Subwoofer Crossover - please critique

[mightydub]

Please tell me what you think of this design and how it could be improved.

The basic concept is a L+R mixer, normal / reversed phase selection, 12dB/octave crossover with selectable crossover points, and an output buffer to drive a single cable to a powered subwoofer. The subwoofer will have a Linkwitz transform circuit tuned for the driver and box plus a power amp.

pdf of the LTspice circuit , jpeg of simulation result
pdf of Eagle schematic
pdf of Eagle pcb layout (preliminary)


Credit where it is due: This is all an adaptation of various circuits and ideas from Rod Elliot's ESP website, where I have learned many things. Thanks Rod!

[mightydub]

Eagle schem

[mightydub]

Eagle PCB

[mightydub]

filter response

[gregorx]

Why does the output attenuation change with frequency selection?

[mightydub]

Originally posted by gregorx
Why does the output attenuation change with frequency selection?

It's the same curve, just translated 10Hz with each step. LTspice file attached if you want to experiment.

[gregorx]

TL072.sub not found.
The amplitude of the curve appears to change also with the frequency unless I am just completely seeing something incorrectly.

[mightydub]

from the TI website:

* TL072 OPERATIONAL AMPLIFIER "MACROMODEL" SUBCIRCUIT
* CREATED USING PARTS RELEASE 4.01 ON 06/16/89 AT 13:08
* (REV N/A) SUPPLY VOLTAGE: +/-15V
* CONNECTIONS: NON-INVERTING INPUT
* | INVERTING INPUT
* | | POSITIVE POWER SUPPLY
* | | | NEGATIVE POWER SUPPLY
* | | | | OUTPUT
* | | | | |
.SUBCKT TL072 1 2 3 4 5
*
C1 11 12 3.498E-12
C2 6 7 15.00E-12
DC 5 53 DX
DE 54 5 DX
DLP 90 91 DX
DLN 92 90 DX
DP 4 3 DX
EGND 99 0 POLY(2) (3,0) (4,0) 0 .5 .5
FB 7 99 POLY(5) VB VC VE VLP VLN 0 4.715E6 -5E6 5E6 5E6 -5E6
GA 6 0 11 12 282.8E-6
GCM 0 6 10 99 8.942E-9
ISS 3 10 DC 195.0E-6
HLIM 90 0 VLIM 1K
J1 11 2 10 JX
J2 12 1 10 JX
R2 6 9 100.0E3
RD1 4 11 3.536E3
RD2 4 12 3.536E3
RO1 8 5 150
RO2 7 99 150
RP 3 4 2.143E3
RSS 10 99 1.026E6
VB 9 0 DC 0
VC 3 53 DC 2.200
VE 54 4 DC 2.200
VLIM 7 8 DC 0
VLP 91 0 DC 25
VLN 0 92 DC 25
.MODEL DX D(IS=800.0E-18)
.MODEL JX PJF(IS=15.00E-12 BETA=270.1E-6 VTO=-1)
.ENDS


[gregorx]

Ok I got it to run. I was confused previously by the stepped attenuation in your simulation. I turned those off for a second (but I am going to copy them for my own simulations soon) and made the attached graph.

I like how fast the high end rolls off but assuming I did the simulation correctly --big assumption-- it appears that the low end rolls off too quickly.

[mightydub]

There's two sets of spice directives - one for the AC simulation which steps the resistor values to change the crossover point, and one to step through the gain values for a time domain simulation. I toggle them between comment and spice directive depending on which one I want to run.

Delete the two 0.22u caps on the input to get rid of the low end rolloff.