Midbass punch: spl, voice coil heating and Bl linearity - Page 2 - AVS Forum
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Old 03-11-2014, 07:19 AM
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Originally Posted by Martycool007 View Post

Nice post! I am curious though, with regards to your statements about using an 8" mid-bass driver covering the frequency up to 2000hz in this critical range, versus a 15" mid-bass driver in the same frequency region, you state that the 8" driver simply is not capable of the large dynamic range and overall accurate SPL levels compared to the 15" driver. What I am curious about is how this same 15" driver would sound in the higher mid-range frequencies, such as 1,500hz and above, compared to the smaller 8" mid-bass driver? Would the 8" driver not have as much breakup and beaming at the higher frequencies?

I have always had the impression that the larger, (ie 15"), drivers have a harder time on the upper end of the mid frequencies compared to a similar 8" or 10" driver. Correct me if I am wrong, though.

I have the same impression and is why I believe in more speakers to cover smaller ranges.
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Old 03-11-2014, 11:51 AM
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Originally Posted by Bill Fitzmaurice View Post

Not very good, because it will start beaming around 1.2kHz. Better designs seldom run a fifteen higher than 800Hz. PA cabs routinely run fifteens to 2kHz., but they tend to be used at listening distances where wide dispersion is far less of a concern than high output.

Bill, you're tightly integrated into the Pro Audio world. Can I ask you a question?
Is the reason for 15's instead of multiple 8's based primarily on cost & ease of assembly or something else?
I would think a quantity of 8's or 10's that achieve the same SD would sound better than a single 15.

"The boom is dead, long live the bass"
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Old 03-11-2014, 01:06 PM - Thread Starter
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So if we take out thermal compression and only address Bl non-linearity via xmax and Sd, we can draw some conclusions.
(One of the Mbentz links gets even more interesting. Check out the abreviated poster http://www.klippel.de/fileadmin/klippel/Files/Know_How/Literature/Papers/Klippel_Nonlinearity_Poster.pdf)

Lets take LTD02's thought of wanting to keep peak content to 50% xmax as the base idea and go from there...(bass idea!)

I'm going to bring this to the home theater front instead of rock concerts since it has more application here.

Most home theater environments use an 80 Hz 2nd order HP filter on mains, so lets use that in the model as a starting point.

Lets consider the SEOS speakers and use them represetatively to other designs

Kit (alignment): driver, xmax, sd, power at 50% xmax, spl (1m) at 50% xmax
Fusion 6 (sealed): FaitalPRO 6FE100, 5.25 mm, 143 cm^2, 19 watts, 102 db @ 1m
Fusion 8 (vented):Eminence Beta-8A, 3 mm, 210 cm^2, 14 watts, 105.5 db @1m
Fusion-10 Pure (vented): Eminence Delta-10A, 3.5 mm, 345 cm^2, 45 watts, 113 db @1m
Fusion-12 Tempest(vented): Eminence Delta Pro-12A, 4.6 mm, 532 cm^2, 90 watts, 117 db @1m
Fusion-15 Sentinal(vented): B&C 15PS76, 7.5 mm, 855 cm^2, 375 watts, 123 db @ 1m


We know that we don't listen at 1 meter away, but are more like ~3 meters. This distance is a a -9 db penalty (-6 db for 2 meters)
We also know that woofers have to contend with baffle step, so lets figure a -4db penalty.
We know that you need +20db of dynamic headroom.


So we can take this information to figure out what is the maximum reference level for each of these speakers
RealRef=db@ 50% xmax -9 db (distance) -4 db (baffle step) -20db (peak headroom)

Fusion 6 = 69 db (75 db in MTM)
Fusion 8 = 72.5 db (78.5 db in MTM)
Fusion 10 pure= 80 db (86 db in MTM)
Fusion 12 tempest= 84 db (90 db in MTM)
Fusion 15 sentinal= 90 db (96 db in MTM)

Note #1: If you use a higher XO, you can gain a few more db headroom. If you lower, you lose headroom.
Note #2: THX theater ref is 85 db. Home ref is often set to 75-85 db.
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Old 03-11-2014, 01:23 PM
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1/2 of xmax is playing it conservative, but then again, I like that. Better to size it this way.

I think you'll get 6db going MTM because you can double the power as well.

