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[David Parker]

Eventually......

Say the light bulb project is completed.  Now when you're doing whatever is frying the drivers, the light bulb does its job and opens the circuit.  What have you gained?

The show still stops

Until you learn the root cause you're just putting on band-aids.

Theoretically the light bulbs act as a compressor and cut the voltage going to the horn driver back when it gets too high. They are only supposed to blow like a fuse with a really high current.

[David Parker]

Had the same issue when I had an MRX setup. replaced HF drivers constantly, even at moderate levels and the same happened when a PRO user Friend borrowed my system. My ultimate fix was replacing all the HF drivers with a Selenium D220Ti. 2 things happened didn't blow any drivers for the rest of the life of the system and clarity in the highs drastically improved. Just my .02

I've been using the same selenium driver except the neodymium model (uses the same diaphragm) in my home brew 2-15 mains for about 3 years with no problems. The selenium replacement diaphragm is less than $15. I never understood why the JBL diaphragms were so much higher than the others, and historically, they are much less dependable.

[Chuck Simon]

I never understood why the JBL diaphragms were so much higher than the others, and historically, they are much less dependable.

My experience would not support that statement.  I have been a JBL user for a few decades and have had to change very few diaphragms, three that I can think of, and two of those were damaged by drinks spilled into monitors. 

I think adding a light bulb is a bad idea.  If the speakers are not up to the task, sell them and move on to something better.

[Jeff Bankston]

My experience would not support that statement.  I have been a JBL user for a few decades and have had to change very few diaphragms, three that I can think of, and two of those were damaged by drinks spilled into monitors. 

I think adding a light bulb is a bad idea.  If the speakers are not up to the task, sell them and move on to something better.

+1 , jbl diaphrams will last as long as you dont overpower them. match the amp power to speaker handling power. you can do a series or parralell or series parralell wiring of the hfd's to come up with an impedance/power handling combo to get close to amp power output. use the rms/aes output of the amp and the rms/aes power handling of the drivers. i wouldnt use a light bulb. my dad had some bose speakers with the light bulb on the tweeters.

[David Parker]

My experience would not support that statement.  I have been a JBL user for a few decades and have had to change very few diaphragms, three that I can think of, and two of those were damaged by drinks spilled into monitors. 

I think adding a light bulb is a bad idea.  If the speakers are not up to the task, sell them and move on to something better.

I ran JBL 2445 compression drivers on my mains for many years and never had any problems, but I've never had any problems with any compression drivers. I have heard about a lot more problems from other people with the smaller JBL compression drivers. Correct, if you properly manage them they do fine, but it appears that they are less resistant to abuse than other brands.

[Tim Perry]

repair du jure:  protectors in JBL eon

[Ivan Beaver]

I may have missed it, but here are the problems with "just installing light bulbs" to protect any loudspeaker.

FIRST you have to determine WHICH bulbs to use-voltage and current.  That is the hard part.

If you use something to large-it won't protect.

If you use something to small-it will "kick in" to soom or burn up all the time.

The use of simple light bulb has its own compromises-as it is not a "hard on" type of device.  It starts to limit the signal a good while before any damage is likely to occur.

This means the sonic quality is going to be compromised.

The bvest protection is to pay attention to your system and how hard you run it.

While that is easy to say-I personally have burnt out probably hundreds of HF drivers over my rental years.

The best protection I ended up using was 50W cathode to cathode zener diodes placed across the HF driver.  I used lamps (larger than would normally be used) in series (as normal)  with the load.

The zeners would remain out of curcuit until the "turn on" voltage was exceeded and then they would fire and  drop the peak.  The light buld acted as a "cushion" between the circuit and the output of the amp.

It worked very well and I never lost a driver that I used that circuit on.

[Yosi Melamed]

I may have missed it, but here are the problems with "just installing light bulbs" to protect any loudspeaker.

FIRST you have to determine WHICH bulbs to use-voltage and current.  That is the hard part.

If you use something to large-it won't protect.

If you use something to small-it will "kick in" to soom or burn up all the time.

The use of simple light bulb has its own compromises-as it is not a "hard on" type of device.  It starts to limit the signal a good while before any damage is likely to occur.

This means the sonic quality is going to be compromised.

The bvest protection is to pay attention to your system and how hard you run it.

While that is easy to say-I personally have burnt out probably hundreds of HF drivers over my rental years.

The best protection I ended up using was 50W cathode to cathode zener diodes placed across the HF driver.  I used lamps (larger than would normally be used) in series (as normal)  with the load.

The zeners would remain out of curcuit until the "turn on" voltage was exceeded and then they would fire and  drop the peak.  The light buld acted as a "cushion" between the circuit and the output of the amp.

It worked very well and I never lost a driver that I used that circuit on.

Dear Ivan,
Would you please elaborate about the calculations needed to fit those zener diodes also the considerations/calculations in choosing the correct lamp for the zener diode implementation and without the diode.

I only see one fault with using zener diodes, once they are engaged there is no active HF driver for the duration of their action Vs the lamp only implementation that the power to the HF driver is gradually compressed as the power goes up while giving visible notice when it's engaged, am I correct?

[Tim Perry]

Dear Ivan,
Would you please elaborate about the calculations needed to fit those zener diodes also the considerations/calculations in choosing the correct lamp for the zener diode implementation and without the diode.

I only see one fault with using zener diodes, once they are engaged there is no active HF driver for the duration of their action Vs the lamp only implementation that the power to the HF driver is gradually compressed as the power goes up while giving visible notice when it's engaged, am I correct?

The lamps act as a variable current limiter, the zeners act as a voltage limiter.

The calculation for the zener would be: at 50 volts peak-to-peak will equal 25 volts peak. multiply by .707 to get  17.675 volts rms. 

To calculate nominal max unclipped power E squared / Z  or 17.675 squared / 8 = 39 watts. (rounded)

[Ivan Beaver]

Dear Ivan,
Would you please elaborate about the calculations needed to fit those zener diodes also the considerations/calculations in choosing the correct lamp for the zener diode implementation and without the diode.

I only see one fault with using zener diodes, once they are engaged there is no active HF driver for the duration of their action Vs the lamp only implementation that the power to the HF driver is gradually compressed as the power goes up while giving visible notice when it's engaged, am I correct?

During our listening tests, we took a BGW750 (a large amp for the time) and bridged it then ran it up to clipping and switched the circuit in and out.  We could not hear any difference in the sound.

I was a bit disappointed-as I was expecting to hear "something" happening.  So I took a scope (you know real test gear) and looked at the signal across the driver.  Without the protection there were a lot of large peaks.  When the circuit was engaged-all the peaks were gone.  Since the diodes were very fast acting-all they did was get rid of the peaks.

Very easy to see the action-but not hear it.

At the time I only used this circuit on the monitors.  I was sending out 4-5 systems per day on the weekends.  I would usually lose at least 1 or often several HF drivers per weekend.  After I put this in-I only lost 1 driver during the next 2 years-and that was due to it getting full of beer.  Nobody ere noticed the circuit working-or least said anything to me.

[ProSoundWeb Community]