SWR super redhead speaker fire

[pontiacpete]

I had this amp come in with one of the speakers burned. Owner said flames were coming out of the speaker while he was playing.
Has anyone seen this happen to a speaker?

Now the amp is back and the owner says there are sparks coming out from the area near the other speaker.
He says that both events the fire and the sparks occur after playing with the amp dimed and for long time about a 1/2 hour to 45min.
Am I right to assume this is caused by speaker rub?

[Leo_Gnardo]

If the voice coil wasn't rubbing before it sure is now! Dimed? WTF does he expect? A good conduct medal? That's abuse.

Solid state amps turn out square waves when overdriven. They push the voice coil far as it can go and continue to apply current. P=IV heats the coil, then it slams in the other direction, does the same thing. More or less the equivalent of sticking a big DC supply across the VC, it's gonna burn if it doesn't fuse open-circuit first.

One of the advantages of tube amps is they don't do this. There's a limit how much energy they can store and deliver, and the output transformer has a hard time delivering big square waves to speaker loads anyway. Go to Rich Koerner's Time Electronics website, he expounds on the matter in case my couple of sentences aren't enough.

If little Sparky's going to continue to play like that I don't know what to offer as a solution. Speakers with higher power handling capability are still not going to be happy driven with square waves. If he can grow up mentally, just a bit, use a fuzz pedal to get his tone instead of using up every last watt in his amp. Otherwise HE's the basket case and he's just going to wreck everything he gets his hands on. Buy new amps every show, hire a roadie to stand by with fire extinguisher handy, make it part of the act.

[Chuck H]

I had an issue with a Kustom 250 where an open ground on the power amp board would dump enormous amounts of unmitigated DC on the speakers. I saw some smoke. No flames, but I did get the situation under control in seconds. I could imagine flames as a possibility if this happened without having immediate control of the power switch. Coincidences happen. Maybe two speakers in a row developed a coil rub. I don't know that a coil rub could result in flames though. It seems unlikely. I would look for an intermittent ground fault in the output devices. Get the amp running and flex the board, poke at leads and components, etc. If anything results in a big fat HUMMMM!!! start re-flowing solder joints and checking cable connections, ground traces and connections, etc.

EDIT: And, as per Leo, is the owner intentionally plowing a square wave from the amp? If he is then 'what Leo said'. I don't know what "cranked" means to this design or what the owner might be doing with his input signal. If he's not getting much distortion look for a ground fault.

[J M Fahey]

I have seen it countless times and have repaired the dead speakers afterwards, I have a couple autopsy pictures somewhere.

It's power abuse pure and simple, plus brainless Bass players .

In fact I have a couple experiences precisely with 2x10" flamethrowing SWR speakers, go figure.
BIG problem is that they make very high quality Bass amps and speakers geared for Jazz Fusion Bass Players
(you know the type, those who actually read their part or play sitting or play along a piano player, a horn section, a drummer using brushes, etc.) where the cabinet has incredibly wide and flat frequency response, (just what the Doctor ordered) , and are used at 1/4 to half power tops, always very clean; the 350W RMS are there for clean headroom.

Enter the clueless Bass player who buys one of these and plays in a Hard Rock or Metal band, or alongside a wanna-be-guitar-god diming his Marshall 100W into a 4x12" .

Compare cone surface of 4x12" with that of 2x10" , the relation being the wrong way, the Bass player, who really needs them, got 1/6 the square inches the guitar player has, sheer madness .

Of course he will dime his amp, to boot being SS and driven into squarewave territory it will put out around 500W RMS, 250W into each poor voice coil, which turns 98% of that into heat.

The two cases I mentioned were SWR Goliath Mini, same speaker complement as here: 2 (excellent) cast frame PAS speakers, very tight and punchy ( a trademark of SWR sound) with curvilinear cones ... and each with a penny sized hole burnt through the VC winding and former you could pass your finger through.
And its partner already almost reaching the same condition.

One had been blown by a large Hartke, the other by an Eden WT800, go figure.

In both cases I saved the original cones because they have a special deep trombone shape not available here (and of course musicians were in a hurry), but to clean them without weakening paper I had to carefully grind away the original voice coil with a handheld dentist type tool, and of course make new voice coils.

I "cheated" (sort of) by making new voice coils 16 ohms each for total 8 ohms instead of original 4 ohms, which cut power to 200/250W RMS and also somewhat longer so speaker would reach deeper with less distortion and when they picked up the repaired speakers I demonstrated their heads first with the SWR alone, then adding one of my 4x10" as extension speaker.

Both were happy and in a few days also bought mine as extensions.

In the Bass World, there's no substitute for square inches.

EDIT: tell him that it will happen again and again, that it's not a Rock amp but a Jazz one, to be played always clean, that for Rock he'll need to buy 4 new speakers, not kidding .

I suggest he gets 2 Eminence Delta 10B in 16 ohms each inside his Redhead, http://www.usspeaker.com/Delta-10B-1.htm , and another 2 inside a 2x10" extension cab.

