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Discussion Starter #1 (Edited)
Using a capacitor to protect tweeter ; polyester vs. polypropylene

Hi,

in the system I'm putting together, crossovers will be handled by the Alpine head unit. However, I've read on this forum about someone putting capacitors in the tweeters' wires to protect them (in case someone messes with the HU settings for example).

Tweeter is 8 ohm, HP around 3 kHz. I've been told I'd need a 20uF cap.

I've contacted Meniscus Audio and they told me:
"We have a good [polyester] film cap at 20uf for $5.85 ea."

I've checked out their website and they also have Solen's polypropylene fast caps for 7.45 ea (20uF).

In this application will it make any difference to get polypropylene caps over polyester caps? I'd rather spend 3 more bucks if it's going to make any difference.

Thanks in advance.
 

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Re: Using a capacitor to protect tweeter from low frequencies "just in case"...

I've heard that polypropylene caps are the best. And Solen makes some very nice caps from what I've heard
 

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Re: Using a capacitor to protect tweeter from low frequencies "just in case"...

take a look at this image... you may want to save it and enlarge it.

it shows you the differences and I definatly think its worth 3 dollars.

http://www.capacitors.com/picking_capacitors/pick18lg.jpg


excellent stability, better at performing at diff. temperature, etc...
just about as good as it gets. (for capacitors at least)
 

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Re: Using a capacitor to protect tweeter from low frequencies "just in case"...

In my experience ribbon tweeters run fine without any protection capacitors from the active crossover. I don't really think the low frequencies will actually get through the crossover.
 

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Discussion Starter #5 (Edited)
Re: Using a capacitor to protect tweeter from low frequencies "just in case"...

Thanks for the chart IceWall. "Good at performing at different temperatures" might be important in Quebec : -30*C in the winter to 30*C in the summer (that's -22F to 86F) :D .

cotdt said:
In my experience ribbon tweeters run fine without any protection capacitors from the active crossover. I don't really think the low frequencies will actually get through the crossover.
I'm using 25NFAs, not ribbon tweeters.

I know low frequencies won't get through the crossovers if they're set-up correctly, this is just extra protection in case they aren't.

Opinion from Meniscus:

"There are those that can hear a difference in capacitors and that is why we
have a few brands. A good film cap is really all you need I think."


I think I'll go for the Solen caps anyway...
 
W

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Re: Using a capacitor to protect tweeter from low frequencies "just in case"...

I'd be happy with the cheaper caps. Here's why :

Regarding temperature coefficient ... which indicates how a cap's value will change with temperature ... it's just not an issue with a protection cap. If it were to be used in the main crossover, you sure wouldn't want the crossover frequency changing by ten or twenty percent over temperature swings. But if used properly, the cutoff or corner frequency of the protection cap should be at least an octave below the intended cutoff. And a ten or twenty percent shift that far below the real crossover won't matter much at all.

I'm all for tweeter protection caps. They help protect the tweeter from amplifier turn on/off transient pops (which occur after the active crossover), and they help protect against accidental tuning mistakes. But if used properly ... well below the intended crossover, where precision matters ... the value is just not that critical. So who cares if it drifts a bit with temperature?

Make sense?
 

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Re: Using a capacitor to protect tweeter from low frequencies "just in case"...

I don't think capacitor choice matters here at all. I don't even think adding a protection capacitor will make any difference. On the other hand, if you were building passive crossovers, I would recommend something more high-end than the Solens, since those remove detail and color the sound.

My point is that if ribbon tweeters don't need protection caps, then neither would dome tweeters in all likelihood.
 

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Re: Using a capacitor to protect tweeter from low frequencies "just in case"...

Ribbons should have protection cap on it. I tried playing ~750hz on them just to see what they would do, and the ribbon element were flapping around like crazy.
 
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Re: Using a capacitor to protect tweeter from low frequencies "just in case"...

I agree on the protective cap for ribbons :

www.diymobileaudio.com/forum/showthread.php?t=2

remember, the cap is there largely to protect the element from nasty, non-ideal things that amplifiers can do : DC offset, turn-on/off transients, etc. The active crossover will do nothing to protect the element from these nasties. I think the cap is also strongly recommended for ribbons, because the transformer inside the ribbon driver presents a VERY low impedance ... approaching a short circuit ... to the amplifier at very low frequencies, approaching DC.
 

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Re: Using a capacitor to protect tweeter from low frequencies "just in case"...

cotdt said:
My point is that if ribbon tweeters don't need protection caps, then neither would dome tweeters in all likelihood.


