I’m going a bit OT here, but this is an observation I see often, and it makes me scratch my head a bit. I certainly don't mean to pick on Thoriated or anyone else in particular, so no offense at all, guys, I just think the idea needs addressing. It seems to be one of those “common knowledge” things in audio circles--possibly summed up as: “Anything obstructing or constricting a cone’s back wave, whether basket member or motor, degrades performance by creating efficiency-robbing constriction or reflecting energy back toward the cone.”
This seems to make fine common sense until one considers how sound waves actually interact with obstructions. Let’s talk about reflections first. In actual fact, an obstruction must be at least a quarter wavelength from the diaphragm and at least a quarter wavelength wide to begin to create a reflection.
So let’s take a big, fat ceramic-magnet woofer motor for example. At maybe 7” across, it would shadow the cone in a 2” wide ring around a typical 3” voice coil. Let’s also say it’s about 2” back from the cone. Well, 2” becomes acoustically relevant (a quarter wavelength) at about 1.6KHz. Who runs their big woofers that high? It’s even harder to make a case for basket legs causing reflections since they’re typically less than an inch wide and located closer to the cone than the magnet. In our worst-case woofer, they might start reflecting at somewhere north of 3KHz.
Regarding overall constriction of the rear wave and possible effects on efficiency, it might be useful to consider another transducer type—the compression driver—that commonly uses 10:1 constriction to actually increase efficiency over a certain passband.
It's fine if folks just like the sleek looks of open baskets and slim motors, I’d just like to point out that other approaches are equally valid. In fact, basket constrictions can be used to great effect to accomplish some very cool things acoustically that I don’t want to go too much into detail on right now. Look at the Lowther EX4 and the now discontinued Babb Lorelei for some ideas of what I mean.
Sadly, though, anyone who comes out with anything but a very open basket these days has to fight upstream against flawed “common knowledge”--a marketing nightmare.
Open areas in woofer baskets are needed
There may be few actual reflections off of motor magnets for woofers and possibly even midranges. However, open baskets are not marketing hype. The real issue in this area is constriction and it is never a benefit for a midrange, midwoofer or woofer.
A constricted opening is a port. Ports have resonance due to being a mass of air with a compliance at the exit of the port. It's a resonator, with one for each basket opening. The newer, large openings in baskets provide a definite benefit, especially if thick baffles are used. The effects are easily measured and at times are not small.
An acoustic reflection does not have to be precisely a quarter wavelength away. The influence of a reflection is based on the phase of the reflection and will have a graduated response based on the phase angle of the reflection relative to the direct signal phase at the back of the cone. The peak interference will be centered at the frequency that is a quarter wavelength away, but it is a distributed phenomenon.
If a resonance is in the area of the stop-band, then the reflection impact will not be symmetric due to the stop-band influence on the originating signal.
An acoustic reflection also definitely does not have to be a quarter wavelength in width to reflect as a resonance. All you need do is look at the reflections in tweeter pole-piece vents and the frequencies impacted to observe this. The energy is going to reflect no matter this "width", but the relative impact of it may be altered by it.
dlr
There may be few actual reflections off of motor magnets for woofers and possibly even midranges. However, open baskets are not marketing hype. The real issue in this area is constriction and it is never a benefit for a midrange, midwoofer or woofer.
A constricted opening is a port. Ports have resonance due to being a mass of air with a compliance at the exit of the port. It's a resonator, with one for each basket opening. The newer, large openings in baskets provide a definite benefit, especially if thick baffles are used. The effects are easily measured and at times are not small.
An acoustic reflection does not have to be precisely a quarter wavelength away. The influence of a reflection is based on the phase of the reflection and will have a graduated response based on the phase angle of the reflection relative to the direct signal phase at the back of the cone. The peak interference will be centered at the frequency that is a quarter wavelength away, but it is a distributed phenomenon.
If a resonance is in the area of the stop-band, then the reflection impact will not be symmetric due to the stop-band influence on the originating signal.
