[Marbles]

Like the RD series?

If so, what did you think?

Thanks

http://www.partsexpress.com/pe/pshowdetl.cfm?&PartNumber=264-700&DID=7

http://www.partsexpress.com/webpage.cfm?&DID=7&WebPage_ID=135

I'm kind of thinking of a 2 piece speaker system with a sub section that would play up to 200hz or so and XO to a long ribbon like these.

I would use a box about the width of the ribbon and about 6" deep to turn it into a monopole.

The subs and ribbons would not be connected except maybe by speaker wire if passively XO'd, or not at all if actively XO'd.

Any thoughts?

[jpsartre]

I've done extensive listening on a system with BG's 50" ribbon but in a dipole configuration. The main difference between the shorter 50" and the longer 75" ribbon is the high frequency window (i.e. the height at which you hear all frequencies) which of course affects the sound based on sitting vs standing. I would think the 75" is more versatile.

Stereophile had a review of their free standing speaker using the 50" ribbon last month and gave it very good marks, short of John Atkinson wishing for more energy in the highs (which can be a valid observation on occasion)

My recollection of the BG ribbon was fantastic and consistenly precise imaging, probably the best imaging I ever encountered. Also the unmistakenly "airy" sound of the ribbon was a perfect match for acoustic/classical/jazz music but sounded weird with rock or compressed music (almost like spraying perfume on a bad smell ). I am sure the dipole config had something to do with this though so a monopole setup is another ball game.

The fact that you can play 350 Hz all the way up without a crossover is a winner in my book and I think is the other main appeal of this ribbon (I don't know if XO at 200 Hz is a little low-you might want to talk to BG about that).

All in all, a very intriguing and underrated IMO piece of engineering.

[Richard U]

I have some bg ribbons. They are rolled off at the top but for my ears they are fine. The main thing I don't like about them is they don't play very loud and the sound becomes compressed with large dynamic swings.

Richard

[Marbles]

Thanks guys, sounds like they are not for me.....

[warnerwh]

Also you wouldn't want to cross them at 200hz. There's a BG forum and you'd find there are problems using frequencies that low. They do sound very good through the midrange but really need a subwoofer and midwoofer along with a tweeter to make a complete system. I spent alot of time looking into this and it just isn't worth the trouble when you can get some RM 40's for the same kind of money.

[Jon L]

Thanks guys, sounds like they are not for me.....

Now come on.  There's nothing a little money won't fix.  For example, Wisdom Audio's flagship speaker uses THREE of the 75 inch B-G (modded) ribbons per side and a large tower of woofers.  They always use about a Gigawatt worth of 3 pairs of mono amps to power these speakers, too.

[audioengr]

I have seven-foot tall speakers with long BG ribbons, crossing over from the 10-inch bass box to the ribbons at 250 Hz.  Not a good idea.  

Better to cross over at 350-400 Hz.  Even after extensive wiring and crossover component replacement, they sound a bit thin in the mid-bass and midrange.  I plan to move the crossover point up or maybe make them 3-ways.

[Danny Richie]

Marbles, here are my thoughts on speakers of this type:

I have worked with a lot of these drivers, of several types, and manufactures.

There are limitations and problems associated with allowing these drivers to play to their lower limits.

The RD 75 is rated to play down to 150Hz, and it will play that low, but so will a set of head phones. But you won't get any useful output out of them in the lower ranges.

The large ribbon or planar magnetic drivers simply have a very limited ability to move any air in the lower wavelengths. How much SPL a driver can produce is a direct relation to its X-max capabilities.

Drivers also have two real limits to them. There are mechanical limits and electrical limits. The first limit is when a woofer, or any other driver, reaches the end of its X-max. In the case of many woofers they begin to receive damaged at this point. The electrical limits are the point at which the voice coil or element begins to burn up.

Now take a small woofer like this one as an example:

http://www.partsexpress.com/pe/pshowdetl.cfm?&DID=7&Partnumber=297-428

It's a nice little woofer with a good sized X-max. Yet its mechanical limits are such that anything over 20 to 30 watts of power in the first or second octave will bottom that baby out. It can only play so loud in the lower ranges by the physics of it alone. Yet, this little woofer can probably play louder than a RD 75 at 150Hz. The RD driver has a good sized surface area but has very limited exertion capabilities.

Now take that little woofer and relieve it from having to play below 400Hz or so and it will handle 3 or 4 times the power all day long.

