Room Acoustics treatment for electrostatics

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Peter_Klim

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I'm reading about room acoustics and treatment and it seems that it is desirable to have the reflections behind the speakers minimized. I thought one of the "magical" aspects of ML speakers is that they fire sound towards that back wall? Or is that an undesirable aspect of ML?

Should that wall be treated when using ML speakers?

Thanks in advance guys!
 

JonFo

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Hi Peter, the ‘magic’ of dipole is actually more of a side-effect of not wanting to have uneven dampening of the diaphragm with some form of rear enclosure.

So the choice of dipole is somewhat of a trade-off. To gain responsiveness from low-dampening of the ESL vs lose out to comb filtering and rear-wave cancelations at lower frequencies.

The challenge that a dipole presents in terms of room placement and listener positioning is a lot larger than for monopoles, as the delayed and out of phase rear wave produces a time-delayed, phase shifted signal that has to be ‘blended’ as it were into the actual information arriving from the front of the panel.

This ‘blending’ is never smooth, which is why there is comb-filtering clearly visible when looking at a frequency response plot.

The dipole effect is literally the same as taking two monopole speakers, spacing one of them away from the other by 6 or more feet and feeding them the same signal, except out of phase. Generally, not a recommended 2ch ‘purist’ type of arrangement ;)

Therefore, we come to the realization that managing that rear energy is something we should pay attention to.

Not that everyone *should* dampen the rear-wave, it’s just you need to think about how the ricochet and delay of that out-of-phase signal is going to affect the soundstage in *your* room.
 
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Brad225

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Try the Google search at the bottom for the ML Owners site. There should be many threads that appear.

As for dampening, absorbing and diffusing, yes to all if that is what sounds good in your room with your equipment
 

JonFo

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Symmetrical air resistance is indeed an important benefit, and a big contributor to the amazing performance of ESL’s. But the price is it forces a dipole config.

At lower frequencies, as I mentioned, the phase cancellation becomes a problem. This why ML’s rarely have the mid-bass ‘slam’ of a dynamic monopole speaker.

And at the lowest frequencies, it’s almost required to have a ‘box’ to ensure no rear wave cancellation occurs. But since I am also a staunch believer in the benefits of symmetrical air resistance, my sub is an infinite baffle alignment. The ‘box’ is the same size as the room (in this case: 3,000 cubic feet). I tell you, it makes a great match for the smoothness and low distortion of the ESL.
 
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radicalsteve

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I have found that rear wall absorption definitely improves soundstage and focus, but overdoing it can reduce the magic sparkle and lively dynamic energy. Side wall absorption panels provide improved clarity in my room. Although I use a combination of batting and foam, I suspect deflection panels are the best as a lot of the absorption is there to tame low end frequency reflections impacting on clean bass at the listener position.
I also use panels on the ceiling as well.

Hemholtz resonators can also tame specific room frequency issues caused by room dimensions and surfaces.

steve
 

kach22i

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Like everyone said lots of threads on the topic. Making the most out of the hobby - take it as a chance to learn and to experiment.

Less is more sometimes, often will have to remove half of what you install.

EDIT: corrected typos in bold.
 
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Brad225

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Like everyone said lots of thread on the topic. Making the most out of the hobby - take it as a chance to lean and to experiment.

Less is more sometimes, often will have to remove half of what you install.
I removed about about 8 of the panels beside and behind my CLS's. I had taken away much of the depth and ability to image accurately with the amount of absorbing material I had.
 

Len44

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Surely...there is a (near)-optimal material / unit that provides neither too much absorbing material or not quite enough. That allows for some measure of absorption yet does not completely kill the "liveliness" aspect of these terrific speakers...

In my case, I liked my Summits with only bare walls behind them, then reversed the room and ended with heavy curtains behind them (about 6 ft from the panel). This sounds pretty darn good also, but of course not as lively.

