Revised technical question:

According to the RFC calculator online at

...

1.5 microFarads has an impedance of ~1000 ohms at 100 Hz. This would give you a 3dB down point at 100 Hz.

To be honest, you will not likely get anywhere very fast asking excedingly cryptic questions like this, however.

We have no way of interpereting what YOU mean by "best" without significantly more context.

1k ohm for audio? as in where in the circuit?? speaker? active part of the circuit? passive crossover?

A capacitor cannot limit bandwidth on the top end, you'd need a bandwidth limiting crossover network to limit frequencies between 100hz and 6khz.

We need the following information:

Application? What you are trying to achieve??

--
Myron Samila
Toronto, ON Canada

A cap cant limit on the high end?? Are you sure about that? If you take an appropriate cap across a speaker, doesnt that short out some of the high end freqs?

circuit?

limiting

Depends on whether the cap is in series in parallel.

Of course we are all guessing because the OP is provding no useful detail about his/her question. I smell a troll.

You wouldn't use a cap to limit bandwidth in parallel in audio.

You'd use a coil to limit high frequencies at a rate of 6db/octave, in series. A cap in series with the speaker will filter low frequencies.

Passive crossovers are horrible anyhow, bi-amping or three way (active xovers) work best.

Yes, the OP won't get his question answered because it is too vague.

--
Myron Samila
Toronto, ON Canada

It depends on his application. As I said in my post "across the speaker" will roll off the top end. As you stated in your post, a cap in series will roll off the low end. We dont know what kind of circuit application he is using, hifi, mono, etc. He may be looking for a filter for his ham radio reciever for all we know so a crossover may not even be what he needs. Anyway, until he is more specific, we wont be able to answer. Brian

series. A cap in

xovers) work best.

How does a cap across the speaker roll off top end? I believe that is incorrect. Hifi, mono, 5 channel, it doesn't matter. A passive filter is a passive filter, period, ham radio or not (I have friends who are operators and I've built many bandwidth filters for them. The only way to roll off high frequencies to a speaker is to put a coil in series with the speaker or resistor across the speaker (high value resistance will absorb frequencies at a specific attenuation, as 6db/octave typical). Putting a capacitor across a speaker is the same as putting it in parallel. Trust me, it won't work, even when a

12db/octave filter is used, the cap goes in series with the load, the coil goes in parallel to the load for low-pass applications, reverse for high pass applications.

A crossover is a filter, exactly that, highpass vs lowpass vs... bandpass..... all crossovers (a term used in the audio field).

Top posting is bad, stop it.

A capacitor's impedance goes down as the frequency increases.

will

is

incorrect. Hifi,

period, ham

bandwidth filters for

coil in series

will absorb

capacitor across

even when a

goes in

applications.

bandpass..... all

I will accomodate your wish about top posting. And dont be telling people what to do. A cap does roll off the frequencies when placed across the speaker. If you study filter design, the coil in series does what a capacitor in parallel does. The point is the capacitor needs to be the correct value to do so. Granted, it may be a large capacitor, but it does work. Try it. Also, the ARRL Handbook has some good theory on filters.' Brian

Someone that understands! B.

Usenet rules.... read the FAQ and rules and regulations of usenet, it is in black and white.

Brian, in my time of designing filter networks, reading books, using crossover/filter design software, there is no where that suggests the use of a capacitor in parallel to a speaker to limit frequency. If so, what is the predictable filter slope??

Anything less than 6db/octave is useless in audio.

Keep studying.

A remarkably rash pronouncement. We'll write it off to youthful indiscression and inexperience.

"There are more things in heaven and earth, Horatio, Than are dreamt of in your philosophy."

-William Shakespeare, "Hamlet"

Why would that be considered rash? if you are trying to limit bandwidth (lets say low pass) from 250hz up to 20khz, then at anything less than 6db/octave, you will still hear a great deal of program material at the next lower octave. The slope is too great, typically, in home audio filter networks employ a minimum of 6db per octave, and then higher quality ones use 24db/octave, Butterworth, Linkwitz, Bessel, Bec... depending on the desired Q.

Look, if you want to limit bandwidth in audio, I am simply suggesting that your method is not practical and not used.

ie: 8ohm speaker, bandpass 500hz-6000hz, use a 40mF (non polarized) cap in series with a coil of .212 mH, this will bandpass at an effective slope of 6db/octave on the upper and lower end of the shelf.

What now?? Qualify yourself, otherwise your posts aren't of any use.

You not only have a remarkably narrow view of the world, but you seem unusually cock-sure that your's is the only valid concept.

You clearly haven't studied many schematics if you think that simple "1-pole" R/C filtering "is not pracical and not used" it is used in virtually every AC-coupled circuit ever made. Perhaps you don't recognize it because it is so pervasive.

Well, if you go back and read the original post, it wasn't even detailed enough to mention anything about using it in speaker crossovers (or any other identifiable application).

