speaker overload protection

[airboss]

Gang:
I'm going to jump in here just to cast a vote so to speak. I'm not sure how much abuse our horns will take, and like you, would like to ensure that they aren't damaged by accident or other means. What I do know though is that compressor/limiters like the one you just bought really don't have much place in a playback system. I have used Urei L-4s and others in broadcast audio and no matter where you set them you are going to get coloration in varying degrees of too much. That's how we make the wimp from down the street sound like he carries his balls in a wheelbarrow on your local FM dial.

For what it's worth, I really like the fuse and the switch bit. Simple, very effective, repeatable, and sonically invisible.

[Richard C.]

Hi all,
I have drawn out the schematic diagram for the model 14 crossover and modeled it with Electronics Workbench. The speaker protection section of the crossover is very similar to the EV STK "tweeter protector". There is "NO" incandescent lamp in series with the 902 driver. There is a 10 Ohm wirewound resistor in series with the crossover input, with a normally closed relay contact across it. When the input Power exceeds 75W "average power" the relay is energized, opening up the relay contact and putting the 10 Ohm resistor in series with the entire speaker. This now gives the model 14 and the 9842 monitor a 200W rating. The 12" woofer has a 75W rating and the 902 driver is attenuated about 10Db or so (7.5W) so the speaker is well protected. Altec called this circuit: "Automatic Power Control". Of course you will hear it when it switches in the 10 Ohm resistor.
Richard C.

[David Deratany]

Dan,

Thanks for reminding me of that. I have used a Craig Anderton designed compressor/limiter built into (along with his tube sounding fuzz tone) the "ne plus ultra" electric guitar my dad and I made 20 plus years go, and the effect works there really well, but that effect is not what I am looking for in my home audio. BTW your characterization of radio dj sound really says it all :-)

I had assumed, without much thought, that the 1712A was little more than a variable cutoff control below which there didn't have to be anything going on.

Fortunately, since I bought a new Fender Telecaster with the Gram Parsons/Clarence White b-string bending mechanism built in, and that instrument is the now one I plan to use most of the time, I can use the 1712A with that, and being rack mount size, it will actually be more convenient than the one I made in a little RS box. I feel naked playing without one, as no matter how choppy and uneven I am playing, for one reason or another, it will still come out so smoooooth :-)
not that I would ever be at less than 100%.

The switch/fuse idea is starting to look better.

Richard C,

I also like the "Automatic Power Control" but building it from scratch (i.e. no kit) might be a stretch for me, unless there is less to it than meets the eye. I am intrigued by it.

[cclark65]

I haven't taken my model 14's apart to check it out, but I do know that my model 6's have a light that comes on when the overload circuit kicks in, and it pulses to the beat of the music until the circuit shuts back off.
And to tell you the truth, I have been doing PA for punk/hardcore shows for a couple years with my Altec equipment (Don't give me grief about the type of music, but I love doing PA for ANYBODY! I do church stuff too...) Anyway, I have never used protectors of any sort on my 902 drivers, just the compressors that I have inline for dropped microphones and really loud screams. The compressors rarely come into the picture. I have never blown out a diaphragm electrically yet, and I have done some fairly large outdoor things with it, covering a football field easily. I have replaced them from stress related problems, such as the aluminum just crumbling to pieces, but have never had a voice coil go out yet. I am crossing them over considerably higher than they were meant to go also, 1200 hz is where they kick in.

[Fitts]

Hi, me again, I forgot to mention that if you use the fuse trick I suggested earlier, be sure to put a 100 ohm resistor across each of the fuses as well. If the fuse ever opens to protect your speaker, your amp will be looking at no load without this resistor. For many amps, especially tube amps, a no load high volume condition can result in harm to the amp. If the fuse blows, the resistor will limit the power to the speaker and maintain some loading to the amp.

[Steve Burger]

To Charles, in the application you mentioned you should probably consider using the 909 pascalite diaphragms. They handle 2.5X the power of the 902 with little, if any, loss of fidelity. Even in hifi most say they cannot tell the difference.

[cclark65]

Truthfully, I am currently not using Altec Diaphgrams in them for live stuff anymore. They are expensive, so I save them for myself!
I am using some $20 units I found at MCM Electronics, and I just modify the terminals and they work fine. Those kids at the shows don't know any different anyway. The ones at MCM fit perfectly, and handle 60 watts, and are cheap to replace, and still sound pretty good. Not as good as the Altece, but very tolerable. I have thought about the 909 ones, but don't have any at this time to play with.

[Jim D]

The 909 diaphragm is incrediably durable. In over ten years of installing them, some in very heavy use, not one has failed. I personally do not think I can tell the difference between them and the 902 unit. Jim

[dazzman]

HOW ABOUT A BIGGER SYSTEM OR TURN IT DOWN !!