Acquiring an relatively inexpensive, but accurate USB powered component (Dayton WT3), I am enabled to run quick impedance tests that draws necessary data for loudspeaker design. Consisting of a wired USB cable on one side, a small labeled box with L.E.D indicator in between, and two wired, polarity color coded, alligator clips on the other end. The unit is quite compact and very portable. After installing on a small Windows XP laptop with the included cd, you make the required sound card adjustments, and a couple of quick & simple calibrating tests that uses a 1k ohm resistor (included) to insure proper readings. The alligator clips are then connected to the leads of the driver to be tested. Free air parameters are revealed with a quick chirp that is repeatable to check for consistency. Differences between repeat tests were noted that were so close as not to be a problem designing from. Here Qts, Qms, Qes, Le, Re is given in seconds. For the Vas test either a test box, known driver Spl (1w/1m), or a set of calibrated measuring weights (in grams) is needed. I opted for the weights (not included) because of the simplicity and not wanting to rely upon any published data. You simply enter in a provided space on the screen menu the weight in grams and the driver's size. Then click "measure Vas, and a small window will tell you to place the weight on the driver's cone and click on "ok". The WT3 will alert you if the weight used is not enough and to add more. Once the proper weight is applied and the test is completed, Vas along with Spl & mms will display on the same screen along with full specs. Only drawback is the lack of xmax readings, which you will have to rely on the driver's published specs. I don't see this as a major problem. If other parameters match the published; it would be safe to assume published xmax is correct.
It is also able to run a impedance sweep on passive crossovers and enclosed subs to check for design accuracy by looking for impedance peaks with the quick chirp as well. I quickly tested a few spare drivers I had laying around to check for accuracy from the unit itself and compared results to manufacturer data. Some speakers (usually the more expensive ones or high name brands) netted very close specs which was proof enough to me the WT3 works good enough to rely on. I also ran a a few impedance sweeps on a a couple of different enclosed subs I had laying around to see if my work was on spot. For the first time I could confirm port tuning which was nice.
In hopes that there still are some decent inexpensive drivers to experiment with, it is becoming more important to verify the true specs of such to insure performance. I have found two drivers( a single 10" & another brand 12") within that category which "seemed" to have somewhat good reviews, but tested off with the manufacturers published specs. While it is known for there to be a minor difference in published & measured at times (more often with lower budget lines or low rate companies), the two that I have tested were quite off with one way off the mark of the published data . Though the recommended box size could be followed, the nature of sealed Q or vented alignment can be different enough to disprove it's use if design requirements are strict enough. In fact the way off one was found to be more of a infinite baffle type and not compatible at all with vented nor medium sealed designs as published. Proof that companies do lie to sell something!
In disbelief I decided to see if anyone else had similar readings or assumptions. While I looked (googled) all over the internet for users actually testing the parameters for the 12" driver, which was none, I did confirm my findings. The users' descriptions of the 12" sub's tonal quality agreed more with the WT3 measured data when ran in the manufacturers recommended enclosure. This proved detrimental as my findings agreed with quite a bit of the reviews, but with the other users not knowing why or at least thought about it. They either liked the product or didn't. I highly think this lead to the misuse of the product's real nature as supposed to what the manufacturer claimed it to be for. In short, the culprit subwoofer possibly even received a bad reputation as a non performer with some. I can honestly say it was really for being assumed as something that it is not, when it could have actually been a good product when used as measured. I can attest that in the company's description, they did state however that it "could be used for the infinite baffle purpose". I guess that could excuse them for wrongful data, but I doubt that would fair well with the average consumer that expects to get what they pay for.
Another test was done on a set of small 8" drivers within the same line as the 12". Again it's published data was totally off. With this one I will present both specs, published & the actual pair tested with the Dayton WT3:
Pub. Test 1 Test 2
Qts= .48 .9081 .804
Qes= .64 1.057 .9239
Qms= 7.50 6.46 6.198
Vas= 1.413 1.756 1.693
Fs= 32hz 48.45hz 49.8hz
Spl(1w/1m)= 85 89.18 89.98
Le(mh)= n/a .3959 .3943
(Sorry about the bunched up specs, can't seem to get them to spread once saved. Hopefully you can still read them...)
