need help designing a cross over circuit for an audio device

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k1pml02144
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need help designing a cross over circuit for an audio device

Post by k1pml02144 » Tue Feb 15, 2022 1:24 pm

Hello all, i am not an electronics or computer person by trade so if i ask foolish questions its simply because i have no real idea about this stuff.
but i recently built an audio device that was commercially available sometime in the 1970's. the company is no longer around but i followed some
simple plans off the web and youtube... basically its a speaker that filters out most signals besides 500 to 800 hz range.. the speaker is designed to improve the audio quality of morse code transmissions without any real electronics involved... its a resonant speaker...

the circuit is a standard stereo cord wired to a 8 ohm .5 watt speaker.... ideally 2" and it is fitted within 2" pvc.. using some plexiglass to act as a baffle for the other frequencies... it does work. but someone suggested i design a cross over to accomplish this... but knowing minimal about designing anything i found myself here..

the audio output of my radio is .5 watts... what would i need to build this simple crossover.. its only going to involve one speaker..

any thoughts..

thank you in advance
pete


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CeaSaR
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Re: need help designing a cross over circuit for an audio device

Post by CeaSaR » Tue Feb 15, 2022 6:21 pm

You'll need a bandpass filter (crossover). Simplest one consists of a nonpolarized capacitor followed by a coil. The capacitor acts as the high pass and is set to 500 Hz and then the coil is a low pass but is set to the higher 800 Hz. That forms the bandpass from 500-800 and everything on either side falls off on a gradual slope. See https://techtalk.parts-express.com/file ... id=1134633 for an older chart that is still good.

At 8 ohms, a 40uF is perfect, but a 47uF will be easier to find. Then a 1.5 mH coil will be needed. These go on the positive or red wire before going into the speaker. So red wire ->capacitor->coil->speaker->black wire.
Hey, what do I know?

k1pml02144
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Re: need help designing a cross over circuit for an audio device

Post by k1pml02144 » Tue Feb 15, 2022 8:17 pm

Ok does the voltage rating matter on the capacitors? They are cheap enough. And with the inductor coil am i looking for a fixed version, trying to navigate the web for these things is difficult. I am hoping when the flea at mit opens back up this spring i may get lucky.

Ty again

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CeaSaR
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Re: need help designing a cross over circuit for an audio device

Post by CeaSaR » Tue Feb 15, 2022 8:59 pm

Usually, I go with 2x's the voltage of the amplifier, just for safety factor. So, for example, if you are using a LM386 and a 9v battery, 18V or somewhere close to that. As long as it exceeds the supply you'll be way more than fine.
Now, if you wanted to get down to the nitty gritty, 0.5 watts at 8 ohms is only 1.465 volts RMS, so you can get away with a much lower rating. You'd be lucky to find one so low, probably the closest voltage rating would be around 6v. Just look at the voltage rating of the cap. And don't worry about going to an audio store for them, I think the lowest rating you'll find at one of those places is 50v. Look at an online place like Mouser, Digikey, Jameco or Newark. You could also look at Parts Express. Just make sure the capacitor is a Non-Polarized (NP) type.
Hey, what do I know?

k1pml02144
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Re: need help designing a cross over circuit for an audio device

Post by k1pml02144 » Wed Feb 16, 2022 7:56 am

thank you Ceasar! its nice to find straight answers without having sarcasm come with it... facebook ham pages are full of that..

just getting interested in electronics as i edge closer to retirement... looking at arduino and raspberry pi kits.. for experimentation...

thanks again

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CeaSaR
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Re: need help designing a cross over circuit for an audio device

Post by CeaSaR » Wed Feb 16, 2022 8:33 am

You're quite welcome.

FB - unfortunately I've seen it become a much more toxic place than it used to be. I help Mod a couple of pages there and I'm just not as interested as I used to be because of that.

R-Pi and Arduino sure do look like a lot of fun. If I could only code them in QBasic... :D
Hey, what do I know?

k1pml02144
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Re: need help designing a cross over circuit for an audio device

Post by k1pml02144 » Wed Feb 16, 2022 10:26 am

my uncle told me to go into computers in college... i went into pre law... ended up working for a large telecom and 27 years later i never learned more than how to log in... now i am so far behind i am just trying to learn computers and electronics to advance my ham radio hobby... i wish i had been exposed to electronics as a kid...

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