[samplesj]

What is everyone's take on ceiling/floor first reflection points for line sources?  Have other line source/array owners need to treat their ceilings and floors as much as other walls?

From what I've read (especially Dr Griffin's white paper) a line source/array shouldn't really reflect much from the floor and ceiling.

However, I've had a vendor's recommend ceiling treatment for my maggies.

Did they just not listen when I said that my speakers are line sources (full height ribbon), trying to recommend more product for more $, or are Dr Griffin's findings flawed?

What is even more interesting about their suggestion is that the ceiling should be fairly absorptive already [drop tile (armstrong fine fissured) with 12+ inches of fluffy fiberglass behind it].  In their defense the treatment recommended for the ceiling was diffusive, so they could have been trying to keep the ceiling from eating it.   Also they may have just been trying to find a good use for the rest of a box since I wanted some diffusion for behind the dipole panels anyway.

[Red Dragon Audio]

Line array speakers have a more controlled dispersion pattern in the vertical plane.  While treating the first reflection point on the ceilling won't hurt, it's not absolutely necessary with line arrays.


Have you experimented with absorption behind your maggies?  In some rooms that is the better route than diffusion.  Perhaps try a combination of both and at different positions behind the maggies.


Good luck and have fun listening!

[JohninCR]

Just test it for yourself.  Put a chair about 6ft in front of your speakers while they are playing and stand up on your chair and listen as your ears go above the plane of the drivers.  If you are getting true line source behavior then as you go above the plane of the ribbon, it should be like someone turned the volume down by at least 80%.  That point should be quite a sharp one and quite dramatic.  You'll also immediately understand why ceiling and floor treatment would be a waste of money with line sources.

Dr Griffin's shared work is right on.  The one thing not well explained is the conversion from nearfield to farfield response is not a specific point like the plane of the array demonstration above.  It is a gradual conversion away from line source behavior, which is good because otherwise we would need floor to ceiling line sources in anything other than a very small room.

[John Casler]

What is everyone's take on ceiling/floor first reflection points for line sources?  Have other line source/array owners need to treat their ceilings and floors as much as other walls?

From what I've read (especially Dr Griffin's white paper) a line source/array shouldn't really reflect much from the floor and ceiling.

However, I've had a vendor's recommend ceiling treatment for my maggies.

Did they just not listen when I said that my speakers are line sources (full height ribbon), trying to recomm ...

Hi Jeremy,

I asked a similar question some time ago and don't really think I received an accurate answer.

I don't think you can "lump" all line source designs into a single basket.

I am not a speaker designer and simply look at this from a "logical conclusion" view.

To me it would stand to reason that if you use a vertical array (line sourse) of "high dispersion" dynamic cone drivers, the orientation will not change the vertical dispersion of the top and bottom drivers.

If it does, that would be some interesting physics.  So either the designer/builder must "attenuate" or in some way modulate those drivers.  Seems to me, when I read the "Griffin paper" on LS (some time ago) he used the term "tapering" but I could be wrong.

Now the use of planar or ribbon drivers with a more limited dispersion in the vertical plane "would" certainly reduce floor and ceiling reflection, depending on the dispersive charachter of the driver.

You can test this yourself with the Maggies and will notice that sitting they are clean and clear, and when you stand with your head above the driver, the HF's are reduced.

Notice that they are "reduced" and not totally gone and there is still Mid Energy that is also reflected off the ceiling and floor.

[JoshK]

The reason maggies have limited vertical dispersion is precisely the same physics that limits the vertical dispersion of line arrays, be it cone dynamic or planar.  

This may seem counterintuitive at first, but what you have to understand is that for a particular SPL level each individual driver is moving a lot lot less than it would if it were the only driver producing its range.  The reason for this is due to the forward wave's coupling together and adding additional SPL.  This usually is quite obvious to most people about the additional gain an MTM has over its MT counterpart and the more slight limiting of vertical dispersin the MTM has.  A line array is taking the same idea further.

Since the individual driver is working a lot less, the upper driver is not putting as much energy out as it would in a 2-way.  So its vertical off-axis energy is much less too.  The vertical off-axis energy for all the drivers doesn't couple the way it does with on-axis.  [lots of hand waving, since I don't care to re-write the Griffin paper]  The end result is the vertical off-axis energy is much less than the on-axis energy, this is why vertical dispersion is "limited".

[ctviggen]

One thing that's bothered me about line sources is that it seems as if you're trading lower side, ceiling, and floor reflections for higher rear wall reflections.  After all, if you have a true line of energy, it's going to create a much stronger enery envelope than a point source would have at the rear wall.  Isn't a stronger reflection from the rear wall and less strong reflections from side/ceiling/floor just as bad as the opposite?  You still have to take care of first reflection points, only now you have to take care of a larger area of a rear wall.

[Red Dragon Audio]

One thing that's bothered me about line sources is that it seems as if you're trading lower side, ceiling, and floor reflections for higher rear wall reflections.  After all, if you have a true line of energy, it's going to create a much stronger enery envelope than a point source would have at the rear wall.  Isn't a stronger reflection from the rear wall and less strong reflections from side/ceiling/floor just as bad as the opposite?  You still have to take care of first reflection points, only now you have to take care of a larger area of a rear wall.

