quick tweeter cap/hi-pass question

[toobhed]

If I have an 8ohm mid/woofer and want to add an 8ohm "helper" tweeter that would be connected in parallel, what microfarad cap value would I use to create about a 5khz high pass for the tweeter? Is there a simple equation I need to learn? ... I'll determine the resistor value by ear....
Thank you,
Mario

[picowallspeaker]

Oh no !!
such messages like mine should be deleted by the Forum rules !!
It is advisable that speakers are very different one from each other ( hopefully , not the same model !!! ) so the first thing to do would to take a look at the specification / measurements of the specific model .
If you need to cut it that high , you can go with higher Fs models ( above 1000 Hz ) ...just check the power if you want to go with 6 dB /Oct crossover , which is a simple cap .
O.k. there are many online calculators for a quick and dirty application of the formulas .
Strassacker: Lautsprecher - Boxen - Selbstbau
for example .

[bunkie]

The quick answer is for an 8 ohm tweeter, 4 microfarads would be about right.

And, yes, there is a formula for calculating values for these so-called first-order networks with 6db/octave slopes (there are formulae for the more complex second, third and fourth order networks as well).

Here's one link: Passive Crossover Design Equations Formulas Calculator - Two Way First Order Network Butterworth

Here's an even better one: How to Build Speaker Crossovers | eHow.com

[picowallspeaker]

Me first !

[toobhed]

Thank you Pico and Bunkie!

[weltersys]

Originally Posted by toobhed

Thank you Pico and Bunkie!

Now you have the simple answer, you may want to read this stickie:

Introduction to designing crossovers without measurement

to find out why the "simple" answer is seldom even close to a good sounding solution.

[PeteMcK]

The main thing to be aware of is that you need to use the actual impedance of your drivers at the crossover frequency, not the nominal impedance. To find this you need either a manufacturer's data sheet, or to measure the drivers yourself.

[toobhed]

Thanks Weltersys, it's a great concise read that highlights all the levels involved and will be useful to me. ...and will be checking impedance at crossover frequency...I appreciate the quick responses and links

[weltersys]

Originally Posted by toobhed

Thanks Weltersys, it's a great concise read that highlights all the levels involved and will be useful to me. ...and will be checking impedance at crossover frequency...I appreciate the quick responses and links

Knowing the impedance at the crossover frequency still will not insure a 6 dB per octave acoustic crossover at the crossover point using a capacitor.
And of course, your woofer is not falling off at exactly 6 dB per octave either.

Placing a resistor in series with the tweeter can help make the crossover more predictable, but without measurement you only get close, but no cigar.

That said, order several resistors and capacitors in various values, by playing with series and parallel arrangements you can get a vast amount of response variations with just a handful of parts, one of which will suit your taste.

Then send the parts you don't use to me, I had dozens of capacitors, resistors and coils, after padding my kitchen speakers noticed the resistor pile was down to a handful again...

Art