# The decline of rear-fill



## Kenneth M (Oct 14, 2014)

Back in the 80's, the best speakers were always in the back. Almost always located on the rear shelf, these speakers had more space to be bigger, so that's what manufacturers did; make them bigger than the fronts. When I was a child I would experiment with fading the volume to the back so that I could turn the bass lower and test the limits of the stock sound system. 

In the 90's, car stereo got hot. Really hot. Suddenly the front stage became ever so important. We had center channels that hung from rear view mirrors, we were hitting mega watts in 1/2 an ohm, and the magazines looked like half swimsuit models, and half car audio. But we were still buying the same brand and model type for our fronts and rears. 

Then in the 2000's it was introduced to me that high end for the front, and low end for the rear. "It really doesn't matter...it's just rear-fill" is how it was put to me. "You would be wasting your money if you got high-end speakers for the rear."

Now, in the 2010's, most people only put subs behind the front seats. All the mids and highs get channelled to the front occupants, abandoning rear-fill altogether.


So what are the rules now? In which cases should rear fill be addressed, and in which cases should it be ignored altogether?


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## 1996blackmax (Aug 29, 2007)

Rear fill can add to the overall sound, but it has to be done right. Heavily delayed, attenuated, & limiting the higher frequencies is what worked for me. Basically to the point that you can't really tell that it's there until you completely take it away.


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## Sprocket3 (Mar 16, 2014)

I run a three way active system 6.5" splits up front with dual 10's aimed backwards in the rear, the rules are the closest speaker gets the most delay followed by the next closest and so on, this is of course dependent on all phase being corrected beforehand.


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## SPLEclipse (Aug 17, 2012)

_"Now, in the 2010's, most people only put subs behind the front seats. All the mids and highs get channelled to the front occupants, abandoning rear-fill altogether."_

Probably 90+% of all aftermarket car audio installs still use rear speakers. Hell, now people are putting speakers under their hoods, in the bumpers, etc...

I will agree that there has been a rise in people who want a home-audio level experience in their car - and because of that equipment has gotten better (and less expensive) and expectations have gotten higher. Rear-fill isn't used in a stereo home-audio experience, and if that's the goal then why use it in a car?

There are no "rules" per se, your install depends on your goals.


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## subterFUSE (Sep 21, 2009)

Home "stereo" setups are always 2 speakers. Actually, when stereo sound was first introduced it was 3 channels with a center speaker. But manufacturers quickly decided that consumers would not spend the money for a third speaker and so the standard was reduced to 2 speakers only.

With that in mind, if the goal of a car audio system is to accurately reproduce the home stereo experience, then rear speakers are not necessary.

As stated earlier in this thread, if the goal is to maintain a solid front image while still using rear speakers to add ambiance, then it certainly can be done. It just takes more work and attention to the design and tuning to prevent the rears from pulling your attention to the back. Of course, having rear speakers will always mean more expense. You must buy the speakers, install them, use additional processing/amplified channels, and then tune it all. I think that is probably the primary reason you don't see much rear fill in SQ cars. Added expense and effort for something that is seen as unnecessary.

I think another reason you don't see a lot of rear fill in SQ systems has been that most DSP units available don't have enough channels to do it all actively. Until just recently, the highest number of channels we have seen on most of the popular car audio DSP units has been 8. With 8 channels you can run 3-way active fronts, and have 2 channels left for subwoofer and rear. That means mono rear. You could do a 2-way active front and then do stereo rears that use passive crossovers, and then an active subwoofer.

The new Helix DSP Pro which has just been released is a 10 channel DSP. I believe that with 10 channels of processing, we might begin to see more people trying to go with rears. Maybe someone will eventually release a 12 channel DSP that can do 3-way active front, 2-way active rear and subs?


