Acoustic 408 problem

jj4001 · #1 01-21-2012, 12:21 AM

I just got a 408 today. It has the original Eminence drivers in it from '78. The bottom two speakers work fine (and sound real nice, too). The top two speakers have problems, though. They sound like there is metal vibrating against metal somewhere. I took the speakers out to inspect them and the inside of the cab. Everything looks fine except for one of the bad speakers has a dented dust cap that has an inch long split from the cone. The other bad speaker has no visible damage.

I tried the 9 volt battery test and all four speakers moved in unison. Any more than that is beyond my expertise.

I'd very much prefer repairing the speakers to replacing them, if possible.

Any advice or recommendations? Anyone know of a good speaker tech in the RI/MA area?

chillerthanmost · #2 01-21-2012, 01:16 AM

I don't know any speaker repair places but I definitely recommend getting them fixed. I have a blown speaker in my 408 so I have it wired as a 2x15 at the moment (4 ohms) and it still sounds awesome. My blown speaker is non original though so I'm just looking for an original to replace it with. Great cab. I love the stock speakers. You can play it as a 2x15 like I am until you get those two fixed (unless your amp pushes more than 150w). Good luck.

Also, my third good original speaker didn't seem like it was working at first because it wasn't getting signal from my blown speaker since it was wired after in the chain. But it passed the battery test and sounds fine on its own. Try it out on its own or wired in a 2x15 (within the cab itself) to make sure it's bad before you send it off. Though it could still be buzzing even with no physical damage. It's worth a try if you haven't done it yet.

craig.p · #3 01-21-2012, 06:40 AM

I would get all of them reconed so they all perform identically. Check out Orange Country Speaker. Parts Express (one of my favorite sources) also has a speaker repair service.

jj4001 · #4 01-21-2012, 07:26 AM

Appreciate the advice, fellas.

My main amp is an Acoustic 320 and I bought the 408 to have the matching cab. I believe the 320 is 225 watts at 4 Ohms so I'd be a little nervous running it into the 408 as a 2x15. The cab I've been gigging with is an Acoustic 402 loaded with two 15" Peavey Black Widows and this thing is a beast on its own so at least I don't need to rush into a decision on the stock 408 drivers.

Like I said, the two bad speakers sound like metal vibrating against metal. I don't recall any blown speakers I've come across sounding quite like this (although I have no prior experience with vintage Eminence speakers). I hope this doesn't sound like a stupid question, but does this noise typically indicate a re-cone is necessary or is there anything else that could be causing the issue?

Bass_Pounder · #5 01-21-2012, 08:09 AM

Are you sure it's BOTH of the top speakers ?

The seperating dust cap will definitely cause some issues.

jj4001 · #6 01-21-2012, 08:18 AM

Yes, it's both of the top two speakers. I tested them individually and they both sound the same.

I haven't tried out the bottom two speakers individually because they sounded fantastic when I took the top two out.

Bass_Pounder · #7 01-21-2012, 08:21 AM

Hmmmm........................

Have you checked for voice coil rub (gently pushing cone in/out with hands) ?

Possible warped frame/bad gasket (try rotating the driver and remounting) ?

Wires or leads that go into the cone/voice coil vibrating against the back of the cone ?

jj4001 · #8 01-21-2012, 08:37 AM

The two offending speakers have been rotated and remounted. The frames aren't warped and the gaskets seem to be as they should.

I did not check the voice coil since I'm not too experienced with this stuff. (I used to just bring things to a tech before discovering TB!) I'll be sure to try this when I get home later. What exactly should I be looking for when I try this? I would imaging rubbing against a side, correct?

Also, I'll have to re-check the speaker wired inside. It really does sound like they could be the culprit because they aren't tied down. It sounds like the metallic sounding vibration is coming from inside the cab as opposed to the speakers. That could be my imagination, though as it seems wires as light as these wouldn't make that much noise, but again, I'm far from an expert.

Again, thank you for taking the time to reply. I want to figure this out so I'm not throwing money at the wrong issue.

Bass_Pounder · #9 01-21-2012, 08:55 AM

Take the speaker out of the cab and lay it down face up. With both hands, gently and slowly move the cone in and allow it to return out (with fingers still touching). The cone should move freely. If there is voice coil rubbing, you will feel it as "scratchy".

And yes, something as small as a wire touching the back of the cone while vibrating will give off a terrible sound.

Check the interior of the cab thoroughly too. Since you say it sounds like vibrating metal INSIDE the cab, there could be loose bracing, a loose baffle, or loose hardware causing the issue.

Try eliminating all the possible culprits before reconing/replacing the speakers. It would surely suck to replace them only to have the same thing happen because of an issue with the cab and not the speakers themselves.

jj4001 · #10 01-21-2012, 09:03 AM

OK, just checked the voice coils. The two bad speakers are scratchy and the two good speakers are not.

Bass_Pounder · #11 01-21-2012, 09:07 AM

Bummer - sounds like recone/replace time

jj4001 · #12 01-21-2012, 09:10 AM

D'oh!

Thanks so much for the help. Time to find a good speaker guy. Hope the pretty white dust caps can be saved!

rad69cam · #13 01-23-2012, 01:17 PM

Quote:

Originally Posted by jj4001

D'oh!

Thanks so much for the help. Time to find a good speaker guy. Hope the pretty white dust caps can be saved!

Unfortunately that likely won't happen. Best of luck.

jj4001 · #14 01-23-2012, 01:26 PM

Just got off the phone with a speaker guy who has a great reputation locally. He says saving the white dust caps shouldn't be a problem. I'll be bringing the speakers to his shop tomorrow so we'll see what happens.

If the dust caps can't be saved, I guess I'll just put them in the cab's internal chamber and put the remaining good speakers in the top and bottom, outward facing position.