Well, im very faaaar on RATIONAL side, but i can confirm that sharp resonances with very high Q are not minimum phase and cannot be corrected. They are very high directivity by nature and they look very different if you change mic position. Only thing you can is EQ trend.
How are you confirming that?
Like I said, "practicality aside". There are plenty of reasons not to use a driver through its breakup issues.
18Sound's paper looks at it as a means of lowering inductance - particularly the usual rising impedance with increasing frequency:
http://www.eighteensound.com/staticContent/technologies/products/aic.pdf
It's their "sim.s" that are more interesting - specifically with respect to field integrity. Even then, they are NOT simulating any effects of counter current with respect to a moving coil - even at that discreet freq..
Imagine what a lower freq. transient (generating excursion, generating back emf), does to the magnet's field integrity if only very briefly. From there, think about the result on VC's position.
Of course as mentioned in the article (and as Lynn touched on), the strength of the magnet circuit and its saturation play large roll in the effects of field integrity. Basically stronger motors are in some respects the brute-force work-around. (..though this is also dependent on the mass of the driver - where a high mass driver could create more back emf that will "overcome" its strong magnetic field).
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Scott,
Yes I use a shorting ring in my design and it does much to help the impedance curve. What I am wondering is what happens if the inner and out windings are in counter rotation during the winding, that may actually be a bad idea as you could cancel some of the field that way? From what I caught on the 18Sound site the main attempt was to increase temperature transfer to the motor assembly and lower the power compression effects. My design is of a very underhung design and there is massive amounts of metal to absorb the heat, but every little bit helps so it is still something to look at. One other issue is the heating of any magnets that are close to or in the gap, Neo magnets do not like this much, there are not that many grades that have high temperature capabilities though that isn't mentioned by any speaker manufacturer that I have seen. The higher the MgOe Neo grade the greater the problem. So heat transfer is a real consideration because of that one fact alone. I think this has much to do with the preference for some of the Alnico grades, but they aren't happy if you drop them so it can be a trade off, though I wouldn't want to drop my speakers for any reason anyway.
Yes I use a shorting ring in my design and it does much to help the impedance curve. What I am wondering is what happens if the inner and out windings are in counter rotation during the winding, that may actually be a bad idea as you could cancel some of the field that way? From what I caught on the 18Sound site the main attempt was to increase temperature transfer to the motor assembly and lower the power compression effects. My design is of a very underhung design and there is massive amounts of metal to absorb the heat, but every little bit helps so it is still something to look at. One other issue is the heating of any magnets that are close to or in the gap, Neo magnets do not like this much, there are not that many grades that have high temperature capabilities though that isn't mentioned by any speaker manufacturer that I have seen. The higher the MgOe Neo grade the greater the problem. So heat transfer is a real consideration because of that one fact alone. I think this has much to do with the preference for some of the Alnico grades, but they aren't happy if you drop them so it can be a trade off, though I wouldn't want to drop my speakers for any reason anyway.
Although I use mystical-sounding mumbo-jumbo to describe what I hear ... for lack of any better language ... the reasons for this or that sound are nearly always physical.
But ... you have to step away from idealized models and look very carefully at the physical driver, and all the mischief it can get into. There's only a limited frequency range where most of the cone is moving in-phase, and that's considered piston-band. Note that I said most of the cone. The surround and spider are going to be up to their usual tricks, which show up as very small ripples in the response in the 300~800 Hz region. The dust cap, unless it's a really lossy, non-radiating material like felt, is a low-quality dome radiator that isn't even attached directly to the voice coil. So even in the piston band things aren't exactly 100% close to the ideal model.
Things are sort of controlled when we hit the first mode on the cone, depending on whole lot of factors. The inside of the cone moves in while the outside moves out, which does weird things to the polar pattern ... at the most basic level, we see an on-axis null, which disappears off-axis, and can be replaced by a bump far off-axis.
This is the absolute simplest description for what happens as we leave the piston-band region. Polar patterns get funky, thanks to the diaphragm no longer being in phase with itself ... we now have multiple centers of radiation with complex phase relations with each other.
Looking at the first and simplest mode, EQ is already kind of problematic, since on-axis correction will not be correct for off-axis (because the inside and outside of the cone are not in phase with each other, creating a spatial vector-sum problem). Damping can be our friend here, broadening the Q of the first mode, and giving a much softer entry in and out of the first-mode region. This is what we see with high-quality 12" and 15" paper-cone drivers ... a broad, wide peak in the 1.2 to 1.5 kHz region, and yes, it does respond to equalization, with good minimum-phase characteristics after equalization.
So this is a way of saying that if EQ is used, it works best on drivers that already have a considerable degree of self-damping.
Because things get really ugly once we go above the first mode. If the driver is well-damped, with any luck, the output drops like a stone, and this is what we see in the better-behaved 12" and 15" paper-cone drivers. The 5.5" Vifa I used in the Ariel had the smoothest dropoff curve I've ever seen in any driver. Whoever engineered the polypropylene cone in that driver, they knew what they were doing.
