hi folks,
wire stators i've a couple of questions.
1. wire tension how much or little.
2. wire thickness is it important i.e. thick vs thin
3. where do you get wires that will deal with a couple of kv i've been using wire rated for 600v for headphone bias connection but what about the big stuff.
4. why has nobody built a panel with variable stator to diaphram thickness in other words make the s/d? change from 1mm to 2mm along the width of the panel. feed the relevant voltage to the relevant wires to provide the sound required this would in effect do the job of both a wide spaced bass panel and narrow spaced tweeter panel but without the extra construction effort?
wire stators i've a couple of questions.
1. wire tension how much or little.
2. wire thickness is it important i.e. thick vs thin
3. where do you get wires that will deal with a couple of kv i've been using wire rated for 600v for headphone bias connection but what about the big stuff.
4. why has nobody built a panel with variable stator to diaphram thickness in other words make the s/d? change from 1mm to 2mm along the width of the panel. feed the relevant voltage to the relevant wires to provide the sound required this would in effect do the job of both a wide spaced bass panel and narrow spaced tweeter panel but without the extra construction effort?
oublie said:
Since nobody with more experience has chimed in yet, I'll take a stab at this.
1. wire tension: I hold as little tension as possible, just enough to pull the wires straight, while gluing the wires to the cross bars. Remember, whatever tension you are holding will be transferred to the cross bars once the glue has dried and you release the wires from your stretching jig. Too much tension and the crossbars will bend and sometimes come unglued from the spacers.
2. Wire thickness: For me the choice of wire diameter is more a construction/availability choice rather than a performance choice. Thinner wire is cheaper and easier to tension, but you need more wires and your crossbars need to be closer together to provide enough support. I have used between 18 -22 guage solid copper wire with 0.40mm PVC insulation.
As long as 1) the distance from the outside of the insulation to the diaphragm is the same, and 2) the % open area is the same then the SPL output will be quite similar for different wire sizes using the same HV bias and drive voltage. Most people use 40% - 50% open area.
3) Wire insulation: from what I have read, the most important thing is that the insulation be PVC. As insulations go, it has a rather low resistance, so most of the HV bias shows up in the air gap rather than wasted in the insulation; even in high humidity. PVC also has a rather large dielectric constant, so essentially all of the signal drive voltage shows up on the outside of the insulation rather than being wasted crossing it.
A 600V rating works fine since the majority of the voltage is dropping across the air gap to the diaphragm, not the thru the insulation. I prefer irradiated PVC as it is tougher, less prone to being nicked, and doesn't get soft and shrink back when soldering the way the standard soft PVC does.
4) Variable wire spacing can, and has been done, but usually it works out better if separate diaphragms are used for the two spacings. If one diaphragm is used, and you have a section of 1mm spacing that you drive with just high frequencies, and the rest of the panel has 3mm spacing and you drive it with low frequencies, all is well until low frequencies near the fundamental resonance of the diaphragm are reproduced. Then, the whole diaphragm moves with large excursion, even if the signal isn't being sent to the wires driving the 1mm spaced section, the diaphragm here will move with nearly as large excursion as the driven 3mm section; usually hitting the stator wires in the 1mm spaced section.
The other thing to consider is that gaining efficiency for high frequencies is not really the biggest problem for ESLs. Since most ESLs are dipoles, the low frequencies roll off at 6dB per octave. With typical panel widths of 12" - 18" this starts at 300-500Hz. So you need 6dB - 18dB more output at low frequencies than at high frequencies depending how low you plan to have your ESL response go.
Hope this helps...
I second Bolserst's advice, but of course everyone puts their own twist on it. Here's where I might add a few variations to what you've already heard:
1 & 2) I'm leaning toward more wire tension in my current wire stator project, rather than as little as possible, but because I haven't completed my project I don't feel cocky enough to claim you ought to follow my lead. I'm using double build magnet wire with nylon insulation--about 24 AWG and 45% open area. It's taken awhile to devise a satisfactory way to stretch the wires, but I think I've now got it worked out. Anyway, if I were to do it again I'd go with finer wires rather than heavier ones. I think 24 AWG will be fine, but I don't think I'd want to go heavier.
