Car "soundstage" options?

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I have two 6.5" components sets that I plan to active x-over. How best to utilize them?


1) 1 set front, 1 set rear (set 1-2dB down from the fronts).
2) 1 set front, only the 6.5" rear (like a really badly placed TMMW).
3) 1 set front, nothing rear.

There will also be a 12" in a sealed box if that makes any difference.

use time delay to help get the phase well-matched with the airspace of the cabin.
there are two options here:
1. you use the time delay accurately & keep the excessive overlap down
2. you use the time delay inaccurately to get really wrong phase speakers twisted to something acceptable.

as for the speakers themselves, not all speakers are the same phase.
some will be a match with the time delay accurately set for the true distance,
while other speakers will need more or less time delay to twist the phase until it is a match.

obviously the same exact thing can be said for the rear speakers & subwoofer too.

when you dont have any time delay to adjust, the other option is to find the best location mixed with the best matching phase to get a strong soundstage.
but this is more like a 'showcar' where the speaker location gets fiberglassed into place regardless of what it looks like because of how it sounds.

if you don't need reference sound, you can easily expand the soundstage by extending the time delay towards measurements 'greater' than speaker to listening position distance.
one easy place to start is the distance from the speaker to a reflection.
that reflection might be 'the middle space' between the two doors, allowing the reflection to brush the radio area.
maybe you measure from the above middle position, then from that position add the distance to the windshield.

there are only two ways for a soundstage to properly work:
1. the soundwaves exist one time without overlap, with as much even pressure from the low notes up into the midrange & treble
2. the soundwaves overlap as if reverb, simply to fill the entire cabin with audio as if it is coming from more than one location (or make the sound appear swelled in size).

basically you need to look at the interior space like a tank of air.
you either go positive with pressure that gets in the way (unless you've got sound processing to make the collisions go away)
you go negative with pressure where the overlaps simply don't happen unless you turn up the amount of effect until the soundwaves touch eachother.
the truth about phase is,
it is a time delay.. but it is much smaller than the milliseconds of adjustment used for distance delay.

some distance delays use only millisecond delay.
others mix in different phase adjusts too.

the reason mixing the phase into the distance delay works is because perfect phase is 0 degrees.
and the only thing about changing the phase with distance is because the air itself gets in the way and it changes the phase with more distance between ear & speaker.

now the audio engineers see the option to include a floor (or a floor & ceiling combination) because they know most places will be with a floor.
...see, if your speakers are on stands in the middle between the floor and the ceiling, the speaker's wont be very big (because if they are then the midrange & treble starts to really scream) and they know if the speaker is big, then there will be a large distance between the speaker & ear.
they know there isn't any need to not include the floor with long distances, they know there is a stable equation regardless of short or long distance.

the sad truth is when the 'air' that is being compensated for simply isn't the same 'texture' as the air your speaker is in.

it is also sad when the amount of phase adjustment mixed into the distance delay is not a perfect match for the speaker (well, speaker & room combination) being used.
Wow, thanks for all that. I think you overshot my question a little though.

I just want to know if having rear speakers can be a benefit in any way, or if I should just leave them out.

No time alignment options here. This isn't for a show car and I can live with some flaws in the setup. Just trying to get the most out of what I already have.
can rear speakers be a benefit? yes

though the answer, it is application specific.
a car with a lousy interior matched with speakers that are neutral to the problem or make the problem worse wouldn't be a benefit compared to speakers that neutralize the problem.

best thing to try is hook them up and see what it sounds like before & after.
then hook them up out of phase with the front speakers and see if it sounds better before or after.

you've got three different opportunities to flip the phase and see if it sounds any better.

too many variables to answer your question, to begin.. you shouldn't expect people to know what you like or dislike in the context of perfect or sacrifice.
opinions vary widely.

a way to form a logical answer would need to know what vehicle it is, if the interior is cloth or leather, what speakers they are, what amplifiers are used, and where your geographical location is.
all that needs to be known before anybody can do a model or calculation (not that anybody is going to be there to do it, because i certainly haven't seen such participation).

all that modeling & calculation is master quality response.
they know what perfect is, and it's no wonder sadness blankets the place because they don't present or advertise themselves.
with that said, the next best answer is trying it yourself.

one pair of speakers might make the option of rear speakers appear undesirable, while another pair of speakers might make the option of rear speakers pleasing.
sometimes it is a combination of the front & rear speakers as a compromise.

perhaps you don't like the idea of time delay, but using it with a much smaller distance than the length between speaker and listener can still help dial in the speakers to make them match the installation.

if you want a simple yes or no answer, such an answer doesn't exist.

i've installed rear speakers and the difference in quality & purpose has been on both sides of the scale.
to get the most out of what you already have is going to boil down to some simple rules.

1. flip the speaker wires around and see if you get any more detail & clarity
2. use an equalizer to get the tones to the same level of amplitude

number 1 wont necessarily help with the soundstage, but the clarity in the air could improve.
number 2 can help the soundstage some, but the amount of difference is typically less than the comparable alternatives.

maybe you don't have an equalizer.
but to 'get the most' out of what you already have might come with an addition in equipment.
if you've got a laptop, there are audio plugins that might help improve the soundstage if you can connect the audio output of the laptop into the radio.
i haven't much experience with the phones & all their applications that can be downloaded, but i figure it might be worth a look to browse the selection to hunt for something that could help (if any help is even necessary).

an equalizer can help the soundstage, and it is basically the same thing between two door speakers and the door speakers mixed with the subwoofer.
if you play some test tones and come to find one of the tones is much louder than everything else, that amount of amplitude is going to push onto the soundwaves from the other speakers.
not only does the sound get drowned out, it can literally shove the pocket of air.. whether it is a large shove that moves towards the dash & windshield .. or if it is sending ripples of excess soundwaves through the pocket of sound from the other speakers .. either one is potentially damaging.

when you equalize the door & rear speakers, it is the same thing with amplitude.
a large peak can shove the pocket of air until it loses that linear sound .. sometimes it is physically , sometimes it is only audible.

when the amplitudes are even, there is an improved opportunity for the soundstage to make a presence.
even if you don't own an equalizer..
there is the option to create passive filters to tone down the worst peaks in the system response.

you can find calculators on the internet to obtain the values needed to build the filter.
and there is more than one type of filter design.
some are simply a capacitor and an inductor soldered together that installs before the speaker like a bass blocker (dunno if you've ever seen them).

i know it is possible for the passive filter to work, but i don't know if the complex designs work any better than the simple ones (or if it is simply a matter of amplitude reduction different from one design to the next).
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