[Marbles]

I started a new thread so it could be flushed easily if needed.

One of the big selling points of the VMPS speakers using the 8" planars was the limited dispersion of the planars, thus taking sidwall reflections out of the equation.  With the new "waveguide" (WG) you now want to have an extremely wide dispersion, bringing the room into the equation.

Maybe it's one of those deals where if you have a treated room you get the waveguide, and if you don't you get the unguided VMPS...


Why is the guide around the woofers?

When we got the upgraded (mid) woofers, we changed the XO values.  Since this WG changes the tweeter and midrange output, why aren't there changes to the XO?

It looks like this is a good design to retrofit speakers "in the field", and the  planars are inexpensive to buy in bulk.  Wouldn't it be better going forward to design a new speaker that uses 8" H   2/3"w ribbons to begin with?  That way there would be little need for a WG (if I understand what you are trying to do).

Again I know you are limited to what you can technically say on the new  waveguide and hope you can answer some of these questions without harming your patent application.

[ctviggen]

Are there pictures or figures yet?  Once the application is filed, there's nothing that will harm it.

[Marbles]

Pics can be found on page 2 of this thread..

http://www.audiocircle.com/index.php?topic=22340&postdays=0&postorder=asc&start=10

[ctviggen]

Sorry, Marbles, I didn't realize that other thread had gotten so large.  Actually, what would help me most is a copy of the patent application.  The drawings and text should be such that one could easily determine exactly what is happening.

[JoshK]

Right now we are all just speculating because we don't know the real details, so any inference we make is at best half informed.   However, you and dwk both brought up a very good point about CD (into 180º) going to cause more room interaction.  I don't know how you can get around that.  

The Modula MTMs that I recently built are built around a few design goals, one of which is that power response (related closely to CD) should be smooth throughout its transitions.  This provides for a wider dispersion as well.  Its imaging and soundstaging are more natural imo than the RM40's but it engages the room much more than the RM40s, so it is a tradeoff in my mind.  Do you want your cake or do you want to eat it?

[brj]

However, you and dwk both brought up a very good point about CD (into 180º) going to cause more room interaction.  I don't know how you can get around that.

The only methoeds that spring to mind are more extensive room treatments, or a very large, wide open room.  There are several speakers that have similar issues, such as the Gallo Ref III with its 330 degree dispersion cylindrical diaphram tweeter.  I think the uneven public and professional reviews of some speakers with wide dispersion patterns may be due to insufficient room treatment for the speaker being tested.  Every speaker will load a room differently, and I suspect that people occasionally forget that.  Such design goals might also alter your selection of a long-wall or short-wall placement.

Do you want your cake or do you want to eat it?

Yes!

[woodsyi]

Marbles,

As always, anything thing I say could be completely wrong but I will take a shot at answering your questions.  The woofer hole around the CD guide may just be logistical in that the guide attatches(?) to the front using existing grill taps.  The filter poles not needing change could be that  frequency range does not change -- only the output level of the ribbons changes.  A thinner line source may not be able extend down to 275 Hz or provide sufficient spl.  The attractiveness of VMPS for me is that single driver type provides the midrange.  I would hate to have to deal with x-over issues in the critical vocal range.

From what I gather, CD wave guide adds cohesiveness and constancy to the combined output of FST and the neo panels in a wider area of the room at the expense of overall spl of the ribbons.  Like Brian said, some sort of eq may be needed between the FST and the Neos and definitely between the ribbons and the woofers.  A case waiting for direct drivers with digital crossover?  I am hoping that I can address the woofer/ribbon balance with my active biamping set up without having to replace the PRs.  With wider dispersion, I agree that placement and room dimensions/treatment would weigh more.  I will give CDWG a shot.

[BradJudy]

Before the pictures were shown, I was envisioning something more like a replacement panel driver with an integrated waveguide plate.  I wonder if this might be the another possible direction.

At least it shouldn't be an expensive item.  While the backing material is unknown, it looks like the bulk is simply a CNCed piece of MDF with grill pegs and optional (?) grill cloth.  

