What makes a speaker IB capable?

[Thieroff 10+ year member]

I searched, to no avail. I do a lot more reading on the computer than writing, and I've never come across this specific topic.

Is there like a parameter value that makes a speaker, being a mid or a subwoofer, more well suited to IB apps?

If so, what kind of specs would I look for?

I'm thinking it's related to the qts and the vas, but not sure

Could somebody chime in on this

Thanks

CT

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[CBFryman2 5,000+ posts]

drivers well suited for IB have:

High Vas

High Xmax

low mechanical compliance.

 

[GemaRastem 10+ year member]

mmmm you actually don't want a high vas if you don't have a big trunk. You want the total area for the backwave to be atleast 4 times the woofers vas. the backwave being the wave that comes off the back of the woofer. You also want a high xmax and a qts around .3-.69. If space is a concern you may also want to look into AP or Aperiodic enclosures

 

[RumbleNTheTrunk 10+ year member]

mmmm you actually don't want a high vas if you don't have a big trunk. You want the total area for the backwave to be atleast 4 times the woofers vas. the backwave being the wave that comes off the back of the woofer. You also want a high xmax and a qts around .3-.69. If space is a concern you may also want to look into AP or Aperiodic enclosures

'06 xxx fit the bill? has a high vas and xmax anyways.

 

[ksin291 10+ year member]

Qoute:

"I still stand by my original point however, that the criteria for picking IB subs is much the same as picking a sealed box sub... powerhandling, low end sensitivity, and excursion, which I believe you just said."

http://forum.elitecaraudio.com/showthread.php?threadid=129616&pagenumber=2

 

[ksin291 10+ year member]

Quote:

"A few points :

- yes, in general you're looking for a rather high Qts sub for Infinite Baffle use, because you get no "Q enhancement" from an enclosure. However, a low-Q sub can also do well IB, if the resonsant frequency (Fs) is also low. As an extreme example ... if the Fs of the sub is 10Hz (none that I know of, just an extreme to illustrate a point), does it really matter what the Q is? The response will be quite flat down to 20kHz in any case.

- If you have some EQ at your disposal, including possibly a Linkwitz Transform, and a relatively healthy xmax ... you can pretty much "dial-in" the response you want.

- Rememeber that power requirements to reach full excursion will be less for IB. There's really nothing to be concluded from the fact that subs in small enclosures can "handle" more power, other than the fact that smaller enclosures are less efficient.

- Aperiodic enclosures are not the same as Infinite Baffle, except in a limiting case. AP means you've really got two enclosures for the sub, separated by a resistive membrane. The enclosure closest to the driver is quite small, and the other enclosure is quite large ... perhaps "infinitely" so The resistive membrane gives you some "tuning" flexibility. In one extreme, the acoustic resitance is so high (thick, dense) that you really only have the very small enclosure, right near the sub. In the other limiting case, the acoustic resistance is so small (thin, light) that the two enclosures are very tightly coupled, meaning that you're practically running IB (if the second enclosure is huge ... remember, IB is identical in all respects to a very, VERY large enclosure)."

http://forum.elitecaraudio.com/showthread.php?threadid=127544&pagenumber=2

Here's a concrete example to demonstrate my point ... the point being that a low Qts can be very acceptable in an IB alignment, providing that the Fs is also low. Consider the Image Dynamics IDMAX, specs found here (D2 and D4):

http://www.imagedynamicsusa.com/tech_page.php?name=IDMAX12D2%20V.3&type=sub&id=idmax

http://www.imagedynamicsusa.com/tech_page.php?name=IDMAX12D4%20V.3&type=sub&id=idmax

Qts on the order of 0.34~0.35 (which would seem pretty "borderline", if not downright too low, for IB), but the Fs is about 20Hz. And ain't nobody complaining about DEEP bass from IDMAX drivers in IB mounts

So I'm thinking a better "Figue of Merit" might be Qts/Fs, or something along those lines ...

 

[CBFryman2 5,000+ posts]

a true IB setup you want vas to be large. large vas means soft suspension which means less power to move the driver.

 

[GemaRastem 10+ year member]

^^wrong, if you have too big of vas and not enough air behind the woofer it's gonna sound crappy and distort to hell.

read what some people have posted, you want a vas that fits the size of your trunk/how many woofers you will be using, a low fs lower than 25 at most, high xmax 12mm atleast, and a qts from ~.35 to .69.

 

[CBFryman2 5,000+ posts]

^^^wrong, if it isnt true IB then it will act like a low Qtc enclosure.

learn WTF you are talking about.

also, low FS doesnt always mean low extension. FS is where Re is greatest.

 

[GemaRastem 10+ year member]

no matter what it's going to act like an enclosure, you're putting it in a trunk

http://home.comcast.net/~infinitelybaffled/

http://home.comcast.net/~infinitelybaffled/page13-10timesVas.html

you can't really get a "true" IB setup in a car

 

[helotaxi 5,000+ posts]

IIRC IB is an enclosure larger than the Vas. The basic idea is that the airspace does not affect the compliance of the driver. If the airspace is bigger than the exquivelent compliance it will have no effect.

 

[CBFryman2 5,000+ posts]

it still has some effect. And yo ucan do a true IB if the backwaves vent outside //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

 

[thch 10+ year member]

So I'm thinking a better "Figue of Merit" might be Qts/Fs, or something along those lines ...

thats interesting becuase in the equations for a second order system, that actually appears. the denominator of a 2nd order system is:

s^2 + F/Q s + F^2

in anycase i just find that interesting.

still i think there is a grain of salt here. it seems a high Qts would be favorable, but a Qts of 3 may not be what you want.

 

[Thieroff 10+ year member]

This is a good thread guys, thanks for your help

 

[helotaxi 5,000+ posts]

it still has some effect. And yo ucan do a true IB if the backwaves vent outside //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

The effect is negligilbe. Even with the rear wave outside, the cabin of the car will act as an enclosure and have "some" effect on the driver's response. It would be the same negligible effect as an enclosure larger than the Vas. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif