# Rear fill, L-R stereo/mono question



## kapone (Sep 22, 2009)

I'm getting to the point in my install where I'll start wiring in a few days. I have read every single thread here , and information in other places, about doing rear fill using L-R, but I still don't have any definitive answer.

If we are trying to do the Haas effect, do the rear fill speakers (with the assumption that you have more than one speaker, in the doors or in the rear deck) need a "stereo" signal, different signal for each side, or can you use a "mono" signal for both sides?

Here's the system diagram I'm "planning" to use, including the connections for rear fill. Will this "work"?










Thanks.


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## DarkScorpion (Nov 22, 2009)

I honestly have no idea, but I'd like to know what you'll be using as your carPC, if you don't mind.


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## kapone (Sep 22, 2009)

The CarPC is nothing special. An Intel D945GCLF2 motherboard with the built in dual core Atom processor and GMA 950 graphics. More than enough for my (current) needs. The video will initially be just composite video, before I start experimenting with sync-on-green and RGB signals that the BMW LCD expects. The CarPC will be connected to a SpaceNavigator (in the center console) for control, and hooked into the car's IBUS via a Resler IBUS interface.


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## kapone (Sep 22, 2009)

As far as rear fill goes...Geo? werewolf? Any of you guys around??


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## Indiansprings (Dec 2, 2009)

Looks good, but.....
You should either use the crossover, or dont use the crossover on both your component sets. My opinion only.


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## pionkej (Feb 29, 2008)

kapone said:


> As far as rear fill goes...Geo? werewolf? Any of you guys around??


I would think a mono signal would not work. If the sound is already mono and run into one cable, how (even if you split it into two cables) could the amp filter out the common information? It is all common to both channels in mono so there would be no sound. 

What you could do is run the fronts passive also and get l-r rear fill. Or you could get an Alpine H701 and sell the 360.2, and run two-way front/l-r rear fill/sub. The last option is have a headunit with two RCA outs (not sure if you do), run the one set to your 360.2 (connected to midbass, l-r rear fill, and sub) and run the second to your tweets (the JL crossover is high enough @ 5khz on their amps and the tweets are more sesitive to amplitude to t/a isn't as needed--but you would loose eq).

I'm sure it isn't what you wanted to hear, but I hope it helps in your decision.



Indiansprings said:


> Looks good, but.....
> You should either use the crossover, or dont use the crossover on both your component sets. My opinion only.


WHY???? His plan is to run the front stage active which gives better tuning options if done properly. The rear is just for ambiance, no need to run it active and no need to "hurt" the front stage because of this. 

Not trying to sound mean at all, but I do think you should read a bit more about what the OP is trying to do if you don't understand it before giving advice.


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## kapone (Sep 22, 2009)

pionkej said:


> I would think a mono signal would not work. If the sound is already mono and run into one cable, how (even if you split it into two cables) could the amp filter out the common information? It is all common to both channels in mono so there would be no sound.
> 
> What you could do is run the fronts passive also and get l-r rear fill. Or you could get an Alpine H701 and sell the 360.2, and run two-way front/l-r rear fill/sub. The last option is have a headunit with two RCA outs (not sure if you do), run the one set to your 360.2 (connected to midbass, l-r rear fill, and sub) and run the second to your tweets (the JL crossover is high enough @ 5khz on their amps and the tweets are more sesitive to amplitude to t/a isn't as needed--but you would loose eq).
> 
> I'm sure it isn't what you wanted to hear, but I hope it helps in your decision.


Lemme back up, I don't think I may have explained myself correctly. The system is being hooked up to the stock head unit in the BMW. The stock HU has balanced outs for FL, FR, RL and RR. The plan is to derive the L-R signal BEFORE things even hit the 3Sixty by tapping the L+ and R+ from the RL (which consists of +/-) and RR (which consists of +/-) signals. The *L+* signal would on the +ve pin of the RCA/wire and the *R+* (_instead of the usual L-_) signal would be on the -ve pin of the RCA/wire. 

When this is fed to the 3Sixty (which is "supposed" to accept balanced differential signals starting from v2 units, which is what I have), as far as the 3Sixty is concerned, it will be seeing the difference between the +ve and -ve signals, i.e.

(L+ input) - (R+ input) = L-R signal.

