A question that probably has an answer that is way beyond my scope of understanding:

[Dookietwo]

Here are the requested screenshots. Screenshot 5- 2 subs, 40' apart, opposite polarity, 63Hz, angled toward each other Screenshot 6- Single sub, 80Hz, no boundaries Screenshot 7- Single sub, 80Hz, 3.5' from painted concrete block wall Screenshot 8- Single sub, 80Hz, 3.5' from painted concrete block corner Screenshot 9- Single sub, 80Hz, 3.5' from painted concrete block corner, panned 45* Screenshots 1-5 intentionally have no boarders because I wanted to clearly demonstrate how 2 subs inter-react with each other without the clutter of boundaries. The more stuff you add to a screen shot, the harder it is to read. Earlier in this thread, the point of subs aimed at each other was brought up and all kinds of opinions were shared. My point was, it makes little difference where you aim your subs and I illustrated it with the simplest screen shot that I could. And when using 2 subs, changing the polarity of one sub makes the "power allies" and the cancellations trade places no matter where you aim them. On the screenshots requested by Dookietwo, I have inserted walls only where requested in order to keep it simple. (I didnt insert 4 walls and make a concrete room.) of course, we can go there but I wanted to show a clean reaction of sub and wall(s). Dennis

 

 

Thanks;

Easy to see the spl loss in comparsion to image 2. If possible could you have image 4 ( screen shot 8 ) with the sub placed all the way to the wall to show the difference to everyone?

Great program.

 

Dookietwo

[twostone]

Here are the requested screenshots. Screenshot 5- 2 subs, 40' apart, opposite polarity, 63Hz, angled toward each other Screenshot 6- Single sub, 80Hz, no boundaries Screenshot 7- Single sub, 80Hz, 3.5' from painted concrete block wall Screenshot 8- Single sub, 80Hz, 3.5' from painted concrete block corner Screenshot 9- Single sub, 80Hz, 3.5' from painted concrete block corner, panned 45* Screenshots 1-5 intentionally have no boarders because I wanted to clearly demonstrate how 2 subs inter-react with each other without the clutter of boundaries. The more stuff you add to a screen shot, the harder it is to read. Earlier in this thread, the point of subs aimed at each other was brought up and all kinds of opinions were shared. My point was, it makes little difference where you aim your subs and I illustrated it with the simplest screen shot that I could. And when using 2 subs, changing the polarity of one sub makes the "power allies" and the cancellations trade places no matter where you aim them. On the screenshots requested by Dookietwo, I have inserted walls only where requested in order to keep it simple. (I didnt insert 4 walls and make a concrete room.) of course, we can go there but I wanted to show a clean reaction of sub and wall(s). Dennis

 

 

Be cool if I understood exactly what I'm looking at .

Looks like tye dye tee's to me because don't have a trained eye unlike my ears.

 

So where's one supposed to put a pair of subs?

[Mogwix]

So where's one supposed to put a pair of subs?

 

Preferably in the same room as the rest of the PA.

 

What he was getting at is that there's tradeoffs and compromise no matter where you position them. It's up to you to decide where everything goes when you get to the venue.

[Coaster]

 

So where's one supposed to put a pair of subs?

 

 

it depends. i prefer the floor or ground, spaced or clustered, against the wall or not.

[Dookietwo]

Be cool if I understood exactly what I'm looking at . Looks like tye dye tee's to me because don't have a trained eye unlike my ears. So where's one supposed to put a pair of subs?

 

 

Look on the right hand side. You will see a SPL (Sound Pressure Level) chart. The lightest color is the higher spl. The darker colors is the lower spl caused by the boundary.

An 80hz Wave Length is APROX 14.1 feet in length. ( 7 feet positive / 7 feet neg ) When a boundary is 1/4 wave length in distance away from a sub and is large enough in size it will cause boundary cancellation. 3.5 feet is 1/4 wave length. The 80 hz wave travels 3.5 feet. Hits the wall and comes back out of phase. It travels another 3.5 feet and reaches the sub. A total of 7 feet. Now this out of phase (or polarity) signal causes the next + wave to be lowered in output. This is why it is better to have a sub right up next to a wall or 7 feet away from it. Avoid having you sub 3.5 feet away from a wall or 1/4 wave length in regards to what freq. you want to avoid boundary cancellation from happing.

