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What value Capacitor ?


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Can anyone tell me what Value Capacitor I would need, I want to use a Capacitor in line on the positive side of Fostex T90A super tweeters, They say the Tweeters are 8 OHM and can run from 5000 - 35000HZ. They also say I can use 0.33uf, through 0.68uf but they dont give any kind of information on approx cut off for any of the given capacitor values.  I would like to Cut off somewhere close to 9000 HZ (Tweeter playing above that only)  Basically want to add air on top end.  The caps can get quite pricey so I am trying to get by buying 1 pair VS having a couple hundred $$ worth lying around gathering Dust.  Any help appreciated

 

Joe  

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"We recommend using a capacitor as a crossover in the plus line to the tweeter, something from 0.47mfd to 1.5mfd. The smaller the capacitor value the higher it will crossover and the quieter the tweeter becomes. If the tweeter is still too bright after trying different capacitors, you can add a 1 ohm resistor in series with the capacitor and try the different capacitors again."

 

I would start with 1.5uF, which is 1.3kHz. This sounds high, but the Fs for that tweeter is pretty high at 5kHz. 1.5uF would put you 6dB down just slightly above resonance -- which sounds right to me. If the tweeter sounds too hot, use the .68uF. Buy cheap caps to dial it in, then buy some nice films once you feel like you have it where you want it.

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15 minutes ago, Deang said:

"We recommend using a capacitor as a crossover in the plus line to the tweeter, something from 0.47mfd to 1.5mfd. The smaller the capacitor value the higher it will crossover and the quieter the tweeter becomes. If the tweeter is still too bright after trying different capacitors, you can add a 1 ohm resistor in series with the capacitor and try the different capacitors again."

 

I would start with 1.5uF, which is 1.3kHz. This sounds high, but the Fs for that tweeter is pretty high at 5kHz. 1.5uF would put you 6dB down just slightly above resonance -- which sounds right to me. If the tweeter sounds too hot, use the .68uF. Buy cheap caps to dial it in, then buy some nice films once you feel like you have it where you want it.

Thanks Dean. Buy Cheap Caps, Do I understand correctly that pretty much any 5.00 / cheap  cap so long as it is the proper value will be safe, IE not fry the tweeter ?

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I just received this response from Madisound, Reading below am I correct that when he says Padding he is saying resistor / resistance, IE take a 30 ohm resistor and run it across the positive / negative terminals, and also adding 1.5 ohm resistor b-4 the cap 

 

"The T90A has been used with the BK16  with a .68uf cap, the padding is
1.5 ohms before the cap and 30 ohms across the driver, this could be
your starting point. Vary the 1.5 ohm for level. The proper level is
when you really don’t know the T90A is there till it is disconnected."

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Also would this Capacitor be adequate for testing

 

https://www.parts-express.com/dayton-audio-dmpc-033-033uf-250v-polypropylene-capacitor--027-404

 

Would this be a suitable resistor

 

https://www.parts-express.com/30k-ohm-1w-flameproof-resistor-10-pcs--003-30k

 

I know I am asking alot here but I have never stepped into this arena and would hate to fry a 200.00+ tweeter I do appreciate advice / help

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Is this for the BK16?

 

Yes, they are telling you to use a .68uF capacitor in series with positive, and a L-pad, using a 1.5 ohm resistor between the the capacitor and the driver, and a 30 ohm resistor between positive and negative of the driver. 

 

https://www.parts-express.com/mills-30-ohm-12w-non-inductive-resistor--005-30

 

https://www.parts-express.com/mills-15-ohm-12w-non-inductive-resistor--005-1.5

 

These are the resistors I like. However, you can find much cheaper for experimenting. 

 

The capacitor you found is fine. Don’t get too comfortable with it  🙂

 

I like these quite a bit - best of the metalized type. 

 

https://www.parts-express.com/jantzen-audio-068uf-800v-z-superior-capacitor--027-472

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Thanks a ton Dean,

 

I am going to play with the BK16 and the Audio Nirvana 15, I dont feel like i am missing anything on the top end of either but I do like air on the top end and so just basically curious how the super tweeter will affect overall sound

 

all the parts I listed above are cheapo for testing ONLY,  I know once the blend sounds right I will get much better parts just hated the idea of spending 30-40.00 per cap to have them end up setting in a box for years with no use. I wont mind tossing a 2.00 cap or better yet donate them to the next person looking to find there sweet spot on a tweeter

 

You really helped me out here

 

Thanks again

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I see the spec sheet has a contraction to some extent. 

 

In text it recommends a 12 dB crossover designed to crossover above 7000 Hz.  This will require a cap and inductor.  

 

But they show a schematic with only a cap, which results in a 6 dB rolloff.  

 

If I were doing this I'd use a 12 dB or even 18 dB (two caps and an inductor for this highpass application).  

 

You can find calculators on line to figure values.  

 

WMcD

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You can use this to calculate/confirm your crossover design and L-pad.  If possible, the driver's actual impedance at the desired crossover frequency should be used.  The crossover point should be set above fs and one octave above the horn's cut-off (2x) (and a point where the horizontal dispersion is similar to the driver that plays the next lower frequencies, if you can find that).

 

http://ccs.exl.info/installation/crossovers-installation-tweaking/crossover-calculators/#first

 

If you are replacing a K-77, moving the crossover below the recommended 12 dB/octave at 7k should require at least an 18 dB/oct crossover.  Apparently the impedance is such that the original Klipsch 18 dB crossover in many models will work.

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I am and your advice as well Dean I ordered the resistors you recommended and the cheap dayton caps for experimentation. While I appreciate the other advice they may as well be speaking Hungarian. It is all over my head. If I could pick  up how to design and build crossovers I would be a speaker manufacturer :)  I have a hard enough time figuring out bi-amp 

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  • 5 years later...

What type of in-line capacitors do I need for my tweeters I have 2 pairs Rockville X8C competition speakers with titanium tweeters from Rockville please been looking for help for a very long time also what type of amp will I need to power 4 pairs of Rockville x8c with 8 tweeters from Rockville let me know asap 

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3 hours ago, New2caraudio said:

What type of in-line capacitors do I need for my tweeters I have 2 pairs Rockville X8C competition speakers with titanium tweeters from Rockville please been looking for help for a very long time also what type of amp will I need to power 4 pairs of Rockville x8c with 8 tweeters from Rockville let me know asap 

What are these going in?

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