# Tweeter Capacitor Selection / Did I do this right?



## Adrock (Jan 21, 2019)

I have searched for this specific question and I scoured the internet for the answer. Can someone take a look at what I have come up with and let me know if I am making the right choice? This is my first dive into an active setup and I want to make sure I have a layer of protection on the tweeters in case I make a mistake. 

I am using a set of Morel Hybrid 602's with an AudioControl D-4.800 amp. I took a picture of the MT230 tweeter specs to help explain my selection. 










I am going to start my crossover point at double the FS of the tweeter. So 2400 hz at a 24db slope. (the DSP is 12db or 24db selectable). I used posts from respected speaker designers and others to formulate the following and I also have used calculations and calculators available from various sources. I just couldn't find the answer I needed in other posts on the site etc. 

I found that while the ohms of the tweeter is important, it is better to equate the capacitor to the DC resistance of the tweeter and the desired freq. cutoff. I tested the tweeters and both are spot on at 5.28 resistance DC. By using the calculations I found that a 17uf non-polarized electrolytic capacitor will yield protection to 1771.39 hz. This is within the freq. range of the MT230 (1600 hz - 25000 hz)tweeter and is a little more than 600 hz below my crossover point. If I ran a 12uf and a 6.8uf capacitor in parallel, than I would be protected down to 1601.79 hz. The 17uf is currently the cheapest option. 

Now, the million dollar question...... Does the protection need to be within the freq. range of the tweeter, or should it be slightly below the lowest range of 1600 hz? I just cant seem to find any information on what people generally shoot for when selecting the capacitor and if it really has any affect on the performance of tweeter if it is to close to the selected crossover point. 

Any input would be greatly appreciated. :beerchug:


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## miniSQ (Aug 4, 2009)

Andy can explain it better than i can.

https://www.audiofrog.com/community...p-tweeters-in-systems-with-active-crossovers/


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## Adrock (Jan 21, 2019)

miniSQ said:


> Andy can explain it better than i can.
> 
> https://www.audiofrog.com/community...p-tweeters-in-systems-with-active-crossovers/


Thanks for looking out. I have read that already and it was very useful. 

While he mentions that you want the protection outside of the desired frequency range of your crossover point, I don't have the ability to plot the slope (terminology?). And if a cap at 1800 hz is low enough to have no affect on the over SQ of the initial crossover point. And if I wanted to lower the crossover point during tuning, would a frequency of 1771 hz limit how low I can set my crossover point without having a noticable affect on SQ? I may also want to try a 12db slope and would hate to have the cap hinder tuning. 

So, the ultimate question is if it is better to shoot for the lowest freq. range of the tweeter, or can the target freq. of the cap go lower than the stated lowest freq range of 1600 hz, or if the current range of 1771 hz is more than sufficient to give me room for tuning?


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## miniSQ (Aug 4, 2009)

Adrock said:


> Thanks for looking out. I have read that already and it was very useful.
> 
> While he mentions that you want the protection outside of the desired frequency range of your crossover point, I don't have the ability to plot the slope (terminology?). And if a cap at 1800 hz is low enough to have no affect on the over SQ of the initial crossover point. And if I wanted to lower the crossover point during tuning, would a frequency of 1771 hz limit how low I can set my crossover point without having a noticable effect on SQ? I may also want to try a 12db slope and would hate to have the cap hinder tuning.
> 
> So, the ultimate question is if it is better to shoot for the lowest freq. range of the tweeter, or can the target freq. of the cap go lower than the stated lowest freq range of 1600 hz, or if the current range of 1771 hz is more than sufficient to give me room for tuning?


He suggested crossing the tweeter over around 600hz (68uf). Well below the usable range of the tweeter.


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## maybebigfootisblurr (Nov 4, 2011)

Could the crossover point on the spec sheet you posted essentially be the "recommended" initial setting? Might be enough to get you solid numbers to crunch.


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## Adrock (Jan 21, 2019)

Ok, so the issue with the post from Andy is that all of the screen shots are gone. I read the post and re-read it and then read it again. Its hard to know the parameters of the tweeters he is using because of this. There are some replies in that forum asking for how he made his selection and his response was that the value doesn't really matter as long as its below the selected crossover point. 

However, in my research it has been indicated by others that a capacitor too close to the chosen crossover frequency can cause issues in phase shift and time alignment etc. That the general rule of thumb is to protect at least two octave or more below the active crossover frequency selection. 

