B&W like yours with the small kevlar mid can sound bewitching and life like.
So redesigning your crossover will certainly change the sound signature and character of your speaker. I wouldn't do that if they were my speakers. I'd just stick to the original design as close as possible by adhering to inductor DCR and insert.0.5 - 1 ohm when switching from electrolytics to film caps. I use 0.5 on anything that was smaller than 10uf, but most of the time it wont make much of a difference if the caps have aged well and haven't increased much in DF. The series cap to the mid has to be PP for sure. Won't be cheap but will be worth it - trust me on this one. If you do go PP, that one needs about 0.5 ohm extra series R (I would bump up R1 or R2 to 10 ohms and call it a day). If the mids are still a little too hot then make both R1 and R2 10ohms. A tiny bit more mid level will compensate for the mid bass heaviness found in the typical B&W speaker voicing.
Nevermind the comment regarding the terminal cup - your crossover is mounted inside, not on the terminal cup like most other DM series. Just ripping out those nasty inductors and replacing the series caps with PP (I prefer Solens for this speaker) along with freshening the other parallel electrolytics will transform these things into a giant killer. I've used this recipe on alot of older B&Ws of this vintage with similar results. Its worth the extra cost for the recommended parts. Don't skimp on the inductors and series caps.
Sorry to hijack (sort of) but I found this as I was looking for help with my DM640’s. I’ve had these forever, bought them for $50 completely blown and replaced the frozen base drivers but nothing else. They have sounded great until recently my teenage son decided to stream loads of compressed K-pop through them daily. The other day he started complaining about the sound saying they were extremely bright and horrible. Well frankly he is right. Something happened and now the tweeters are harsh and unbearable. The mids and lows still sound good but it’s just not right. I picked up a new pair of 606s2 bookshelf B&Ws and the tweeter difference is huge but they don’t have the fullness and mid to low bass presence of the DM640’s even with the subwoofer. So what happened? Did he torch a crossover? Bad tweeter? Clearly the speakers underwent significant abuse before I got them and I only occasionally drove them hard. While trying to figure out if it was amp or speaker I hooked up a 170 w/ch Cambridge amp and one of the tweeters gave an ear bending POP twice on only moderately loud volume. Sorry for the log post but hoping to save these speakers… the 606s2 just don’t cut it and I’ll end up spending 000’s on new floor standers if I can’t fix this.
Under the circumstances described, it is most likely that the tweeters are fried. If they are still producing sound, their voice coils are not open circuit, but are likely to have been distorted out of shape by overheating.
There is a possibility that the tweeter diaphragm/voice coil assembly is replaceable on this model of tweeter, but you would have to check that out.
You would be advised to inspect the two capacitors and single inductor in each tweeter filter for signs of overheating.
EDIT: Those are C4, C5 and L4 on the crossover schematic shown earlier.
There is a possibility that the tweeter diaphragm/voice coil assembly is replaceable on this model of tweeter, but you would have to check that out.
You would be advised to inspect the two capacitors and single inductor in each tweeter filter for signs of overheating.
EDIT: Those are C4, C5 and L4 on the crossover schematic shown earlier.
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Use your nose and eyes to detect burnt components. Capacitors don't get hot as resistors do.
The most common reason for heat damaged tweeters is using an amp that's too low powered, running into distortion.
The most common reason for heat damaged tweeters is using an amp that's too low powered, running into distortion.
Components should be measured by lifting one of their legs from the circuit board. To measure the capacitors, you would need a multimeter with a capacitance scale. The inductor should only require a visual inspection - if it looks unscorched it probably will be electrically OK.
Another way to test the tweeter filter is to connect it to any available alternative tweeter or small speaker driver.
P.S. I'm pretty sure the damage is confined to the tweeters themselves, so the driver substitution method would be my first port of call.
Another way to test the tweeter filter is to connect it to any available alternative tweeter or small speaker driver.
P.S. I'm pretty sure the damage is confined to the tweeters themselves, so the driver substitution method would be my first port of call.
Inductor inner turns can overheat and melt their insulation without it being obvious from the outside.
At a glance everything looks okay. My multi-meter does not have capacitance. I do have access to some replacement tweeters and a DM640i crossover at a reasonable cost so perhaps I’ll swap the tweeters in first. The 640i crossover has the same caps and very similar resistors but a slightly different board layout. I have no way of knowing if the original owners underpowered them but as a bunch of college age kids I’m sure they were played loud. As I said all 4 woofers no longer moved.
In which case, one would require a meter with an inductance scale in order to check the inductor.
EDIT: Replying to AllenB.
EDIT: Replying to AllenB.
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@B&W_Rules; you could swap the tweeters, if the problem moves with the tweeter; it’s the tweeter. If the problem stays with the speaker, it’s the crossover.
If it’s the tweeter, you can buy a new membrame. Make sure to also order new ferofluid and clean the old fluid out of the magnet before adding new fluid and reassembly.
https://speakerrepairshop.nl/en/dia...m500-and-dm600-series-tweeter/a-3653-10000077
In case it’s the crossover (what I don’t expect), measure components and replace what’s not within tolerance.
