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Car Audio Phase problems
LocrianGroove
post Aug 21 2012, 05:04
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I can't seem to get the phase right in my 2010 Camry with an aftermarket stereo system. I have 2-way component speakers in the front, and they sound better with one side wired with reverse polarity. For a given polarity for the subwoofer, such that it sounds best from the driver side, it needs to be reversed for the passenger seat. The problem is present even with a LPF set far below the crossover frequency.

Is it common for car audio to have this problem? How do the poor acoustics inside a car account for the need to switch one side to reverse polarity? I wonder if I need to design a system with phase shifters. My goal is to find a setup that sounds good to both driver and passenger.
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Arnold B. Kruege...
post Aug 21 2012, 07:35
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QUOTE (LocrianGroove @ Aug 21 2012, 00:04) *
I can't seem to get the phase right in my 2010 Camry with an aftermarket stereo system. I have 2-way component speakers in the front, and they sound better with one side wired with reverse polarity. For a given polarity for the subwoofer, such that it sounds best from the driver side, it needs to be reversed for the passenger seat. The problem is present even with a LPF set far below the crossover frequency.


What is your criteria for "sounds better"?

Are you sure that each of the 2-way speakers in the front are actually wired the same, or is there a possibility that one of the woofers or tweeters is itself wired with reverse phase compared to the same speaker in the other channel?

Notice that there is no global standard convention for wiring woofers and tweeters. Depending on the crossover design, the tweeter may be wired in phase with the woofer, or in opposite phase.

QUOTE
Is it common for car audio to have this problem?


No.

QUOTE
How do the poor acoustics inside a car account for the need to switch one side to reverse polarity?


The acoustics inside a car have their own set of problems, but compared to a typical room, they are generally quite a bit better. For example a car has a lot more absorbtive material in it for the given amount of surface area than a typical listening room since the car's interior volume is dominated by heavily cushioned and upholstered seats.

QUOTE
I wonder if I need to design a system with phase shifters. My goal is to find a setup that sounds good to both driver and passenger.



The inherent problem with balancing sound for both the passenger and driver is that the driver sits close to (virtually on top of) one pair of speakers (which pair depends on where the steering wheel is since this is an international forum) and the passenger sits close to (virtually on top of) the other pair of speakers. There is therefore a strong tendency for the driver and the passenger to each be listening to almost-mono and with a pronounced left-right bias.

This problem is addressed two ways. First off, you can put a set of speakers in the middle of the car which forms one channel for both riders, and hook the outside speakers to the other channel. The second approach is trickier but is sometimes pulled off. What you do is make the speakers directional and oriented in such a way that the person sitting closer, is a much higher angle off-axis and therefore the intensity of the sound that reaches his ears from the near speaker is far less.
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LocrianGroove
post Aug 22 2012, 03:53
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QUOTE (Arnold B. Krueger @ Aug 21 2012, 02:35) *
Are you sure that each of the 2-way speakers in the front are actually wired the same, or is there a possibility that one of the woofers or tweeters is itself wired with reverse phase compared to the same speaker in the other channel?

I did some more testing, this time with the tweeters disconnected, so that just the 2 front door woofers are connected.


QUOTE (Arnold B. Krueger @ Aug 21 2012, 02:35) *
What is your criteria for "sounds better"?

When the speakers are wired correctly, they sound fine from either of the back seats of the car, or from a position in the center of the car. However, when sitting in either of the two front seats, the speakers sound as if one of them is wired with reverse polarity. It sounds like it does on a home system with one channel inverted. When I actually do invert a channel, I get some relief from the out of phase sound, and it sounds closer to normal. This is what I meant by "sounds better." The wiring that sounds less like the speakers are wired out of phase is "better," though it is incorrect. When I move to the center of the car, the speakers are now obviously out of phase.

It would be interesting to find which frequencies are causing this problem, and what relative phase is required to correct it. Is there software that would allow me to play stereo test tones and change the phase of one channel in real time?
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probedb
post Aug 22 2012, 08:23
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Even the cheapest cars stereos generally allow you to alter things like phase, seating position etc all with equalization.

What stereo do you have?

I have a cheap Kenwood and can do all this, right down to setting the size of the car and where I want the best listening position to be i.e. the drivers seat.
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Arnold B. Kruege...
post Aug 22 2012, 11:32
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QUOTE (LocrianGroove @ Aug 21 2012, 22:53) *
QUOTE (Arnold B. Krueger @ Aug 21 2012, 02:35) *
Are you sure that each of the 2-way speakers in the front are actually wired the same, or is there a possibility that one of the woofers or tweeters is itself wired with reverse phase compared to the same speaker in the other channel?

