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



## 346 (Aug 22, 2005)

*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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## atomicquad (Sep 19, 2005)

*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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## IceWaLL (May 30, 2005)

*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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## cotdt (Oct 3, 2005)

*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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## 346 (Aug 22, 2005)

*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)  .



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...


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## Guest (Nov 23, 2005)

*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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## 346 (Aug 22, 2005)

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



werewolf said:


> Make sense?


Perfect sense .

Thanks!


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## cotdt (Oct 3, 2005)

*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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## 95Legend (Jun 24, 2005)

*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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## Guest (Nov 23, 2005)

*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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## FaintReality (May 15, 2005)

*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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## IceWaLL (May 30, 2005)

*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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## Guest (Nov 24, 2005)

*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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## Guest (Nov 24, 2005)

*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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## t3sn4f2 (Jan 3, 2007)

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

Bump.


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## kyheng (Jan 31, 2007)

*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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## t3sn4f2 (Jan 3, 2007)

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



kyheng said:


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


What's your point? 

Are you saying that the type of cap matters when they are used as _protection caps_?


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## sigma6 (Mar 28, 2006)

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



t3sn4f2 said:


> Bump.


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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## t3sn4f2 (Jan 3, 2007)

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



sigma6 said:


> 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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## sigma6 (Mar 28, 2006)

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



t3sn4f2 said:


> 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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## kyheng (Jan 31, 2007)

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



t3sn4f2 said:


> What's your point?
> 
> Are you saying that the type of cap matters when they are used as _protection caps_?


Yes sir..... 
Bare in mind that protecting a tweeter is 1 thing, but most importantly, we want a good sounded system. I guess this will be the ultimate goal for everyone regardless of location they are. Not necessary you have to follow me to use MKT caps, but atleast try 2 different types and you might be amazed on wonders of quality of cap affecting the sound.


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## 14642 (May 19, 2008)

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

Maybe my ears are broken. I never hear the benefits of all of this esoteric stuff. Maybe I should remove the books from my ears and replace them with brochures. Think that would help?


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## trebor (Jun 30, 2008)

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

Maybe someone can help me, I'm wanting to use safety caps and am using autoformers to move impedance up on some compression drivers. To get the right safety cap value, am I to use the impedance with the autoformer installed or just the impedance of the driver itself?


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## kyheng (Jan 31, 2007)

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

I guess by just putting a cap is good enough.


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## NSTar (Feb 24, 2010)

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



t3sn4f2 said:


> What's your point?
> 
> Are you saying that the type of cap matters when they are used as _protection caps_?


I'm confused myself... doesn't the signal run through it no matter if it's used as protection or not as long as it's there?...so, it does matter.


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## t3sn4f2 (Jan 3, 2007)

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



NSTar said:


> I'm confused myself... doesn't the signal run through it no matter if it's used as protection or not as long as it's there?...so, it does matter.


True. It would matter to those that think highend caps improve the sound then.


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## NSTar (Feb 24, 2010)

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



t3sn4f2 said:


> True. It would matter to those that think highend caps improve the sound then.


agreed, as long as it does improve sound..then it matters.


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## lycan (Dec 20, 2009)

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

"everything matters" is a non-productive philosophy ... because you have no way to _quantify_ if you should spend $1, $5, $10, or $100 for each capacitor & resistor in your system.

So let's break it down a bit, and QUANTIFY the protection cap a bit more 

What can possibly cause a capacitor to be a "crappy" one? And how much will that matter for a _protection_ capacitor, compared to a _crossover_ capacitor?

1. *Error in absolute value*. If the _crossover_ cap is in error by, say, 10% ... then the crossover frequency will be wrong by 10%. Could VERY well be audible ... causing a peak or dip in the system response. Now if a _protection_ cap value is in error by 10%, the impact on system response will be MUCH less severe ... because the high-pass frequency response is, by design, well _below_ the intended crossover frequency.

2. *Temperature drift*. This is very similar to the category above. The "sensitivity" to temp drift in the value of the protection cap is MUCH less severe, because of where the high-pass frequency is.

3. *Voltage coefficient*. This describes a nonlinear distortion mechanism, and it's magnitude will depend on the magnitude of the voltage across the cap. For a _crossover cap_, this may be a concern ... at the crossover frequency, the voltage across the cap is on the order of the voltage across the tweeter. But for a _protection_ cap, the active crossover in front of it (combined with where the protection high-pass frequency is) always makes sure that the voltage across the protection cap is SMALL (in other words, if the voltage across the protection cap were large ... or on the order of the voltage across the tweet ... in normal operation, the protection cap would be doing a lot more than "protecting"!). So once again, the protection cap is much more "tolerant" of this particular anomaly.

*Bottom line* : don't waste too much money on the "sonic quality" of the protection cap. YES, it is in the signal path. But we must look in much more detail, to determine the _value_ of where we choose to spend finite money.


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## RattyMcClelland (Nov 28, 2008)

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

Iv got a poly 12uF cap after the amps on my HAT L1pro SE. Apart from the headunit what else is there to protect a £450 tweeter. A £15 cap does the job.

But im so glad i have. On a number of occasions i have disconnected my battery and then reconnected and played music as normal forgetting that my saved settings on my headunit will have disappeared and the tweeter outputs by default are at full range. The cap protects it and gives a crossover slope of 6db/oct at around 2k.

I personally hear no change in sound with the caps in or out.


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## southpawskater (Feb 17, 2010)

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

I have been searching this forum all day (instead of working :laugh and have yet to find if there is a calculation or a reference chart as to what value cap to use for what crossover settings. If any one has this information or a link to it I would greatly appreciate it. Sorry if I missed something already discussed.


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## SQ_Bronco (Jul 31, 2005)

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



southpawskater said:


> I have been searching this forum all day (instead of working :laugh and have yet to find if there is a calculation or a reference chart as to what value cap to use for what crossover settings. If any one has this information or a link to it I would greatly appreciate it. Sorry if I missed something already discussed.


Passive Crossovers, Capacitor and Coil Calculator


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## southpawskater (Feb 17, 2010)

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

SQ_Bronco, thanks a million! :thumbsup:


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## Pdogg (Jan 24, 2011)

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

Would it not make sense to also add some kind of current-limiting device to protect the tweeter? Like say a fuse or PTC or heck even a light bulb?


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## kyheng (Jan 31, 2007)

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

Can...


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## SSSnake (Mar 8, 2007)

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

Only if you are afraid of accidentally running too much power to them in the intended passband of the tweeter. Then which will blow first the tweet or the fuse? Just something to consider...

Typically I say no but several manufacturers used current limiting solutions on tweets for their full range boxes. However, this was specifically to limit customer abuse issues.


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## t3sn4f2 (Jan 3, 2007)

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



cajunner said:


> my bought in '80 home speaker boxes (technics 10" 3-ways) had a protection reset that saved those tweeters for a long time.
> 
> I used to light those puppies up all the time, I think it's a great idea if frying your tweeters presents as a problem.
> 
> ...


And it's even harder to do in a biamped setup where the often clipped lower midrange frequencies and resulting harmonics from the amp channel can not travel into the tweeter and increase its average input.


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