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Discussion Starter · #1 ·
I would like to start a thread about the discussion of rear fill and center channels in car audio system. I know a lot of people say rear fill and center channel are unnecessary or detrimental to their sound stage.

I for one love Rear Fill when it is done right especially with a surround sound processor. I feel like it helps widen my sound stage and provide some ambiance like you would hear at a live concert.

Article on how to add rear fill in car: https://drive.google.com/open?id=1cx8fWOM8DTfmvzMCzCfYLcPNT4WzpzLw

Article on how to add center channel speaker in car: https://drive.google.com/open?id=17AKh3lc_n2MdJSZV5M1elBdLC1csl940

Article on 2 channel stereo vs. surround sound in car: https://drive.google.com/open?id=1mf8ae_M4velGuQVeydVkfXeoc4xvf98G

Article on how to set up a proper soundstage in car: https://drive.google.com/open?id=1Hu1hq5_M1zdRhCjPmCD6C8yhiGPwc_hp

PassMag Article on JBL MS-8: https://drive.google.com/open?id=12l2jrqHxuNEBVhBjbgfPNVAUUkta5WoI

Fosgate Gavotte (car stereo surround sound processor that started it all in the early 1980s) https://drive.google.com/open?id=1U6Sva-yu9WxOtSWCFdxeuRtNtOrC4CoN

AudioControl ESP-3 Manual: https://drive.google.com/open?id=1rQ838gYnuvMU5q0xupLixDCUWsX8YLkM

I know Alpine and others had Surround Sound processors but, I don't have any information on them.

It seems to me that factory OEM systems are coming more with surround sound processors and the aftermarket systems are lagging behind.

Please free to add an articles or other information that either helps prove or disapprove that rear fill helps. P.S. I would like to thank and acknowledge the writers of these articles!
 

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I didn't read them, but these articles are 25 years old. Things have changed and technology has greatly improved, so no matter what they may or may not say, I would take it with a grain of salt.

That said, in order to execute a center channel PROPERLY you need a processor with an upmixer. The Alpine h800 is the only one that I know of currently in production that offers this.

Rear fill is a bit easier. What you want to do is simulate the echo of a larger room. You do L-R signal routing on the rear speakers, bandpass them, attenuate them, and heavily delay them. There's a hand full of processors that can do this.



Are they helpful or hurtfull.. Well either done right shouldn't hurt. A properly executed center channel will give stereo imaging from two seats, not just single seat. Rear fill isn't that hard to help improve the overall feel and ambience of the system. A standard stereo system is easier though if your only concerned about the sound from the drivers seat.


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Opinion from an MS8 user with no other DSP experience.

As far as rear fill I've never felt it distracted from or was detrimental to my front stage. I like the ambience that Logic 7 with rear fill provides, but accept that some don't care for it, no worries (though I gotta wonder if they're listening to well-implemented and tuned rear fill). With some recordings the effect is more apparent than others, but always a subtle enhancement for me. When I turn off processing it all goes south in a big-bad way but admit I've not really focused on trying to achieve a great tune in that mode.

As far as the center.... I ran without for a long time and had a great front stage for driver only occupancy. Early efforts with an added center were a bit frustrating, seeming to pull my stage a bit closer for driver only. Adding broader frequency capability to the center (went 2-way) and tweaking both levels and XOs now have me happy with the center, even when alone in the car. No question in my mind at all that a superior 'second-occupant experience' is facilitated with the processed center and as things stand now after a fair amount of tuning I don't feel the 'driver only' experience is compromised.

IMHO SkizeR nailed it with the comment about proper upmixing being an essential element for any chance of a good 'with center' listening experience. From that starting point all the usual tuning efforts come into play to optimize for a particular cabin. For me it all goes totally south with the processing defeated .... I can't imagine achieving a good effect with a center but without the MS8 L7 processing / upmixing (or similar, at least in concept as I understand it, Alpine H800 Dolby center processing / upmixing).