So when manufactures push these long ribbons or multiple planar magnetic drivers down into these ranges below 200Hz all kinds of problems occur. 300 to 400Hz and there are still problems and it better be a very small and very fast woofer.

For one, there is a thinness and compression as power is applied because they have no ability to increase power output in the bottom end, yet higher frequency ranges are no problem.

Then there is blending the sonic signature of a planar magnetic driver with a woofer. Differences in spectral decay of those drivers is considerable. Meaning that while one driver has a start and stop time that is very fast, the other is very slow. Getting any kind driver blending going on is not likely. Ever listen to the Wisdom audio speakers? I have.

Moving the crossover up will elevate some of the problems and keep the planar magnetic driver from being stressed out, but that puts a crossover point right in the heart of the fundamental vocal range. My experience from trying this in the past has concluded this to be a big no no. Splitting the vocals into dissimilar drivers with phase shifts and delays makes them far from natural.

I have worked with planar magnetic drivers in true line source configurations with crossover point that ranged from 500Hz to 2kHz.

While the speed of the planar magnetic drivers is great, they still have a limited X-max. To reach high output levels with easy, they really can't be used down low. They just do not sound natural. Take the hit of a drum for instance. The planar's are fast and it may sound like a drum but there is no real impact. This is again back to the thin sound. Not natural sounding!

My conclusion was that anything below 1kHz really needs to be covered by a driver capable of moving enough air to easily recreate the output level that the rest of the system is capable of. Anything above 1kHz and there is no woofer than can compete with the planar magnetic drivers in many ways.

Then there is the line source propagation verses point source propagation, and one (the line source) loosing 3db of output per every doubling of distance while the other (point source) loosing 6db for every doubling of distance. At what distance does one match the output levels? It will only be equal at one distance. Then all distances before and after will have an unequal output level. The same goes for topping a line source off with a point source tweeter.

Now take those RD drivers that you posted the link to. Line them with an equally or slightly longer line of small woofer and cross them over in the 1kHz region and you will really have something. Of course you will have to bi-amp them and actively cross them off because the true 1 watt/1 meter output of the RD 75 is in the 83db or less range while a line of just about any woofer you can find will be, ah, much louder.

Then of coarse those drivers (the RD series drivers) are a little soft in the top end as others here have noted. Always pros and cons, huh.

[Brian Cheney]

It appears to me that the above poster's experience with planar magnetic midranges is not as extensive as he claims.

For one thing he confuses the Xmax of a driver which is supposed to move pistonically (a cone) with that of the planar, which has its maximum excursion in the center of the diaphragm and whose motion more closely resembles that of a bowstring.

I have used the BG ribbons (RD50 and 75) in the past, and because they are narrow and clamped on either side, they have little linear travel.  However, our panels sourced from Level 9 in Canada and modified by us, have nearly +/-3.5mm of travel in the center of the panel, a fact I became familiar with when early versions of this panel buzzed on energetic music passages with a 280Hz crossover at 12 dB/oct.  The solution was to raise the stator to double its original height.  The panel then became quite capable of reproducing the 300Hz to 7kHz range we asked it to do st high levels. Note that our panel is more than twice as wide as the BG 50 or 75 with a PEN diaphragm stretchier than BG's mylar.
Their "Xmax" is now more than sufficient.

We have 20,000 owners who can testify to how well our panels work in their speakers.  If problems existed, I would hear about it on the VMPS Forum elsewhere on this board.

[Danny Richie]

It appears to me that the above poster's experience with planar magnetic midranges is not as extensive as he claims.

Now I'm the above poster.        You'd be surprised what I get sent, what I have, and what I've tested.    Actually my experience is more extensive that I would like to mention.

For one thing he confuses the Xmax of a driver which is supposed to move pistonically (a cone) with that of the planar,

Confuses? Not at all. Comparing it. Certainly.

which has its maximum excursion in the center of the diaphragm and whose motion more closely resembles that of a bowstring.

You are exactly right. The planar driver does not allow the entire diaphragm to move linearly. The greatest point of movement is at the center. As one moves closer to the edges it can hardly move at all.

I have used the BG ribbons (RD50 and 75) in the past, and because they are narrow and clamped on either side, they have little linear travel.

Correct again.

However, our panels sourced from Level 9 in Canada and modified by us, have nearly +/-3.5mm of travel in the center of the panel,

Hmmm... that seams pretty huge. +/-3.5mm, Wow! That would be a 7mm peak to peak movement. Let's see...



