[woodsyi]

I am moving this from the VMPS circle as I realize that it also concerns other AC manufacturer's equipments.

Background information:

1)  Long ago I was inspired by John Casler's idea of push pull quad sub concept. 

2)  Recently I set up Audiokinesis Storm in a room to augment 2 electrostats.  4 little subs in a quad arrangement really worked better than 2 SVS towers.

3)  Some months ago, I got DIY Cable to make me 2 sealed box subs using the 18" Extremis drivers.


4)  I already had 2 VMPS Larger subs.

5)  My room from a year ago.


So I was going to do a lot of rearrangement and put the new subs behind my listening position, but I just couldn't.  I couldn't juggle the furniture and the logistics of getting the subs and the sub-amps powered and connected was just too much.  So I stacked up 2 subs on each side of my RM40s.  I put the largers on top because they were much lighter than the Extremis subs.  since I now had the subs parallel to ribbons on my mains, I recessed the subs about a foot to reduce any baffle refraction/diffraction.   I played around for a while but I could not get them to all work together. 

Then I read Big B's comment on his dipole sub arrangement at CES.  So I tried it.  I flipped the Largers (they were already on top) and put them on opposite phase.  Now I have a dipole sub tower with a 12" and a 15" drivers firing back out of phase while an 18" driver fires forward in phase.  Each sub is driven by a Parts Express Dayton HPSA1000-R 1000W Rackmount Subwoofer Amplifier.  The rear firing subs are filtered with my active x-over.  The front firing subs are filtered with the amp's internal low-pass filter which also has one channel parametric eq.

After a lot of tweaking I finally got things to sound good.  I am really using less power (1/4 power level on each amp) and getting more bass.  When I say more, I don't mean louder.  The bass is thicker and more pervasive in the room.  Oh, it's as tight as can be with incredible precision.  Just that it's everywhere.  I want to say that my tight bass is diffused.  It's kind of a Zen thing.    Anyway, I am liking it.   


P.S. I got pictures but I am having trouble up-loading them.  I will put them up eventually.  The Extremis subs, firing forward, are where the largers are in the picture and the largers, firing backward, are where the Omega speakers are in the picture.  The passives are facing out. 

[Brian Cheney]

In our live vs recorded CES demo the dipole configuration of stacked VSS woofers was the only one which yielded accurate bass in our 28x38x17' ballroom.

Still, we had to notch out the 33Hz floor to ceiling mode (about 6dB of cut) with a single band of parametric EQ.  We also carefully adjusted the crossover point to the mains (66Hz) as well as relative bass levels using 0.1dB increments. 

Dipole bass generates a figure 8 dispersion pattern that excited the other room modes far less than in phase or bipole operation.

We also ended up with the mains as full dipoles and had the woofers standing about four feet behind them, all with a mid-room placement. 

[John Casler]

Rim,

Now you know how much fun I have been having.

Had to laugh when you said that you put the "LARGER" on top because it was "smaller".

Seems like there is a George Carlin type joke in there somewhere.

In any event, exploring the bass potential in a room with at least 3 to 4 subs is very interesting.  Just getting those big subs up off the ground and more in the middle of the room does interesting things.

Too bad you couldn't play with the Quadratic (front/back) Push/Pull.

Each change will "affect" the bass.  Moving the LARGER's off the floor obviously reduces their coupling and you lose a bit of a couple "low" frequencies, but the balance that "can" be gained in some rooms is a good thing.

The dipole config as you have it might need a bit of boost in some rooms, but in others it ends up being perfect.  Some swear by dipole bass as far as clarity.

Have fun aa