Hi All,
Really enjoying this thread on mid/base driver freq ranges. I think most people participating here have similar tastes and desires as do I.
We need a single driver that can reproduce the human voice, male and female in its entire range.
I do not know why OEMs cannot make a 160-180 mm size driver with flat response along with a smooth roll off. the roll off ideally the same rate on axis well as 60 degrees off axis at 3-4Khz with fair eff at around 90dB at 1W.
Directivity being the key, means there is a ideal cone shape and material to accomplish this task. It has been done before by dynaudio but did not prove to be too popular. Too early for its time I guess. But alas it is no longer available. I have used this beauty and think it is the best midrange bar none. The model is the 17M-75. I think if anybody remembers it or has used it properly, they would certainly agree. I think it was a major redesign of the the venerable 17W-75 version. The main difference was the poly cone shape was completely concave and quite shallow with a stiffer rubber surround. Not too sure, but the VC and gap was modified as well.
The hi end response was beautifully smooth that you really didn't need a LP crossover. Inband Distortion was measured to very low as well. The only tradeoff of the redesign was higher fs at 74 Hz and little less at Xmax 5,5 mm. also Qt was higher at 1.02. I think the only one to come close is the Quenze unit.
Really enjoying this thread on mid/base driver freq ranges. I think most people participating here have similar tastes and desires as do I.
We need a single driver that can reproduce the human voice, male and female in its entire range.
I do not know why OEMs cannot make a 160-180 mm size driver with flat response along with a smooth roll off. the roll off ideally the same rate on axis well as 60 degrees off axis at 3-4Khz with fair eff at around 90dB at 1W.
Directivity being the key, means there is a ideal cone shape and material to accomplish this task. It has been done before by dynaudio but did not prove to be too popular. Too early for its time I guess. But alas it is no longer available. I have used this beauty and think it is the best midrange bar none. The model is the 17M-75. I think if anybody remembers it or has used it properly, they would certainly agree. I think it was a major redesign of the the venerable 17W-75 version. The main difference was the poly cone shape was completely concave and quite shallow with a stiffer rubber surround. Not too sure, but the VC and gap was modified as well.
The hi end response was beautifully smooth that you really didn't need a LP crossover. Inband Distortion was measured to very low as well. The only tradeoff of the redesign was higher fs at 74 Hz and little less at Xmax 5,5 mm. also Qt was higher at 1.02. I think the only one to come close is the Quenze unit.
Maybe someone can help my ignorance here. I am of the belief that directivity was dominated by cone diameter. Above the frequency where the diameter equals the wavelength you will get nodes and standing waves. As far as I know, the shape of these can probably be influenced by the cone angle but you can not make them go away.
So if I am correct, dispersion is affected very little below this frequency and will be sort of lousy above it. For a 6" (150mm) midrange dispersion will show lobing characteristics or become poor above about 2,200 Hz. I do understand that the devil is in the details, but it seems that for a given size driver this effect will be largely similar.
As I have posted before the Quenze units are spectacular but not cheap.
So if I am correct, dispersion is affected very little below this frequency and will be sort of lousy above it. For a 6" (150mm) midrange dispersion will show lobing characteristics or become poor above about 2,200 Hz. I do understand that the devil is in the details, but it seems that for a given size driver this effect will be largely similar.
As I have posted before the Quenze units are spectacular but not cheap.
Directivity in theory is mostly influenced after the transition from a pure piston movement to other modes. This transition certainly cannot be abrupt as I would venture a guess, so shape should influence the transition chacteristics more or less.
Remember wizzer cones? Then look at some of the modern designs that have bullet shaped centers. I notice the smoothest rolloff responses are due to some drivers simple concave shapes. Not like the majority of drivers that use a dome dust cap. I dunno just my observations. I'm sure cone material stiffness and energey storage chacteristics come to play during the transition as well. What do you think?
Remember wizzer cones? Then look at some of the modern designs that have bullet shaped centers. I notice the smoothest rolloff responses are due to some drivers simple concave shapes. Not like the majority of drivers that use a dome dust cap. I dunno just my observations. I'm sure cone material stiffness and energey storage chacteristics come to play during the transition as well. What do you think?
I don't have enough knowledge to argue the point. I think wizzer cones had a steeper angle to prevent cone breakup (i.e. they were stiffer by being a more acute angle) rather than that shape to improve directivity.