I am thinking perhaps a free-standing panel holding some "ideal" material that would be placed about 4-5 ft behind each speaker. I imagine that this will need to be something I custom build...:rolleyes:

Any thoughts?
 

kach22i

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Surely...there is a (near)-optimal material / unit that provides neither too much absorbing material or not quite enough. That allows for some measure of absorption yet does not completely kill the "liveliness" aspect of these terrific speakers...
One day I would like to build a wood block skyline like diffuser, or purchase a work of art based on wood blocks (or panels) of some sort. Something like pictured below, but covering the full wall top to bottom and right to left. A sealed air cavity behind the wood panel art could be tuned to problematic frequencies with insulation and or sand mass.

http://www.artlex.com/ArtLex/Fm.html


http://www.jazzgreen.com/


http://www.hotfrog.com/Companies/Ka...Wall-Art-Buddha-Pacceka-Wood-Wall-Panel-81608



Some people have suggested that a series of wall shelves (or cubes) of stacked/stored vinyl records behind the speakers would do much of the same.
 
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Gordon Gray

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George,

I'm confident that the first picture may cause some heated discussions between the audiophile and his or her partner.

GG
 

JonFo

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Len, there are several commercial products besides tube traps, including this one designed specifically for electrostats:

The SoundLab Sallie


The problem with this one is that it only operates from 250Hz up.

As much of my research (and general acoustical science) shows, the low-frequency phase cancellation caused by the rear wave is something that should be absorbed with treatments designed for those frequencies.
This allows for better mid-bass performance in the system.
 

C.A.P

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I concur with Gordon on that !George that first thing looks like a spray painted Sanford and Son design !
 

JMAUSGP

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Kind of looks like the back of the truck from the Beverly Hillbillies, without the Grandma sitting in the chair on top.....oh wait that's the chair in the lower left hand corner, in a box......maybe Grandma is in there somewhere too.:D
 

kach22i

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The "junkyard art" is a rough idea, gives a good picture of depth for that front wall. Something of natural wood carved with skill and with textured reliefs would be much prettier to look at.

The "something simple" behind the speakers might just be "a typical wall". A typical wall has a sheathing of gypsum board (drywall) which will flex a little with bass frequencies and has the depth of wood framing studs to form an air cavity.

The typical wall can be insulated which should attenuate the energy absorption.

The typical wall can be covered or layered with a second layer of drywall, or drywall over homasote.

Better yet the typical wall can be furred out with resilient metal channels and more layers of suspended drywall added.

The finished face of the wall behind the speakers may also be finish grade wood veneer plywood in lieu of drywall, but sealing the joints may become a design issue. I favor the wood solution, and would use a grid design using reveal channels (caulking them) or surface applied wood trim (caulking them) in a pattern of some sort worked out ahead of time.

Look at photos of the insides of churches and auditoriums to get a clearer idea. Or you could just hire me to sketch something up.;)

EDIT: Just found this article which does a good job of explaining what I touched on.

http://www.audioholics.com/education/acoustics-principles/bass-traps-not-just-for-fisherman
At very low frequencies sound waves tend to pass right through most walls, which is why you hear mainly thumping in an adjacent room. Standard sheet rock walls also tend to absorb very low frequencies as they vibrate in sympathy. But the higher bass frequencies are reflected instead of being passed and absorbed, and this is the cause of both modal ringing and a skewed low frequency response in the mid to high bass range.
 
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MOON

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Hi George,

I also plan on building skyline diffusers for behind my Odyssey's. Here are the plans http://www.pmerecords.com/Diffusor.cfm and also here showing the step by step pictures of building the skyline diffusers http://www.canuckaudiomart.com/forum/viewtopic.php?f=21&t=8456&hilit=skyline I prefer diffussion to absorbtion and like some ambience.Panels will be 2x4 ft. I was thinking of sanding each peice of wood and having a natural clear finish over it which should look nice.I plan on a small frame around the diffuser, probably 1x2 to make it look a bit more finished.
Cheers, Greg
 
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kach22i

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I was thinking of sanding each peice of wood and having a natural clear finish over it
Some of the painted home-made examples do look a bit rough. I imagine that the natural grain of wood would aid in hiding imperfections. Also I know that if you paint acoustic ceiling tile they lose much of their absorption properties, gotta wonder if painting wood does much of the same and if so is that desired? Would many coats of clear finish act like paint in sealing the open wood cells?

I like the photo of the project sitting on the floor looking like a city.

I bet that if one were to spend the money on acrylic solid rectangular tubes (clear or colored) and back light it (any color light or strobe), it would have a very Sci-Fi look.

Great links, I've bookmarked them - thanks Moon.
 
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Jimna

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isnt the basis of a diffusor to reflect not absorb? thats my understanding, so the painted/not paint makes no difference right?

i do know that most of the difussors for sale online are plastic which has no absorption at all.
 

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