An acoustic reflection also definitely does not have to be a quarter wavelength in width to reflect as a resonance. All you need do is look at the reflections in tweeter pole-piece vents and the frequencies impacted to observe this. The energy is going to reflect no matter this "width", but the relative impact of it may be altered by it.
dlr
Hi DLR,
You are obviously 100% correct that constrictions--specifically with acoustically significant Z dimensions (say, a thick baffle with straight cut)--display Helmholtz behavior that is easily measured. A constriction without an acoustically significant Z dimension would present mostly flow resistance. And then there's the coupled air mass behind the cone. What do they equate to? Acoustic analogs of L, R, and C--very useful tools when deliberately tailored to refine the bandpass behavior of a transducer, not things to be avoided like the plague.
As I mentioned, there are a few reasons I don't want get much deeper into this, but I think you see where I'm going. Acoustic solutions for acoustic problems.
Yes, tweeter pole vents do make themselves known, but you're again referring to a port structure here with Helmholtz behavior in the passband, not as I was to an individual obstruction (basket leg) in the cone's pressure zone. Also, basket windows are far less likely to act as simple resonators. Their geometry is usually very non-uniform and/or their z dimensions are often acoustically insignificant.
Getting back to the question of basket leg reflections, here's a Ripple Tank sim of an obstruction approaching 1/4 wavelength in width and about 2 wavelengths from the source. I've drawn a circle around it to highlight it, and I've noted the approx. wavelength beside it. Note that even at ~1/4 wavelength wide, the perturbations (reflections) it causes are very minor.
You are obviously 100% correct that constrictions--specifically with acoustically significant Z dimensions (say, a thick baffle with straight cut)--display Helmholtz behavior that is easily measured. A constriction without an acoustically significant Z dimension would present mostly flow resistance. And then there's the coupled air mass behind the cone. What do they equate to? Acoustic analogs of L, R, and C--very useful tools when deliberately tailored to refine the bandpass behavior of a transducer, not things to be avoided like the plague.
As I mentioned, there are a few reasons I don't want get much deeper into this, but I think you see where I'm going. Acoustic solutions for acoustic problems.
Yes, tweeter pole vents do make themselves known, but you're again referring to a port structure here with Helmholtz behavior in the passband, not as I was to an individual obstruction (basket leg) in the cone's pressure zone. Also, basket windows are far less likely to act as simple resonators. Their geometry is usually very non-uniform and/or their z dimensions are often acoustically insignificant.
Getting back to the question of basket leg reflections, here's a Ripple Tank sim of an obstruction approaching 1/4 wavelength in width and about 2 wavelengths from the source. I've drawn a circle around it to highlight it, and I've noted the approx. wavelength beside it. Note that even at ~1/4 wavelength wide, the perturbations (reflections) it causes are very minor.
Attachments
Most of that's pretty standard
My points were two-fold. First, there may be some specific advantages for a specific driver to incorporate some kind of resonance, but the typical driver has no such need. Past drivers are replete with poorly designed baskets that did indeed introduce resonances that affected the passband, though the true nature was not evident to many.
Your statement here
Specialty driver manufacturers, of which I am unaware so please provide some direct links if you have them, should be able to sufficiently explain specifically why they are designed as they are.
The fact that the majority of drivers would and most did suffer from bad baskets is not flawed thinking. Rather the other specialty driver makers simply have to do a better job of their own marketing to distinguish themselves. There's no flaw involved.
Second, I wasn't thinking in terms of basket reflections, just the comment about the width that seemed to be generalized. The basket legs are made narrow, but strong primarily in order to reduce the Helmholtz resonance so often exhibited in the past. I agree on your reflection point WRT to basket legs, I have found little evidence of reflections on the interior sections of the older, wider legs. There is no disadvantage, however, to making open, narrow-legged baskets that I'm aware of. Acoustic solution to an acoustic problem.
