Diaphragm, check polarity, and cleaning

[baldrick]

How can one identify if the diaphragm in a MF driver (2447) is installed correct regarding polarity?

And is there a "best practice" on how to clean/maintain a used driver?

[grumpy]

There should be one terminal with red or green mark between the screws on the diaphragm
(green in example pic below of D8R2450). This goes to the red wire/terminal on the "motor".

[baldrick]

That part is OK, but as far as I've understood it also matter were you put (how you turn) the diaphragm into the gap onto the magnet/motor... Or is this wrong and it doesn't matter how it's turned?

[grumpy]

You want the leads on the bottom (where the screws are) to coincide with the milled out areas and small
pair of notches (180 deg apart) along the inner edge of the voice coil gap (extra room for the flat lead
voice coil wire running up the inside of the VC former).

[baldrick]

Thanx!!

If I do understand you correct, do this means that on this Picture the red and black should be switched? (they are marked were the + and - were on the diaphragm today)



I cleaned the gap with maskingtape, but any good advice how to clean the driver otherwise? Does it really matter or is really just cosmetic?

[Earl K]

There should be one terminal with red or green mark between the screws on the diaphragm
(green in example pic below of D8R2450). This goes to the red wire/terminal on the "motor".

I don't think so Dave.

I'm pretty sure that one attaches the wire ( that's connected to the black terminal of the back-cap / which represents positive ) onto the diaphragm connections having the colored mark ( at least with drivers of that vintage or older ) .

Do I need to check ?

[JeffW]

Makes me wonder about TruExtent and how their polarity markings fit in with JBL's polarity system. Their 'phragms fit a number of manufacturer's drivers IIRC, and I wouldn't be surprised if red = + on some of those.

[grumpy]

I don't think so Dave.

Fair enough ... I could be wrong.
I can pop open several when I get home, as my "strong recollection"
has failed me before I tried looking it up via several types of sources
and found nothing definitive, so I punted. I'll try again in a bit.

I'd expect Ken or subwoof would know this in their sleep.

re cleaning, compressed air (goggles), and inside out masking tape held to an old business or credit card
has been sufficient for me when there's no corrosion or deformed gap issues.

[Earl K]

My apologies to all ,

Dave, you are right & I am wrong ( sorry for the side-track ) .

There should be one terminal with red or green mark between the screws on the diaphragm
(green in example pic below of D8R2450). This goes to the red wire/terminal on the "motor".

FWIW, I opened 4 ( different ) JBL drivers & they were all as you described ( with the red wire coming from the back-cap & connecting to the diaphragm terminal that has the green or red nail-polish dot / marking ) .

- I even connected an electronic polarity check ( from LA Audio ) & tested one setup for it's acoustic polarity ( after metering all the included cables ) .

- That testing confirmed that my memory has now gone "etch-a-sketch" .

[grumpy]

Saved me a trip to the garage!

[baldrick]

Thanx guys!

What I realized yesterday was that it is in fact difficult placeing the diaphragm wrong (except 180' wrong) The back can just be placed in one way and the leads are too short to make errors. So the only way to do wrong seems to mix + and -.

Regarding corrosion, is there something to do to fix (and does it matter) or should I just leave it as the one in the picture?

Another question that came up yesterday... BUGSCREEN! There are some corrosion on it, is there a good way to fix/clean or/should I remove the Whole screen? (the drivers are going to be used at home from now on, no PA use)

[Horn Fanatic]

re cleaning, compressed air (goggles), and inside out masking tape held to an old business or credit card
has been sufficient for me when there's no corrosion or deformed gap issues.

Using compressed air only goes so far. I use the business card, or half of rather, with the masking tape as you do. There are times when I find ferrous metal particles in voice coil gaps that compressed air cannot remove, whereas several passes with the tape does remove them. How the metal particles got into the gap in the first place is a mystery, especially since compression drivers have bug screens.

Step #7 for the benefit of baldrick;

http://www.greatplainsaudio.com/LgDrvrDiaRepl.pdf

H.F.

[ivica]

Using compressed air only goes so far. I use the business card, or half of rather, with the masking tape as you do. There are times when I find ferrous metal particles in voice coil gaps that compressed air cannot remove, whereas several passes with the tape does remove them. How the metal particles got into the gap in the first place is a mystery, especially since compression drivers have bug screens.

Step #7 for the benefit of baldrick;

http://www.greatplainsaudio.com/LgDrvrDiaRepl.pdf

H.F.

Hi Horn Fanatic,

Interesting for me is the explanation in the Step #9, #10 , #11.... #14

regards
Ivica

[Horn Fanatic]

Hi Horn Fanatic,

Interesting for me is the explanation in the Step #9, #10 , #11.... #14

regards
Ivica

Hi ivica -

No doubt, but it's the ALTEC large format driver. I can't say I know of any other compression driver that has adjustable locating pins.

Funny thing, Bill Hanuschak republished the vintage ALTEC instruction sheet with his name on it. When he left TELEX to start GPA, he inherited cartons and cartons of documents. Bill also told me there were cartons full of microfiche film. Talk about old school.

H.F.

[Horn Fanatic]

Thanx guys!


Another question that came up yesterday... BUGSCREEN! There are some corrosion on it, is there a good way to fix/clean or/should I remove the Whole screen? (the drivers are going to be used at home from now on, no PA use)

Greeting baldrick -

The bug screen really serves no purpose in a domestic environment. When compression drivers were deployed outdoors they were typically mounted in near inaccessible locations. The screens were put in place to keep dust particles out, and small insects from laying eggs inside the driver. As I have a pair of the 604-8H III, they do not have the bug screen. I don't think Bill Hanuschak even uses bug screens anymore unless he knows his drivers will be used out doors. The down side of using bug screens, is that they present and acoustic resistance to the output of the driver. Who needs that in a domestic listening environment? If someone has an insect problem in their home, they don't need bug screens, they need an exterminator.

One thing that is cool about the ALTEC/GPA drivers, with the Tangerine phase plug, you can actually see the diaphragm.