My take on "rear fill"

[Mr Marv]

I posted this on my build thread and Hic suggested I post it here as well. As usual this is my actual experience based on my actual experimenting using methods from a guru on the forums back when who went by werewolf however I have seen numerous "tutorials" using different settings so best bet as usual is to experiment for yourself!

Re: Marv's Silverado Regular Cab build

Originally Posted by Hic
Is rear fill even worth bothering "With"?



I used to believe in the myth that "rear speakers just mess up your front stage" until I heard a car with rear fill set up "properly" and now I won't be without it. One thing to note is "rear speakers" not processed can be "considered" rear fill however to implement rear fill that will actually "enhance" your front stage instead of taking away from it you will need specific
processing.

I used instructions from JL on how to set up the inputs of the twk88 for a left minus right signal and from what I understand there are many dsps/amps with balanced inputs that can accomplish this (my old JL slash 500/5 actually had left minus right built in on the rear channels). Per guru werewolfs instructions I band pass the rears from 100hz-7khz and if my calculations are correct they are delayed approximately 18ms from the front stage for now (ideally you want around 20-21 ms depending on who you talk to however the twk88 will only allow a max of 21 ms delay per channel so when I get time I am going to loop the remaining output so I can get additional delay).

It took just a little experimenting to find the right output level for the rears and if you go past that "sweet spot" you'll know. After getting it dialed in I set 2 other presets for quick comparison, 1 with all settings the same but no left minus right (just bandpass, delay and attenuation) and one with rear fill muted.

Switching from no rear fill to rear fill you immediately hear the stage gets wider/higher/deeper and has a sense of a larger space WITHOUT smearing the center imaging as some believe (stage is well beyond the a pillars, center is eye level right about at the windshield and stage extends well onto the hood)

A few things to note:

My left rear speaker in my regular cab pickup is only 11" from the center of my head yet you cannot "hear" it even if you turn your head towards the speaker (best I can understand from my reading is that its one of those scientific "effects" where your brain somehow disregards the delayed sound and only hears the direct sound of the same frequencies) however if you mute the front stage you definitely hear the rears playing. From what I recall werewolf stating the rear speakers ideally should be above and to the outside of your ears (the car I originally heard this in had them in the side "C" pillars between the rear window and rear door instead of on the rear shelf) however I have never done a direct comparison so I cannot say how much difference location makes.

Without the left minus right engaged the stage still gets deeper/wider/higher however the center image gets more "pronounced" for lack of a better word. Interestingly it did not totally destroy the imaging so my belief has always been the delay/attenuation are the most critical part of this.

"Well engineered" recordings do not get too affected by this however the "lesser quality" recordings are greatly enhanced (I listen to Satellite a lot and it makes a big difference).

Is it worth the time/expense to you? Can't say however I can say it is the "icing on the cake" for me AFTER getting the best front stage I can without rears.

As usual, "I can't hear what you can hear and you can't hear what I can hear so our results may differ" and if you happen to be near Monterey Ca you are welcome to come by and listen!

[Hic]

S-W-E-E-T !

[Hillbilly SQ]

I'm also a single cab truck guy and figured rearfill would be a waste. Might see about doing it at some point in mine but don't have the amp or processing power right now. Well I have the processing power but it would mean my cdsp8x12 would have to go back in and I'm quite fond of my Helix dsp.2. I might go back to a 2-way front with rears like I had in the Grand Cherokee and see how far I can take that. I did l-r rears with the stock d-pillar rears that were high and wide and that gave really nice results depending on the song and recording. Have also heard a few cars with rears playing regular and bandpassed and couldn't tell they were playing but they obviously were adding something nice to the overall presentation. This will be a project for the coming years.

[Hic]

Where there`s a will , there`s a way ! You got the tools , make the time! Your guages are on either side of your head , had mine right out-of-the-box (back in `58`).
The best part , is Marv is only a phone call away and at the next GTG your truck will be a "Must hear" !
"Whole Lotta Love"~Led Zeppelin should be worth a listen, when it is dialed in!

[Hic]

"Good Vibrations"~Beach Boys ( Todd Rungren made it happen on keyboards ) , raising a surfer band to a new high.

[Hic]

Hillbilly SQ,
You gonna give this a try ? Marv can talk you through problem areas.

[Hillbilly SQ]

I'll give it a try when I'm ready and not a second sooner

[Hic]

It`s like sex , waiting is "One Option"!

[NoDestiny]

I've been pretty curious to try this out. One question I have is: What is the optimal placement and aiming direction for rear fill in a hatchback? I'm making my trunk from scratch, so I have a lot of options. For instance: Rear fire VS forward firing VS upward firing? As far back in the trunk as possible VS closer to the seating position? My assumption is I'd want them as far back as possible and rear or up firing, but figured I'd ask.

Also, how critical is it to separate them L/R wise? I'd also make assumptions that further apart is better.

[Mr Marv]

I've been pretty curious to try this out. One question I have is: What is the optimal placement and aiming direction for rear fill in a hatchback? I'm making my trunk from scratch, so I have a lot of options. For instance: Rear fire VS forward firing VS upward firing? As far back in the trunk as possible VS closer to the seating position? My assumption is I'd want them as far back as possible and rear or up firing, but figured I'd ask.

Also, how critical is it to separate them L/R wise? I'd also make assumptions that further apart is better.

My "guess" is your assumption is correct. I was taught that outside and above your ears is ideal placement which makes sense to me as it's the same way you'd set up a home surround system (my understanding is this process is actually derived from the process the original Dolby engineers used) however I have seen others gain success in other locations as well as with different aiming. My non scientific mind tells me it shouldn't matter how far back you place the rear speakers as your goal is to delay them 20+ milliseconds "from the front stage" i.e. the further back the less "additional" delay is needed to reach that. In my case my left rear speaker is actually my closest speaker so it took me a while to get the confusing math correct so I could delay them the proper amount which is why I need to loop my left over dsp channel.