Also, I think it's quite important for the end user to look at the required power to get there. 375 watts is a fairly large amp, where as 90 watts for the Fusion 12 is very common. What if you reran those numbers at say 100watts (a realistic output from a quality receiver) what would you get. The race would be much closer. If someone doens't plan on putting 400 watts to their speakers, they won't get the benefits out of the sentinel. Might as well save the space and go with the tempest (I'm overlooking the other benefits for the sake of discussion).
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Old 03-11-2014, 01:37 PM - Thread Starter
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MTM doubles the volume displacement, so you gain 3db of headroom with respect to 50% xmax, but in parallel, 6db of efficiency. Two different beasts.


if you put 100 watts into the Sentinal, you are at 117.5 -33 = 84.5db. This says that there is no major point in getting the sentinel vs the tempest if you don't have a big amp as you pointed out smile.gif
I was just trying to look at this from the perspective of just headroom of the speaker, not the amp smile.gif
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Old 03-11-2014, 01:39 PM
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Originally Posted by CZ Eddie View Post

Bill, you're tightly integrated into the Pro Audio world. Can I ask you a question?
Is the reason for 15's instead of multiple 8's based primarily on cost & ease of assembly or something else?
I would think a quantity of 8's or 10's that achieve the same SD would sound better than a single 15.
Cost, and inertia. New concepts don't take hold easily in pro-sound, especially at the lower end of the scale, where users are far less likely to have a strong knowledge of how gear works. Innovation starts at the high end and gradually works its way down to entry level, a few decades later. Where point sources are concerned cabs like what JTR is making are a lot more sense than what's available at the same price points from JBL. But ask an average DJ or bar band what they think about JTR and they won't know who you're talking about. rolleyes.gif
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Old 03-11-2014, 01:52 PM
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Originally Posted by Anthony_Gomez View Post

MTM doubles the volume displacement, so you gain 3db of headroom with respect to 50% xmax, but in parallel, 6db of efficiency. Two different beasts.

I understand that. But take the Fusion 8 for example. Only takes 14 watts to achieve 1/2 xmax. Everyone has at least 28 watts (I hope). So you add another driver, and you double the power going to the speaker. The xmax will remain at 1/2, but you'll get 6db extra from the speaker. And I'm not talking about halving the impedance, this is true for series or parallel wiring. IF you can power it. With the Sentinel, it might not be so. Add another driver to the Sentinel and now you need 750 watts! That might not be practical. But with the Fusion 8 MTM, it's very fair to give it a 6db increase.
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Old 03-11-2014, 01:59 PM
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Originally Posted by Anthony_Gomez View Post

MTM doubles the volume displacement, so you gain 3db of headroom with respect to 50% xmax, but in parallel, 6db of efficiency. Two different beasts.

2X volume displacement + 2X efficiency gives 6 dB more headroom.

Noah
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Old 03-11-2014, 02:00 PM - Thread Starter
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thanks you two. I wasn't thinking clearly and had to convince myself by modeling it in winISD. I'll correct the top post smile.gif
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Old 03-11-2014, 04:05 PM
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Originally Posted by tuxedocivic View Post

1/2 of xmax is playing it conservative, but then again, I like that. Better to size it this way.

I think you'll get 6db going MTM because you can double the power as well.

Also, I think it's quite important for the end user to look at the required power to get there. 375 watts is a fairly large amp, where as 90 watts for the Fusion 12 is very common. What if you reran those numbers at say 100watts (a realistic output from a quality receiver) what would you get. The race would be much closer. If someone doens't plan on putting 400 watts to their speakers, they won't get the benefits out of the sentinel. Might as well save the space and go with the tempest (I'm overlooking the other benefits for the sake of discussion).

The consideration of power, and more directly current through the voice coils, is an important one if looking at dynamic tracking. While I lots of talk of thermal and static BL vs. excursion limits, that entirely ignores the more complex, and higher order distortions created by high current through a voice coil, especially in the multi-dimension condition of the moving coil through different surroundings and magnetic field.

The anecdotal example I will always remember that drove home just how much field a bit VC can create was when I had a 12" sealed subwoofer at home in the living room. On the other side of the wall was my office where I still had an old CRT computer monitor. One day I fired up some bass heavy music and turned it up a bit before I went back to the computer... Sure enough, the picture on the monitor was wiggling to the music from the woofer on the other side of the wall...

