# Tweeter Capacitor; Bass blocker. What value? (Specifically the Boston Acoustics 6.43)



## iregret (Jul 27, 2009)

Hello. 

I'm just about finished with my MS-8 install. I'll be running Boston Acoustics 6.43x, with out the passive crossover network. I'm not really sure what capacitor I should install inline to the tweeters. Could one of you electrical geniuses please help me?

I can't find the documentation, but I want to say that the speakers are 3 ohm. I've seen "Bass Blockers" with values ranging from 5.5uF to 20uF to 47uF. Then they all have different voltage ratings.


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## iregret (Jul 27, 2009)

Sweet! Look what I found. Kinda answered my own question!!

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

We should have this info on this site too!


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## iregret (Jul 27, 2009)

I'm still confused on the voltage though. Is that just what the capacitor is rated for? Do I just ignore it for my application? That link above doesn't mention compactor voltage at all.


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## eddieg (Dec 20, 2009)

Hi, 

Well there are certain things that are to be taken in mind when planning a crossover network. 

In this case you are simply trying to protect the speaker (twitter) against low frequencies.

What you need to know is: 

1. Speaker nominal impedance
2. Desired crossover point.

With the two details above you can use a first order (6 DB slope) calculator and find the required value of your capacitor. 

Now - the other values of the capacitor which are important for you are:

1. What is the max temperature the capacitor can withstand - do not go under 85 degrees Celsius and it would be best to find one that can go above 100. 

Solen capacitors for example are very (considerably that is) cheap, they can stand a voltage of up to 400V but only 85 degrees heat.

2. The voltage - now this is critical, although most amps do not go beyond the 30V AC, the capacitors are rated at DC, from my experience the 100VDC capacitors simply don't deliver the goods so I would avoid going anywhere below the 150V endurance. 

Usually I am working with Clarity CAP PX series which are colored blue, can stand high temp and 250VDC or Solen capacitors. 

Also the crossovers I built with them are great sounding (not that I ever noticed a difference between one capacitor to another). 

Another thing that could be important when dealing with capacitors is to make sure you purchase a bi-polar (no polarity marking) capacitors - but the bennics, millar, clarity, solen, jentsen, wima etc are all audio caps and are all bipolars usually if you buy them from dedicated sites. 

However - is it a good method to just use a capacitor in order to protect a twitter? 

The answer is no, why? The reasons are: 

1. The calculator for a first order crossover is rubbish as the impedance of the speaker changes per frequency - this means that your actual crossover point would be dancing up and down all over the place as the speaker impedance changes as it plays. 

2. A first order crossover does a very low margin of noise filtering which a twitter is very sensitive for, the higher the slope the more noise you filter out from a signal.

3. A twitter is a very fast component - the higher the slope you cut it with, the more chance you have to delay it from other bigger components such as mids and woofers and subs - in other words you have better time alinement between the component set elements. 


So, what would be the recommendations - 

1. Add a L-pad (look for l-pad calculator) which would set the impedance the capacitor is "seeing" to be fixed thus would also set a more fixed crossover point and as well the l-pad is an attenuator which would decrease the twitters volume and balance it better in front of the rest of the elements in that set (usually I find an attenuation of 6 DB best for twitters and that is a very simple Lpad at 4 ohms - check it out for your self and see, all you require are two resistors, any sand resistor of 25Watts would do fine for most cases with twitters). 

2. Set a higher slope crossover if you can - 2nd order would be recommended in most cases, as well it might reverse the twitter polarity so try to reverse the wires as well for best results). 


For midbasses I usually like to plan a first order cross and to twitters 2nd or higher but each case to its own... 


To conclude, for now, simply try to build a first degree crossover but I highly recommend to add an LPAD to it. 

Check sites such as madisound and parts-express

Good luck!

Eddie


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## iregret (Jul 27, 2009)

Woah! Thanks for the thorough explanation! What I ended up buying were 47uF capacitors with a 35vdc rating. Basically, because that's what I could find locally. 

I'll start googling around and look into what you suggested, but wouldn't it kind of he overkill for my application because of the MS-8? It's electronically crossing the tweeters off a a given frequency. I just want to attempt to save the tweeters invade of failure. 

Thanks so much for your input. I really appreciate it!


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## iregret (Jul 27, 2009)

I believe these are the ones I bought. 

47µF 35V 20% Axial-Lead Electrolytic Capacitor : Electrolytic Capacitors | RadioShack.com


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## eddieg (Dec 20, 2009)

Well for what I understand, you are not using your twitters as a part of a component set, meaning you are using active crossover and active amplification channels on your sound system elements. 

To put it short your twitter is amplified in separate from the rest of the set and the MS-8 is doing the crossing to that amp. 

In such case there is really no need for a capacitor on the twitter but if you dread so much for not heaving it ruined and you still want to provide it with some "thermal" protection using a capacitor then choose a capacitor which is a bit below the crossover point you set to that twitter at the ms-8 so you won't have overlapping cuts. 

In general - it is not required in your case as the MS-8 does the job. 

As for the capacitors you baught - you have no use for them in a crossover, the voltage value is simply too low and they are not bi-polar.

Try Madisound Speaker Components: distributor of loudspeaker drivers and parts for speaker builders. instead.

Good luck!

Eddie


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## minbari (Mar 3, 2011)

iregret said:


> Woah! Thanks for the thorough explanation! What I ended up buying were 47uF capacitors with a 35vdc rating. Basically, because that's what I could find locally.
> 
> I'll start googling around and look into what you suggested, but wouldn't it kind of he overkill for my application because of the MS-8? It's electronically crossing the tweeters off a a given frequency. I just want to attempt to save the tweeters invade of failure.
> 
> Thanks so much for your input. I really appreciate it!


what kid of capacitors? if they are electrolytic make sure they are not polarized or they will explode.

how much wattage and what ohm are the speakers?, 35v caps is pretty low for an audio system.

what is the crossover freq of the tweeter? if you are using a 4ohm tweeter then 47uF will cross it at 800hz, if it is 8ohm it will be 400hz. 

that is not going to protect your tweeters against an "oops". it will protect against your amplifier taking a puke and sending DC, but if the tweeter has a crossover point of 4khz and you "protect" it with 800hz high pass. it will still pop it in no time flat.


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