He wants them for protection like I did. Say you take your car to the shop and they need to pull the battery for some reason and your crossover settings are erased. Once they finish there work, they see your stereo and decide to give it a quick listen before you pick your car up... Now your tweet is blown cause it was receiving full range. <-------- tweet would not have been blown if he had that cap for protection.

Dave
 

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Re: Using a capacitor to protect tweeter from low frequencies "just in case"...

werewolf said:
because the transformer inside the ribbon driver presents a VERY low impedance ... approaching a short circuit ... to the amplifier at very low frequencies, approaching DC.

I agreed with everything you said till this.

maybe you said it wrong but its the transformer that gives it a useable load, without one would make it approach a short circuit.

and I would agree that for a protection cap it wouldnt make much difference what cap you choose... but when it comes to crossover parts I personally only accept the BEST that I can afford. I'm sure some of you know how frustrating it can be to pop a cap and either not have a tweeter connection anymore or blow the tweeter cuz it played fullrange.

if that was the case id just get higher voltage caps.

but maybe the better cap just gives me peace of mind :)
 
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Re: Using a capacitor to protect tweeter from low frequencies "just in case"...

no, I didn't say it wrong.

The ribbon itself is, of course, a very low impedance element. The transformer does indeed transform that impedance to a more friendly load for the amplifier ... but not at DC. At very low frequencies, the input impedance of the primary of the transformer is dictated by the so-called "magnetizing inductance", no matter what load is put on the secondary. This is why transformers do not have a usable bandwidth that extends down to DC ... the magnetizing inductance defines a low frequency pole, or cutoff.

So as you approach DC, the input impedance of the primary of any transformer approaches the DC resistance of the primary ... again, no matter what load is put on the secondary. You simply can't "see" the transformed secondary impedance at DC, because the ideal transformer action is shunted by the magnetizing inductance.

Now it may be that the DC resistance of the primary is large enough with ribbon transducers, so as not to cause any problems with most power amps. But what the heck, add the protection cap and all worries disappear :)
 
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Re: Using a capacitor to protect tweeter from low frequencies "just in case"...

Here's a quick link to demonstrate what I'm talking about ... namely, that transformers don't work at DC, leaving only the resistance of the primary winding as the input impedance at very low frequencies. Check the nominal impedance of the Fountek ribbon, compare to the DC resistance (DCR), and finally check the warnings at the end :

www.madisound.com/neopro5i.html
 

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Re: Using a capacitor to protect tweeter from low frequencies "just in case"...

Capacitor have 2 functions :
1. as high pass filter
2. as conditioner

Different capacitor's inside material will greatly affect how your tweeter sounds. You may get a cheapest bipolar cap to the most high end Mundorf silver/gold/oil cap and all of them sounds different.
But so far I only tried with cheapest bipolar vs Panasonic bipolar vs Visaton MKT caps and Visaton sounds the best.
 

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Re: Using a capacitor to protect tweeter from low frequencies "just in case"...

Capacitor have 2 functions :
1. as high pass filter
2. as conditioner

Different capacitor's inside material will greatly affect how your tweeter sounds. You may get a cheapest bipolar cap to the most high end Mundorf silver/gold/oil cap and all of them sounds different.
But so far I only tried with cheapest bipolar vs Panasonic bipolar vs Visaton MKT caps and Visaton sounds the best.
What's your point? :confused:

Are you saying that the type of cap matters when they are used as protection caps?
 

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Re: Using a capacitor to protect tweeter from low frequencies "just in case"...

Good timing. I am just installing my old 26NA and Gladius into a new car and was looking at the caps I used in my old installing, wondering whether I should leave them out or install them. I have some Bennic caps sized for protection, above the tweeter Fs but quite a bit under the xover frequency I will be using.
Am I going to hear them or not?
 

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Re: Using a capacitor to protect tweeter from low frequencies "just in case"...

Good timing. I am just installing my old 26NA and Gladius into a new car and was looking at the caps I used in my old installing, wondering whether I should leave them out or install them. I have some Bennic caps sized for protection, above the tweeter Fs but quite a bit under the xover frequency I will be using.
Am I going to hear them or not?
If they are of the appropriate value, then science says no you won't know they are there, but people say yes you will. That's the best answer I can give.
 

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Re: Using a capacitor to protect tweeter from low frequencies "just in case"...

If they are of the appropriate value, then science says no you won't know they are there, but people say yes you will. That's the best answer I can give.
Gotcha. Thanks. I don't think my ears are that good, and it's worth what would be to me an insignificant degradation to save my tweets from the pops. Actually, it's rather nice just not hearing those pops!
 
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