Subwoofer phase: normal and reverse??

[itscool]

Hi all,
I am not quite up to this, what is the difference of normal and reverse phase?

Thanks alot to your explanations

ADMIN Response:

Subwoofer Phase Switch: Normal vs Reverse

• Normal: keeps the polarity (+/-) of the Sub the same relative to the rest of your speakers.
• Reverse: flips the polarity (-/+) of the Sub relative to the rest of your speakers. This essentially puts the sub 180 degrees out of phase.

Some subwoofers offer variable phase which is adjustable from 0 to 180 degrees. It's a good idea to experiment by having one person vary the phase while you listen at the primary listening position to see which setting sounds best with bass intense music. You can also use an SPL meter to see how it affects output with pink noise. It is usually recommended to use the setting that yields the highest pink noise output when the sub + main channels are playing together.

 

[craigsub]

Let's say normal is 0 degrees, and reverse is 180 degrees. Many subwoofers have switches for just the purpose of going between the two.

IF you have two subwoofers next to each other, picture this: The 180 degree switch would have the driver pushing "out" in one sub while the 0 degree switch would have the driver pushing "in" on the other sub.

Thus: "normal" and "reverse"

Make sense now ?

 

[MDS]

Normal - the subwoofer is 'in-phase' with the other speakers; ie when the other speakers move in, the subwoofer moves in and when the other speakers move out, the subwoofer moves out.

Reverse - 180 degrees out of phase. The subwoofer moves in when the other speakers move out.

Some subwoofers have a continuously variable phase control which allows you to set the phase anywhere from 0 degrees (normal) to 180 in small increments.

Use of the phase switch is to help with integrating the sub with the rest of the speakers and the best setting depends on the placement of the other speakers relative to the subwoofer and room acoustics.

 

[itscool]

Re: sub phase norm and rev

Let's say normal is 0 degrees, and reverse is 180 degrees. Many subwoofers have switches for just the purpose of going between the two.

IF you have two subwoofers next to each other, picture this: The 180 degree switch would have the driver pushing "out" in one sub while the 0 degree switch would have the driver pushing "in" on the other sub.

Thus: "normal" and "reverse"

Make sense now ?

Ah, got it now! so which phase would it be much better in line with main speakers then?

 

[craigsub]

Ah, got it now! so which phase would it be much better in line with main speakers then?

What you want to do is grab a Rad shack SPL meter for $40. Set your mains to small, and run an 80 Hz signal through your system. Measure both settings, 0 and 180 degrees. Whichever is louder (meaning higher SPL) is the one you use.

And yes, the $40 on the RAD Shack meter is paramount for getting a system done right.

 

[itscool]

What you want to do is grab a Rad shack SPL meter for $40. Set your mains to small, and run an 80 Hz signal through your system. Measure both settings, 0 and 180 degrees. Whichever is louder (meaning higher SPL) is the one you use.

And yes, the $40 on the RAD Shack meter is paramount for getting a system done right.

Great advice, i'm using floorstanding main speakers, should i set it to small also? Anyway, i'll make a try to see any difference

Thanks a lot

 

[craigsub]

Great advice, i'm using floorstanding main speakers, should i set it to small also? Anyway, i'll make a try to see any difference

Thanks a lot

For checking phase, yes, use small. At the crossover frequency, both the subwoofer and speakers are (in theory) equally putting out sound. So, if they are in phase, even if you switch back to large later, they will still be in phase with each other, which is the goal here.

In-Phase = Working together.

 

[9f9c7z]

Normal - the subwoofer is 'in-phase' with the other speakers; ie when the other speakers move in, the subwoofer moves in and when the other speakers move out, the subwoofer moves out.

Reverse - 180 degrees out of phase. The subwoofer moves in when the other speakers move out.

Some subwoofers have a continuously variable phase control which allows you to set the phase anywhere from 0 degrees (normal) to 180 in small increments.

So at 90-degrees 'out of phase' the speaker is ... ???

What’s happening at all the other variable ‘out of phase’ degrees between 0 and 180 ???

 

[craigsub]

So at 90-degrees 'out of phase' the speaker is ... ???

What’s happening at all the other variable ‘out of phase’ degrees between 0 and 180 ???

Next lesson ...

Ok ... Now picture a driver fully extended out - we will call the 0 degrees.

One fully extended in is 180 degrees.

One half way in is 90 degrees.

One halfway back out is 270 degrees.

So - When driver A is fully extended out, while driver B is halfway back - If driver A is in phase then B is at 90 degrees out of phase.

 

[9f9c7z]

Thanks, Craig. Good stuff! If you are up for a couple more questions…

(1a) Does the subwoofer create a sound wave when moving in, toward the cabinet, 180-deg out of phase? I’m thinking that sound is a pressure wave that moves thru the atmosphere. I can see a surface that moves toward the ear creating that pressure/noise that can be heard, but a surface moving away from the ear would pull the atmosphere toward the cabinet, i.e. sucking the pressure wave away from the ear. (1b) If a speaker does create a sound wave while moving away from the ear (180 deg out of phase), is it as effective as when it moves toward the ear (in phase)?

(2a) If some speakers are making noise moving forward (in phase), and some are making noise moving backward (180 deg out of phase), isn’t the sound from the different speakers arriving at different times? (2b) If so, I’m guessing it’s not enough of a difference that the brain can distinguish the variation?!? I’m thinking about a sub being 180-deg out of phase with the rest of the speakers.

