[Randy]

This is probably a stupid question, but could a ribbon tweeter be used with the waveguide?

[Aether Audio]

Randy,

Welcome to our circle!   Also, that's not a stupid question.  A ribbon "could" be used in a waveguide.  In fact, I've already looked at one and experimented with it in cooperation with another party.  Depending on the design criteria, it could be used.  The one I've looked at didn't quite have the HF extension I would prefer but...the decision is somewhat up to them.

There are differences though.  Due to the larger diaphragm area one does not get the kind of LF loading that we see with domes.  Time will tell if it is important in that application though.  As of right now I have not experimented with a unit that I would personally choose to use in a final product for SP Technology.

As a side note, I'm not convinced that ribbons hold any particular advantage over domes - at least not in a waveguide application.  IMHO much of their claimed "air," "speed," "detail," etc., are the result of distortion artifacts in the 8kHz to 20kHz region.  There is a fair amount of data generated by others to support this idea, but then again...time will tell.

Never say never.

-Bob

[Randy]

"IMHO much of their claimed "air," "speed," "detail," etc., are the result of distortion artifacts in the 8kHz to 20kHz region. There is a fair amount of data generated by others to support this idea, but then again...time will tell."

Bob- Thanks for the reply.  Regarding your quote above, all I can say is, wow, I never heard that about ribbons before, but since I am far from being a techie, I cannot disagree with you, nor would I want to.

I have been a lurker on the SP pages for some time and from what I've read, I have been drooling over your speakers.   Maybe, one of these days. . .   Will you be at RMAF this fall?

[Aether Audio]

Randy,

I doubt we'll be at RMAF this year - too much going on.  We might have our speakers there though.  It all depends on what kind of arrangements we can make with other demonstrating manufacturers between then and now.

As far as the ribbon issue goes...there's quite a bit involved technically.  On a certain level a ribbon and a soft dome tweeter are similar.  They are both designed to operate in a controlled "break-up" mode.  That simply means that both of their diaphragms are designed such that different parts of the diaphragm move independently of the others.  Specifically, at the lower end of their operating range the entire diaphragm operates in unison - like a solid piston moving back and forth.  As frequency is increased that changes.  In the ribbon, the center of the diaphragm tends to operate more and more independently from the outer parts.  As frequency continues on up, the moving surface gets smaller and smaller such that only a small area at the center is moving,

In the soft dome tweeter, the opposite is occurring.  As the frequency increases, a "ring shaped" area located near where the voice-coil attaches behind it...is the part that continues to move.  There comes a frequency wherein the center of the dome hardly moves at all..  It's from this very concept that the new Vifa/ScanSpeak "ring radiator" tweeters evolved.  The thinking is..."Well, if the center of the diaphragm doesn't move anyway - get rid of it.  Doing so will lower the total mass of the system and allow the tweeter to go higher in frequency."

Well...this obviously is true as they're making them and they work, but...there's no "free lunch."  They do go out to 40kHz or more, but how important is that really?  Removing that center part reduces the total air load on the moving surface and thereby reduces the drivers ability to push air at lower frequencies.  The same concept is true with woofers.  All else being equal (excursion limits), bigger cones (more cone area) make more bass.  Because the center has been removed on these tweeters, they are notorious for producing high distortion when operated below 2kHz and are essentially useless below that point.

But I digress.  Why would a ribbon be potentially inferior to a dome then?  Well with the dome, the outer supporting suspension that supports it and keeps the voice-coil centered in the magnetic air-gap, is "de-coupled" from the center of the diaphragm where it attaches to the voice-coil.  Because of this the suspension can be optimized to do its job with less fear of interaction with the rest of the moving diaphragm.  Then that permits the center part to be optimized to do its job with a high degree of control and precision as well.  Therefore, the two distinctly different and necessary jobs can be engineered to a higher degree of accuracy.

With any typical ribbon, both of the above mentioned functions must be integrated into one moving element.  Although on a certain level it simplifies the design, it is also likely that compromises will be made.  

As an example: A bicycle with a rigid frame that depends on rubber tires to dampen road vibration is simpler and will work, but it's likely to provide a rougher ride than one equiped with shock absorbers and offers the same rubber tires as well.

Hope this all makes sense.
-Bob

[Russell Dawkins]

I think this phenomenon is supported by an experiment that was done around 1986 in the bad early days of CD, shortly after its introduction. A common complaint at the time was the "lack of air" with CD playback.

A set up was rigged where the high frequency component of the surface noise of a vinyl disc (the hiss of stylus scraping vinyl) was added to a digital recording  in such a way that it could be switched in and out. All subjects commented that the hiss-added version seemed to have more HF extension - more "air". The recordings were otherwise identical. There was no perception of hiss being added.

Most ribbons and most planars, whether electrostatic or electromagnetic show a pretty messy waterfall plot, where the signal to noise ratio is not great at all. The residual noise is equivalent in some ways to vinyl hiss being added, especially in the 8-20kHz range being spoken of.

[bhobba]

All subjects commented that the hiss-added version seemed to have more HF extension - more "air". The recordings were otherwise identical. There was no perception of hiss being added.

Hmmmm.  Coud it be the same with valve sound?
http://www.mcrow.net/Preamp%20Emulator%20VST.htm

Not as romantic as the warm glow of tubes.

Thanks
Bill

[Randy]

Bob,
  Thanks.  It makes sense to me.  I used to have speakers (Dunlavy) that had plenty of so-called "air" as you describe it, but which I lost when I purchased superior speakers with a Cabasse dome tweeter.  They took some getting used to as for some time I thought the new speakers lacked upper frequency "sparkle" or "air" which, afterall, may just have been distortion in my former speakers' tweeters and can easily crossover to excessive brightness with some recordings. That exaggerated airy sound can be rather seductive, especially with the massed strings of an orchestra, but isn't realistic.  You don't hear anything like it in a concert hall.