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Old 26th February 2008, 02:54 PM   #1
arc2v is offline arc2v  United States
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Default Low impedance -- ideas to fix?

I will post plots later when I finally get them off my other computer.

I recently finished my prototype open-baffle center channel speaker. It ended up being a three way using Dayton RS 8" woofers, Neo3 PDR dipole tweeter, and 3" Tangband bamboo midranges.

Crossover points are 500Hz and 3.5kHz, 2nd and 4th order L-R acoustic slopes.

The ONLY thing I don't like about the finished design is two low points in the impedance plot at 1kHz and 8kHz. With the exception of crossover point peaks, the average is around 4 Ohms, which was the target.

Those two aforementioned dips go down to 2.5 and 2.2 Ohms, respectively. It is a pretty steep dip, it doesn't linger down there.

My first thought is panic and redesign the crossover so I don't cook my amp. But then I'm thinking because it's at higher frequencies, even a low impedance won't demand a lot of current (and it's the current and heat that kills the amps)

Any advice on this? Am I being too paranoid? Ideas to fix it? Would a Zobel on the woofers or mids help?

Thanks,
Anthony
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Old 26th February 2008, 04:29 PM   #2
arc2v is offline arc2v  United States
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Here's the impedance plot in question:
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Old 26th February 2008, 08:33 PM   #3
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Hi Anthony,

Can you please post the XO schematic too.

Thanks,
David.
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Old 26th February 2008, 08:47 PM   #4
arc2v is offline arc2v  United States
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I will have to check the actual values, as some of those were tweaked a bit to coincide with what I had available, but for the most part I stayed pretty close.

Thanks for the help.
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Old 26th February 2008, 08:58 PM   #5
SY is offline SY  United States
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What kind of amp are we talking about?
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And while they may not be as strong as apes, don't lock eyes with 'em, don't do it. Puts 'em on edge. They might go into berzerker mode; come at you like a whirling dervish, all fists and elbows.
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Old 26th February 2008, 09:01 PM   #6
arc2v is offline arc2v  United States
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Outlaw 1050 or 955, I believe. 5 channel and has run flat 4 Ohm magnepans for years without breaking a sweat.
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Old 26th February 2008, 09:22 PM   #7
arc2v is offline arc2v  United States
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I've been studying this for a while today, the only thing I can think of is that I wired the Mid low-pass ahead of the Mid high-pass.

In a band-pass filter, does it matter what order you put the elements in? I thought the resonances being so far apart would mean it would not matter.

If it does make a difference, could I just switch them, or would I have to redesign since it would mess up both sides of the crossover?
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Old 26th February 2008, 10:03 PM   #8
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Well, I'll be the first to admit, I'm over my head here, but I would be curious to see the frequency response graphs. I think that would give the Impedance graphs more perspective.

Also, the precise model numbers of the speakers would help.

At best I'll be an observer, but I'll probably learn a bunch.

steve/bluewizard
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Old 27th February 2008, 12:09 AM   #9
arc2v is offline arc2v  United States
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Sure thing, here's the REW measurement (non-gated, in room). 2m, on axis (blue), 30 degree off axis (red). BTW, 30 degrees puts this well outside the seats of my HT.

There's a room anomaly at 200 Hz. It shows up on measurements of my Magnepans as well.
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Old 27th February 2008, 12:29 AM   #10
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I not this isn't exactly what you are after.... but I presume you are paralleling the RS180's and TB3s. You might need to use series connections and a new crossover.
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