Wayne, if you're reading this, how about setting up a DAM GTG when you have a pair of these for your RM30s and we can A/B the difference (assuming you have an appropriate EQ that can be switched in/out).

[Marbles]

Thanks Woodsyi that makes sense.

[KJ]

Wouldn't it be better going forward to design a new speaker that uses 8" H 2/3"w ribbons to begin with? That way there would be little need for a WG (if I understand what you are trying to do).

One would hypothesize that reflections hitting the wave guide and the baffle would be minimized by doing so.  However, perhaps there is a greater degree of difficulty building and/or mounting a 2/3" ribbon?

-KJ

[woodsyi]

Before the pictures were shown, I was envisioning something more like a replacement panel driver with an integrated waveguide plate.  I wonder if this might be the another possible direction.

I was kind of thinking panel "bra" that would be attatched using the screws already there sticking out.  

[ScottMayo]

However, perhaps there is a greater degree of difficulty building and/or mounting a 2/3" ribbon?

-KJ

Panels distort near the edges. Putting edges closer together doesn't eliminate that, if anything, it might be worse. It looks like the goal is to mask off the edges, instead.

[John Casler]

Although I don't have all the answers, and am not at liberty to disclose all of them in a few cases, I might be able to clear thing up a bit.

1) This device "is not" a simple peice of plywood with slots and holes cutout.  While that is what you see in these rough prototypes, the actual technolgy (other than the slot) is not shown.

2) In its final production model it will have "specific" shape, thickness, texture, width, and any number of parameters to accomplish the sonic goals

3) The rear portion (that you don't see), also has specific materials, functions, and properties that move it to the sonic goal.

4) It is anticipated that the aesthetic appeal will be enhanced by the fact that we can "finish" the exterior portion (as mentioned before) in veneer, fabric, or paint.

5) The actual production model is still some ways away. There is still some very important testing and listening to be done, as well as assigning it to the appropriate manufacturer.  While Brian wanted to deliver the "story" and show the technology, what is shown is far from what will arrive.

6) It is anticipated (as guessed by some) that the CD waveguide will "snap on" to the speaker using the already available grill slots

Hope that clears up some questions.

[Duke]

In my opinion, the 180 degree pattern is quite beneficial, and is a significant net improvement in terms of room interaction.

It's not like without the diffraction-slot waveguide you have negligible energy in the reverberant field.   Instead, what you have (compared to the waveguide case) is a little bit less relative reverberant energy, but its tonal balance is screwed up.   The reverberant sound is GOING TO BE THERE ANYWAY, and will have a significant influence on perceived timbre, naturalness, and long-term enjoyment.   So we might as well get it right.

With a point-source loudspeaker, the reverberant sound typically dominates at listening distances greater than 5 or 6 feet (at lesser distances, the direct sound dominates).  With a line source speaker, the "critical distance " (where domination passes from direct to reverberant sound) will be a bit farther back - maybe twice as far.  So a  line source speaker is already ahead of the game in that respect.

But note that, despite a great deal of press to the contrary, the reverberant sound is not the enemy!   A well-energized, diffuse reverberant field adds richness and warmth to the sound.   The enemy is strong, distinct early reflections - and it is indeed beneficial to diffuse or (if necessary) absorb these.

For five or six years now I've lived with a line-source planar that has a uniform 180 degree radiation pattern up and down the spectrum.   Its pattern is 90 degrees forward and 90 degrees rearwards, but the net direct-to-reverberant relationship is very similar to what Brian is doing here.   I use a bit of diffusion of the early reflection zones, and that's it.  As I sell this speaker, I've accumulated a fair amount of direct and second-hand experience with such a radiation pattern in a wide variety of rooms.  In practice, it is very easy to accomodate such a speaker in a wide variety of rooms because the reverberant sound isn't screwing up the tonal balance of the speaker!  You don't have to room treat to correct the tonal balance of the reverberant sound (which is very difficult to do), instead you only need consider taming the early reflections to improve the imaging (and this is relatively easy to do).

Nope I'm not a VMPS dealer, though I suppose that could conceivably change.   But my background is that of a strong proponent of getting the reverberant field right, and I don't have to hear Brian's invention to be convinced of its benefits.