Since the whole unit is only .4 inches thick, and that would equal 10.16mm of total thickness. Then if I carefully measure the thickness of the frame down to the inside edge of the magnet that is mounted to it, then it comes to right at .15 inches. That would be 3.81mm. And it is that thick on each side. So take the 10.16mm and deduct 3.81mm twice, that leaves 2.54mm of gap left for the diaphragm and the air gap. That would leave a total peak travel of +/-1.27mm if the diaphragm had zero thickness. Since it is corrugated and does have some thickness to it then I would have to presume that the maximum distance it can travel is even less.

Now if it can actually move far enough to hit the magnet that would be quite a bit of movement all things considered, but still not leaving it capable of playing any low frequency signals to any high SPL levels. That would still be less air moving capability than most 3" woofers.

We have 20,000 owners who can testify to how well our panels work in their speakers. If problems existed, I would hear about it on the VMPS Forum elsewhere on this board.

Really? That's a lot of customers, and no one has called? They call me all the time. Another one just last week. They seamed to feel the planar's in their speakers were playing too low.

But what do I know? My experience with planar magnetic mid-ranges may not be as extensive as I claim.      

[Brian Cheney]

Your measurements are on the earlier, low stator version of our panel, and do not apply.

I have had requests to move the crossover frequency up somewhat, and have done so on single, dual and triple panel versions of our speaker.  The systems with four or more panels remain crossed over at around 200Hz.

[Brian Cheney]

I'll ask Dragoslav Colich, designer of the Level 9 panel (currently with Magnetic Audio Devices in San Diego) , to come here and explain the "linear travel" issue on this panel.

Regardless of how one measures this "X max" it is adequate to our purposes.

[Mike Dzurko]

I can't add anything about the ribbons Brian uses because I have no experience with those. I did a lot of work with the 72" BGs when they first came out (early 90s) and Danny's assessmet is spot on.

[audioengr]

Now take those RD drivers that you posted the link to. Line them with an equally or slightly longer line of small woofer and cross them over in the 1kHz region and you will really have something. Of course you will have to bi-amp them and actively cross them off because the true 1 watt/1 meter output of the RD 75 is in the 83db or less range while a line of just about any woofer you can find will be, ah, much louder.
..

Danny - If I added a vertical line of 4-5" woofers to my Soundlines and crossed them over as a 3-way, what kind of spacing between drivers would I have to use the get good near-field results?  I have read that many of these line-sources must be listened-to at a distance to eliminate the nulling effect of so many drivers.

Steve N.

[_scotty_]

Something missing so far from this discussion is a consideration of how quickly distortion products rise in this type of driver when the excursion requirements necessary to reproduce lower frequencies at the same volume as midrange frquencies is factored in.  This  essentially nonlinear behavior of the driver when the center of the membrane moves much farther than the edges has to contribute to a rapid  rise in distortion products of all kinds
as the driver attempts to reproduce  lower frequencies.  The fact that a driver is a planer magnetic design does not exempt it from the laws of physics governing such devices. Curiously I have been unable to find any information on this subject  online.  If the distortion products are  primarily 2nd  harmonic in nature up to a certain drive level
with a given size transducer  this may explain some listeners  relative insensitivity to the the distortion produced by their loudspeakers.
If anyone has measurements of this behavior or knows were it can be found online I would be interested in this information. Scotty

[Danny Richie]

Okay I can't resist.

We have 20,000 owners who can testify to how well our panels work in their speakers. If problems existed, I would hear about it on the VMPS Forum elsewhere on this board.

First there were no problems with the planar's playing down low and no one complained.

Then....

I have had requests to move the crossover frequency up somewhat, and have done so on single, dual and triple panel versions of our speaker. The systems with four or more panels remain crossed over at around 200Hz.

Actually I received more calls from your customers with the larger models regarding this problem.

Oh well, on to something else.

I can't add anything about the ribbons Brian uses because I have no experience with those. I did a lot of work with the 72" BGs when they first came out (early 90s) and Danny's assessmet is spot on.

Thanks Mike. It sure was nice to meet you at CES. Your product line sure looked good. I wish you all the best, but already know you're doing great.

Danny - If I added a vertical line of 4-5" woofers to my Soundlines and crossed them over as a 3-way, what kind of spacing between drivers would I have to use the get good near-field results? I have read that many of these line-sources must be listened-to at a distance to eliminate the nulling effect of so many drivers.

