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B&W DM70's - top end lacking

I have a pair of DM70’s.
They sound really good with vocal, blues and opera.
The bass is overblown with complex orchestral or progressive.

I am already replacing the bass units with Leak sandwich, as I found that the original units had not been repaired correctly.
They had some sort of home made surround made of thick paper with a 12 inch foam surround stuck on top.
The leaks seem to solve some of the bass issues.
I will get the bass units professionally repaired at some point.

Now to the treble units.
The mid and lower treble seems great, but things like symbols seem muted.
I was told that the electrostatic units had been repaired by One Thing, but now I am not so sure.

I am driving them with an Art Audio Quintet fed from a Conrad Johnson PV9a pre.
My CD is a Unison Unico and I am using a Focus One turntable just now.
Cables are from Chord. (Yes they do help a bit)

These are frustrating speakers, as when at their best, they sound so good.
First I need to know what to expect (especially from the treble).
Then I need to know how to fix any issues.

Sometimes they sound so so good and other times . . .
iscm
iscm OP
40 posts
 
Just to make it clear, I am not pushing One Thing, but I know of no one else in the UK with DM70 expertise.
There is a chap in Germany, but he is expensive.

I did see the speaker surrounds being offered as a kit for £35,
https://www.ebay.co.uk/itm/B-W-DM-70-hochwertiges-Lautsprecher-Sicken-Set-speaker-foam-surround-315/183148017101?hash=item2aa478f5cd:g:3xEAAOSwlStauOhM 

but in my case I think I need a specialist, as one of my original bass units makes a pinging sound and needs a total strip down.
Hears hoping Wembley Speakers can do this.
dylanthecat
11 posts
 
Hi Ian,

I have reformed the bass drivers with the Dutch oversized 12" foams. Though tight, they are just large enough and a great sonic improvement over the felt DIY surrounds.

I have removed the cotton gauze and all the damping. This has been replaced with a medium density acoustic foam on the rear panel and top panel. Lambswool quilting has been applied to the sides and based. A synthetic matting acoustic curtain has been hung directly behind the bass driver and folder over the base quilting.

The speakers have been lifted onto layered marble plinths with isolating silicon feet between each of the three layers. I have slotted four heavy duty rubber mounts (designed for hydraulic car jacks) under the speakers frame with isolates the metal base from the marble.

Very happy with the results, the bass has been transformed. The speakers sound better across the frequencies.

The speakers were definitely over damped!

Martin
dylanthecat
11 posts
 
Hi Ian,

I have ordered those other foams as a spare. Thanks for the link.

Have you changed your drivers over to eliminate the crossover?
Have you changed the speakers overs to eliminate the amp outputs?

Does it sound like metal hitting a dense hardwood block? I have heard of dry joints causing noises like this in bass drivers.

Best regards, Martin
iscm OP
40 posts
 
Hi Martin

Have you changed your drivers over to eliminate the crossover?
Have you changed the speakers overs to eliminate the amp outputs?
So far I have made no changes to the crossover(s).
I only changed the drivers because my original bass units are faulty.
The first thing that I plan to do is get the diodes in the HT section changed and take it from there.

Does it sound like metal hitting a dense hardwood block? I have heard of dry joints causing noises like this in bass drivers.
One of the original bass units makes a metallic ping when it reaches full excursion.
This is why I am holding back on changing the surrounds myself.
I feel that it is beyond my expertise.
Just now, the Leak bass units work very well.
I friend of mine, who also has a pair of DM70’s, thought that mine sounded very good this last weekend and that is before replacing my diodes.

The speakers were definitely over damped!
I agree about the damping and now use only half of the original damping plus the door mats glued to the rear panel.
The original damping is now in three zip laundry bags per unit.
This keeps the damping from getting into the rear of the bass units and help stop the fibreglass from settling too much.

Lambswool quilting has been applied to the sides and base
Where did you get your Lambswool quilting, as I have had trouble getting hold of this kind of thing?
I would also like to replace the fibreglass with long fibre wool if possible.

This is my other thread:
http://theartofsound.net/forum/showthread.php?57264-B-amp-W-DM70-my-journey-so-far
and another relevant thread:
http://theartofsound.net/forum/showthread.php?50077-B-amp-W-DM70-rebuilding-an-Icon

Ian

dylanthecat
11 posts
 
Hi Ian,

I brought my DM70 through AoS as 'not working' for only £100.

I have had great difficulty getting hold of natural lambswool quilting. The material that I have used came from the thermal insulation that Completely Fresh previously used in their delivery boxes. It is perfect for my needs. Unfortunately they have changed the material now.

I removed 2 black bin bags full of glass fibre (I loath the stuff) from the cabs.

One of the problems when I first listened to them was that the damping was pushing up against the cone despite the cotton gauze.

I will upload some photos onto your AoS thread.

Martin
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