What type of Capacitors should be used as bass blockers?

[FatDoug]

I have a 2010 Nissan Altima with the Bose system. With that factory Bose system, most of the bass was from the 6x9s mounted in the rear deck. It sounded OK for a lot of music, but the rear 6x9s really fall apart when playing low frequencies at even moderate volume. So I disconnected the rear speakers and added an inline app/subwoofer.

However, I really miss the midrange backfill the 6x9s provided. So I want to hook them back up, but without the low frequencies that the subwoofer is now handling. I want to use capacitors or "bass blockers" to prevent these low frequencies from hitting the 6x9s. These rear 6x9s have an impedance of 1 Ohm so I think that I need a capacitor with 1600 uF to block below 100 hertz or 2000 uF to block below 80 Hertz. When I see "bass blocker"s designed for car audio available on the internet, they never have a capacitance greater than 500. These bass blockers are always non-polarized. I can find 1600 uF and 2000 uF capacitors at electronics shops, but only polarized versions are available.

This leads to a few questions:

1) Do "bass blocker" capacitors have to be non-polarized? Why?

2) What 1600 uF - 2000 uF capacitor should I use and where can I buy it?

3) Can I use multiple capacitors to achieve the results I want? Like stringing 4 500 uF to get a total of 2000 uF?

Thanks!!

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[nudels 10+ year member]

1. yes,.. i do not know the specifics as to why, but polarized is highly recommended against for passive crossover applications

2. electrolytic, mylar, polypropylene, or polyester,.. can be bought online at parts express, fryes electronics, or radio shack, but im pretty sure the local radio shack should have something in stock

3. yes, paralleling capacitors totals all capacitance values, in series capacitance is devided

 

[mat3833 10+ year member]

wait, so you can basicly make a cheap crossover by just wireinf in a small cap?

Matt

 

[nudels 10+ year member]

wait, so you can basicly make a cheap crossover by just wireinf in a small cap?
Matt

yep, the capacitor bank (1 single, or 2 or more paralleled) in series with a driver creates a high pass,.. an induction coil in series with the driver will create a low pass.

wiring the capacitor/s, inductors, and driver all in series creates a bandpass.

one thing i forgot to mention is that using a single cap load or single inductor renders only a 6db rolloff,.. not sure if im right on this or not, but adding a cap or coil in parallel with the driver will augment the decay (roll off) or attack (roll in) to a steeper slope

 

[mat3833 10+ year member]

holy crap, so say i wanted to low pass my subs at ~70hz with a 12 DB rolloff. what would i have to use to accomplish that? and how would you make it adjustable? how much power can these take before bad things happen? you may have just made my life a heck of alot better!

Matt

 

[nudels 10+ year member]

holy crap, so say i wanted to low pass my subs at ~70hz with a 12 DB rolloff. what would i have to use to accomplish that? and how would you make it adjustable? how much power can these take before bad things happen? you may have just made my life a heck of alot better!
Matt

to get a 12db rolloff on a sub, you would need to wire an inductor no.2 in parallel with the driver after the inductor no.1 that is seriesed for the low pass.

your capacitor or inductor value will be dependent upon the impedance of the driver,.. i made a chart as a visual for a how-to im writing up as i go to show the different reactive loads needed for a given crossover point,.. blue are the caps, red are the inductors. as you can see, you can use the same capacitor or inductor for different impedance drivers, but your reactive load determines the target crossover point,.. does that make sense?

graph is small and im having probs resizing,.. take it to paint and zoom in //content.invisioncic.com/y282845/emoticons/pissed.gif.9f665f96bc89e98e708dabd4580bb591.gif

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[mat3833 10+ year member]

yes it actually does! well i find myself in need of a crosssover. and i would prefer it to be adjustable. 50-120hz would be prefered for the low pass and 100-200 would be prefered for the High pass. if i can make this work then i can ditch my current amp and run my subs off of my receiver for ~100W each. im in the process of googeling more on this subject as we type.

Matt

 

[nudels 10+ year member]

yes it actually does! well i find myself in need of a crosssover. and i would prefer it to be adjustable. 50-120hz would be prefered for the low pass and 100-200 would be prefered for the High pass. if i can make this work then i can ditch my current amp and run my subs off of my receiver for ~100W each. im in the process of googeling more on this subject as we type.
Matt

go to http://www(dot)bcae1(dot)com/passxovr.htm (links are disabled for me, fill in the 'dots' with '.')

 

[keep_hope_alive Premium Member]

here is a good crossover calculator site:

Passive Crossovers, Capacitor and Coil Calculator

click on the other links for plenty of information and diagrams.

Passive Crossover Networks

polarized caps essentially work "one way". in audio we need a non-polarized cap since the signal is positive and negative. that is an oversimplification, but close enough for general audiences.

for low frequencies, caps can get expensive, so staying with cheap electrolytic is common.

you won't be able to build an adjustable crossover without having jumpers to engage additional components - that will be pricey. the easiest adjustable crossovers are electronic (active).

 

[FatDoug]

Thanks for all of the messages guys. I was not able to find non-polar capacitors over 500 uF on the web sites for Parts Express, Fryes, Radio Shack or even Mouser Electronics - who seem to have 459,169 different capacitors! I have found many caps at over 500 uF but they all see to be polar. It is difficult to filter/search these sites for non-polar so I have called their customer support lines and the humans that I talked to could not help me find the 1500 - 2000 uF non-polar caps that I want to use as bass blockers for my 1 ohm speakers.

So I have decided to serially wire three 500 uF caps and one 330 uF caps for each speaker. Per my calculations, this should block out the frequencies below 86.89 Hertz based on an impedance of 1 ohm. Of course using a single capacitor would be much more elegant, but I have been told that serially wiring four caps like this will not cause any serious loss of fidelity.

Any thoughts?

 

[jdawg 5,000+ posts]

thats the inpedance of of the speakers? unless i missed it

 

[FatDoug]

These Bose 6x9 Rear deck speakers have an impedance of 1 Ohm. I think that is why I am having such a hard time finding "bass blocker" marketed non-polar capacitors. They are usually for 4 Ohm speakers.

 

[maylar 10+ year member]

Thanks for all of the messages guys. I was not able to find non-polar capacitors over 500 uF on the web sites for Parts Express, Fryes, Radio Shack or even Mouser Electronics - who seem to have 459,169 different capacitors! I have found many caps at over 500 uF but they all see to be polar. It is difficult to filter/search these sites for non-polar so I have called their customer support lines and the humans that I talked to could not help me find the 1500 - 2000 uF non-polar caps that I want to use as bass blockers for my 1 ohm speakers.
So I have decided to serially wire three 500 uF caps and one 330 uF caps for each speaker. Per my calculations, this should block out the frequencies below 86.89 Hertz based on an impedance of 1 ohm. Of course using a single capacitor would be much more elegant, but I have been told that serially wiring four caps like this will not cause any serious loss of fidelity.

Any thoughts?

Capacitors in series decrease the total capacitance, like putting resistors in parallel. If you're looking for 1800 uF you'd want 2 x 3600 uF in series, back-to-back for non-polar operation.

Caps that size will be electrolytic type and have a wide tolerance, typically +80/-20%. Not exactly a precision crossover. You'll be way better off with an active HPF if possible.