There was no "break in" period as that is debatable and shouldn't change any particular spec by any large margin. I would think no more than 10%. Way less than the difference in the above examples. With fresh drivers here we can plainly see there is a major contradiction between published & measured data. Notice how mostly Qts, Fs, and Vas is dead off! Also pay close attention to the tested pair. Notice the inconsistencies between the two and how this could affect the final product when building an enclosure for a pair. Not a major difference in specs, but enough to cause up to a .5ft^3 or better change between the two. A sign of poor quality control.... The differences between all 3 driver's data alone will change the box size and frequency plot drastically enough to abandon use if the installer cannot accomodate the requirements.
When modeled in a box building program, the tested drivers did not agree at all with an acceptable vented enclosure size (unlike published data states). A smooth frequency plot within the recommended box size was also unattainable. When a smooth plot with an acceptable rolloff (-3db @ 50hz) was finally attained through manipulation of box & port sizes, the enclosure's size was so enormous that you would easily outdo it with a larger woofer/small box design.
Modeled in the manufacturer's minimum recommended 1ft^3 sealed, tonality of the tested drivers was as high as 1.5 Qtc and exhibited a +5db curve centered around 90-100hz. To bring them down to a usable but still somewhat high Qtc (.9-1.1), required volumes reaching up around 8ft^3!!! Surely this would be overly problematic considering the drivers already low power handling (100 watts rms). Clearly with the measured high Qts, these drivers fall well within the infinite baffle range. An online review of this driver when used as a IB door installed midbass parallels this finding as the user stated decent performance. Assuming the door was properly dampened, there still would be minor leaks from drainage holes, window openings, and such. This would provide the driver with a sort of resistive leaky path(s) and simulate a larger enclosure than the standard assumed 1ft^3 door interior space. It would be even viable to consider them as a rear deck IB subwoofer accompanying some low- medium powered full ranges for a efficient & stealthy system rather than to force them into a situation where the performance would be less than par. Perhaps an rear aperiodic vent assisted sealed enclosure may suffice. The main point is measure and see them for what they are. Do not always rely on company data as you can see even that can be wrong.
At this point it would be quite hard to even believe that it's xmax is a true 6mm seeing that other parameters were falsely given. Until there is a simple way for the average installer to test xmax, it would be a good idea to assume it is at least somewhat a few mm less when other specs are off. Once a proper enclosure is built, then one can listen out for any mechanical noises indicating xmax is being reached, then you can adjust system gain accordingly if you can live with the limited output. Staying on the higher side of Qtc or later filling a larger box with solid materials would be a better start if tolerable.
I must admit that a personal audition of the 12" driver in the minimum recommended sealed (1.5ft^3 ea) did produce robust bass with good Spl. Yet, in keeping with the same honesty, it did exhibit tuning problems even with an active crossover and lacked a lot of extended bottom end. It was listenable with certain music genres, but nothing I would call sound quality. I found it necessary to at least have a steep order crossover (-24db octave) to tame them enough to tolerate and a few added decibels of bass boost centered around 45hz. Being installed in different autos either helped or hendered the low end output, but that was attributed to transfer function and not the sub itself. Real power handling of course was questionable as it goes up quite a bit as higher Q's add to mechanical handling to a point. Thermal handling is something else to contend with and I would expect them to be quite short lived if driven hard enough beyond a certain point. When modeled with the measured parameters in the recommended 1.5ft^3, it detailed a whopping 1.84 Qtc! Like the 8", a +5.59db gain centered around 80hz was shown. -3db down from that point was about 64hz and 130hz and zeroing out at 57hz on the low end. The steep crossover and transfer function is surely played a part with this setup as it naturally showed a frequency response typical of a Spl rig (nasty!). No further testing in a larger box was done, only modeling that ended with unacceptable sizes to get a lower Q & flatter response. I am pushing towards installing them in an infinite baffle design to confirm this and which also models decent performance. Ported like the 8" as well proved to be more of a headache than what it was worth. Despite these findings there still were a good amount of positive reviews given. Isn't it amazing what some people find acceptable?!!!
With the proper extraction of T/S parameters, it still is possible to find inexpensive drivers that will work in specific projects. Obviously these companies' QC department are not going to spend a lot of time on low cost products when warranty backing (if any) for such items is low compared to their premium lines. However, the 10" driver is offered with a full 5 year warranty like it's premium siblings while it's specs are nowhere near as off as the 8" & 12". Still you need to extract the true parameters to be able to design and predict any particular project especially in vented designs.. A possible major drawback would be the cost of testing more than one driver per model to compare consistency within the manufacturers production. That is if you want a perfectly matching pair. If you had to order several just to keep a few that match, it could get quite expensive real quick unless the retailer has a good return policy. Some companies will even match them for you before shipping at an extra fee. Other than that, slight differences that still allow the use of the same size enclosure with a similar response is tolerable. Anything outside of this would not be exceptable unless certain constraints can be met. I'm quite sure expensive and more than a few medium priced drivers are accurate in specs, but after this, there would be no question as to should I check. If building a vented design, you truly need the real parameters to get accurate results.