While it should be no surprise when a woofer's magnet distorts some colors on a CRT, a moving image can only come from a changing magnetic field. Sure enough, rotating the woofer 90 deg pretty much eliminated the image modulation. The fact that this was visibly demonstrable from probably 3-4' distance through a wall really gave it some tangible scale. I tested more than a few other drivers in the same spot and orientation, and the effect was not universal. It's comparable to plugging in a torch-light or other dimming light on the same outlet as your amplifiers and dimming it down to a low level. It makes for an amusing display of real world Voltage sag on the line...

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Old 03-11-2014, 06:08 PM
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Quote:
Originally Posted by CZ Eddie View Post

Lets consider the SEOS speakers and use them represetatively to other designs

Kit (alignment): driver, xmax, sd, power at 50% xmax, spl (1m) at 50% xmax
Fusion 6 (sealed): FaitalPRO 6FE100, 5.25 mm, 143 cm^2, 19 watts, 102 db @ 1m
Fusion 8 (vented):Eminence Beta-8A, 3 mm, 210 cm^2, 14 watts, 105.5 db @1m
Fusion-10 Pure (vented): Eminence Delta-10A, 3.5 mm, 345 cm^2, 45 watts, 113 db @1m
Fusion-12 Tempest(vented): Eminence Delta Pro-12A, 4.6 mm, 532 cm^2, 90 watts, 117 db @1m
Fusion-15 Sentinal(vented): B&C 15PS76, 7.5 mm, 855 cm^2, 375 watts, 123 db @ 1m

I see what you're trying to do here, but to understand the theory it would be better to use the same motor and change the diaphragm size and suspension to achieve a true apples to apples comparison.

For the same bandwidth, and the same motor (magnet + voicecoil), you're going to see an increase in efficiency as you increase the diaphragm size (assuming you can get the suspension adjusted to achieve the same bandwidth). The dominant correlation will be related to the Sd of the driver. So for the same excursion, your 855cm^2 (15") driver will be 2dB louder than your 532cm^2 (12") driver.

As you're noting in your example, the B&C 15PS76 7.5mm excursion is roughly 2dB more than the Eminence Delta Pro-12A 4.6 mm excursion. This is giving you another 2dB advantage to the 15" in your example. Then if we investigate the bandwidth, the B&C 15PS76 is being used over a narrower range, which should explain the last 2dB of difference between the two.

All that to say, if you take PWK's doppler arguments seriously, and account for the Klippel linearity behavior, then we're talking a roughly 2dB difference per step when going from a 15" -> 12" -> 10" -> 8" -> "6" driver.


Increasing power handling and xmax does not decrease the doppler effect. The only things we can do there is reduce bandwidth, or find other means of reducing excursion (like hornloading or doubling up on drivers).

Ignoring doppler effect, the next stage is improving linearity - which your Klippel marketing poster shows. One thing not mentioned yet is that improving the suspension linearity moves a lateral reflection lower in frequency. At some point, that gets into the passband of the system and you get a distinct peak/dip thing in the frequency response. Even though you can EQ it out, the resultant distortion is very noticeable in a side-by-side comparison with a driver that doesn't exhibit that behavior. Is it worth reducing the high excursion suspension distortion with a decrease in performance at lower amplitudes? That will be up to the listener, but I personally don't think it's worth the tradeoff. The shorting rings, however, appear to free lunches for the most part - at least I've not found a system that sounds worse when moving to a driver with a shorting ring. Improved pole pieces and the like are simply cost-adders, but at some point the doppler effects are going to dominate.


All that to say - and not to beat the horn drum too hard - but I totally get why PWK was so adamant about horn loading. Horns have justifiably earned themselves a bad track record, but that scene is quickly changing. When talking about midbass punch, the horns are gonna leave the direct radiators in the dust. Unfortunately those horns are so blasted huge - but I think we're often too quick to run to the smaller solutions. I get it if aesthetics / budget absolutely dictate it, but after hearing hundreds of systems I will never run a 12" 2-way for a simple PA system with the speakers on stands: even for vocal applications. The cone breakup and inductance modulation from the 15" woofer is less annoying than the increased IMD from the 12" system. Once we start talking big festival and touring rigs, then we start looking for solutions that maximize the summation of A LOT of surface area.....lots of bass cabinets and lots of xovers to help narrow the bandwidth regions. If you get artistic about it (what soundguy isn't?) then you start playing games with the actual xover frequencies to help embellish the dominant genre of your tour. Back to the home scenario, high-fidelity listening requires very good cohesion between the various drive units - there is a ton of justified elegance in trying to achieve that cohesive sound with as low distortion as possible. Minimizing the number of drive units is the most straightforward way to accomplish this, which means maximizing bandwidth and we're butting up against doppler again. And don't forget the doppler effects are true for perfect drivers....
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Old 03-11-2014, 06:28 PM
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When talking about midbass punch, the horns are gonna leave the direct radiators in the dust

