[guf]

I purchased a pair or Fostex T90a to add to my Omega speakers, not because they were lacking but because I wanted to try it. I followed the instructions and the suggestions from Madisonsound,  I used a L pad and a ClarityCap 1.0 mfd.( I also have and .47.) I also purchased a few resistors that I think I could use if I choose not to use the L pad?  Now I set it up with some banana clips and it works! But what did I do? Did I build a high pass filter? A simple crossover? What are some experiments I can do with it? Following some other threads I'm aiming it in different directions. And I think with the L pad I'm adjusting where the T90a is crossing over, taking over, blending? Is this measurable? Any input is greatly appreciated!

[ClefChef]

you have created a simple high pass filter with a 90 degree phase shift, the smaller the cap value - the higher the frequency. You should probably use one resistor (high quality non-inductive) in series with the cap, not the L-pad.

[roscoe65]

I purchased a pair or Fostex T90a to add to my Omega speakers, not because they were lacking but because I wanted to try it. I followed the instructions and the suggestions from Madisonsound,  I used a L pad and a ClarityCap 1.0 mfd.( I also have and .47.) I also purchased a few resistors that I think I could use if I choose not to use the L pad?  Now I set it up with some banana clips and it works! But what did I do? Did I build a high pass filter? A simple crossover? What are some experiments I can do with it? Following some other threads I'm aiming it in different directions. And I think with the L pad I'm adjusting where the T90a is crossing over, taking over, blending? Is this measurable? Any input is greatly appreciated!

The L-pad maintains a constant impedance as seen by the amp as you vary the attenuation on the supertweeter.  Your 1uF cap brings your supertweeter in at a nominal 20khz.  Assuming you are blending this in with a single Omega driver, you probably have to pad down by 10-12dB, in which case you want the L-pad.  Alternatively, you can cut the supertweeter in even higher and try it without the l-pad.  Your .47uF capacitor should give your a crossover point of about 36khz.  At 6dB/octave this should be 12dB down at 9khz.  It might be perfect as a true supertweeter.

[DaveC113]

Omegas already extend high enough I don't think you need a L-pad, you can just reduce the size of the cap to attenuate... If you xo one octave higher that makes for 6dB attenuation.

[guf]

Omegas already extend high enough I don't think you need a L-pad, you can just reduce the size of the cap to attenuate... If you xo one octave higher that makes for 6dB attenuation.

Thanks you guys. So if I have the 1.0 cap in there now and barely turn on L pad on that means I could use the .47 and no L pad and get the same results?

[sebrof]

I'm not sure how you have it set up, but the other posters seem to know so they can add or correct me.

Usually the L-Pad is to adjust the level (volume) of the tweeter. The sensitivity of the Omega driver and the tweeter won't usually be the same, so the L-Pad allows you to adjust so the tweeter isn't too loud vs. the main (Omega) driver.
Many people replace the L-Pad with a good resistor(s) once they figure out the value that sounds best.

 The cap sets the frequency the tweeter crosses over. A cap in series (which I assume is what you have) will be a 1st order high pass filter. 6db per octave which is a gentle slope.
For your 1 uf cap assuming the tweeter is 8 ohms, you will be down approximately 3db at 20 KHz, 9db at 10KHz (1 octave), 15db at 5KHz (2 octaves)...
I'm pretty sure the numbers are correct but in any case that's the idea.

[guf]

I'm not sure how you have it set up, but the other posters seem to know so they can add or correct me.

Usually the L-Pad is to adjust the level (volume) of the tweeter. The sensitivity of the Omega driver and the tweeter won't usually be the same, so the L-Pad allows you to adjust so the tweeter isn't too loud vs. the main (Omega) driver.
Many people replace the L-Pad with a good resistor(s) once they figure out the value that sounds best.

 The cap sets the frequency the tweeter crosses over. A cap in series (which I assume is what you have) will be a 1st order high pass filter. 6db per octave which is a gentle slope.
For your 1 uf cap assuming the tweeter is 8 ohms, you will be down approximately 3db at 20 KHz, 9db at 10KHz (1 octave), 15db at 5KHz (2 octaves)...
I'm pretty sure the numbers are correct but in any case that's the idea.

wow thanks, helpful.
I spend hours reading stuff and it's like I'm reading a foreign language. I'm trying to understand. I appreciate your input.

[DaveC113]

Thanks you guys. So if I have the 1.0 cap in there now and barely turn on L pad on that means I could use the .47 and no L pad and get the same results?

