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Old 24th July 2009, 04:54 PM   #1
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Default correct capacitor values

Hi there, a total noob here...

I've been searching the forum to an answer to this but to no avail.

I'm looking at replacing/rebuilding the crossovers on my speakers because they are no longer outputting anything through the tweeters. They are a couple of tannoy mercury mx1's.

I've located the equations and a funky calculator to give the correct capacitor values for the crossover frequency given in the manual.

However, I can't locate any capacitors with exactly the correct farad value. What should you do in this situation? Do you just select the nearest available cap? The same can be said for the inductors too....

Thanks in advance
Jon
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Old 24th July 2009, 05:46 PM   #2
DcibeL is offline DcibeL  Canada
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Crossover "calculators" are completely useless for the most part. You'll want to replace parts with the same value currently in the crossover.

That said, you can use a multimeter to check that caps are not blown, check your inductors are not blown, and check that your tweeter is not blown. Basically, use a multimeter to check continuity of everything so you know what is wrong before you start changing out parts all willy nilly.
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Old 24th July 2009, 07:40 PM   #3
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Cheers for that, I will invest in one and do the recommended checks. showing my lack of knowledge methinks!
Still, what would be the situation if I needed to replace the capacitors and the value of the caps in my speakers aren't available? Would it be curtains for my speakers or could i opt for a slightly different rating and compensate in another way or some such?
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Old 25th July 2009, 12:59 AM   #4
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Hi jpjsenior, I might be able to help a bit ?

L x C

Just say your calculator came up with values of C = 4.42 uf & L = 0.64 mH;

0.64 x 4.42 = 2.83

You could choose a cap, 4.7 uf & an inductor 0.60mH

0.6 x 4.7 = 2.82

If you not happy with that buy larger inductors (or make your own) & reduce them to the value you want, & use more than 1 cap to get the exact value you require.

Steve
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Old 25th July 2009, 06:04 AM   #5
Stu is offline Stu  Australia
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Quote:
Originally posted by jpjsenior
Cheers for that, I will invest in one and do the recommended checks. showing my lack of knowledge methinks!
Still, what would be the situation if I needed to replace the capacitors and the value of the caps in my speakers aren't available? Would it be curtains for my speakers or could i opt for a slightly different rating and compensate in another way or some such?
Easy - find TWO capacitors that sum to a value close to what you want, and use them in parallel.

For example, say you need a 3.3 µF capacitor - run a 1 µF and a 2.2 µF in parallel and you'll get a 3.2 µF capacitor (should definitely be close enough, particularly if you do the same for both speakers, but if you're really concerned, just add a third 100 nF cap in parallel).
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Old 25th July 2009, 04:45 PM   #6
hllchan is offline hllchan  Hong Kong
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hi there,

I got a repaired mini-autograph drive (I believe is the Tannoy Dual Concentric). I plan to use this as my HT center speaker but don't know how to hook this up to my power amp. Someone do suggested simply to add a 3.3uF capacitor connecting both the HF + and the LF +, and simply use a bi-wire spk cable to connect that to my power amp... will this work ?

Many Thanks.

Spec of the Dual Concentric listed below:-
Autograph Mini
PERFORMANCE
Recommended amplifier power 20 - 100 Watts
Continuous power handling 50 Watts RMS
Frequency response 68Hz - 54kHz -6dB
Sensitivity 88dB (2.83 Volts @ 1 metre)
Nominal impedance 8 Ohms
DRIVE UNITS
Dual Concentric™ high frequency 19mm (0.75”) titanium dome with Tulip WaveGuide™
Dual Concentric™ low frequency 100mm (4.00”) treated paper pulp cone with rubber surround. 33mm (1.33”) edge wound voice coil
Dispersion 90 degrees conical
CROSSOVER
Frequency 2.3kHz
Type Passive low loss 2nd order compensated LF, 1st order compensated HF
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Old 25th July 2009, 04:45 PM   #7
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thanks guys,

Each one of your posts has been helpful. Will be looking at making these repairs over the next couple of weeks-can't wait
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