# Tweeter capacitor Location



## Alrojoca (Oct 5, 2012)

What is your preferred location?

By the amplifier just like many place their passive crossovers?

Or close to the Tweeter driver?

20uf freaking cap I want to install is huge, I wanted to avoid placing it inside the door card panel and thought the about the sail panel location but it is like a freaking D size battery in size.


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## trumpet (Nov 14, 2010)

Put it in a place where you can brace it to avoid stressing the wire connections. It can be anywhere in the circuit. Electrolytic non-polar, 85C, 50V. It should not be that large.


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## REGULARCAB (Sep 26, 2013)

He may have one of the larger 250v varieties or the like. But i agree brace it somewhere so you dont stress the leads. It can go anywhere you like on the positive or negative run (as long as you are just running the cap)


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## SkizeR (Apr 19, 2011)

REGULARCAB said:


> He may have one of the larger 250v varieties or the like. But i agree brace it somewhere so you dont stress the leads. It can go anywhere you like on the positive or negative run (as long as you are just running the cap)


so a cap will work as a high pass filter even if its on the negative side of the speaker wire?


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## REGULARCAB (Sep 26, 2013)

A little caption from bcae1.com

"6dB/octave High Pass Crossover:
The diagram below shows how capacitors would be used/connected in a high pass passive crossover system. Notice how one capacitor is in a positive wire and one is in a negative wire. Audio is an AC voltage which means that current flows both ways in the circuit. For a simple crossover like this, it doesn't matter which terminal you have the capacitor connected to. The same is true for the inductors in the next section."


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## Alrojoca (Oct 5, 2012)

Thanks for the advice.


yes, it is a 250V the only options were 400 and 250V.

This is just for protection not quite a passive use.


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## REGULARCAB (Sep 26, 2013)

Alrojoca said:


> This is just for protection not quite a passive use.


Kind of the same deal  But yeah they are a little larger wich isnt really a bad thing. Just make sure she is secure and dry and you are good to go.


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## Pitmaster (Feb 16, 2010)

REGULARCAB said:


> A little caption from bcae1.com
> 
> "6dB/octave High Pass Crossover:
> The diagram below shows how capacitors would be used/connected in a high pass passive crossover system. Notice how one capacitor is in a positive wire and one is in a negative wire. Audio is an AC voltage which means that current flows both ways in the circuit. For a simple crossover like this, it doesn't matter which terminal you have the capacitor connected to. The same is true for the inductors in the next section."


Good stuff! Where's that thank you button...


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## Alrojoca (Oct 5, 2012)

REGULARCAB said:


> Kind of the same deal  But yeah they are a little larger wich isnt really a bad thing. Just make sure she is secure and dry and you are good to go.


Should I Shrink wrap it also? I was planing to do that, Solder or bullet connectors?


I have to check out your build project thread I need to catch up and pick up


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## CrossFired (Jan 24, 2008)

Not much protection. Try a 10 uf cap for 6 ohms.




Alrojoca said:


> Thanks for the advice.
> 
> 
> yes, it is a 250V the only options were 400 and 250V.
> ...


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## REGULARCAB (Sep 26, 2013)

Alrojoca said:


> Should I Shrink wrap it also? I was planing to do that, Solder or bullet connectors?


I would twist and solder for a nice solid mechanical connection, then as always heatshrink any exposed metal.


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## amomacko (Sep 14, 2010)

Caps wired in series with a tweeter can be used to protect tweeters in the event your amp has or starts to have a DC offset (i.e. there is DC voltage on the speaker lines). It doesnt matter if the cap it is on the positive or negative lead going to the tweeter. 

All caps will block DC. The issue is what other fequencies will the capacitor block? 

One should choose a capacitor large enough so that it's 3db down attenuation point is at a frequency that is lower than the lowest frequencies to be played through the tweeter. 

A single capcitor in series with the tweeter creates a high pass filter. The frequency at which the 3db down attenuation point ocures is a function of the size of the capacitor and the impedance of the tweeter.

Here is a great table that lets you choose what cap size, 3db attenuation point for a given tweeter impedance.

 Crossover Chart and Capacitance vs. Frequency Calculator(High-pass)

For expample, one has a 4 ohm tweeter and wants to cross it over at 2000 Hz. To select the DC blocking capacitor size I would 1/2 the desired cross over frequency (one octave down) 2000Hz/2 =1000Hz. Then choose a capacitor size that is no smaller than the one listed in the table from the link above. In this example the cap should be larger than 39.75 uF. For my build I chose a 70uF cap - overkill yes. And yes they are big!