I found that I had all sorts of "why doesn't anyone do it this way?" questions before I built my first or second ESL. Since that time I've found that it often turns out that the reality of trying to construct these things has a way of making some of the more creative solutions seem less than practical. I certainly encourage you to try new and creative solutions--I'm hoping to learn from you!--but I've also found there are also good reasons many people converge on similar solutions to the same problems. Bolserst's advice does a good job of explaining some of the issues, such as those surrounding the variable spacing design. I think you'll find the "without the extra construction effort" part quickly dissipates when you start to carefully consider the design and take all the details into account. On the other hand, if you come up with a creative solution that the rest of us haven't thought of before, by all means share it! We'd be very appreciative. There's no doubt that there's still room for some creative design solutions.
Best of luck,
Few
1 & 2) I'm leaning toward more wire tension in my current wire stator project, rather than as little as possible, but because I haven't completed my project I don't feel cocky enough to claim you ought to follow my lead. I'm using double build magnet wire with nylon insulation--about 24 AWG and 45% open area. It's taken awhile to devise a satisfactory way to stretch the wires, but I think I've now got it worked out. Anyway, if I were to do it again I'd go with finer wires rather than heavier ones. I think 24 AWG will be fine, but I don't think I'd want to go heavier.
I found that I had all sorts of "why doesn't anyone do it this way?" questions before I built my first or second ESL. Since that time I've found that it often turns out that the reality of trying to construct these things has a way of making some of the more creative solutions seem less than practical. I certainly encourage you to try new and creative solutions--I'm hoping to learn from you!--but I've also found there are also good reasons many people converge on similar solutions to the same problems. Bolserst's advice does a good job of explaining some of the issues, such as those surrounding the variable spacing design. I think you'll find the "without the extra construction effort" part quickly dissipates when you start to carefully consider the design and take all the details into account. On the other hand, if you come up with a creative solution that the rest of us haven't thought of before, by all means share it! We'd be very appreciative. There's no doubt that there's still room for some creative design solutions.
Best of luck,
Few
Hi,
1) it depends ,-)
One way is to use stranded litz wire. Since this wire is soft it has to be kept under constant tension.When building the stator frame is sligthly bowed. You will need a stator frame with high mechanical strength and lots of closely distanced supporting points, like the often used louvre. Straigthening the frame tensions and straightens the wires. Acoustat used this method and it is described in Fikier´s little book too. The advantage is that winding the wire is easy because of its softness and it will become perfectly straight when tensioned.
Personally I don´t like the idea of considerably large forces ´stored´ within the wires and frame construction. Using soft wire which has the tendency to wobble around unless the free ´swinging´ distance is very small will lead to ugly optics, which only can be camouflaged with cloth.
The other way is to use single stranded wires. Here tension is applied only to straighten the wires after winding. The tension has to be so high that the copper just starts to ´flow´. The wires straighten perfectly flat. Then You can release tension completely and glue the wires to the supporting structure. Since the wire is hard the distance between supporting points can be larger and allows for optically more pleasing open designs. The possibility of breaking glue joints between wires and support is low because there is no stressing mechanical tension.
2) it depends ;-)
The thicker the wire the more distance is allowed between supporting points. H07VU for example spans up to 100mm of distance. This is often the same distance that supporting spacers on the diaphragm need. A fine example of this ´coincidence´ are the audiostatics. Thick wire comes with larger distances between the wires and as such larger variations of the electrical field in close proximity to the conductors. They work well with rather large d/s values. Thinner wire accordingly spans less distance, but it allows for smaller stator-diaphragm distances.
Since with most wires the insulation grows in thickness as the wire diameter grows You should choose the wire thickness after the voltage needs.
3) the voltage withstand capabilities of insulated wires is much higher than the rated voltage. From the thickness of the insulation and the used material You can roughly calculate the maximum withstand voltage.
A good insulator for ESL-usage has a high withstand voltage, a value of surface and volume resistivity in the slightly dissipative range, low creep an track and a high value of the dielectric constant epsilon. Of course mechanical strength and resistance against aging, breaks and last but not least the glueability have to be kept in mind too.
The most critical situation is when touching the stators, because the stators are grounded through the audio tranny and Your body closes the current loop. If You can´t touch the stators the insulation may be chosen thinner.
PVC is a often used material because its cheap and easily available in lots of colours and sizes.
Other materials like PU or Kynar (a Nylon-derivative) might be even superior but do cost more.
4) if the membrane is allowed to swing freely over its complete area the smallest d/s defines the maximum dynamics. In this case different d/s don´t make sense, because in the area of higher d/s You´d loose considerably on efficiency.