By using that rule of thumb you can possibly use the information in Andy's post to draw conclusion to his capacitor selection. His crossover point is 24dB/oct Linkwitz-Riley high pass filter at 2.5 kHz. 2 Octave rule would yield 625 Hz. He said that the tweeter has a nominal impedance @ 4 ohms and chose a 68uf cap. By calculation that would be a freq. of 584.56 Hz, which is just below the 625 Hz 2 octave rule. I bet that with some work and multiple caps the 625 Hz could be more closely obtained, but it appears that it might not be that imperative? His post also doesnt list the DCR for the tweeter and his last post indicates that this is what you want to calculate with. With that in mind and guessing the DCR, it appears the the 68uf cap is now very close to that 2 octave rule.

I am just so unfamiliar with this process and what a tweeter can handle as far as a cutoff point to not sustain damage..... 585 Hz seems really low for a tweeter, but the figures don't lie, that's what he chose for protection. So, utilizing that logic I could get close to the 2 octave rule for a 24db slope at 2.4 kHz by using a 50uf cap. It would be 602 Hz @ 5.28 DCR. If I do go with a lower crossover freq. I might be out of the rule of thumb, but it wouldn't be by much. Only by about 50 Hz if I went with the Morel crossover point of 2.2 kHz. 

This stuff is so interesting! Any thoughts on these findings?


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## Z-Nuttz (Jan 20, 2011)

Following, as I’m thinking of cap size as well for my upcoming install.

I have the morel hybrid 602’s as well. Just need to decide on amp/dsp. 

Have you noticed the owners manual lists mt230 as 6 ohm, yet 4 ohm is clearly stamped on back of tweeter? Not sure it makes a big difference either way??


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## Adrock (Jan 21, 2019)

Z-Nuttz said:


> Following, as I’m thinking of cap size as well for my upcoming install.
> 
> I have the morel hybrid 602’s as well. Just need to decide on amp/dsp.
> 
> Have you noticed the owners manual lists mt230 as 6 ohm, yet 4 ohm is clearly stamped on back of tweeter? Not sure it makes a big difference either way??


Interesting.... I just pulled mine and they do say 4 ohms on the back. The DC resistance I measured matched the specs sheet though. I measured 5.28 and the spec sheet shows 5.2. I think it would be safe to say that if the calculations are based on the DC resistance as Andy stats in his post, we should be alright. 

Can you measure the DC resistance of your MT230's and see how it compares?


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## Z-Nuttz (Jan 20, 2011)

I’m away from the house and will be for at least another couple weeks.

So that’s the ohm reading you’re getting I take it? I’ve never done that before, however I added some parts express caps to my previous install but don’t remember what value I chose. They were large though (think D battery size) and may have been close to $20 a side.

I’m thinking for my previous 4 ohm tweets the value was 800-1000 high pass as my crossover was 2500-3000 or so.

I spent some time calculating values on the12volt website, which helped tremendously. The site does mention +-5% of your target.


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## bluesman1 (Mar 2, 2010)

Honestly, I think you are overthinking this. He probably chose the 68uf cap because it's a common value. You can find in between values but very common values above and below 68uF are 80uF and 50uF. If he was shooting for 2 octaves below the crossover point and the closest, common cap value (68uF) put him at 585Hz instead of 625Hz, he probably said good enough and called it a day. But that's just an educated guess.


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## Adrock (Jan 21, 2019)

bluesman1 said:


> Honestly, I think you are overthinking this. He probably chose the 68uf cap because it's a common value. You can find in between values but very common values above and below 68uF are 80uF and 50uF. If he was shooting for 2 octaves below the crossover point and the closest, common cap value (68uF) put him at 585Hz instead of 625Hz, he probably said good enough and called it a day. But that's just an educated guess.


Yeah..... That's exactly what I already said.


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## Holmz (Jul 12, 2017)

The beauty of the 68 uF is that they sit perfectly in a 1/2 conduit metal clip.
If you are not screwing that into a wooden box, then it is not that beautiful.

Probably best to be around 20uF if you think you will be plugging them into a woofer channel and not realise it for a long time.
If it is just for turn on pops and similar, then the 68uF makes sense.

The values, 25, 33, and 47 uF are also able to be cogently argued.
33 is a nice number. Not as nice as 33-1/3 but close enough.

