[Porcupine]

I've noticed that large ribbons used for midrange panels, or for tall linear-radiation towers, all seem to have dropping high-frequency response. Why is that? What is the physical reason behind that, if I may ask?

What about for conventional cone drivers? They also seem to obey the same rule. The bigger the driver, the more ideal for low-frequency response, but the poorer for high-frequency response. Is it the same physical reason for them as well, or are some other factors at work as well?

I do have my own ideas about these reasons but I have no idea if they are right or not. I'd like to hear the truth from the experts if possible.

[_scotty_]

In one word mass.  The higher the mass the harder it is to start and stop the driver and accurately reproduce a waveform.  If the mass goes up the motor
has to be correspondingly stronger to accelerate the diaphragm or cone and
deceleration also has to be accomplished to prevent overshoot. There is a physical limit  to the magnetic field strength that can be incorporated into a conventional driver design. As far as I know room temperature superconducting magnets don't exist yet.  In the case of a planer magnetic
driver the available magnetic flux density per unit of area vs the mass of the diaphragm is a factor as is the the area of the diaphragm covered by the "voicecoil" pattern. If there are more conductive paths present on the surface of the diaphragm then greater force will be available to accelerate the diaphragm but there are physical and electrical limits to this aspect of design as well.  These parameters must be balanced against one another if the driver is to function correctly.  Of course at the end of the day it also has to sound good.  Experts are in short supply and I am not one of them.Scotty

[Porcupine]

Hmm I am not sure if that very simple one word answer was what I "wanted" or was "looking" for....hmm.

Let me pry further. Though a larger driver might have more mass, proportional to Radius^2 of the driver (assumed planar and circular here for simplicity) wouldn't it then push an amount of air also proportional to Radius^2 of the driver? Therefore the driver could and should be made to extend/play with lesser amplitude (maybe inversely proportional to R^2) to compensate. And the acceleration A of the driver at any give time is equal to the second time derivative of the driver displacement, thus also being inversely proportional to R^2.

Mass M of said driver would also be proportional to R^2. Thus by Newton's second law F=MA we see that the Forces need to push this driver around is the same regardless of how big or small the driver is.

I fully realize that things are not as simple as this, but I'm trying to pry and say that you can't just tell me Mass is the answer to all my questions. How does frequency of oscillation come into this argument/equation? etc etc

I don't necessarily need to see all the super complicated equations but a little more complicated answer than just one word Mass would be nice.

[_scotty_]

Your hypothesesis might hold up in an ideal system with non-real components and zero losses of mechanical energy due flexure, friction and absorption. In the real world of non-ideal systems mass is most of the problem. The non-ideal behavior of real world materials used in driver construction probably leads to even more losses than is accounted for in my earlier list.     In loudspeaker terms a woofer is not a tweeter. Or lower excursion requirements for high frequency reproduction does not a tweeter make. The behavior of real world materials conspires to make it this way. This may not be a satisfactory explanation but it is the only one I know that fits the observed phenomena, Scotty

[_scotty_]

As a followup to my earlier post consider the behavior of a full range electrostatic loudspeaker. In many ways it behaves in an ideal manner
and seems to fit your mathmatical formulas.  Alas,however, it is not perfect  and not everyone likes the sound of them either.
To quote Rosanne Rosannadanna,"It's always something! If it's not one thing,it's another thing.".
Scotty

[ctviggen]

Mass M of said driver would also be proportional to R^2. Thus by Newton's second law F=MA we see that the Forces need to push this driver around is the same regardless of how big or small the driver is.

If F=MA in the real word, then a larger driver will have a larger mass, which means more force is necessary.  Additionally, in order to vibrate something like a ribbon (or a cone), you need to start the ribbon at one point, which entails acceleration, let it travel through a certain range of motion, decelerate the ribbon to stop the motion, accelerate the ribbon in the opposite direction, etc.  The larger the ribbon (or cone), which implies more mass, the harder this is to do.  That's why people have been going to metal cones -- lighter weight is better (though ringing can become a problem).

[ScottMayo]

People have developed plasma drivers that reacted very nicely to magnetic manipulation. In other words, a small quantity of really hot gas, that acted as a diaphram. Pretty much ideal moving mass.

But plasma, while pretty, is, um, messy for home environments. Makes a real good tweeter, though. And you can get a suntan at the same time...

[ScottMayo]

http://www.nutshellhifi.com/library/speaker-design1.html

Might be of interest.

[JeffB]

Thanks for the link ScottMayo.  A great read.

[_scotty_]

ctviggen, unfortunately metal cone drivers are about midpack when it
comes to MMS. A quick check of the Madisound website shows this.
Here are links to four different manufacturers of " 7in. drivers" which illustrate my point. The SDs are close to the same for all drivers :
Accuton driver no.C95-T6  http://www.madisound.com/accuton.html
Skaaning driver no.SK130-308  http://www.madisound.com/skaaning.html
Seas driver no. W18EX001  http://www.madisound.com/pdf/seas/e017.pdf
Hi-Vi driver no. F6  http://www.madisound.com/pdf/hivi/f6.pdf
Metal cone drivers are popular with the consumer and some designers use them but not because the MMS is lower than drivers with cones made from
other  materials.
Scotty

[Porcupine]

ScottMayo, I went to that link and to my surprise it is essentially the same document I found on my computer's hard drive last week. So I read that thoroughly just last week lol. The version on my computer was 10 years old though but I guess people still look at it. (10 years ago was when I bought my speaker system. This month is when I bought my second. So during both periods I temporarily did what speaker research I could, made my purchase, then was happy for a time).

I also tried to find Infinity EMIT-R ribbon tweeter white paper specifications online this month and had no luck. I know that information was available 10 years ago. I looked on my computer's hard drive for it but apparently 10 years ago I was too stupid to have saved it! Grrr! ;D If anyone has the EMIT-R white papers file I'd love to get a copy.

[_scotty_]

Porcupine, here are some links to some information that may be of interest to you.   http://ldsg.snippets.org/idx.php3
http://www.e-speakers.com/
http://www.expolinear.de/produkte/chassis/baendchen/index.html
http://www.linkwitzlab.com/
http://www.swanspeaker.com/drivers/buglelist.asp?type=10
Scotty

[ScottMayo]

I also tried to find Infinity EMIT-R ribbon tweeter white paper specifications online this month and had no luck. I know that information was available 10 years ago. I looked on my computer's hard drive for it but apparently 10 years ago I was too stupid to have saved it! Grrr! ;D If anyone has the EMIT-R white papers file I'd love to get a copy

I don't have the white paper, but I do have some EMIT tweeters I might be willing to part with. I have an aging pair of Infinity QLS-1's that I occasionally flirt with selling off as parts (or even intact). It would mean buying RM-40's to replace them, so I'd have to charge top dollar for the QLS-1's...  

[Porcupine]

I already have speakers with EMIT-Rs,  thanks though.