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I am blowing speakers every two weeks...

#81
Jerrold Tiers said:
Cerwin-Vega, I believe used to have an advert that bragged they could reproduce a square wave of some low frequency.
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It's 100% true, but not much of a claim, because any subwoofer will do so. Send a 50 Hz square wave, just as a for instance, through a high order electronic crossover and see what happens. With the harmonic components of the wave removed you end up with something that far more closely resembles a sine wave than a square wave, and any sub driver will handle it quite easily. Taking the crossover out of the equation, would it reproduce a pure 50 Hz square wave? Sure, those components of the wave within its bandwidth. The problem with thinking about what a driver is trying to reproduce is we keep going back to that oscilloscope trace. But no driver has that kind of bandwidth, and no driver ever actually has to deal with a square wave form that pure.
 
#82
Bob Lee (QSC) said:
What I was trying to get across is that if the voltage stays at a particular instantaneous value in a segment of a waveform, as during clipping or with a square wave, the accelerative force on the cone is constant for that duration, instead of the commonly held belief that the cone freezes in position.
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Hi Bob,

I was thinking about a model of the electro-mechanical-acoustic system here. The EMF is applied to a suspended mass-spring-damper system that also generates its own back-EMF voltage when the coil is in motion. Note that the spring (suspension) also results in an equilibrium displacement for a fixed direct-current input.

Do you have a way of measuring and displaying in your labs the following quantities simultaneously?
* input voltage to the loudspeaker terminals
* coil current
* diaphragm displacement (and/or velocity or acceleration)
* near-field SPL
If you could show us a chart with these, given square-wave inputs at 5 Hz., 10 Hz., 20 Hz., 40 Hz., and 80 Hz. for a typical bass guitar woofer, it would be really instructive to see them.

I would be tempted to write a computational model of these things myself, but it would take a lot of time, and most of my texts are still packed in boxes.

- Mike
 
#84
OP here.

I greatly appreciate all of the responses my original post received. To say the least, it has been an education.

I took my cabs up to the local music store and the tech there was convinced I had melted the voice coil. He resommended getting a more powerful amp that would have more headroom. He also recommended trying 15" speakers because of the way they respond to low frequency demands placed on them. I'm not convinced on his second recommendation.

I also called Dave at Avatar and told him my situation. I would like to take a moment and reiterate what awesome customer service they have at Avatar. Dave rules.

Dave also recommended a more powerful amp with more headroom.

Getting a more powerful amp makes good sense to me, but I was curious what people here would recommend, particularly you experts (Bill Fitzmaurice, Bob Lee, etc.). All opinions are welcome.

Thanks again.
 
#85
Bob Lee (QSC) said:
Uh, no, that's not true.

There actually is no such thing as underpowering a loudspeaker. However, you can make an amp put out much more power than it's rated for by pushing it into clipping. That can overpower the loudspeaker.

Single Coil, do you have any information on how the drivers failed? Were the cones creased? Were the voice coils burned, bubbly, etc.? These would be vital clues to whether the failures are due to excessive power or excessive excursion.
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Bob? Holy crap! I had no idea you hung out in these parts; I didn't know you got around beyond the LAB (Live Audio Board, for some of the other folks around here). Nice to see you! :hyper:

And I will defer my somewhat improper statement earlier to Bob...he is one of the smartest I've ever seen on amp design and function.

-Mark "Flounder"
 
#87
So the guy "is convinced you melted the coils"?

Did he LOOK at them?

Did he SHOW them to you?

If not, then whatever he thinks is a lot of hot air and there is no reason whatever for you to believe it.

His term of "melting the coil" also is just one of those sayings that are right up there with "this amp is shorted out", used for any problem at all. Most coils will not "melt" but may be burned, distorted, may shed wires or allow them to slip, etc.

