t/s specs and theoretical comparisons

Ah well Dave you and I will have to disagree on that one.  For any two woofers of the same size diaphragm and similar power utilization efficiency, the one with the longer Xmax always has more dbSPL capability  More swept volume = more air pressure generated = more output.Support the12volt.com

...but this is what I'm SAYin'... You'll RARELY if ever see a long throw woofer with an n0 even close to a short throw woofer. If their n0 numbers are similar, then they CAN'T have huge differences in output, at the same input power levels. To say such a thing infers that the power conversion curve isn't linear, and that a given woofer COULD have a better power conversion efficiency at high input power than it does at a low input power... Right?It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

While those things are possible that's not what I'm saying.  If woofer A converts 100 watts of input to 6mm of linear motion and woofer B converts 100 watts of input to 16mm of linear motion, which one will produce higher dbSPL?Support the12volt.com

DYohn: It still could be woofer A. How, why? Because woofer B might be far slower. Remember, "SPL is determined by rate-of-change". So if woofer B had a lower rate-of-change because of being slow to transition from the low-pressure trough to the high-pressure peak, then woofer A would produce more SPL. Right haemphyst? Here's another thought: What does the n0 mean exactly? Yes, I know it's the efficiency of the woofer turning electrical energy to sound energy. But, what does it mean mechanically for the woofer? If I understand this all correctly, it means that when comparing two woofers, the woofer with the higher n0 either moves faster, farther, or some mixture of the two with a given power than a woofer with a lower n0. Humm, basically all I did was repeat other conclusions... I'm seeing a common theme here :) Now, what about the compliance of a woofer. If a woofer is more compliant and another, then that leads to the idea that a compliant woofer is more efficient because it takes less power to move it, right?

I've been away from my keyboard... :P DYohn: At what frequency? If woofer B is converting the SAME 100 watts at a frequency that is a full octave below what woofer A's Fs is, then no; as you know that lower frequency demands the extension of the suspension. If you are putting them on an equal playing field, 100 watts, 100Hz, similar n0, and equivalent alignments, then yes, you are absolutely correct. I never denied that though. *My* issue is that there AREN'T any long-throw woofers, certainly not any woofer B's with three times the throw of woofer A's, AND with an equivalent n0. THAT'S what my stand is. *IF* all things are equal EXCEPT excursion, then yes, the long throw woofer SHOULD be able to produce a higher SPL. Such a woofer doesn't exist, though. Consider this: If everything is equal as stated above, then why would woofer B EVER HAVE TO EXTEND like that? It simply wouldn't ever happen. For the same frequency, for the same Sd, for the same power, for the same alignment, for the same n0, the extension WOULD HAVE TO BE THE SAME, yes? All above the same, the SPL would be too... Am I right? For additional extension, there would have to be either a: lower frequency b: more power c: higher n0 I think I'd stand on those conclusions... KyferEz, you are correct. To your second conclusion: n0 could be said to be a mathematical representation of the strength of the motor. The stronger the motor, the higher the conversion percentage. That's the mechanical difference. A smaller magnet, fewer turns on the voice coil, smaller wire in the voice coil, a thick top-plate, heavier diaphragm, higher impedance... Those could all affect the strength of the motor, and directly affect the conversion capability, thus the SPL ability. To your third conclusion: I honestly do not know... I've never really looked at that aspect of SPL. It does stand to reason that a softer compliance would react faster to a large-signal input. That one, I'll have to ask or research a bit. Good question! It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

Perhaps we're talking at cross purposes here Dave.  According to Boyle's Law, the more displacement a piston creates the higher it will pressurize a space.  Since a woofer is a piston (and it is power that creates excursion, not frequency) the farther it is displaced the higher the pressure wave it can create.  higher air pressure = higher sound pressure.  I am not talking about efficiency or driver Q, merely physics of sound.Support the12volt.com

I don't disagree with that... Not one bit. But what I *am* saying is that if: Sd is the same Power is the same n0 is the same Alignment is the same Frequency is the same Then excursion MUST be the same, as well... It has to be. JUST because a driver CAN have a longer linear excursion, that in no way means it WILL, especially if the conversion efficiency and the power applied are the same, AND if the frequency being reproduced is ALSO the same. Those are your test requirements/parameters. I'm trying to understand your explanations while living inside that same box. What am I missing if this is not the case? At a lower frequency, I know the driver will take advantage of the longer throw, but it's for lower frequency efficiency than you can achieve with a driver built with a shorter throw. I understand completely that power creates SPL. I also understand that SPL is NOT just pressure. SPL is (as I've stated) rate of change. It's pressure DIFFERENCES, in a given time period. Without a strong motor (high n0) to take advantage of the current being created by the amplifier, then a given woofer CAN MOST CERTAINLY have a lower peak SPL even with substantially more power being applied to the voice coil. This is typically the long throw motor. Am I wrong? If I am wrong, please tell me WHERE I am getting disconnected! :)It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

Well of course.  If the motors are the same the performance is going to be very close and only affected by the Qms of the drivers.  So we were talking about two different things.  You said earlier that a woofer with a shorter throw would generate more SPL than one with a longer throw.  I said rubbish, meaning in general a long throw woofer is capable of generating greater SPL.  But of course I missed the assumption you were making that they would have the same power efficiency.  If they do, then equal power will generate equal displacement.  You're right.  BUT, what if the short throw woofer runs out of Xmax with your power input while the long throw woofer has 50% of its travel left to go?  Which one would you want then?  :)

Me, I say go for large Xmax and feed it the power it needs. 

Support the12volt.com

...and perhaps to "poke the bear" one more time... Go for large Xmax, feed it the power it needs (not wants) and tune for really deep Fb. (Where it will work better...) When feeding more power to a longer throw woofer, WITH SIMILAR n0, yes. Longer throw woofer, please. I still maintain that you'll never see a really long throw woofer with efficiencies like the short-throw PA woofers for example.It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

No, the sensitivity of a short throw woofer will almost always be higher since there is less wire in the voice coil.  But you go ahead and build a sub system with the PA woofer of your choice with 98db sensitivity and I'll build mine with the long throw woofer of my choice with 89db sensitivity and we'll see who can hit the highest numbers on the Term Lab.  Assuming you can fit yours into your car.  There is a reason people do not build SPL vehicles using Peavy PA woofers.  Support the12volt.com