My take on "rear fill"

[xTHANATOPSISx]

Flipping the polarity of one signal is what removes the common information from the signal your sending to the amp. So if you didn't flip the polarity then yes, you'd have a mono signal. Which is what you don't want ideally so you flip the polarity and have L-R instead.

Not that maybe some folks want mono rear fill I suppose. That's just not my understanding of what works best and wouldn't be "differential" rear fill as far as I know.

[Hillbilly SQ]

Here's how you do it in the minidsp 8x12. Followed the cdsp manual. Green indicates flipped polarity. Helix does it the same way from what I remember in Skizer's tutorial. In my simple mind this just looks like mono to me like it would be bouncing off the back wall of a big concert hall. Unless you really are cancelling out the mono info of each channel to only leave left and right info that's still in stereo

[xTHANATOPSISx]

That's correct to my understanding. You're canceling out any common signals to the extent that they are present in both channels. So you would be left with no common information since two identical signals of opposite phase will cancel out. Nominally speaking the signals will be out of 180° out of phase if they are of opposite polarity.

There will be some stuff left over where the amplitude isn't the same on both channels and such, but then that means you still only hear the difference, hence differential rear fill. You only hear what's not in both speakers.

[Jdunk54nl]

I am wondering if we are confusing (and it might just be me questioning what DIY Audio Guy means) mono signal being output and single DSP channel output. Mono output would be like L+R, single channel output is just using a single output from the DSP, as in you only use channel 7 of the dsp outputs.

Which one do you mean DIY audio guy? Do you mean you just want to sum both inputs to create a mono signal or just use one channel of output on your dsp?

[Hillbilly SQ]

I am wondering if we are confusing (and it might just be me questioning what DIY Audio Guy means) mono signal being output and single DSP channel output. Mono output would be like L+R, single channel output is just using a single output from the DSP, as in you only use channel 7 of the dsp outputs.

Which one do you mean DIY audio guy? Do you mean you just want to sum both inputs to create a mono signal or just use one channel of output on your dsp?

I think it's more about doing the l-r thing olskool and getting it through the wiring instead of clicking buttons in the dsp software. Yes it's guaranteed to be mono doing it olskool but it's better than nothing. You can get the same effect by twisting the two negatives together and just sticking the positives to each speaker into the amp. I did it in my Grand Cherokee for a bit during an experiment and it worked fine. Can't say I really noticed a difference between that way and doing it the way most seem to do it these days with a channel per speaker and doing the l-r through the processor. Still got the same eq and delay both ways for the factory speakers up high in the d-pillars.

[NoDestiny]

These are on sale...
https://www.parts-express.com/dayton...8-ohm--295-349

I was eyeballing them for rear fill experimenting anyways. Since they'll be bandpassed for the effect, seems the response should be decent for this. Also, don't need a ton of output. Wanted smaller to make it easier to tuck them out of the way (I'm doing a custom build from scratch basically anyways).

Thoughts?

[Queef]

NoDestiny How about
https://www.parts-express.com/07g2-2...-ohm--289-2318

"smooth response from 100 to 13,000 Hz"

[nadams5755]

i can say it's tough to get rear-fill correct.

not enough delay? pulls back.
too much output? pulls back.
too much delay? unnatural echos.
not enough output? no effect.
not centered correctly? steers staging cues left or right.

if you've got a 4ch radio, it might be easier to map rear channel radio outputs to the rear channel inputs of your dsp, and map those to rearfill. then you can play with the radio's fader to adjust rearfill levels without having to get out the laptop

[diy.phil]

If it's logic7 we can stand outside behind the rear bumper, with the hatch/trunk open, and hear the music/stage is at the front/dash.

[nadams5755]

i wish there were more algorithm-based rear-fill options available to us.