If you choose a 10uF cap (as suggested in a post above) with a 6 ohm tweeter the 3db down frequency would be 2600 Hz (you have to use the calculator futher down the page on the above link). In order to not have the DC blocking cap attenuate any frequencies in the pass band (the frequencies you want the tweeter to play) then you should cross over the tweeter no lower than 5.2 KHz. This may be a bit high and a larger cap may be a better choice.

You can use the above methodogy to choose a cap size based on desired cross over freq and tweeter impedance.


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## Alrojoca (Oct 5, 2012)

Thanks
I thought a 20uf cap will protect any tweeter either 4 ohms or 6 ohms for use with DSP active pass. For passive then the calculator needs to be used complicated with passives because I have heard different methods, like doubling the FS and use that to calculate it or like described here divide the FS and add the half to fs and use that to calculate it


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## Alrojoca (Oct 5, 2012)

Here is another calculator it is confusing

Passive Crossovers, Capacitor and Coil Calculator

and another one this one included the impedance for the mid bass driver

all give different values.

2-Way Crossover Designer / Calculator


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## t3sn4f2 (Jan 3, 2007)

amomacko said:


> Caps wired in series with a tweeter can be used to protect tweeters in the event your amp has or starts to have a DC offset (i.e. there is DC voltage on the speaker lines). It doesnt matter if the cap it is on the positive or negative lead going to the tweeter.
> 
> All caps will block DC. The issue is what other fequencies will the capacitor block?
> 
> ...


^this

The cap will also protect the tweeter from accidental DSP/amp crossover settings.


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## minbari (Mar 3, 2011)

SkizeR said:


> so a cap will work as a high pass filter even if its on the negative side of the speaker wire?


positive and negative is a bit of a misnomer in AC. its inverted or non-inverted, really. And yes it doesnt matter.


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## ATOMICTECH62 (Jan 24, 2009)

Just make sure the leads dont flex where they meet the cap.Those things are so fragile its a joke.Being the pack rat I am I have a tool box drawer full of them Ive pulled from cars that have the leads broke off flush with the end.If it ever does happen a dremal will take a couple MM out of the epoxy to expose just enough of it to solder a wire to.
Just a little DIY/FIY tip.


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## Alrojoca (Oct 5, 2012)

amomacko said:


> Caps wired in series with a tweeter can be used to protect tweeters in the event your amp has or starts to have a DC offset (i.e. there is DC voltage on the speaker lines). It doesnt matter if the cap it is on the positive or negative lead going to the tweeter.
> 
> All caps will block DC. The issue is what other fequencies will the capacitor block?
> 
> ...


I thought it was the complete opposite, try to choose a cap that will block frequencies just above the tweeters specs, using this method the cap will let frequencies below the caps specs risking damage, better sound? Probably, better mids wider range for the tweeter to play lower. Risky

I'm I missing something here?


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## amomacko (Sep 14, 2010)

The reason I use a cap is to protect the tweeter against DC. A commercial amp should not output DC (DC offset) but sometimes things go wrong and they do.

As stated above by t3sn4f2 a cap will also limit (attenuate) low frequencies from getting to the cap if one accidently sets the high pass crossover point to low for a tweeter.

A capacitor in series with a tweeter creates a high pass filter. This means it passes frequencies that are higher than the 3db down point and blocks frequencies that are lower than the 3db down point. The attenuation is not a hard stop but a curve that attenuates the signal more as the frequency of the signal get lower. 

The bigger the cap the lower (in frequency) the 3db down point is. This is why if you want to cross a tweeter over at a lower frequency, the cap needs to be bigger.

One choice for the 3 db down point, for a DC blocking cap, is an octave lower than the target crossover frequency (high pass) for the tweeter. An octave is twice a given frequency or 1/2 a given frequency. Some argue the 3db down point, for a DC blocking cap, should be 2 octaves away from the target crossover frequency. It is your choice. I usually choose a value that is one octave lower than the target cross over frequency for the tweeter.

With respect to the comment:

"try to choose a cap that will block frequencies just above the tweeters specs"

What spec are you refering too? If you choose a target frequency that is above the high pass frequency of the crossover you are casading another high pass filter at a frequency higher that the high pass filter of the crossover. 

If you choose the same frequency as the high pass crossover you will increase steepnesss of the crossover slope of the filter. If you choose a frequency significantly higher that the frequency of the high pass crossover you will end up with a gradual filter slope from the chosen frequency to frequency of the cross over and then the slope of the crossover will kick in at its 3 db down frequency.