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## LaserSVT (Feb 1, 2009)

My best friend always complains there is not enough rear fill in my truck. Well that's because it does not have rear speakers. LOL
He much prefers his cars sound but has the same speakers front and rear and when I sit in it the entire stage is on the side you are sitting. Its like wearing headphones that are biased a bit to one side. Drives me nuts but he likes it so oh well.
I haven't run rear speakers in a system since my very first system in 1990.... which was only rear speakers. A pair of KLH bookshelves powered off a Pyramid amp in my hatch. LOL


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## sirbOOm (Jan 24, 2013)

SPLEclipse said:


> _Probably 90+% of all aftermarket car audio installs still use rear speakers._


_

We almost always do rear speakers at my shop.

Don't be mislead by the common opinion on this forum representing .000000001% of all potential car audio customers. :laugh:

I like SQ and I like "rear fill". The "decline" of rear fill among we SQ-focused DIYMA members, I think, has more to do with the lack of a 10-channel processor than it has to do with rear fill being somehow technically incorrect._


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## DFW40 (Jun 3, 2014)

It really just depends on what you like and with enough channels etc you can have it both ways. It just takes more time and money. If you listen to dubstep and other music like that then having that surround sound and loads of volume can get you the sound of a club. Which to some ppl is what they are after and it also gives you louder mids and highs to keep up with high power sub systems. There really is no right or wrong way despite what many ppl will tell you. The "live" concert concept or the home audio experience is just what most ppl really into this hobby think a car should replicate. Like mentioned earlier some ppl will get into your car and dislike the front stage only install it will sound 50% empty to them so who is to say their opinion is completely wrong.


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## LaserSVT (Feb 1, 2009)

DFW40 said:


> It really just depends on what you like and with enough channels etc you can have it both ways. It just takes more time and money. If you listen to dubstep and other music like that then having that surround sound and loads of volume can get you the sound of a club. Which to some ppl is what they are after and it also gives you louder mids and highs to keep up with high power sub systems. There really is no right or wrong way despite what many ppl will tell you. The "live" concert concept or the home audio experience is just what most ppl really into this hobby think a car should replicate. Like mentioned earlier some ppl will get into your car and dislike the front stage only install it will sound 50% empty to them so who is to say their opinion is completely wrong.


Really that's about the best response.


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## tbomb (Nov 28, 2007)

SPLEclipse said:


> _". Rear-fill isn't used in a stereo home-audio experience, and if that's the goal then why use it in a car?_


_

because you have a room that provides the rear fill/ambiance. The car cant do this with just front stage....at least very well. So we have to manipulate it with rear speakers/steering algorithms to provide that sense of space._


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## hot9dog (Mar 23, 2013)

Rear fill when done correctly is nearly not detectable, just slight presence. For a lot of people its alot of effort for very little return. In my current build i plan on having rear fill, but that might change . The rear fill subject is dependent on your overall goals for your system.


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## DFW40 (Jun 3, 2014)

hot9dog said:


> Rear fill when done correctly is nearly not detectable, just slight presence. For a lot of people its alot of effort for very little return. In my current build i plan on having rear fill, but that might change . The rear fill subject is dependent on your overall goals for your system.


I agree it is all in your goals. I have some cheap Focal 6.5's running off of the deck in the rear and I can just fade them in or out and occasionally use time alignment to play around with when I get bored. I have kids and when listening to some of their songs I can fade to the back to help keep my sanity.


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## hot9dog (Mar 23, 2013)

DFW40, its funny you should mention the kid subject. My 3 yr old daughter will be in the back seat so i too want to be able to fade open the rear fill so she can hear her music (taylor swift is her favorite right now). I love that my kids have been exposed to all forms of music, i want them to be exposed to magic that happens when driving down the road listening to a nice system.... but not be blown out of the back seat. Lol


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## trumpet (Nov 14, 2010)

You guys would enjoy Floyd Toole's book Sound Reproduction: The Acoustics and Psychoacoustics of Loudspeakers and Rooms. It discusses how we hear and why more speakers and reflections can make for a very pleasing listening experience.


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## sirbOOm (Jan 24, 2013)

Taylor Swift... I'd hit that.