But ... if the driver output does not drop above the first mode, it gets pretty nasty. The cone now radiates from several locations, with very complex phase relations between the regions. The size and shape of the regions can be dramatically different with small changes in frequency, and linear acceleration is no longer assured.
This region is where we see sudden spikes in distortion that are extremely narrow in frequency. Move the microphone a few inches to the left or right, and things are very different. It's fairly common for the on-axis response to be the worst in the group, with 5~10 degrees off-axis looking better. The group delay response disintegrates, with rapid shifts depending on frequency and angle of emission.
When I see this happening (looking at departure from minimum-phase and checking how much it changes with movement of the microphone), the driver is all gone. This is a non-usable frequency region, and can only be eliminated with very sharp filtering to push it below audibility. If digital filtering is employed, this is where the brickwall filter gets used. In the analog world, it probably takes an elliptical filter to remove the worst of the junk from audibility.
Cones or diaphragms with a reasonably amount of self-damping just make the design a lot easier and hassle-free. It's true that rigid diaphragms sound more "crisp", but some of that impression might be a little hint of the breakup region, not low distortion. They can sound alike, if you're not careful. Reviewers fall into this trap all the time.
Whenever you start to get into the sound of "crisp", it's time to take a short vacation from hifi and listen to live acoustic music for a while. That's reality. What comes out of a complex electroacoustical system is not. Your job is to create a pleasant, sometimes even exciting, approximation of reality.
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I don't know.
I've not seen anything with respect to AIC and thermal compression. Perhaps this was another "technology"?
In any event, heat in general is something of a red-herring for domestic use (modest spl) with reasonably efficient drivers and even modest venting, certainly nowhere near a demagnetization potential with neo.
Looks like a pint-sized successor to the 5.5" Vifa ... unfortunately efficiency is down, and Fs is up, so it really is a midrange driver. It would be nice if it could drop in and replace the 5.5" Vifa in the Ariel, but that doesn't look possible.
The trick is getting fairly decent performance out of high-efficiency (93 to 99 dB/meter/watt) 7" to 15" drivers. They do exist, but they're not common.
The trick is getting fairly decent performance out of high-efficiency (93 to 99 dB/meter/watt) 7" to 15" drivers. They do exist, but they're not common.
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Thanks for the tip about the Enviee driver. Interesting. I don't care for the peak at 3.5 kHz, but that could be the whizzer cone, which always have rather awkward mechanical crossovers. If the driver was available without the whizzer that would make it even more interesting.
In a non-whizzer configuration, a pair would have an efficiency of 98.2 dB, not bad at all. Cone area would be similar to a single 12" driver.
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Yes, the fullrange is a bit different than the bass version, and includes the use of Alnico (where the bass driver uses neo). I believe the bass version is considerably less expensive than the fullrange version.
Here it is in a pricey commercial design:
6moons audioreviews: Soundkaos Wave 40
..and I have this desire to scream "DIFFRACTION" when looking at the recessing of the drivers in their cabinets.
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Not really an issue here- the panel's not that thick and the driver beamwidth is surely very narrow by any freq it'd be an issue at.
Of course, I'd prefer if it were mounted against a beveled or rounded edge.
To my eyes, that is impressive. Makes me wonder about accuracy. Low MMS as well.
A couple things about the those speaker shown above are that they look interesting to say the least, but I would still think that you would have the typical edge diffraction due to the rather sharp corner transition to the side panels. Another thing that most don't think about when recessing a driver behind a baffle is that you have create a resonant chamber immediately in front of the driver. You can calculate the resonance of the chamber by the volume and depth of the chamber, it will show up in the frequency response curve if you look for it.
On the RMS front with two divers with identical values but differing Compliance values you need to look at a few other things. Given that they have different values tells you the compliance and the moving mass are going to be different. I would think that the cone with the lighter cone mass and softer suspension would sound different at low volume and would probably have a better impulse response, though I would have to test that hypothesis to prove it. It just makes sense that a lighter moving mass should be able to accelerate faster than a similar cone with a heavier mass and stiffer suspension. This is to say that all other parameters are equivalent such as the BL factor in the gap and let's say the same gap length and width, and equal voicecoil length. Of course the two would have different VAS and would use different box size to have equivalent low frequency tuning.
On the RMS front with two divers with identical values but differing Compliance values you need to look at a few other things. Given that they have different values tells you the compliance and the moving mass are going to be different. I would think that the cone with the lighter cone mass and softer suspension would sound different at low volume and would probably have a better impulse response, though I would have to test that hypothesis to prove it. It just makes sense that a lighter moving mass should be able to accelerate faster than a similar cone with a heavier mass and stiffer suspension. This is to say that all other parameters are equivalent such as the BL factor in the gap and let's say the same gap length and width, and equal voicecoil length. Of course the two would have different VAS and would use different box size to have equivalent low frequency tuning.