After parameters are extracted and compared to the published data, again one would have to assume that stated xmax would be only as accurate if both measured specs and published data is close. This would simply be relying on the company's honesty in being descriptive. The importance of a overly large xmax is highly debatable and is dependent on other factors that can even negate it's worth. There has been quite a bit of a successful drivers on the market whose xmax is medium at best. As long as it's linear throw is usable to an extent that makes the speaker worth using is all that matters in this aspect.
Just a bit of info I thought you guys would be interested in. THINK
Ash,
Replies (4)
cplkittle on 01/24/2008 22:40:19
How accurate do you assume the WT3 is?
qts was approx. 1/2 I wonder how that works into the equation...
how did you test spl?
and what do you think of the WT3? The cheapest I could find was $99.... Looks like a neat little toy.. I mean tool.
swez on 01/25/2008 01:08:01
The thought that "break in time" has minimal import to a given drivers' test results seems a bit disturbing. Have you measured one/them out of the package and then after a reasonable break in period?
A new sub is often very stiff and restrictive until the cone, spider and surround have been well worked. After that, I would expect X-max to improve a few mm's and lower Fs to some degree as well. It seems that your tests reflect otherwise? That is troublesome to me on a good quality subwoofer. Are they really that far off? It would seem like a good idea to have a "bonified standard" as the reference point. From there, it's more a matter of comparing apples to apples or apples to sour grapes. (Any thoughts?)
Swez
PS Can you give an "Executive Summary" of your present findings on the speakers/woofers tested to date? Once we see the "Big Picture", then look at the details, would be most helpful. Am pretty certain that quality drivers will be somewhat consistant from one lot to another. When looking at low budget drivers, it's probably more hit or miss?
Am a "Big Picture" type and once that is established, then I look at the details that correlate/deviates from the norms would be next. Am I missing something here? Is so, put a light on these aspects so we can learn together. :-)
Ash on 01/25/2008 04:19:45
The Dayton WT3 is highly accurate. Although a bit pricey for the small module, but for what it does and it's simplicity, it's hard to beat without expensive & complex gear.
Spl is automatically given when extracting vas from a test box or gram weight measure. When used on various drivers I have laying around (Audax, Dayton RS, & Bostwick) the results were dead within about 10-15%. I account this difference to be due to break-in for these drivers were used quite a bit. A couple of new drivers measured closely the same as published. Yeah that took me for a loop as it was proof that the WT3 is consistent and those "tested" drivers above mentioned were just off....
In the enclosures the impedance sweep shows a peak at the correlated tuning, twice for vented. One sealed box with the 3 Bostwicks showed a peak around 62hz. Figures, for I knew I had skimped on airspace a bit.
The difference after break-in is measurable, but is known to be around 20% after about 40-50 hours. That's fair enough being that anything beyond that would make a driver that's impossible to design with. Besides one spec changes the others, they won't all see an increase or decrease at the same time. The one driver that I own that should have around that type of break-in is the Dayton RS HO 10". I believe the Audax midbass should be around there too. Still they measured close to specs compared to the "tested drivers".
Here's a some good info from some reputable sources:
http://www.gr-research.com/burnin.shtm
Once the subs are used quite a bit, I'll update on them. Right now they are just sitting around waiting for an install. 40-50 hours is a lot of break in time.
swez on 01/25/2008 09:17:30
Very good article on burn in/break in time allotments for various T/S parameters. I suspected the spider compliance shift would be the major player as it's very stiff out ouf the box. Now we know why... the micro-cracking of the epoxy coatings often used for spiders makes much sense. (As the bonds break down over time with use, the spider compliance will shift, become more compliant and stretch to a permanent point and remain fixed for the duration)
It also makes sense that Re and impedance would change based on heating the voice coils with electrical energy. Wire resistance will go up as it is heated. As the coil cools, Re returns to near the original values. That too makes sense. The shift is nominal, minimal and measurable.
As for impedance changes in the coil at various frequencies, that too is measurable and predictable. At resonance frequency, impedance is at it's highest levels. That just means the inductive reactance has shifted as the coil field is saturated with energy.
