DBL bass driver rebuild

My beloved DBL bass drivers need repair -- the foam surround at the edge of the cone is going sticky as it breaks up, and has already torn in a few places.

I understand that Naim dont stock the drivers any more. However, they are made by the good people at ATC outside Cirencester.

I emailed them -- they recommended a full recone at the factory which costs 125 pounds plus one hour of labour at 30 pounds. Plus you need a set of transit boxes (these are very big and heavy drivers!) which cost 20.50 pounds each.

This is excellent value service by ATC, and considerably cheaper that the cost of a new DBL driver (which is still available - model SB75-375-SC)

For those with DBLs, I would strongly advise getting the bass drivers reconed. The surround lasts around 20 years, unlike the surrounds on the midrange which should go on forever.

I shall be attacking the speakers shorting with a screwdriver. And jackhammer. and a fork lift truck. And a plasma cutter, probably :-)

Does Naim have any specific advise on DBL bass unit removal? I was going to dismantle the speaker boxes, and place the bass box on its back so the driver points upwards. That way it hopefully wont drop/crash/slide when the bolts are undone

Original Post

Jon, I've only heard good reports on the ATC repair service for the DBL bass drivers, and the cost seems quite reasonable.  I'd recommend you contact Naim regarding tips on removing the drivers without doing any damage - Mike Shord was the man to know in my day.  Certainly the drivers are very heavy so lying the bass boxes on their back must be a good idea.

Best method for contacting Mr Shord?

I am assuming the internal wires are soldered on - certainly the ones on the tweeters were (fond memories of 3am at JVs house, replacing a blown tweeter cos we had been a trifle overexcited with the volume.... and really rather lubricated on some fine tipple too, of course)

Hi Jon,

that's exactly what's happening now with my DBL woofers at ATC :-)

For the removal of the drivers I was told: "The driver is held in by the screws and a bead of silicon is then applied round the perimeter to ensure a seal. This should come away quite easily, apparently.  The traditional method for releasing a driver is to undo all the screws and then insert an oversized screw into one hole, using grippers / pliers to pull the driver away from the cabinet. It would probably be worth running a blade around the sealant to release its grip on the driver. "  worked just fine for me, and yes, the driver is soldered.

Sure the driver is not the ATC SB 100-375SC ?

Here is a pic of mine

 

 

 

oh, forgot to add that when I opened the LF cabinet, the acoustic foam within would crumble with the slightest touch so I'm changing that too; if you need the exact specs just send me an email (in my profile page).

The HF Cabinet foam on the other hand is different and is still in good condition; the foam is around the mid driver zone whilst in the top tweeter zone of the cabinet you have a wool mesh kind of padding.

All the best.

Stefano

Jon:

I'm sorry to hear your beloved DBLs need some repair. The ravages of time, I suppose. Thanks for posting this for future reference for all of us DBL owners. I hope the repair goes smoothly and that your DBLs are up and running soon. I look forward to your updates. 

Jay

A friend of mine had his DBL bass units serviced by ATC only a few months ago and is happy to report that they sound better than ever.

He's having far more of a problem getting replacement foam grills though! He's had a pair from someone in the UK that don't sound as good as the Naim originals and he's ordered a pair from a guy in the States but they seem to be in the middle of a factory move or something. If anyone has a better source then please let me know? 

it might well be the sb100, but Pete Guppy at ATC said it was an SB75. Not that it matters, it is what it is

Glad to hear others are having a good experience with ATC

Foam front grills -- always run mine with grills off.

jon honeyball posted:

I emailed them -- they recommended a full recone at the factory which costs 125 pounds plus one hour of labour at 30 pounds. Plus you need a set of transit boxes (these are very big and heavy drivers!) which cost 20.50 pounds each.

This is excellent value service by ATC, and considerably cheaper that the cost of a new DBL driver (which is still available - model SB75-375-SC)

Jon,

much pleased for you, this is fantastic value for money considering the £800 costs for 'little' SBL bass drivers at Naim HQ not so long ago when they were still available. I'm wondering if ATC have a workable replacement bass-driver for SBL (?).

Debs

jon honeyball posted:

it might well be the sb100, but Pete Guppy at ATC said it was an SB75. Not that it matters, it is what it is

Glad to hear others are having a good experience with ATC

Foam front grills -- always run mine with grills off.

The SB75 looks like it is 'only' a 12" driver. The DBLs use 15". ISTR that Naim extensively reworked the bass drivers from ATC, so it may not be as easy as a part for part swap if you get new ones. 

Geko posted:

He's having far more of a problem getting replacement foam grills though! He's had a pair from someone in the UK that don't sound as good as the Naim originals and he's ordered a pair from a guy in the States but they seem to be in the middle of a factory move or something. If anyone has a better source then please let me know? 

I posted about an American source of "Speaker Grille" that worked out very well.  Pictures included too.  If the link doesn't work, search the term in quotes.

https://forums.naimaudio.com/topic/speaker-grilles-1

I can also vouch for the benefit of replacing the foam cone surround.  I shipped the whole driver unit to my dealer - I assumed ATC removed/replaced the driver.

