Low impedance -- ideas to fix?

arc2v · 26th February 2008, 01:54 PM

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

arc2v · 26th February 2008, 03:29 PM

Here's the impedance plot in question:

Dave Bullet · 26th February 2008, 07:33 PM

Hi Anthony,

Can you please post the XO schematic too.

Thanks,
David.

arc2v · 26th February 2008, 07:47 PM

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.

SY · 26th February 2008, 07:58 PM

What kind of amp are we talking about?

arc2v · 26th February 2008, 08:01 PM

Outlaw 1050 or 955, I believe. 5 channel and has run flat 4 Ohm magnepans for years without breaking a sweat.

arc2v · 26th February 2008, 08:22 PM

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?

BlueWizard · 26th February 2008, 09:03 PM

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

arc2v · 26th February 2008, 11:09 PM

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.

Dave Bullet · 26th February 2008, 11:29 PM

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.

26th February 2008, 01:54 PM	#1
arc2v diyAudio Member Join Date: May 2007	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

26th February 2008, 07:58 PM	#5
SY diyAudio Moderator Join Date: Oct 2002 Location: Chicagoland Blog Entries: 1	What kind of amp are we talking about? __________________ If there's a sucker born every minute, where do the rest of them come from?

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26th February 2008, 07:33 PM	#3
Dave Bullet diyAudio Member Join Date: Jan 2002 Location: Wellington, New Zealand	Hi Anthony, Can you please post the XO schematic too. Thanks, David.

26th February 2008, 08:01 PM	#6
arc2v diyAudio Member Join Date: May 2007	Outlaw 1050 or 955, I believe. 5 channel and has run flat 4 Ohm magnepans for years without breaking a sweat.

26th February 2008, 08:22 PM	#7
arc2v diyAudio Member Join Date: May 2007	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?

26th February 2008, 09:03 PM	#8
BlueWizard diyAudio Member Join Date: Jun 2007	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

26th February 2008, 11:29 PM	#10
Dave Bullet diyAudio Member Join Date: Jan 2002 Location: Wellington, New Zealand	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.