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## Alrojoca (Oct 5, 2012)

Rear speakers in a car have 3 purposes as it was mentioned already 

Ambience for the front seats

Music for the rear seats

Loud music with the purpose of hearing more noise or loud music without caring about stage or SQ


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## caragon (Jul 11, 2014)

Kenneth M
It's funny that you bring up this subject as I am pondering the same subject on my active front stage system that was recently installed in my car. My original plan was to install my two components sets for front & rear passive being powered by a five channel amp and a 12" subwoofer powered by the amps 5th channel. I have always had passive/rear fill type systems on all my cars since back in the 80's and have been extremely happy with results. Well for this latest system (the only one I have done since 1998) I was a bit overwhelmed with all the new audio companies, technologies and DSP's etc. Everyone kept telling me to install my system active up front using the builtin DSP in my deck and forget about the rear cocmponents. Well, I listen to everyone and went ahead and just installed a set of components up front "Active" and single 10" subwoofer instead of the 12" by following most people input. After installing the system and tweeking all the settings, the "active" system sound really clean & detailed, but I am really missing that rear fill surround sound affect that I am so used too. To me front only "active" systems sound great while parked in your garage at night and nothing else to distract you. While I am driving through traffic I like a system I can raise up the volume with decent SQ and have rear fill to comensate for road noise that filters through to the inside cabin. Currently with my front stage only active system I find full enjoyment while parked and not while fighting traffic to and from work. I guess it's all a personal taste in sound.


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## diy.phil (May 23, 2011)

^hey every decade this no-rear-fill comes up. So I did just that 2 decades ago. Then had to install some rear fill speakers on that vehicle lol.


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## Alrojoca (Oct 5, 2012)

Every car is different, rear fill may not be for every car. Some rear speakers are below knee level and a set of coax will not help other than have some extra noise.

A good rear fill is having components in the back, with the tweeteres placed

On the center console pointing to the back or B pillars on axxis pointing to the center between the rear seats.

It takes time and a lot of critical listening to get used to a good front stage to not miss the rears. For the rear passengers.

For the front passengers, 2 iidentical set of tweeter's and placed on the rear door sail panels and maybe pointing at the front or off axxis

Once you TA and get all the bass up front, the rears will not even be heard or that may make up for any road noise heard while driving.


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## sqnut (Dec 24, 2009)

tbomb said:


> because you have a room that provides the rear fill/ambiance. The car cant do this with just front stage....at least very well. So we have to manipulate it with rear speakers/steering algorithms to provide that sense of space.


To make the car sound like a bigger space you need late reflections, in a car there are no late reflections. Practically everything we hear in a car is within ~10-15m/s of the incident sound. Rears with delay give you the late reflections. But all algorithms create artifacts which one will hear. All the while crosstalk is telling your mind that the space is actually much smaller. 

If you're trying to replicate the tonality and imaging of a 2ch then rears are are really not required. If you want to replicate the space from the 2ch then you'd go the rears+delay route.

If you just want to get loud run components up front and beefy 6x9 on the rear deck.


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## captainscarlett (Mar 15, 2011)

Kenneth M said:


> Back in the 80's, the best speakers were always in the back. Almost always located on the rear shelf, these speakers had more space to be bigger, so that's what manufacturers did; make them bigger than the fronts. When I was a child I would experiment with fading the volume to the back so that I could turn the bass lower and test the limits of the stock sound system.


Was it that the 'Best' speakers were in the rear, or just that the 'Biggest' speakers were in the rear re: 6x9's?


*Pretty interesting video on the history of car audio. *


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## seafish (Aug 1, 2012)

subbed......


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## sirbOOm (Jan 24, 2013)

Here's how I'd do rear fill with an aftermarket deck that has time alignment (only). This can be done with any head unit but I'd want to be able to time align (even roughly) the rear speakers which a stock deck or lower-end aftermarket deck won't be able to do.

