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Author Topic: fusing horn drivers.  (Read 9295 times)

John Sabine

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fusing horn drivers.
« on: May 06, 2014, 12:54:52 PM »

I need some help from the gurus. I want to fuse or use a lightbulb to protect the hf drivers in my line array boxes.  a couple of years ago I hand an amp go dc on the outputs and kill 8 of the 16 hf drivers in my line array. once I got the drivers replaced I put a capacitor inline with the + lead to the hf drivers to block dc. since then I've never been completely satisfied with the sound of my hf and I think that the caps are causing issues.  this weekend I came across another guy who had the same problem an had installed fuses inline with his hf drivers using external fuse holders on his jbl srx's.
my questions are is this truly a viable option? would bulbs be better? be it fuses or bulbs what is the best solution for 2 16 ohm 50 watt drivers in parallel?


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Tim McCulloch

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Re: fusing horn drivers.
« Reply #1 on: May 06, 2014, 01:09:54 PM »

I need some help from the gurus. I want to fuse or use a lightbulb to protect the hf drivers in my line array boxes.  a couple of years ago I hand an amp go dc on the outputs and kill 8 of the 16 hf drivers in my line array. once I got the drivers replaced I put a capacitor inline with the + lead to the hf drivers to block dc. since then I've never been completely satisfied with the sound of my hf and I think that the caps are causing issues.  this weekend I came across another guy who had the same problem an had installed fuses inline with his hf drivers using external fuse holders on his jbl srx's.
my questions are is this truly a viable option? would bulbs be better? be it fuses or bulbs what is the best solution for 2 16 ohm 50 watt drivers in parallel?


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About 27 years ago I have fuses inline with my Renkus SSD1800 drivers.  Finding the right value was the challenge - either the fuses blew before things got loud enough or the VCs blew before the fuse.  The light bulb might be a better approach.

In my case I was wanting 2" exit driver performance from a 1" exit driver.  Your amp going DC means you need different amps (or find out why the amp's protection circuit failed to protect).  The other fellow you encountered has the same problem I had:  Not Enough Rig for the Gig®.
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John Sabine

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Re: fusing horn drivers.
« Reply #2 on: May 06, 2014, 01:53:28 PM »

I wasn't very specific in my previous post the amplifier actually smoked all the horn drivers upon being switched on. i've never actually blown any horn drivers on this rig while running a job although in the spirit of full disclosure I did have a few diaphragm to go bad early on due to defective glue being Used. The voice coils would cleanly.separate from the diaphragms resulting in lots of rattling.


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Richard Turner

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Re: fusing horn drivers.
« Reply #3 on: May 06, 2014, 04:18:03 PM »

I need some help from the gurus. I want to fuse or use a lightbulb to protect the hf drivers in my line array boxes.  a couple of years ago I hand an amp go dc on the outputs and kill 8 of the 16 hf drivers in my line array. once I got the drivers replaced I put a capacitor inline with the + lead to the hf drivers to block dc. since then I've never been completely satisfied with the sound of my hf and I think that the caps are causing issues.  this weekend I came across another guy who had the same problem an had installed fuses inline with his hf drivers using external fuse holders on his jbl srx's.
my questions are is this truly a viable option? would bulbs be better? be it fuses or bulbs what is the best solution for 2 16 ohm 50 watt drivers in parallel?


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Yorkville used part # 3652 on the ef508, and possibly some of the older tx2/4/5/8

by specs it is a phillips 13620 R2 Duplo-d 24v 55/50w bulb. these are used on the high freq circut in series with the HF driver which is a 2" exit B&C compression. just the high beam circut of the bulb is used but the low beam will work in a pinch till it can be replaced.

any time I went looking Yorkville was the cheapest and fastest source for them as its a not common anymore auto bulb.


On smaller 1" horns the usual suspect was an 1156LL standard tail light bulb.
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Jens Droessler

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Re: fusing horn drivers.
« Reply #4 on: May 06, 2014, 06:07:55 PM »

A fuse would be a viable way. Leave that cap in and put the fuse in parallel to the cap. So if the fuse blows, you will still have highs, just not as nice as before. The problem with the caps alone is that the settings in your processor would need a modification to include the difference in phase and response the cap adds.