Definitive from atc re dbl driver model:

"Hello Jon,
I have checked with my colleagues and these Naim drivers are SB75-375SC, not SB100-375SC, i.e 3” voice coil, not 4” voice coil. The packing set will still be correct for a 15” driver..
The SB100-375SC was only used for early SCM300 monitors, I believe. Both are 15” (375mm) however, the 12” would be 314mm….
regards
Pete Guppy"

jon honeyball posted:

However, they are made by the good people at ATC outside Cirencester.

I emailed them -- they recommended a full recone at the factory which costs 125 pounds plus one hour of labour at 30 pounds. Plus you need a set of transit boxes (these are very big and heavy drivers!) which cost 20.50 pounds each.

This is excellent value service by ATC, and considerably cheaper that the cost of a new DBL driver (which is still available - model SB75-375-SC)

 

Good to see a company offering such a reasonably priced service. No wonder they are so well regarded. 

jon honeyball posted:

 

.....

I shall be attacking the speakers shorting with a screwdriver. And jackhammer. and a fork lift truck. And a plasma cutter, probably :-)

.......

"Shorting with a screwdriver" is probably more likely to attack your amplifier. Sounds a little excessive in any case. Couldn't you just disconnect them?

Update -- boxes have arrived from ATC -- look very strong and up to the job

Realised I need a DBL gasket kit just to be sure. 

Part number 01-006-0117 Gasket Kit, DBL. 

Which costs the princely RRP sum of £167.49.

Which elicited a "HOW MUCH???" from me. Out loud. Heard across the lab.

Nevertheless, I need it, so have placed order with my dealer, Cymbiosis

jon

Try gasket tape...you can buy it from DIY stores by the roll for the price of a pint. I used it with one of the DBLs, and it passed the 'driver compression test' and was indistinguishable from the genuine gasket in that regard. Why spend near 200 quid for tar that can be gotten for a ha'penny ;-)

Out if interest I tried the gasket tape initially without the silicone sealant....it failed the compression test. After the required sealant bead was applied it was as good as new. 

Ron -- no harm in having a proper naim kit even if i can recover the one in use. The driver rebuild should see another decade or more of life in the speakers

I shouldnt have gone to the cymbiosis site -- I appear to have had a little shopping accident on an ex dem XPS2DR for my ndac. I have something to drive the ndac with which deserves the best chance. Hence improving the psu. 

 

I hope you did not misplace the slippery 'spacers' that are inserted between the mid-bass cabinet and the mothership...without those it is impossible to gently lower the cabinet onto its silicone bead. DBLs are much easier to take apart than to put together...but then again-what isn't?

Ron Toolsie posted:

Try gasket tape...you can buy it from DIY stores by the roll for the price of a pint. I used it with one of the DBLs, and it passed the 'driver compression test' and was indistinguishable from the genuine gasket in that regard. Why spend near 200 quid for tar that can be gotten for a ha'penny ;-)

Out if interest I tried the gasket tape initially without the silicone sealant....it failed the compression test. After the required sealant bead was applied it was as good as new. 

What kind of gasket tape would that be Ron ? (Neoprene Sponge, PVC foam, ...)

Mine are fine but good to know.

sbilotta posted:
Ron Toolsie posted:

Try gasket tape...you can buy it from DIY stores by the roll for the price of a pint. I used it with one of the DBLs, and it passed the 'driver compression test' and was indistinguishable from the genuine gasket in that regard. Why spend near 200 quid for tar that can be gotten for a ha'penny ;-)

Out if interest I tried the gasket tape initially without the silicone sealant....it failed the compression test. After the required sealant bead was applied it was as good as new. 

What kind of gasket tape would that be Ron ? (Neoprene Sponge, PVC foam, ...)

Mine are fine but good to know.

I think I used the neoprene one. It may be a bit more durable than the PVC one. But like any other gasket replacement, the trick is to get the bead of silicone sealer just right and uniform. The gasket just supplies a compliant base for the sealant. And if it passes the driver poke test, it is doing its job. 

jon honeyball posted:

Update -- boxes have arrived from ATC -- look very strong and up to the job

Realised I need a DBL gasket kit just to be sure. 

Part number 01-006-0117 Gasket Kit, DBL. 

Which costs the princely RRP sum of £167.49.

Which elicited a "HOW MUCH???" from me. Out loud. Heard across the lab.

Everything was going very nice until this!

Words fail.

jon honeyball posted:

Update -- boxes have arrived from ATC -- look very strong and up to the job

Realised I need a DBL gasket kit just to be sure. 

Part number 01-006-0117 Gasket Kit, DBL. 

Which costs the princely RRP sum of £167.49.

Which elicited a "HOW MUCH???" from me. Out loud. Heard across the lab.

Nevertheless, I need it, so have placed order with my dealer, Cymbiosis

jon

Almost as good value as the y-splitter for the S-600 (when running actively using 2 amps not three) that are essentially two pieces of flat plate metal for the princely sum of £149.

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