what effect does a 4 driver have on an 8 ohm crossover? - Page 2 - diyAudio
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Old 5th June 2011, 01:40 AM   #11
AllenB is offline AllenB  Australia
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The way it does this is by controlling the response near the knee. I've attached a plot that shows a 150Hz filter working into an 8 ohm resistor (green) and a 4 ohm resistor.

Second plot is how the filter should ideally work, and third shows real drivers - a 4 ohm 15" driver and an 8 ohm 6" driver.
Attached Images
File Type: gif 1.gif (7.9 KB, 56 views)
File Type: gif 2.gif (8.0 KB, 51 views)
File Type: gif 3.gif (8.9 KB, 51 views)
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Old 5th June 2011, 02:00 AM   #12
60ndown is offline 60ndown  United States
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interesting graphs thank you.

if i understand the graphs correctly? and green is always the 8 ohm, red is 4 ohm.

it looks to me in the 3rd graph, like the 8 ohm drops off and stays gone (above 150hz),

and the the 4 ohm drops out and then returns?
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Old 5th June 2011, 02:31 AM   #13
AllenB is offline AllenB  Australia
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No, in the first graph it is 8 ohm versus 4 ohm. The others show the high pass section and the low pass section.

For the second and third, I modelled a second order high pass instead of first order by mistake (low pass is correct) but it really doesn't matter, the carnage is identified pretty much as I intended.

The third image is the way it is because drivers don't behave like resistors. The fact that it is 4 ohm versus 8 ohm really becomes a minor issue here. Trying to cross woofers over passively at the low end without regard for their impedance variations, is the greater issue.
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Old 5th June 2011, 02:43 AM   #14
tinitus is offline tinitus  Europe
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Allen, I think you are mistaken, or I am

but I think its a stereo sub filter only
meaning a filter for two subs
no filter for mid/midwoofer

so you don't have any info for the third graph showing summed output
at least thats how I see it
tho it does say 2way, its really not
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Old 5th June 2011, 02:59 AM   #15
60ndown is offline 60ndown  United States
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yes i believe the xover sends everything below 150hz to the sub/s and everything above 150hz to any speaker/s you connect to it.
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Old 5th June 2011, 03:13 AM   #16
AllenB is offline AllenB  Australia
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Hmmm, I'll describe what I see in it. Two inductors and four caps. It claims stereo and it claims two way. It claims 12dB low and 6dB high. It shows stereo inputs and stereo outputs, and also claims to have stereo outputs as flyleads meant to be connected to the subs inside the box that it is mounted on.

I'm guessing it's something like this.
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File Type: gif t.gif (2.9 KB, 50 views)
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Old 5th June 2011, 03:14 AM   #17
tinitus is offline tinitus  Europe
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ah, ok, my mistake, you are absolutely correct, sorry

wires for the subs, and output terminal goes to main speakers, ofcourse

still, you need to know the acoustic rolloff of the main speakers to predict anything
so I would still question the third graph

probably works best with a small 5" in closed box
or other driver with high Fs
and lowish Qts for early rolloff

I might be tempted to paralel the two caps, and have no xo on main speakers
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Old 5th June 2011, 03:25 AM   #18
AllenB is offline AllenB  Australia
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Quote:
Originally Posted by tinitus View Post
so you don't have any info for the third graph showing summed output
Wired in phase and out.
Attached Images
File Type: gif in.gif (8.6 KB, 49 views)
File Type: gif out.gif (8.5 KB, 11 views)

Last edited by AllenB; 5th June 2011 at 03:33 AM.
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Old 5th June 2011, 03:31 AM   #19
tinitus is offline tinitus  Europe
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another issue

its not like its a 3way system
even if it really should be

but summed output may also depend on how subs are placed in relation to main speakers
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Old 5th June 2011, 03:33 AM   #20
AllenB is offline AllenB  Australia
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I should point out that the sim uses real impedance information (with phase) and text book component values as I would expect in this unit.

The sim uses flat responses not real speakers. This is to display the transfer functions. It is also why I didn't include the summed responses. I thought the graphs served their purpose of illustration as best as I intended but please note these limitations.
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