Diying DBL Mids

Firstly credit to @Charlie for researching suitable replacement mids for the DBLs now that OEM replacements are no longer available. Whilst these Scanspeak replacements are a good frequency match they are larger than the original Octagonish Naim mids. Here’s the profile of the original superimposed on the Scanspeak.

IIRC Scanspeak trimmed a pair for Charlie but since that wasn’t an option for me I’ve had to do that myself. I could have simply marked them up, masked them up and got stuck in with the bandsaw but in all probability I’d make a balls if I tackled it freehand. Also it’s not in my nature to do anything so straightforward :grinning:

After several weeks of contemplation I sketched up some designs and had a friend model them up in 3D for printing. The bottom jig is solid, has a groove for an O ring and four holes I’ve tapped (M5).

The drive is loaded atop that as so…

…with another O ring on top and then the upper jig is added…

…and then bolted down. The “dust cover” on the top jig is paper and duct tape to allow maximum flexibility in fitting through the band saw. There’s not much clearance and it’s much easier and cheaper than trying to model and print something.

Then with a new blade in the bandsaw I set about cutting them down using the top jig as a visual cutting guide.

Finally a bit of finishing of the edges…

and we have the finished article.

I haven’t cut them back to the absolute size of the OEMs, leaving an extra 2mm as I’d determined that it wouldn’t interfere with the suspension cut into the DBL face (indeed IIRC someone else has determined the unmodified units fit OK).

The cutting isn’t perfect, because I had to have the bandsaw set to its maximum height to clear the drive unit the blade had scope to flex, but they’re not bad and freehand would have been “interesting”.

I’d love to crack on and fit them this afternoon but I’m home alone and getting the top box off the DBL is a two person task (or possibly some human octopus hybrid). Hopefully this weekend. Also have a set of new foam for inside the speakers though will probably only do the mid/HF boxes immediately.

Willy.

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Outstanding, what a great job Willy, what size O ring did you use? And are both jigs pretty much the same, with the drive unit basket sandwiched in between? I have a busted mid from a friend NBL’s that I could probably trace and hand make the jigs. Cant wait to hear about their performance, they may be better than the originals!

Wow……impressed Willy👍

Mario,

Outer profile of the jigs is the same. The upper has a through hole and a boss (to attach the dust cover).

Also the holes in it are larger (5.2mm).

The O rings are both 115 ID, 125 OD. (EBay) The one in the lower jig sits in a groove, the upper just rests on the mid and the upper jig on top, located by the threaded rods.

I’m happy to share the stl files if anyone fancies printing their own. (Assuming @Richard.Dane is ok with that).

I suspect that they may be better than my current OEM ones, unless of course Radio 3 have taken to broadcasting buzzing sopranos.

Willy.

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Good job i say, especially as it keeps them going.
Probably a router would have been easier than a band saw and given a perfect edge.

@Willy
Wow, very impressive !
Just don’t dump the original drivers.
I have meanwhile found a chap in Germany who mainly does refurbishing of older drivers out of production. I actually will visit him next week with a mid pair dbl drivers and see what he has to say. It may turn out that it’s possible to get a decent refurb of the original ones…so keep your fingers crossed :crossed_fingers:

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Charlie,

It’s not in my nature to throw things out, something, someday, I’m sure my kids will curse me for.

Most interested to hear how you get on with having the OEMs refurbished.

Willy.

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Almost ready for the trip to potential rejuvenation :wink:

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That’s great news. A friend of mine has just blown up his active DBL’s and lost two tweeters and one mid-range unit. He’s just ordered the ScanSpeak replacements. A bit careless I know but he is renowned for playing his system very loud. The system doubles as a surround sound source for his massive projector driven by twelve 135’s and a 250. Believe me, when you get an explosion it moves the roof at least a couple of inches!

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On Saturday, late afternoon, after all day building a new bench for Mrs Willy I finally got around to tending to my DBLs.

First off removing…

What an absolute mess. Most of the existing form had to be removed with a vacuum cleaner. Wool came out looking fresh though had to be taken outside to shake off foam dust. Not sure what was done to brutalise the finish around in the past but the veneer is in good shape, simply missing any paint.

Due to time pressures (OK call it impatience if you must) I’ve done nothing on the cosmetics, that’s a project for another day.

The machined scanspeaks were masked up and the mounting holes carefully extended inward with needle files (helps sometimes to be married to a goldsmith).

New foam and (bagged) wool reinstalled.

Bead of Blue Hylomar applied, drivers installed and torqued. They’re a reasonably tight fit and part of me is curious to know if easing the baffles would affect the sound.

Finally the Franken-Dibbles were alive!

Fired them up with Gillian Welch’s Soul Journey and immediately it was clear that there was an improvement. More body to the vocal, Previously it had become somewhat recessed.

Left them running with Radio 3 playing whilst I fed myself. About 90 minutes later I was helplessly drawn into the room by a rendition of Copeland’s Rhapsody in Blue. A return of dynamics, piano sounding like the scale it should have.

So, on the dynamics, and @Geko 's friends explosions…abut 11:30 on Saturday night poor Zhukov was splayed out on the floor, if not asleep then close to it. Just then the bounder Onegin shot Lensky! Almost instantly he was at the door, looking back at me bleary-eyed with a distinct wtf expression.

Over the first couple of days ongoing improvements, still a bit strange at times, a bit of thickness/harshness in upper vocals but definitely heading in the right direction. Now unrecognisable compared to a week ago, in particular starting to hear some of the delicacy that DBLs do so well creeping in. Don’t recall ever having replaced mids before but assuming the run in of a similar duration to tweeters. Have been through a few of those over the years. :grinning:

Now keen to see what replacing the rest of the foam delivers. Will probably wait until the builders finish as my floor is currently home to all the slate kitchen worktops.

Willy.

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Almost forgot, mid unit (before I cleaned it up and packed it away).

Clearly marked NAC-4090 on the back of the cone.

Also there’s what is possibly a date in the format:

smudge” (possibly month?) 24 (day?) then 199? (year? - last digit unreadable).

Same for both drivers.

Regards,

Willy.

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According to this it should:
http://www.troelsgravesen.dk/chamfer.htm

The DBL baffles are chamfered at the rear and there’s plenty of space for the scanspeak mids to breathe in there, a scenario “C” if you like. The issue is rather that the basket legs of the mid are an interference fit with the hole in the baffle. I was wondering whether this mechanical coupling of the drive and baffle would have any negative effect on the sound. Given that the mid is bolted firmly to the baffle face I’d like to think not.

Willy.

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@Willy
So do I read you correctly that you find an improvement of the performance of the DBLs now with the new scan speak mid drivers or you attribute it more to the new foaming you have replaced at the same time ?

Probably not a date exactly as you suggest because it’s only in the US that the month comes before the day of the month. But 199? is probably a year of manufacture. Could easily be week 24 if 199? as well.

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I wouldn’t be able to answer this, but my suspicion is further coupling might actually be beneficial. But I’m just speculating.

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@Charlie
There was an initial improvement on changing the foam and mids and I believe some of this would have been down to the foam.

However, there has been an even more significant improvement since then, hopefully ongoing, and I struggle to imagine that much, if any, of that can be down to the foam.

To be fair, my existing OEM mids were past their best. Hardly a week would pass without some soprano on Radio 3 setting them buzzing. With hindsight (or should that be hindhearing?) it is clear that they had lost a lot of drive over the past couple of years.

Given how they’re performing now and that they appear to be on an improving trajectory, I’m quietly optimistic that they’re a good fit. Very grateful for you having taken the effort to track them down and of course still interested to hear what might be achieved with the originals.

Willy.

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