Here, a woofer with a very low Fs value would be most desirable. (Peaks at well below 25 Hz.) As frequency changes upwardly, inductive reactance becomes less a factor and we see either a very linear or near flat response curve in the usable range of the speaker/woofer in question. (Say 35-150 Hz. for a well designed woofer)
Very good tuitorial material here. I have read many of Dan Wiggins "White Papers" on Adire drivers in the past and respect his attention to detail and engineering skills. He's not pretentious, overly technical and able to break down the complex nature of his designs in ways that make sense to non-technical folk. Yes, he can back it with all the technical data as needed, but in plain english, this man is very gifted and will be back in action again at some point later.
Thanks for the link and sharing your present findings. Keep up the good work!
Swez
It is also able to run a impedance sweep on passive crossovers and enclosed subs to check for design accuracy by looking for impedance peaks with the quick chirp as well. I quickly tested a few spare drivers I had laying around to check for accuracy from the unit itself and compared results to manufacturer data. Some speakers (usually the more expensive ones or high name brands) netted very close specs which was proof enough to me the WT3 works good enough to rely on. I also ran a a few impedance sweeps on a a couple of different enclosed subs I had laying around to see if my work was on spot. For the first time I could confirm port tuning which was nice.
In hopes that there still are some decent inexpensive drivers to experiment with, it is becoming more important to verify the true specs of such to insure performance. I have found two drivers( a single 10" & another brand 12") within that category which "seemed" to have somewhat good reviews, but tested off with the manufacturers published specs. While it is known for there to be a minor difference in published & measured at times (more often with lower budget lines or low rate companies), the two that I have tested were quite off with one way off the mark of the published data . Though the recommended box size could be followed, the nature of sealed Q or vented alignment can be different enough to disprove it's use if design requirements are strict enough. In fact the way off one was found to be more of a infinite baffle type and not compatible at all with vented nor medium sealed designs as published. Proof that companies do lie to sell something!
In disbelief I decided to see if anyone else had similar readings or assumptions. While I looked (googled) all over the internet for users actually testing the parameters for the 12" driver, which was none, I did confirm my findings. The users' descriptions of the 12" sub's tonal quality agreed more with the WT3 measured data when ran in the manufacturers recommended enclosure. This proved detrimental as my findings agreed with quite a bit of the reviews, but with the other users not knowing why or at least thought about it. They either liked the product or didn't. I highly think this lead to the misuse of the product's real nature as supposed to what the manufacturer claimed it to be for. In short, the culprit subwoofer possibly even received a bad reputation as a non performer with some. I can honestly say it was really for being assumed as something that it is not, when it could have actually been a good product when used as measured. I can attest that in the company's description, they did state however that it "could be used for the infinite baffle purpose". I guess that could excuse them for wrongful data, but I doubt that would fair well with the average consumer that expects to get what they pay for.
Another test was done on a set of small 8" drivers within the same line as the 12". Again it's published data was totally off. With this one I will present both specs, published & the actual pair tested with the Dayton WT3:
Pub. Test 1 Test 2
Qts= .48 .9081 .804
Qes= .64 1.057 .9239
Qms= 7.50 6.46 6.198
Vas= 1.413 1.756 1.693
Fs= 32hz 48.45hz 49.8hz
Spl(1w/1m)= 85 89.18 89.98
Le(mh)= n/a .3959 .3943
(Sorry about the bunched up specs, can't seem to get them to spread once saved. Hopefully you can still read them...)
There was no "break in" period as that is debatable and shouldn't change any particular spec by any large margin. I would think no more than 10%. Way less than the difference in the above examples. With fresh drivers here we can plainly see there is a major contradiction between published & measured data. Notice how mostly Qts, Fs, and Vas is dead off! Also pay close attention to the tested pair. Notice the inconsistencies between the two and how this could affect the final product when building an enclosure for a pair. Not a major difference in specs, but enough to cause up to a .5ft^3 or better change between the two. A sign of poor quality control.... The differences between all 3 driver's data alone will change the box size and frequency plot drastically enough to abandon use if the installer cannot accomodate the requirements.
When modeled in a box building program, the tested drivers did not agree at all with an acceptable vented enclosure size (unlike published data states). A smooth frequency plot within the recommended box size was also unattainable. When a smooth plot with an acceptable rolloff (-3db @ 50hz) was finally attained through manipulation of box & port sizes, the enclosure's size was so enormous that you would easily outdo it with a larger woofer/small box design.