A bulb OTOH wouldn't be such a good idea. They change their resistance heavily with the current flowing through them. Worst case you get pumping in the highs. Best case you get don't get enough highs out of your boxes when driving them hard, so the tonal balance tilts. Surely both aren't desirable for you.
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John Sabine

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Re: fusing horn drivers.
« Reply #5 on: May 06, 2014, 10:15:56 PM »

wow.  that's either crazy, genius, or crazy genius! :)


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Matthew Knischewsky

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Re: fusing horn drivers.
« Reply #6 on: May 07, 2014, 10:27:28 AM »

Hi John,

What value capacitors did you use for protection? Usually you'd pick a value that would be considered very low for a crossover point but would be sufficiently out of band in normal operation while still offering DC protection. Also helps if there's a mis-patch or wrong processor setting used, the idea is hopefully someone would notice it's wrong before running the rig all the way up.

As has been stated, finding the "right" value for a fuse is usually trial and error.

Using a light bulb... that's a compromise too and if you are having sound quality issues with capacitors I think using a bulb is going down a similar path. That said, if I was to try a bulb the 1156 recommended by Richard would be my starting place for 50 watt drivers.

Bypassing the cap with a fuse is a good idea but one possible downside is you might not know the fuse is blown unless you inspect every fuse in the array. Yes the drivers continue to operate but with different response curves.

As always in audio...everything is a compromise.

Matt
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Joseph D. Macry

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Re: fusing horn drivers.
« Reply #7 on: May 07, 2014, 10:32:58 AM »

I wasn't very specific in my previous post the amplifier actually smoked all the horn drivers upon being switched on. i've never actually blown any horn drivers on this rig while running a job although in the spirit of full disclosure I did have a few diaphragm to go bad early on due to defective glue being Used. The voice coils would cleanly.separate from the diaphragms resulting in lots of rattling.

I had a similar problem with some Community R.5's at a baseball field, powered by a QSC CX902 amp. The speaker lines have Edco lightning protection blocks in series, meant to open like a fuse if the voltage exceeds (in this case) 43 volts. Remarkably, the amp would smoke these protectors upon being turned OFF. A quick check with the multimeter showed the amp was delivering a burst of 56 VDC upon turn off. I sent it back to QSC for repair.
My point? Your amp may need service if it is delivering such a burst of DC voltage.
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John Sabine

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Re: fusing horn drivers.
« Reply #8 on: May 07, 2014, 12:00:49 PM »

the offending amp was repaired and immediately sold.


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David Allred

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Re: fusing horn drivers.
« Reply #9 on: May 07, 2014, 01:09:01 PM »

If you go the fuse route... use a slow-blo at the cont rating in-line with a fast-blo at the peak rating.
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John Sabine

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Re: fusing horn drivers.
« Reply #10 on: May 07, 2014, 04:32:26 PM »

And so my question goes back to what it was in the beginning what size fuses should I use? The horn drivers continuous power handling is 100 W and The load is 8 ohms. according to the lovely calculator on the crown website 100 watch at 8 ohms should be about 3 1/2 Amps. does that sound right to the guys who have experience and knowledge in this area?


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John Sabine

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Re: fusing horn drivers.
« Reply #11 on: May 07, 2014, 04:33:56 PM »

all I really want to do with this fuses protect the speaker in the event of DC.


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John Sabine

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Re: fusing horn drivers.
« Reply #12 on: May 07, 2014, 04:50:13 PM »

I just looked at my original post and I was not completely clear that I was requesting some of the gurus to help me figure which values of fuses to use in this application.


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Tim Perry

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Re: fusing horn drivers.
« Reply #13 on: May 07, 2014, 11:51:28 PM »

I just looked at my original post and I was not completely clear that I was requesting some of the gurus to help me figure which values of fuses to use in this application.


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Here you go: 16 ohms at 50 watts.  use the formula I= sq rt P/R to get  1.77 amps.   Use the nearest standard fuse value depending on your personal philosophy 1.5 or 2 amps.   

Personally I do not recommend doing this: in general fuses and breaker are to prevent fires, not protect loads.

You said the amp went DC. Likely the coil will fry before the fuse blows. Even a fast blow.

If the fuse  (or breaker) is followed by a "crowbar circuit" you will stand more of a chance of achieving your goal.  In this case a Triac or SCR acts very fast. Often the crowbar give is life in the protection of the load.  Search crowbar circuit for examples.

This would be one fuse and circuit per speaker.

