Speaker is HOT! - Help & Suggestions Please!

[palabra]

Hello all,
Last night I opened the back of my right speaker cab to find that the insulation behind and underneath the speaker magnet had been melted! Not a lot, but not a little either; probably a little smaller than a baseball's diameter on the back of the cabinet and maybe a ping pong ball on the bottom of the cabinet. What's going on here!?

The Facts:
Speakers - Altec 604-8G's
Amplification - 2A3 SET Monoblocks (2.5-3 wpc)
Wire - DIY 999 silver, 16 ga

Questions:
- Am I underpowering these speakers and could this be a source of the heat?
- Did these get hot enough to damage the voice coil?
- How do I determine if the voice coil is damaged? Can it be done empirically?
- Is my speaker wire gauge and issue?
- Is there something I'm missing?

It's worth noting that the volume pot is on the phono stage, NOT the monoblocks; does this mean the amps are going full bore all the time (clipping)?

It is also worth noting that I sometimes feel that the music is not as dynamic as it should be, also a symptom of underpowering... Advice?

Your expertise would be greatly appreciated!

Thanks

[Robh3606]

Amplification - 2A3 SET Monoblocks (2.5-3 wpc)


?? Doesn't make any sense they could take that kind of power indefinately it shouldn't heat them up at all. You have any woofer cone offset?? Maybe you have some DC in the mix??

Rob:)

[palabra]

How do I got about measuring the DC offset?

I haven't noticed and excursion on the woofer when it shouldn't be.

You don't think it's any of the other items I listed though? Underpowering, wire gauge, etc.?

Thanks

[Eaulive]

I doubt that any speaker can get hot enough to melt enclosure insulation, let alone survive it.
All this apart, 3W is a ridiculously small amount of power and the heat that it can produce in a speaker of this kind would be barely noticeable_if at all_ even if you ran it for three days straight, forget it.

Look for another reason for the melted stuff, don't worry ;)

[edgewound]

Have you checked the crossovers? Resistors? Is the stuffing dacron polyester? Fiberglass might get discolored but it won't burn,

[Mr. Widget]

As has been mentioned above, 3 watts isn't enough energy to burn much... more over, I have seen PA speakers over driven and the cabinets burned after the paper cones caught fire. It can happen, but it takes a big amp and serious abuse.


Widget

[hjames]

Do you open the back of the cabinet often?

What I mean is, how do you know this is a recent event -
was the speaker/magnet still hot to the touch?


Hello all,
Last night I opened the back of my right speaker cab to find that the insulation behind and underneath the speaker magnet had been melted! Not a lot, but not a little either; probably a little smaller than a baseball's diameter on the back of the cabinet and maybe a ping pong ball on the bottom of the cabinet. What's going on here!?

The Facts:
Speakers - Altec 604-8G's
Amplification - 2A3 SET Monoblocks (2.5-3 wpc)
Wire - DIY 999 silver, 16 ga

Questions:
- Am I underpowering these speakers and could this be a source of the heat?
- Did these get hot enough to damage the voice coil?
- How do I determine if the voice coil is damaged? Can it be done empirically?
- Is my speaker wire gauge and issue?
- Is there something I'm missing?

It's worth noting that the volume pot is on the phono stage, NOT the monoblocks; does this mean the amps are going full bore all the time (clipping)?

It is also worth noting that I sometimes feel that the music is not as dynamic as it should be, also a symptom of underpowering... Advice?

Your expertise would be greatly appreciated!

Thanks

[palabra]

I do not open the cabinets very often therefore I don't know if this is an ongoing issue or if it just happened once or twice.

To measure the possibility of a DC offset I use a dmm on the speaker terminals? In a tube amp they're supposed to be zero, correct?

[Allanvh5150]

I do not open the cabinets very often therefore I don't know if this is an ongoing issue or if it just happened once or twice.

To measure the possibility of a DC offset I use a dmm on the speaker terminals? In a tube amp they're supposed to be zero, correct?

Unless you have a failed output transformer there will not be DC on the amp output. Are you sure the melted look isn't just ageing?

Allan.

[Lee in Montreal]

I vote for too much DC going to the drivers. :eek:

[Allanvh5150]

I vote for too much DC going to the drivers. :eek:

DC from the amp will not get through the output transformer. A direct short on the output transformer that would allow full plate voltage to reach the output with blow the power supply fuse in an instant. For a 3w amplifier to cause a loudspeaker to heat up to melt its surrounding materials is very doubtful. Large drivers with 1000 watts driving them dont even get hot. Sure, I have seen voice coils go up in flame but the magnets never got hot to melt stuff. Get a thermometer and put it on the speaker while it is running.

Allan.

[BMWCCA]

I vote for too much DC going to the drivers. :eek:
I'd look for some contact/chemical reaction with something touching the insulation that has nothing to do with heat. A glue or solvent of some kind? :dont-know:

Have we seen an answer to what material is used in this insulation?

[Eaulive]

I vote for too much DC going to the drivers. :eek:

Never a driver will receive enough DC to melt the cabinet insulation and survive it, I don't buy this. :no:

[Lee in Montreal]

Never a driver will receive enough DC to melt the cabinet insulation and survive it, I don't buy this. :no:

Well, last summer I welded a voice coil in a 2118 after shorting a power amp. In this particular case, I suspect some DC heating up the voice coil. Warmed up air is pushed thru the rear opening of the woofer. If it is not DC, I doubt that 3W of clean power will do anything :D

[sonofagun]

Probably caused by just a local sub-ether densification of the cross-

temporal matrix in that particular corporeal region.

A fairly common occurence with Altec 604s.

Some anti-matter plasmodic shielding might help.

:D

[louped garouv]

I'd look for some contact/chemical reaction with something touching the insulation that has nothing to do with heat. A glue or solvent of some kind? :dont-know:

Have we seen an answer to what material is used in this insulation?

I kind of lean this way, sight unseen.... and damaged material unconfirmed....

Is it possible for the OP to present us with a picture of the damage?

[Eaulive]

Well, last summer I welded a voice coil in a 2118 after shorting a power amp.

2119 - 0, Yamaha - 1 :D