Modeled in the manufacturer's minimum recommended 1ft^3 sealed, tonality of the tested drivers was as high as 1.5 Qtc and exhibited a +5db curve centered around 90-100hz. To bring them down to a usable but still somewhat high Qtc (.9-1.1), required volumes reaching up around 8ft^3!!! Surely this would be overly problematic considering the drivers already low power handling (100 watts rms). Clearly with the measured high Qts, these drivers fall well within the infinite baffle range. An online review of this driver when used as a IB door installed midbass parallels this finding as the user stated decent performance. Assuming the door was properly dampened, there still would be minor leaks from drainage holes, window openings, and such. This would provide the driver with a sort of resistive leaky path(s) and simulate a larger enclosure than the standard assumed 1ft^3 door interior space. It would be even viable to consider them as a rear deck IB subwoofer accompanying some low- medium powered full ranges for a efficient & stealthy system rather than to force them into a situation where the performance would be less than par. Perhaps an rear aperiodic vent assisted sealed enclosure may suffice. The main point is measure and see them for what they are. Do not always rely on company data as you can see even that can be wrong.
At this point it would be quite hard to even believe that it's xmax is a true 6mm seeing that other parameters were falsely given. Until there is a simple way for the average installer to test xmax, it would be a good idea to assume it is at least somewhat a few mm less when other specs are off. Once a proper enclosure is built, then one can listen out for any mechanical noises indicating xmax is being reached, then you can adjust system gain accordingly if you can live with the limited output. Staying on the higher side of Qtc or later filling a larger box with solid materials would be a better start if tolerable.
I must admit that a personal audition of the 12" driver in the minimum recommended sealed (1.5ft^3 ea) did produce robust bass with good Spl. Yet, in keeping with the same honesty, it did exhibit tuning problems even with an active crossover and lacked a lot of extended bottom end. It was listenable with certain music genres, but nothing I would call sound quality. I found it necessary to at least have a steep order crossover (-24db octave) to tame them enough to tolerate and a few added decibels of bass boost centered around 45hz. Being installed in different autos either helped or hendered the low end output, but that was attributed to transfer function and not the sub itself. Real power handling of course was questionable as it goes up quite a bit as higher Q's add to mechanical handling to a point. Thermal handling is something else to contend with and I would expect them to be quite short lived if driven hard enough beyond a certain point. When modeled with the measured parameters in the recommended 1.5ft^3, it detailed a whopping 1.84 Qtc! Like the 8", a +5.59db gain centered around 80hz was shown. -3db down from that point was about 64hz and 130hz and zeroing out at 57hz on the low end. The steep crossover and transfer function is surely played a part with this setup as it naturally showed a frequency response typical of a Spl rig (nasty!). No further testing in a larger box was done, only modeling that ended with unacceptable sizes to get a lower Q & flatter response. I am pushing towards installing them in an infinite baffle design to confirm this and which also models decent performance. Ported like the 8" as well proved to be more of a headache than what it was worth. Despite these findings there still were a good amount of positive reviews given. Isn't it amazing what some people find acceptable?!!!
With the proper extraction of T/S parameters, it still is possible to find inexpensive drivers that will work in specific projects. Obviously these companies' QC department are not going to spend a lot of time on low cost products when warranty backing (if any) for such items is low compared to their premium lines. However, the 10" driver is offered with a full 5 year warranty like it's premium siblings while it's specs are nowhere near as off as the 8" & 12". Still you need to extract the true parameters to be able to design and predict any particular project especially in vented designs.. A possible major drawback would be the cost of testing more than one driver per model to compare consistency within the manufacturers production. That is if you want a perfectly matching pair. If you had to order several just to keep a few that match, it could get quite expensive real quick unless the retailer has a good return policy. Some companies will even match them for you before shipping at an extra fee. Other than that, slight differences that still allow the use of the same size enclosure with a similar response is tolerable. Anything outside of this would not be exceptable unless certain constraints can be met. I'm quite sure expensive and more than a few medium priced drivers are accurate in specs, but after this, there would be no question as to should I check. If building a vented design, you truly need the real parameters to get accurate results.
After parameters are extracted and compared to the published data, again one would have to assume that stated xmax would be only as accurate if both measured specs and published data is close. This would simply be relying on the company's honesty in being descriptive. The importance of a overly large xmax is highly debatable and is dependent on other factors that can even negate it's worth. There has been quite a bit of a successful drivers on the market whose xmax is medium at best. As long as it's linear throw is usable to an extent that makes the speaker worth using is all that matters in this aspect.
