Total impedance when running tweeter in parallel with a FE206E? - diyAudio
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Old 7th April 2008, 11:45 PM   #1
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Default Total impedance when running tweeter in parallel with a FE206E?

Hi all. I plan on building these speakers.:

http://www.quarter-wave.com/Project0..._Enclosure.pdf

I also want to mount some Fostex FT17H tweeters directly underneath the FE206Es with like 1/8th inch between them. I plan on using a simple single cap crossover and a L pad. It seems that I read somewhere that this type of setup is still considered to be a 8 ohm load even though the tweeter and the driver will be connected in parallel. Something about the reactance of the cap and the inductance of the voice coils. Am I remembering this right?
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Old 8th April 2008, 12:14 AM   #2
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Hello G, The general statement that this is still a nominal 8 ohm load is correct. Because of the natural rolloff of the fullrange, and the capacitor acting as a high pass filter for the tweeter, the amp sees the parallel combination as a nominal 8 ohm load. I say nominal because any speakers impedance is going to vary based upon the frequency, and based upon how hard it is driven. When the driver moves around it is moving the voice coil in the magnetic field, this will also cause some change to the impedance.
But in general, if you hook a tweeter and cap in series, then hook this in parallel with your full range (or dare I say it in this forum, mid range and woofer) the general impedance will stay the same.

Peace,

Dave
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Old 8th April 2008, 12:58 AM   #3
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Thank you very much for your reply Dave. I just wanted to get that straightened out before ordering parts and building the amp that I plan on using with these speakers. I will have to do some studying to understand the theory behind the reality but I needed a quick answer to calm my worried mind. I'm sure you understand.
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Old 8th April 2008, 01:08 AM   #4
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Just my 2 cents, I started with Martins MLTL with a 206E powered by Zen V9 and after following the half chang thread, decided to build them on Martins recommendation. The build is no harder than the MLTL. I finished my half chang's a couple of weekend ago and agree with Martins recommendation that they are a step up from the MLTL. There is clearly more base with a larger and more distinct soundstage. The half chang's are a little taller, but the foot print is pretty much the same.

Either build is great, just more base from the chang's
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Old 8th April 2008, 02:06 AM   #5
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Can someone point me to the schematics and diagrams of the "Half Chang"? I don't seem to be able to find them.
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Old 8th April 2008, 02:47 AM   #6
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http://www.frugal-horn.com/spawn-plans.html

Scroll down until you find the chang family of plans
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Old 8th April 2008, 03:45 AM   #7
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It all comes down to the impedance (resistance) at the XO frequency, not the rated nominal impedance of the driver. This impedance changes with load and heat. As the transducer is required to produce more energy the unit (VC) heats and the resistance is greater. If there is more mechanical loading the VC also heats to a greater degree. Energy is never gained or lost, just transformed.

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Old 8th April 2008, 11:33 AM   #8
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Quote:
Originally posted by ronc
It all comes down to the impedance (resistance) at the XO frequency, not the rated nominal impedance of the driver. This impedance changes with load and heat. As the transducer is required to produce more energy the unit (VC) heats and the resistance is greater. If there is more mechanical loading the VC also heats to a greater degree. Energy is never gained or lost, just transformed.

ron
I guess that makes the crossover cap critical huh? Can anyone explain to me how to calculate the crossover cap?
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Old 8th April 2008, 02:02 PM   #9
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For a simple 1st order cap, C=0.159/(Rxf)

where
C is in Farads (F) not uF
R is resistance at the xo point (not driver nominal or Re)
f is frequency (Hz)

There are online calculators.
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Old 8th April 2008, 08:14 PM   #10
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Quote:
Originally posted by bluemartini
http://www.frugal-horn.com/spawn-plans.html

Scroll down until you find the chang family of plans

Can someone expand the "BVR" TLA please.
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