If the movement of the membrane is restricted by spacers, different d/s are possible, if the signal to the smaller d/s´ed panel segment is highpass-filtered. But that would mean the same as building two different panels.
jauu
Calvin
1) it depends ,-)
One way is to use stranded litz wire. Since this wire is soft it has to be kept under constant tension.When building the stator frame is sligthly bowed. You will need a stator frame with high mechanical strength and lots of closely distanced supporting points, like the often used louvre. Straigthening the frame tensions and straightens the wires. Acoustat used this method and it is described in Fikier´s little book too. The advantage is that winding the wire is easy because of its softness and it will become perfectly straight when tensioned.
Personally I don´t like the idea of considerably large forces ´stored´ within the wires and frame construction. Using soft wire which has the tendency to wobble around unless the free ´swinging´ distance is very small will lead to ugly optics, which only can be camouflaged with cloth.
The other way is to use single stranded wires. Here tension is applied only to straighten the wires after winding. The tension has to be so high that the copper just starts to ´flow´. The wires straighten perfectly flat. Then You can release tension completely and glue the wires to the supporting structure. Since the wire is hard the distance between supporting points can be larger and allows for optically more pleasing open designs. The possibility of breaking glue joints between wires and support is low because there is no stressing mechanical tension.
2) it depends ;-)
The thicker the wire the more distance is allowed between supporting points. H07VU for example spans up to 100mm of distance. This is often the same distance that supporting spacers on the diaphragm need. A fine example of this ´coincidence´ are the audiostatics. Thick wire comes with larger distances between the wires and as such larger variations of the electrical field in close proximity to the conductors. They work well with rather large d/s values. Thinner wire accordingly spans less distance, but it allows for smaller stator-diaphragm distances.
Since with most wires the insulation grows in thickness as the wire diameter grows You should choose the wire thickness after the voltage needs.
3) the voltage withstand capabilities of insulated wires is much higher than the rated voltage. From the thickness of the insulation and the used material You can roughly calculate the maximum withstand voltage.
A good insulator for ESL-usage has a high withstand voltage, a value of surface and volume resistivity in the slightly dissipative range, low creep an track and a high value of the dielectric constant epsilon. Of course mechanical strength and resistance against aging, breaks and last but not least the glueability have to be kept in mind too.
The most critical situation is when touching the stators, because the stators are grounded through the audio tranny and Your body closes the current loop. If You can´t touch the stators the insulation may be chosen thinner.
PVC is a often used material because its cheap and easily available in lots of colours and sizes.
Other materials like PU or Kynar (a Nylon-derivative) might be even superior but do cost more.
4) if the membrane is allowed to swing freely over its complete area the smallest d/s defines the maximum dynamics. In this case different d/s don´t make sense, because in the area of higher d/s You´d loose considerably on efficiency.
If the movement of the membrane is restricted by spacers, different d/s are possible, if the signal to the smaller d/s´ed panel segment is highpass-filtered. But that would mean the same as building two different panels.
jauu
Calvin
magnet wire
A word of caution when working with magnet wire...
Unlike PVC insulation, the double build coating on magnet wire does not take kindly to being stretched. With PVC wire, you can stretch the wire 3% or so as Calvin mentioned to straighten and cold-work (harden) the copper wire without much concern for the integrity of the PVC insulation. Not so with magnet wire....at least in my experience using high quality Essex magnet wire. Even stretched just 0.5% I had problems with multiple fine radial cracks forming in the insulation. The completed panels would arc at high volume levels. I couldn't see the cracks with my eye, but they would draw an arc when probed with HV. Once located I fixed many of the cracks with corona dope, but over time more developed.
It was a pretty panel(red magnet wire), but I considered it a learn from failure experience.
I hope you have better luck, or have better magnet wire insulation.
Keep us advised on your progress.
Few said:
A word of caution when working with magnet wire...
Unlike PVC insulation, the double build coating on magnet wire does not take kindly to being stretched. With PVC wire, you can stretch the wire 3% or so as Calvin mentioned to straighten and cold-work (harden) the copper wire without much concern for the integrity of the PVC insulation. Not so with magnet wire....at least in my experience using high quality Essex magnet wire. Even stretched just 0.5% I had problems with multiple fine radial cracks forming in the insulation. The completed panels would arc at high volume levels. I couldn't see the cracks with my eye, but they would draw an arc when probed with HV. Once located I fixed many of the cracks with corona dope, but over time more developed.
It was a pretty panel(red magnet wire), but I considered it a learn from failure experience.
I hope you have better luck, or have better magnet wire insulation.
Keep us advised on your progress.
Actually, I did. They specified a recommended tension range for each gauge of wire when winding coils and motors. I don't have the exact numbers handy, sorry.