Just a bit of info I thought you guys would be interested in. THINK
Ash,
Replies (4)
cplkittle on 01/24/2008 22:40:19
How accurate do you assume the WT3 is?
qts was approx. 1/2 I wonder how that works into the equation...
how did you test spl?
and what do you think of the WT3? The cheapest I could find was $99.... Looks like a neat little toy.. I mean tool.
swez on 01/25/2008 01:08:01
The thought that "break in time" has minimal import to a given drivers' test results seems a bit disturbing. Have you measured one/them out of the package and then after a reasonable break in period?
A new sub is often very stiff and restrictive until the cone, spider and surround have been well worked. After that, I would expect X-max to improve a few mm's and lower Fs to some degree as well. It seems that your tests reflect otherwise? That is troublesome to me on a good quality subwoofer. Are they really that far off? It would seem like a good idea to have a "bonified standard" as the reference point. From there, it's more a matter of comparing apples to apples or apples to sour grapes. (Any thoughts?)
Swez
PS Can you give an "Executive Summary" of your present findings on the speakers/woofers tested to date? Once we see the "Big Picture", then look at the details, would be most helpful. Am pretty certain that quality drivers will be somewhat consistant from one lot to another. When looking at low budget drivers, it's probably more hit or miss?
Am a "Big Picture" type and once that is established, then I look at the details that correlate/deviates from the norms would be next. Am I missing something here? Is so, put a light on these aspects so we can learn together. :-)
Ash on 01/25/2008 04:19:45
The Dayton WT3 is highly accurate. Although a bit pricey for the small module, but for what it does and it's simplicity, it's hard to beat without expensive & complex gear.
Spl is automatically given when extracting vas from a test box or gram weight measure. When used on various drivers I have laying around (Audax, Dayton RS, & Bostwick) the results were dead within about 10-15%. I account this difference to be due to break-in for these drivers were used quite a bit. A couple of new drivers measured closely the same as published. Yeah that took me for a loop as it was proof that the WT3 is consistent and those "tested" drivers above mentioned were just off....
In the enclosures the impedance sweep shows a peak at the correlated tuning, twice for vented. One sealed box with the 3 Bostwicks showed a peak around 62hz. Figures, for I knew I had skimped on airspace a bit.
The difference after break-in is measurable, but is known to be around 20% after about 40-50 hours. That's fair enough being that anything beyond that would make a driver that's impossible to design with. Besides one spec changes the others, they won't all see an increase or decrease at the same time. The one driver that I own that should have around that type of break-in is the Dayton RS HO 10". I believe the Audax midbass should be around there too. Still they measured close to specs compared to the "tested drivers".
Here's a some good info from some reputable sources:
http://www.gr-research.com/burnin.shtm
Once the subs are used quite a bit, I'll update on them. Right now they are just sitting around waiting for an install. 40-50 hours is a lot of break in time.
swez on 01/25/2008 09:17:30
Very good article on burn in/break in time allotments for various T/S parameters. I suspected the spider compliance shift would be the major player as it's very stiff out ouf the box. Now we know why... the micro-cracking of the epoxy coatings often used for spiders makes much sense. (As the bonds break down over time with use, the spider compliance will shift, become more compliant and stretch to a permanent point and remain fixed for the duration)
It also makes sense that Re and impedance would change based on heating the voice coils with electrical energy. Wire resistance will go up as it is heated. As the coil cools, Re returns to near the original values. That too makes sense. The shift is nominal, minimal and measurable.
As for impedance changes in the coil at various frequencies, that too is measurable and predictable. At resonance frequency, impedance is at it's highest levels. That just means the inductive reactance has shifted as the coil field is saturated with energy.
Here, a woofer with a very low Fs value would be most desirable. (Peaks at well below 25 Hz.) As frequency changes upwardly, inductive reactance becomes less a factor and we see either a very linear or near flat response curve in the usable range of the speaker/woofer in question. (Say 35-150 Hz. for a well designed woofer)
Very good tuitorial material here. I have read many of Dan Wiggins "White Papers" on Adire drivers in the past and respect his attention to detail and engineering skills. He's not pretentious, overly technical and able to break down the complex nature of his designs in ways that make sense to non-technical folk. Yes, he can back it with all the technical data as needed, but in plain english, this man is very gifted and will be back in action again at some point later.
Thanks for the link and sharing your present findings. Keep up the good work!
Swez
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