 

(EDIT) Divide 1128 by the freq you have in question.

 

To fine 80hz. 1128 divided by 80 = 14.1 Feet. Then divide 14.1 by 4 for a 3.5 foot 1/4 wave length.

 

This is a very simple explanation and there is allot more to it when you add the rest of the room to this but it does give you a basic idea as what to look out for or maybe why speaker placement is important in lower freq reproduction.

 

http://www.acousticsciences.com/articles/db1191.htm

 

Dookietwo

[twostone]

Look on the right hand side. You will see a SPL (Sound Pressure Level) chart. The lightest color is the higher spl. The darker colors is the lower spl caused by the boundary. An 80hz Wave Length is APROX 14.1 feet in length. ( 7 feet positive / 7 feet neg ) When a boundary is 1/4 wave length in distance away from a sub and is large enough in size it will cause boundary cancellation. 3.5 feet is 1/4 wave length. The 80 hz wave travels 3.5 feet. Hits the wall and comes back out of phase. It travels another 3.5 feet and reaches the sub. A total of 7 feet. Now this out of phase (or polarity) signal causes the next + wave to be lowered in output. This is why it is better to have a sub right up next to a wall or 7 feet away from it. Avoid having you sub 3.5 feet away from a wall or 1/4 wave length in regards to what freq. you want to avoid boundary cancellation from happing. Divide the freq in question by 1128 for total wave length. To fine 80hz. 1128 divided by 80 = 14.1 Feet. Then divide 14.1 by 4 for a 3.5 foot 1/4 wave length. This is a very simple explanation and there is allot more to it when you add the rest of the room to this but it does give you a basic idea as what to look out for or maybe why speaker placement is important in lower freq reproduction. http://www.acousticsciences.com/articles/db1191.htm Dookietwo

Thanks for info.

[dennis a]

If possible could you have image 4 ( screen shot 8 ) with the sub placed all the way to the wall to show the difference to everyone?

 

I think this is what you were asking for.

 

Screenshot 10 - Single sub, 80Hz, 0' from painted concrete block corner

[Dookietwo]

I think this is what you were asking for. Screenshot 10 - Single sub, 80Hz, 0' from painted concrete block corner

 

 

Yes! Thanks.

 

You can see the difference moving a sub just 3.5 feet away from the walls makes. It looks to be about 28dbs down in level about 15 feet out. With the sub placed 7 feet out it should give much better response.

 

Dookietwo

[IsildursBane]

The sum of equal opposites is 0. It's tempting to visualize the opposite phase sound as two pistons squishing the air in a tube, but that isn't how speakers in a room will perform.

 

 

Are we talking about signals in phase or out of phase? You said, "Identical sound waves directed at each other in the same phase."

 

If you feed the same signal into two identical speakers (all wiring polarity/etc identical) and point those speakers at each other, the sound pressure will be doubled at the point halfway between the two speakers, will it not?

 

And if you flip the polarity of one of the speakers, the signal will cancel at the halfway point.

 

-Dan.

[jasps]

Polarity switch is on the back of both subs

I have not read the whole thread...

I would suggest you:
1. download "Bink's Test Tone CD,"
2. put it into your CD player and sound system and put the pink noise track on repeat.
3. Turn on only the Left side sub and top.
4. Change the polarity on the sub
5. Evaluate whether you have more bass. If so, leave it in that position and repeat steps 1-4 for the right side and turn the left side off. If not, go back to the original position.

After that, you can go about making proper mixing choices such as inverting polarity on the kick channel itself, etc.

[agedhorse]

As soon as you place the subs in a real room, all the ideal predictions go to hell. In theory and in practice have two different solutions that may or may not agree.