This.
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Old 03-11-2014, 08:34 PM
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Quote:
Originally Posted by Bill Fitzmaurice View Post

Quote:
Originally Posted by Martycool007 View Post

What I am curious about is how this same 15" driver would sound in the higher mid-range frequencies, such as 1,500hz and above, compared to the smaller 8" mid-bass driver?
.
Not very good, because it will start beaming around 1.2kHz. Better designs seldom run a fifteen higher than 800Hz. PA cabs routinely run fifteens to 2kHz., but they tend to be used at listening distances where wide dispersion is far less of a concern than high output.

^^ +1 Marty. additionally, cone resonances, inductance issues, and all the rest of it really point to keeping even a really good 15" to somewhere in the 1khz region, and even a little lower would be better.

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Old 03-11-2014, 08:43 PM
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Quote:
Originally Posted by tuxedocivic View Post

1/2 of xmax is playing it conservative, but then again, I like that. Better to size it this way.

I think you'll get 6db going MTM because you can double the power as well.

Also, I think it's quite important for the end user to look at the required power to get there. 375 watts is a fairly large amp, where as 90 watts for the Fusion 12 is very common. What if you reran those numbers at say 100watts (a realistic output from a quality receiver) what would you get. The race would be much closer. If someone doens't plan on putting 400 watts to their speakers, they won't get the benefits out of the sentinel. Might as well save the space and go with the tempest (I'm overlooking the other benefits for the sake of discussion).

+1

this is a really good point that is worth repeating. most folks like to look to the high power handling numbers (or large xmax numbers) as a measure of how loud the speaker will go.

BUT the higher power handling (and greater excursion) means a beefier coil and that means more weight, which means *less* sensitivity. so what you are really trying to balance is how much amp you are actually going to use, sensitivity, and excursion.
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Old 03-11-2014, 09:00 PM
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great post mike in #41!

for a sidebar conversation

|| the question then turns to how does one go about measuring doppler distortion and what level is 'good enough'? or, is it there a way to back it out (at least for a home environment) by relating a driver diameter to a cutoff frequency? such as dd is kept sufficiently low with an 8" crossed at 200hz and a net ~4th order high pass giving about 2mm of excursion and a 15" gives the same dd crossed at 100hz again ~2mm excursion. or maybe 4mm is the right number... i suppose the question is how many mm of excursion does the woofer need to be modulated before dd distortion is noticeable. then again, maybe that isn't even the right question, as other factors may actually creep in and dominate before dd. ||

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Old 03-11-2014, 09:06 PM
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for a 80hz highpass or so, it would seem that high sensitivity horns could be designed that aren't too big. bfm has one with about a 100hz corner or so that mk is using iirc. i've hornresp'd up several that are about the size of the la scala or a little larger, but with a much more linear response. but now we are talking ~105db 1w1m sensitivity and high "intensity" (velocity) output. maybe just go back to that!



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Old 03-11-2014, 09:30 PM
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The depth will be the a$$-kicker, unless you fold and cross to a midrange horn, but that comes with it's own set of problems (not being point source like Synergy, etc). Given a generous baffle wall with depth, a multi-horn or synergy would be awesome (like pnw's setup). Great thread, by the way. Reminds me of the older threads that used to be commonplace around here, with tons of useful info.

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Old 03-11-2014, 09:33 PM - Thread Starter
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So, I just came across this thread and thought I'd share for those interested in hornresp, but have never tinkered with it.

http://www.hometheatershack.com/forums/diy-subwoofers-general-discussion/36532-hornresp-dum-hmm-everyone.html
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Old 03-11-2014, 09:47 PM - Thread Starter
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Quote:
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I see what you're trying to do here, but to understand the theory it would be better to use the same motor and change the diaphragm size and suspension to achieve a true apples to apples comparison.
I agree. I really do. It's just not easy to do this all on paper...and that's how it has to be done as I don't think there are a set of speakers to do do actual tests on to achieve those goals. My goal with that post was simply to take what I have so far learned in this thread, and apply it to real world speakers that we see frequently in these forums, and get numbers that made practical sense.
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Old 03-11-2014, 11:06 PM
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Ya, there's definitely some merit in the real world examples....I was actually surprised by those numbers which is why I had to go back to some of the theory to see what was affecting what.

