crossover changes for a sloped baffle?

Jim85IROC · 15th March 2004, 08:42 PM

Typically, would crossover changes be necessary to impliment a sloped baffle to time-align the drivers, or in reverse, to use a flat baffle with a crossover designed to be used with drivers on a sloped baffle? I'm heavily considering building the Usher CP-737s, which have the tweeter on a sloped baffle to time-align it with the woofer, but I'm leaning toward a flat baffle so that I can position the tweeter closer to the mid. Can I still use that crossover without causing a collapse of the universe?

Bill Fitzpatrick · 15th March 2004, 09:09 PM

Enough of a slope to time align the drivers means you will have to consider the off axis response of the driver rather than the on axis response. The crosssover will, in most cases, need to modified.

Jim85IROC · 16th March 2004, 11:54 AM

The usher in question has what appears to be approximately a 10 degree tilt, which I would imagine wouldn't be enough to effect too much except the highest octave of the response, and the tweeter filter is a simple 3rd order with a series resistor for attenuation. Since I tend to like my highs a tad bright anyway, I guess I can take a chance with a flat baffle.

rabbitz · 16th March 2004, 01:18 PM

There is a paragraph in the Loudspeaker Design Cookbook the states that "experts" often suggest the inverted driver position when you use odd order networks with reversed polarity for the tweeter on third order in order to compensate for polar tilt. The theory is that driver geometry would give you +15º tilt and odd order filter give you a -15º tilt would sum to a 0º Zero Delay Plane.

For this to work the drivers have to have horizontal and vertical offsets so the tan of this would be 15º. In other words:

Tan 15º = (horizontal offset / vertical offest)

Vertical offset is the centre distance between the drivers.
Horizontal offset is the difference between the voice coil centre of the drivers (use the centre of the motor driver frontplate).

Phew! Hope this might be of some help, if you can follow my explanation.

Jim85IROC · 16th March 2004, 02:33 PM

The crossover schematic indicates normal polarity on the tweeter, and the accompanied write-up doesn't mention reversing the polarity.

The plot thickens.

rabbitz · 17th March 2004, 02:06 PM

If it's a proven design you are better off sticking with it.

This is just a method to help with alignment on a flat baffle. BTW, my understanding is that the preferred polarity for 3rd order is reversed, but it all come down to listening tests in the end.

15th March 2004, 08:42 PM	#1
Jim85IROC diyAudio Member Join Date: Dec 2003 Location: Stamford VT	crossover changes for a sloped baffle? Typically, would crossover changes be necessary to impliment a sloped baffle to time-align the drivers, or in reverse, to use a flat baffle with a crossover designed to be used with drivers on a sloped baffle? I'm heavily considering building the Usher CP-737s, which have the tweeter on a sloped baffle to time-align it with the woofer, but I'm leaning toward a flat baffle so that I can position the tweeter closer to the mid. Can I still use that crossover without causing a collapse of the universe?

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15th March 2004, 09:09 PM	#2
Bill Fitzpatrick diyAudio Member Join Date: Jun 2001 Location: Eugene, OR	Enough of a slope to time align the drivers means you will have to consider the off axis response of the driver rather than the on axis response. The crosssover will, in most cases, need to modified.

16th March 2004, 11:54 AM	#3
Jim85IROC diyAudio Member Join Date: Dec 2003 Location: Stamford VT	The usher in question has what appears to be approximately a 10 degree tilt, which I would imagine wouldn't be enough to effect too much except the highest octave of the response, and the tweeter filter is a simple 3rd order with a series resistor for attenuation. Since I tend to like my highs a tad bright anyway, I guess I can take a chance with a flat baffle.

16th March 2004, 01:18 PM	#4
rabbitz diyAudio Member Join Date: Jul 2003 Location: Newcastle, Australia	There is a paragraph in the Loudspeaker Design Cookbook the states that "experts" often suggest the inverted driver position when you use odd order networks with reversed polarity for the tweeter on third order in order to compensate for polar tilt. The theory is that driver geometry would give you +15º tilt and odd order filter give you a -15º tilt would sum to a 0º Zero Delay Plane. For this to work the drivers have to have horizontal and vertical offsets so the tan of this would be 15º. In other words: Tan 15º = (horizontal offset / vertical offest) Vertical offset is the centre distance between the drivers. Horizontal offset is the difference between the voice coil centre of the drivers (use the centre of the motor driver frontplate). Phew! Hope this might be of some help, if you can follow my explanation.

16th March 2004, 02:33 PM	#5
Jim85IROC diyAudio Member Join Date: Dec 2003 Location: Stamford VT	The crossover schematic indicates normal polarity on the tweeter, and the accompanied write-up doesn't mention reversing the polarity. The plot thickens.

17th March 2004, 02:06 PM	#6
rabbitz diyAudio Member Join Date: Jul 2003 Location: Newcastle, Australia	If it's a proven design you are better off sticking with it. This is just a method to help with alignment on a flat baffle. BTW, my understanding is that the preferred polarity for 3rd order is reversed, but it all come down to listening tests in the end.

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