For good technical data see Jim Griffin's paper on these:

http://www.audiodiycentral.com/resource/pdf/nflawp.pdf

In short, the spacing between your drivers (center to center) is relative to how high they are allowed to play. The spacing must be shorter than the wavelengths that they are playing to avoid comb filtering. Say your center to center spacing is 5.25", then comb filtering will be present down to as low as 2,560Hz. If the crossover point is below that then you are home free. Then you will not hear nulling taking place. There is also still some comb filtering that takes place from the top of the speaker to the bottom of the speaker as there are various distance discrepancies.

As a rule of thumb you really need to be further away from them than the length of the array, if not twice that distance. The closer you get, the more cancellation occurs in the higher frequency ranges. This is why when you measure your tweeter array at 1 meter your highs look rolled off and at 3 meters not so bad. It's the distance differential.

Something missing so far from this discussion is a consideration of how quickly distortion products rise in this type of driver when the excursion requirements necessary to reproduce lower frequencies at the same volume as midrange frquencies is factored in.

Wow, what a good point. You know there has to be some issues there. It would be a little bit like the flexing of a woofer cone. Distortion rises...

Great point, and worth further study.

[Rick Craig]

Like the RD series?

If so, what did you think?

Thanks

http://www.partsexpress.com/pe/pshowdetl.cfm?&PartNumber=264-700&DID=7

http://www.partsexpress.com/webpage.cfm?&DID=7&WebPage_ID=135

I'm kind of thinking of a 2 piece speaker system with a sub section that would play up to 200hz or so and XO to a long ribbon like these.

I would use a box about the width of the ribbon and about 6" deep to turn it into a monopole.

The subs and ribbons would not be connected except maybe by speaker wire if passively XO'd, or not at all if actively XO'd.

Any thoughts?

I've heard them and I think there are better solutions. The top octave is a little rolled off plus they have a nasty cavity resonance that must be notched out. You really need to cross them around 500hz because of the limited amount of excursion available. Add to that the low sensitivity and it then makes it difficult to match them to an array of woofers. A point source woofer section won't work either because of the different radiation pattern. IMO it's not the way to go.

Rick

[Rick Craig]

It appears to me that the above poster's experience with planar magnetic midranges is not as extensive as he claims.

For one thing he confuses the Xmax of a driver which is supposed to move pistonically (a cone) with that of the planar, which has its maximum excursion in the center of the diaphragm and whose motion more closely resembles that of a bowstring.

I have used the BG ribbons (RD50 and 75) in the past, and because they are narrow and clamped on either side, they have little linear travel.  Ho ...

Actually in Danny's defense (and this is a rarity coming from me) he is a friend of Igor Levitsky who has designed planar drivers for BG and HiVi so he has access to Igor's new design which will cross fairly low.

If your midrange has 3.5mm of travel then the suspension won't have much control over the radiating area. That loss of control with a flexible element is a recipe for disaster.

[Brian Cheney]

The stators are about 7mm apart, the diaphragm thickness is about a third of a millimeter.  Tensioning the diaphragm is most critical to proper performance.  Over the years we have seen buzzing from three sources:

1. Loss of tension in the diaphragm, either from stretching or glue coming loose.  Relatively infrequent.

2. Magnets dislodged during transport.  A loose magnet can touch the diaphragm causing problems. Most common failure mode.

3. Thermal failure of trace or diaphragm, caused by overpowering.  Surprisingly infrequent.

Overall failure rate has stayed below 1%.

If I can get Dragoslav to comment on his design decisions it would be most enlightening.

Moving mass of our diaphragm is less than a gram.  Properly crossed over its sound is marvelous.  I am committed to first order (series) networks, as I think their listening quality is unsurpassed.  Higher order slopes might smooth dispersion patterns (reducing lobing) but I feel this less important than maintaining the best overall listening quality of the speaker. We wire all drivers electrically in phase.  I do not feel having improved amplitude response in the crossover region is worth the sacrifice of inverted polarity drivers causing a phase inversion in the passband.

I look forward to anything you discover about the panels or the crossover.  Feel free to share on this forum.  All designs involve compomise, but our planar mid panel has proven itself an outstanding performer for nearly four years now.

[_scotty_]

Brian, how much amplitude error and lobing anomolies due to combfilter induced cancellation at the crossover transition point is allowable before you consider it objectionable? Which is worse the phase error due the amplitude error or the phase inversion resulting from a reversed driver? Also do you have any information on distortion products as a function of drive level in the form of graphs showing harmonic and intermodulation distortion with regards to frequency?  Thanks, Scotty