[jasps]

I have not read the whole thread... I would suggest you: 1. download "Bink's Test Tone CD," 2. put it into your CD player and sound system and put the pink noise track on repeat. 3. Turn on only the Left side sub and top. 4. Change the polarity on the sub 5. Evaluate whether you have more bass. If so, leave it in that position and repeat steps 1-4 for the right side and turn the left side off. If not, go back to the original position. After that, you can go about making proper mixing choices such as inverting polarity on the kick channel itself, etc.

 

I also wanted to point out that your signal cables should be checked to be of like polarity. If you have a miswired cable, fix it!

[Coaster]

there is one location i work at that seems to defy all my experiences, everything seems opposite there.

this is a low roof, no walls, cement floor. i've tried setting up PA everyway possible at one time or another, and in this location for whatever reason subs behave in a bizzare manner. if i center cluster the subs, i may as well not brought any subs at all - no bass. i have to push the subs all the way to the sides past where your eye would tell you to put them to get any type of low end that doesnt have a crazy cancellation pattern under the roof. when they are all the way to the sides (35' apart) i get a fairly uniform coverage with only a small area of cancelation near the center at the rear. centered the subs cancle nearly everywhere.

you kindof have to guess where to put things based on experience and then experiment over time if things dont sound right or have odd pockets around the room.

i did one room a few weeks ago (normal room) that had a reverse power alley; no bass in the center of the room but the sides were pounding to beat hell. the next night with the same system in a different room i had a typical power alley.

[dennis a]

As soon as you place the subs in a real room, all the ideal predictions go to hell. In theory and in practice have two different solutions that may or may not agree.

 

I feel that understanding the concepts of the "ideal predictions" is useful info to have prior to deploying speakers in the "room from hell". Also, MAPP Online is capable of predicting the "room from hell".....I just didn't go there.

 

Dennis

[Coaster]

I feel that understanding the concepts of the "ideal predictions" is useful info to have prior to deploying speakers in the "room from hell". Also, MAPP Online is capable of predicting the "room from hell".....I just didn't go there. Dennis

 

 

nothing wrong with having a good old academic argument, but experience dictates that reality has no place in academia. the two are different.

[Craig Vecchione]

I feel that understanding the concepts of the "ideal predictions" is useful info to have prior to deploying speakers in the "room from hell". Also, MAPP Online is capable of predicting the "room from hell".....I just didn't go there. Dennis

 

Well, it gives you something to say when {censored} goes south. "Oh, yeah, it must be comb-filtering due to a phase reversal in the framus".

[bnelly428]

A single sub has a "dispersion angle" of 360*....angling it in a bit will do very little. Dennis

 

 

should have clarified, i was referring to the mains being "crossed" and their angle dispersion or whathaveyou, not the subs. opps

[Mogwix]

there is one location i work at that seems to defy all my experiences, everything seems opposite there.

 

In my high school physics class we did the typical experiment to find acceleration due to gravity. Me and my partner did the lab (time how long it takes an object to fall a measured distance) and over five trials, ended up with a number around 7.5m/s

[Coaster]

In my high school physics class we did the typical experiment to find acceleration due to gravity. Me and my partner did the lab (time how long it takes an object to fall a measured distance) and over five trials, ended up with a number around 7.5m/s

[Craig Vecchione]

In my high school physics class we did the typical experiment to find acceleration due to gravity. Me and my partner did the lab (time how long it takes an object to fall a measured distance) and over five trials, ended up with a number around 7.5m/s

[Coaster]

What was the object? Ferrous by any chance?

 

 

maybe it was the objects' day off(?)

[6Imzadi]

Sounds like some kind of flubber.

[Craig Vecchione]

 

maybe it was the objects' day off(?)

 

 

 

 

 

Bueller?

 

 

 

 

 

Bueller?

[davidss1]

i thought most schools have a "go slow in the hallway" policy

[6Imzadi]

 

... we never did figure out the reason for our crazy numbers in the lab room. It makes no sense.

 

 

....'cause you're in the great white north?