[warnerwh]

Eric if you short the posts on the RM/x's they'll have less affect on your bass I believe, it may sound better shorted.

[ekovalsky]

What I don't have (currently) is the ability to adjust or "fine tune" that phase to adjust for the distance between the front and back subs.

John,

It may be fun to try  a Behringer Ultradrive Pro DCX2496.  It can implement the delay and also has flexible DSP crossover slopes.  Probably not what you would want on the 626s (though Newform recommends them for use on their speakers), but for a rear pair of Largers it may be just the ticket!  It's dirt cheap too.

Without adding the delay, I would think the front and rear subs even though out of phase would cause some undesireable cancellation.  Have you done any measurements or relied on your ears ?

These are early plans for my room expansion, which shows a double bass array setup.  Rear subs will be powered units, maybe Velodynes, or array subs from GR or Selah.  Four identical subs is best (as you already have with your Largers), but obviously I am not going to buy another set of Alon towers!

[John Casler]

Hi Eric,

I think, the key is that the listener be equidistant from each sub.

I did look at the Berhringer unit, but as you said it is dirt cheap and I was suspect about its sound quality

But I did experiment, (but there is no way to really measure anything except actual frequency response) with using 2 x-overs

I also had a Dahlquist DLP-1 which has variable phase so I had the X2 on the front subs, and the DLP-1 on the rears.

That allowed me to adjust the phases independently of the front to back.

As long as the listening position remained equidistant the bass was "crystal" clear, with great depth and envelopment.

However, I do think that the subs themselves might work better if they are not "exact" mirror images.  If the room like yours is exact dimensions, then to place all 4 subs at the exact same place in each corner, will excite the exact same mode/node set.

If you move the front subs out to align with the acoustic centers of the main speakers, then they will react to the room in such a way that the mode/node set will move accordingly.  Additionally, you won't have to use any delay (or actually in your case "advance") to keep them in time or phase alignment with the mains.

[ekovalsky]

Key to this arrangement is the long delay on the rear subs.  Before any sound comes out of them, I've already heard the primary bass wave coming from the front subs.  Then just when that primary wave is ready to reflect off the rear wall, to subsequently develop cancellation and reinforcement nodes in the room, it is cancelled by the out of phase output of the rear subs.  Some of the Germans with four subs who have done this report in-room bass going from +/- 10dB to +/-3 dB without room correction.  That means a 14dB improvement of bass nodes and dips!

The Alons come with a DLP-1 which I am not using, rather I let the TacT provides a DSP crossover and delay to the subs.   The DLP-1 does give control over phase, but it cannot give the added delay.

As far as the Behringer, to me its main problem is the unfortunate lack of a digital output.  Thus one has no choice but to use its internal DAC which may not be of great quality.  For restricted use on a subwoofer in the bottom couple octaves it probably would be okay.  A DEQX would undoubtedly be better, but at much higher cost.

[PLMONROE]

Eric, Steve Nugent of Empirical Audio can add a digital output to the Behringer for a nominal  charge. Also he can upgrade it to sound MUCH  better. It is an amazing unit for the price.

Paul

[John Casler]

Key to this arrangement is the long delay on the rear subs.  Before any sound comes out of them, I've already heard the primary bass wave coming from the front subs.  Then just when that primary wave is ready to reflect off the rear wall, to subsequently develop cancellation and reinforcement nodes in the room, it is cancelled by the out of phase output of the rear subs.  Some of the Germans with four subs who have done this report in-room bass going from +/- 10dB to +/-3 dB without room correction.  That m ...

Hmmm...  Not quite the same as my Push/Pull system.  Actually, in fact it sounds like a rather strange relationship.   Almost like some kind of "active bass traps".

Mine is more like being in side a "dual driver" DIPOLE subwoofer and the room is the cabinet.

Large delay isn't nessessary since the only reason you actually need it at all is to compensate for sitting slightly out of the direct center between all four.

That is why a phase control (which has only the delay of a single cycle as in 180 degrees out of phase) seemed good enough.

What your talking about would seem far more involved and delicate (as in would require a good amount of measuring.

I wasn't aware of this system.  Who is doing it?

[ekovalsky]

John, you're exactly right.  It is effectively an active bass trap covering the full range of frequencies covered by the subs.  The rear subs are not used to augment SPL or introduce different room nodes (which is basically what the Harmon paper advocating quad subs does), but rather prevent problematic nodes from developing by making the rear wall of the room "invisible".

All the literature I've seen is in German.  I'll post some links later but you'll need Babelfish or another translator unless your Deutsche is a lot better than mine.  If you google for "Double Bass Array" you can get some hits, some of which it will automatically translate.

I have not heard this type of system myself, and I'm not sure anyone in the USA has tried it.  But the concept is most interesting and very promising results have been described on some of the German audiphile forums.

After my room is built out I plan to give it a try with a pair of used Velodyne subs.

The relationship between phase and delay can be a bit complex, but you are basically right.  Added delay keeps the phase of the wave intact but starts it at a different point in time, which may be more than one period later.  Changing the phase only may or may not introduce any delay, if it does it will be less than either one period or one half period.

Good bass is definitely cool and addictive.  As you describe your system, mine is definitely not overemphasized or "body crushing" but when the program material calls for it, the weight and authority are simply awesome.  When the program material lacks deep bass, the subs sonically (if not visually) vanish as they should.

[Florian]

Ok, I understand that your speakers are better than anything else ever made.  However, could you please stop posting this bs?  First, I will never be able to afford these speakers, so it's like reading a review of the latest Ferrari.  Second, this is becoming a peeing match between you and anyone else who likes VMPS.  I'm personally sick of it.  Seriously, this "my Ferrari is better than your Yugo" is beginning to get old.  So, your speakers are better than ours.  Having never heard the Alons, I state it an ...

This is the typical crap which makes forums quite bad. I dont think the Alons are the best nor do i think any speaker is the best. There is the Supertower, Apogee Scintilla, Fullrange, Grand or the Perigee Difinitive along with the Wilson Audio Alexandria etc....

So what if he owns a speaker worth 10's of thousands. If i had the money i would try it too, but for you to attack and critize him is plain wrong in my opinion. I also heard the big Dali speakers and the Megaline yesterday with a custom made aprox 13x 10 foot subwoofer with phase inversion (one per wall) with digital room correction and i almost flipped out when the room shook at 10Hz !!  

There is no limit in the High End, and critizing a person for owning one of the best is plain stupid.

-Flo

PS: See the wall inbetween the speakers ? Thats one of the subwoofers !!!!

[CornellAlum]

Are you telling me that there is an 8x6 (guessing) sub buried behind that wall>>>?  Why would you cover it up?

[Florian]

Are you telling me that there is an 8x6 (guessing) sub buried behind that wall>>>?  Why would you cover it up?

The pic looks kinda small, but the room is actually darn big. There are custom made viva scanspeak woofers on the side of the walls running from top to bottom. Dont know exactly how it works, but its unbelieveable!!!

[Bingenito]

They look like IB subs in the alcove of the wall. Very simple design but it works!