It really doesn't matter that people thought that the problem was reflections off of the leg or the motor rather than a Helmholtz resonance of the air through the openings, they were phenomena related to the basket construction and the baffle cutouts. The problem was real, not imagined. Open baskets pretty much minimize this. Why would a manufacturer NOT advertise this aspect?
My points were two-fold. First, there may be some specific advantages for a specific driver to incorporate some kind of resonance, but the typical driver has no such need. Past drivers are replete with poorly designed baskets that did indeed introduce resonances that affected the passband, though the true nature was not evident to many.
Your statement here
is a bit mis-guided, I think. The "common knowledge" is perfectly valid for most drivers. Acoustic solutions (better baskets) for acoustic problems (Helmholtz resonance inducements).
Specialty driver manufacturers, of which I am unaware so please provide some direct links if you have them, should be able to sufficiently explain specifically why they are designed as they are.
The fact that the majority of drivers would and most did suffer from bad baskets is not flawed thinking. Rather the other specialty driver makers simply have to do a better job of their own marketing to distinguish themselves. There's no flaw involved.
Second, I wasn't thinking in terms of basket reflections, just the comment about the width that seemed to be generalized. The basket legs are made narrow, but strong primarily in order to reduce the Helmholtz resonance so often exhibited in the past. I agree on your reflection point WRT to basket legs, I have found little evidence of reflections on the interior sections of the older, wider legs. There is no disadvantage, however, to making open, narrow-legged baskets that I'm aware of. Acoustic solution to an acoustic problem.
It really doesn't matter that people thought that the problem was reflections off of the leg or the motor rather than a Helmholtz resonance of the air through the openings, they were phenomena related to the basket construction and the baffle cutouts. The problem was real, not imagined. Open baskets pretty much minimize this. Why would a manufacturer NOT advertise this aspect?
Ok, I guess we're basically agreeing here.
I don't at all dispute that poorly designed baskets--ancient and recent--and thoughtlessly done baffle cutouts have caused real problems. It's akin to tossing a few random elements into a electrical crossover network.
And there's nothing wrong with putting a very open basket on your driver products and highlighting the fact that it isn't a horrible design with spurious resonances.
What I don't like is the implicit (sometimes explicit) idea that anything but a wide-open basket is bad. This idea closes people's minds to the possibility of using deliberately designed-in acoustic R, L, and C elements to improve performance in ways that would otherwise require additional electrical crossover elements, and in other ways beyond the reach of electrical networks.
Thanks for helping me clarify this if it was unclear.
I don't at all dispute that poorly designed baskets--ancient and recent--and thoughtlessly done baffle cutouts have caused real problems. It's akin to tossing a few random elements into a electrical crossover network.
And there's nothing wrong with putting a very open basket on your driver products and highlighting the fact that it isn't a horrible design with spurious resonances.
What I don't like is the implicit (sometimes explicit) idea that anything but a wide-open basket is bad. This idea closes people's minds to the possibility of using deliberately designed-in acoustic R, L, and C elements to improve performance in ways that would otherwise require additional electrical crossover elements, and in other ways beyond the reach of electrical networks.
Thanks for helping me clarify this if it was unclear.
I'm interested in the driver details
Bill, I was serious when asking about any links to specialty drivers that might use some special design details the way you described. I'm not interested in anything such as a compression driver, but any that might be more like a standard dynamic driver that utilizes something of this nature would be interested to read about. I've not seen any such as that.
Bill, I was serious when asking about any links to specialty drivers that might use some special design details the way you described. I'm not interested in anything such as a compression driver, but any that might be more like a standard dynamic driver that utilizes something of this nature would be interested to read about. I've not seen any such as that.
Hi Dave,
Public info about this type of thing is pretty scarce.
I mentioned the discontinued Babb Lorelei, which has since been reborn as the DC Gold Lorelei. It uses about a 3:1 tuned basket constriction and damping material behind the cone and a tuned perforated grill on the front. Good luck finding technical info. I haven't seen any since the original discussions with Alan Babb on the fullrangedriver.com forum a number of years ago.