1) 3-way active front using 6-channels of the DSP of my choice. DSP receives signal for these speakers from the FRONT RCA output only.
2) Rear speakers powered by rear speaker wires of head unit's amp (or small amplifier using the rear RCA outs if I have the space, the money, and the time to waste)
3) Subwoofers getting the last 2 of 8-channels of the DPS, as per usual

In my processor, I would have at least 2 tunes. One that includes the rear speakers for which time alignment and adjustments come from the head unit (call this the "I'm driving on one of those loud concrete highways and I can't hear my damn music" tune or maybe "I have someone else's kid in the back who I'd like to drown out with additional dBs of music" tune). Another that does not include the rear speakers (call it "the competition (even though I don't compete because I don't have the time or money for that" tune) and, to turn off those rear speakers, just fade the head unit forward... rear speakers off.

You may shorten the names of your tunes as you see fit.


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## DDBear (Jan 30, 2015)

subterFUSE said:


> I think another reason you don't see a lot of rear fill in SQ systems has been that most DSP units available don't have enough channels to do it all actively. Until just recently, the highest number of channels we have seen on most of the popular car audio DSP units has been 8. With 8 channels you can run 3-way active fronts, and have 2 channels left for subwoofer and rear. That means mono rear. You could do a 2-way active front and then do stereo rears that use passive crossovers, and then an active subwoofer.


Excellent observation. My own experience supports your theory. I had my original high end system installed in my car in 2001, and in recent weeks started researching a major upgrade, overhaul of the system. Having been out of the car audio scene for a while, I thought for sure I'd be getting new speakers for the rear door as well. Then I discovered that audio processors exist, and based on my experience with Audessy MultEQ XT32 for my home theater system making a night and day difference in home theater SQ, it was easy to decide that I wanted to make all channels active in my new car audio system, to apply the Bit one processor to the max extent possible. 

Then I ran into a dilemma - not enough channels to use the sound processor with the rear door speakers. I started pulling hairs out, going back and forth whether it would be better to run the rear fill in mono, or use a passive crossover on the mid and tweeter in the 3 way Focals in the front. I didn't like either solution, and then started reading the forums (after skipping 10 years researching car audio) and it was so interesting to see this new trend to entirely delete the rear fill. Now I've decided to skip the rear speakers, assuming that the sound processor will create enough 3D ambience with just the ones in the front (based on the experience I have with Audessy doing the same to the home theater system). Will be interesting to see how it turns out!


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## Rodek (Aug 19, 2006)

In the 60's and 70's, people used reverb equipment. I believe the idea behind reverberating equipment was to add "spaciousness" to the sound.


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## Victor_inox (Apr 27, 2012)

I`d use two DSP if I have to before dismissing rear fill altogether.


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## garysummers (Oct 25, 2010)

Something that has not been mentioned in creating soundstage expanding rear fill is that you must remove as much of the coincident information in the stereo signal that you send as rear fill. It is the coincident or mono information in rear fill that will collapse and skew your front stage. This is what is done by the up-mix surround sound algorithms. If you do this, and there are ways to do it without an up-mix system, you will find you can play the rear fill louder and not have to restrict the hi-frequencies as much, which is where a lot of the "ambience" is.


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## subterFUSE (Sep 21, 2009)

DDBear said:


> Excellent observation. My own experience supports your theory. I had my original high end system installed in my car in 2001, and in recent weeks started researching a major upgrade, overhaul of the system. Having been out of the car audio scene for a while, I thought for sure I'd be getting new speakers for the rear door as well. Then I discovered that audio processors exist, and based on my experience with Audessy MultEQ XT32 for my home theater system making a night and day difference in home theater SQ, it was easy to decide that I wanted to make all channels active in my new car audio system, to apply the Bit one processor to the max extent possible.
> 
> 
> 
> Then I ran into a dilemma - not enough channels to use the sound processor with the rear door speakers. I started pulling hairs out, going back and forth whether it would be better to run the rear fill in mono, or use a passive crossover on the mid and tweeter in the 3 way Focals in the front. I didn't like either solution, and then started reading the forums (after skipping 10 years researching car audio) and it was so interesting to see this new trend to entirely delete the rear fill. Now I've decided to skip the rear speakers, assuming that the sound processor will create enough 3D ambience with just the ones in the front (based on the experience I have with Audessy doing the same to the home theater system). Will be interesting to see how it turns out!



