Sub Phase for the begginer
Thread Starter
50 Watt CAFz'r
Joined: Mar 2005
Posts: 253
Just because you have plus on you amplifier wired to plus on you subwoofer and minus wired to minus does not always mean that your subwoofer is in phase, does this sound like crazy talk? There is a big difference between electrically in phase and acoustically in phase. When we talk about phase we really are referring to the polarity of the sound as it leaves the speaker, a speaker either creates pressure or vacuum depending on if it is moving out (compressing the air around it) or moving in (expanding the air). By moving back and forth very fast (20 90 times per second for a subwoofer) the subwoofer modulates the
surrounding air and is what your ear drum (or rectal cavity) detect as kickin *** bass.
What really matters is what happens when the sound hits your ears (or your chest for a pounding subwoofer). Because subwoofers are usually mounted in the back of your ride they are a very long distance from your front speakers and the sound from your speakers does not reach your ear at the same time. From a distance and time point of view the speaker closest to you will hit your ear first (time alignment can fix this problem but that is a totally different tech tip) and the speakers further away will arrive some time later (usually measured in Milliseconds).
The problem is that when the two speakers are playing the same note separated by distance (measured in time for sound to travel from your speaker to your ear) when they arrive at your ear they can have opposite polarity and cancel each other out. This is commonly referred to as phase cancellation, which in a vehicle can be a huge problem. Careful attention paid to the correct polarity of your speakers can make a huge improvement to the overall performance of your system regardless of what equipment you are
using. How do I check for proper speaker phase?
Electrical phase is very easy to check for; this is the first place to start. The + and labeled on your speaker terminal are very important markings, what these mean is that if you apply a battery to your speaker (I recommend a 9V battery not the big high current battery found in your car to test this) and you hook the + terminal of your battery up to the + terminal of your speaker (and minus to minus) the speaker cone should move outward. Go through every speaker in your vehicle and verify at the amplifier and verify that all you speaker cones move out when applied a positive voltage. This will verify that all speakers in your system are electrically in phase. Dont rely 100% on the + and markings on your speaker, I have seen many speakers that were magnetized backwards,checking with a battery is the only way to truly know. Once you have the polarity sorted out you are ready to adjust the crossover frequencies and gain for proper balance between your speakers.
With your source unit (CD player, MP3, DVD or 8-track) volume set at 3/4 adjust the gain so that
the system is about as loud as you would ever play it (this counts showing off to your buddies on Saturday night after a few to many). Start adjusting the subwoofer crossover frequency until you find a nice blend between your full range speakers and your subwoofer (usually around 75Hz 90Hz),the subwoofer should start disappear and you should not be able to localize it consistently in the back of the vehicle.
At this point we are ready to acoustically check if the subwoofer is in Phase. Find a musical track that has low frequency notes (not bass drum hits) that go up in frequency that transition from the subwoofer into your front speakers, listen to this track repeatedly and memorize each notes volume and location (front or rear of the vehicle). Now go to you subwoofer and swap + and -, then go back and listen to the same track again at the exact same volume. What you looking for is a smooth transition from high notes (front speakers) to low notes (subwoofer) where all the notes are the same volume and it becomes very difficult to tell if the sound is coming from the midrange or the subwoofer. Go back and forth between polarity settings until you find the setting the most faithfully
reproduces each note. This is the setting that you should use for your system, it is OK to wire you subwoofers electrically out of phase if you follow this procedure and determine that it sounds better wired with reverse polarity.
If you care, you can sit in the passenger seat or rear seats of the vehicle and perform the same routine, you might find that what sound best at the drivers seat will not hold true for other locations in the vehicle. You paid for the system so you better make sure it sounds its absolute best in the drivers seats, unless you have a designated driver then tune it for where ever you will be sitting.
[ June 17, 2005, 03:21 PM: Message edited by: AudioVault ]
surrounding air and is what your ear drum (or rectal cavity) detect as kickin *** bass.
What really matters is what happens when the sound hits your ears (or your chest for a pounding subwoofer). Because subwoofers are usually mounted in the back of your ride they are a very long distance from your front speakers and the sound from your speakers does not reach your ear at the same time. From a distance and time point of view the speaker closest to you will hit your ear first (time alignment can fix this problem but that is a totally different tech tip) and the speakers further away will arrive some time later (usually measured in Milliseconds).
The problem is that when the two speakers are playing the same note separated by distance (measured in time for sound to travel from your speaker to your ear) when they arrive at your ear they can have opposite polarity and cancel each other out. This is commonly referred to as phase cancellation, which in a vehicle can be a huge problem. Careful attention paid to the correct polarity of your speakers can make a huge improvement to the overall performance of your system regardless of what equipment you are
using. How do I check for proper speaker phase?
Electrical phase is very easy to check for; this is the first place to start. The + and labeled on your speaker terminal are very important markings, what these mean is that if you apply a battery to your speaker (I recommend a 9V battery not the big high current battery found in your car to test this) and you hook the + terminal of your battery up to the + terminal of your speaker (and minus to minus) the speaker cone should move outward. Go through every speaker in your vehicle and verify at the amplifier and verify that all you speaker cones move out when applied a positive voltage. This will verify that all speakers in your system are electrically in phase. Dont rely 100% on the + and markings on your speaker, I have seen many speakers that were magnetized backwards,checking with a battery is the only way to truly know. Once you have the polarity sorted out you are ready to adjust the crossover frequencies and gain for proper balance between your speakers.
With your source unit (CD player, MP3, DVD or 8-track) volume set at 3/4 adjust the gain so that
the system is about as loud as you would ever play it (this counts showing off to your buddies on Saturday night after a few to many). Start adjusting the subwoofer crossover frequency until you find a nice blend between your full range speakers and your subwoofer (usually around 75Hz 90Hz),the subwoofer should start disappear and you should not be able to localize it consistently in the back of the vehicle.
At this point we are ready to acoustically check if the subwoofer is in Phase. Find a musical track that has low frequency notes (not bass drum hits) that go up in frequency that transition from the subwoofer into your front speakers, listen to this track repeatedly and memorize each notes volume and location (front or rear of the vehicle). Now go to you subwoofer and swap + and -, then go back and listen to the same track again at the exact same volume. What you looking for is a smooth transition from high notes (front speakers) to low notes (subwoofer) where all the notes are the same volume and it becomes very difficult to tell if the sound is coming from the midrange or the subwoofer. Go back and forth between polarity settings until you find the setting the most faithfully
reproduces each note. This is the setting that you should use for your system, it is OK to wire you subwoofers electrically out of phase if you follow this procedure and determine that it sounds better wired with reverse polarity.
If you care, you can sit in the passenger seat or rear seats of the vehicle and perform the same routine, you might find that what sound best at the drivers seat will not hold true for other locations in the vehicle. You paid for the system so you better make sure it sounds its absolute best in the drivers seats, unless you have a designated driver then tune it for where ever you will be sitting.
[ June 17, 2005, 03:21 PM: Message edited by: AudioVault ]
Cheddar
Joined: Sep 2004
Posts: 558
Can you make that readable please?
BTW, good read, AV. [img]graemlins/thumb.gif[/img]
Cheddar
Joined: Sep 2004
Posts: 558
Originally posted by aneonrider:
O, I know how phase works, just really hard to read the post, still is IMO.
O, I know how phase works, just really hard to read the post, still is IMO.
Anyway, the guy took a lot of time to contribute. Good for him.
Thread
Thread Starter
Forum
Replies
Last Post