You're confusing a Line Array(monopole) with a Dipole Line Array.

Let me clarify.

DIPOLE LINE ARRAY EXAMPLES
Magnepan
Martin Logan
Sound Lab
Apogee

LINE ARRAY (monopole)
Pipe Dreams
Dali Megaline
Selah Audio
GR Research

Examples of Monopole Line Array




Examples of Dipole Line Array

[John Casler]

The reason maggies have limited vertical dispersion is precisely the same physics that limits the vertical dispersion of line arrays, be it cone dynamic or planar.  

This may seem counterintuitive at first, but what you have to understand is that for a particular SPL level each individual driver is moving a lot lot less than it would if it were the only driver producing its range.  The reason for this is due to the forward wave's coupling together and adding additional SPL.  This usually is quite obvious ...

Hi Josh,

As ususal, good info.

I wonder however how this answers the posters question about Maggies.

While dynamic driver line source behave that way, don't planar and ribbon still operate with a very restricted vertical dispersion?

I'm thinking that a planar or ribbon line is actually closer to a "point source" to the ear, since the ear is not hearing the top and bottom portions like in a "line array" of multiple cone drivers.

That is, in a multiple driver array with high dispersion, the listener can hear "all" the drivers or some part of their dispersion, where in a planar like the Magnaplanar, the listener only hears the window of vertical dispersion of the driver "section" pretty much in front of them (if they are listening rather nearfield)

I know that when I listen to multi-cone arrays like the Dali or Pipes, I hear what sounds like smearing or cloudiness in the areas covered by the cones, but not in the ribbon frequencies.

I get the impression that this is caused by the top and bottom drivers being heard at the ear with timing differences due to the different distance from the ear as the center drivers.

I never heard this with my old Maggies.

Do you have any ideas on that?

[John Casler]

You're confusing a Line Array(monopole) with a Dipole Line Array.
 ...

Hi Ryan,

I think Bob is actually talking about the "rear" wall, (in the back of the room) not the front wall where the rear wave is reflected.

Am I reading you correctly Bob.

I think he is recognizing that LS speakers are known for having and maintaining higher SPL for longer distances, and that it may translate into a greater reflection off the "rear" wall.

PS, I sent a client your way for some cable elevators.  You still offer those correct?

[JoshK]

John,

I don't mean to condescending or otherwise disrespectful at all, I am only here to help share what I am learning, the more I learn.  But in answer to your reply, you have missed some of what I *tried* to explain..... Let me try to clarify.

While dynamic driver line source behave that way, don't planar and ribbon still operate with a very restricted vertical dispersion?

They both do.

I'm thinking that a planar or ribbon line is actually closer to a "point source" to the ear, since the ear is not hearing the top and bottom portions like in a "line array" of multiple cone drivers.

planar lines are not a point source, they are very much a line source, however they are probably a better line source then what else you heard.

I know that when I listen to multi-cone arrays like the Dali or Pipes, I hear what sounds like smearing or cloudiness in the areas covered by the cones, but not in the ribbon frequencies.

I get the impression that this is caused by the top and bottom drivers being heard at the ear with timing differences due to the different distance from the ear as the center drivers.

I never heard this with my old Maggies.

I have never heard the dali or pipes, so I can't comment on them, I can only surmise that they used too high of a xo point for the c-t-c spacing their drivers dictated. That is the only reason I have to explain the discontinuity you heard.  There should be no such smearing in a properly designed line array, such as the Selah Audio Linus3 I have for reference. I carefully and distinctly was listening for exactly this when auditioning the Linus3 as I wanted to learn if the science of line arrays actually correlated with my own hearing.  

If there was such a smearing it would show up in the impulse response and hence the frequency response.  It doesn't.  The reason is the time delayed signal is partially cancelled with other off-axis signal and is also incredibly attenuated relative to the coupled signal you are listening to.  

I am not saying line arrays are perfect, they offer a very different perspective, but they aren't flawed the way that would first seem obvious. Your reservations are precisely the same as mine at first, but further examination reveals why it doesn't have those problems.

[JoshK]

You're confusing a Line Array(monopole) with a Dipole Line Array.

Let me clarify.

DIPOLE LINE ARRAY EXAMPLES
Magnepan
Martin Logan
Sound Lab
Apogee

LINE ARRAY (monopole)
Pipe Dreams
Dali Megaline
Selah Audio
GR Research

Examples of Monopole Line Array


[img]http://www.ultraaudio.com/features/pics/200410_dali. ...

No actually he isn't confusing the two, he has a very good point.  Since the SPL falls not at 1/d^2 but linearly (1/d) there will be much more energy fired at the rear wall so treatment there will be paramount (relative to other types of speakers).

[Red Dragon Audio]

I think Bob is actually talking about the "rear" wall, (in the back of the room) not the front wall where the rear wave is reflected.

Am I reading you correctly Bob.

