[Eric D]

I kinda follow the VMPS forum at a low level (for future possible consideration), and I'm certainly not any kind of expert, so take this for what worth you find.  But with your conversation here about time coherence, thought you might want to check out the upcoming SOCS (speaker-only correction software) we were discussing in this thread:
http://www.audiocircle.com/index.php?topic=5708

[hmmm, am I in trouble for linking from one mfr forum to another?  at least MLS and Brian Cheney are talking about joint ventures....]

I think the intent is to let any speaker operate like a time-coherent single-driver.

Discussing how it relates to some of the earlier points in this thread:

My biggest question regarding time correctness is this: On a stage the performers are situated at different depths; therefore, in most set-ups the sound waves of the guitar, bass and vocals are going to reach the listeners ears before the percussion instruments (drums, bongos, cymbols etc.), and keyboards. So, if this isn't a concern at a concert, why should it be a conern in your listening environment? Having said that, based on what I've read I think phase shifts are much more important in speaker design.

I think this was discussed fairly well, but the one thing I didn't catch was that yes, the performers being at different depths reach the microphones at different times as well, and that when recorded and reproduced well, allow us to place them in depth as well as side to side by the audio cues.

[edit]  What I expereinced when I got to hear a SOCS demo was that the images thrown by the speaker really came into focus. [/edit]

All that said, correcting for time can be done for exactly one point in three dimensional space. Move a little off that point and it all goes to hell. So then how is the designer suppose to correct for a point that will work for all peoples, both farfield and nearfield setups?

You know, I wonder the same thing.  Trying to leave the majority of the discussion to the appropriate forum and thread, I wonder about that issue more as it relates to RCS (room correction software) than for speaker-only.  SOCS just removes the error introduced by the speaker.

Now I think I want some stew for lunch.  

enjoy!

[Audiobudha]

Sorry guys I got my alignment wrong between sound waves and stew.


Here is the correct link. It's worth the time.

http://forum.audiogon.com/cgi-bin/fr.pl?cspkr&1032037028&openflup&55&4#55

[James Romeyn]

One of the best things VMPS ribbons have going for them, apparently audible, is the fact the mid covers about 5 octaves of the 10+ octave musical range, from about 166-7k or 10kHz, depending on tweeter.  I think universal agreement is that the human ear's maximum phase sensitivity is between 1500-3k, the range from 750-1500 being the 2nd most critical.  I've read that this phase sensitivity allows a blindfolded person to follow a coin's trajectory while it turns in circles on a flat surface.  Virtually every multi-way speaker is crossed in that range.  Plus the ribbon has 30-100x less moving mass than a cone.  Remember that minimizing midrange cone weight helps little, as most of the moving mass exists in the coil.  So regarding time coherency or time alignment, the VMPS use only one driver where cones/domes use 2.  Just my 2c.

[Ric Schultz]

I love the fact that the VMPS midrange ribbon has such a lot of range too and think it is very very transparent, but time aligning (via moving the midrange back to align with acoustical center of woofer) does work (even when the xover is 200hz).  Physically time aligning a tweeter to midrange works as well (no matter what the frequency....especially if using low order xovers).  The phase errors in the xover also have to be taken into account as well as the driver parameters. This I have experienced while designing/tweaking several speakers, both planar and cone type.

I believe the stated mass of the VMPS midrange is a little over one gram.  A five inch driver has about 7 grams of moving mass....this is hardly 30 to 100 time more.  If you used multiple 3 inch drivers (I heard a speaker years ago with nine 3 inchers running full range (100-10K) with ribbon super tweeter and woofs that was amazing) then the distortion goes way, way down.  Several multiway speakers use one driver from say 100 hz all the way to say 7 to 8K (my friend Vince Christians 2 way speakers...for instance).  Then you have the full range driver crowd that use a driver from 60 to 10K and use a supertweet on top and sub underneath.....less phase shift than using any xover.  Many ways up the mountain.

[James Romeyn]

I love the fact that the VMPS midrange ribbon has such a lot of range too and think it is very very transparent, but time aligning (via moving the midrange back to align with acoustical center of woofer) does work (even when the xover is 200hz).  Physically time aligning a tweeter to midrange works as well (no matter what the frequency....especially if using low order xovers).  The phase errors in the xover also have to be taken into account as well as the driver parameters. This I have experienced while de ...

Mind if I ask where you got the 7 gram figure?  I admit that I just reiterated Brian's quote of the mass difference.  7 grams for a cone & voice coil sounds kinda low.  Plus the fact that the ribbon is push pull = 4x the energy controlling the cone even if the mass were equal, no?

