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Old 5th October 2012, 05:36 AM   #1
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Question Newbie with a 500/3500 Crossover

I'm just trying to understand the crossover frequencies and slopes that I'm dealing with here.

The crossover is a three-way with points at 500 and 3,500Hz. The LP slope is -12dB/octave, the MP slope is -6dB/octave, and the HP slope is -18dB/octave. Claims to be Butterworth type (Eminence part PXB3:3K5).

Is the following correct?
The woofer would see 1,000Hz at -24dB, 500Hz at -12dB, and 250Hz at 0dB with everything lower than 250Hz flat.

The midrange on its lower end would see 63Hz at -24dB, 125Hz at -18dB, 250Hz at -12dB, 500Hz at -6dB, and 1,000Hz at 0dB. Then at the upper end, 1,750Hz at 0dB, 3,500Hz at -6dB, 7,000Hz at -12dB, and 14,000Hz at -18dB.

The tweeter would see 1,750Hz at -36dB, 3,500Hz at -18dB, and 7,000Hz at 0dB which then is flat to its highest frequency possible.

Is this correct?

I admit that I'm still reading how to use the Passive Crossover Designer 7 spreadsheet. It looks very thorough!

I'm in a bind because the midrange is seeing a LOT of lower frequencies and only at around a puny 75W continuous with bass drum/bass guitar heavy program material (think Rush 'YYZ' perhaps or your fave bass heavy track). Each speaker's midrange is in a completely sealed enclosure of its own. But, each midrange is tracking the woofer's longest excursions at only around 75W so the effect/problem must be electrical and not acoustical?

Is this just the result of a -6dB/octave midrange slope? Would even the slightest air leak cause pressure inside the mid's separate enclosure? I could check again.

They do sound very nice but I'm worried that a mid will be blown/fried at some time or another.

Thanks.
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Old 5th October 2012, 06:27 AM   #2
puppet is offline puppet  United States
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Woofer would be -3db@500(the xo pole) ... -12db@1k <---- 2nd order BW LP

HP Midrange is -3db@500(the xo pole) ... -24db@30 <-------- 1st order BW HP
LP Midrange is -3db@3.5k(the xo pole) ... -12db@12k(?) <-------1st order BW LP

HP Tweeter is -3db@3.5k(the xo pole) ... -24db@1.5k <------- 3rd order BW HP

... your midrange driver is getting a real workout :P

Last edited by puppet; 5th October 2012 at 06:29 AM.
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Old 5th October 2012, 08:28 AM   #3
Tomom is offline Tomom  Australia
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I apologize to PrecisionAudio for tapping in, but it may help us all; I am trying to tune ported box. If Zobel correction will be included on the woofer, should the tuning be done with zobel across woofer, or added later, after tuning is done... Thanks..
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Old 5th October 2012, 01:43 PM   #4
Dissi is online now Dissi  Switzerland
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Location: Winterthur
Tomom:
The zobel does not influence the vent tuning and can be done later.

PecisionAudio:
A first order crossover does not attenuate the drivers resonance very much and causes high excursions at lower frequencies. But i don't think that there will be a power handling problem. Attachment: Simulation of what may happen, component values and driver are fictional (estimated).
Attached Images
File Type: jpg Midrange.jpg (112.4 KB, 51 views)

Last edited by Dissi; 5th October 2012 at 01:46 PM.
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Old 5th October 2012, 02:44 PM   #5
Dissi is online now Dissi  Switzerland
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Default Turn around

Adding a resistor in parallel to the driver should help to reduce the resonance peak and the low frequency excursions.
Attached Images
File Type: jpg MidrangeImproved.jpg (113.7 KB, 49 views)

Last edited by Dissi; 5th October 2012 at 03:07 PM.
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Old 6th October 2012, 01:30 PM   #6
Tomom is offline Tomom  Australia
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Thank you Dissi, and good luck with your project PrecissionAudio...
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Old 8th October 2012, 12:05 AM   #7
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Thanks puppet and Dissi!

I was trying to understand how the xo points and slopes that are given for an xo unit can be used to discover the equations (by trying to work backwards, I got the math wrong apparently) and then make an excel spreadsheet that would plot it out. Instead of using another's work, I would like to learn this stuff for myself by programming it into excel and making the graphs.

Is there a super basic spreadsheet that just takes a xo point, the slope, and if it is HP or LP? I could work from there I guess.

And, I do like the resistor in parallel with the midrange idea. Again, as a newbie, this would be the same as taking the resistor's wire ends and soldering one to the driver's positive terminal and the other to the negative terminal, right? I'd probably not permanently solder it though but use some sort of wiring.

Thanks again!
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