Poly Switch? Polyfuse?
I am doubtful... it may be polyfuses - though I tried running audio through samples I got and they did something to the sound... A polyfuse (or polyswitch?) sort of looks like a small film cap in the nano range... you can buy those from lots of electronics vendors and they are rated by current and voltage
anyway - the device Han S. is talking about, I think, is a thermal break switch...
...if he means it looks like an electrolytic cap - sort of in the
220@25 range and may have one lead out each end or two leads out each end... well that physical description and function are the same as a device I had to replace in several pairs of MDM-4's, including mine. They heat up and just disconnect the speaker. They look electrically like a resistor and a relay contact. Occasionally one would "weaken" and switch off at way too low levels. It's essentially a small inline thermal self reset breaker.
I eventually ripped the thermal break switches out of my MDM-4's and used fuses. Now I've shorted the fuse holders out. Nobody I know likes or uses MDM-4's - I think I am the only person left who likes those things - they were really the first near field speakers designed as such - and they are horribly inefficient...
as far as the fuse thing goes it's a little tricky and I have mixed opinions. You want to protect the speakers but fuses have a dynamic resistive character that varies with temperature - same as light bulbs. I don't like what light bulbs do - UREI 813's sound better with them shorted out for one thing.
One thing I noticed in NS-10's early on was that, after installing fuses, I started seeing more woofers blowing with certain program that, it seemed to me, pushed the speaker into overshoots. Overall the woofer blowouts were reduced but the reports were that they would sometimes pop at what seemed to be more moderate (or less immoderate) levels. The in-line fuse may have been ruining amplifier to speaker damping - that was my theory anyway and I went with it. Damping keeps the speaker from overshooting by presenting a very low source to the speaker that essentially shunts back EMF generated by the speaker as it moves on its own... you see woofers shipping with shorting clips across the terminals for this reason... this keeps the cones from bouncing around too much in shipment... anyway I just learned how to keep my levels low and gave up on fuses for my speakers. I go to bigger speakers to HEAR the bass instead of staying on NS-10's and watching how the cone crinkles.
In studios that have outside engineers coming in and blowing speakers all the time the fuses are pretty much the most practical way to do... and you want the lowest amp rating you can get away with. Use a standard fast blow fuse. The ultra fast instrumentation ones just blow too fast and cost too much.
Leave a bucket of fuses available near the speakers and mount the fuse holders on the front of NS-10's. It's ugly but makes the whole process less of a pain in the butt. Buy fuses in bags of hundreds - you'll save a ton of money - and keep a waste basket nearby for the blown fuses to go into. Now... that said... I have seen few engineers pull 10 amp fuses out their pocket to avoid the annoyance of fuse pops.
There was a product made by Acoustilog in NY that was an active box and you ran speaker level through them. The speaker signal went in one set of binding posts and out another. In the box were some relays and a circuit bridging that bridged across the signal that monitored the level. You set the thresholds from the front of the box and it would just open up until you turn the volume down with trimmers behind the panel. This was some time ago - it could have been line level but the idea is the same.
These days, if we have a studio where the studio's clients just go nuts we slip a limiter in to the amp rack and lock the door. It pisses people off and if anyone asks me about it I say (and I tell the studio owners to say the same thing) with a straight face (important) that OSHA did a pop inspection and they laid down the law... it's either that or people have to wear hearing protection or the place is fined heavily. The client has to put up a bond to cover OSHA fines and/or damaged equipment before you'll take the limiters out and turn the other way. Sometimes this works and other times they don't buy it. Technically, if you are listening loud enough to blow speakers that are three or four feet from your ears, you are permanently damaging your hearing and, I think, you really are exceeding the OSHA guidelines for noise levels in the workplace.
None of this will stop me from building a custom monitor system for a client that wants to hit more than 130 dB clean... but I won't do it unless they sign release from liability.
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Topic: Fuse protecting NS10's (Read 5875 times)