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Bass Blockers - Type of capacitor to use?



 
 
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  #1  
Old November 14th 06, 03:36 PM posted to rec.audio.car
[email protected]
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Default Bass Blockers - Type of capacitor to use?

I need to install some capacitors to serve as bass blockers for door
speakers in my car.

Since my car is parked outside a lot, it seems like it may not be a
good idea to use electrolytic capacitors, but instead use something
like ceramic or mylar which don't have a paste that could dry up in the
heat.

Can anyone help me determine whether this would work? Or must
capacitors in this role be electrolytic?

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  #2  
Old November 14th 06, 03:46 PM posted to rec.audio.car
e-nigma
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Posts: 180
Default Bass Blockers - Type of capacitor to use?


> wrote in message
ups.com...
>I need to install some capacitors to serve as bass blockers for door
> speakers in my car.
>
> Since my car is parked outside a lot, it seems like it may not be a
> good idea to use electrolytic capacitors, but instead use something
> like ceramic or mylar which don't have a paste that could dry up in the
> heat.
>
> Can anyone help me determine whether this would work? Or must
> capacitors in this role be electrolytic?
>


I've seen electolytic (must be nonpolar or bipolar) bass blockers work in
car doors for years here in Central Florida with no adverse effects.
I've installed for 27 years and do not recall a time where it looked like
bass blockers were heat damaged.


  #3  
Old November 14th 06, 04:11 PM posted to rec.audio.car
[email protected]
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Default Bass Blockers - Type of capacitor to use?

Thanks, ok I'll just go with electrolytics. I'm in central FL as well.
:-)

  #5  
Old November 14th 06, 05:55 PM posted to rec.audio.car
John
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Default Bass Blockers - Type of capacitor to use?


Check out partsexpress.com, they should have a variety of bass blockers
for sale. This should offer you a wider selection and invol


--
John
  #6  
Old November 14th 06, 07:09 PM posted to rec.audio.car
D.Kreft
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Default Bass Blockers - Type of capacitor to use?

On Nov 14, 7:36 am, wrote:

> Since my car is parked outside a lot, it seems like it may not be a
> good idea to use electrolytic capacitors, but instead use something
> like ceramic or mylar which don't have a paste that could dry up in the
> heat.


I used to work in the industry in *south* Florida...no problems on my
end with the heat and electrolytics, either.

> Can anyone help me determine whether this would work? Or must
> capacitors in this role be electrolytic?


I have to wonder why you're just going to use just capacitors? A
capacitor alone has a 6dB/octave roll-off--which is pretty darn
gradual. This means that you're going to have to choose a pretty high
-3dB (crossover) point to give your speakers the protection they need.
Of course, how high the point has to be depends upon the size of the
speaker and the amount of power your amp is churning out--the more
power you apply to the speaker, the higher the crossover point is going
to have to be.

I would strongly encourage you to consider using a "second-order"
(12db/octave) or even a third-order (18dB/octave) filter instead.
Using a higher-order filter means that you'll be attenuating
potentially damaging low frequencies much more rapdily, which means
that you'll be able to choose a lower -3dB point and/or apply more
power without damaging your drivers.

There's also something to be said about the quality of the sound you
get when using a higher-ordered filter. Some "golden-eared tweaks"
might argue that the lesser degree of phase shift encountered with
lower-ordered filters leads to a more "pure" (whatever that means)
sound, but this is *highly* debateable. In a typical install, you're
actually likely to do more damage, in my experience, using 6dB/octave
crossovers to your soundstage due to there being less of a clear
"boundary" between the frequencies reproduced by your separates up
front...but this is rather esoteric stuff that the "average Joe"
doesn't care much about. :-)

You also didn't mention what kind of speakers these are...are they
separates (discrete tweeter and woofer) or are they coaxials? Adding a
capacitor (or any passive crossover for that matter) inline with a
coaxial that doesn't have discrete inputs is going to muck with the
crossover point of the tweeter. It's been a long time since I've built
a passive XO network, so I don't remember the precise effect or the
degree thereof, but it's something worth looking into to make sure you
don't do the wrong thing.

In a nutshell, go with a good (mylar capacitor, air-core coil)
second-order (12dB/octave) filter--I think you'll be better off.

-dan

  #7  
Old November 15th 06, 06:14 AM posted to rec.audio.car
Matt Ion
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Posts: 420
Default Bass Blockers - Type of capacitor to use?

wrote:
> I need to install some capacitors to serve as bass blockers for door
> speakers in my car.
>
> Since my car is parked outside a lot, it seems like it may not be a
> good idea to use electrolytic capacitors, but instead use something
> like ceramic or mylar which don't have a paste that could dry up in the
> heat.
>
> Can anyone help me determine whether this would work? Or must
> capacitors in this role be electrolytic?


Just to clarify: no, they don't HAVE to be electrolytics. HOWEVER, about the
only caps you'll find in the capacitance range you need (several hundred
microfarads - a 200Hz cutoff on a 4-ohm speaker should have about a 200uF cap)
for a reasonable cost, will be electrolytics.

Most other types (ceramic, mylar, tantalum, etc.) are not generally available in
those values (tatalum caps, IIRC, tend to be relatively high-value,
high-tolerance, high-voltage for a fairly small size, but also tend to be
comparitively expensive).

If you can't find a non-polarized cap, you can always connect two standard
electrolytics back-to-back (ie. negative of each cap connected together;
positive of one to the speaker, positive of the other to the feed wire), just
remember that doing so will cut the total capacitance in half... so if you need
200uF total, you'd have to use two 400uF caps.

See here for some useful charts/calculators:
http://www.carstereo.com/help/Articles.cfm?id=1
  #8  
Old November 15th 06, 07:22 AM posted to rec.audio.car
D.Kreft
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Posts: 296
Default Bass Blockers - Type of capacitor to use?

On Nov 14, 11:09 am, "D.Kreft" > wrote:

> In a nutshell, go with a good (mylar capacitor, air-core coil)
> second-order (12dB/octave) filter--I think you'll be better off.


Just had a flashback to "the day"...both air-core coils and mylar caps
are likely going to be difficult to find for a high pass filter of any
reasonable low frequency (90Hz - 150Hz or so), and the use of a mylar
or other more "exotic" cap isn't going to benefit you too much on a
midrange speaker--the benefits of using air-cores and mylars are
typically best realized on tweeters. For a midrange driver, a
non-polarized electrolytic cap and an iron core coil will do just fine.
They'll also be cheaper and smaller than their equivalent
air-core/mylar counterparts.

Sorry about that.

-dan

  #10  
Old November 15th 06, 03:08 PM posted to rec.audio.car
D.Kreft
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Posts: 296
Default Bass Blockers - Type of capacitor to use?

On Nov 15, 6:16 am, (GregS) wrote:

> Bass blockers are a poor substitute for active crossovers. The bass blocker
> increases driving impedance causing the resonant peak of the midrange to
> further increase.


Well, if he's poor, then the "poor" solution may be his only option at
present. :-)

But yeah, nothing beats an electronic crossover...you should be able to
pick one up for about $150 or so. I once bought an L.A. Sound crossover
for my mom's car for $99. It produced a noticeable detrimental impact
on the brightness of the tweeters (substandard electronics), but at
least she never fried her midrange speakers. :-)

-dan

 




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