I used a small pull scale and applied the maximum recommended tension for the wire I was using to one wire to see if it was enough to permanently lengthen and straighten the wire. It was not. It did stretch the wire, but when tension was released, the wire returned to the original length. I had to increase the tension about 30% before permanent stretching occurred.
My general construction technique for wire stators is to wind all the wires as tightly as possible on a jig and then stretch all of them at once, enough to straighten and strengthen(cold work) the wires, then realease most of the tension before glueing wires to crossbars. For a 60" long panel, I needed to stretch the Essex wire about 1/4" to permanently straighten the small waves & kinks in the wire. For PVC wire 1/2" - 3/4" is typical for uniform straightening.
As a reference, Janszen stretched his wires ~6% according to USpatent 2896025.
http://www.google.com/patents/about?id=WBACAAAAEBAJ&dq=2896025
(column 4, line 40)
If/when I use magnet wire again, I would plan to pull the wire tight, but not stretch it. This should avoid the possibility of cracks forming in the insulation.
I should have said that I would plan to pull the wire tight, but not with enough force to permanently lengthen the wire.
My suggestion,
start reading here:
http://www.diyaudio.com/forums/forumdisplay.php?f=54
you will find more interesting answers than you have questions right now!
start reading here:
http://www.diyaudio.com/forums/forumdisplay.php?f=54
you will find more interesting answers than you have questions right now!
I can think of a few reasons...there may be others.
1) Wires allow you to minimize the capacity of the panel by only putting wires over the driven area of the diaphragm. Most perforated metal ESLs have the metal extending on to the spacers where they are supported and attached. The dielectric constant of the spacers are usually ~3 times that of air, so this can add considerable "wasted" capacitive load to the panel. Wasted, because the amplifier has to drive it, but it is not used to produce sound. The lower the capacitive load of the panel, the higher the step-up ratio of your transformer can be for the same high frequency cut off, and similar load on the amplifier. ie. higher efficiency.
2) Wires allow you the flexibility to modify the directivity and radiation pattern vs frequency by segmentation. This can reduce beaming of the high frequencies from a large panel.
3) Most builders will find it much easier to build "arc-proof" panels using PVC insulated wires than with perforated metal. Personally, I have found it very difficult, if not impossible, to properly coat around the sharp edges of the perforation holes. This may not be a problem if high resistance coating is used on the diaphragm, and the transformer step up ratio is not too high. But, when trying to maximize efficiency with high step up ratios, or high power solid state amplifiers, the sharp edges around the perforation holes will promote corona and arcing unless properly coated.
4) I have found the material cost to be lower for wire stators.
Hi,
right so far, but to be precise, it´s not at all desirable to use high transformation factors U. Better is to use only as much U as needed and as low U as possible.
Lower capacitance values mean higher impedance levels, means higher transformation factors needed to match amplifier and panel, means higher voltage levels needed to drive the capacitance, means more losses in the tranny because of thicker insulation, means lower dynamics, means a loss in sonic quality of the tranny, means a loss in safety margin, means a loss in lifetime and so on and so on.
High U-Values are rather a sign of inefficient panels. Even though most metal sheet panels ´suffer´ from a higher percentage of ´dead´ or ´wasted´ capacitance, they are in fact more efficient than wire panels. Typically transformation factors for wideband sheet metal panels are around 60-80, sometimes even lower. Wire panels of similar dimensions usually need Us of >100. Segmented wire panels reduce the active membrane area with rising frequency. This allows to control distribution character and frequency response to a certain degree and leads to a slightly different sonic fingerprint to a flat metal sheet panel or curved metal sheet panels.
The real decicive points are #3 and #4. Ease of building and material supply -with a good chance of success with the first try- and low cost is what speaks for wire.
jauu
Calvin
right so far, but to be precise, it´s not at all desirable to use high transformation factors U. Better is to use only as much U as needed and as low U as possible.
Lower capacitance values mean higher impedance levels, means higher transformation factors needed to match amplifier and panel, means higher voltage levels needed to drive the capacitance, means more losses in the tranny because of thicker insulation, means lower dynamics, means a loss in sonic quality of the tranny, means a loss in safety margin, means a loss in lifetime and so on and so on.
High U-Values are rather a sign of inefficient panels. Even though most metal sheet panels ´suffer´ from a higher percentage of ´dead´ or ´wasted´ capacitance, they are in fact more efficient than wire panels. Typically transformation factors for wideband sheet metal panels are around 60-80, sometimes even lower. Wire panels of similar dimensions usually need Us of >100. Segmented wire panels reduce the active membrane area with rising frequency. This allows to control distribution character and frequency response to a certain degree and leads to a slightly different sonic fingerprint to a flat metal sheet panel or curved metal sheet panels.