 

[craigsub]

Thanks, Craig. Good stuff! If you are up for a couple more questions…

(1a) Does the subwoofer create a sound wave when moving in, toward the cabinet, 180-deg out of phase? I’m thinking that sound is a pressure wave that moves thru the atmosphere. I can see a surface that moves toward the ear creating that pressure/noise that can be heard, but a surface moving away from the ear would pull the atmosphere toward the cabinet, i.e. sucking the pressure wave away from the ear. (1b) If a speaker does create a sound wave while moving away from the ear (180 deg out of phase), is it as effective as when it moves toward the ear (in phase)?

(2a) If some speakers are making noise moving forward (in phase), and some are making noise moving backward (180 deg out of phase), isn’t the sound from the different speakers arriving at different times? (2b) If so, I’m guessing it’s not enough of a difference that the brain can distinguish the variation?!? I’m thinking about a sub being 180-deg out of phase with the rest of the speakers.

1... Yes, the back wave begins as 180 degrees out of phase with the front wave. In a sealed design, or Infinite Baffle, the wave is basically "unused", and thus is inaudible.

In a ported design, you can actually get some computer simulations of what will occur, but if the design is properly executed (which good ones are), the phase issues of the sound directly from the driver and the sound from the port are eliminated.

2. Actually, this is one of the reasons getting a flat response in room is so difficult. For example, if you have a 100 dB, 100 Hz signal and apply the identical signal at 180 degrees out of phase, you will hear nothing, in a true anechoic environment. They will cancel each other out.

This is also why, when you get your speakers and subwoofer in phase with each other, the SPL's, as measured in dB, will be higher.

 

[9f9c7z]

Craig – thanks for the great info!!! Are you affiliated with a manf of subwoofers?

 

[craigsub]

Craig – thanks for the great info!!! Are you affiliated with a manf of subwoofers?

LMAO ... No, I just love this stuff.

 

[Mr. Lamb Fries]

Craigsub- do you know anything about car sub boxes?

 

[craigsub]

Craigsub- do you know anything about car sub boxes?

Unfortunately, no. I have always stayed with the factory system in my vehicles, primarily because I listen mostly to news stations while driving to a client.

Think about it - It is hard to get a good "game face" for a business meeting when you were just singing "Highway to Hell" at the top of your lungs ...

 

[9f9c7z]

Think about it - It is hard to get a good "game face" for a business meeting when you were just singing "Highway to Hell" at the top of your lungs ...

You could try that ”Don’t worry, be happy…” song.

 

[Mr. Lamb Fries]

your right! But I do a lot of long distance traveling and love loud music! Ive got an older system but need to build a different box for my newer truck. I listen to a lot of talk radio too so I refuse to invest any more money in my car stereo. I thought I would build another box so When I want to Make my ears bleed with Angus, Malcom, Bon, Phil, & Cliff I can!

 

[craigsub]

your right! But I do a lot of long distance traveling and love loud music! Ive got an older system but need to build a different box for my newer truck. I listen to a lot of talk radio too so I refuse to invest any more money in my car stereo. I thought I would build another box so When I want to Make my ears bleed with Angus, Malcom, Bon, Phil, & Cliff I can!

I can tell you a bit about the layout of a car, and why a subwoofer is not too hard to accomplish in one, with certain caveats.

A typical passenger car as about 100-130 cubic feet of interior space. They also have about a 10 to 20 Cubic foot trunk.

Building an IB subwoofer into a car is not a difficult task, using the trunk for the driver loading.

A 20x15x8 foot family room is 2400^3 feet - or about 20 times the volume of the car. Needless to say, a single, 12 inch driver of reasonable performance will deliver VERY strong bass into the car's interior.

The downside of the car is "leakage" of sound - Think about the car "booming" as it goes down the street - You don't hear this coming from the normal home.

Find a good 12 inch driver, make sure you have a good seal into the trunk, and proper amplification and EQ, and you are on your way.

 

[Mr. Lamb Fries]

My problem is that i have 4-12" RF Punch phase 2. and they were in a sealed box in the back of a 4-runner. Now ive got a Chevy suburban and the box wont fit-go figure. There are storage compartments in the back of the chevy that make the floor space about 4 inches too narrow. I made a temp. box just to get it installed and lost a bit of the sound quality. not to mention the Earl Shibe construction job i did is quite a site!! If you have any Ideas what kind of box (open air...lots of space,) would suit best (ported, seales, isobaric(sp)) , i would appreciate it. i can get the cubic foot requirements fron the factory but what kind of box is most accomidating to different types of music?
thanks for the help
Greg

 

[craigsub]

My problem is that i have 4-12" RF Punch phase 2. and they were in a sealed box in the back of a 4-runner. Now ive got a Chevy suburban and the box wont fit-go figure. There are storage compartments in the back of the chevy that make the floor space about 4 inches too narrow. I made a temp. box just to get it installed and lost a bit of the sound quality. not to mention the Earl Shibe construction job i did is quite a site!! If you have any Ideas what kind of box (open air...lots of space,) would suit best (ported, seales, isobaric(sp)) , i would appreciate it. i can get the cubic foot requirements fron the factory but what kind of box is most accomidating to different types of music?
thanks for the help
Greg

I would go with a sealed box again - Much easier to design and build.