displacement as a function of cabinet preferences

[Codger]

Originally Posted by KJung

You still seem to be overfocused on cone diameter. I again don't even see why that is part of this discussion, because it doesn't matter. Confused a bit on why you constantly bring it up. I again agree (per my example), as long as the vd is relatively constant, it doesn't matter what size of driver you use for comparison.

Well I am certainly confused because I thought the OP was about surface area vs displacement. In that context surface area matters because in relative terms it changes radiation efficiency and pattern (doesn't it?)

[KJung]

Originally Posted by Codger

Well I am certainly confused because I thought the OP was about surface area vs displacement. In that context surface area matters because in relative terms it changes radiation efficiency and pattern (doesn't it?)

Total surface area of the system, not limited to an individual driver IMO (at least that is the path I took with my example). My example was also in the spirit of keeping box size relatively the same.

Of course, nothing is completely apples to apples, and the OP's example of dual 15's with roughly half the xmax of a single 15 takes the radiation pattern off the table.

In 'real life', I view this fun thought experiment as: Ok, I need this amount of volume, have this much to spend, and want a box of roughly this size (e.g., small, medium or large). That is exactly the exercise I went through when choosing my two VERY different sounding small cabs, that happen to be about the same cost, about the same size, have about the same maximum volume capability (and even the same sensitivity due to the lower efficiency cab being 4ohms and the higher efficiency cab being 8ohms). They happen to have a single larger driver versus two smaller drivers, but that is not a particularly big deal IMO.

Kind of a nice 'real world' example of the different approaches and tonal/performance impact of the variation in sd and xmax ratio, while holding box size and vd relatively constant. Of course, you could do the same thing with a larger box and holding cone diameter constant (per the OP's example above).

[ThisBass]

Originally Posted by dhsierra1

not surprising, many materials (and mechanical structures) have frequency dependent mechanical properties, didn't know that was looked at by the AES peeps, bet that's an interesting read

Sorry for the thread derail, folks, won't happen again

No problem anyway but:
mechanical compliance [Meters/Newton] which is the inverse of D [Newton/Meter] equals electrical capacitance [Farad].
Both are independent of frequency.

But:

Z = R + j(2*pi*f*L) -j/(2*pi*f*C)

that is a very different animal of course.

So you have to do the analog equation for mechanical Z, and C (or complience) is only one part of Z

[makohund]

Originally Posted by Codger

Well I am certainly confused because I thought the OP was about surface area vs displacement. In that context surface area matters because in relative terms it changes radiation efficiency and pattern (doesn't it?)

Not quite surface area vs displacement, though that is a direction the answers to the question could lead.

It was "Getting displacement via more surface area, vs getting displacement via more Xmax." So... surface area vs Xmax. Though you are right... if one came out ahead for some reason, that would make the next question "X vs displacement".

I don't the "barryaudio is focusing on driver size" thing at all, I don't see him writing anything of the sort anywhere. So I'm confused at that, too. (I thought the reverse, at least for a little while, when it was said that the comparison required different driver sizes, which it does not.) He's a Greenboy/BFM builder, hardly the sort one expects to find dealing in driver size mythologies.


I think all three comparisons have merit, for different reasons.

Berg 210 vs Thunderchild TC112:
A good example of how far apart the variables in play can take you. Wildly different tone results, via completely different approaches, in the same size box, that end up with similar SPL to the user's ear. Not enough hard data to draw firm conclusions from, but certainly enough for an educated guess. Bonus points for being a first-hand real-world comparison.

Berg 210 vs Berg 212 --or-- Basslite S2012 x1 vs S2010 x2:
Eliminates a lot of variables, to get to the heart of the matter. (The fewer in play, the better, for getting a solid answer.) Same designer/manufacturer, same driver manufacturer, likely same driver family. No crossovers & multi-way behavior to consider. Likely much closer in tone, making it easier to eliminate that factor. Very close in displacement, one with higher Xmax/lower Sd, the other via higher Sd/lower Xmax. Even has a reasonable probability of finding someone who owns both.


Eminence Kappa 15s vs Delta 15s.
Eliminates even more variables. Same driver size, almost identical Sd, difference in Xmax large enough to compare multiples against each other in varying Sd/Xmax ratios.

