Buying Used Drivers - What to look out for

[mortron]

I am going to be looking at some used drivers and was curious if anyone had a cheat sheet or something to aid in checking them out. As it stands I will be:

- Checking that Voice coils don't rub.
- Inspecting cone for tears.
- Checking that foams are intact if applicable.
- Measuring the resistance of the drivers.
- Ensuring the horns themselves are in sound condition physically.

I know some basics, but wonder about things like:

- How to identify a recone/new diaphragm? How can you tell when one is needed?
- Which drivers are the ones to look out for where the surrounds are supposed to be mounted to the rear of the cone?
- How much variance between resistances can be acceptable? Ideally they should match, but is say a 12.2 and 12.5 (blindly pulling #'s) reading acceptable too?
- Should I be wary of Alnico?
- Did JBL make the actual enclosures for their designs or was the woodwork usually shopped out?
- If I can't demo them due to logistics etc, should I walk away, change my offer or what?

As I said, I know a bit, but not a lot, and have an opportunity to get myself set on a good starting path. I am trying to read as much as I can, but there is a wealth of knowledge here that one has little chance of absorbing in a single evening, much less a lifetime.

Thanks in advance.

[JeffW]

I am going to be looking at some used drivers and was curious if anyone had a cheat sheet or something to aid in checking them out. As it stands I will be:

- Checking that Voice coils don't rub.
- Inspecting cone for tears.
- Checking that foams are intact if applicable.
- Measuring the resistance of the drivers.
- Ensuring the horns themselves are in sound condition physically.

I know some basics, but wonder about things like:

- How to identify a recone/new diaphragm? How can you tell when one is needed?

That's a tough one without some experience. Guys post pics of old drivers on here from time to time and sometimes identification is a slam dunk, sometimes it stumps the panel. Do as much research you can on prospective models would be a good start. Post pics here if possible - some of these guys are pretty sharp.


- Which drivers are the ones to look out for where the surrounds are supposed to be mounted to the rear of the cone?

Much easier. All of the foam surround models, which is basically the only models where the surround is routinely replaced. Some of the Lansaloy drivers had the surround affixed to the front of the cone IIRC, and putting a replacement foam surround on the front could hide some of the cosmetic leftovers, but it's fairly safe to say that if you see a JBL driver with the foam surround mounted to the front of the cone, it's incorrect.


- How much variance between resistances can be acceptable? Ideally they should match, but is say a 12.2 and 12.5 (blindly pulling #'s) reading acceptable too?

Maybe 10% or less? Closer together is better, but I'd think an 11 or 13 in your example would be OK. If it's radically different, it's either damaged to has been replaced by a different spec part.


- Should I be wary of Alnico?

If the driver needs a recone, you can get it recharged - or at least checked - at the same time (I guess there are still shops that do it?) If it's a nice driver, you just have to hope it wasn't played hard I guess. Compression drivers, I don't know. Seems to me it'd take a lot more to thermally damage a compression driver than a woofer, maybe somebody else can offer up a better opinion.


- Did JBL make the actual enclosures for their designs or was the woodwork usually shopped out?

Made 'em, but also sold driver loads for DIY/3rd party enclosures. Depends on the era, I think. I'm not sure when they quit selling the driver load kits but somebody will.


- If I can't demo them due to logistics etc, should I walk away, change my offer or what?

Depends. eBay seller with zero feedback, or a long time member here with a good reputation? Circumstances will vary. Tiny details can also raise flags to experienced members, where the casual observer will think nothing of it. Arm yourself with as much knowledge as possible.


As I said, I know a bit, but not a lot, and have an opportunity to get myself set on a good starting path. I am trying to read as much as I can, but there is a wealth of knowledge here that one has little chance of absorbing in a single evening, much less a lifetime.

Thanks in advance.

Keep doing what you're doing. Try to focus your research on models that interest you - there's way too many models of speakers/drivers to learn about them all without spending years at it.

Also, a final thought: Restoring vintage JBL speakers back to vintage JBL speakers can be a really expensive and/or time consuming proposition. A seemingly nice looking, inexpensive set of speakers might have incorrect drivers installed. Finding a acceptable pair (or more pairs if woofers/mids/tweeters, etc.) of drivers can cost more than what the speaker acquisition cost. Small things, like replacement ring radiator diaphragms, can quickly drive the cost of restoration up $400/pr in a flash. This tempts people into using non-JBL parts and now you don't really have JBL speakers.

[mortron]

Thanks,

It is a local person who I am going to visit. The drivers are out of the cabinets, so will be easy to inspect and measure.

As far as my research has gone, the woofer I am looking at mates with the cabinet, so that should be alright.

The horns I will have to check the models on and compare it with ones that are best mated with the compression driver. They should be phenolic according to what I've read.

I anticipate a project.