Need Speaker Help - Blown And Ohm Question

KraftyBob

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Hello:

I have a post in the amps section about a cab I bought but now I want to focus on the speakers. Long story short I bought a headless Marshall 2x12 Solid-state something (not sure what amp it was) with the intention of pulling the assuming crappy 2x12's and making a 1x12 baffle and loading it with a V-Type to accompany my DSL40C w/Creamback 65. I bought this because the DSL is a wider than normal combo and it's hard to find a 1x12 extension as wide. I paid a whopping $30 for it.

I get the cab home, open it up and low and behold it looks like it has two Black Shadow/C90 speakers in it. They are not labeled but one has SP.0287 stamped on the magnet - which from what I read seems to be the C90. The other is not stamped but looks physically identical.

Here are my questions/problem...

Speaker #1 (stamped w/SP.0287)
This one does not have anything written on it but when I test it with a meter I get 13 ohms which tells me this is a 16 ohm speaker - perfect, that's what I need. The cone responds well to a 1.5v battery too. Problem: There's a slight scratchiness when I press down on the cone (see video - turn up your volume). I connected it to my amp and it sounds great - I don't hear anything that would indicate the speaker is bad. I've also read other people say a lot of their speakers make some noise when they press down, and others say the speaker should be dead quiet. BTW the other speaker doesn't make any noise and is a little tighter.

Question: If there's noise when pushing down on a speaker does that automatically mean it's bad? If I used this in a 2x12 setup with the internal speaker and it eventually goes, do I risk ruining my amp? I'm thinking my the other speaker will maintain a load so I should be ok?

Speaker #2
This one is not stamped with a model # but is an exact twin of speaker #1 so I'm assuming it's also a C90. There is an ink stamp on the frame that indicates 16 ohms. Problem: When I measure it with a meter I get 7.3 ohms. That tells me it's actually an 8 ohm speaker, but then why the 16 ohm marking?

Question: When a speaker starts to go bad does it lose resistance or just completely go (and read open)? I haven't tested this with my amp as I'm not sure which output to use. I suppose I could use the 8 ohm output and it would be fine to test with whether it's 8 or 16 ohms?

The problem here, assuming the speaker is good and it's actually 8 ohms, is I can't use as I need a 16 ohm speaker. At that point I guess I'm back to my original plan which is I bought it for the cab and didn't care about the speakers.



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mickeydg5

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A partial short can happen between coil wraps. I am not sure I would trust either.

If the speaker cone is pushed off center it can rub but if it makes no noise when playing I would not worry about it.
 

KraftyBob

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Here's another video - a little more detail. When I press and 9:00 & 12:00 there's no noise. It starts around 3:00 and up to 6:00.

 

ampmadscientist

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"If there's noise when pushing down on a speaker does that automatically mean it's bad?"

Yes
The speaker must be free to move in/out like a piston without any scraping what-so-ever.
Move the speaker in AND out to check to see if it's free to move.

"When I measure it with a meter I get 7.3 ohms."

16 ohm speaker Should read about 12.6 ohms. So....It's bad. Or, your meter has a dead battery?

"I suppose I could use the 8 ohm output and it would be fine to test with whether it's 8 or 16 ohms?"

8 ohm speaker should read about 6.3 ohms...

If the speaker scrapes: don't use it.
Never hook damaged speakers up to your amplifier. You are just asking for problems.
 

MemphisMarshallMan

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That scratching noise you are hearing are the wire wraps being forced off center in the voice coil gap of the speaker magnet because the cone is not being pushed straight down.
Pushing in the cone is damaging those fine wire wraps. The voice coil gap is not very wide and it doesnt take much to damage those fine little wires.
If it were me I would not do that any more.
 

BygoneTones

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It sounds like a loose coil wire on that first speaker. I'm surprised you cant hear that noise with your guitar and amp, but maybe you are playing too quietly? Play loudly enough so that you can see the cone physically moving up and down, and then you will hear it I'm sure. The wire will probably break if you keep using it.

At low volume the cone only vibrates a very microscopic amount, invisible to the naked eye, and this is why sometimes you dont hear coil rub when playing at low volume. The cone just isn't moving enough.

The 8 Ohm speaker maybe a recone? Personally I have never seen them lose resistance. They are usually either dead or not dead.
 

BygoneTones

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That scratching noise you are hearing are the wire wraps being forced off center in the voice coil gap of the speaker magnet because the cone is not being pushed straight down.
Pushing in the cone is damaging those fine wire wraps. The voice coil gap is not very wide and it doesnt take much to damage those fine little wires.
If it were me I would not do that any more.

Pressing around the edge of the cone like that is the correct way to check for coil rub, and can help locate where the problem is. It is OK to move it slightly off axis, good speakers will not rub.

I would not recommend using a thumb on it's own like that though as it might damage the cone, better to use both hands close together. Use light pressure.
 

KraftyBob

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Thanks everyone for your replies. Last night I also emailed Celestion to find out about these speakers and while they didn't comment on the scratching (although I think there's enough consensus here), he said the writing stamped on the frame (T4416) indicates these are 16 ohm Vintage 30's. As far as the 7.3 ohm rating - he said that is low for a 16 ohm speaker so without knowing the history he could only speculate this was a re-cone.

I definitely won't be using speaker 1 as all of you are in agreement it's bad. Speaker 2 doesn't help me so now I need to decide what to do. Toss one and sell the other, or for $65 recone the bad one and use it in the cab? I might have to recone the 7.3 ohm because it might be tough selling a speaker that's stamped 16 ohms but only reading 7.3 - I would be skeptical.