17 is also a fine choice.


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## Adrock (Jan 21, 2019)

So I just found a post by Andy where he specifically stated what capacitor to use.... 

"Note: Use capacitors on the tweeters in an active system. This is to protect the tweeters in case of a malfunction, incorrect crossover settings or a customer who fiddles with the settings. Choose a capacitor that provides a filter frequency that at least an octave below the crossover frequency you’ll use in your DSP. Good starting values are somewhere between 30uF at 60uF. This isn’t critical. This won’t have any effect whatsoever on the tune, but it will prevent damage. Blown tweeters aren’t defective."

This was in a part 5 of a time alignment post. 

https://www.audiofrog.com/community/tech-tips/time-alignment-part-5-putting-it-all-together/

One octave below crossover? Seems there are varying opinions on the matter.


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## miniSQ (Aug 4, 2009)

Adrock said:


> So I just found a post by Andy where he specifically stated what capacitor to use....
> 
> "Note: Use capacitors on the tweeters in an active system. This is to protect the tweeters in case of a malfunction, incorrect crossover settings or a customer who fiddles with the settings. Choose a capacitor that provides a filter frequency that at least an octave below the crossover frequency you’ll use in your DSP. Good starting values are somewhere between 30uF at 60uF. This isn’t critical. This won’t have any effect whatsoever on the tune, but it will prevent damage. Blown tweeters aren’t defective."
> 
> ...


at least an octave below the crossover frequency is what he said. Stop over thinking this, you are basically just trying to protect the tweeter from bass notes. You are not concerned with SQ here. It won't matter.


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## Adrock (Jan 21, 2019)

miniSQ said:


> Adrock said:
> 
> 
> > So I just found a post by Andy where he specifically stated what capacitor to use....
> ...


I'm trying to learn something here and I am sharing what I find. Last I checked this is the technical discussion thread. Sorry if trying to find a definitive and correct answer to share is a frustration for you. If you don't like it, you don't have to do contribute. And judging by your last post, you're not contributing!


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## miniSQ (Aug 4, 2009)

Adrock said:


> I'm trying to learn something here and I am sharing what I find. Last I checked this is the technical discussion thread. Sorry if trying to find a definitive and correct answer to share is a frustration for you. If you don't like it, you don't have to do contribute. And judging by your last post, you're not contributing!


Sorry, but there is nothing technical or advanced about adding bass blocker to a tweeter in order to protect if from a malfunction. But not my post, so i am happy to step out.


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## SkizeR (Apr 19, 2011)

47uf or higher. the caps crossover should not be interfering with at least the first octave of your ACTUAL crossover


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## Adrock (Jan 21, 2019)

miniSQ said:


> Sorry, but there is nothing technical or advanced about adding bass blocker to a tweeter in order to protect if from a malfunction. But not my post, so i am happy to step out.


There is nothing technical about choosing the correct capacitor to add enough protection for your tweeter while avoiding creating potential phase shift/eq'ing/TA issues? Or using formulas to chose the correct capacitor(s) to obtain your goals on an active speaker setup? Doesn't seem like a run of the mill setup that is entry level audio tuning to me..... I didn't find an answer to the question where all the information was located in one place so if this helps someone else that's my goal. Seems like that's what this site is touted as being about. Maybe I'm wrong? Maybe the sticky at the top of this discussion forum is wrong too? But the more I read other posts it seems like peoples opinions about the way things go on this forum have changed over the years. It's about ego rather than contribution.

But at least you tried to save face and throw some shade at the same time. So, I guess you contributed that.


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## miniSQ (Aug 4, 2009)

Adrock said:


> There is nothing technical about choosing the correct capacitor to add enough protection for your tweeter while avoiding creating potential phase shift/eq'ing/TA issues? Or using formulas to chose the correct capacitor(s) to obtain your goals on an active speaker setup? Doesn't seem like a run of the mill setup that is entry level audio tuning to me..... I didn't find an answer to the question where all the information was located in one place so if this helps someone else that's my goal. Seems like that's what this site is touted as being about. Maybe I'm wrong? Maybe the sticky at the top of this discussion forum is wrong too? But the more I read other posts it seems like peoples opinions about the way things go on this forum have changed over the years. It's about ego rather than contribution.
> 
> But at least you tried to save face and throw some shade at the same time. So, I guess you contributed that.


