Subwoofer crossover / subwoofer module design

[derMichi]

hey guys,

after doing a lot of internet research about active subwoofer modules like e.g. the mivoc am 80 or detonation dt 50, i decided to have a go on building one on my own.
my setup: my main speakers are cyburgs needles, which some of you might know, with frs8-speakers. some day, i will upgrade them to tangbands, but for now,a subwoofer seems more important to me.

i'm building an 41hz amp3 to power them (maybe i don't f**k up the second one, which i ordered last week)

my plan for the module is to use a buffer opamp, a 4th-order-linkwitz-riley crossover and maybe add a phase shift, quite like in this project at sound.westhost.com
now the questions are:

*do i split up the audio signal before the power amp for the needles and should i use a higpass-lr-crossover for the needles?
*or do i extract the bass signal with a crossover behind the poweramp, as one would usually do with standard subwoofer modules? a problem in this case might be, that the amp3 runs in bridged mode, and therefore none of the outputs is on ground, which might cause a lot of problems.

I'm really looking forward on some input from you guys, and I will do a documentation of my build,as soon as it has left the planning stadium.

all the best,

michi

[Khron]

Usually, active filters are placed BEFORE the power amps.

Yes, a high-pass for the needles may very well be justified (we don't want any humps in the frequency response, if possible), because your needles might overlap too much with your sub.

I intend on doing something like that someday (when i'll have the cash to buy a decent sub driver)

[richie00boy]

I would use a filter before the Needles, but make it more of a 'protective' filter than a crossover filter, i.e. set it to cut in below the bandwidth/resonance of the needles. This way it doesn't take any noticable sound away from the Needles (necessary to get good integration with a mono sub), but it stops them being driven so hard.

[derMichi]

thanks for the quick replies!
so now my plan is as follows:
+ a buffer opamp on each channel

highpass section:
+ a 24 dB/octave lr-crossover (i'm not sure yet about the crossover frequency, i think 80 Hz should do, as the needles play quite happy down to 50 Hz) on each channel

lowpass section:
+ another buffer to add the two channels
+ a 24 dB/octave lr-crossover with the same crossover frequency

What do you think - should i use output buffers with adjustable gain to match the volumes, or would potentiometers do the job?

i ordered all the parts now, and as soon as I get them, I will start building.

[richie00boy]

The level matching can be achieved simply with the power amp volume control.