One way to think of this is as follows:

Tweeters should play from a given frequency up to 20 kHz (the generally accepted upper limit of human hearing however, the upper limit varries from person to person). So say it was decided that a chosen tweeter was to play from 3 kHz up, then one would set the high pass point for their crossover at 3 kHz. The key word is high pass. This means the crossover allows frequencies higher than 3 kHz to go through or be passed to the tweeter. Frequencies below 3 kHz are attenuated or reduced or stoped from reaching the tweeter. 

So to not interfere with the crossover, one would choose a frequency for the 3 db down point of the DC blocking capacitor that is one octave (or two octaves - your choice) lower than the high pass frequency of the crossover. In this example (one octave lower is 3/2=1.5 kHz).

Hope this helps.


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## amomacko (Sep 14, 2010)

To address the OP comments earlier in this thread......

"I thought a 20uf cap will protect any tweeter either 4 ohms or 6 ohms for use with DSP active pass. "

If you choose the 3 db down frequency, for the DC blocking cap to be one octave lower than the desired crossover frequency and you are OK with crossing the tweeter over at the underlined values given below then the answer is yes

6 ohm tweeter, with a 20 uF cap => 3db down freq = 1325 Hz
Multiple by 2 to get lowest crossover freq => 1325 x 2 = 2650 Hz

4 ohm tweeter, with a 20 uF cap => 3db down freq = 1988 Hz
Multiple by 2 to get lowest crossover freq => 1988 x 2 = 3976 Hz

"For passive then the calculator needs to be used complicated with passives because I have heard different methods, like doubling the FS and use that to calculate it or like described here divide the FS and add the half to fs and use that to calculate it"

Hmmm not sure what that means but...when some passive filters are implemented they have a capacitor in series with the tweeter. In this case the DC blocking cap is already implemented.

I think the in second part of the above statement you may be confusing how to choose the crossover point vs choosing the 3 db down frequency so one can calculate the value of a DC blocking cap.

2 x fs is a rule of thumb that is often used to determine the lowest crossover freqency (high pass) for a given tweeter. A better approach is to look at distoration measurements and cross the tweeter high enough so it operates in the area where distortion is minimized. These two techniqes are really just starting points and optimal choice of crossover point is much more difficult to arrive at.


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## Alrojoca (Oct 5, 2012)

Thanks 
My knowledge and interpretation of the minus 3 db or plus 3 db and octaves is something that will take me time to learn and I may not want to get too deep in to it.

Basically without all the technical terms, you are saying, it is safe to use a cap to high pass frequencies above a lower spec frequency point given for the tweeter. 

from 1500Hz up to 20-22Khz even though the tweeter lower frequency spec is 3000 hz. Playing the tweeter from 1500Hz up to 2OKhz plus with the cap connected will not damage the tweeter.

And this can be applied to either a basic 1st order passive, cap connected in series with the tweeter and mid driver connected in parallel with the tweeter or biamping with DSP that can offer High passing from say 500Hz to 22Khz except that we would set the frequency on the DSP at around 3000Hz for the high pass? I guess the slope I am guess should be set at 12db.


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## ATOMICTECH62 (Jan 24, 2009)

My best friend and I put a system in his car using Morel supreme tweeters and morel EM dome midranges.We used caps that were 2oct down from his crossover frequencies.It was no big deal since he knew what he was doing.But.His wife and her girlfriends took the car out for a night of clubbing and ran the battery dead in one of the parking lots while smoking fatties,chugging bubbles and bumpin to Nelly and Usher.Those where her words.
You can pretty much guess the rest.Some really nice cute guy gave them a jump and they drove around the rest of the night bumpin with all crossovers disabled.She killed almost a $1k in domes.
I doubt it would have made any difference if they were only 1 octave down instead of 2 but I always think about those poor domes when designing active systems.
If 1 octave is used it will be down 1db at the crossover point if 2 octaves are used it will be close to .5db at the crossover point.Not much difference.I tend to stick to the 1 octave to be on the safe side and this is my reasoning.
When using a HP filter in the amp the only real threat is if the amp takes a dump and sends DC to the tweeter or if the amp has a turn off/on thump.But the biggest threat to tweeters,dome mids or even some small cones is if an active deck or processor is used upstream of the amp.Too many things can go wrong just like girls night out,loosing any RCA ground,unexpected ground loop causing motor noise or thumps from the brake pedal,turn signal,window/AC motor(this could happen in the deck,processor,stand alone crossover or amp),accidentally changing a slope or frequency,a dirt or scratchy push button or slide switch and the dreaded RCA coming unplugged with the system on.
Just the other day I was trying to narrow down a low output problem on one unknown channel by unplugging RCA's going into my amps with music playing.It wasn't till I saw one of the 8's jump about an inch I realized my total disregard for the AMT's and 2"domes that I had already unplugged a few times.Cold chills,then a sigh of relief.Ahh protection caps.They did their job.
I look at them like I do a gun.You are better off having one and never needing to use it then not having one when you really need it.


