Box effect on crossover???

Milzie · 11th December 2002, 04:48 PM

I recently built some 12L sealed bookshelves using Morel MW-164 woofers. I am now interested in putting them into a ported enclosure of about 30L just for kicks. I want to see how this affects the low frequency response. I am also interested if by porting, the speaker will loose its nice tight mid-bass punch.

My question is regarding the crossover. I had Madisound design the crossover for me with LEAP according to the 12L sealed enclosure. What would be required to modify the crossover if I were to put it into the ported enclosure? Would the inductors remain the same and only tweak the capacitors and the resistors? Is this a complete crossover redesign?

Any help, thoughts, or suggestions are appreciated.
Jeff

daatkins · 11th December 2002, 05:36 PM

Should work fine without any crossover mods since porting a box only affects frequencies below, say, 100Hz to 200Hz.

The only exceptions are if any baffle correction has been applied or if the resonant hump has been notched out. Baffle correction is only usually done in TMM boxes and you can tell if a notch filter has been applied if there's a series R-L-C circuit directly across the XO input.

Nice one,
David.

Milzie · 11th December 2002, 07:35 PM

By the resonant hump notched out, I assume you mean impedance correction. If so, then this has been implemented into the design with the inductor being incorporated into the filters inductor (make sense????).

daatkins · 11th December 2002, 07:47 PM

By the resonant hump, I mean the large peak in impedance at the box/driver's resonant frequency and NOT the rise in impedance caused by the voice coil inductance. To correct for the former you use an R-L-C notch filter directly across the woofer or the XO input whereas correcting the latter requires a R-C Zobel network across the woofer only. The only kits I've seen which use a notch filter are from Dynaudio.

The reason that this will affect your transition from a sealed box to a ported is that sealed only has one hump at resonance whereas a ported box has two humps, one either side of the tuning frequency.

Nice one,
David.

Milzie · 11th December 2002, 08:22 PM

What is the nice one???

Here is the schematic. Could it be done?

daatkins · 11th December 2002, 08:42 PM

The 10mfd cap and 12R resistor across the woofer cancel the imdedance rise caused by voice coil inductance.

You should be fine with this crossover in a ported box.

Nice one,
David.

FrankDIY · 11th December 2002, 10:15 PM

I think the LPad should be before the crossover network of the tweeter.

And yes, this crossover is fine for ported box

Milzie · 11th December 2002, 11:41 PM

What is the benefit of putting the L-pad in front of the crossover?

Will this effect the values of the capacitor and inductor?

pinkmouse · 11th December 2002, 11:51 PM

IMHO the L-pad should be nearest the driver, so the rest of the crossover sees an even, level impedance.

Depending on your drivers, you may need to adjust the rest of the crossover, as L-pads will attenuate the HF, and cause some response variations.

FrankDIY · 12th December 2002, 01:46 AM

my mistake, sorry.

11th December 2002, 04:48 PM	#1
Milzie diyAudio Member Join Date: Oct 2002 Location: Barrie, Ontario, Canada	Box effect on crossover??? I recently built some 12L sealed bookshelves using Morel MW-164 woofers. I am now interested in putting them into a ported enclosure of about 30L just for kicks. I want to see how this affects the low frequency response. I am also interested if by porting, the speaker will loose its nice tight mid-bass punch. My question is regarding the crossover. I had Madisound design the crossover for me with LEAP according to the 12L sealed enclosure. What would be required to modify the crossover if I were to put it into the ported enclosure? Would the inductors remain the same and only tweak the capacitors and the resistors? Is this a complete crossover redesign? Any help, thoughts, or suggestions are appreciated. Jeff __________________ The *** is a muscle that MUST be rested!

11th December 2002, 07:35 PM	#3
Milzie diyAudio Member Join Date: Oct 2002 Location: Barrie, Ontario, Canada	By the resonant hump notched out, I assume you mean impedance correction. If so, then this has been implemented into the design with the inductor being incorporated into the filters inductor (make sense????). __________________ The *** is a muscle that MUST be rested!

11th December 2002, 10:15 PM	#7
FrankDIY diyAudio Member Join Date: Mar 2001 Location: Quebec City	I think the LPad should be before the crossover network of the tweeter. And yes, this crossover is fine for ported box __________________ Imagination is more important than knowledge. knowledge is limited, imagination encircles the world. Albert Einstein FrankDIY's Audio Corner

11th December 2002, 11:41 PM	#8
Milzie diyAudio Member Join Date: Oct 2002 Location: Barrie, Ontario, Canada	What is the benefit of putting the L-pad in front of the crossover? Will this effect the values of the capacitor and inductor? __________________ The *** is a muscle that MUST be rested!

11th December 2002, 11:51 PM	#9
pinkmouse diyAudio Moderator Join Date: Apr 2002 Location: Chatham, England	IMHO the L-pad should be nearest the driver, so the rest of the crossover sees an even, level impedance. Depending on your drivers, you may need to adjust the rest of the crossover, as L-pads will attenuate the HF, and cause some response variations. __________________ Al I conceive of nothing, in religion, science or philosophy, that is more than the proper thing to wear, for a while. Charles Fort


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11th December 2002, 05:36 PM	#2
daatkins diyAudio Member Join Date: Aug 2001 Location: Bath, UK	Should work fine without any crossover mods since porting a box only affects frequencies below, say, 100Hz to 200Hz. The only exceptions are if any baffle correction has been applied or if the resonant hump has been notched out. Baffle correction is only usually done in TMM boxes and you can tell if a notch filter has been applied if there's a series R-L-C circuit directly across the XO input. Nice one, David.

11th December 2002, 07:47 PM	#4
daatkins diyAudio Member Join Date: Aug 2001 Location: Bath, UK	By the resonant hump, I mean the large peak in impedance at the box/driver's resonant frequency and NOT the rise in impedance caused by the voice coil inductance. To correct for the former you use an R-L-C notch filter directly across the woofer or the XO input whereas correcting the latter requires a R-C Zobel network across the woofer only. The only kits I've seen which use a notch filter are from Dynaudio. The reason that this will affect your transition from a sealed box to a ported is that sealed only has one hump at resonance whereas a ported box has two humps, one either side of the tuning frequency. Nice one, David.

11th December 2002, 08:42 PM	#6
daatkins diyAudio Member Join Date: Aug 2001 Location: Bath, UK	The 10mfd cap and 12R resistor across the woofer cancel the imdedance rise caused by voice coil inductance. You should be fine with this crossover in a ported box. Nice one, David.

12th December 2002, 01:46 AM	#10
FrankDIY diyAudio Member Join Date: Mar 2001 Location: Quebec City	my mistake, sorry. __________________ Imagination is more important than knowledge. knowledge is limited, imagination encircles the world. Albert Einstein FrankDIY's Audio Corner

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