Then there's the Lowther EX4, featured on the Lowther website. Again, I haven't seen much technical discussion about its back chamber, though it may be out there. I haven't taken much time to really look. Their perforated phase plug is another related example of what I'm talking about.
And, in the nothing-new-under-the-sun category, there's the Eckmiller (scroll down to the bottom) from the '30s-'40s that used extreme basket constriction to aperiodically damp a low-loss suspension.
If you're an AES member, you can also look up Olsen's paper on using basket constriction and a two-driver array to accomplish an acoustic second-order gradient loudspeaker.
There may be other examples I've forgotten...
Public info about this type of thing is pretty scarce.
I mentioned the discontinued Babb Lorelei, which has since been reborn as the DC Gold Lorelei. It uses about a 3:1 tuned basket constriction and damping material behind the cone and a tuned perforated grill on the front. Good luck finding technical info. I haven't seen any since the original discussions with Alan Babb on the fullrangedriver.com forum a number of years ago.
Then there's the Lowther EX4, featured on the Lowther website. Again, I haven't seen much technical discussion about its back chamber, though it may be out there. I haven't taken much time to really look. Their perforated phase plug is another related example of what I'm talking about.
And, in the nothing-new-under-the-sun category, there's the Eckmiller (scroll down to the bottom) from the '30s-'40s that used extreme basket constriction to aperiodically damp a low-loss suspension.
If you're an AES member, you can also look up Olsen's paper on using basket constriction and a two-driver array to accomplish an acoustic second-order gradient loudspeaker.
There may be other examples I've forgotten...
tomtt said:
In general, I believe so... More importantly, I believe that the lack of sales points does NOT indicate quality. Esoteric little brands that sell 100 speakers a year do not indicate quality of reproduction.
See, you're arguing about preference, and that's 100% subjective. What you like is obviously not what I like. So you and I will never agree.
But we CAN use the marketplace to determine what most people like, and from that we can infer a general suitability of a technology/product/method in terms of quality for the population at a whole.
The audio world does exist beyond just you and me!
But I see you dodged the points I made, so I'll ask you to address them again:
Why use AlNiCo when neo is available?
1. Neo doesn't have the problems of demagnetization
2. Neo can provide more flux per cross sectional area than AlNiCo
3. Neo isn't as brittle as AlNiCo
AlNiCo really doesn't have ANY advantage over neo, and the only one it has over ceramic is the same that neo has - a lot more flux per cross sectional area. It costs more than the other options, demagnetizes much more readily, can't stand flux compression, and is more brittle.
AlNiCo works well in small niche markets - high efficiency, low power. But outside that realm it's seriously inferior, which is why it's just not used (outside a few MI applications where the compression is actually desired as a sonic trait).
Why use AlNiCo rather than neo? Knowing that N45SH handles as much temperature as any voice coil could come close to reaching and still not melt, and the fact that it is much stronger than just about any grade of AlNiCo, and it's readily available, what's the draw to AlNiCo?
Personally, I do not buy in to the myth of AlNiCo, or - what I believe drives this myth - the belief that high efficiency designs from years ago represented the pinnacle of reproduction. Compressed, limited bandwidth, uneven response. Loud with a few Watts, sure - but at a cost that - to me - is unacceptable.
I have heard more than a few high efficiency systems. Were they nice to listen to? Some were, sure. But accurate or lifelike? Outside of dynamics, not a chance.
Give me some nice linear, well-behaved speakers that can handle a few hundred Watts and I'm set...
OTOH, Bose is proof that the existence of sales points certainly has nothing to do with quality.
One day, if I get around to it, I may design a high efficiency speaker, with an alnico magnet and an underhung VC to obviate Alnico's traditional weakness. As a special feature, I would also specify VC wire with a very low resistive tempco to complement the uniquely low flux tempco of alnico. I think any resulting design challenges are readily surmountable and the result with the appropriate cone technology would be a truly unique bass or bass/midrange driver.
