B&W DM70's - top end lacking

Assuming the DM70 ESL panels themselves are good.
Another reason for the lack of ESL Panel output could be related to the 3- 800m ohm resistors in the EHT power supply, whose values may have drifted much higher and are preventing the panel from being charged properly.
Carbon resistors values have a tendency to drift higher over time and those are Carbon resistors - in the Panels power supply.

A megaohmeter is required to test them. They can be bought for cheap at Amazon.

Hi Iscm

Well I never thought I would come across another owner of these speakers here. :^)

A few things I found for optimum setup and assuming your speakers are functional.

First are your’s version one or two? The recommended amp 25 - 100 watts. I would recommend at least 100 wpc due to that woofer. If using Solid State make sure its wattage doubles at 4 ohms as they dip to 4 ohms. The amplifier you are using appears to be 15 wpc - This is not enough to hear what they can do.
That appears to be problem one. You need more power.

Floor Setup
These speakers do not have matrix bracing so they MUST not be placed "as is" on a suspended wood floor. if they are on a suspended wood floor your description of

"the bass is overblown with complex orchestral or progressive"

is pretty accurate.

Solution.
They must be raised on a solid platform, to where the tweeter panel is level with your ears. This fixes two aspects.

It ensures the bass stays tight and clean, and the ESL panel is the most resolving. They like a larger space, do not put them up against walls. They should be free standing.  

Pic 21 on my virtual system shows how I had them setup.

B&W ESL DM70

I used them with and without external tweeters. If your room is heavily damped you may need external tweeters. They are the total opposite of B&W 801’s, in that they like an un damped room just like my Quad 57’s.

The thin curved ESL panel needs to be at ear level, but its shape does give a decent sized sweetspot.

Any ESL repair shop can fix the speakers if they need repairs.

Hope this helps. .

iscm -  I found the panels sounded best at ear level and by raising the speaker to achieve this, the bass improved as well. I have a device that gives voltage readout. Plugging components into it also shows how much voltage they are using. Any voltmeter can be used to check AC voltage on the mains. When it sounds good and when you notice a problem. If there is a difference that tells you something is up with your main. But if the mains voltage is good both ways, I would suspect an issue with the power supply in the cabinet so it should be looked at. That is not a difficult repair.      

Did you make your own super tweeter?

iscm

the one in the linked picture is a simple dome tweeter. On the (plus +) side of the line there are 6 or 7 resistors.  I add / subtract resistors to get the desired effect, if needed. Very subtle. The curtains that can be seen in that room can be slid open to reveal pine walls and drywall, removing damping as needed. I have tried both the Music Reference RM10 and Rm9 Tube amps with them, as well as an assortment of SS amps. They were quite a load for the Rm10. They sound great with the Rm9. Well, everything sounds great with that amp.

My DM70 are not hooked up right now but your thread is making me want to hook them up, upstairs. :^)

Hi iscm

I acquired my DM70 ESL already refurbished.

here is a link that shows a pic of the woofer as well as an experiment with the Quad ESL. The experiment did not go well as the B&W crossover Woofer to ESL Panel is 400hz.

https://photos.app.goo.gl/jB2ocyZ1sMjUI86X2

It is using silver wiring.

If there are periods when they sound great, and other times when not so, that tells me the ESL panel may be ok and I suspect the ESL power supply / capacitors. So I would be tempted from your posts to have the capacitors / power supply checked out and recapped. I am pretty sure the DM70 are using electrolytic capacitors versus the polypropylene film capacitors of the 800 matrix series.

The manual recommends that they not be closer than 8 feet apart.

Owners manuals can be found here.

http://bwgroupsupport.com/manuals/bw-archive#ID_DMSeries

Service manuals can be found here.

http://bwgroupsupport.com/manuals/bw-service#ID_DMSeries

ct0517: With the Quads, I would have thought that around 200 Hz would be better.

Hi iscm

A 200 hz setting is much too high for the Quads. the Quads are wonderful to 50 hz with the Music Reference RM10 which was designed for them.
they needed help below that for the bottom Octave only, and to help create fill /SPL in the room.

For the experiments I placed the DM70 as shown in the picture I linked,  and did not plug them in so only the woofer was active. The woofer plays to 400 hz as designed. This was way too high and the reason it did not work well. Did not mix well with the Quad ESL bass panels. 

In room 2 I have the 57's set up with two Dynaudio BM12s Subs. The subs come with their own Class A/B amp - 250 watts each - they are set to play 60 hz and down only. The RM10 is full out on the 57's.
The preamp used in that room has two direct outputs to allow for separate connections to the RM10 and the BM12s subs. 
So the subs are filling in 60 hz and down only.

Iscm
I have heard mixed reports about the results of subs with ELS57’s?

Yes. If your subs are across the room, near the main speakers, and one listens to different genres of music, high and low SPL levels, IMO, one needs to have remote DSP management. A remote control that allows you to control phase, crossover level and db levels from your listening position.
The Dynaudio brand version that I have looks like

this.

Once one has used a remote DSP you can’t go back to a Sub with controls only on the box.
I have detailed the Quad 57 and subs experience on my virtual system page and my Quad 57 review page. See my post here from the Quad 57 review.

https://forum.audiogon.com/discussions/review-quad-57/post?postid=1324755#1324755

The B&W DM70 ESL’s are probably the rarest known speakers I can think of in North America. I assume more common in Europe. Here is a speaker that cost more to make than what it sold for !
Unheard of today - B&W became a bean counter company (post - John Bowers era - RIP). They are definitely worth the time to restore.

Iscm

from the manual.

Impedance
Nominally 8 ohms but rising throughout the mid frequencies to some 20 ohms, falling at 20 khz to 4 ohms.

The manual specifies the following for frequency response.
better than plus or minus 4db - 50 hz to 15khz
plus or minus 5db - 40hz - 20khz

This tells me they need really good setup or people will hear 50hz - 15khz (or less) with an average setup..

The manual also states the ESL panel has a removable pad to control the rear radiation pattern. Make them more dipole. This would be very important for a full midrange and keeping them a few feet at least from the front wall. You don't have a lot to work with - its a small panel. Everything helps. 

My feeling is if B&W kept producing them, the ESL panel would have grown in size - taller, as ESL Panels become more efficient with size. Interesting that the Quad 57 treble & bass panels are vertical. The DM70 mid/treble panel is horizontal. From what I remember the DM70’s have a bigger sweet spot over the 57’s when the 57’s are kept on the ground on their stock feet.

Mentioned earlier I was thinking of taking them out of the stored spot and setting them up. But this needs my son’s lifting help so maybe when he visits. The power supply finding is interesting. Will check the setting on mine before they do get turned on again. I have multiple dedicated lines in the house and live in the country so the demand is not high - Its a solid 121 volts. So the 115 setting it is, and it is low.