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## REGULARCAB (Sep 26, 2013)

Very well put.


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## amomacko (Sep 14, 2010)

ATOMICTEK62

That is a very interesting story - who would of "thunk" that the processor would loose its settings? Do you know what processor this happened with?

Alrojoca

"Basically without all the technical terms, you are saying, it is safe to use a cap to high pass frequencies above a lower spec frequency point given for the tweeter"

Very close - it is safe (and desirable) to insert a cap in series with the speaker to high pass frequencies above a frequency that is one octave below the chosen high pass cross over point for a given tweeter.

"from 1500Hz up to 20-22Khz even though the tweeter lower frequency spec is 3000 hz."

Correct - the DC blocking cap starts to attenuate the signal at a frequency lower than the cross over point chosen. This way the DC blocking cap does not interfere with or change the chosen cross over point. When you say "tweeter lower frequency spec" please understand that this is the cross over frequency that you choose, either by using the 2 x fs rule of thumb or by looking at distortion measurements for the tweeter.

"Playing the tweeter from 1500Hz up to 2OKhz plus with the cap connected will not damage the tweeter."

Correct - as the DC blocking capacitor is attenuating/reducing the signal starting at (and below) a frequency that is below the chosen cross over frequency.


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## Alrojoca (Oct 5, 2012)

Thanks for clearing that up amomacko, thanks Atomic for sharing that story.

To summarize this, higher value caps do not protect better than lower value caps but they are safe to use? or simply we should not be afraid to use a cap (just to throw a number since most 1-1.3 inh tweeters play at 3KHz) 1000hz below the lower frequency range for the tweeter.

Lower value caps tend to pass at or above the tweeter lower Freq spec.
Of course calculators should be used to get the correct cap value.

Only issue I see is with a higher value cap, the coil number increases and at what point will a coil be needed? using the 12volt site calculator it shows a coil value in millihenries, this value increases even with the 6 db slope per octave ( is the 6db slope also called one octave?)
A 6 ohm tweeter crossed at 1Khz calls for a 0.95 millihenry coil in most cases under 0.5 millihenrie coil using lower impedance tweeters.

The 12V site calculator when clicked on diagrams after the value is calculated, it does not show the coil, and it is only needed to be used as a bandpass perhaps to limit the upper range frequencies. I'll take that we should ignore the coil on the first order 6db one octave.


Passive Crossovers, Capacitor and Coil Calculator


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## ATOMICTECH62 (Jan 24, 2009)

How ironic is this?
I just got a call from a DIY member.He has been having problems with intermittent motor noise.Today he said one of his tweeters started smoking so he shut it down.I ask if he had a cap on his tweeters,his answer was "No".


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## amomacko (Sep 14, 2010)

Hi Alrojoca

I address your questions

"To summarize this, higher value caps do not protect better than lower value caps but they are safe to use?"

They are very safe to use

"or simply we should not be afraid to use a cap (just to throw a number since most 1-1.3 inh tweeters play at 3KHz) 1000hz below the lower frequency range for the tweeter."

A reasonable choice for the target freqency for the 3db down point when selecting a cap to block DC is 1 octave down from the crossover point. So with your example above, and choosing a 3 KHz crossover point then one octave lower is 1.5 KHz. This is 1.5 Khz lower than 3 KHz and not 1 KHz as you ahve used in the example. It is probably best to stick to the formula and not choose fixed values. So if one had a 2 way systemn and was crossing the tweeter over at 2 KHz (note: Not all tweeters can play this low) then the target 3 db down point for the DC blocking cap is 2 KHz / 2 = 1 KHz.

"Lower value caps tend to pass at or above the tweeter lower Freq spec.
Of course calculators should be used to get the correct cap value."