From that point, downstream, it's just a regular signal, except the information carried on it is the difference between L and R channels. 

Does that make sense? (or am I completely off base?:blush

The reason I was asking about the stereo/mono issue is because if I'm running a 2 way active front stage with the 3Sixty, the only input left on the unit that can be TAed and bandpassed is the Center input, and obviously that's mono. I was hoping that once this input gets TA applied to it in the 3Sixty, and then fed to a two channel amp (or two of the 4 channels on the USB 3085, in my case) by splitting the center OUT on the 3Sixty, it would work. I can try and see if it's possible to do any phase switching on one of the signals on the amp and/or switch the +/- wires on that rear speaker vs the other rear speaker.


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## audiguy (Jul 30, 2007)

You are going to need both Time delay and EQ for your rear channels. Do you have that covered? I do a L-R set-up and I use a Zapco DC200.2 for my amp which gives me both. I get my L-R set up using the Zapco balanced cables.


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## kapone (Sep 22, 2009)

audiguy said:


> You are going to need both Time delay and EQ for your rear channels. Do you have that covered? I do a L-R set-up and I use a Zapco DC200.2 for my amp which gives me both. I get my L-R set up using the Zapco balanced cables.


Well...since that L-R signal is going into the 3Sixty, it can do TA/EQ etc on that. However, the $64,000 question is that if I'm running two speakers for rear fill, one on each side of the car, do they need L-R and R-L, or can L-R be fed to both of them?

Since L-R is removing all common information between L and R, L-R should "potentially" be the same as R-L, except "maybe" 180 out of phase (which I don't know yet).


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## audiguy (Jul 30, 2007)

I don't have the car I have this set up in in my possession right this moment, but a not from my work says that I am running L+ and R+ to each of the left and right channels. That doesn't mean that you want to run mono, because you will want to run separate EQ and TA for each side.


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## kapone (Sep 22, 2009)

audiguy said:


> I don't have the car I have this set up in in my possession right this moment, but a not from my work says that I am running L+ and R+ to each of the left and right channels. That doesn't mean that you want to run mono, because you will want to run separate EQ and TA for each side.


Now that makes sense, since the path lengths for the left and right rear speakers will be different as seen from the driver's seat. But, what's encouraging is that the same L-R signal can work for both of those speakers. Hmm....I guess, since I have only one channel of processing left on the 3Sixty, I'll live with the less than ideal scenario. Maybe attenuate the nearer rear speaker, bit more than the opposing one?


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## pionkej (Feb 29, 2008)

Doing l-r before the 360 would work and it would remove the center info, but when you run it from the center channel, it would still be mono meaning that the far right sound would come out the left speaker with the far left sound (so it would still be the same sound out of both speakers just minus "center" information such as vocals). I think it would be better than rear speakers, but still not true rear fill.


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## kapone (Sep 22, 2009)

pionkej said:


> Doing l-r before the 360 would work and it would remove the center info, but when you run it from the center channel, it would still be mono meaning that the far right sound would come out the left speaker with the far left sound (so it would still be the same sound out of both speakers just minus "center" information such as vocals). I think it would be better than rear speakers, but still not true rear fill.


Well, in that case, what would be "true" rear fill? Isn't L-R the same as R-L?? Seriously, I'm not being a dick, just trying to understand. This whole dicking around with rear L/R signals for rear fill, has me totally confused!:blush:


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## audiguy (Jul 30, 2007)

How much delay can you get out of that 360 in the center channel? You will need 25ms or so.


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## pionkej (Feb 29, 2008)

Man, I had a HUGE response typed out and my computer at work shut down. But here is a shortered version.

You can get a l-r signal (centered information cancelled out), bandpass it, eq it, and delay it. That is what is needed for true rear fill. These are all the things needed for proper l-r rear fill. The problem is that the output your using on the 360 is a single mono channel likely into a y-cable that splits the rca's so you have one for both left and right input at the amp. This means that instead of hard left information playing from the left speaker it will play from the left AND right speaker (since it is mono) and instead of hard right information playing from the right speaker it will play from the right AND left speaker (again in mono).

