# Set up 4 surrounds?



## jmschnur (May 31, 2011)

I have 4 surrounds . 2 are dipole and are the middle surrounds off the sides of the mlp couch and are set as out of phase with mains as directed by NHT. My question is how the rear surrounds that are behind the couch should be set up. In phase with the main speakers or the middle surrounds?


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## Mark Techer (Jan 17, 2008)

If the speakers are selectable for Dipole use, then they should be marked "Left" and "Right" so that the in-phase lobe fires at the screen. The side speakers simply go as the assignment suggests.

The trick is the back surrounds have to be placed on the opposite side so that you avoid phase errors between side and back surrounds. If you simply place the dipoles according to their L and R assignment, you end up with the + of the LBS and - of the LS both firing into the corner. This prevents sounds from forming phantoms between the speakers (the half tone test tone on JPK DVE will be a good test) which mean your sound will snap from speaker to speaker instead of letting you hear a smooth pan.


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## jmschnur (May 31, 2011)

Mark Techer said:


> If the speakers are selectable for Dipole use, then they should be marked "Left" and "Right" so that the in-phase lobe fires at the screen. The side speakers simply go as the assignment suggests.
> 
> The trick is the back surrounds have to be placed on the opposite side so that you avoid phase errors between side and back surrounds. If you simply place the dipoles according to their L and R assignment, you end up with the + of the LBS and - of the LS both firing into the corner. This prevents sounds from forming phantoms between the speakers (the half tone test tone on JPK DVE will be a good test) which mean your sound will snap from speaker to speaker instead of letting you hear a smooth pan.


Not clear on how the rear monopoles should be phased location is as you have drawn. Are you suggesting the monopole rears be out of phase with the fronts so they will match the rear firing dipoles?


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## Mark Techer (Jan 17, 2008)

jmschnur said:


> Not clear on how the rear monopoles should be phased location is as you have drawn.
> S


All speakers should be wired in-phase.
If the Back Surrounds are monopoles (direct radiators), then you mount them on the back wall so they fire right at the screen. 

Is your system THX by chance? If not, does not matter. THX (ULTRA 2) use mono poles placed together on the back wall. You can spread them apart for better separation of the back surrounds for 7.1 program if you want.


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## jmschnur (May 31, 2011)

It could be thx . I have the rear speakers firing at the ceiling since they are close to the rear couch from the floor per your advice.


I am using PLII x right now. 

Edit:

Yes U2 THX works well. I set the rears to be in phase with the rear firing dipoles.


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## Mark Techer (Jan 17, 2008)

I am not a fan of the direct radiator for surrounds and think that firing them up so you hear reflected sound would be better than having them blast direct sound at your seating position.

If you do this, you might want to experiment with firing them up from the floor as well. 

I did this many years ago (1992) with a set of very small direct radiators as side surrounds (there was no back surrounds back then) and it provided a very enveloping sound field. This will be speaker and room dependent, hence why I said experiment.


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## jmschnur (May 31, 2011)

Mark Techer said:


> I am not a fan of the direct radiator for surrounds and think that firing them up so you hear reflected sound would be better than having them blast direct sound at your seating position.
> 
> If you do this, you might want to experiment with firing them up from the floor as well.
> 
> I did this many years ago (1992) with a set of very small direct radiators as side surrounds (there was no back surrounds back then) and it provided a very enveloping sound field. This will be speaker and room dependent, hence why I said experiment.


This works well.thanks for the help. I have the direct radiators set up as you show below but on the floor point at the ceiling about 6 feet apart. With thx U2 it sounds very nice indeed.


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## Mark Techer (Jan 17, 2008)

I just modded the diagram and made two other to show the different ways to run a 4 speaker surround system using dipoles and bipoles. 

Hopefully this will answer any questions from others reading as well. 

*Top image*: 4 Bipoles (this is what I currently use myself). There are no phase errors between speakers. Even though you get no direct sound, the sound you hear is a "sum" and the speakers are still quite directional.
*Middle Image*: 4 Dipoles (I will go back to this at some point). As the diagram shows, you need to physically swap the L and R speakers over to correct the phase error. This was never explained when EX systems were introduced back in 2000 and partly why I think THX took on the pair of Direct Radiators for their system. It was much easier to explain. In any case, DO NOT reverse the polarity of the speaker. It is an acoustic error that needs correcting not an electrical one. 
*Bottom Image*: The THX Ultra 2 speaker layout using a pair of Dipoles at the sides and a pair of Direct Radiators at the back of the room. I've never set one of these up like this, so will not comment.


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