I'm not sure it's reasonable to damn or praise rear fill or (even 'properly upmixed') center channels just on face. IMHO the devilish details that make-or-break the proposition are, as with most other 'traditional' arrangements, in the tune.
 

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Another key to a good center channel that many don't realize is that you need a lot of cone area. A lot more than the standard 3" opening that is in most cars. You want it to play down to at least the mid to low 100's hz.

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Another key to a good center channel that many don't realize is that you need a lot of cone area. A lot more than the standard 3" opening that is in most cars. You want it to play down to at least the mid to low 100's hz.

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So, if I’m running GB25’s and 10’s in my pillars, I would want to use a 4” as a center? Would I also need a center tweeter? Maybe a coax? I’ve never heard a car with a center channel, so this is intriguing.
 

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I didn't read them, but these articles are 25 years old. Things have changed and technology has greatly improved, so no matter what they may or may not say, I would take it with a grain of salt.

That said, in order to execute a center channel PROPERLY you need a processor with an upmixer. The Alpine h800 is the only one that I know of currently in production that offers this.

Rear fill is a bit easier. What you want to do is simulate the echo of a larger room. You do L-R signal routing on the rear speakers, bandpass them, attenuate them, and heavily delay them. There's a hand full of processors that can do this.



Are they helpful or hurtfull.. Well either done right shouldn't hurt. A properly executed center channel will give stereo imaging from two seats, not just single seat. Rear fill isn't that hard to help improve the overall feel and ambience of the system. A standard stereo system is easier though if your only concerned about the sound from the drivers seat.


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The helix can do rear fill right?


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So, if I’m running GB25’s and 10’s in my pillars, I would want to use a 4” as a center? Would I also need a center tweeter? Maybe a coax? I’ve never heard a car with a center channel, so this is intriguing.
Put it thisbway, Andy W is running a pair of gb40s (which have a recommended high pass of at least 110 @ 12db) and a gb10 for his center channel.

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I think this is one of those things where you just have to try it (and do it right) before you'll know.

I've messed around with rear fill a few times over the past 7-8 years. Ultimately, though, I'm not a huge fan. There's the delicate balance of blending the output level of the rear fill to that of the front speakers and even when you get it right, there will be instances where you'll find it as a distraction. IMO the music you listen to will be a prime factor in how you feel about it. It can help with some tracks but it can also hurt; namely on tracks where the info is panned to the extreme ends of the soundstage and will pull, by nature of the difference signal, in the center behind you. If you drop the levels to avoid this then the *other* times it wouldn't matter... the signal is just too low to make any impact.


As for center channels, as has been noted, you really need a good upmixer to handle the signal and steer accordingly. Using summed mono (L+R) for center will hurt the width of the soundstage, namely in the midrange. And with regards to it being the perfect solution for 2-seat listening, I'm still on the fence.
 

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The helix can do rear fill right?


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Yes. You do this on the input matrix. Add the left input and right inputs together. Then flip the polarity of one of them (whichever you want to subtract) by double-clicking on it and setting the polarity to 180 deg. You'll have to set this up on two output channels and you'll have: L-R and R-L signals from those outputs.
 

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Discussion Starter · #10 ·
I am running two Focal ES 4" and two 1" as my center channel speakers. Crossed over @ 200hz @ 24dB.

I probably could have crossed them over a little lower hz but, I am overdriving them to keep up with my door speakers.
 

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Would the new jl vxi amps, and the HUB involved, make it possible, or even easier to do a center and/or rear fill? The info upon rollout made it seem as if there are almost endless possibilities and configurations using these amps.
 

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Yes. You do this on the input matrix. Add the left input and right inputs together. Then flip the polarity of one of them (whichever you want to subtract) by double-clicking on it and setting the polarity to 180 deg. You'll have to set this up on two output channels and you'll have: L-R and R-L signals from those outputs.


Thanks Erin - just curious may or may not use it... more for the kids in the car really...