Any other comparisons worth considering? Such as:
Kappa vs Delta
Kappa Pro vs Delta Pro
Kappalite vs Deltalite

Kappa vs Kappa Pro vs Kappalite
Delta vs Delta Pro vs Deltalite

When I get a chance I can look at some numbers again and see.

If I were a proficient with modeling software, I'd probably be mucking around in it already at this point.

[will33]

Delta12A vs. Delta12LFA.

One has exactly twice the xmax spec as the other.

Other things will come into play though. Sensitivities differ but output in the bass end of things is all about displacement. Still, you're left with the conundrum that both have to reach deep in the first place to accurately compare down there. Obviously, one of those reaches deeper than the other.

I don't think there are 2 drivers to compare where all else is equal....different designs...different goals.

[makohund]

Originally Posted by ThisBass

No problem anyway but:
mechanical compliance [Meters/Newton] which is the inverse of D [Newton/Meter] equals electrical capacitance [Farad].
Both are independent of frequency.

But:

Z = R + j(2*pi*f*L) -j/(2*pi*f*C)

that is a very different animal of course.

So you have to do the analog equation for mechanical Z, and C (or complience) is only one part of Z

Ah! The very person that said they'd always take Sd over Xmax in the thread I was reading.

I found that interesting, and asked (much more succinctly) essentially the exact same question I'm asking here:

"All times? Ok, two 15s with an Xmax of 1mm. One 15 with an Xmax of of 8mm. Choose."

The reply was "You probably don't understand the physics".


I never got to respond, as mods axed the thread before I got a chance. Excellent, now I will.


Perhaps, perhaps not. My understanding is rudimentary, but I'm not entirely ignorant. I'm also eager to learn. So if you could be so kind as to answer the question, we shall see if I do or if I don't. If I don't, I'm thrilled to have it explained, and will do my best to stumble along. Thanks.

OK, back to this thread... it appears you might know what you're talking about. Do you have any input on the original question, or craig.p's "air impedence" post, or will33's water displacement analogy? That would be cool. Though you may have to translate some standard formulas into english for those that might not be intimately familiar with them.

[ThisBass]

A pinhead with endless Xmax.

[rpsands]

It's all about balance and tradeoffs. Period.

[makohund]

Originally Posted by will33

Delta12A vs. Delta12LFA.

One has exactly twice the xmax spec as the other.

Hmm. Yep. Cool.

Delta12LFA x1  SD= 506.7 Xmax=4.8 VD=243
Delta12A   x2  SD=1039.0 Xmax=2.4 VD=250

Other things will come into play though. Sensitivities differ but output in the bass end of things is all about displacement. Still, you're left with the conundrum that both have to reach deep in the first place to accurately compare down there. Obviously, one of those reaches deeper than the other.

I don't think there are 2 drivers to compare where all else is equal....different designs...different goals.

Of course won't be able to get everything else equal. Just need to be in the ballpark down low... maybe 60-250Hz is a good range to consider? 1st overtone of a B is plenty low for this I think.

[ThisBass]

Originally Posted by rpsands

It's all about balance and tradeoffs. Period.

As long as the tradeoff fits in between some physical "borders".

[makohund]

Originally Posted by ThisBass

A pinhead with endless Xmax.

Lol...

Kansas, with zero Xmax.

That kinda works both ways, doesn't it?

At least the pinhead will create some sort of of wave, if there is an atmosphere involved.

Surely there is something in the middle worth speaking of?

[will33]

Originally Posted by ThisBass

A pinhead with endless Xmax.

That would be one extreme, yes. The wall of an infinitely large building moving a hairsbreadth being the other.

Neither will work at a real gig.

[will33]

Originally Posted by makohund

Hmm. Yep. Cool.

Delta12LFA x1  SD= 506.7 Xmax=4.8 VD=243
Delta12A   x2  SD=1039.0 Xmax=2.4 VD=250

Of course won't be able to get everything else equal. Just need to be in the ballpark down low... maybe 60-250Hz is a good range to consider? 1st overtone of a B is plenty low for this I think.

It would have to be LF only. Anything higher than 200hz, maybe even a bit lower than that and other stuff comes into play, meaning the cone no longer just acts like a piston.

[ThisBass]

Originally Posted by makohund

"All times? Ok, two 15s with an Xmax of 1mm. One 15 with an Xmax of of 8mm. Choose."

The reply was "You probably don't understand the physics".