If it’s the tweeter, you can buy a new membrame. Make sure to also order new ferofluid and clean the old fluid out of the magnet before adding new fluid and reassembly.
https://speakerrepairshop.nl/en/dia...m500-and-dm600-series-tweeter/a-3653-10000077
In case it’s the crossover (what I don’t expect), measure components and replace what’s not within tolerance.
There is a way to measure L and C with a basic multimeter.
https://www.diyaudio.com/community/threads/measure-l-and-c-with-a-multimeter-and-a-phone.303938/
https://www.diyaudio.com/community/threads/measure-l-and-c-with-a-multimeter-and-a-phone.303938/
@B&W_Rules
Replacing ferrofluid in B&W series 600 tweeter guide: https://speakerrepairshop.nl/en/instructions/replace-ferrofluid-in-tweeter/c-36
Replacing ferrofluid in B&W series 600 tweeter guide: https://speakerrepairshop.nl/en/instructions/replace-ferrofluid-in-tweeter/c-36
Well, it was a long time comming, but life got in the way. Anyway, I just finished the first speaker!
I've just AB'd to evaluate the difference, which is quite noticeable. It's best discribed as if a blanket has been lifted between you and the speaker. Instruments seem to be more 'separated'. How much is because of the type of components or how much was maybe the old electrolytics being out of spec after more than 30 years of service, I don't know. But they did make an old quite nice sounding speaker even better!
I know there are people who believe it's a waste of money to buy more expensive components than replacing with similar spec, however there are people who build $400 Lego kits. I've build this and had a lot of fun doing so. I think they look AWESOME and it's a shame they are out of sight inside the cabinets. I'm toying with the idea to make external enclosures because I think they turned out as pieces of art.
I've created the boards in CAD and they are 3D printed in ASA-CF. I decided to split the LF and MF/HF portions of the filter to their own boards. This was because of a mistake in the order. The 2.5mH inductor was supposed to be a P-core, but I accidentally ordered an aircore 2.5, which turned out to be quite large! However, I think it looks bad *** so I decided to keep it.
All in all, the production of the boards cost me close to 300 for both crossovers, using all new components.
I've included a photo with the new boards and the original, and ofcourse a banana as size reference.
Thanks all for the advise and hope you can appreciate my frankenstein creation.
I've just AB'd to evaluate the difference, which is quite noticeable. It's best discribed as if a blanket has been lifted between you and the speaker. Instruments seem to be more 'separated'. How much is because of the type of components or how much was maybe the old electrolytics being out of spec after more than 30 years of service, I don't know. But they did make an old quite nice sounding speaker even better!
I know there are people who believe it's a waste of money to buy more expensive components than replacing with similar spec, however there are people who build $400 Lego kits. I've build this and had a lot of fun doing so. I think they look AWESOME and it's a shame they are out of sight inside the cabinets. I'm toying with the idea to make external enclosures because I think they turned out as pieces of art.
I've created the boards in CAD and they are 3D printed in ASA-CF. I decided to split the LF and MF/HF portions of the filter to their own boards. This was because of a mistake in the order. The 2.5mH inductor was supposed to be a P-core, but I accidentally ordered an aircore 2.5, which turned out to be quite large! However, I think it looks bad *** so I decided to keep it.
All in all, the production of the boards cost me close to 300 for both crossovers, using all new components.
I've included a photo with the new boards and the original, and ofcourse a banana as size reference.
Thanks all for the advise and hope you can appreciate my frankenstein creation.
I was timed out as my ancient laptop struggled to download those massive images!
I'll try again later, but from what I've seen that's some neat and professional looking work (and what a perfect banana!).
EDIT: Yep, I've now seen 'em all.
I'll try again later, but from what I've seen that's some neat and professional looking work (and what a perfect banana!).
EDIT: Yep, I've now seen 'em all.
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Yes there's some difference of opinion whether pictures should be posted full size, it looks different on phones than desktop.
However Galu is probably talking file size, and the forum optimises image file sizes... unless you view the post soon after it was made and is still in the optimising queue.
However Galu is probably talking file size, and the forum optimises image file sizes... unless you view the post soon after it was made and is still in the optimising queue.
Galu is probably talking nonsense as usual!
When I post large pictures using my laptop, I resize them on screen so they don't take up as much space on the page.
I hope to save wear on member's scrolling fingers, but admit to not knowing how that action pans out on other devices.
Finished the second speaker today.
This modification has totally transformed these speakers! Couldn't be happier. Or could I? So what's next? Butyl rubber dampening mats on the interior panels underneath the factory isolation? 🤔
What more can be done to optimize these bad boys?
I would love some accoustic treatment of the room too, but unless I want a divorce, I probably shouldnt...
Some more pictures. @Galu, I've resized them for you!
This modification has totally transformed these speakers! Couldn't be happier. Or could I? So what's next? Butyl rubber dampening mats on the interior panels underneath the factory isolation? 🤔
What more can be done to optimize these bad boys?
I would love some accoustic treatment of the room too, but unless I want a divorce, I probably shouldnt...
Some more pictures. @Galu, I've resized them for you!