I did some more testing, this time with the tweeters disconnected, so that just the 2 front door woofers are connected.


QUOTE (Arnold B. Krueger @ Aug 21 2012, 02:35) *
What is your criteria for "sounds better"?

When the speakers are wired correctly, they sound fine from either of the back seats of the car, or from a position in the center of the car. However, when sitting in either of the two front seats, the speakers sound as if one of them is wired with reverse polarity. It sounds like it does on a home system with one channel inverted. When I actually do invert a channel, I get some relief from the out of phase sound, and it sounds closer to normal. This is what I meant by "sounds better." The wiring that sounds less like the speakers are wired out of phase is "better," though it is incorrect. When I move to the center of the car, the speakers are now obviously out of phase.

It would be interesting to find which frequencies are causing this problem, and what relative phase is required to correct it. Is there software that would allow me to play stereo test tones and change the phase of one channel in real time?


This sounds like a strong reflection from the inside of the vehicle might be the problem.

You should be able to use a CD with test tones recorded on it to determine which frequencies are causing problems. Make or buy!
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LocrianGroove
post Aug 23 2012, 03:31
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QUOTE (probedb @ Aug 22 2012, 03:23) *
What stereo do you have?

I have an Eclipse CD5030. It has settings for "time alignment" with 100 microsecond increments and a parametric eq, which both have some usefulness.

QUOTE (Arnold B. Krueger @ Aug 22 2012, 06:32) *
This sounds like a strong reflection from the inside of the vehicle might be the problem.

You should be able to use a CD with test tones recorded on it to determine which frequencies are causing problems. Make or buy!

I could make a CD with test tones (or use a signal generator and my radio's time alignment to control phase), but I would have a lot more control with software that did arbitrary phase shifting or delay on the fly. I'd like to plug my laptop into my radio, play a tone, then dial in the phase that sounds correct. Does anything (free) come to mind that would have this feature?
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DVDdoug
post Aug 23 2012, 19:40
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Very strange problem... If the left & right channels are in phase, I don't see how it's possible to get different results on the left & right sides of the car... Everything should be symetrical. (That's assuming no "time alignment" adjustments.) With only 2 speakers (no sub and no rear speakers), it should be symetrical, even when out-of-phase.

How many speakers are there? Is the subwoofer mounted in the center, so that everything is physically symetrical?

You said you disconnected the tweeters... Are the door speakers 2-way or 3-way? I'm thinking that one of the drivers in the 2-way or 3-way speaker might be mis-wired (by the manufacturer) so that either the woofer, tweeter, or midrange is is out-of-phase, and switching the connections causes the other driver(s) to go out-of-phase.

Maybe something's screwed-up or defective in the "location" time-alignment firmware in the head-unit. Do you have a portable stereo or something you can plug-into the car speakers in place of the head unit?

QUOTE
...but I would have a lot more control with software that did arbitrary phase shifting or delay on the fly. I'd like to plug my laptop into my radio, play a tone, then dial in the phase that sounds correct. Does anything (free) come to mind that would have this feature?
I don't think so... You are dealing with at least 3 channels (left, right, and sub), more channels if there are rear left & right speakers.


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LocrianGroove
post Aug 24 2012, 00:45
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QUOTE (DVDdoug @ Aug 23 2012, 14:40) *
Very strange problem... If the left & right channels are in phase, I don't see how it's possible to get different results on the left & right sides of the car... Everything should be symetrical. (That's assuming no "time alignment" adjustments.) With only 2 speakers (no sub and no rear speakers), it should be symetrical, even when out-of-phase.

With correct wiring, it sounds fine from the center of the car, but it sounds out-of-phase from the left side and right side of the car. With reversed wiring on one channel, it sounds out-of-phase from the center of the car, but improved from the left side and right side. The effect is symmetrical.

QUOTE (DVDdoug @ Aug 23 2012, 14:40) *
You said you disconnected the tweeters... Are the door speakers 2-way or 3-way? I'm thinking that one of the drivers in the 2-way or 3-way speaker might be mis-wired (by the manufacturer) so that either the woofer, tweeter, or midrange is is out-of-phase, and switching the connections causes the other driver(s) to go out-of-phase.

Maybe something's screwed-up or defective in the "location" time-alignment firmware in the head-unit. Do you have a portable stereo or something you can plug-into the car speakers in place of the head unit?

I did have 2-way door speakers, rear speakers, and a sub, but to simplify troubleshooting, I'm now testing with only the left door woofer and the right door woofer. Tweeters, rear speakers, and sub are not connected. I'm also using a 2-channel home stereo amp to drive the speakers. The source is now my laptop, instead of the car radio. I'm still using the crossovers with the woofers, however.
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