Air displacement

[Nukedsodapop 5,000+ posts]

I read somewhere that the total displacement that a woofer puts out can be calculated by sd x XMAX

So if I wanted to do a total air displacement of 4 10" subs with a Sd of .0307cm^3 and a XMAX of 15 would it go like this

0.0307 x 4 = 0.1228 x 45 = 5.526

or like this

0.0307 x 15 = .4605 x 4 = 1.842

I was wondering because I wanted to know which would move more air, 4 10's with 15MM XMAX each or 1 18 with 27mm XMAX

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[MikeofTulsa Moderator]

i would imagine it would be the area of the cone * Xmax(2(for both forward and backward) im just speculating tho.

 

[Nukedsodapop 5,000+ posts]

so would that be all of them put together then the xmax of all of them together or???? I'm confused ha

 

[squeak9798 5,000+ posts]

I read somewhere that the total displacement that a woofer puts out can be calculated by sd x XMAX
So if I wanted to do a total air displacement of 4 10" subs with a Sd of .0307cm^3 and a XMAX of 15 would it go like this

0.0307 x 4 = 0.1228 x 45 = 5.526

or like this

0.0307 x 15 = .4605 x 4 = 1.842

I was wondering because I wanted to know which would move more air, 4 10's with 15MM XMAX each or 1 18 with 27mm XMAX

The 18" would move more air.

Assuming your 10's have an Sd of 307cm^2 (and not .0307cm^2) with 15mm Xmax they would have a one-way displacement of .46L each.

.46L * 4 = 1.84L

Assuming the 18" is the Fi Q (just guessing based on the Xmax)....it has an Sd of 1210cm^2 and an Xmax of 27mm which has a one-way displacement of 3.27L

 

[Nukedsodapop 5,000+ posts]

so the 18 has more potential?

 

[its_bacon12 10+ year member]

it moves more air.

it will be louder. yes.

 

[squeak9798 5,000+ posts]

so the 18 has more potential?

20*log(3.27/1.84) = 4.9945db

So right at 5db more output potential

 

[Nukedsodapop 5,000+ posts]

alright, but then again XMAX Isnt everything, and the 18 is an SQL woofer, and the Fosgates are more of an spl speaker, would that make any difference

 

[envengineer 10+ year member]

alright, but then again XMAX Isnt everything, and the 18 is an SQL woofer, and the Fosgates are more of an spl speaker, would that make any difference

SQL or SPL doesn't mean anything. Those are arbitrary designations applied by marketing. I have w12gti subs, they could be called SPL, SQL, SQ depending upon the application.

Look at sensativity, power handling, xmax etc. Everything you need to know is in the specs. Higher efficiency = louder, all else being equal. More xmax = louder, all else being equal. Higher power handling = louder (assuming you have the power on tap). You'll find there has to be a compromise in there somewhere. You also need to consider the impacts that the enclosure will have on powerhandling, excursion, etc. There is no one spec that is going to tell the whole story.

 

[squeak9798 5,000+ posts]

Higher efficiency = louder, all else being equal.

All else being equal implies they have the same peak displacement potential, which means they both have the same maximum output. The power levels to reach those output levels may vary but the net result is the same.

Higher power handling = louder (assuming you have the power on tap).

The inverse of the above; One may require more power to reach a certain output level but if they both have the same peak displacement potential then they have the same maximum output level aswell. So while one may handle more power it won't necessarily be any louder.

alright, but then again XMAX Isnt everything, and the 18 is an SQL woofer, and the Fosgates are more of an spl speaker, would that make any difference

Those are arbitrary labels.

We would need to know the actual drivers and their specs along with the power you plan to use and what enclosures they will be in order to give you any further insight.

 

[envengineer 10+ year member]

All else being equal implies they have the same peak displacement potential, which means they both have the same maximum output. The power levels to reach those output levels may vary but the net result is the same.


The inverse of the above; One may require more power to reach a certain output level but if they both have the same peak displacement potential then they have the same maximum output level aswell. So while one may handle more power it won't necessarily be any louder.

Those are arbitrary labels.

We would need to know the actual drivers and their specs along with the power you plan to use and what enclosures they will be in order to give you any further insight.

Well put, squeak.

When I said all else being equal, I intended to include power in my first statement. It seems every time I try to simplify things and be relatively concise, I end up leaving out important info or incompletely detailing the caveats of my explanation.

My method of explanation is not well suited to forum posts, I'm better off when I'm in my office with my dry-erase wall.

 

[Nukedsodapop 5,000+ posts]

the specs for the fosgate woofers are in the OP

the specs for the Rl-p are

Qts: 0.436 Mounting Depth: 26 cm

Qes: 0.482 Total Depth: 26.5 cm

Qms: 4.535 Outside Diameter: 46.7 cm

Fs: 20.71 Hz Weight: 41 lbs

Re: 3.74 Ohm Magnet Width: 18.8 cm

Ls: 3.317 mH Mounting Cutout: 43.2 cm

Rp: 7.629 Displacement: 0.2 cu ft

Vas: 314.2 L

Mms: 376.7 g

Cms: 156.7 u

Bl: 19.50 T*m

SPL: 89.45 dB

Sd: 0.1188 m^2 Sd:

Xmax: 27.4 mm

On the Rl-p I would probably have a 7 cube box ported to 29Hz where the backseat is supposed to be in a firebird with about 1200 watts going to it

With the fosgates I would have a 6 cube box ported tuned to 32Hz built out of the back well with around 1500Watts going to them

the fosgate woofers are the Power series from the 90's, the model number is PWR-410, and I can't find too much about them.

The 18 is a 18 Rl-p, so I'm sure people aleady know about that one

 

[Nukedsodapop 5,000+ posts]

Oops, the specs for the rockford woofers are on this page

http://www.rockfordfosgate.com/scripts/rightnow.cfg/php.exe/enduser/fattach_get.php?p_sid=JMhtx7Fi&p_tbl=9&p_id=391&p_created=1084383055

 

[audioholic 5,000+ posts]

You really shouldn't look strictly at linear displacement potential (xmax * sd) unless you are comparing speakers in sealed enclosures. If they are sealed, yes cone area times excursion gives you a very good ideal of potential. But in vented systems things get much more complex. Given the grossly large disfference in displacement potentials here, I doubt the 18 has much to worry about from the 4 10's, but that wouldn't always be the case (vented).

 

[Nukedsodapop 5,000+ posts]

Lol well, I dont even know

here's a picture of the 10's though