The .47 uF cap would be ~6dB less SPL vs the 1 uF cap.

Since the Omegas hit nearly 20 kHz anyways there is no need for an l-pad, just use a smaller cap. 

[guf]

The .47 uF cap would be ~6dB less SPL vs the 1 uF cap.

Since the Omegas hit nearly 20 kHz anyways there is no need for an l-pad, just use a smaller cap.

thats working great thanks!

[guf]

wait.....if I'm hearing lots of sound from the super tweeter with the .47 does that mean I did something wrong? Because I should barely hear any thing right?

[roscoe65]

wait.....if I'm hearing lots of sound from the super tweeter with the .47 does that mean I did something wrong? Because I should barely hear any thing right?

Wrong.  The T90A is rated at 106dB.  If you are crossing over at 40khz, you would expect 103dB from one watt at that frequency.  One octave down (20khz) you should hear 97dB.  One octave below that (10khz) you should expect to hear 91 dB.  If the rated response of the T90A is correct, you might want to cross over even higher, say 60khz (.33uF) which should put you closer to where you want to be with a true (>15khz) supertweeter.

[guf]

Digging through a few things I found a pair of 630v .1s  I don't have any .33s but I like the subtleness of these .1s

[Big Red Machine]

You guys keep discussing as I am getting closer to getting a pair of these myself!

[roscoe65]

Digging through a few things I found a pair of 630v .1s  I don't have any .33s but I like the subtleness of these .1s

I'm going to assume that with the rising impedance of the T90A it is acting as a 16 ohm driver at very high frequencies.  A .1 uF filter will result in a 90khz crossover point, putting you at 97 dB at 45 khz and 91 dB at 22.5khz.  Of course, the driver's response is unlikely to go beyond 30khz, so you're really just adding a bit of air above 20khz.  It should be barely detectable.

[guf]

You guys keep discussing as I am getting closer to getting a pair of these myself!

Yeah your thread turned a thought into it happening. Thanks

[Big Red Machine]

I don't feel like I have a deficiency. I'm just bored.

[DaveC113]

Wrong.  The T90A is rated at 106dB.  If you are crossing over at 40khz, you would expect 103dB from one watt at that frequency.  One octave down (20khz) you should hear 97dB.  One octave below that (10khz) you should expect to hear 91 dB.  If the rated response of the T90A is correct, you might want to cross over even higher, say 60khz (.33uF) which should put you closer to where you want to be with a true (>15khz) supertweeter.

Yup, I'd guess .3ish would be about right. I'm using .57 uF on T500s but the mids are closer to 100 dB.

[guf]

Yup, I'd guess .3ish would be about right. I'm using .57 uF on T500s but the mids are closer to 100 dB.

Wrong.  The T90A is rated at 106dB.  If you are crossing over at 40khz, you would expect 103dB from one watt at that frequency.  One octave down (20khz) you should hear 97dB.  One octave below that (10khz) you should expect to hear 91 dB.  If the rated response of the T90A is correct, you might want to cross over even higher, say 60khz (.33uF) which should put you closer to where you want to be with a true (>15khz) supertweeter.

....Making in completely obvious that I know nothing...how do you guys know this?! Does everybody know this? Is there a chart or calculator? Is it basic electronics that I should have learned in science class?

 And If I'm using .1 what does that mean? I'm crossover at what and my db should be????

[DaveC113]

....Making in completely obvious that I know nothing...how do you guys know this?! Does everybody know this? Is there a chart or calculator? Is it basic electronics that I should have learned in science class?

 And If I'm using .1 what does that mean? I'm crossover at what and my db should be????

Well, I own a lot of books on speaker design and have done a lot of research designing my own speaker.

If you google crossover calculator you'll find applets and charts for calculating all sorts of xos and tons of info on the subject.

Basically, the smaller the cap the higher the xo point and with one cap you get a 6 dB/octave slope, so for a super tweeter you can simply raise teh xo point in order to attenuate output rather than use resistors, which add another part between the amp and driver. In your case it ultimately doesn't really matter as you'll have to experiement with cap values to get the sound you prefer and I'd agree w/Roscoe that you'll probably find a good balance around .3 uF for your setup but it depends a lot on personal preference.

[roscoe65]

....Making in completely obvious that I know nothing...how do you guys know this?! Does everybody know this? Is there a chart or calculator? Is it basic electronics that I should have learned in science class?

 And If I'm using .1 what does that mean? I'm crossover at what and my db should be????

https://www.v-cap.com/speaker-crossover-calculator.php