EX--If you have a guitar playing on the left side of the stage:
2-way: It will play from the left side front speaker
2-way w/ l-r rear fill: It will play from the left side front and rear speakers
2-way w/ l-r rear fill in mono: It will play from the left side front and the left AND right rear speakers

So you would have information on the left side "pulling" back to the right. Will it be noticeable? I don't know. Personally, I would do everything like you planned and see how it works. If it doesn't work well, just disconnect the rear fill. You could then wait until the JBL MS-8 comes out (it should actually come out in 2010) and it will actually auto eq AND is set up for l-r rear fill. You could put it right in place of the 360 and sell it later. That seems to be the cheapest way to me.

Also, I didn't take you as being a dick. As long as I feel a person has tried there hand at searching (or I feel the need to stop bad advice from being given), I have no problem helping out.


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## kapone (Sep 22, 2009)

audiguy said:


> How much delay can you get out of that 360 in the center channel? You will need 25ms or so.


Oh crap...  I just realized (late light bulb moment) that the 3Sixty can delay only up to 5ft, which would equate to roughly 5-5.5ms of delay. Crap crap, that may not be enough for rear fill..... 



pionkej said:


> Man, I had a HUGE response typed out and my computer at work shut down. But here is a shortered version.
> 
> You can get a l-r signal (centered information cancelled out), bandpass it, eq it, and delay it. That is what is needed for true rear fill. These are all the things needed for proper l-r rear fill. The problem is that the output your using on the 360 is a single mono channel likely into a y-cable that splits the rca's so you have one for both left and right input at the amp. This means that instead of hard left information playing from the left speaker it will play from the left AND right speaker (since it is mono) and instead of hard right information playing from the right speaker it will play from the right AND left speaker (again in mono).
> 
> ...


pionkej, I very much appreciate the detailed information that you keep providing.  Thank you. I'll have to think about this a bit more I guess....


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## BigRed (Aug 12, 2007)

pionkej said:


> You can get a l-r signal (centered information cancelled out), bandpass it, eq it, and delay it. That is what is needed for true rear fill.


says who? true rear fill? there are many ways to acheive a rear fill that will help add to the front stage and a sense of ambience and openness. I've tried several. I don't think its fair to say a rear mono center will not work unless you have tried it.

I would say hook up the 360 and try it 

Pionkej, can you describe your setup now? what are you using or used to achieve true rear fill?


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## pionkej (Feb 29, 2008)

BigRed said:


> says who? true rear fill? there are many ways to acheive a rear fill that will help add to the front stage and a sense of ambience and openness. I've tried several. I don't think its fair to say a rear mono center will not work unless you have tried it.
> 
> I would say hook up the 360 and try it
> 
> Pionkej, can you describe your setup now? what are you using or used to achieve true rear fill?


From what I understood by reading Werewolf's posts, "true" rear fill is how I described it. I also said that he should try it (see bold below) since that was his best option, but from what I had read, it wouldn't be ideal. I honestly wasn't trying to tell the guy he couldn't do it, just what might be an obstacle from my view.

Also, I currently have no setup. I sold my 300zx TT (2 seater) and will by selling my 1989 Nissan Hardbody Pickup (little light in the safety department) in an effort to get a single "fun/functional/safe" vehicle that will work for starting a family. I am planning to use the new Pioneer P01 (already own) to set up a 3-way active front with sub. I also plan to look for a used Zapco DC200.2. I want to run it off the pre-amp midrange signal from my front. It already is bandpassed and eq'ed (which I can change with the DC should I need to), and I can add the additional delay with the DC and get the l-r by hacking up the symbilink cable like geo showed. That was the plan anyway. 

I may end up going H701 with mono l-r based on what you are telling me. It would be easier than my plan. Again, I had never read that mono was a good option for l-r rear fill, and I don't think the OP had either since that is why he asked the question. I was going off what I had read from others, not what I had personally tried in this situation (which is again why I said what I said in bold below).



pionkej said:


> Man, I had a HUGE response typed out and my computer at work shut down. But here is a shortered version.
> 
> You can get a l-r signal (centered information cancelled out), bandpass it, eq it, and delay it. That is what is needed for true rear fill. These are all the things needed for proper l-r rear fill. The problem is that the output your using on the 360 is a single mono channel likely into a y-cable that splits the rca's so you have one for both left and right input at the amp. This means that instead of hard left information playing from the left speaker it will play from the left AND right speaker (since it is mono) and instead of hard right information playing from the right speaker it will play from the right AND left speaker (again in mono).
> 
> ...


