Is there a safe way to test speakers with rotted foam surrounds?

[trutrent]

As some of you know I found a very nice pair of JBL L150 free while garage saleing. The 4 surrounds around the woofers and passives are completely gone.
Now before I invest the time and money into a refoam, how can I tell if they're worth repairing.
I have zero knowledge on these and have not tried powering them up (yet).
thanks.

 

[Urizen]

Remove the drivers and measure Ohms with a DMM across the terminals. Also check for frozen or seized voice coils. The passives, of course, will not need these tests.

 

[trutrent]

Great. thanks for the speedy reply. I hope my amatureish ways can handle that.

 

[pustelniakr]

You can lay them on their backs and put some audio through them, BRIEFLY. You won't know if you have lightly bubbled voice coil varnish (overheat damage) until you drive them, post re-foam. Before hooking them to your amp, connect an ohm meter to the input terminals and disconnect. If the speakers click, you have voice coil continuity. If they measure 0 ohms, don't connect them to your amp until you find out why.

Unless you have previous experience and developed feel and skill, always decap and shim during a refoam. Its a pain, I know, but it is better than having to do it again because of a slight cocking of the voice coil in the magnet gap (rubbing).

Enjoy,
Rich P

 

[Fred Sanford]

Before hooking them to your amp, connect an ohm meter to the input terminals and disconnect. If the speakers click, you have voice coil continuity.

Enjoy,
Rich P

I'm with you in general, but I only get an audible 'click' with my old analog meters, not with any of my digital meters.

je

 

[Cosmos]

They are JBL L150. They are worth your time, effort and expense. If you are asking this question, I would seriously recommend sending them to a pro for the re-foam.

There is no safe way to test them by listening to them. Just check for a reading of around 6.5 ohms on the woofers

 

[Nat]

I have never had a problem testing speakers which need foam by playing them quietly. Many speaker with bad foam have been played, often loudly, with the bad foam, so you aren't doing anything to them that hasn't been done already. And VOMs give you a reading by putting DC through the voice coil -- not any less (or more) dangerous than a low level music signal.
And playing gives more information about loose wires etc than simply testing continuity. And may even give information about cold solder joints which can be intermittant and conduct occasisionally during play, but might read no continuity with a meter.

 

[Tom Brennan]

I have never had a problem testing speakers which need foam by playing them quietly. Many speaker with bad foam have been played, often loudly, with the bad foam, so you aren't doing anything to them that hasn't been done already.

My experience as well. Besides, the spider is doing far more to hold the coil properly in the gap than the surround is.

 

[aidynphoenix]

i always tested them by laying them on there faces.. i figured its better than laying them on there backs because the weight of the cone may help keep them straight. than always put very little volume into them.
if they make music. the biggest concerns are voice coil overheating, and magnets that have become de-magnatized, as far as i know.

 

[Coconuts 500]

I tried playing some large speakers with rotted foam. The foam was mostly intact, but of course very brittle. I played some music with them, worked fine, then I pushed the loudness button (bad idea) and shortly after that, there was a big bass thump in the song, and the foam just shot out of the speaker in a million pieces. It was a fun thing to watch.

 

[tmad40blue]

I tried playing some large speakers with rotted foam. The foam was mostly intact, but of course very brittle. I played some music with them, worked fine, then I pushed the loudness button (bad idea) and shortly after that, there was a big bass thump in the song, and the foam just shot out of the speaker in a million pieces. It was a fun thing to watch.

I would love to do this to a pair of Thrusters or similar...

 

[michiganpat]

I haven't had a problem testing them face up with low volume...usually I do it with the bare driver (removed from the enclosure)