[PLMONROE]

I hope that this isn't a  stupid question but I am assuming that optimum room treatment for Monopole, Open Baffle, and Dipole speakers may differ considerably. If so, can anyone tell me in what ways please?

[JohninCR]

Corner bass traps would be ineffective with open alignments, because the bass doesn't accumulate in the corners like with boxed speakers.  Although open alignments stimulate room resonances to a lesser degree, the effect of boundaries can become much more noticeable.  eg  If you have a solid wall directly behind your listening position, the effect on bass can be dramatic enough that a panel trap may be required.

The greater directionality of OB's (dipole or not) will definitely impact the placement of your room's acoustic treatments.  The effect of room treatments in the front of your room is even greater than with boxes, because with open alignments the room (especially the front portion) is an integral part of your speaker.  How you reflect, diffuse, and absorb the rear wave is part of the tuning process.

[Ethan Winer]

I hope that this isn't a  stupid question

There's no such thing as a stupid question. Well, okay, some questions are stupid. But yours is not.

> I am assuming that optimum room treatment for Monopole, Open Baffle, and Dipole speakers may differ considerably. If so, can anyone tell me in what ways please? <

As far as I'm concerned, the only real difference is that dipole speakers require more absorption on the front wall. The fact that sound comes from the rear of those speakers as well as the front is a side effect, not intentional in their design.

--Ethan

[bpape]

Sorry John, but bass does in fact still build up in corners.  A dipole arrangement simple causes a null to the sides of the speakers so they don't interact in terms of SBIR as much in relation to the side walls.  Take a measurement in the corners with ANY speaker and there will be buildup of level in the bottom end.

Bryan

[Housteau]

While bass is bass, the higher frequencies for a dipole often do require different thinking.  I have owned Acoustats, Martin Logans and Infinities.  The manuals suggested in their set-up more of a live diffusive wall behind the speakers as opposed to one that is more absorptive.

Correct diffusion allows the full ambiance to remain, while being able to tune in a sharper center image.  With many dipoles that is where the balancing act revolves, between air and issues of focus.

I have found tall artificial plants to work well as controls and they are easy to move around behind the speakers.  The center of the wall between the speakers is kept highly absorptive as are other reflection points.  I was having focus issues that I had blamed solely on my choice of speakers, until I realized it was my cathedral ceiling causing strange beaming effects.  Once treated properly the problem with focus disappeared.

[samplesj]

In my room with diffusion instead of absorbtion behind I get a very well defined image from my Maggies, but I've still kept the ambience.

In this case I strongly disagree with Ethan.  Their rear radiation is a not side effect and is part of what makes them special.

Here is a site I thought had a lot of useful dipole info (http://homepage.mac.com/tzagar/)

[ctviggen]

I have to disagree with Ethan, too.  Sorry, Ethan!    I think that dipoles serve important functions, and I think you'd want more diffusion along the rear wave.  Granted, that would have to be for the mids/upper range of frequencies, but I still think you'd want diffusion and not absorption. 

[Ethan Winer]

I have to disagree with Ethan, too.  Sorry, Ethan! 

Hey, no need to apologize! If that's what you prefer, who am I to say otherwise?

I will say this in my defense.

Speakers that radiate equally out the rear increase the problem known as SBIR - Speaker Boundary Interference Response - a series of peaks and deep nulls. In conventional speakers SBIR is restricted to the bass range, because those speakers radiate omnidirectionally below the midrange only. But with a planar speaker the rear radiation occurs at all frequencies, and this creates "early" reflections that (IMO) cloud imaging in addition to the peaks and nulls. This was one of my big objections to Bose 901s too, because the full range was sent both forward and back. Yes, it does make the sound more spacious, but it always sounded a little unnatural to me.

Then again, if this means I get to sell more diffusors I'm all for it!

Seriously, I'm friends with a fellow who imports and sells a line of very nice planar speakers, and he always suggests absorption behind them to avoid the early reflections off the front wall. I'd be interested to hear what the manufacturers of your speakers have to say about this. Have any of you ever asked?

--Ethan

[DTB300]

While bass is bass, the higher frequencies for a dipole often do require different thinking.  I have owned Acoustats, Martin Logans and Infinities.  The manuals suggested in their set-up more of a live diffusive wall behind the speakers as opposed to one that is more absorptive.

In my experience with stats, it really depends on the room, equipment, and the listener. 

Too much Diffusion can bring the image too far forward.  On the other hand with absorption, you can go the complete opposite way, putting the image too far back, and killing the high end.  Some applications can benefit from some or both.  Each need to try them and see.  And below I see you mention artifical trees, which is a nice cheap way to see what diffusion can do.  For absoprtion, heavy blankets, pillows, etc can also give you an idea of what absorption can do for you.  Then you can go out and purchase the real deal to properly treat your room.