Sorta correct. It is true to say that caps with lower values have a 3 db down point that is higher in freqency. Whether a cap with a low value will pass at or above the tweeter lower frequency cross over point depends on what the cap value is, the impedance of the tweeters, and the chosen frequency to cross the tweeter over at.

"Only issue I see is with a higher value cap, the coil number increases and at what point will a coil be needed? using the 12volt site calculator it shows a coil value in millihenries, this value increases even with the 6 db slope per octave ( is the 6db slope also called one octave?)
A 6 ohm tweeter crossed at 1Khz calls for a 0.95 millihenry coil in most cases under 0.5 millihenrie coil using lower impedance tweeters"

Now you have gone and changed the topic! We were discussing using capacitors as DC blocking filters. Coils are not required to block DC! It is true that a combination of caps and coils produces filters often of higher order than a single cap. But for blocking DC (and provinding some protection against other low frequencies that might make their way to a tweeter) coils are not required!

If you are running a processor (thats where this thread started) and you are trying to implement a DC blocking cap then coils are not required. I strongly recomend one uses the web page below to calculate the cap value based on the tweeter impedance and chosen 3 db down frequency for the DC blocking cap.

Crossover Chart and Capacitance vs. Frequency Calculator(High-pass)


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## Alrojoca (Oct 5, 2012)

Okay thanks again. Any changes in cap value when using a processor DSP then? based on the information it looks like by having a higher cap value, the only thing we need to do is using the processor to set the freq right at the tweeter crossing point or always higher than the cap's freq setting. Using the same example again the cap high passes at 1.5khz and the processor somewhere above the 1.5Khz or right around 3K or wherever it sounds better depending on the midbass driver's crossing point. Meaning no need to change the cap value.

Thanks again for your help


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## amomacko (Sep 14, 2010)

Alrojoca

A few more answers....

"Any changes in cap value when using a processor DSP then?"

Nope

"based on the information it looks like by having a higher cap value, the only thing we need to do is using the processor to set the freq right at the tweeter crossing point or always higher than the cap's freq setting"

The cross over should be set at minimum 2x the 3 db down frequency of the DC blocking cap.

"Using the same example again the cap high passes at 1.5khz and the processor somewhere above the 1.5 Khz or right around 3K or wherever it sounds better depending on the midbass driver's crossing point."

Use the 2x cap freq rule to get the minimum crossover frequency - then with your example the minimum crossover freqency is 3 KHz not lower - so not just somewhere above the 1.5Khz - it should be at a mimium 3 Khz or higher.

My I suggest changing your approach?

First select the crossover frequency for the tweeters. 

Then divide the crossover frequency by 2

Take the result and calulate the cap size (for Blocking DC) using the web page I posted previously. You will need to know the impedance of the tweeter.

For my system I use a 70uF cap with a 4 ohm tweeter. The cap will pass all frequencies above 567 Hz. This means the lowest I can set the tweeter crossover to is 576 x 2 = 1152 Hz. I am not concerned as I actually cross my tweeters over at 3.5 KHz. Which is way above 1152 Hz. Remeber the cap passes high frequencies and blocks lower frequencies (including DC). The crossover frequency is way above the DC blocking cap 3 db down frequency so it has no effect on the crossover setting. Thats what we want!


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## Alrojoca (Oct 5, 2012)

Gotcha! Perfect thanks
I Guess now since I got two 20uf caps If I need to I can connect 1 extra cap in series with the 20uf to get to the value I need to be at.


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## minbari (Mar 3, 2011)

Alrojoca said:


> Gotcha! Perfect thanks
> I Guess now since I got two 20uf caps If I need to I can connect 1 extra cap in series with the 20uf to get to the value I need to be at.


I didnt read all this, but remember, caps in series, the uF value gets smaller. In parallel, the uF value gets larger 

sent from my phone using digital farts


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## Alrojoca (Oct 5, 2012)

minbari said:


> I didnt read all this, but remember, caps in series, the uF value gets smaller. In parallel, the uF value gets larger
> 
> sent from my phone using digital farts


Mmmm okay, sounds complex better get the right value then, thanks.
I think the 20 if by itself would be ok just passes a bit higher than the point needed giving it a bit of extra protection from lower freq.

Curious about your take on this approach, being that one single cap value is good for 1st order passive and also for active, convenient and economical 
Thanks.


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## minbari (Mar 3, 2011)

http://www.the12volt.com/caraudio/crosscalc.asp#ccc

Nice easy site to use. Input your ohm rating for the tweeter, then put in the freq you want. Larger the cap, the lower it will be.

sent from my phone using digital farts


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