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Protection for irreplaceable tweeters

R

resoundpdx

New Member
Hi folks-

Long time reader, first time poster here. I am looking for some experienced advice on a subject I know has a lot of history. I have read all I can find but still have a dilemma.

I have a pair of ultra rare speakers (Panasonic SB-636) with absolutely irreplaceable, very unusual tweeters. I want to make sure the tweeters are not blown inadvertently. They are rated at only 20w so you can see the danger.

The tweeters are nominally 8 ohms, but I have measured down to 6 ohms, as we all know impedance varies. The alternatives I have seen and considered:
1. Put a fast 2.5A or slow 2A fuse in series with each tweeter.
2. Ditto a circuit breaker.
3. Put head-to-head 10v zener diodes across each tweeter.
4. Put a fuse protection bulb in series with each tweeter.

Regarding #3, the zeners I can find max out at 5w (higher power ones exist, but are very large and $$$). So what happens when they see sustained power greater than this? In other words, would they fail as a short (thus protecting the tweeters) or as an open (not protecting the tweeters)?

Regarding #4, the fuse bulbs I can find seem to be designed for 40w tweeters, so might not be enough to protect mine.

I have spend a lot of time and treasure restoring these speakers, and don't want them to go up in smoke. Recommendations?
 
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Fuses would seem to be the way to go, I'd use much smaller than 2A though....
There's also a surefire way to not blow them - don't crank the volume and play them with reliable amplifiers.
 
Most tweeters are rated at a very low power handling, so yours are not unique in that aspect. The crossover limits the amount of power in their direction. Sending clipped signals is what damages tweeters, so don't push whatever you are using to drive them into clipping and you've got nothing to worry about.
 
ivandezande said:
Fuses would seem to be the way to go, I'd use much smaller than 2A though....
There's also a surefire way to not blow them - don't crank the volume and play them with reliable amplifiers.
Click to expand...
Indeed. I am always very careful in this regard. Worried about other family members...
 
F1nut said:
Most tweeters are rated at a very low power handling, so yours are not unique in that aspect. The crossover limits the amount of power in their direction. Sending clipped signals is what damages tweeters, so don't push whatever you are using to drive them into clipping and you've got nothing to worry about.
Click to expand...
Forgot to mention that the speakers overall are only rated at 40W.
 
ivandezande said:
Fuses would seem to be the way to go, I'd use much smaller than 2A though....
There's also a surefire way to not blow them - don't crank the volume and play them with reliable amplifiers.
Click to expand...
Fast or slo-blo? The 20 watt rating on the tweeters would seem to be continuous power. Since I will be mounting the fuses inside the cabinets, I am a little afraid of spurious blows of fast blow fuses. But rather have that than blown tweeters...
 
There are auto- resetting switches (fuse). I believe this is one type.
0.50 amp polyswitch.
I know little about them. But think they have been used in crossovers.
15566454112884161147728875792563.jpg
EDIT:
Of course, one help is turning down volume knob when changing sources and queuing records. And being only one running stereo.

If that's not in the cards:
How about a second pair of speakers if amp has A-B speaker selector? Have rest of family use the alternate pair of speakers.
 
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Old Guy8 said:
There are auto- resetting switches (fuse). I believe this is one type.
0.50 amp polyswitch.
I know little about them. But think they have been used in crossovers.
View attachment 1495018
Click to expand...

Polyswitches are commonly used in Klipsch crossovers. And they are also commonly removed from the circuit by many people when rebuilding the crossover (people like me).
 
A polyswitch acts much like a fast blow fuse, but resets itself after it cools down. However, it becomes hypersensitive after being tripped a few times. A fuse or polyswitch also affect the output of the tweeter, usually around .5 ohm of attenuation, which is audible.
 
A solution might be to extend the input wires to the tweeters to the outside of the cabinet and mount a fuse holder on the outside of the box. A fast-blow 1 A fuse is what I would use. As was mentioned, reasonable volume control and protection from clipping is a good way to accomplish your tweeter safety.
 
Thanks for all of the suggestions. Polyswitches are available from Parts Express in a variety of current ratings - but I had no prior experience with them so did not know if this was a viable option. I appreciate your collective insights on these, fuses, etc.
BTW, there is also an active, outboard speaker protection component at PE for $215 : "Eminence D-fend SA300 Loudspeaker Protection Unit". Now there is an economical solution!
I have been at this long enough to know that clipping is a real danger, so always have amps that have lots of reserve and keep them turned down low. Probably I am worrying too much. I am very conservative, generally listen to classical music, and have never blown any speakers in my long life. But since I had to scour the planet for these tweeters I am a bit gun shy.
 
I guess "economical" is subjective.
I think an 50 cent fuse and a $2 fuse holder is economical.

ADDED--It was economical until I realized two would be needed, one set for each speaker.
 
I put 0.5 amp fast blow fuses, for tweeters, in back panel mounted fuse holders of New Large Advents and model ones. Lowest value 1-1/4" glass fuse I could find. That done, I had no idea if the tweeters or fuse would go first, if pressed. Not being a speaker designer. I never pushed them anyway. Don't know that I felt less stressed after adding.
You could start with verry low value fuses and see if they trip with normal volume. And go up if do.
 
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Old Guy8 said:
I put 0.5 amp fast blow fuses, for tweeters, in back panel mounted fuse holders of New Large Advents and model ones. Lowest value 1-1/4" glass fuse I could find. That done, I had no idea if the tweeters or fuse would go first, if pressed. Not being a speaker designer. I never pushed them anyway. Don't know that I felt less stressed after adding.
You could start with verry low value fuses and see if they trip with normal volume. And go up if do.
Click to expand...

That's a reasonable solution, though I need to keep F1nut's caution in mind. I also need to think about location - these oddball speakers present some challenges in that realm. But I like the simple and adjustable (fuse rating) approach. Also will threaten the rest of the family with dire consequences if they touch or use these speakers ;-)
 
One thing I haven't seen mentioned yet is that those have a horn tweeter. I imagine there is a replaceable diaphragm, which may or may not be currently available. If you can find a part number on the tweeter driver section, you may be able to purchase replacement diaphragms which would be the best protection of all.
 
markshan said:
One thing I haven't seen mentioned yet is that those have a horn tweeter. I imagine there is a replaceable diaphragm, which may or may not be currently available. If you can find a part number on the tweeter driver section, you may be able to purchase replacement diaphragms which would be the best protection of all.
Click to expand...

Perhaps so. A good part of the horn is integral to the cabinet, but the tweeters themselves have a horn-like face. It might be that further disassembly would yield a more replaceable driver. I never investigated this with the original pair of tweeters (both toast when I bought the speakers to restore) I have not seen another "drop in" tweeter (same configuration and dimensions, without considering electrical specs), but it might exist. And I imagine the surgery necessary to replace the tweeter voice coils would be daunting. But at least I have a spare pair to experiment on...
 
resoundpdx said:
Perhaps so. A good part of the horn is integral to the cabinet, but the tweeters themselves have a horn-like face. It might be that further disassembly would yield a more replaceable driver. I never investigated this with the original pair of tweeters (both toast when I bought the speakers to restore) I have not seen another "drop in" tweeter (same configuration and dimensions, without considering electrical specs), but it might exist. And I imagine the surgery necessary to replace the tweeter voice coils would be daunting. But at least I have a spare pair to experiment on...
Click to expand...
Most are very similar...


Not all of them will have the plastic casing. Many will simply be the aluminum part and the coil.
 
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