Did you even understand the concept of the Shakespear quote?

We are talking audio (AC), not any other type of AC coupled circuit. You are clearly (not to you though) missing the point.

Someone suggested you can bandpass audio using only a cap, how?(bandpass passively on the output of an amp) Where does it filter the low end? Are you going to put a

100,000 mF capacitor at 200V to cut out frequencies at 8 ohms? Practical? ummmmmm.......

The suggestion of bandpass came up regarding ham radios........ that is why we are on the topic of audio, nothing to do with the OP.

I was responding to someone who said you can use a capacitor across a speaker to achieve bandpass, not the OP.

We're talking electronics here.....I'm not in the alt.shakespear.chat.forum, his rants are about as out of date as your theorems.

You're still incorrect unless you can prove otherwise. Show me an example using ONE capacitor how you would filter frequencies between 100hz and 5000hz with an 8ohm speaker load?? we are assuming the signal is audio, from an amp. That is what I was arguing, it is incorrect and cannot be done, period......

Lets stop the misinformation here. I wasn't referring to the OP at all, all previous posts have snips of the question I was answering.

Do you own a stereo? ;) Do you understand what I'm talking about at all??!?! That is my only question. If there is any other way of doing what I'm suggesting, why doensn't anyone else do it?

Just like the thread about 50hz vs 60hz motors, oh my, don't even get me started on that one. So much WRONG information, I only wish I jumped in on that one.

Hate to say it Richard,

This person is right........ You cannot create a bandpass audio filter with just a cap across a speaker load as was mentioned that you could in a previous post. If you put a cap in series with the speaker load, you create a filter. (filtering out low frequencies).

I think you missed the initial point that I brought up in this thread a while back.

And you don't need to study schematics to understand how a speaker crossover or bandpass filter works. Usually, there are no more than 4 components (in a 24db/octave slope passive crossover), this is the only component between a speaker and an amplifier.

I think I also talked about the ham radio application and such, but whatever. Points get missed, heheh.

All I do is live and breathe professional audio, have done so for the past 10 years, wind my own air core coils, built hundreds of passive and active crossover networks ;). I've never put a cap in parallel (across) a speaker load to achieve what you guys are arguing about, ?!?! heheh. If a cap could be used as a bandpass device in audio, that would be great, since then I would start to wonder why we use coils (which are expensive, power robbing, expensive, oh and did I mention expensive?, high quality audio air core coils can reach upwards of $400!!!! or more (Cnd), for only 100Watts power dissipation!!!

Anyhow, great discussion!! A lot can be learned here!

--
Myron Samila
Toronto, ON Canada

people

in black and

Doesnt matter, its not your job to tell people what to do. You can explain the rules, but assuming to be the boss doesnt make you someones boss kid.

with just a cap

If you put a

low frequencies).

while back.

crossover or bandpass

24db/octave slope

amplifier.

whatever. Points get

10 years, wind

networks ;). I've

guys are arguing

that would be

expensive, power

air core coils can

dissipation!!!

I think the question that Switch asked was how does a cap across a speaker roll off frequenceis at the top end. He didnt say anything about bandpass. A bandpass filter consists of several poles made up of caps and coils. But a cap across an 8 ohm load can roll off frequencies at the top end. Like I said it depends on the size and type of the cap. Xc =2pi*f*C. This is the formula one would use to calculate the capactive reactance to frequencies with a given capacitance. Plug in the frequency in question with the reactance in question and it will give you a capacitance that you need. Find a good electronics book and a physics book. it does work.

are clearly (not

No I think he understands the point as it was originally described in the original post.

passively on the

a 100,000 mF

ummmmmm.......

why we are on the

The original post about filtering in ham radios was my post. It doesnt mention bandpass, nor 8 ohm load for that matter. The original post says

1000 ohm impedence. There are a lot of things you can do with audio at 1000 ohms that may not be practical at 8 ohms. We are not talking hi fi audio here. We are more than likely talking about a lowpass filter using a cap across the speaker leads of a 1Kohm speaker (or headphones).

speaker to achieve

Im not sure where you keep getting the idea about bandPASS. BandWIDTH was what was mentioned, and a cap can effectively limit the bandwidth by rolling off the high end frequenceis. We were talking about a rolloff filter, one that rolls off the higher frequencies. Theres a big difference.

alt.shakespear.chat.forum, his rants are

using ONE

an 8ohm speaker

was arguing, it

Again, 8 ohms was not mentioned in the original post. 1000 ohms was the load. For all you kids out there that dont know it, there is a lot of older equipment that use higher impedence output audio. It can range from 6k ohms on down to 8 these days. If Im not mistaken, PA systems use higher impedence loads to limit the current drawn from the system.

all previous

all??!?! That is my

why doensn't

Like I said above, youre thinking high end hifi, not high impedence communication audio amplifiers.

started on that

Not gonna comment on that. Brian