To LTD's question, it's not just a function of excursion, but also of bandwidth. I've seen some sources talking about it in octaves, and others in actual Hz...I need to work through the math again to deduce which dominates the trend. For example, is 20-80Hz (two octaves) the same as 200-800Hz (two octaves) or 200-260Hz (60Hz bandwidth)? Octaves makes more sense to me conceptually.

Either way, a rule of thumb here would need to include diaphragm size, excursion, and intended bandwidth.

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Old 03-12-2014, 12:09 PM
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Quote:
Originally Posted by MBentz View Post


As you're noting in your example, the B&C 15PS76 7.5mm excursion is roughly 2dB more than the Eminence Delta Pro-12A 4.6 mm excursion. This is giving you another 2dB advantage to the 15" in your example. Then if we investigate the bandwidth, the B&C 15PS76 is being used over a narrower range, which should explain the last 2dB of difference between the two.

Isn't the bandwidth the same? 80hz high pass. The upper bandwidth is different, but I don't think that's an influence here.

Quote:
Originally Posted by MBentz View Post


Ignoring doppler effect, the next stage is improving linearity - which your Klippel marketing poster shows. One thing not mentioned yet is that improving the suspension linearity moves a lateral reflection lower in frequency. At some point, that gets into the passband of the system and you get a distinct peak/dip thing in the frequency response.

I've seen this on some of the newer SB Acoustics Satori woofers and wondered why this was left in place. The woofers tend to Klippel very well, but they have a peak dip combo right in the midrange. Is this what you're talking about, or something else I'm not understanding?
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The shorting rings, however, appear to free lunches for the most part - at least I've not found a system that sounds worse when moving to a driver with a shorting ring.

Except they cost more money, and what improvement do we get? Le linearity. Is that audible if the driver's passband remains within a reasonable limit, say up to 1khz for a 12". Maybe even more. ?
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Old 03-12-2014, 12:19 PM
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Wait. No. You may not necessarily get Le linearity just by having a shorting ring.

I hope someone who knows this better can it explain it but ...

Let's say we have a two motors: one with no shorting ring and one with. The one without doesn't necessarily have a high Le it's just that it doesn't have a ring. Now the one with the ring may have a lower static Le rating but whether it is more linear is another thing. Let's just say you have a shorting ring in a position that only allows it to be effective with an outward stroke of excursion. What happens when that moving inductor of a voicecoil moves inward? That inductance has now shifted massively. This is bad. This is inductance that is not linear. It is said that how linear the inductance of a driver is has more to do with it's perceived SQ over it's static value.

Simply put, the implementation of the inductance fighting methods is just as important as using them at all.

Hope this helps.

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Old 03-12-2014, 12:43 PM
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I agree that Le @ 1khz is a fairly useless number. And I agree that implementation of a shorting ring is as important as simply having one. But I'm making the assumption that the driver designer has implemented it well enough that is linearizes Le somewhat. The question isn't whether it's implemented well. The question is, if outputting massive amounts of midbass, will a (properly implemented) shorting ring linearize Le enough to be audible with a low pass filter? And at what frequency should the low pass be set?
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Old 03-13-2014, 02:48 AM
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"Except they cost more money, and what improvement do we get?"

a reduction in intermodulation distortion is the primary benefit. clearer sound.

Listen. It's All Good.
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Old 03-13-2014, 07:11 AM
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Can you explain how this is so? I understand that Le will be more consistent over the excursion stroke, but if the passband is limited at the high end where inductance doesn't change much, I'm not sure it matters.

Sorry, a bit OT. But if mid bass is desired, then excursion is required and we gotta make sure we don't muck up the rest right.
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Old 03-13-2014, 09:03 AM
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Do we have examples of shorting rings that don't improve Le linearity? Do we have examples where it causes some other negative artifact? And do we have examples where Le linearity cannot be improved with a shorting ring?

Btw, I agree that linearity only matters over the intended bandwidth, but I think you'd be hard pressed to find a design where that was the case. Maybe the acoustic elegance stuff....

-Mike Bentz
~It's all about compromise~
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