You have misunderstood what i am trying to say. With so many things in car audio complicated enough to spend time researching them, this is not one of them. No shade, no ego. I have been coming here for 15plus years trying to help people and also get help.


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## bluesman1 (Mar 2, 2010)

Adrock said:


> Yeah..... That's exactly what I already said.


Sorry. Wasn't my intent to step on your toes.

Good luck with it.


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## Blu (Nov 3, 2008)

Adrock - not sure if you came across this recent post that is very similar in nature to your posting here.

https://www.diymobileaudio.com/forum/technical-advanced-car-audio-discussion/414193-do-i-need-capacitors.html

There is some good information therein - and if you look, you will find the formula for calculating Safety Capacitor values to be used in conjunction with an Active Crossover system as you are discussing.

Not to be confused with formulas to determine passive Networks (using both Capacitors AND Inductors).

Hope this helps


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## Holmz (Jul 12, 2017)

Adrock said:


> So I just found a post by Andy where he specifically stated what capacitor to use....
> 
> "Note: Use capacitors on the tweeters in an active system. This is to protect the tweeters in case of a malfunction, incorrect crossover settings or a customer who fiddles with the settings. Choose a capacitor that provides a filter frequency that at least an octave below the crossover frequency you’ll use in your DSP. Good starting values are somewhere between 30uF at 60uF. This isn’t critical. This won’t have any effect whatsoever on the tune, but it will prevent damage. Blown tweeters aren’t defective."
> 
> ...


While he is generally correct, and certainly correct in this specific example...
If one actually plugged the tweeters into the woofer channel, then the 17uF would be limiting the energy below the trweeter's lower limit to be almost nothing.
One octave down is a lot of energy in the region where the tweeter would loose its magic smoke.

If you are using it as general protection, then 47 uF is probably good, and it will have less effect upon the DSP's tuning.

If you want to make it more "bone head proof", then 17 uF is arguably better.

Either number, or no capacitor, are also options... I have no dog in the fight.
So I can argue for high low and no capacitor equally.

By the way, does the moniker "Adrock" imply "Kid"?
(I read it that way, which is musically influenced.
If it does then the obserservation should come across as a compliment, and if not then please do not take it as an insult)


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## Adrock (Jan 21, 2019)

Holmz said:


> While he is generally correct, and certainly correct in this specific example...
> If one actually plugged the tweeters into the woofer channel, then the 17uF would be limiting the energy below the trweeter's lower limit to be almost nothing.
> One octave down is a lot of energy in the region where the tweeter would loose its magic smoke.
> 
> ...


Thanks. I have never brought a tweeter down to so low of a frequency that it fried it, so that was one of my concerns. I guess I've been lucky so far. 

2 octaves seemed like a lot. One octave, not as bad. A 33uf would put protection on my specific tweeter down to 920ish hz which is below an octave. Too low? Maybe I'll just give the 33uf a shot and hope for the best. The next easy step up is 22uf and that would be in the 1370 hz range.

BTW, it is homage to the Kid Adrock. Beastie Boys have been in my weekly rotation since License to I'll.


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## Holmz (Jul 12, 2017)

Adrock said:


> Thanks. I have never brought a tweeter down to so low of a frequency that it fried it, so that was one of my concerns. I guess I've been lucky so far.
> ...


Or you were careful not to make the rookie mistake.




Adrock said:


> ...
> 2 octaves seemed like a lot. One octave, not as bad. A 33uf would put protection on my specific tweeter down to 920ish hz which is below an octave. Too low? Maybe I'll just give the 33uf a shot and hope for the best. The next easy step up is 22uf and that would be in the 1370 hz range.
> ...


I would go 17, 33, or the 47 and then once it is lovely... then at some point you are married to the system and just remove the protection.




Adrock said:


> ...
> ...
> BTW, it is homage to the Kid Adrock. Beastie Boys have been in my weekly rotation since License to I'll.


You do not have to explain it to me kid 
Like the "she's Crafty" verse, I thought that avatar looked familiar.

There is a vegan/vegetarian restaurant in Denver called "Root Down", we'll have to see if Redliner99 knows it, or maybe GIJoe.

I still like the Flute loop a lot, and Stieg too in more of an origional sense.
The OJ chronicals segment, in one of the 5 boroughs songs was bizarre to hear.


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