Yes, I paid careful attention to Le linearity in my woofers because I tended to take them higher than what most people would.
As you show, B&C do this well.
The 12" has an Le of 1.35mH, the 15" 1.4mH, the 18" 1.48mH.
The difference in the proximity of the coil to the aluminum frames could account for that little change.
There is over 900 gram difference between the frame weights.
I measured a nominal 2 mH air core inductor & former (180 grams) at 1.95 mH.
Placed on top a 60 gram 40 cm long aluminum angle, the coil read 1.87 mH.
Carbon fiber, if used in the larger cones, might also affect the inductance.
At any rate, the materials surrounding the magnetic structure and coil do have an effect on inductance.
We're 'talking' peak dB SPL and in speaker design we're always trading acoustic efficiency for bandwidth, so decrease effective Qt' (more powerful motor) = less LF gain BW and vice versa.
Seems like you ignored what I wrote after the first sentence. As an illustrative example, I modelled a woofer in a simple, very large closed box (Fc = 36.8 Hz), one time with low Qts, another time with the same driver but with decreased Bl, so higher Qts:
Qts = 0.32 -> 88.3 dB at 50 Hz at 23.4 Ohm
Qts = 0.59 -> 90.4 dB at 50 Hz at 13.4 Ohm
Okay, there is no info about electrical phase angles, but you can see the tendency. It seems the more powerful motor have only lower Voltage sensitivity in the LF region, but its true efficiency (dB/W) is not decreased, because the higher Bl leaded to higher electrical impedance so less current will flow trough the voice coil for the same Voltage.
Last edited:
You're right, I only know for fact (as I understand the physics of the situation) from experience what I wrote. 
Regardless, anyone uses a simming program can plainly see it, so if my semi-technical generalization isn't technically correct, then ya'll post it and I'll include it with my simpleton one as I'm only interested in posting the most correct information, i.e. don't tolerate any marketing 'flooby dust'.
Regardless, anyone uses a simming program can plainly see it, so if my semi-technical generalization isn't technically correct, then ya'll post it and I'll include it with my simpleton one as I'm only interested in posting the most correct information, i.e. don't tolerate any marketing 'flooby dust'.
@GM what matters in woofer specs that don't show up in simulations? For example, I see things like shorting rings listed but I don't know which of those things are worth paying for and what isn't because I don't know how to see their effects in simulations. Some things require experience to know if they are real or marketing flobby dust and I don't have any experience.
Shorting rings show up in the driver's inductance that governs its FR above its Fhm.
For strictly narrow (~2 octaves) BW sub duty, one can make an argument that it's a waste of $$$, but used as a wide range (sub) mid woofer out to 3-500 Hz with some out to 1200 Hz as I historically used and especially 'FR' drivers, definitely worth it IME, i.e. there's no such thing as too 'clean' in the critical telephone BWs (250-2500 Hz analog, 300-3000 Hz digital) since it's what we pay most attention to.
For strictly narrow (~2 octaves) BW sub duty, one can make an argument that it's a waste of $$$, but used as a wide range (sub) mid woofer out to 3-500 Hz with some out to 1200 Hz as I historically used and especially 'FR' drivers, definitely worth it IME, i.e. there's no such thing as too 'clean' in the critical telephone BWs (250-2500 Hz analog, 300-3000 Hz digital) since it's what we pay most attention to.
what if potentially due to Increased Sd changes the driver's coupling to air, potentially affecting the back EMF and thus impedance curve?
The vent tuning and damping material and other acoustical events manipulate the impedance response, the acoustical event difference between Sd's probably have type of influence.
The above response is particular good for being marked le1.8mh...
The vent tuning and damping material and other acoustical events manipulate the impedance response, the acoustical event difference between Sd's probably have type of influence.
The above response is particular good for being marked le1.8mh...
Sd doubled...
Electrical input impedance unaffected at high frequencies, assuming pistonic behaviour.
Attachments
Sorry,but poorly written article.
Skips way to fast over formulas and simplifies certain formulas, which makes it hard to understand where certain constants (numbers) come from.
Just go to the Thiele/Small wiki page.
Also keep the page from like a RLC circuit or resonator next to and you will understand immediately how things work and what they represent.
This one sums it up very easily and graphically for anyone interested.
Watch it to the end, and you will hear Geddes's comments too.
Again, what he's saying is correct if you have a subwoofer that is big enough and has plenty of output and headroom.
Still, as I showed a couple of posts back incl Keele's paper, that if there is to big of a mismatch, you just have to boost way to much or it will cost you a lot of electrical power.
Also keep in mind that he's talking from a subwoofer point of view with all freedom and control with a DSP for example.
So in the end I find his answer a bit over simplified. Because it skips over these nuances that are extremely important.
Yet it comes across as a general statement.
Even putting a 18 inch subwoofer in a very small cabinet can create problems if you're not careful.
Same goes for a BL that is so high that you just have to boost enormous amounts in the low end (again see my posts and Keele's paper)
I do agree with the idea that a lot of people make this a much bigger deal than it really is.
This is again backed up by Erin's measurements and listening.
He rarely complains about Q of the low end part.
That being said, for smaller systems optimizing is an absolute necessaty.
Because there is a trade-off between max output, smooth response and making sure you don't damage your woofer.
In theory no.
In practice it's tight on such a way that the type of voice coil and the way it's being wound can change the Mms.
Since you also want to optimize that with the diameter and application of the woofer, it will change.
But obviously that's just the practicality of it. There is no direct relationship.
With plenty of demodulation, you can make the impedance practically flat.
It only doesn't add much for subwoofer applications, but that's a different story.
Actually, this isn't even true in theory only in practice.
In theory we only care about a moving mass, not how this mass is composed.
Incorrect. The larger Sd changes the acoustical mass loading on the diaphragm, but since this air mass is a small fraction of the cone mass it's effect is small.
That is what I meant, I just worded it on a weird way.
What I meant was that there is only mass from the moving parts as a whole + the mass of the air.
So the Sd only says something about the air mass, but nothing about the other part of the mass.