Duke

[dwk]

In my opinion, the 180 degree pattern is quite beneficial, and is a significant net improvement in terms of room interaction.

Well, the benefits you describe in the rest of your post aren't really due to the 180 degree pattern, but rather due to the constant directivity.  I agree completely that uniform power response is far better than non-uniform power response, and in this regard the 'new VMPS' is likely to be better than the majority of speakers.

However, I actually believe that you can do even better by constraining radiation to an even smaller pattern. Some of my view is due to the fact that I'm in a very small narrow room which makes reflections a big problem, but I think it generalizes. What it effectively does is move the nearfield/farfield transition farther out, which is almost always a good thing.  

Your point about line sources being better in this regard is a good one, though.  (although since any finite line source reverts towards point source behavior at lower freqs, it's a pretty complex situation).   I have a pair of 60" Carver planars and Iwould love to find time/space to try them in a decent waveguide. I really think the results could be good.

[ctviggen]

From what I know of acoustics (which isn't much), the direct reflection is bad and should be minimized, while the reverberant (or indirect) reflection should be adjusted.  A nice diffuse reverberation will give more richness (I know there's a better word) to the sound; not enough diffuse reverberation will either muck up the sound (poor diffusion) or make the sound dead (too much absorption).  However, some people don't mind dead sounding rooms, and thus for them, they might like more absorption relative to diffusion.

[Duke]

Hi dwk,

Thanks for your reply.  Yes, you are correct that the bulk of my post is really arguing in favor of constant directivity rather than the 180 degree pattern per se.   I've owned, and now own, CD speakers that radiate into  considerably smaller angles, and they also work quite well.   Wide-pattern CD does some things better, and narrow-pattern CD does some things better.   They are both, in my opinion, much much better than non-CD.  

A 180-degree waveguide is a relatively easy device to build and retrofit.  I'll concede that a 90-degree device would do several things better, but designing a low-coloration 90 degree waveguide is far from trivial.   And a 90-degree device would introduce a much greater discrepancy when we cross over to the woofer, transitioning from a 90-degree line source to a much wider (nearly omnidirectional) point source.   By using a 180 degree line source, the discrepancy in the crossover region is minimized.  I believe this is well worthwhile, as the discrepancy in radiation characteristics between a line source planar and its companion point source woofer is a major problem with most hybrid systems.  Note that Brian's spacing the woofers as far apart as possible in the vertical plane on the RM40 introduces vertical beaming in the upper range of the woofer's output, which helps reduce radiation pattern discrepancies.  

From where I sit, Brian's juggling of the tradeoffs looks masterful.

Duke

[KJ]

Panels distort near the edges. Putting edges closer together doesn't eliminate that, if anything, it might be worse. It looks like the goal is to mask off the edges, instead.

Perhaps to a small degree because it would result in a larger baffle.  Following this logic, is the waveguide flat or does it increase in depth as you move from the edge towards the ribbons?

-KJ

[James Romeyn]

Marbles, here's my stab at it.

I think the reason can be explained like this. Yes, the untreated ribbon may have less overall dispersion & this may be experienced as an improvement vs. a typical cone/dome system (I concur here wholeheartedly, the ribbons image better in my room vs. any cone/dome sampled).  But in both the case of the non-CDWG-equipped VMPS ribbon & your average cone/dome, the polar response is frequency dependent & non-linear.

In the case of the CDWG-equipped VMPS ribbons, you have a virtually uniform & linear 180-degree polar response from about 280 Hz up. And that may be the magic. Both the non-CDWG-equipped VMPS speaker & your average cone/dome have varying degrees of ragged polar response, not generally a good thing. The CDWG-equipped VMPS ribbon has linear & even polar response (a good thing as Martha says). Even though the non-CDWG-equipped VMPS ribbon has less overall polar output, I'd imagine at some frequencies above 280 Hz it does have 180-degree dispersion, but far less than this at other frequencies.

[Bob Wilcox]

John

Will the speaker grills still fit with this option? It seems like it might be difficult to match the veneer on cabinets with African Ebony or Rosewood finishes that wrap to the front.

Bob