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## kapone (Sep 22, 2009)

I appreciate the info guys. Here's another thought and it gets more complex...  Forgetting the issue of the 3Sixty having only about 5.5ms of delay for a second, let's focus on the single channel issue.

That channel can obviously have only L-R or R-L, but not both, and you can apply TA and EQ to it. I understand that the delay "ideally" should be different for the rear left and rear right "rear fill" speakers, but these are going to be attenuated a lot, and I'm not sure how much "actual" difference may be there between the two approaches.

Now, if we have only one channel for rear fill and it's L-R, we could potentially also use amp bridging to get L-R and R-L to the respective speakers, couldn't we?

Quoting WhteRabbit here from the thread "Rear Fill: do you use it" - 



Whiterabbit said:


> to my knowledge, the opposite. a bridged amp will sum the input signals. By inverting one signal, the summation will result in an L-R (as in, L + (-R)) signal. This would be run as a bridged output to a rear speaker.
> 
> By running the two rear speakers in series, they both get this L-R signal.
> 
> ...


That would potentially work, right?


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## pionkej (Feb 29, 2008)

That only works on amps that aren't meant to be bridged or have a bridge switch (where you actually flip a switch if you want to bridge channels-for l-r you just leave it unswitched). These are old school amps we're talking about here. Like some old A/D/S power plates.

Newer amps flip the phase automatically when they "sense" the channels are briged. Which means the L + (-R) doesn't happen, it just runs the two speakers in series at an 8 ohm load and doesn't cancel the center information. 

You are better off with your original idea. Since BMW's have balanced lines, you can get l-r from there.

EDIT: Try it though on the amps you have. When I tried it in my truck, no center information was cancelled out.


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## BigRed (Aug 12, 2007)

Thanks Pion for the explanation. you are right. werewolf's idea of rear fill is exactly what you described, however, and I want to apologize in advance if I seemed argumentative, is that you can still acheive some good results with a less than perfect setup 

my experience with the delay is 15-20ms is ideal...5ms was not enough. you might have to attenuate it more as a tradeoff. it created an echo effect if you will and made the midrange sound strange.

I dont have an answer to the other question you asked OP


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## pionkej (Feb 29, 2008)

BigRed said:


> Thanks Pion for the explanation. you are right. werewolf's idea of rear fill is exactly what you described, however, and I want to apologize in advance if I seemed argumentative, is that you can still acheive some good results with a less than perfect setup
> 
> my experience with the delay is 15-20ms is ideal...5ms was not enough. you might have to attenuate it more as a tradeoff. it created an echo effect if you will and made the midrange sound strange.
> 
> I dont have an answer to the other question you asked OP


No offense taken. I like when discussion can be opened up like this as it betters everyone (or at least anyone who searches in the future before asking the same question  ). I honestly had no idea that could work in mono, so it is very good to know that it has been tried and people have satisfactory results.


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## audiguy (Jul 30, 2007)

kapone said:


> Oh crap...  I just realized (late light bulb moment) that the 3Sixty can delay only up to 5ft, which would equate to roughly 5-5.5ms of delay. Crap crap, that may not be enough for rear fill.....
> 
> 
> 
> More correct would be that it definitely won't be enough. And that doesn't include any delay that you might add to the other channels, which would subtract from what you send to the L-R rears. I like the DC200.2 idea.


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## kapone (Sep 22, 2009)

audiguy said:


> More correct would be that it definitely won't be enough. And that doesn't include any delay that you might add to the other channels, which would subtract from what you send to the L-R rears. I like the DC200.2 idea.


Well, my thinking is that the 740 is a pretty big car... and the rear fill speakers will be in the rear deck at the farthest ends, so it is already a fair distance away from the front seat, and even with the 5ft max delay in the 360, it "might" be ok. Obviously I won't know until I try it. I think that's what I'm gonna do. Hook up the damn thing and see if I blow up something.


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## methodsound (Oct 1, 2009)

What if you just did not connect the center or subwoofer input on the 360? The 360 should create the center image ( and sub channel ) for you? 

