brahma vs w6

Actually a greater excursion is a good thing for an SQ subwoofer.  The reason being that if you increase the excursion capabilities, you increase the linearity of the motor under low excursion. 

I know this seems to be true because more and more high excursion subs come out in the car audio market and they all have lower efficiency.  However it isn't the high excursion that causes the lower efficiency.  The reason is because power is cheap now, so there is no real reason to design for high efficiency anymore.  So instead speakers are being designed for smaller enclosures with still good low end response, while giving up efficiency.  Just to prove it, our Parthanon does 80mm one way linear excursion and IIRC has an efficiency of 97 dB.  We can get it to move 3" off a 9 volt battery.  In fact there is an excursion video of it I took where it is pumping away off of a small 250 watt amp.

Steven Kephart

Adire Audio

But what are you giving up for that efficiency?  You are either stuck with a refrigerator size enclosure, or a large midbass driver with absolutely no low end response.  You just can't beat Hoffmans Iron Law. 

Steven Kephart

Adire Audio

Very hardpressed is better language than "*ever*".  :-)

The improvement in sound quality isn't related to the excursion capability.  Excursion capability simply has no direct relation to sound quality.  HOWEVER, many high excursion subwoofers are designed for use in small boxes.  My guess is that you simply have the high excursion drivers in boxes of the Q you prefer.  Lower Q applications equal less "peaky" bass and more extension.  This is probably what you're hearing.  You may also be noticing what Steven suggested - thanks for the input and correction, Steven. 

Additionally, your experience that lower excursion drivers have been "absolute[ly] the loudest subs" is easily explained.  You've not heard correctly applied high excursion subs.  With enough power a high excursion subwoofer of similar cone area will simply displace more air and produce more SPL.  The potential SPL is usually louder.  Now, most folks, for the power reasons we've highlighted, never apply enough power to equal the two situations out.  With substantially similar amounts of power all you're noticing is efficiency differences between drivers.  This isn't a new phenomenon.

These situations are most certainly not pointless for discussion.  IF a person has the means and the want to implement the right amount of power they can easily trump more woofers.  I'm not talking about db drag racing either.  I'm talking about regular system planning.  A doubling of cone area nets a person a 3db increase in SPL.  JUST LIKE A DOUBLING OF POWER.  So, driver efficiency being equal, 2 12" subs with 1000w will be JUST AS LOUD as 4 12" subs with 500w to the system.  2 12" subs with 600w will be just as loud as 4 12" subs with 300w to the system.  Yada yada yada... didn't take much "concocting," did it?

Steven, thanks for the input and the corrections.

Help me out with the last point, if you will, I'm still a newb when it comes to the physical characteristics of drivers.  Isn't xmax proportional to the voice coil length?  Doesn't a longer voice coil have more windings than a shorter voice coil?  Now, doesn't the effiency drop as the gap covers a smaller portion of the voice coil, since the current passing throught the coil is distributed along a longer area outside of the gap? 

Any or all of the above may be wrong.  However, I find it somewhat counter-intuitive that more excursion would not lead to lower efficiency.  Like I said, help me out.

Now, I agree, most car subwoofer further exaggerate excursion related inefficiency by building the subs for small enclosures.  This small enclosure capability usually requires stiffening the suspension and adding mass to the woofer, correct?  These features add to the inefficiency, right?

Now, take the Parthenon.  Maybe this isn't a good example here - my first instinct is to say it isn't - because xmax / motor related inefficiencies are trumped and made up for by the extreme amount of area related displacement.  Right? ;-)

I suppose that is the problem; there are a couple definitions for Xmax out there.  Some companies rate their subs based on coil length compared to gap height.  However this does not work with an underhung motor, or our XBL^2 motor.  I prefer a more accurate measurement that puts the limits at a certain distortion level produced by the driver.  The excursion measurement on the motor of the Brahma is at the point where BL is 70% down from rest, which will be about where distortion products from the motor are at 10%.  I believe JL uses the same point in their ratings.

