Wall behind a Planar speaker

bonzo75 · Jan 7, 2015

My front wall (wall behind the planars) is currently flat and symmetrical, causing no issues.

My guess is that those who have windows behind the panel, lose bass. Is this correct? Does pulling a curtain help?

What if the wall behind is slanting and asymmetrical (one panel is 4 ft from the wall and the other 5), does that work?

What if one panel has a door behind, opening into another space, while the other has a wall behind?

Asking as contemplating a new place next year

DonH50 · Jan 7, 2015

An untreated wall behind a dipole speaker will always introduce signal cancellation and reinforcement (comb filtering) caused by the reflections.

Windows usually flex more than walls, and thus reflect less, which can reduce bass. I suspect the loss is in the mud for most of us.

Flat or slanted, whatever, those pesky rear waves still reflect around and lead to cancellations and reinforcement. You will change the frequency response depending on the wall behind, natch.

The dipole firing into an opening will essentially have no reflections coming back. Bass will usually be less and frequency response flatter (an open is essentially the same as treating the wall behind with absorbers). Bass response does depend upon total volume and thus is affected by the opening. Bottom line is the speakers will sound different if what behind them is different; keep the door closed.

If you can treat the wall behind the dipoles these differences probably don't matter. My room is heavily treated, including a panel hung on the door (which is closed whilst listening).

FWIWFM - Don

bonzo75 · Jan 7, 2015

Yes, I am one of those who preferred my front wall untreated so the rear wave would reflect causing a large sound. I also liked the bass reinforcement. So it is important to keep the walls behind the same, I guess, unless it is glass, where you can lose bass.

DonH50 · Jan 7, 2015

Yes, if you like a very "live" presentation then for the speakers to sound the same the area behind should be identical. Since planer speakers tend to act like dipoles for mid-bass'ish (depending upon panel size) frequencies and above there is little radiation directly to the sides or top and bottom (vertical).

Check one of the sites that provides absorption data for various materials (I do not have any of my references handy). I suspect the difference between normal sheetrock and glass is not great.

BobM · Jan 8, 2015

I built these diffusers after I saw something very similar made by Shakti, I think, at a show. Just simple varying sized dowels in a sort of random pattern. They made a nice improvement in the soundstage, especially the depth of the presentation.

bonzo75 · Jan 8, 2015

Heard a classy Duetta Sigs over the weekend, he had built with an all aluminium frame and extrenal crossovers, sounded really good, as Iheard his previous pair and wan't impressed. Rest set up remaining the same, they just player more easily as if they had higher sensitivity due to the energy save by the Aluminium frame.

Btw, your wall behind the panels is symmetrical too, so should not be an issue.

As for Shakti, they do a different thing? They lock in soundstage in a particular space, depending on what angle you turn them in at

BobM · Jan 8, 2015

The Shakti's I was talking about were not the usual black and wood colored sticks on a pillar thing everyone knows about. These looked very much like what I built, only taller.

Another thing you may want to consider are Helmholtz Resonators, popularized by Argent Room Lens some years ago. There are several DIY articles on how to make these yourself on the web.

bonzo75 · Jan 8, 2015

Hi Bob, my query is regarding how windows or an asymmetrical wall (slanted, or with an opening behind one panel but not the other) behind the panels affect sound - if the sound is adversely affected.

Can a Helmholtz help there?

BobM · Jan 8, 2015

Thanks for the clarity, I misunderstood. I have an asymmetrical setup as well, with a wall on my right but no wall on my left. In the past, with cone speakers, I found placing a GIK panel at the first reflection point of each helped balance the sound. The one on the left was essentially free standing, but did enough to "mimic" a wall there to help center the image.

However, with panels, sidewall reflections are not really much of an issue. Frontwall reflections are definitely more important, and having an opening behind one speaker and not the other will throw some things off, I would presume. You may want to try something more solid than I devised, or more solid than a Helmholtz, to mimic a wall where there isn't one. Though placing a diffuser like mine on the wall behind the speaker that has a walll will help too.

Of course, moving panels farther into the room is always a good idea if you have the space.

bonzo75 · Jan 8, 2015

In which case, how much further into the room should correct the balance. In central London, I doubt I will get them more than 5 feet from the wall.

BobM · Jan 8, 2015

It's really a balancing act. You want them far enough from your listening position to have the soundstage "gel", so it is not a nearfield giant headphone presentation. Plus you want some room behind your listening seat, and maybe put an absorptive panel there. And you also want them 1/4-1/3 of the way into the room.

