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Blown tweeter: a question...

Schwinn

Schwinn

Dec 4, 2002
1,378
6
48
Sarasota, FL
www.splinteredimage.com
#1
Last night it finally happened. While g string poppin' on my Carvin during 'brickhouse' at ear-splitting volume the smell of buring paper and electronics filled the rehearsal shed before the end of the song.

The Foster compression horn in my Avatar 212 is toast. I can't even turn the attentuator in back - must have melted something. Anyway, shouldn't be to hard to replace. All a part of rock n roll. Actually, I was relieved the burning wasn't coming from my QSC!!!

My question is, can I disconnect the fried horn and use the cab 'as is' until I replace it. Will taking the horn out of the circuit change the cab's impedence in some negative way? I want to take it out so I don't start a fire in there. Also, if you have some advice on a replacement horn that would be cool.

:bassist: :help: :rollno:
 
#3
Sounds like you fried the attenuator, not the tweeter. Well, you may have blown the tweeter also, but you're definitely going to need to do something about the attenuator.

Disconnecting the horn will not significantly affect the impedance of the cab.

I don't think it's teribbly wise to play it with that half-fried attenuator in there, though. Your QSC has protection against shorted circuits, but I still wouldn't knowingly risk seeing how well that protection works........

If you have to have this cab running, I'd just take the entire crossover and attenuator out of the cab and run the 12's by themselves. Then I'd order an attenuator that handles more wattage from PartsExpress, as well as a tweeter.

I highly recommend the Peerless 811647 tweeter. It handles lots o' watts, it should fit in the same hole as the Foster (not sure - it may take just a little work, it may drop right in - the size is very close), and it sounds MUCH nicer. It's a silk dome so it's way smoother than a compression horn. The problem with most silk dome tweets is that they aren't very loud; but this particular model is horn-loaded, so it pumps up the efficiency to 99db, which is very usable. I've got one in a 2x10 that I built, and it is very nice. Plenty of highs without the harshness.
 
#5
Schwinn...how low did you have your tweeter set? Dave had commented that while he hasn't had customers blow a tweeter, he has had them burn out attenuators when they're set very low.

If you can't rotate the level control, that tells me that you probably fried the attenuator. Dave can hook you up with a new one, or you can buy one with a much higher power rating from www.partsexpress.com for a reasonable price.

You can disconnect the tweeter by removing the input plate and unsoldering the capacitor from the + terminal of the jack.

Kaz...aren't Foster and Fostex horns the samething?
 
#9
Schwinn...like BruceWane wrote, your tweeter is probably fine.

If you want to play around, disconnect the capacitor from the attenuator and connect it to the + terminal of the tweeter. The + of the tweeter is connected to the center terminal of the attenuator.

Since the attenuator is fried down by the grounded end, you'll probably want to disconnect the other two terminals to conduct the experiment. Or, if you have an ohmeter, measure the resistance of the horn with one terminal disconnected from the attenuator.
 
#11
A thought...

how about ordering a new wiring harness from Avatar (attentuator back plate, crossover capacitor) and using the Peerless tweeter as a replacement for the original horn.

Do you think that would work? I'm looking for an easy way to get my cab going again while maybe improving the harshness of the tweeter. I'm not sure about using a different crossover.
 
#12
Schwinn said:
A thought...

how about ordering a new wiring harness from Avatar (attentuator back plate, crossover capacitor) and using the Peerless tweeter as a replacement for the original horn.

Do you think that would work? I'm looking for an easy way to get my cab going again while maybe improving the harshness of the tweeter. I'm not sure about using a different crossover.
Click to expand...

Yeah, that would work. The Peerless tweeter goes a lot lower than the Foster, so you could cross it over a lot lower. But since those delta's are good up to about 3k, it's probably no big deal. You might ask the guy at Avatar what frequency he's crossing the Foster over at; if it's much above 3k, you might want to order a 6.8uf capacitor along with the Peerless tweeter, so you can replace the current cap with one that's more appropriate for the Peerless. Crossing it over above 3k is going to leave a hole scooped out of your frequency range.

For that matter, if your going to order a tweeter anyway, I'd go ahead and order a capacitor; they're only a buck or two.

PartsExpress.com part # 027-424 is just whatcha need. They have the Peerless tweeter under part #277-406.

You need to be a bit more careful in how you use the attenuator so you don't cook another one. Undestand the way an attenuator works; when you turn down the volume, the attenuator takes the wattage that was headed for the tweeter and turns it into heat instead. So the more you turn down the volume, the more likely it is that it's going to fry. Do what you can to get your sound right before it hits the cab; try to avoid using the attenuator as a tone control as much as possible.

With a really good tweeter in there, you'll probably leave it turned up a lot more anyway.
 
#14
If Avatar's gonna charge you anything for the new attenuator.......Try PartsExpress part #260-265 instead. Handles 100 watts (plenty for a tweeter circuit), costs $6.35. They've got one that .50 cheaper without the knob & plate, but just in case your existing knob won't fit, I'd get this one. You'll have a hard time blowing this one.
 
#15
Schwinn said:
A thought...

how about ordering a new wiring harness from Avatar (attentuator back plate, crossover capacitor) and using the Peerless tweeter as a replacement for the original horn.

Do you think that would work? I'm looking for an easy way to get my cab going again while maybe improving the harshness of the tweeter. I'm not sure about using a different crossover.
Click to expand...

You might want to check that the peerless tweeter has the same nominal impedance as the Foster horn. If so, no problem. If they're different, it will screw up your crossover point if you keep the existing crossover components. As Bruce says, the crossover can be reworked if necessary.
 
#16
I finally got all the parts I needed (well, almost). I wired in the new capacitor and the peerless tweeter, which literally took only about 30 minutes. The only problem encountered is that the mounting face of the peerless is too small for the plywood hole in the cab. (In other words, it doesn't "fall through" the hole but there is not quite enough overlap to mount it.) What I'm going to do is look for 3/4" flat brackets that I can screw to the mounting holes and then mate with the holes that are already in the cab from the old tweeter. I should be able to take of this tonight if I can find what I'm looking for. Any suggestions btw?

Now, I will post the results when I'm done, but I did test it with my GK MB150 to see if the wiring was correct. Initial impression: I'm going to love this tweeter. That's why I'm going through the trouble of mounting it even though it's a tad small for a drop-in replacement. It appears to be a lot quieter than the old one, which is great because the attenuator can be turned up and solve my problems with burning that out again. Less hiss and it does appear to blend well with the other speakers - very smooth! But I need to try it out with my high powered system before I can make any final judgements. More to come!
 
#17
I would take a square piece of 1/2 in. plywood, cut out a hole to fit the Peerless, either paint it flat black or cover it in carpet or black felt (which you should be able to get locally), mount the Peerless tweeter to it and then secure the new mounting plate to the cabinet by screws. If you orient it like the existing tweeter (point at the top) it will look stylish and nobody will probably even notice.

The alternative would be to remove one of the woofers, attach a piece of plywood from the inside with a big enough hole for the tweeter's magnet, etc. to protrude through and then drive screws into it. You'll need to be careful if the tweeter's mounting ring isn't really stiff.

I'd go with the external plate...

Good luck!
 
#18
Yeah, I'd do like Billy said. You want to be sure that the tweeter is completely sealed against the cabinet face so there are no air leaks. If it's not air tight, you can get a hissing sound from the air pumping in and out of the leak.

It'll also get your mounting screws a little farther away from the hole, which is a good idea. When they're too close to the edge, the wood is awfully weak for driving a screw into.
 

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