Advise to buy a larger amp seems like back to the old, tired, "underpowering" myth. Of course, I don't think you would be UNHAPPY with a larger amp....... :D ...... but a cheap repair it is not.

it did occur to me that there IS a way you can blow a 1000 watt speaker (or at least a very high rated one) with a 50 or 100 watt amp.

That is if the speaker is vented, and the amp is set in such a way EQ wise that it puts out plenty of lows BELOW the box frequency. Then the speaker motion is uncontrolled, aside from suspension friction, and the speaker can move way too far. it may hit the limits, bang on the magnet back, or spend so much time with part of the coil outside the magnet gap that it is insufficiently cooled and fries part of the coil which then sheds wires or loosens them.

I don't recall what your speakers are, nor if they are vented.

Are they vented?

Could you have set the low EQ high enough to have potentially zapped them that way?

Were you using an octave box?
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BTW: Bill F..... The Cerwin Vega claim really related to the speaker being able to reproduce accurate square waves where other speakers were already differentiating and having severe sag of the acoustic square wave as a result. Sag is a measure of LOW frequency bandwidth, and not harmonics.

We are not getting hung up on waveforms etc, and this was really an "aside", not directly related to the problem of the OP.

I agree that unless the clipping is really crazy OR AN OCTAVE BOX IS USED, that the square waves are likely to be rounded and un-square, and unlikely to be extremely low frequency.
 
#88
Single Coil said:
Getting a more powerful amp makes good sense to me, but I was curious what people here would recommend, particularly you experts (Bill Fitzmaurice, Bob Lee, etc.). All opinions are welcome.

Thanks again.
Click to expand...
If you're blowing drivers it's because they aren't sufficient to deliver the output that you're trying to get from them. Imagine you're in a drag racer and when you pop the clutch your tires just spin and smoke while the car goes nowhere, until the tires burn right through and blow. Is the cure a bigger engine? I'd be looking at bigger tires.
 
#89
I can't help thinking that if there were more speaker protection circuits that this underpowering myth would just go away.
It'd have to be more sophisticated so people didn't just get frustrated with it, i.e.:
Link Removed
Then the question would be "I keep tripping my speaker protections - should I get a bigger amp?" :-)
 
#90
seamonkey said:
I can't help thinking that if there were more speaker protection circuits that this underpowering myth would just go away.
It'd have to be more sophisticated so people didn't just get frustrated with it, i.e.:
Link Removed
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I don't recall ever seeing a driver toasted by DC, and the only way it happens in real life is by a totally toasted amp, which leaves absolutely no doubt about the cause. I've seen many blown amps sending pure DC from the rails to the drivers and the drivers survived.:hyper: I've seen blown amps sending AC straight from the power transformer to the drivers and the drivers survived. :D And I've seen perfectly good amps fry a driver in the blink of an eye with a turn-on transient.:crying:
 
#91
One thing I will say after hearing your fender played through my acmes and throught the Ampeg SVT610 is that it does not cut very well. Were the strings really old?
I use to have a problem overdriving my rig until I stopped boosting the lows and let things stay flat.

However, if thats the sound you want(and it does sound very good to me) then maybe an amp with a limiter is in order.

Best of luck,
Jonathan
 
#92
JonathanD said:
One thing I will say after hearing your fender played through my acmes and throught the Ampeg SVT610 is that it does not cut very well. Were the strings really old?
I use to have a problem overdriving my rig until I stopped boosting the lows and let things stay flat.

However, if thats the sound you want(and it does sound very good to me) then maybe an amp with a limiter is in order.

Best of luck,
Jonathan
Click to expand...

Yes, the strings were very old. As a matter of fact, they were the original strings from about 18 months ago. Yes, I know I should change my strings more often than that. I just got new strings and it does sound much better.

I run my GK700 flat; that is part of what is confusing me. If I were boosting lows I would expect trouble with my speakers.
 
