zero vibration subwoofer?

[dfidler]

Hi All,

I am such a noob that I don't even know what I don't know so please forgive me these really stupid questions.

My current sub (ASW610XP) with it's 10", front firing, driver has a seizure on it's plinth every time it tries to convince me that there's a helicopter flying through my lounge (and all of that paper that I stack ontop of it falls off).

This is obviously because the driver is able to deliver enough kinetic energy to move the enclosure laterally (no carpet spikes being used to protect my damage deposit). So, to me, it makes sense that a down firing enclosure would reduce the lateral movement of the enclosure (provided that the enclosure was suitably heavy). But I suspect that the driver would still cause the enclosure vibrate, unless the enclosure is massively, massively, massively heavy.

I've seen other subs that had a plinth that was attached to the enclosure (and the driver fired down at the plinth); my guess is that this kind of setup would further reduce the vibration of the enclosure (but having never seen one up front, I really don't know)

So my questions:

1. Is there a way to make a zero vibration enclosure for a sub that I want to move prodigious amounts of air? I want to transmit absolutely no vibration at all from the driver to the enclosure.
2. LFE is radial; so if I built a down firing sub (say, into an end table or something) and closed off the front entirely, and placed it nearly against a wall, would that dramatically affect the performance of the sub? (my guess is "no" provided that the other two remaining sides are raised up sufficiently to allow for the appropriate amount of air flow, but what do I know).
3. If another [multi] speaker were to be placed relatively close to one of the two remaining open air areas, would the sub's machinations affect the performance of the multi significantly or would their relative frequencies simply not overlap enough to affect each other.

Note: I'm assuming that the sub is MDF and, so is the majority of the multi.

Cheers,
Dave.

[Cal Weldon]

Hi Dave,

Put a woofer on either side of the cabinet. Movement all but canceled.

[jwmbro]

Originally Posted by Cal Weldon

Hi Dave,

Put a woofer on either side of the cabinet. Movement all but canceled.

Both wired the same, right? ie, symmetrical wavefront, not dipole?

[dfidler]

@Cal, but then they'd have to be out of phase, otherwise the movement of the drivers would increase the amplitude of their vibrations.

So if I wire them out of phase, what is that going to do to my room acoustics? Isn't that going to create a bunch of dead zones throughout my space?

And if they were out of phase, what would I do with the enclosure? It strikes me as a bad thing if they were sharing the same air... unless, I guess, if the enclosure volume was suitably large.

[dfidler]

sorry, out of phase was the wrong term... dipole (thanks klankyman)

[richie00boy]

Yes so they push out at the same time. If you wired them the opposite way you would not get much output at all.

[wolf_teeth]

Yes, moving out of the box at the same moment in time, or Bipolar.

Albeit, imnipolar, because they are bass-freqs.

Later,
Wolf

[Joachim Gerhard]

Put them on two sides of a ceramic or metal tube ( expensive ) turn one magnet system inside out and wire them in antiphase for distortion cancelation. A tube is the most stable form after a sphere.

[dfidler]

Thanks for the responses so far everyone; they've been really informative.

So biploar arrangements are one way; are there other ways to accomplish this? I ask because I'm looking at making this system stealth (to appease the ruler of the house) so having one speaker on each side of the enclosure isn't going to work.... unless I can put that tube inside of another enclosure or something.

That's why I was asking about maybe firing the driver toward a plinth; I was hoping that the force of the air hitting the plinth would help to counteract the movement of the driver.

[Andrew Eckhardt]

The trick involves counterforce from the same moving masses being driven against one another with the same signal. The driver moving mass includes the air load. You need 2 same drivers firing away from each other. A tube is not necessary, a cubic enclosure is ok. However, if you have one built for a 10, you will probably need less than 2 8's to work well in the same volume.

In any case, anything you do with the air in front of the cone can't compensate for the rest of the moving mass, which is actually the larger and therefore more problematic part anyway.