I don't see it having an Xmax such that it can go into the kitchen and fetch you a beer, but 7-10mm linear one way should be plenty for any coherent listening experience.
One day, if I get around to it, I may design a high efficiency speaker, with an alnico magnet and an underhung VC to obviate Alnico's traditional weakness. As a special feature, I would also specify VC wire with a very low resistive tempco to complement the uniquely low flux tempco of alnico. I think any resulting design challenges are readily surmountable and the result with the appropriate cone technology would be a truly unique bass or bass/midrange driver.
I don't see it having an Xmax such that it can go into the kitchen and fetch you a beer, but 7-10mm linear one way should be plenty for any coherent listening experience.
Dan Wiggins has written:
"The audio world does exist beyond just you and me!"
Dan is correct of course, which is why I have decided to respond. Part of my responsibilities as the "World's Foremost Authority" is to occasionally step in and resolve, correct or instruct in matters of a technical or aesthetic nature. To do otherwise would constitute a flagrant abrogation of Audio Authority!
"But I see you dodged the points I made, so I'll ask you to address them again:
Why use AlNiCo when neo is available?
1. Neo doesn't have the problems of demagnetization
2. Neo can provide more flux per cross sectional area than AlNiCo
3. Neo isn't as brittle as AlNiCo
AlNiCo really doesn't have ANY advantage over neo, and the only one it has over ceramic is the same that neo has - a lot more flux per cross sectional area. It costs more than the other options, demagnetizes much more readily, can't stand flux compression, and is more brittle."
Dan is again correct, at least as far as the attributes he mentions, however he has failed to mention the theoretical advances that our team has developed to take neo to the next level.
While many of the details of our work contains information that falls under the Atomic Energy Commission's Industrial Intelligence Security Secret Directive #26 (IISS DIRT 26), a few of the general aspects can be revealed without compromising National Security Protocols.
These are:
1. Neo can be subjected to Hypermagnetism in an intensive Multi-atmospheric vacuum
until molecular density packing stabilizes.
2. Flux density is further improved by use of a Transmogrified Vortex Regeneration Intensifier
Circuit which utilizes our purpose built Bidirectional Diodes that
(Section Redacted per IISS DIRT 26)
been observed to effectively cancel Electron Over-Oscillation Axial Spin which contributes to a seldom documented and little known form of Tubular Phase Shift.
I believe that this explanation illustrates the advantages not only of the current form of NEO but also details the tremendous advances that are available through the use of our NEO/2.
I could continue with this discussion, but evidently some guests have just arrived in several Black Helicopters. I'm certain that the Official Press Release was scheduled for tomorrow, so I'll have to go for now and clear this up.
Best Regards,
( Name Redacted per IISS DIRT 26)
"The audio world does exist beyond just you and me!"
Dan is correct of course, which is why I have decided to respond. Part of my responsibilities as the "World's Foremost Authority" is to occasionally step in and resolve, correct or instruct in matters of a technical or aesthetic nature. To do otherwise would constitute a flagrant abrogation of Audio Authority!
"But I see you dodged the points I made, so I'll ask you to address them again:
Why use AlNiCo when neo is available?
1. Neo doesn't have the problems of demagnetization
2. Neo can provide more flux per cross sectional area than AlNiCo
3. Neo isn't as brittle as AlNiCo
AlNiCo really doesn't have ANY advantage over neo, and the only one it has over ceramic is the same that neo has - a lot more flux per cross sectional area. It costs more than the other options, demagnetizes much more readily, can't stand flux compression, and is more brittle."
Dan is again correct, at least as far as the attributes he mentions, however he has failed to mention the theoretical advances that our team has developed to take neo to the next level.
While many of the details of our work contains information that falls under the Atomic Energy Commission's Industrial Intelligence Security Secret Directive #26 (IISS DIRT 26), a few of the general aspects can be revealed without compromising National Security Protocols.
These are:
1. Neo can be subjected to Hypermagnetism in an intensive Multi-atmospheric vacuum
until molecular density packing stabilizes.