#93
When I saw the title of this thread, the first thing that came to mind was "Blowing speakers every other week? The man has "issues"...or he's a congressional page..." :eek: ;) :D

Seriously, though, check your speaker cables. I had a problem with one where one piece of a strand had broken loose from the solder joint on one end, and strayed across to the other solder joint. Made life "interesting" for a while.
 
#94
Have you checked everything for polarity/phase? If something is arse about it has the potenetial to kill drivers at high volume. Check each cab individually with a 9v battery and make sure all the drivers in a cab jump the same way. Check that all the cabs jump the same way, ie all drivers in all cabs move forward (or back, as long as they're the same) when a +ve voltage is applied to the tip of a speaker cable. Check all your speaker cables are wired the same way.
 
#95
Hi there, you need to see the voice coils of some of the blown spkrs. You or your tech can cut the cones and spider,cut the v/c leads and pull the cone assembly out of the magnet. If the v/c is burnt,discolored or you see signs of melted lacquer,it's to much power. If it's burnt only at the bottom of the v/c, its D.C. volts. Check the v/c with an ohms meter to see if it's been "blown" open. If the v/c looks fine but there is no reading on the meter, then it's probably been over excurted,it jumped to far and ripped or broke teh lead in wire some where between the v/c and the terminal. Good luck Mel.
 
#96
billfitzmaurice said:
I don't recall ever seeing a driver toasted by DC, and the only way it happens in real life is by a totally toasted amp, which leaves absolutely no doubt about the cause.
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Not actually. I have in fact seen a number of them. Cases where I KNEW there was DC, and found the bad speaker. NOT "large" amounts of DC, but relatively small offsets.

The DC itself does NOT "blow" them.

What happens is the DC biases the speaker coil off-center with one part sticking out partly, not centered evenly with respect to the "top plate" of the magnet structure. Then one end of the coil gets overheated from the NORMAL AC signal, because of insufficient cooling. The main cooling for a voice coil is radiation into the much cooler magnet structure across the small gap where the coil moves.

if the end of the coil never gets inside the gap, or if it spends very little time there, it won't be cooled as much, if at all. The voice coil itself, without the magnet, cannot handle anything like the wattage the speaker can as a unit. Hence it gets 'cooked".

"Cooked" speakers often develop a "loose section" of the voice coil, where the cement that holds it to the kapton etc "former" is damaged by heat, and allows that part of the coil to slide back and forth.

When part of the coil is loose and slides, you get a soft buzz noise with the sound. Eventually, there is a failure due to the coil wires breaking from fatigue, or possibly insulation wearing off and shorting, etc.
 
#97
Mel Mckinnon said:
If it's burnt only at the bottom of the v/c, its D.C. volts.
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Vance Dickason has covered this point a number of times in the driver trade magazines, but if you're not in the industry you wouldn't see it. The top plate serves as the primary heat sink of heat for the voice coil. The center portion of an overhung coil spends most of its time within the gap, while the ends spend most of their time outside the gap. Since the ends aren't as effectively heaksunk as the middle when the coil is overheated the damage takes place at the ends. The only voice coils I've ever seen that were toasted in the middle were underhung.
 
#98
If ONE end is toasted, DC is suspected, that or a manufacturing defect. If BOTH ends are toast, power may be the problem. I mentioned this stuff back on page 2 of this thread.

However, it makes a bunch of difference how long the coil is. Some coils are about the top plate thickness long, and are solidly in the gap. Some are shorter, and are very solidly in the gap. As mentioned by Bill F , they tend to toast evenly from over-power.

As the Xmax goes up, generally the coil gets longer, longer than the top plate thickness (overhung). If so, the ends are not so effectively heatsunk. Then the ends will toast quicker, especially the end nearer the cone, where the center pole does not extend.
 
#100
Your speakers should be able to handle that GK. You've been playing for years and you're not stupid. There is either a problem with your head (have it bench tested), your speaker cable is bad (replace it), or for some odd reason, every speaker you touch is a piece of crap.
 

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