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Would the new jl vxi amps, and the HUB involved, make it possible, or even easier to do a center and/or rear fill? The info upon rollout made it seem as if there are almost endless possibilities and configurations using the amps.
The vxi doesn't have upmixing; so there is nothing more than simple addition/subtraction. Which means no 'steering' for center and sides. You can do difference signals on the input matrix, though, to achieve the rear fill effect.
 

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Thanks Erin - just curious may or may not use it... more for the kids in the car really...


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If you're doing it for the kids, I'd just stick with regular ol' stereo. The (differential) rear fill will sound weird to them (if you haven't heard it, set it up and listen and you'll see what I mean). Just run the rears as standard left/right for the kiddos.
 

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If you're doing it for the kids, I'd just stick with regular ol' stereo. The (differential) rear fill will sound weird to them (if you haven't heard it, set it up and listen and you'll see what I mean). Just run the rears as standard left/right for the kiddos.


Yeah God forbid if Ed Sheeren sounds a bit off... lol!


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Discussion Starter · #16 ·
I have tossed around the idea of using a MS-8 or another upmixer with the new vXI amps but, I am so happy with my current system that I see it being at the point of diminishing or non returns.
 

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Yeah God forbid if Ed Sheeren sounds a bit off... lol!


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Haha.

Well, it's not even that ('a bit off'). It's a very odd effect. I wouldn't even describe it as a 'echo'... just a very weird effect.

In nominal usage it's level is low so that you barely discern it. But since the kids would be closer to the rear speakers than they would be the front they'll likely hear the rears as twice as loud... so all that... 'mess'... will override the 'normal' stereo sound. So, yea, if you're doing it for them to hear music or video or whatever, I'd stick to regular stereo in the rears.
 

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Haha.



Well, it's not even that ('a bit off'). It's a very odd effect. I wouldn't even describe it as a 'echo'... just a very weird effect.



In nominal usage it's level is low so that you barely discern it. But since the kids would be closer to the rear speakers than they would be the front they'll likely hear the rears as twice as loud... so all that... 'mess'... will override the 'normal' stereo sound. So, yea, if you're doing it for them to hear music or video or whatever, I'd stick to regular stereo in the rears.


Thanks Erin for the input and advice...


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My current set up has no rear fill,just active 2-way.I haven't tried using the rear fill that's available from my HU and stock rear deck speakers.Maybe I'll open the trunk and plug the speakers in to see how it sounds.

Barring a few annoying rattles,I am very happy with how my stuff sounds and the imaging is still something I can't believe.Vocals coming from dead center of my windshield and majority of instruments on sides of dash.There's a slight bit of rainbowing but not enough to bother me.I haven't touched my tune since November and really don't want to.I'm so glad I finally listened to people here and got a DSP.Compared to passive it is night and day!
 

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In regard to rear fill would like to add that for me (with an MS8) it was important to realize that the fill needed to be very subtle for IMHO best effect. When tuned so it was 'readily apparent' it wasn't nearly as satisfactory as when tuned to a level that I almost didn't notice it was there until I switched it off.

Struggling to find the words to explain .... for me rear fill works best solely as an ambience enhancer, not as an immediately perceived apparent additional sound source, if that makes any sense.

And I do agree with ErinH's suggestion that it's highly dependent on the recording .... I over-reached when I said in my previous post that it's "always" an enhancement. Better to have said it's usually an enhancement with the music I listen to.

As far as the center, I certainly wouldn't say it's the panacea or perfection for two-seat listening (certain I've not encountered either). But IMHO with proper upmixing and tuning it does increase the probability of achieving a better two-seat listening experience than a no-center system provides in the small confines of a car cabin.

I've wondered if some sort of arrangement of multiple discrete L&R (only) channels and speakers could do better, somehow creating an almost headphone-like 'capsule of sound' around each separate occupant in a car cabin, working with the frequencies that are most 'locatable' in human hearing and perception. But I digress .... that's far from an approach supported, I suspect, by any of the 'produced for car audio DSPs' currently on the market.
 
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