[Ric Schultz]

Right out of the spec sheets for the drivers.  The 5 inch Audax Carbon fiber,  5 inch Accuton and a 5 inch Jordan JX92S all have 7 grams of moving mass.  The 4 inch (as used in the Pipedreams) Audax Carbon Fiber is 4.1 grams.  The Bandor full range 3.5 incher (2 inch diameter cone) is 1.8 grams.  It is being developed for use by Audience in their line source speaker.  They run a bunch wide open from 100hz to 20K, just a cap in series for the 100 hz crossover and use them with a sub.

Yes, I think push pull magnets distributed evenly over the diaphram contribute to the VMPS drivers excellence and low distortion.  The execution of a driver plus the driver equals what it is capable of.  I have had cone speakers that simply killed stock electrostats.....now when the electrostats were modified......well, tables turned.  So, no matter how good a particular technology is, it must be implemented in the absolute best way to hear its potential.  Cones done right beat planars not done right.  Some cones done right sound outrageous.  The VMPS midrange is indeed a state of the art device.

[BrunoB]

...
I believe the stated mass of the VMPS midrange is a little over one gram.
...
The 5 inch Audax Carbon fiber, 5 inch Accuton and a 5 inch Jordan JX92S all have 7 grams of moving mass.

What if the mid panel would be two times larger? It would have two times more moving mass. Would it be two times slower? No, because it would be equivalent to having two mid panels.

My point is that the moving mass is not a meaningful quality  criteria. I suggest to use the ratio of the moving surface to the moving mass instead.

Following this idea, I calculated the "moving ratio" for three drivers:

Code: [Select]


-----------------------------------------------------------------------------
Driver                   mass (g)          surface (cm2)    ratio (cm2/g)
-----------------------------------------------------------------------------
 5' cone                    7                       130                 19
VMPS mid panel             1                       116                116
VMPS HET(FST)              0.013                     5                385
-----------------------------------------------------------------------------


The higher the moving ratio, the better.
Note:
- I estimated the surface of a 5' cone using the disk surface formula (Pi R2), which underestimated the area for a cone driver.



Bruno

[Brian Cheney]

The moving mass specifications for cone dynamic drivers are fudged by omitting the surround, a substantial contributor.

Typical 5" cone with surround, bobbin and voicecoil comes in around 15g.

Moving mass is not the most critical performance characteristic.  The Neo push pull planar distributes its drive force evenly over the entire diaphragm, while the apex-driven cone requires point A to point B rigidity for pistonic motion, and as we know, all materials flex to some degree.

[robertwb]

I've heard RM40s(hey kevin), RM2s,GMA C-3 and the europas recently and the GM C-3s left me feeling like something was missing-mostly mid bass I think-after 4 hrs I left dissapointed-I've heard many speakers I could live with-the C-3s aren't one of them-even the europas which I think are a better value aren't anything special IMO

both the RMs I heard I think are in the top 5 best speakers I've ever heard and I would be very happy to own either one(if/when I can afford it )

[meilankev]

Hello Robert.

I didn't know you were a member of AudioCircle.  I would say "welcome", but I see you have 7 posts (beginning back in November), so you are hardly a rookie.  But I will say I'm happy to see you here.

I'm sorry for using your opinions about the RM40s and Continuums without your permission, but again, I didn't know you were a member.  I'm glad you came and put a "name" to the "opinion".  Not many people would have as much exposure to various speakers by VMPS and GMA than you would.

You know, we need to get together again soon.  Of course, there's nothing "new" to hear at my house (as I still have another 10 years or so before I look to change anything in my system).  But it's still enjoyable having you over.  And I'm still looking forward to getting out to your place, particularly since you've gotten all the "improvements" incorporated.

Also, I still haven't heard from your friend here who has the RM2s.  I'm excited about getting to know him.  It's hard to believe I've still never heard any VMPS speakers other than the one I own.  If he's a little uncomfortable meeting up with someone he hasn't spoken with, maybe the three of us can hook up - your place, his place, my place - it doesn't matter to me.

Kevin

[TheeeChosenOne]

I've heard RM40s(hey kevin), RM2s,GMA C-3 and the europas recently and the GM C-3s left me feeling like something was missing-mostly mid bass I think-after 4 hrs I left dissapointed-I've heard many speakers I could live with-the C-3s aren't one of them-even the europas which I think are a better value aren't anything special IMO

Robert,
Perhaps the speakers were improperly set up or were mated with the wrong equipment.

I've heard only raves about GM's current line.........

[WerTicus]

yeah and i only hear raves about bose but... what does that mean

i cant wait to hear a pair of vmps speakers of any kind!