So, doing the math,

5 ft from the front wall, 9-10 feet to your seat, 3 ft behind you means a room length of @17-18 feet. Can you swing that? I would still prefer to have more room between the speaker and the front wall than space behind me if you have to make a tradeoff.

JonFo · Jan 8, 2015

bonzo75 said:
Hi Bob, my query is regarding how windows or an asymmetrical wall (slanted, or with an opening behind one panel but not the other) behind the panels affect sound - if the sound is adversely affected.

Can a Helmholtz help there?

Hi Bonzo, my views on rear wall treatment will be well known to you from all my posts on the MartinLogan owners forum, so I won't repeat them here other than to reiterate that absorption is your friend, and everything DonH50 mentioned above is correct.

To specifically answer your query, yes, an asymmetric rear wall disposition as you describe will severely affect the soundstage. Here's why:

1- The rear wave reflection paths will have different delay times, skewing the imaging in favor of the side with the shortest path (usually)
2- the varying delay will also shift the FR between sides due to different comb-filtering impacts on the frequency domain
3- variations in absorption (open door, window, etc.) also affects the mid-bass cancellation/reinforcement between sides, further affecting the FR balance between sides.

In essence, your soundstage is skewed both temporal domains and frequency domains. Not good.

But judicious use of absorption can help rebalance, or at least mitigate, some of these challenges.

Audioseduction · Jan 8, 2015

I agree with Jonathan 100% I use both mid/hi freq. and bass panels on my front wall as I have a huge window. I also have curtains in front of panels. This setup provides me crystal clear imaging and depth you just want to dive into. Also excellent controlled bass response. The holographic extensions are just amazing. The artwork in front is transparent to the audio mostly. It's a print on thin like cotton material. I also have bass traps to the left and right of the stage.

MrAcoustat · Jan 9, 2015

bonzo75 said:
Yes, I am one of those who preferred my front wall untreated so the rear wave would reflect causing a large sound. I also liked the bass reinforcement. So it is important to keep the walls behind the same, I guess, unless it is glass, where you can lose bass.

Same for me BUT whe must do with what whe have, my room is not perfect BUT that is good for my wife if it was she would have a very hard time getting me out of the house.

Jonathan90 · Jan 9, 2015

Years of trial and errors eventually led to present set-up - at day’s end it’s really all about the treated space.

BobM · Jan 9, 2015

I bet the goose helps tremendously. Except for the "honking"!

FrantzM · Jan 9, 2015

Jonathan90 said:
Years of trial and errors eventually led to present set-up - at day’s end it’s really all about the treated space.

Very nice space!!

Speakers look like Magnepan?

Whatmore · Jan 9, 2015

MrAcoustat said:
Same for me BUT whe must do with what whe have, my room is not perfect BUT that is good for my wife if it was she would have a very hard time getting me out of the house.

View attachment 18438

Where's the shot with you in it? We haven't seen that for a while

MrAcoustat · Jan 10, 2015

Whatmore said:
Where's the shot with you in it? We haven't seen that for a while

Sorry but the photo was to show the WALL behind the planar speaker NOT of me.

Big Dog RJ · Jan 10, 2015

bonzo75 said:
My front wall (wall behind the planars) is currently flat and symmetrical, causing no issues.

My guess is that those who have windows behind the panel, lose bass. Is this correct? Does pulling a curtain help?

What if the wall behind is slanting and asymmetrical (one panel is 4 ft from the wall and the other 5), does that work?

What if one panel has a door behind, opening into another space, while the other has a wall behind?

Asking as contemplating a new place next year

Hey Bonzo,

Referring to your room and wall query mate, I can only suggest one thing, experiment! There really is no one solution for all.
Back in my home country where I had the maggies and Apogees, there was no back wall! The back wall were all French windows that would open up into a large lawn. This was also a pain in the butt because whenever it rained, a certain amount of moisture would creep in and affect the tubes as well as the Panels. I had to then seal all apparent openings and virtually keep the windows completely shut, also adding heavy curtains to keep off the moisture along with heavy carpeting on which the entire system was located. This helped with the closed environment but didn't improve the sound at all. It lacked depth and soundstage, nothing compared to my present Quads.

I then had to re-locate the entire system and panels to where there were more solid walls. This dramatically improved the overall sound, especially with the Apogee's. Fantastic depth and centre fill of soundstage, great dynamic presence overall. However, one HUGE problem, the main door to the house opened right between the panels! And to top that, whenever the door was opened to let someone in, it nearly knocked off the left panel!

Solution to this problem; migrated to Australia! Now everything is sweet & dandy...
Cheers, RJ

Wall behind a Planar speaker

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