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Passive high pass filter for tweeters

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dnbpc View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dnbpc Quote  Post ReplyReply Direct Link To This Post Topic: Passive high pass filter for tweeters
    Posted: 04 February 2016 at 1:37pm
If I wanted to make a passive high pass filter for a tweeter box @ 10khz is it as simple as adding a capacitor of a certain value to the circuit or would I have to make a complete crossover? If so can anyone give me a basic explanation of where to start? 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote stevie Quote  Post ReplyReply Direct Link To This Post Posted: 04 February 2016 at 1:48pm
It's more complicated than that but, yes, you could make a start by adding a capacitor in series with the tweeter. A film capacitor of around 2.2uF should work with an 8 ohm tweeter. Get 3 values 1, 2.2 and 3.3uF and try them out. The Loudpeaker Design Cookbook is very good as a primer on this kind of thing.

10kHz isn't a critical area - so it could work at a pinch. Also try swapping the phase of the tweeter in circuit to see what sounds best.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dnbpc Quote  Post ReplyReply Direct Link To This Post Posted: 04 February 2016 at 2:50pm
Cheers I'll order a few different value capacitors and have a mess about, I'll make sure to check out the book as well.

Am I right in thinking that if I wanted to increase the slope of the filter I would need to add a resistor as well?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote stevie Quote  Post ReplyReply Direct Link To This Post Posted: 04 February 2016 at 4:41pm
You'll need to add an inductor.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote odc04r Quote  Post ReplyReply Direct Link To This Post Posted: 04 February 2016 at 4:57pm
Not necessarily. A first order high pass can be made using a single series capacitor. Start simple.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote stevie Quote  Post ReplyReply Direct Link To This Post Posted: 04 February 2016 at 6:07pm
You'll need to add an inductor (rather than a resistor) if you want to increase the slope of the filter.


Edited by stevie - 04 February 2016 at 6:08pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote _djk_ Quote  Post ReplyReply Direct Link To This Post Posted: 05 February 2016 at 7:31am
I would not use a crossover with less than a 12dB slope.

1.5µF + 0.4mH = 10Khz Q=.5 (Linkwitz/Riley)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dnbpc Quote  Post ReplyReply Direct Link To This Post Posted: 05 February 2016 at 1:33pm
Right I think I've got a better understanding, so to get a 10khz 12db slope I would connect a 1.5µF capacitor and a 0.4mH inductor in series before the tweeter?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote markie Quote  Post ReplyReply Direct Link To This Post Posted: 05 February 2016 at 4:24pm
The cap goes in series with the tweeter but the inductor goes in parallel. This will give you an idea:-

http://www.diyaudioandvideo.com/Calculator/SpeakerCrossover/


Edited by markie - 05 February 2016 at 4:26pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tv00 Quote  Post ReplyReply Direct Link To This Post Posted: 05 February 2016 at 5:27pm
There's lots of crossover calculators out there, I'd do a 18/db slope one, takes a few components but for a electronic circuit it's very simple, components are big though, use at least 100V components, probably more, depending on power, so they don't blow up.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MarjanM Quote  Post ReplyReply Direct Link To This Post Posted: 06 February 2016 at 9:10am
Crossovers are not made with calculators but with measurements. 
Calculators assume a flat line response which never is.
What is below the tweeter? Is sensitivity matched to the rest of the components?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tv00 Quote  Post ReplyReply Direct Link To This Post Posted: 06 February 2016 at 9:18am
You still have to calculate the xover rather than connecting random components!Dead

You're right, sensivity has to match +impedance has to match the xover, also a hard part is to get a smooth transition, drivers might couple /decouple at xover as phase also gets twisted.

I really don't know too much about this, but I saw a couple of interesting posts about this.
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