I think he is recognizing that LS speakers are known for having and maintaining higher SPL for longer distances, and that it may translate into a greater reflection off the "rear" wall.

Good point.

Line Arrays lose 3dB with every doubling of distance.

Typical speakers (point source) lose 6dB with every doubling of distance.

of course these numbers don't account for room gain but it's a good guide.

If someone finds that rear wall reflections from a line array are more bothersome (which may or may not be the case) - place some nice acoustic room treatments at the back. Really this is likely to be needed with either type of speaker.

PS, I sent a client your way for some cable elevators.  You still offer those correct?

I sure do - Thanks! (click picture)

[samplesj]

No actually he isn't confusing the two, he has a very good point.  Since the SPL falls not at 1/d^2 but linearly (1/d) there will be much more energy fired at the rear wall so treatment there will be paramount (relative to other types of speakers).

Actually I do agree that this is a concern.  Luckily I have a local source for rigid fiberglass so I'm going to keep adding absoption on the rear until it starts hurting the sound.  Although they seem to have fallen out of style something like a LEDE might not be a bad idea for line sources/arrays.

While the lesser falloff 3db vs 6db per doubling makes the rear wall more important, it does have several benfits like nice even sound through out the listening area so it is a tradeoff I'm willing to make.

[samplesj]

Hi Josh,
I'm thinking that a planar or ribbon line is actually closer to a "point source" to the ear, since the ear is not hearing the top and bottom portions like in a "line array" of multiple cone drivers.

That is, in a multiple driver array with high dispersion, the listener can hear "all" the drivers or some part of their dispersion, where in a planar like the Magnaplanar, the listener only hears the window of vertical dispersion of the driver "section" pretty much in front of them (if they are listening rather nearfield)

Why would this be?  

As far as I can tell the ribbon element in my 3.6s is full length.  It is braced periodically with tiny fingers that alternate sides, but it isn't seperate pieces of ribbon.  This means that if it is vibrating it will all vibrate.  Of course I realize that the tops and bottoms don't have the same excursion (is that the primary reason for limited vertical dispersion), but it will all move.  If it all vibrates why will I not hear all parts like a line array/source?

[Red Dragon Audio]

No actually he isn't confusing the two, he has a very good point.  Since the SPL falls not at 1/d^2 but linearly (1/d) there will be much more energy fired at the rear wall so treatment there will be paramount (relative to other types of speakers).

I misunderstood his  post.
He does indeed have a valid and good point.  

[JoshK]

Yeah I realized you probably understood rear wall as front wall , which is understandeable, didn't mean to be harsh.

[John Casler]

Yeah I realized you probably understood rear wall as front wall , which is understandeable, didn't mean to be harsh.

Now how can a "purple Hippo" be harsh?

     

[John Casler]

Why would this be?  

As far as I can tell the ribbon element in my 3.6s is full length.  It is braced periodically with tiny fingers that alternate sides, but it isn't seperate pieces of ribbon.  This means that if it is vibrating it will all vibrate.  Of course I realize that the tops and bottoms don't have the same excursion (is that the primary reason for limited vertical dispersion), but it will all move.  If it all vibrates why will I not hear all parts like a line array/source?

I defer to Josh, who is far more into the physics than myself, but I would still question what we actually hear.

To be sure a "line Source" is a special animal.  The energy of the driver above and below the middle driver "has" to improve the efficiency of the center driver simply by making its job easier.  They work together to set the immediate air in motion.

The very utmost and bottom most drivers have no help.

What I can't see (or a better term would be understand) is how you will hear the sound from the top and bottom "planar or ribbon" drivers, if they do not (by themselves) have dispersion within that angle or plane.

This concept still deserves "cogitation" before assimilation.

[samplesj]

To be sure a "line Source" is a special animal. The energy of the driver above and below the middle driver "has" to improve the efficiency of the center driver simply by making its job easier. They work together to set the immediate air in motion.

The very utmost and bottom most drivers have no help.

What I can't see (or a better term would be understand) is how you will hear the sound from the top and bottom "planar or ribbon" drivers, if they do not (by themselves) have dispersion within that angle or plane.

Ah, but your reply to me was on my reply to your previous post where you mentioned that a maggie wouldn't behave like a true line source and you would only hear from the middle because a ribbon has limited vertical dispersion.

As far as I can tell from looking at the actual ribbon on a 3.6, the true ribbon Maggies (3.6 and 20.1) have a single 55" ribbon.  It isn't multiple drivers.  Maybe someone who has fried one can confirm what they saw in their replacement.

With just 1 driver how can you not hear up and down the ribbon?  The dispersion limits would only apply above and below the ribbon itself which is fairly close to the ground and appears to be slightly around my ear level when standing (5'11').

edit to fix ribbon length

[Red Dragon Audio]

Yeah I realized you probably understood rear wall as front wall , which is understandeable, didn't mean to be harsh.

Hey Josh  - no offense taken at all.  
Somtimes things I say need correction so it's good folks are around to do that for me.


...and now back to line arrays, their dispersion patterns and how we deal with them in our listening rooms.