The real decicive points are #3 and #4. Ease of building and material supply -with a good chance of success with the first try- and low cost is what speaks for wire.
jauu
Calvin
I would agree that "typical" wire ESLs tend to be less efficient than "typical" PSM(perforated sheet metal) ESLs. I believe that this is mainly due to the fact that most wire ESLs are built with larger spacing and segmentation. As you mentioned, both reduce the efficiency.
Before pursuing wire ESLs, I built and compared two panels(one wire, one PSM) of identical size and spacing (48" x 6" with 1/16" spacing and 45% open area). Driven without segmentation, the same bias voltage, and the same transformers(80:1 ratio), the wire ESL was identical in SPL to the PSM ESL at 10Vrms input. At 28Vrms, the wire ESL was, perhaps, +1.0dB more efficient. I can't recall the exact panel capacities, but it was roughly 500pF for the wire ESL, and 700pF for the PSM. This resulted in the impedance at 20kHz being about 0.5 ohm lower for the PSM.
I'm not sure of the dimensions of the chicken fencing you're considering, but the fencing I'm familiar with would be terrible for an ESL panel. Maybe I'm just envisioning the wrong material. How big is the wire and what is the size of the holes? You probably don't want to deviate too far from a 50% open area (maybe plus or minus 10%).
I'm building wire ESLs primarily because I want to control the directivity of the speakers. I love the dynamics of the flat perforated metal ESLs I've been living with for a decade, but the directivity pattern isn't one I want to continue living with. Others might have a different set of priorities, and perforated metal might make more sense for them. The perf. metal panels are certainly easier to build if you're not too picky about the insulation. If you want reliable insulation, well, that's another situation entirely. I've enjoyed listening to panels with less than state of the art insulation, but I'm sure I could improve things with more careful attention to the insulation. (I used epoxy paint as insulation on perforated steel panels.)
Few
I'm building wire ESLs primarily because I want to control the directivity of the speakers. I love the dynamics of the flat perforated metal ESLs I've been living with for a decade, but the directivity pattern isn't one I want to continue living with. Others might have a different set of priorities, and perforated metal might make more sense for them. The perf. metal panels are certainly easier to build if you're not too picky about the insulation. If you want reliable insulation, well, that's another situation entirely. I've enjoyed listening to panels with less than state of the art insulation, but I'm sure I could improve things with more careful attention to the insulation. (I used epoxy paint as insulation on perforated steel panels.)
Few
Hi,
the results in Matthew Lattis´s Report in AudioXpress 2005 says the opposite.
He found too that PSMs (perforated sheet metal stators) typically gave higher efficiency values. Admittedly it is difficult to compare in a ´truely comparable´ way, since there are several factors affecting efficiency which are hard to control or difficult to change without affecting other parameters as well.
For example what value is chosen for d/s? Whilst with SMS there is a plain with holes in --> easy measurement, because of constant d/s. But with round shaped wires of a WS (wire stators) You probabely have to calculate with a ´effective´ d/s value which is larger than the measured d/s. Next the insulation wires is typically a bit thicker than the insulation thickness of SMS. Next there are usually differences in the material choice of insulation and as such the epsilon-value of he insulation material itself. The open area %age is affected by this too. Really high precision built of the panels is needed with very small dimensional deviations, because even small variations affect very much the outcome.
In practise You find the more efficient panels (lower U for same SPL) amongst the PSM-hybrids.
jauu
Calvin
the results in Matthew Lattis´s Report in AudioXpress 2005 says the opposite.
He found too that PSMs (perforated sheet metal stators) typically gave higher efficiency values. Admittedly it is difficult to compare in a ´truely comparable´ way, since there are several factors affecting efficiency which are hard to control or difficult to change without affecting other parameters as well.
For example what value is chosen for d/s? Whilst with SMS there is a plain with holes in --> easy measurement, because of constant d/s. But with round shaped wires of a WS (wire stators) You probabely have to calculate with a ´effective´ d/s value which is larger than the measured d/s. Next the insulation wires is typically a bit thicker than the insulation thickness of SMS. Next there are usually differences in the material choice of insulation and as such the epsilon-value of he insulation material itself. The open area %age is affected by this too. Really high precision built of the panels is needed with very small dimensional deviations, because even small variations affect very much the outcome.
In practise You find the more efficient panels (lower U for same SPL) amongst the PSM-hybrids.
jauu
Calvin
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