Sorry but there's no other way, you can't beat Physics Laws.

At least get 2 of these Deltas inside his combo.

Personallly I wouldn't even tell him about the expected power reduction if used alone, because his knee jerk reaction will be to reject your suggestion, no matter how sensible it may be.

[tedmich]

back to GC, fire is my signature sound (yes that's Billy Joel ^)

[g1]

If he wants to play "dimed", SWR is not the way to go.
Maybe one of these:

[tedmich]

If he wants to play "dimed", SWR is not the way to go.
Maybe one of these:

[ATTACH=CONFIG]33230[/ATTACH]

(I believe the lower right red corner is so Lemmy can visually find the input jack as he can't remember where it is)

[g1]

(I believe the lower right red corner is so Lemmy can visually find the input jack as he can't remember where it is)

That's on the nights he can still see. There's probably a "braille bump" on that same corner for the other nights.

[J M Fahey]

Diming these is fine:



..... and probably what he was tryingto achieve.

Only problem is:

"hey !!!!! I was also using 10" speakers !!!!!"

[Leo_Gnardo]

Diming these is fine:..... and probably what he was tryingto achieve. Only problem is: "hey !!!!! I was also using 10" speakers !!!!!"

Original SVT kit was two 8x10 cabs. Spread the wattage wealth and go for double squinches of cone area. I got to play one early days, having got used to a borrowed B-15. With volume not quite up to quarter-way, holey smokes! Who would need more?

SWR Sparky's looking for some distortion in his tone, let him put a fuzzy wuzzy under his footie wootie.

Looks like Reddy Kilowatt already blew the dust caps off the ones in your photo Juan. Something about hearing the whistle of air zipping thru those voice coil gaps, that's the charm.

[pontiacpete]

Thanks to everyone for all the interesting information. I'll go thru the amp and do as Chuck suggested, tightened up any loose connections, grounds etc.
I did recommend that he not use this amp if he has to play it maxed out to get by on a gig. I don't think a distorted sound is what he's looking for anyway since they are a party band that does 70's 80's covers. My guess is that he probably was able to get a clean sound up to some point then would keep pushing it as the band gets louder or the hearing dulls as the gig goes on.
I know that players in this city are often trying to find the rig that they can get a sound and get to and from a gig, in and out of the trunks of cabs and up and down stairs in tenement building walk-ups. I personally think this is really a clunker in size, a 2X10 cab with a GK800rb would be my choice.
I'll probably put another Delta 10 in like I did last time.
Thanks again!!

[Leo_Gnardo]

My guess is that he probably was able to get a clean sound up to some point then would keep pushing it as the band gets louder or the hearing dulls as the gig goes on.

The hearing also dulls as alcohol is consumed. As well as other anesthetics.

I know that players in this city are often trying to find the rig that they can get a sound and get to and from a gig, in and out of the trunks of cabs and up and down stairs in tenement building walk-ups. I personally think this is really a clunker in size, a 2X10 cab with a GK800rb would be my choice. I'll probably put another Delta 10 in like I did last time.

I like your plan. FWIW I favor Eminence Kappa-pro. Lots of power handling and if you place the speaker in a 3-way room corner (the poor man's subwoofer) you can get a surprising amount of bass volume. They weigh more, cost more, that's the tradeoff.

What happened to the good ol' days when you could shanghai a friend or 2, get 'em to lug coffin-size cabs in & out. Doesn't anyone have energy anymore? Oh yeah, we get our exercise doing the 12-ounce lift while watching video now. And swallow a couple Red Bull & vodkas to work up enough motivation to dance. None left to accomplish anything useful.

[TimmyP1955]

The square wave has nothing to do with it - a square wave is just a bunch of sine waves stuck together (look at it on a spectrum analyser, not an oscilloscope). What matters is the total power, and his speakers handle less than he's pushing. 'Not enough rig for the gig' is common for bassists - if it were not, I would not have to replace so many speakers every year (most of which suffer from cone collapse as opposed to coil damage). He needs an SVT cabinet and a Bassman or Bassman 100.

[The Dude]

Respectfully, the square wave has everything to do with it. Leo nails it in post 2. It has to do with the length of time the speaker is conducting at excursion and incursion. With a normal sine wave, the speaker is not at full excursion or incursion for nearly as long and therefore, the voice coil is conducting for much less of the waveform's time constant. It has time to cool. With a square wave, the speaker is held at peak conduction for much longer creating much more heat in the voice coil. Look at a square wave and imagine the speaker movement necessary to attempt recreating it. The speaker is slammed up, held, and then slammed down and held. It is never resting or gradually crossing zero. It is full on conducting all of the time. Voice coils are not meant to recreate square waves and this is why it's always better to overpower a speaker with clean power than clip it with not enough power.

Also, the "bunch of sine waves stuck together" that you see on a spectrum analyzer are harmonics and have little to do with the fundamental frequency.

[olddawg]

Back in the day, old Acoustic 360s were famous for speakers catching fire. It was the glue used in their first production speakers. They changed the glue in later runs, but those suckers were lighting up for years!