Xmax is the linear excursion but not the limit.
Excursion beyond Xmax at Peaks does not mean the sound farts out.
Excursion beyond Xmax means the Peaks are beyond Xmax but does not mean the average program (the swinging note) is beyond Xmax.

[dhsierra1]

Originally Posted by ThisBass

No problem anyway but:
mechanical compliance [Meters/Newton] which is the inverse of D [Newton/Meter] equals electrical capacitance [Farad].
Both are independent of frequency.

But:

Z = R + j(2*pi*f*L) -j/(2*pi*f*C)

that is a very different animal of course.

So you have to do the analog equation for mechanical Z, and C (or complience) is only one part of Z

in dynamic mechanics, notably in materials with visco-elastic behavior there is a dynamic resistive element (ie impedence) in the modulus equations, ie viscosity which is in fact frequency dependent by definition.

Agreed in the linear domain that does not exist, but that's not what I was talking about originally in my thread derail, which was solely about dynamic equivalents, I ignored the capacitance aspect, obviously for the purposes of replying to a post as perhaps over-simply as possible, thank you for completing the picture

Edit: Sorry OP, back to your original discussion, the lab coat and pocket protector wearing set snuck in again.......

[makohund]

Originally Posted by ThisBass

As long as the tradeoff fits in between some physical "borders".

OK, some borders.

The sound production devices must be drivers/speakers currently possible to be manufactured by existing speaker manufacturers. They may be grouped together to form what would be considered by the average TB reader a "speaker cabinet".

The result must be capable of producing audible sound through the Earth's atmosphere, in an open space on a dry surface in an environment walkable and breathable by humans without mechanical assistance.

Sound produced must reach a minimum of 50dB between 100 and 200Hz.

In the case of a circular driver/speaker (likely roughly "cone shaped"), the diameter of the circle will fall somewhere equal to or between 1 and 100 cm. In the case of a non-circular speaker, the closest equivalent measurement will follow the same rule.

The Xmax must be a minimum of 0.5 mm, and may not exceed the above measurement.

That work?

[makohund]

Originally Posted by will33

It would have to be LF only. Anything higher than 200hz, maybe even a bit lower than that and other stuff comes into play, meaning the cone no longer just acts like a piston.

OK, got it.

[makohund]

Originally Posted by ThisBass

Xmax is the linear excursion but not the limit.
Excursion beyond Xmax at Peaks does not mean the sound farts out.
Excursion beyond Xmax means the Peaks are beyond Xmax but does not mean the average program (the swinging note) is beyond Xmax.

Yes, all true, all known.

I'm using Xmax as my figure simply to steer clear of Xlim, looking to push hard but not damage.

Also because between Xmax and Xlim there will be distortion, which may or may not be desired. (Subjective, matter of taste, etc.)

Now in terms of your original statement from the other thread...

OK, sounds like you'll take Sd over Xmax because your tonal tastes don't mind (or even prefer) pushing past Xmax. That's simple, easy enough.

But does that preference for Sd over Xmax extend to the spirit of my question, though? Preferring Sd to excursion, even if the result is less Vd?

It'd take drivers with Xlim quadruple the Xmax in that example I gave, to get to equal Vd. Don't see that much.

[ThisBass]

Originally Posted by dhsierra1

in dynamic mechanics, notably in materials with visco-elastic behavior there is a dynamic resistive element (ie impedence) in the modulus equations, ie viscosity which is in fact frequency dependent by definition.

Agreed in the linear domain that does not exist, but that's not what I was talking about originally in my thread derail, which was solely about dynamic equivalents, I ignored the capacitance aspect, obviously for the purposes of replying to a post as perhaps over-simply as possible, thank you for completing the picture

Edit: Sorry OP, back to your original discussion, the lab coat and pocket protector wearing set snuck in again.......

Your link:
http://en.wikipedia.org/wiki/Mechanical_impedance

At resonance frequencies, the mechanical impedance will be lower, meaning less force is needed to cause a structure to move at a given velocity. The simplest example of this is when a child pushes another on a swing. For the greatest swing amplitude, the frequency of the pushes must be near the resonant frequency of the system.

That's applied physics

So please tell me what you like to point out?

[ThisBass]

Originally Posted by makohund

Also because between Xmax and Xlim there will be distortion, which may or may not be desired. (Subjective, matter of taste, etc.)

That's true for swinging notes (or appro average) but not peaks.
Similar like clipped portion of peaks at power amps you can't notice.