Yeah, I really think it's the processing that has dictated a lot of this.

Although, I must admit that I'm not sure how "recent" or "new" the shift away from rear fill in cars is. In 1996, I built my 2nd car audio system and it was the first car system for me without rear fill. I was copying industry trends at the time: Image Dynamics horns. 8" ID midbass up front. JL Audio subs. Precision Power Art Series amps. No rear fill.

Ever since then I have not used rear fill in any of my cars.


Sent from my iPad using Tapatalk


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## Blackbeard (Nov 19, 2014)

Rodek said:


> In the 60's and 70's, people used reverb equipment. I believe the idea behind reverberating equipment was to add "spaciousness" to the sound.


In the 70's I used a Hafler circuit to get that "spacious" sound in in my 69 Stang. Much more subtle than using reverb.


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## Soundaddict (Feb 20, 2014)

Depends on speaker placement..if youre using stock location in rear, alot of the time they are low in the doors so you are aiming your speakers at the floor, or passangers feet, not your ears or anyones ears. My system has rear fill... Front is C5 rear is Focal Polyglass coaxials... They sound awesome..providing I lean backward between my seats and really listen to them. They handle a ton of power no problem and I imagine if I was a passanger I would appreciate them. But when Im jamming, and I fade them it makes no peceptible difference in my front seat experience. The front stage is just so good by itself, I dont miss it. And the expense.. The speakers, the mounts, the install, the extra 2 channels on the amp...


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## 1fishman (Dec 22, 2012)

garysummers said:


> Something that has not been mentioned in creating soundstage expanding rear fill is that you must remove as much of the coincident information in the stereo signal that you send as rear fill. It is the coincident or mono information in rear fill that will collapse and skew your front stage. This is what is done by the up-mix surround sound algorithms. If you do this, and there are ways to do it without an up-mix system, you will find you can play the rear fill louder and not have to restrict the hi-frequencies as much, which is where a lot of the "ambience" is.


What's a up mix system? 

Does the placement of the rears play a roll in the how they effect the sound stage? If the mono part is bad, i assume the further back and more center they are the more skewed the stage is also. 


Is it safe to assume that speaker quality is not very important for rear speakers if ambiance is the goal since you don't want high frequency's in the rear


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## ImK'ed (Aug 12, 2013)

Recently i was reading and admiring a build that simplicity in sound did for a customer which had rear shelf mounted midbass and i think the plan was to use 2 dsps, think it was a accord coupe. Customer was going to do the tuning i wonder what his ideas were


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## SO20thCentury (Sep 18, 2014)

1fishman said:


> What's a up mix system?
> 
> Does the placement of the rears play a roll in the how they effect the sound stage? If the mono part is bad, i assume the further back and more center they are the more skewed the stage is also.
> 
> ...


anyone?
:snacks:
I have 3-way 6x9s on the sides up behind the rear seats and bet I'd miss them.


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## AAAAAAA (Oct 5, 2007)

I think a lot has to do with how it's done at home and that there is more emphasis on proper staging and less on other things. Having rears has advantages to

With rear fill the FR response gets more normalised, less peaks and valleys and it gets much louder as well (potentially doubling cone area and power that's 6DBs) . Better for multiple seats as all seats are somewhat equal.

No rear fill or ambiance rear fill doesn't do anything for loudness and will generally have more phase and FR issues... like turning your head will make things sound strange or uneven. It also optimises one seat while worsening the others.


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## garysummers (Oct 25, 2010)

1fishman said:


> What's a up mix system?
> 
> Does the placement of the rears play a roll in the how they effect the sound stage? If the mono part is bad, i assume the further back and more center they are the more skewed the stage is also.
> 
> ...


