Odd dipole surround positioning

[Vaughan Odendaa]

Hi there,

I recently encountered an installation where a pair of dipole rear speakers were mounted 1.5 meters ahead of the listening position. Yes, you heard that right, ahead.

The speaker package used are Polk RTI speakers with corresponding dipoles for rears. What are your thoughts concerning the dipole arrangement ? Correct me if I'm wrong but for dipole radiation to be realized, you must be sitting in the acoustic null center of those dipoles ?

If you sit in the null that is where diffusion is greatest. But then does that mean that dipoles can only work on the side walls ? Because if one installs them on the rear wall your ears are going to hear direct sound (you aren't exactly sitting in the null area anymore) and are in the line of sight of the driver ?

Thoughts would be appreciated.

--Regards,

 

[Vaughan Odendaa]

My way of thinking is that if one does not sit exactly within the null area that the diffusive sound field collapses entirely. The tolerance for error is extremely high on positioning and if you don't get it precisely right then it's a real hit and miss affair.

Unless I'm missing something.

--Regards,

 

[MDS]

Ideally you do want your ears in line with the null of the speaker. If the null is slightly ahead of your ears then you'd hear the sound from the left-facing driver of the left speaker or the right-facing driver of the right speaker first. But since the two drivers are out of phase, it might not make a huge difference - have to listen and see.

If dipoles are mounted on the rear wall you are still in the null as the drivers fire left and right behind you as opposed to forward and backwards if they were mounted on the side walls.

 

[Vaughan Odendaa]

Yes, exactly. You don't want to hear direct sound from the dipole otherwise that would defeat the purpose of a dipole. In the installation I mentioned, the client will not appreciate a diffusive sound field because that diffusion cannot exist without him being in the null of that dipole.

I actually cringed when I saw that the dipole surrounds where in front of his ears. A complete waste of money IMO.

--Regards,

 

[MDS]

What if the room layout prohibited ideal placement of the dipole surrounds and slightly ahead of the listener was the best they could do?

I think dipoles in that position would still be better than monopoles as you'd definitely notice the 'surround' info coming from slightly in front of you with monopoles.