Now that we have a definition somewhat agreed upon by the two companies involved, we can move on.  Your comment about Xmax determined by coil length is incorrect.  The excursion in overhung motors, like what's in the W6, is mostly determined by the coil height. The excursion in underhung motors is mostly determined by the gap height, and our XBL^2 motor is determined by a combination of the two.  But note that it is the coil height that is important, not the coil length.  This is because you can increase or decrease the number of layers of windings used in the coil.  An example of this is in the W7 where they have a VERY long coil, but it is only 2 layers thick. 

Efficiency is at it's root is effected by BL and Mms.  Increasing excursion in some cases might increase Mms, however there are things you can do to get around that (aluminum wire, fewer layers of windings, reduced mass elsewhere, etc.).

Anyway, I have to go to bed now.  So I will continue this tomorrow when I have time, and when I can be sure that I am lucid.

Steven Kephart

Adire Audio

Ok.  I didn't know there was another definition out there.  Thank you for the correction.  However, for all practical purposes, won't a certain higher distortion level produced by the driver almost always substantially approach the traditional xmax definition anyway?  Certainly at least your BL based measurement results in xmax numbers proportional to the traditional definition.  For the purposes of our discussion here it probably doesn't really matter, right?  Again, not trying to argue, just trying to learn.

Excellent.  This type of learning is why I love this board.  Thank you for the correction.  So, now that I will use the coil height instead of the length, here's a couple follow up questions. 

1) Is coil height almost always increased as excursion is increased? 

Well, yeah, but isn't BL also partially a function of what we've been talking about this entire time? 

Oh, I know you aren't arguing.  I think you are asking some very good questions actually. 

Well how would you describe the excursion of an underhung motor using that technique?  Does it have negative excursion since the coil is much shorter than the gap?  Also, how would you describe our motor?  Our coil is shorter than the top plate height, so would it have negative excursion?  Or would you use just one gap, so it would be a very short overhung.  If that were true then the Brahma would have an excursion around 7 mm.  However DUMAX put it at around 29mm for the Brahma 10 (BL 70% down).

In theory the above works only for overhung motors.  However in practice, it doesn't provide an accurate number because it doesn't take into account the fringe field.  Also, the optimization within the motor can make a difference like whether it is an LGLC (long gap long coil) or SGLC (short gap long coil). 

And now for your follow-up questions.

1) Not necessarily.  You can decrease your gap height and gain excursion as well.  And of course this is only true of Overhung motors. 

2)  Due to the added mass, yes it would.

3)  The only negative I can see is reduced heat dissipation.  However there is more to it than that as you will see below.

That actually get's into the rest of what I was going to add to my previous post.  The probablem is that this topic is such a HUGE one.  It is difficult to cover without writing a novel about it. 

The main problem here is to fully understand where excursion comes from.  Here's a quote by Dan Wiggins: "Xmax isn't really a physical parameter of the driver - it's a "side effect" of a given driver design. Note that you can have the same 6 physical parameters, but Xmax values all over the place. And Xmax does not affect any of the derived T/S parameters."  You can't just increase the coil length to gain excursion.  This is because you change everything else in the driver as well.  Engineering is a practice of compromises.  You try to make the best compromises to obtain your goals. 

Now let's look at what effects efficiency in subwoofers.  For the most part, efficiency in subwoofers is dictated by the enclosure, and not the driver.  The drivers efficiency is only prominent around where most people cut off their subs anyway.  For a good visual of this, try running a subwoofer free-air and in an enclosure.  You can really get a subwoofer moving free air with very little power.  However if you throw the subwoofer into an enclosure, it takes a lot more power to get it to move the same amount. 

We actually had a really good conversation about everything subwoofers on another forum.  Here's a link to the thread where you can learn a great deal: http://caraudiotalk.com/forum/index.php?s=ea3f16efc348fcc6db95f47bd7607938&showtopic=2384

Steven Kephart

Adire Audio