An up-mix system is one that will derive multi-channel playback of a stereo signal. Dolby Pro-logic2, Logic7 are two commonly used up-mix systems used in car audio.

If you are using the rears strictly for rear-fill, the speakers will need to be a quality that can accurately reproduce the derived rear fill bandwidth at the desired level. Not wanting "hi-frequencies in the rear" is only relevant when you are unable to remove the coincident information in the signal fed to the rears. If you are able to derive the proper L-R rear fill information, then it is not necessary to restrict the hi-end in the rears.


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## papasin (Jan 24, 2011)

garysummers said:


> An up-mix system is one that will derive multi-channel playback of a stereo signal. Dolby Pro-logic2, Logic7 are two commonly used up-mix systems used in car audio.
> 
> If you are using the rears strictly for rear-fill, the speakers will need to be a quality that can accurately reproduce the derived rear fill bandwidth at the desired level. Not wanting "hi-frequencies in the rear" is only relevant when you are unable to remove the coincident information in the signal fed to the rears. If you are able to derive the proper L-R rear fill information, then it is not necessary to restrict the hi-end in the rears.


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## #1BigMike (Aug 17, 2014)

So I probably should hook my rear fill back up? I currently have the following rear components in my truck but not hooked up.

Passive Setup
Focal Utopia 165 W-RC
Focal W-RC crossovers
Focal TN-52

If I decide to hook them back up, I would have to purchase another 2 channel amp for them.

When I had them hooked up there was a difference but not a huge difference. I am new to the audio scene so I am just experimenting right now. Seems to be the only real way to learn.


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## AAAAAAA (Oct 5, 2007)

Imo of you don't have a processor and aren't working on getting perfect image then rears will only help


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## #1BigMike (Aug 17, 2014)

AAAAAAA said:


> Imo of you don't have a processor and aren't working on getting perfect image then rears will only help


sorry for not posting more info. I do have a processor (mosconi 6 to 8) and I would love to get a perfect image if there is such a thing.


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## WestCo (Aug 19, 2012)

1996blackmax said:


> Rear fill can add to the overall sound, but it has to be done right. Heavily delayed, attenuated, & limiting the higher frequencies is what worked for me. Basically to the point that you can't really tell that it's there until you completely take it away.


Yes I agree with this, but too often it's not done correctly.


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## cajunner (Apr 13, 2007)

question:

if the designers at the car companies, paid consultants, etc. find the purpose of creating an acoustic space that supersedes the regular bullet points of a stock system, what do they then do?


do they make this "rear fill" part of their equation, do they time-align mostly for the driver, does the UBER natch, highest tier audio system available from the manufacturer, become one of a kind, and deliver all that can be expected?

with all that wood at their disposal, the bean counters at bay, shouldn't the Martin Levinson, Burmester, or whatever, be near the highest performers at MECA Sound trials?

what I'd like to know is whether or not rear fill is more than that in the eyes of the engineers at these vaunted studio-grade namesakes being affixed to the speaker screens.

it surely is more than that to us, the small cadre of affected particular sorts, peculiar and all that, with the inclusion of it by design by the makers of the MS-8, Logic7, whatever, even the RF and Alpine have their 5.1 peaks, is the DD or DTS not advanced enough for 2-channel upmixing work?


and if that's too complicated, how many people who drop their rears, have to "adjust" or allot for a time frame where you acknowledge you lost something, to gain that forward staging?

I think a lot of people chained to the concept of drum tracks rotating neatly in front of them, forget the immersion experience, or just are willing to sacrifice one for the other, in the name of sound....


and that's all part of it.

if your musicography extends from hard rock, to heavy metal, to the occasional pop romp, and much of the classic rock pantheon, NONE of that source material is really developed as an acoustic scene with players cleanly delineated aurally by spacing and what not.

so, you make a system that wows the judges playing Spanish Harlem, (right?) and forget your true headbanger's nature, you hypocrite!


haha...


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