2. Flux density is further improved by use of a Transmogrified Vortex Regeneration Intensifier
Circuit which utilizes our purpose built Bidirectional Diodes that
(Section Redacted per IISS DIRT 26)
been observed to effectively cancel Electron Over-Oscillation Axial Spin which contributes to a seldom documented and little known form of Tubular Phase Shift.
I believe that this explanation illustrates the advantages not only of the current form of NEO but also details the tremendous advances that are available through the use of our NEO/2.
I could continue with this discussion, but evidently some guests have just arrived in several Black Helicopters. I'm certain that the Official Press Release was scheduled for tomorrow, so I'll have to go for now and clear this up.
Best Regards,
( Name Redacted per IISS DIRT 26)
Ex4..
Hi fellows,
I had a look at the EX4 on the following link: http://www.lowtherloudspeakers.co.uk/EXseries.html
it appears to me, that both the backside with what to me seem to be foam stuffing inside behind the holes as well as the "phase plugg" with holes (which I actually read on another link that it is actually filled with foam damping material), that this is kind of a variovent construction which is good for damping out resonaces but also comes with some efficiency losses.
The choice of damping material also reveals that they want the the damping system to act from around midrange audio frequencies and upwards.
I think I still would chose an open basket construction at least for the backside construction.
Also I think we could make the pole plate conical so it wont reflect anything back into the direction of the backside of the cone even if we would use a 7" magnet.
What I am saying explicitly is that a conical shape of the poleplate of the magnet motor in a loudspeaker element construction where the perpendicular line from said pole plates surface is of such an angel that it points beyond the outer sphere of the said loudspeakers cone will not reflect any audio energy back to the backside of said cone.
Cheers Michael
Hi fellows,
I had a look at the EX4 on the following link: http://www.lowtherloudspeakers.co.uk/EXseries.html
it appears to me, that both the backside with what to me seem to be foam stuffing inside behind the holes as well as the "phase plugg" with holes (which I actually read on another link that it is actually filled with foam damping material), that this is kind of a variovent construction which is good for damping out resonaces but also comes with some efficiency losses.
The choice of damping material also reveals that they want the the damping system to act from around midrange audio frequencies and upwards.
I think I still would chose an open basket construction at least for the backside construction.
Also I think we could make the pole plate conical so it wont reflect anything back into the direction of the backside of the cone even if we would use a 7" magnet.
What I am saying explicitly is that a conical shape of the poleplate of the magnet motor in a loudspeaker element construction where the perpendicular line from said pole plates surface is of such an angel that it points beyond the outer sphere of the said loudspeakers cone will not reflect any audio energy back to the backside of said cone.
Cheers Michael
Faraday rings versus Super Linear
Hi,
reading about faraday ring motor construction available from several manufacturers I understand that this lowers VC inductance and decreases 2nd harmonics.
Reading about SLMM Super Linear motor construction available from ATC I understand that this increases VC inductance and decreases 3rd harmonics.
http://www.atc.gb.net/technology/Su...r_Technical.zip
"http://www.atc.gb.net/technology/Super_Linear_Technical.zip"
judging from what is available on harmonic distortion graphs, both attempts seems to work as intended though that is pretty confusing to me.
Anyone who can give a good explanation?
Are there any other companies than ATC using a technique to lower the more serious 3rd harmonics?
Greetings
Michael
Hi,
reading about faraday ring motor construction available from several manufacturers I understand that this lowers VC inductance and decreases 2nd harmonics.
Reading about SLMM Super Linear motor construction available from ATC I understand that this increases VC inductance and decreases 3rd harmonics.
http://www.atc.gb.net/technology/Su...r_Technical.zip
"http://www.atc.gb.net/technology/Super_Linear_Technical.zip"
judging from what is available on harmonic distortion graphs, both attempts seems to work as intended though that is pretty confusing to me.
Anyone who can give a good explanation?
Are there any other companies than ATC using a technique to lower the more serious 3rd harmonics?
Greetings
Michael
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