Note to engineers: basic calculations were used for simplicity. Certain assumptions were made in the interest of not playing 20 questions with this. 

edit: addendum:  The DC resistance of voice coils is always less then the nominal impedance however 16 ohms was used to get a ballpark answer.  In most cases the voice coil IS in effect the fuse.
« Last Edit: May 08, 2014, 12:04:29 AM by Tim Perry »
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John Sabine

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Re: fusing horn drivers.
« Reply #14 on: May 08, 2014, 08:43:22 AM »

Thank you for your answer Mr. Perry :) I had actually gotten a few free minutes to think about it yesterday and decided to use a 4 amp fuse in series with the drivers but in parallel with the capacitor as suggested by Jens Droessler. I had decided on a 4a fuse since the drivers are in parallel in the cabs (2 16ohm 50w drivers in parallel = 8 ohms, 100w). I also remembered that I have a couple of diaphragms laying around from when some suffered glue failure so today I'm going to use my 15a DC power supply to try to confirm that a 4A fuse will do the trick by connecting the diaphragms in parallel just like in the cabinet, connect them to the power supply and insert fuses in series with the circuit until I find the point where the drivers smoke before the fuse blows then back down one size.
Here you go: 16 ohms at 50 watts.  use the formula I= sq rt P/R to get  1.77 amps.   Use the nearest standard fuse value depending on your personal philosophy 1.5 or 2 amps.   

Personally I do not recommend doing this: in general fuses and breaker are to prevent fires, not protect loads.

You said the amp went DC. Likely the coil will fry before the fuse blows. Even a fast blow.

If the fuse  (or breaker) is followed by a "crowbar circuit" you will stand more of a chance of achieving your goal.  In this case a Triac or SCR acts very fast. Often the crowbar give is life in the protection of the load.  Search crowbar circuit for examples.

This would be one fuse and circuit per speaker.

Note to engineers: basic calculations were used for simplicity. Certain assumptions were made in the interest of not playing 20 questions with this. 

edit: addendum:  The DC resistance of voice coils is always less then the nominal impedance however 16 ohms was used to get a ballpark answer.  In most cases the voice coil IS in effect the fuse.
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Tim Perry

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Re: fusing horn drivers.
« Reply #15 on: May 08, 2014, 10:22:18 AM »

Thank you for your answer Mr. Perry :) I had actually gotten a few free minutes to think about it yesterday and decided to use a 4 amp fuse in series with the drivers but in parallel with the capacitor as suggested by Jens Droessler. I had decided on a 4a fuse since the drivers are in parallel in the cabs (2 16ohm 50w drivers in parallel = 8 ohms, 100w). I also remembered that I have a couple of diaphragms laying around from when some suffered glue failure so today I'm going to use my 15a DC power supply to try to confirm that a 4A fuse will do the trick by connecting the diaphragms in parallel just like in the cabinet, connect them to the power supply and insert fuses in series with the circuit until I find the point where the drivers smoke before the fuse blows then back down one size.

Every bit of this sounds like an exercise in futility.

Discard the amplifier that "goes DC". Replace with modern amp. Bring enough rig for the gig. Forget about fuses.
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Tim McCulloch

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Re: fusing horn drivers.
« Reply #16 on: May 08, 2014, 10:34:41 AM »

Every bit of this sounds like an exercise in futility.

Discard the amplifier that "goes DC". Replace with modern amp. Bring enough rig for the gig. Forget about fuses.

This.  Right.  Here.
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Art Welter

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Re: fusing horn drivers.
« Reply #17 on: May 08, 2014, 11:18:18 AM »

Every bit of this sounds like an exercise in futility.

Discard the amplifier that "goes DC". Replace with modern amp. Bring enough rig for the gig. Forget about fuses.
Absolutely. Back in the days of "Flame Linear" amps, fuses (or capacitors) were always used. The fast blow fuses would blow regularly on peaks, and would be replaced with progressively larger fuses that eventually would make it through a show without failure. Then, when the Phase Linear amp would blow an output transistor then would dump it's full PSU DC on the output, the drivers would smoke.

Capacitors were sure "fire" prevention, but muck up phase and frequency response even when chosen to be nominally an octave or more below the crossover point.

An amp using output relay or crowbar protection is the way to go.
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Joseph D. Macry

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Re: fusing horn drivers.
« Reply #18 on: May 08, 2014, 11:25:10 AM »

When I used to sell retail PA gear, some Community speakers (thinking specifically of CPL46 3-way) would come back with the complaint, "I see sparking coming from the inside." I would explain that the crossovers have a small lamp for tweeter protection; the flashing light was the protection circuit working.
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John Sabine

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Re: fusing horn drivers.
« Reply #19 on: May 08, 2014, 11:29:48 AM »

The amp has been gone for 2 years. I placed non polarized capacitors inline with the horn drivers to block DC in the event of some future calamity but feel that they effect the sound quality of the horns. Looking for an option that would allow me to protect the horns from a random mishap (such as the amp that went nuclear and fried 8 horn drivers on the night before a festival) but won't effect the sound of the horns.