I have found tall artificial plants to work well as controls and they are easy to move around behind the speakers.  The center of the wall between the speakers is kept highly absorptive as are other reflection points.  I was having focus issues that I had blamed solely on my choice of speakers, until I realized it was my cathedral ceiling causing strange beaming effects.  Once treated properly the problem with focus disappeared.

See, as you and other have discovered, the combination of diffusion and absorption helped out!!!

Tall artifical Fiscus is a very common one that I have seen.

In my room, which is in a partial basement - a "Bunker" if you will, strategically place absorption behind my stats and at first reflection points worked out the best for my sound.  Of course some of the best treatments was the four corners of the room with bass traps going from floor to ceiling.

Dan

[8thnerve]

I hope that this isn't a  stupid question but I am assuming that optimum room treatment for Monopole, Open Baffle, and Dipole speakers may differ considerably. If so, can anyone tell me in what ways please?

I've used both Maggies and Martin Logans.  They both respond dramatically to reduction of the corner return wave.  Absorption almost always takes a lot of the life and spaciousness out of these speakers, which is one of their best attributes!  Diffusion, well, I feel the same about diffusion with all speakers.  To me it's like pearlescent paint.  It's shiny and it looks nice, but it's not the true color.  Fix the problems where they begin, and neither absorption or diffusion are necessary.

[ctviggen]

Here's what Linkwitz says about the Orions:

"The wall behind the speakers should be diffusive. The rear radiation from a dipole must not be absorbed or it is no longer a dipole. Similarly, the side walls should not absorb sound at the reflection points but diffuse it. A dipole can even be towed in so that the listener sees the radiation null axis in a wall reflection mirror."

(Italics added) http://www.linkwitzlab.com/rooms.htm

So, he likes diffusion.  Not sure I'd necessarily agree with him about the first reflection points, but I also don't have dipoles. 

[Housteau]

It is a balance of things, no doubt.  The corners do need to be taken care of and in my case, so did the peak of my cathedral ceiling.

   

I have a stack of 11 or 12" diameter tube traps that I have had in place, and in conjunction with the artificial plants.  The sound does change and it was also dependant on which speaker system was set-up at the time, the Pure Infinity, or the Infinity / ML hybrid.  I think each speaker system, room  and listener combination will be different, and dictate that proper balance.   

[rajacat]

I have Omega Hemp Bipoles http://www.omegaloudspeakers.com/super3bipole.html. They can be run as bipoles or dipoles. Presently, I'm using the dipole configuration. These unique speakers employ two opposing drivers in separate ported chambers. Would the speakers respond best to diffusion or absorption, a mixture of both? I guess the placement of the different accoustical treatments would be most important. Any suggestions to get me started. I like to DIY.

Raj 

[PLMONROE]

This is a GREAT forum! Thanks for all your insight. Here is what prompted my original question. I have just received delivery of the first of Brian Cheny's RM-V60 speakers (see VMPS forum here on Audio Circle) . This insofar as I know is a truly unique design. As best as I can briefly describe, frequencies above 260Hz are produced by ribbon planers placed in the apex of a V shaped cabinet. The back of the cabinet is open but has a thick foam damper which can be inserted fully, partially, or completely removed. Thus one is able to persue many "tuning" options. So  is it a dipole, open baffle, horn, hybrid combination  or what?? I really don't care to debate how they should be categorized -- they simply sound WONFERFUL!  What I am trying to ascertain is the optimum acoustic treatment to insure I am getting the best from them.

[ctviggen]

I think they're a dipole.  Dipoles fire both ways (front and back) but are out of phase.  Bipoles fire both ways but are in phase.  I'm also thinking of transitioning to dipoles (I'd love to have the RM60s), and what I was going to do was order diffussive elements as I have Realtraps absorptive elements.  I was going to try the diffussive elements behind the speakers and compare with absorptive.  I'd perform the same test with first reflection points.  So, you have the time, energy, and cash, this is the best way to go. 

[srlaudio]

Hey there!
    We have been experimenting with our diffusors today in a professional studio.  The problem was a bass null at the engineer position and we cured this as well as enhanced the mids by holding a 2'X8' diffusor on the the ceiling over the engineers head.  He ordered one to be flushed into his ceiling grid.  This flies in the face of a lot of the "talk" surrounding diffusor implementation, but it is really fun to experiment with diffusor placement.  A lot of the "accepted standards" become stale rapidly!

Allen Rumbaugh

[PLMONROE]

I will apologize in advance if this offends any advocates of Argent Room Lenses. I have had two sets for some time and could never figure out at all what they were good for (except perhaps for tipping over at the slightest touch and bashing things up). This afternoon just for kicks, I put two behind each speaker and darn if the sound didn't improve a bit. I haven't the slightest clue why, but I trust my ears enough to know that there clearly was a slight improvement in imaging.