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Old 2nd January 2013, 07:43 AM   #21
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Quote:
Originally Posted by portreathbeach View Post
I think I see what your talking about know. Use a simple cap so the crossover point is a lot higher than you think you need (say 20KHz), and because the tweeters dB/w is higher than the main driver this will attenuate the signal from 20KHz and under, no need for an L-Pad, right?
Yes.

dave
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Old 2nd January 2013, 09:38 AM   #22
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Sreten, you mention attenuating with a series resistor. I've found various calculators to work out L-Pad attenuation, but how would you work out the resistance for a single series resistor.

Those Dayton ND20FB-4 look interesting. They are only 15W RMS, so could I use 2 in series, or because of their 90dB/W, would one be fine?
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Old 2nd January 2013, 06:30 PM   #23
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one would be fine, up that high they are not stressed much

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Old 2nd January 2013, 06:50 PM   #24
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by portreathbeach View Post
Sreten, you mention attenuating with a series resistor. I've found various
calculators to work out L-Pad attenuation, but how would you work out
the resistance for a single series resistor.

Those Dayton ND20FB-4 look interesting. They are only 15W RMS, so
could I use 2 in series, or because of their 90dB/W, would one be fine?
Hi,

If you need a calculator, search on "voltage divider gain ", 4R in
series with 4 ohm gives an 8 ohm driver attenuated by -6dB, use
8 ohm to calculate the capacitor, and realise you've just doubled
tweeter powerhandling, though with a x/o at 10KHz, irrelevant *.

2R in series with 4 ohm gives a 6ohm driver with -3.5dB.

As stated the capacitor only method would do -6dB at 10KHz
by setting the cap for 4 ohm and 20KHz, same cap value in
fact as 8 ohm - 4R + 4ohm, the difference would be a rising
response in the top octave, that could work very well too.

Experiment I'd say.

rgds, sreten.

* The tweeters power handling is also irrelevant with a normal
x/o in the 3 to 4KHz range with a speaker of normal sensitivity,
say up to 90dB, for smaller lower efficiency speakers it goes
off the radar, it will have plenty in reserve with attenuation.
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Last edited by sreten; 2nd January 2013 at 07:07 PM.
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Old 2nd January 2013, 08:36 PM   #25
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Thanks again Dave and Sreten. That was well explained. I think I may buy the Dayton's. They are cheap and are pretty small. And now I have a bit more info, I can at least experiment now and roughly know what to expect when inserting different values of resistors and caps.

On second thoughts, Dayton ND20FB-4 or the CSS ERT26? I'm leaning towards the Dayton's
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Last edited by portreathbeach; 2nd January 2013 at 08:46 PM. Reason: Added a question at the end
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Old 2nd January 2013, 09:09 PM   #26
sreten is offline sreten  United Kingdom
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Hi,

Make sure you can mount the Dayton properly.

rgds, sreten.

In fact the easier flush mounting version Dayton_ND20FA-6 (6 ohm) :
Dayton Audio ND20FA-6 3/4" Neodymium Dome Tweeter 275-030

Click the image to open in full size.

Looks like it would suit the capacitor only approach much better for a 10KHz x/o.
(Noting a normal 10KHz x/o is -3dB @10KHz, designing for 20KHz is -9dB @ 10KHz.)
Its peak at 10KHz means you'll get a defined roll off at that point with whatever
capacitor value you choose for relative attenuation, probably the best option.
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Last edited by sreten; 2nd January 2013 at 09:25 PM.
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Old 2nd January 2013, 09:23 PM   #27
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Interesting. Never saw the ND20FA-6 when looking for a tweeter. The mounting will not be a problem of either of these tweeters, so the question now is, which one would be better? Has anyone have any experience with these?

Thanks again
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Old 2nd January 2013, 09:50 PM   #28
sreten is offline sreten  United Kingdom
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Hi,

My opinion is the flush mount will be better if 10KHz is the right
x/o point and you simply want to adjust the series capacitor
to effectively set the level of the supertweeter, not the x/o.
Its a minimalist approach. It will be flatter than the
rearmount just using a single series capacitor.

The rear mount is superbly flat, its more flexible, but more
complicated to use in some respects, but gives more options.

Me ? I think I'd go for KISS, and take it from there.

rgds, sreten.
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Last edited by sreten; 2nd January 2013 at 09:58 PM.
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Old 2nd January 2013, 10:00 PM   #29
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I don't have any answers (probably more questions) but this thread is very interesting to me because just last night I was experimenting with adding some "air" to my dual EL70eN microTowers.

I had been considering getting some cheap piezos and playing with them, but last night I found a pair of old Sansui AA-2900 2-way speakers at the local thrift shop for $20 and bought them for sh!ts n' giggles.

First I just connected them up and tested them. They worked, so I went ahead and disconnected the woofers on each of them and ran them along side my EL70s just to see how much "air" the tweeters would add. Perhaps too much, so I aimed the tweeters at the ceiling and this provides perfect attenuation/dispersion.

About 30 minutes later, I had ripped (carefully removed, actually) the crossovers and tweeters out of the boxes. Now the raw tweeters are "mounted" (pointing straight up) with blu-tac on the top corners of my microTowers. The crossovers are just hanging behind the microTowers and I am running them on the "B" speaker leads so I can flip the "air" on or off with my remote.

I have no idea where the crossover is set but it is quite high. If I run just the "B" speakers (just the tweeters) it is really just the last octave I am hearing (I think).

Anyway, they do just what I figured they would do, add "air" and/or "sparkle" and they can keep up with the EL70 drivers with respect to power. Now I just need to make the whole thing a lot prettier.

Bonus: I now have 2 spare 6.5" woofers for another thrifty project.

Last edited by cogitech; 2nd January 2013 at 10:03 PM.
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Old 2nd January 2013, 10:08 PM   #30
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Facing up! I've seen a few designs with speakers facing up. Never really considered it with tweeters, as I always thought the tweeters needed to face the listener.

Sreten.....KISS?
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Last edited by portreathbeach; 2nd January 2013 at 10:14 PM.
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