And you are certainly right that the transistion from piston to other modes is not an instantaneous event. I do not know how narrow the transistion frequency range is. Also remember that B & W brag about their intentional multiple mode midrange cone flex (I believe they claim it never operates as a pure piston)
The bullet shapped centers are called phase plugs, I presume because the driver has a flatter phase response, I don't know how to make a change in phase resopnse that would not affect frequency respose as well.
So as you can see, there is much, for me at least to learn.
An aside, are there any wizzer cones used on the more exotic cone materials; polypropolyne, kevlar, carbon fiber, etc?
And you are certainly right that the transistion from piston to other modes is not an instantaneous event. I do not know how narrow the transistion frequency range is. Also remember that B & W brag about their intentional multiple mode midrange cone flex (I believe they claim it never operates as a pure piston)
The bullet shapped centers are called phase plugs, I presume because the driver has a flatter phase response, I don't know how to make a change in phase resopnse that would not affect frequency respose as well.
So as you can see, there is much, for me at least to learn.
An aside, are there any wizzer cones used on the more exotic cone materials; polypropolyne, kevlar, carbon fiber, etc?
Directivity and constant phase loading with transition from one driver to another with multiple sources ie MTM with the tweeter being horn loaded. Now splain how that one works with a 3rd order xover. Seems like it would be important for the mid to be smooth in that region although im sure phase and group delay is a problem there. My brain hurts now 
The Pass Rushmore has a very small driver for the upper midrange, what I find very reasonable in terms of dispersion. Does anybody know which? Isophon?
http://www.passlabs.com/speakers/rushmore.htm
http://www.passlabs.com/speakers/rushmore.htm
Quote from the Passlabs site:
This is an exceptionally dynamic and tonally balanced active four-way listening system featuring a 15 inch woofer, 10 inch lower midrange, 5 inch upper midrange and a 4 inch ribbon tweeter.
Quote from Rushmore white paper:
The result is a four-way system, with a 15 inch deep bass driver, a 10 inch mid bass driver, and a 6 inch midrange, and a ribbon tweeter. The bass driver is 97 dB/watt efficient, and the remaining drivers are at least 98 dB/watt. The cone drivers are all high quality professional drivers rated at high wattage levels which by coincidence work very well together
So it's a 5" or 6" professional midrange driver with at least 98dB/watt,
Maybe the B&C 6PE13? (http://www.bcspeakers.com/download/prodotti/PDF/more/143.pdf)
This is an exceptionally dynamic and tonally balanced active four-way listening system featuring a 15 inch woofer, 10 inch lower midrange, 5 inch upper midrange and a 4 inch ribbon tweeter.
Quote from Rushmore white paper:
The result is a four-way system, with a 15 inch deep bass driver, a 10 inch mid bass driver, and a 6 inch midrange, and a ribbon tweeter. The bass driver is 97 dB/watt efficient, and the remaining drivers are at least 98 dB/watt. The cone drivers are all high quality professional drivers rated at high wattage levels which by coincidence work very well together
So it's a 5" or 6" professional midrange driver with at least 98dB/watt,
Maybe the B&C 6PE13? (http://www.bcspeakers.com/download/prodotti/PDF/more/143.pdf)
Why isint there more recommendations on the WR125 from 300-3k or higher, the xbl2 motor topology keep distortion extreemly low, as Zaphs tests have shown, the response is very nice, and prices are at $100/pr.
Sure some of the others have more cone area and the sort, but j/w really why there isint more recommendations for the WR125? I ordered a pair to go with some RS225's and LPG 26nafm's.
Distortion measurements show that there is minor 2nd HD at -55db at 2k, and alittle 3rd HD spurt around 800hz thats still -60db. most 3rd order dosent begin till ~100hz and that rises with the imp rise, but still usable from 200- 6/8k with a little EQ bumping at 4k. Other than that its really flat response, and a pretty clean spectral but a little energy storage and sens is a mere 85-86db or so, but if you don't need a really high sensativity network then why not use this driver?
I mean i can see if your running tube amps or something but power is cheap enough today that sensativity theoretically shouldn't really kill you, unless your midbass and tweets are like 95db+, then some padding could help.
Seems to me the best bet for the price conscious person, why no more recommendations, when alot of people rave about the jordan, which iirc is much more expensive.
Anyway J/w really. I can't wait to try my pair out.