I have used the center channel output ( with no center input connected ) for rear fill with good results. (If there were more outputs available on the 360 I would do a stereo rear fill, unless the rear channel was a single speaker in the center of the rear deck though.)


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## kapone (Sep 22, 2009)

methodsound said:


> What if you just did not connect the center or subwoofer input on the 360? The 360 should create the center image ( and sub channel ) for you?
> 
> I have used the center channel output ( with no center input connected ) for rear fill with good results. (If there were more outputs available on the 360 I would do a stereo rear fill, unless the rear channel was a single speaker in the center of the rear deck though.)


Yes it can, but the "regular" center channel output is something that we absolutely do NOT want! It contains vocals! The whole point of L-R is to REMOVE vocals, and leave only the ambient sounds.


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## jkrob21 (Mar 27, 2009)

What is rear fill?


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## pionkej (Feb 29, 2008)

jkrob21 said:


> What is rear fill?


What is search?


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## jkrob21 (Mar 27, 2009)

pionkej said:


> What is search?



LOL One good smart ass comment deserves another. Touche'!


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## audiguy (Jul 30, 2007)

kapone said:


> Well, my thinking is that the 740 is a pretty big car... and the rear fill speakers will be in the rear deck at the farthest ends, so it is already a fair distance away from the front seat, and even with the 5ft max delay in the 360, it "might" be ok. Obviously I won't know until I try it. I think that's what I'm gonna do. Hook up the damn thing and see if I blow up something.


Read this Kapone to understand what I am talking about.

Haas effect - Wikipedia, the free encyclopedia

Your big 740 will add another 2ms to the 5 you started with (minus the delay that you put into the system to time align your other speakers), so you will net about zero.

Under 20ms and it is just going to sound like an echo. As others have mentioned, you can just attenuate it further so you don't notice the echo. If you just turn it down to zero, then you will completely solve that problem.


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## I800C0LLECT (Jan 26, 2009)

I decided not to read majority of this...

Here's what I've started to put together for my application of rear fill. Your over all goal is this...

1) Recombine L and R channels as such: +L(-R) and +R(-L) You do this on your XLR cables using the product in my thread.
2) Bandpass the speakers for ~ 300hz to 3000hz. You can go as high as 5khz or 8khz but it's all up to you. I'd stay away from bass frequencies to prevent localization
3) Time Alignement. if you have the equipment time align per driver. If not, just do 20ms for your speakers and adjust as needed.

http://www.diymobileaudio.com/forum/dumb-question-forum/69956-how-create-difference-sums-l-r-r-l.html


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## kapone (Sep 22, 2009)

I800C0LLECT said:


> I decided not to read majority of this...
> 
> Here's what I've started to put together for my application of rear fill. Your over all goal is this...
> 
> ...




C'mon guys...are you intentionally trying to confuse me??

I thought the pertinent signal that we were trying to derive was L-R, which can be done with L+ and R+? and XLR cables?? huh?? in a CAR??


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## I800C0LLECT (Jan 26, 2009)

Parts-Express.com:ART CleanBOX Stereo Balanced/Unbalanced Converter | interface adaptor line level consumer transformer

Alright, from the start you take the RCA cables from your H/U and plug them into "RCA INPUT". Now you have a balanced XLR output.

Speakers use L+, L-, R+, R-. So do balanced inputs. XLR cables also include a ground. So you recombine the XLR output cables as L+(R-) and R+(L-) and leave the ground alone. The way balanced inputs function you will cancel all common frequencies between L and R on BOTH R & L channels. This will leave you with extreme L & R channels w/o any center channel information in your XLR cables.

Now...after you're recombined you feed the XLR cables to the XLR INPUT.

Finally, feed the RCA OUTPUT/L-R signal into your amps. All done.

FYI: Since I own a 9887 and will possibly attempt a passive setup up front I will have rear channels for T/A and bandpass. Of course before I ever put together my rear fill application I need to fix the setup I have up front.


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## kapone (Sep 22, 2009)

I800C0LLECT said:


> Parts-Express.com:ART CleanBOX Stereo Balanced/Unbalanced Converter | interface adaptor line level consumer transformer
> 
> Alright, from the start you take the RCA cables from your H/U and plug them into "RCA INPUT". Now you have a balanced XLR output.
> 
> ...


