How to filter out low frequencies

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DYohn

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Joined: April 22, 2003

Location: Arizona, United States

Posted: April 30, 2006 at 12:23 PM / IP Logged

I don't want to put words into haemphyst's mouth but what I believe he is saying is polarized caps cannot be used in crossovers BY THEMSELVES in the same way non-polar caps are used. He then goes on to say it is possible to configure polarized caps for this purpose, but that they must be used differently than non-polar ones.

I will add my 2 cents that one should NOT use polarized or electrolytic caps for audio crossovers even if electrically it is possible to do so because they simply sound bad. Non-polar non-electrolytic caps (and for bass blockers you need them to have at least a 100 volt rating) are the best solutions, and yes some of them are very expensive indeed. It is not unusual for a passive crossover to cost more to build than the driver it is controlling.

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haemphyst

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Posted: April 30, 2006 at 12:38 PM / IP Logged

stevdart wrote:

Good thing the thread came this far then. Wired in series with one cap reversed is a bit different than wired in series. Huh, haemphyst? And that latest info you gave is new to me, too. I didn't know that about overcoming the polarized issue.

"But, again, polarized caps, and unusable in this application."

Is that a typo? Because if not it makes your entire statement contradictory.

All right, all right, all right... ya caught me. What I MEANT to say was this: right out of the package, without properly connecting a second one, they will be unusable in this application... How to filter out low frequencies - Page 2 -- posted image.

How to filter out low frequencies - Page 2 -- posted image.

sab0276 wrote:

I have some 3.5" coaxial speakers that I would like to filter out the low frequencies. Is there like a base cap or a resistor or something I can put inline? I would like some thing cheap and easy if possible. I don't really want to use a crossover or anything.

Thanks.

-Scott

And while Dyohn is absolutely correct in his statement above, I was looking for the least expensive (i.e. "cheap" - $1.69 * 4 = $6.76, as opposed to $9.99 plus freight for the lowest frequency "bass blockers"), as well as the fastest method (i.e. "easy" - trek to the local RS and walk out with 'em, as opposed to waiting a week for Parts Express) for him to reach his desired destination. While not COMPLETELY wrong, my suggested method will work, with 100% safe and satisfactory results, sometimes offering additional safety, due to the increased voltage capabilities of two caps in series, rather than a single high voltage cap. I have done it before, on MANY occasions.

It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

stevdart

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Posted: April 30, 2006 at 1:25 PM / IP Logged

...and we get a good learning thread out of the deal, too. Can't complain about that! How to filter out low frequencies - Page 2 -- posted image.

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geepherder

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Posted: April 30, 2006 at 5:32 PM / IP Logged

Yes, that's interesting to know about polarized caps.

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boomer_106

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Posted: April 30, 2006 at 8:38 PM / IP Logged

[/QUOTE]

Those frequencies are FAR too high... You still want SOME bass, right? You are just trying to filter the deepest bass to prevent "flapping", right? These are WAY more expensive, too... All those are? Expensive capacitors... The SAME as I linked for you in my original post.

sab0276 wrote:

I was only showing him an example of a bass blocker. It's up to him to choose what he wants thats all.

sweatyogre

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Posted: April 30, 2006 at 9:29 PM / IP Logged

I'm currently using 200 Hz bass blockers on my 6x8s. Is that too high? The lowest frequency they're supposed to be able to handle is 37 Hz.

sab0276

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Joined: April 21, 2006

Location: United States

Posted: May 01, 2006 at 10:49 AM / IP Logged

Excellent information here. Thank you.

Just to throw another monkey wrench into the equation. The 3.5" are replacements for the 2.5" in the very back of my Yukon. After I installed them I realized that they are wired in series. They only work if both are connected. How will this effect adding a cap?

Thanks again.

-Scott

2002 GMC Yukon SLT non-Bose

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DYohn

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Posted: May 01, 2006 at 11:23 AM / IP Logged

sab0276 wrote:

Excellent information here. Thank you.

Thanks again.

-Scott

If both speakers are 4-ohms, then the total load in series is now 8-ohms. This will change the crossover frequency by a factor of 2. For example, if you use a 4uf capacitor, it will serve as a 6db/oct high-pass filter at 100Hz for a 4-ohm load, but at 50Hz for an 8-ohm load. If you want 100Hz HP with an 8-ohm load, you want a 2uf cap. And, since both speakers are in series, you only want to use one cap on the positive leg of the speaker closest to the amp.

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sab0276

Copper - Posts: 61

Joined: April 21, 2006

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Posted: May 01, 2006 at 11:52 AM / IP Logged

I'm not sure which one is wired closest to the amp. Does it matter?

Also since the speakers have a range of 60Hz-28kHz and I'd like to lose as little bass as possible would the 4uf cap that high pass filters at 50Hz be ok?

Thanks.

-Scott

2002 GMC Yukon SLT non-Bose

Pioneer AVIC N3

DYohn

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Location: Arizona, United States

Posted: May 01, 2006 at 12:04 PM / IP Logged

Ah crap, I composed too quickly and committed the old "shifted decimal place" error. Instead of "4" and "2" uf as I wrote above, it should read "400" and "200." Thanks to stevdart for being my proof-reader. How to filter out low frequencies - Page 2 -- posted image.

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