Sure some of the others have more cone area and the sort, but j/w really why there isint more recommendations for the WR125? I ordered a pair to go with some RS225's and LPG 26nafm's.
Distortion measurements show that there is minor 2nd HD at -55db at 2k, and alittle 3rd HD spurt around 800hz thats still -60db. most 3rd order dosent begin till ~100hz and that rises with the imp rise, but still usable from 200- 6/8k with a little EQ bumping at 4k. Other than that its really flat response, and a pretty clean spectral but a little energy storage and sens is a mere 85-86db or so, but if you don't need a really high sensativity network then why not use this driver?
I mean i can see if your running tube amps or something but power is cheap enough today that sensativity theoretically shouldn't really kill you, unless your midbass and tweets are like 95db+, then some padding could help.
Seems to me the best bet for the price conscious person, why no more recommendations, when alot of people rave about the jordan, which iirc is much more expensive.
Anyway J/w really. I can't wait to try my pair out.
i think the key to a great midrange is finding a light and rigid cone material, one that is not prone to cone breakups. such as diamond or metallic hydrogen. the latter we can go to planet Jupiter and pick some up, it hasn't been discovered on planet Earth yet but they detected it on Jupiter. It's supposed to be very light but rigid, and like diamond is in a metastable state. the cone doesn't have to be overly light since higher BL can make up for it. Inductance should be low as discussed in the other ongoing thread. massive amounts of copper can be used to lower inductance.
a midrange doesn't need much displacement so we can get rid of the rubber surrounds altogether, and allow the cone to rest on foam/felt underneath the cone. this gets rid of nonlinear distortion coming from the surrounds, that "flexing".
So my recommendation for "best cone for 150-3000Hz" would be diamond. You can build a machine and make some, refer to the 2006 discovery of the new technique of synthesizing large pure diamonds. diamond's great thermal conductivity properties (way better than copper or silver) will allow for far greater power handling as well so long as teh voice coil is designed to transmit heat up to the diamond.
a midrange doesn't need much displacement so we can get rid of the rubber surrounds altogether, and allow the cone to rest on foam/felt underneath the cone. this gets rid of nonlinear distortion coming from the surrounds, that "flexing".
So my recommendation for "best cone for 150-3000Hz" would be diamond. You can build a machine and make some, refer to the 2006 discovery of the new technique of synthesizing large pure diamonds. diamond's great thermal conductivity properties (way better than copper or silver) will allow for far greater power handling as well so long as teh voice coil is designed to transmit heat up to the diamond.
cotdt said:
Why use foam for the cone suspension? Magnetic levitating suspensioin driven by superconductors would be much more linear and not prone to suspension rot. The possibilities of cone deviations approaching inches seem quite possible. You could use the same liquid Nitrogen resevoir used for the metallic hydrogen cone for the super conducting magnets. Eventually someone will invent a liquid nitrogen coolant that contains special ingredients to improve sound quality, musk oil or perhaps natural exotic herbs are probably a good place to start.
If you used super conductors for the voice coil just imagine the amplifier power you could have, most good amps double their power every time you halve the impedance, just imagine how much power they would deliver into zero Ohms.
This is great stuff, form a corporation sell stock.
hermanv said:
I could not figure out what you are talking about, but how would it close the gap? Seems like air will leak with your idea. Currently we use foam or rubber surrounds that is a part of the cone and is very non-pistonic. It flexes causing a notable amount of nonlinear distortion that has been measured. But a midrange needs very little xmax, so you can simply place the cone on a layer of felt or foam right underneath. This should still allow for around 2mm of xmax. That way the entire cone is pistonic and nonlinear distortion will be minimized.
I'm thinking of using a Seas Excel W18NX motor and combining it with my own diamond cone ("surroundless") for my future speakers. It's got a great BL and LE curve. Seems like a very low-distortion motor for my use, the best motor I know of right now that has been measured.
Why there are many valid driver designs
No matter what form of spring is used on a cone, foam or rubber, the stiffness is not linear with deflection. So at some point the cone starts to behave in a non-piston mode. The cone will flex from its own inertia at some high frequency so a true pistonic motion cone that covers a broad spectrum is virtually impossible to build. Certainly limiting X max will limit flexure, unfortunately it also limits loudness.
Drivers exists with no surround or spring on the outer cone edge, in these designs the cone must flex. All this is just a matter of degree. Flexing the cone is not intrisically bad. There are just issues, example it important to keep any flex linear and not allow the cone to "oil can". (You know those oils dispensers where you press the bottom and it snaps or clicks between two stable positions).
