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Citation 12 non-complimentary to drive ribbon tweeter
Citation 12 non-complimentary to drive ribbon tweeter
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Old 30th December 2017, 12:25 AM   #21
indra1 is offline indra1  Indonesia
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Are you sure your ribbon will not melt or deform?
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Old 30th December 2017, 01:56 AM   #22
2 picoDumbs is offline 2 picoDumbs  Australia
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Quote:
Originally Posted by woofertester View Post
The dB meter is a vintage Radio Shack analog hand-held unit. I performed the measurements more than once.

3kHz is in the passband of both the tweeter and the midrange.

At this point, I am satisfied that the ribbon will require much more than 100A peaks. It makes sense to have peak current capability of 300 to 400 amps.

That will require a bloody big transformer.
And many large filtering caps.
Not cheap unfortunately.
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Old 30th December 2017, 02:12 AM   #23
indra1 is offline indra1  Indonesia
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Originally Posted by 2 picoDumbs View Post
That will require a bloody big transformer.
. . . .
Big transformer is good, forget the bloody part, creates electric short.
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Old 30th December 2017, 02:32 AM   #24
woofertester is offline woofertester  United States
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Originally Posted by indra1 View Post
Are you sure your ribbon will not melt or deform?
The current peaks will be less than a milli-second. I doubt that heating will be a problem with music.

What breaks ribbons is puffs of air from handling the assembly. Magnepan ships their tweeters with a flexible rubber magnetic strip covering the tweeter to prevent air flow.

If the ribbon breaks, it is very quick and easy to replace. In the picture, you can see the screws/nuts holding small plates in place. Loosen the nuts. Slide out the remnants of the broken ribbon. String a new ribbon. Tighten the nuts. Back in business.
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Old 30th December 2017, 02:51 AM   #25
woofertester is offline woofertester  United States
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Originally Posted by 2 picoDumbs View Post
That will require a bloody big transformer.
And many large filtering caps.
Not cheap unfortunately.
Maybe not. The average power may be very low. The caps may charge fast enough to supply the next peak without needing heavy iron. The tweeter likes to be crossed over no lower then 3kHz and does not like a gentle crossover slope.

Keep in mind that a tweeter supplies less of the acoustic watts of a typical speaker system than a woofer or a midrange. Typical music spectral content falls at 10dB / decade when looked at from 20Hz to 20 kHz if i recall correctly.

I am thinking that a few paralleled conventional TO220 MOSFETs may work in the complementary Citation configuration. Mouser has some TO220 N and P FETs that are in the 3-ish milli-ohm RDSon range and are rated around 200A. I have ordered a few of each to characterize.
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Old 30th December 2017, 03:11 AM   #26
2 picoDumbs is offline 2 picoDumbs  Australia
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Well you said you need 300A capability.
If you only need 20A or 30A that wouldn't be too difficult.
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Old 30th December 2017, 03:38 AM   #27
indra1 is offline indra1  Indonesia
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Originally Posted by woofertester View Post
The current peaks will be less than a milli-second. I doubt that heating will be a problem with music. . . .
I can not say for sure but something is off. As a comparison, we usually weld 0.8mm stainless steel plates at 10-20A, your previous comment about 300-400A will melt the tip of 1/4" steel rod on contact. Initial testing with much lower current say 20A-30A makes a lot of sense. you can easily add more power later.
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Old 30th December 2017, 12:15 PM   #28
jan.didden is offline jan.didden  Europe
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Originally Posted by woofertester View Post
1. My measurements were very near field, about 1 inch from the driver. At a listening position, the dBs will be lower. The 86 dB sensitive midrange only required 12 mW to achieve 85 dB right at the cone. 10*Log (1/0.012) = 19 dB. So, as a wet thumb in the air, subtract 19 dB from your numbers.
Isn't speaker sensitivity normally measured at 1m distance? Like xxdB at 1W at 1m.
That would give better perspective and comparison figures.

Jan
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Old 30th December 2017, 08:02 PM   #29
woofertester is offline woofertester  United States
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Originally Posted by 2 picoDumbs View Post
Well you said you need 300A capability.
If you only need 20A or 30A that wouldn't be too difficult.
That will be the goal of the first attempt; to create more than 20A into the ribbon. It will just be low duty cycle 3kHz pulses to see where the amp clips and how well it works into low a impedance load.
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Old 30th December 2017, 08:08 PM   #30
woofertester is offline woofertester  United States
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Originally Posted by jan.didden View Post
Isn't speaker sensitivity normally measured at 1m distance? Like xxdB at 1W at 1m.
That would give better perspective and comparison figures.

Jan
You can measure sensitivity with an amp and a calibrated mic, etc. You can also measure the T/S parameters and the sensitivity falls out the calculations.

I chose to measure the T/S parameters of the midrange. I have tested these drivers outdoors with a friend's LMS and they are quite flat to 3kHz. The acoustic test I performed was to compare the near field sensitivity of the two drivers. Near field measurements are less prone to room interaction. Measuring at 1m requires either an anechoic chamber or outdoors where there are no reflections. I chose the path of least resistance. (pun intended)
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