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Author Topic: fusing horn drivers.  (Read 4556 times)

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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Portable Gear list, Yorkville Paraline PSA1 x4 PS2S x2 LP-LED4 x4 LP-LED2 x2 E10x4 E210x2 EM526 x2 (smoking tiny things) Allen-Heath Qu-16, also Yorkie trap box rig for sale ef500x4 ls808x4 ap4040x2

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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Ivan Beaver
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