One of the reasons horn speakers still exisit is that their very small diameter cones can be made to act much more like pistons but the amount of air that is moved (loudness) is small so a large cone coupler shape is used to improve their efficiency. Horns like all other drivers have their own set of problems.
The trick to designing a driver is in selecting which set of compromises to enhance or minimize, currently no perfect design exisits or is even possible with todays technology.
This is why there is still art to driver design, if it was a simple mechnical problem, a decent computer program would tell you exactly how to build a driver.
Similarly the best driver for a two way or three way design is likely to be very different. Cone materials that are very stiff like metals or ceramics tend to demand very steep crossovers because if the crossover is of a low order, significant high frequency energy will hit the cone forcing it to flex, since it wasn't designed to flex, the resultant sound will in most cases be quite unpleasant.
So as a result of all this, many different approaches to speaker design exisit, all have some strengths all have some weaknesses. Carefull choice of compatible drivers will make for a good multiway speaker but those drivers may not be inexpensive.
No matter what form of spring is used on a cone, foam or rubber, the stiffness is not linear with deflection. So at some point the cone starts to behave in a non-piston mode. The cone will flex from its own inertia at some high frequency so a true pistonic motion cone that covers a broad spectrum is virtually impossible to build. Certainly limiting X max will limit flexure, unfortunately it also limits loudness.
Drivers exists with no surround or spring on the outer cone edge, in these designs the cone must flex. All this is just a matter of degree. Flexing the cone is not intrisically bad. There are just issues, example it important to keep any flex linear and not allow the cone to "oil can". (You know those oils dispensers where you press the bottom and it snaps or clicks between two stable positions).
One of the reasons horn speakers still exisit is that their very small diameter cones can be made to act much more like pistons but the amount of air that is moved (loudness) is small so a large cone coupler shape is used to improve their efficiency. Horns like all other drivers have their own set of problems.
The trick to designing a driver is in selecting which set of compromises to enhance or minimize, currently no perfect design exisits or is even possible with todays technology.
This is why there is still art to driver design, if it was a simple mechnical problem, a decent computer program would tell you exactly how to build a driver.
Similarly the best driver for a two way or three way design is likely to be very different. Cone materials that are very stiff like metals or ceramics tend to demand very steep crossovers because if the crossover is of a low order, significant high frequency energy will hit the cone forcing it to flex, since it wasn't designed to flex, the resultant sound will in most cases be quite unpleasant.
So as a result of all this, many different approaches to speaker design exisit, all have some strengths all have some weaknesses. Carefull choice of compatible drivers will make for a good multiway speaker but those drivers may not be inexpensive.
With a high enough BL the nonlinearity of the foam/rubber surrounds should be negligible, and this would also apply to the surroundless idea. i wouldn't say a true pistonic cone is impossible to build. Have you seen the data for the Accuton C90-T6 which are good to 5kHz? It looks pistonic up to a high frequency using ceramic material cone, and if you look at the properties of diamond, it should be pistonic even furthur. This is demonstrated by the diamond tweeters which have their breakups moved to extremely high in frequency, with the Accuton D20-6's breakup peak at 70kHz! i don't see any compromises here when diamond cones are used. diamond shouldn't flex either, it'll rather shatter before any significant flexing can occur.
If you cross over the midrange at 200Hz, my simulations show that with even 1mm of xmax, things can get deafening loud, so I don't think much xmax is needed for midranges.
i think flexing is bad, because it colors the sound. it introduces linear and nonlinear distortion, and makes everything sound muddy. in the current rigid-cone midranges, it's the surrounds that do all the flexing in the passband of the drivers. i don't understand why they don't remove the surrounds altogether in favor of "surrounds" underneath the cone which acts like a cushion. It can have the same dampening properties of surrounds.
If you cross over the midrange at 200Hz, my simulations show that with even 1mm of xmax, things can get deafening loud, so I don't think much xmax is needed for midranges.
i think flexing is bad, because it colors the sound. it introduces linear and nonlinear distortion, and makes everything sound muddy. in the current rigid-cone midranges, it's the surrounds that do all the flexing in the passband of the drivers. i don't understand why they don't remove the surrounds altogether in favor of "surrounds" underneath the cone which acts like a cushion. It can have the same dampening properties of surrounds.
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