Dude...I already HAVE balanced outs from my head unit..... and I don't need to convert them to unbalanced, the 3Sixty will accept a balanced signal. (minor issues not withstanding).


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## I800C0LLECT (Jan 26, 2009)

Then grab an amp that accepts balanced and you're done. I believe the 3sixty will bandpass and T/A your signal. Otherwise, you need at least SOMETHING that accepts balanced to filter the signal for L-R prior to going into the amp.


EDIT: Sorry I didn't skim over your post before. Just a little tired of the rear fill questions...my bad.


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## pionkej (Feb 29, 2008)

I800C0LLECT said:


> I decided not to read majority of this...
> 
> Here's what I've started to put together for my application of rear fill. Your over all goal is this...
> 
> ...


I'm a bit confused by the bold. I thought around 3khz was a pretty good cutoff for rear fill. Going lower is fine because it is HARDER to localize low frequencies. That is why subs can sound like they are coming from the front??? Right??? Vibration/rattles are the biggest give away to low frequency location, so if it doesn't vibrate/rattle, then having the lows shouldn't be a problem right???

If I'm wrong, please set me straight, but that comment makes no sense to me as I currently understand it.


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## I800C0LLECT (Jan 26, 2009)

You're right. But while researching, if you have the correct T/A distances some people say that even 20khz is ok when playing the rear fill. But when just using a general T/A for both speakers of say 20ms then you CAN go as high as 8k but it really depends on the vehicle and preference for sound.

personally, I don't plan on going over 3khz.

Remember...I'm just regurgitating  I tried it once and I liked it. That's why I plan on doing it again. I'm just having a hard time finding permanent install hardware for the app. I'd prefer to have a 4-way head unit.


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## pionkej (Feb 29, 2008)

More good information on things you can do with rear fill that I hadn't seen before. Still not sure I would like it either, but certainly would be worth trying if you had the means to do so. Thanks for sharing.


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## Hernan (Jul 9, 2006)

Hafler stereo:

Hafler Stereo

Mono "rear" works. Don't forget that this is CAR audio.


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## kapone (Sep 22, 2009)

OK, to sum it up, is this a fair description? 

- A single L-R signal is "ok" to use even if you have two rear fill speakers (farthest corners, left and right), since we have removed the common information between L and R, and with that removed, the difference between L-R and R-L is negligible/wouldn't have any real world effect.
- A minimum delay for real fill is probably in the 15-20ms and above range. Anything below that will probably kill the whole rear fill effect.
- The rear signal *must* be bandpassed, probably between 150-200 to 2k-3k or so. This of course needs to be fine tuned.
- You _must_ have the ability to attenuate the rear channel(s) to make them blend better (easy with amp controls).

btw, guys I REALLY appreciate all the information, this is good stuff.


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## Notloudenuf (Sep 14, 2008)

I have been researching rear fill for my install and found this website that gives you what L(minus)R sounds like when done.

I found it helpful hopefully you will

Stereo, mono and all those other things


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## I800C0LLECT (Jan 26, 2009)

Notloudenuf said:


> I have been researching rear fill for my install and found this website that gives you what L(minus)R sounds like when done.
> 
> I found it helpful hopefully you will
> 
> Stereo, mono and all those other things


finally a real world comparison. stellar.


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## Gary S (Dec 11, 2007)

I'm a little late to this thread, but thought I would set the record straight.

The rear speakers should be wired out of phase for best results with the L-R signal... so they cannot be localized.

So, you have a single (mono) signal of L-R going to the rear amp... the left speaker + goes to amp +, and negative (-) speaker terminal is wired to negative amp terminal.

Then wire the right rear speaker out of phase... + speaker terminal to negative amp terminal, and - speaker terminal to + amp terminal.

You don't need a delay, a fader works fine.

You don't need a center if you have good placement in the front (kick panels), you'll have a phantom center... the left and right speakers have the center channel information and if they are close enough (kick panels) to each other, will acoustically sum the center.

Dolby specifies a 6db per octave low pass of about 7k for the rears... this sounds best to me, but some have said that 2k works better. You can experiment with it and see what you like.

I usually high pass the rears the same as the fronts... 60 - 90 hz. 