Here's the funny thing - I've never been a fan of the Vintage 30's LOL. Although if it did work I would probably use it for a while before just replacing it as I originally planned. Who knows, maybe that paired up with my M65 Creamback would be a great match? I've never reconed a speaker but I am pretty good with tools so I'd be willing to give it a shot. Worse case I lose $65. Best case I saved myself $35 because I was going to get a V-Type.

Thanks again for your feedback! Bob
 

ampmadscientist

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The speaker is where major problems start.
If the speaker is scraping or measures wrong, don't play it.
Most of the major damage amp repairs can be traced directly back to a bad speaker load.

"Pushing in the cone is damaging those fine wire wraps. The voice coil gap is not very wide and it doesnt take much to damage those fine little wires.
If it were me I would not do that any more."

Bull shit.
Either the speaker is good and doesn't rub.....or it's blown. Don't be afraid to test it THROUGHLY and repeatedly. MOVE IT in and out again and again and again.
Either
it's GOOD or it's JUNK.

Rubbing speaker : will sound like a BUZZING coming from the cabinet while you are playing. If so : the speaker is garbage.
 

GIBSON67

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T4416 is Mesa's V30 made by Celestion. Should have 444 cone and be 16 ohms.

That test is usually a good indicator of a warped coil, but is not always indicative of a bad speaker. And the reason
is exactly what this thread is pointing out...could be user error. So testing with some volume
would be the best back-up test like Bygone has mentioned. Crank it up and see if it is making any funny sounds.
 

mickeydg5

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I was wondering if a comment on the T number was coming.

I did not see the video at first. Rubadeerubrub.

Put a meter on it and push away from the rub area. Does the resistance change? It could be wearing on the wire while contacting metal.

Or it could be partially fried, noncircular or warped like if it was disconnected before total meltdown.
 

KraftyBob

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I was wondering if a comment on the T number was coming.

I did not see the video at first. Rubadeerubrub.

Put a meter on it and push away from the rub area. Does the resistance change? It could be wearing on the wire while contacting metal.

Or it could be partially fried, noncircular or warped like if it was disconnected before total meltdown.
No matter where I push on the speaker the resistance drops to 0 (not open). Same for both speakers. I also noticed, which might be normal, if I slightly lift the cone the resistance increases - and it doesn't take much. As I mentioned before the functional speaker is tighter than the bad one. Is it possible this is a 16 ohm speaker but since it's tight it's not fully returning to it's proper location?

And yes, both cones are stamped 444.
 

ampmadscientist

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The speaker moves in / out hundreds of times per minute, when you are playing it.

It should pass the same test by hand. If it doesn't it's junk.
 

KraftyBob

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The speaker moves in / out hundreds of times per minute, when you are playing it.

It should pass the same test by hand. If it doesn't it's junk.
OK - looks like these two speakers are going in the basement until I decide what, if anything, I want to do with them. I'll save them for a rainy day when I'm looking for something to do.

Time to make a new 1x12 baffle that fills the full front of the amp (covering the old head slot) and get a V-Type.

Thanks to all for your input.
 

mickeydg5

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No matter where I push on the speaker the resistance drops to 0 (not open). Same for both speakers. I also noticed, which might be normal, if I slightly lift the cone the resistance increases - and it doesn't take much. As I mentioned before the functional speaker is tighter than the bad one. Is it possible this is a 16 ohm speaker but since it's tight it's not fully returning to it's proper location?

And yes, both cones are stamped 444.
Sorry, that is a more difficult test, if you will, that requires a good meter and a steady hand. I did not explain that. Why the meter read straight to zero is a bit strange but it may be the meter indicating "overload".

Anyway if the meter can handle it and you press on the cone the measurement can move up or down as you vibrate sort of speak but if it is held basically still then it will stabilize. For instance I have a 16 ohm so I push with the meter fluctuating between lets say 3.4 and 40 ohms but when almost still it will average about 12 -14 ohms on 12.9 ohms (measured resistance). Its something like that.
I was wondering if yours would settle in 13 ohm area or remain in the 7.3 area.

I heard good things about V-Type. Let us know.
 

KraftyBob

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Sorry, that is a more difficult test, if you will, that requires a good meter and a steady hand. I did not explain that. Why the meter read straight to zero is a bit strange but it may be the meter indicating "overload".

Anyway if the meter can handle it and you press on the cone the measurement can move up or down as you vibrate sort of speak but if it is held basically still then it will stabilize. For instance I have a 16 ohm so I push with the meter fluctuating between lets say 3.4 and 40 ohms but when almost still it will average about 12 -14 ohms on 12.9 ohms (measured resistance). Its something like that.
I was wondering if yours would settle in 13 ohm area or remain in the 7.3 area.

I heard good things about V-Type. Let us know.
The speaker settles back to 7.3, 7.4 ohms. I was looking at it really close this morning and if it was reconed somebody did a great job. Other than the color of the glue at the spider I see no difference between the two. Everything else is exactly identical. I suppose the glue color could be attributed to different manufacturing times as the date codes between the two are different. This is a strange one because everything I read indicates the speaker should either read near the rated ohms or nothing at all - I've not seen anything that says the value drops when a speaker starts to go. Oh well.

I'll update when I get the V-Type installed. I have a lot of travel coming up so it might not be for a while.
 


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