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Old 15th September 2008, 11:17 PM   #1
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Default Impedance change for adding a tweeter?

Hi all-
I have built a pair of the BD pipes, and now want to add a ribbon tweeter (hey, I already have them). I'm using two Tang Band drivers in these speakers at 8 ohms each. They are wired in parallel, so total system impedance is 4 ohms.
These speakers are driven by my SE KT88 amp, and I have 4, 8, & 16 ohm taps available (via switch).
My question is, can I just add these tweeters in parallel on top of the speakers (outside)? This give kind of a weird impedance of 2.66 ohms, but maybe it's not an issue?
Anyone have any experience doing something like this?
Thoughts would be appreciated.

Glenn
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Old 16th September 2008, 05:26 AM   #2
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not if you want them to survive,
some reading: http://sound.westhost.com/lr-passive.htm
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Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
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Old 16th September 2008, 12:06 PM   #3
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Interesting reading.
I didn't want to add a Zobel Network because of loss of efficiency of the drivers. The amp is only a few watts as is. All I have on the tweeters is a 2.2uF cap to keep the LF out of the driver.

Thanks for the link.

Glenn
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Old 16th September 2008, 12:13 PM   #4
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The rule in audiophile speaker system:
Never use more than one tweeter in the loudspeaker box.
If you want to build PA speakers than the story is totally different.
Never tune the crossover by naked ears, this will be problem even for the paranormal golden ears
Just use some measure equipment like Clio or some cheeper pc software for this.
Thank you

Regards,
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Old 16th September 2008, 09:15 PM   #5
Sherman is offline Sherman  United States
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What about putting a cap of maybe 1uF in series with the tweet? Should give a high-pass filter of maybe 8-10 KHz (depending on the impedance of the tweet).

That way the tweet isn't part of the circuit until you reach the high-pass limit. By the time you hit that frequency I'm betting the impedance of the TBs is high enough that overall your total impedance would be OK.

Check the impedance curves for your speakers (not the tweeter) and calculate the impedance of the combination at the frequency the cap allows.
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