Speaker placement and installation are still king... for best results, I recommend sealed kick panel placement for the front satellites, and rear deck placement for the rears in sedans. In hatch backs you can customize a rear subwoofer box by putting the sub(s) in the middle of the box, and putting the rear satellites in either end of the box in thier own separate chambers.


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## pionkej (Feb 29, 2008)

Gary S said:


> I'm a little late to this thread, but thought I would set the record straight.
> 
> The rear speakers should be wired out of phase for best results with the L-R signal... so they cannot be localized.
> 
> ...


Good experience based info...thanks. Instead of going 60-7khz or so, I was just planning on matching the range of speakers in my kick. I have tweeters in my kicks and "ambiance" tweeters in my pillars amd then 5.25" in my kicks and 8" in the doors. I'm using a 3" wideband for the rear-fill. I was planning on playing them around 200-5khz to match my 5.25" and kick tweeter. Does that sound like a good starting point?


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## Gary S (Dec 11, 2007)

pionkej said:


> Good experience based info...thanks. Instead of going 60-7khz or so, I was just planning on matching the range of speakers in my kick. I have tweeters in my kicks and "ambiance" tweeters in my pillars amd then 5.25" in my kicks and 8" in the doors. I'm using a 3" wideband for the rear-fill. I was planning on playing them around 200-5khz to match my 5.25" and kick tweeter. Does that sound like a good starting point?


Yes, 200 - 5k would be good.

Ideally, you would want the same 5.25" mid/tweet in the back as you have in the front... look at the original post/diagram... he has the same comp set front and back. Think of it this way... you would not use a different speaker(s) on the front right than the front-left, would you? So, why use something different in the rear? You want to match the characteristics of the front speakers as much as possible (other than the lowpass xover point) Just keep it in mind for your next setup.

I have a '96 Firebird I'm setting up right now... I'm using identical PPI DCX-525S comps front and rear... front set in kicks, and the rear set in a box in the rear luggage well flanking a 15" sub. Of course, the rears will get a surround signal (L-R).


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## jwebster (Feb 9, 2011)

Gary S said:


> I'm a little late to this thread, but thought I would set the record straight.
> 
> The rear speakers should be wired out of phase for best results with the L-R signal... so they cannot be localized.
> 
> ...



pionkej, I strongly disagree with some of the above:

First- Delay IS required if you want to have the best rear fill effect resulting in your system sounding like it is in a much larger space. This is not a few ms's to align the time, but more like 20-30ms in order to simulate a reflected sound off of a wall that is 10 or more feet behind you (like in a large room or concert hall).

Second, since you are trying to mimic a delayed reflection off of a wall, matching your front and rear speakers is absolutely not needed. For example, the characteristics of the initial direct sound from your front stage in a home system or concert hall have a certain characteristic. But the reflected sound off the rear wall might have a completely different type of sound depending on what the rear wall is covered with (tile, wood, carpet, etc.). It is in no way going to resemble the initial direct sound from the speakers.

Third, Don't do L-R AND run your rears out of phase with each other at the same time. That would result in most of your rear fill being cancelled out. An L-R signal is one that removes the common info from the left and right signals (think vocals and other stuff that sounds like it comes from the center of the sound stage). It is a mono signal at that point. Really you could just run one single rear speaker and it would be fine. Two will work as well but they will be playing the exact same signal. If you run one out of phase with the other, the two sound waves will cancel out. 
If on the other hand you don't have the processing power to do L-R, you could run the two stereo rear signals out of phase to sort of acoustically create an L-R. I think this is what Gary S was alluding to. It won't work quite as well as an L-R processor, but could still work as long as you delay, band-limit and attenuate the signals appropriately. 

Attenuation- Start with the rears all the way down and your front stage playing at normal volume. Start to turn the rears up slowly until you are barely able to audibly notice that they are playing. Then turn them down slightly from there.

Band limiting- Start with 300-3500 and play with it from there. Again, since you are trying to recreate a reflection, different low-pass points can make the system sound like it is playing in a more or less reflective room. Generally, a lower lowpass point will give the impression of a less reflective rear surface.

These are only starting points. Play around with them until you get the desired effect. Once you do, it will be like nothing you have heard before (in a car anyway).


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