Every bit of this sounds like an exercise in futility.

Discard the amplifier that "goes DC". Replace with modern amp. Bring enough rig for the gig. Forget about fuses.
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John Sabine

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Re: fusing horn drivers.
« Reply #20 on: May 08, 2014, 12:55:28 PM »

After an entire morning of smoking horn drivers I have the following to report with this qualifying statement:
I discovered that I had discarded the diaphragms that had suffered from glue failure so I ended up substituting Eminence PSD2002-8DIA diaphragms. 8 ohms, 80 watts AES. Same impedence but 20% less power handling than my horn driver circuit so at least any fusing would be on the side of safety if there turns out to be such a thing. Test rig used included 1 channel of a Yorkville AP6040 power amplifier, Tone generator, Amprobe AC ammeter, various AGC type fuses from 1/2 to 4 amps in capacity, one idiot who likes breaking things in the shop so that they don't break on the job. The diaphragm was not installed in a driver so this did not take into account cooling of the air gap and magnet structure.

Test 1 was brute force worst case scenario: Amp gains to max, tone generator to max output @ 50hz , inserting fuses of greater and greater value until the diaphragm goes pop. The result was every fuse below 1.5 amps blew almost immediately, 1.5a fuse held its own and the diaphragm began so show signs of heat but then the fuse blew, the 2a fuse and the diaphragm blew simultaneously.

Test 2 same setup (with new diaphragm) but leaving the 2.0A fuse inline with the diaphragm and slowly increasing the output of the tone generator until the diaphragm gets too hot (heat one up and you can tell when it becomes unhappy) and various frequencies from 20 - 20khz. The result was that up to 1.3a the diaphragm was happily heated away with no signs of distress but by 1.5a there was definitely cooking going on. This was independent of frequency.

Since the power handling of my drivers is 100w and the test subject was 80w I'm going to try the 1.5a fuse in parallel with the cap as by bypass it so worst case if the fuse blows I lose my cap bypass but the cap will still compete the circuit. We'll see how this goes. Hopefully I never have to see if it works anyway.




« Last Edit: May 08, 2014, 02:24:42 PM by John Sabine »
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Art Welter

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Re: fusing horn drivers.
« Reply #21 on: May 08, 2014, 05:43:47 PM »


I discovered that I had discarded the diaphragms that had suffered from glue failure so I ended up substituting Eminence PSD2002-8DIA diaphragms. 8 ohms, 80 watts AES. Same impedence but 20% less power handling than my horn driver circuit so at least any fusing would be on the side of safety if there turns out to be such a thing.

Since the power handling of my drivers is 100w and the test subject was 80w I'm going to try the 1.5a fuse in parallel with the cap as by bypass it so worst case if the fuse blows I lose my cap bypass but the cap will still compete the circuit. We'll see how this goes. Hopefully I never have to see if it works anyway.
John,

AES power is pink noise with a crest factor of 6dB. A sine wave has a crest factor of 3 dB. DC has a crest factor of 0 dB. Unfortunately, testing with a slowly increasing sine wave on a non moving, different impedance, different manufacture diaphragm tells you little about what will happen to the fuses or your actual drivers using normal music which may have 2-3 times the dynamics of the AES signal, or with DC, which heats more rapidly than AC, and will be an instantaneous event if you still use an amp that does not have output protection.

Out of curiosity, what was the voltage when the 1.5 amp fuse blew, and what was the DC resistance of the PSD diaphragm (they vary quite a bit) you burnt?

Art
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Richard Turner

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Re: fusing horn drivers.
« Reply #22 on: May 08, 2014, 08:49:58 PM »

Appears to be a 1.85amp auto reset breaker on the yorkville e152 HF circut, would be a 120w 1.4" B&C compression driver

http://www.yorkville.com/downloads/servman/sm_e152.pdf
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Ivan Beaver

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Re: fusing horn drivers.
« Reply #23 on: May 08, 2014, 08:53:03 PM »

The one thing MISSING from this conversation is discussion about THE IMPEDANCE CURVE-

HF drivers do not have a constant impedance (despite what the specs might "suggest").

At different freq the actual impedance load will be different.

Now granted at a freq that the impedance is higher-the current/power will be less.  And music is a complicated signal and finding a "single value" is not always so easy.

Different test signals will give different results.
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Re: fusing horn drivers.
« Reply #23 on: May 08, 2014, 08:53:03 PM »


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