bose301s
5,000+ posts
I can break these cuffs
True, but BL curves help get a flat response curve.
bose301s
- Thread Starter
- #62
guess i should stop making assumptions ehh?
my badz on teh misinformation folks
my badz on teh misinformation folks
It is a completely semantical argument, where you are setting one reference point and they are setting another. Both arguments are completely plausible.
From a subjective standpoint with subwoofers, flat axial response is one of the driving perceptual factors, which is especially unfortunate in a vehicle where most listeners are incapable of discriminating between the room effects, the driver, and the enclosure.
It is true that we don't listen to BL curves. The Klippel, for example, does statistical fit analysis of contributors to distortion. The only way to know how much distortion is being generated is to physically measure it. However, we know that there is a strong correlation between the linearity of BL, Cms, Le and the physical distortion that is created from a lack of linearity. From an engineering standpoint, it is easiest to start by targeting linearity.
Can you hear the distortion? Well, it depends on the spectrum and amplitude of the distortion, the stimulus, etc. However, I would approach all systems (particularly from the speaker aspect) the same: the elimination of distortion should be a primary goal since the goal of any audio system is to reproduce the source, rather than produce something different that we may interpret favourably.
flat response does not dictate low distortion. If you're going to argue that non-linear BL curves are OK, i would respectfully disagree....
There are MANY tradeoffs today why non-linear BL curves are still the vast majority of speakers and I can tell you without a shadow of doubt that it has everything to do with efficiency.
ya, thats where Dan Wiggins and I were getting into that major disagreement.
where do you set references points????
In my opinion, i would say geometrical xmax is a big one as well as a fixed magnetic source.
otherwise you can always say make this coil longer... make this gap tighter etc etc.
The major problem i see is that xbl and lms both lose about 2.5 dB to a reference overhung design. Not everyone agrees with me on that number, but I have done LOTS of modeling so thats where i end up.
The market also backs me on this.... how many engineers want to include the money to make up 2.5dB of SPL?
whats going to make the average customer happy? nearly a 2 fold advantage in SPL or a two fold advantage in distortion? And like you said... a lot of distortion is hard to detect... there is definitely a psychological component to all of this.
Well the LMS argument focuses on the reference point for the coil: is it a larger coil made smaller, or a smaller coil made larger? There isn't really a way you can definitively say which is which. From a "drop in soft parts" standpoint, it is easier to agree with your concept of taking away windings rather than adding windings.
Can you share some of your modeling?
In terms of efficiency, XBL^2 is rather clever. We can agree that the coil mass is smaller than both LMS and Split Coil (we'll look at these three only for the time being, though there are other approaches we could consider). From there, it must be a question of the number of windings in the gap and the flux density (BL).
If linear BL is the goal, you must manipulate the windings or the flux (or both). In SC and LMS, you manipulate windings. In XBL^2, you manipulate flux. The difference, though, is that suppose we take out some windings: there is no way you will ever get those windings back. With XBL^2, the rebate flux tends to move to the two gaps in the top plate since the steel still has the lowest reluctance. Unless the steel that lines the gap(s) is completely saturated, there is little-to-no flux density lost. Of course, not all of the coil's field rests in the highest flux regions; there are detriments in a maximum efficiency situation with XBL^2, but in practice I think it is a good balance between BL linearity and efficiency. Manipulating the windings rather than the flux also means flux modulation is likely to increase as well.
Can you share some of your modeling?
In terms of efficiency, XBL^2 is rather clever. We can agree that the coil mass is smaller than both LMS and Split Coil (we'll look at these three only for the time being, though there are other approaches we could consider). From there, it must be a question of the number of windings in the gap and the flux density (BL).
If linear BL is the goal, you must manipulate the windings or the flux (or both). In SC and LMS, you manipulate windings. In XBL^2, you manipulate flux. The difference, though, is that suppose we take out some windings: there is no way you will ever get those windings back. With XBL^2, the rebate flux tends to move to the two gaps in the top plate since the steel still has the lowest reluctance. Unless the steel that lines the gap(s) is completely saturated, there is little-to-no flux density lost. Of course, not all of the coil's field rests in the highest flux regions; there are detriments in a maximum efficiency situation with XBL^2, but in practice I think it is a good balance between BL linearity and efficiency. Manipulating the windings rather than the flux also means flux modulation is likely to increase as well.
NDMstang65
10+ year member
Active Noise Control?!
I've got ample access to anechoic chamber and a plethora of testing equipment...
We can look at distortion as well...it does that too //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif
MMAG? //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif
Neil, its not that B is "lost" like L (in the case of LMS) it is that B is unused. In fact XBL^2 motors have on average MORE flux if you integrate the surface area of both gaps... its about 10% more than the overhung/LMS design when you fix a magnetic source... more steel in the magnetic path allows for that (two gaps vs. one)
The way XBL^2 coils couple is that the coil only resides in about 1/2 of each gap..... dividing up a gap into two gaps means you share about 50% of the flux density relative to an overhung design... its actually a little better because of saturation but basically an example will make it more clear.
overhung gap with a Telsa of 0.75 would translate into two xbl^2 gaps (same size) of about 0.4 each. Thats approximation.
now if you had a coil that extended thu both gaps all the way, you would indeed have more BL than the overhung because you're coupling with more L, (this would also be horrible for linearity) but in fact, per split gap design -we reduce the L in each gap to 50%... considering fringe field... XBL^2 BL losses land around 27-28% less than an overhung design. Its not because of the notch (or loss of steal) in fact the notch has nothing to do with it - that was one of the mistakes i made when i first studied the motor, its the fact the coil does not extend thu the gap's all the way (only 50%) and each gap is about 50-60% the flux density of the overhung. It works out to about the same loss that LMS has.
what is MMAG... i have been seraching for a formal definition.
NDMstang65
10+ year member
Active Noise Control?!
Kyle - In which way are you regarding linearity of the split gap? Are you talking in regards to linearity of the Bl curve, or linearity of the soft part assembly?
Have you looked into the differential drive motor that JBL has the patent on? Very similar to what you are talking about minus the xbl^2 gaps..i think that's what your talking about anyhow, very similar if i'm reading that properly.
Have you looked into the differential drive motor that JBL has the patent on? Very similar to what you are talking about minus the xbl^2 gaps..i think that's what your talking about anyhow, very similar if i'm reading that properly.
It's an approach from STEP Technologies. Patrick Turnmire (from Red Rock Acoustics) is the CFO and Enrique Stiles is CEO. I think it's short for Multiple Magnetic Air Gaps. Pretty simple and intuitive: backplate/pole, magnet, steel plate, magnet, steel plate. Where Adire uses a rebate, they use another magnet. I remember they had a good idea where they used an aluminum basket between the middle plate and the magnet for the second gap where the basket would short out eddy currents and work well for thermal compression as well.
wow.. that looks like ***.
ya, no soft parts, i consider that to be a separate issue.
ya, differential drive (two gap, reversed magnetic polarity, two coils, reversed polarity) doest do much for BL linearity, but thats not really the purpose, in fact it kind reduces it because of the "breaking" system. differential drive is good for inductance issues which is why they can be used up past 500Hz... the JBL Everest is a good example (15" woofers are x-over at 700Hz to the compression driver... awesome speaker btw, i got to demo that with the lead engineer of the design at ces a few years back.. very impressive!
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