[John Casler]

Has anyone heard of a set up with an IB (infinite baffle) Sub set up in a DIPOLE configuration?

That is one IB in the front of the room, and the other in the rear run Out of Phase?

While I don't have the freedom to do so, I thought it might be interesting.

Any thoughts on "feasibilty"?

Wonder what it would do to room modes?

I have my ideas.  What say you?

[klh]

The Harmon white papers would suggest it would be great for flattening in room response. My concerns would be if you sat closer to the rear of the room, there may be aural and definitely would be tactile localization from behind. Not only that, but since the rear sub would be closer, the sound would be louder coming from behind; from what I've read and heard, subs coming from behind is a general no-no. I and others have asked these questions before, but nobody seems to know the answer, and nobody wants to cut a second hole in their wall or ceiling to find out. I have a dual Avalanche 18" IB centered at the front of the room. I've considered adding a single Avealanche 18" to the rear. Since I'm over 2/3 of the way to the rear of the room, the volume coming from each IB at the seated position should be approximately equal. I wonder if that would be better.

[JohnR]

I think John is probably referring to sealed boxes - ?

Anyway I don't think it makes a dipole sub. You would need to have them back to back.

[John Casler]

I think John is probably referring to sealed boxes - ?

Anyway I don't think it makes a dipole sub. You would need to have them back to back.

Hi John,

I was actually thinking of the room being like the inside of a dipole sub with an IB front and back.

I'm surprised I haven't heard of anyone doing it, and wondered if anyone else had.

I have already done it with "box subs", in various ways, but thought the IB implementation might be interesting.

Surely others have contemplated such, unless there is some "drawback".

I also wonder what it would do to the sound transmitted through the side walls?  Would it lessen it, by virtue of the dipole effect, or would it not be any different at all than having regular subs.

It would seem that if operated OOP (Out of phase) that the side walls would see less pressurization, but I could be wrong.

[JoshK]

I think John is probably referring to sealed boxes - ?

Anyway I don't think it makes a dipole sub. You would need to have them back to back.

Agreed.  What JC describes is more of a push-pull setup, like the Eric K described some time ago.  It would not be dipole inside the room in terms of cancelling side radiation and what not.  I think the definition of IB is something to do with the inner volume is greater than the VAS or something to that affect.  Basically when it is a "large" box.  

The IB setup has its advantages (low or no box coloration and better transient response) and disadvantages (absolute SPL output, less power handling).

I think it would be a great experiment to try, and if you have the means to delay either the front/rear to offset the distance difference (to listening position; can be done in digital or analog domain via all pass filter) you can have a real in room push-pull setup.

[JoshK]

I also wonder what it would do to the sound transmitted through the side walls?  Would it lessen it, by virtue of the di ...

No, it wouldn't benefit from the side radiation cancellation.  I am guessing that the real benefit you might see in terms of acoustics (rather than SPL)  would be similar to multiple subs spread about the room in that you "average" out the room modes and nulls.  Instead of having a few very well defined modes/nulls you have more of them but less well defined each since one sub add where the other nulls and visa versa, unless of course you happen to align their nulls/modes in which case it'll worsen.

[John Casler]

It might help if I'm more specific.

It is my understanding that an IB sub is actually "outside" the room and the front of the drivers fire into a large slot, firing into the room.  The rear of the IB drivers fire into "infinity".  That is they are again outside the sound room.

Now my example has an IB Sub in the front of the room, firing into the slot and into the room.

The rear of the room also has an IB sub but it fires "out" into infinity.

The rear sub fires "out of phase".  That is, as the front woofer(s) move forward, the rear woofers move rearward.

This in effect creates a dipolar chamber in the room, or I think it does.

I know there are many ways to make a dipolar radiation, but I am not aware of any distance limitations.  I assume if the phasing is correct, the distance could be an inch or a mile.

Josh, could you expand on why the dipolar radiation of "reduced" side waves wouldn't be the same.

If you built a box 20ft L x 3ft w x 3ft h, and put a woofer on each end firing as a dipole, wouldn't the side radiation on the inside (side) walls be reduced?

Hope I'm explaining this well.

[JoshK]

That is what I assumed you meant with your description.  That is an IB, but IB is more general then that type of installation, but I knew what you meant.

Actually the more I think about it, the more I think that the side walls may be pressurized less (relative to a given SPL at the seated position).  I need to think about it some more.  The push-pull arrangement does seem to have some advantages.

[jules]

this help?

http://home.comcast.net/~infinitelybaffled/page2IB-Gallery.html

Wouldn't there be probs with different wave lengths/different frequencies sometimes reinforcing but cancelling out at others with the drivers at opposite ends of the room?

I haven't read the above thread from the Cult of the Infinitely Baffled for some time but I seem to remember that the middle of the room is the highly impractical but suggested placement for this sort of "push-pull" system.

jules

[Russtafarian]

John,

I'm running stereo dipole subs, positioned half way down each side wall.  They fire front to back, minimizing side waves.  Don't know how this relates to what you've described, but it sure sounds good.   You are welcome to drop by for a listen some time.

Russ

[woodsyi]

Interesting question, John.  I would like to know who lives on the other side of the big ass IB woofer that is running out of phase.    Just for kicks, wouldn't it be interesting to crank it up with both IB woofers firing in phase?  

[JoshK]

Jules,

As you illustrated, the "cancellation" of the sides is hard to understand fully as the summing and nulling is hard to predict in this case.  

I think the easiest thing to do might be to play around with some simulator software with such a setup and see what it comes up with.  

Ultimately this setup isn't going to yield any differences from sufficiently large sealed enclosures up against the front and back wall, one out of phase with the other and facing eachother.  In both cases, each sub is radiating effectively into half a sphere.

[John Casler]

Interesting question, John.  I would like to know who lives on the other side of the big ass IB woofer that is running out of phase.    Just for kicks, wouldn't it be interesting to crank it up with both IB woofers firing in phase?  

     

Of course this is all "hypothetical"

That is the orther part of the equation...in phase...out of phase?

Out of phase would have the subs working together as a "dipole" sub enclosure, and In Phase would have them in a bipole.

The big difference is that we are not talking "outside" the enclosure, but "inside".

What acoustical physics are taking place?

The confusing element of explaining this question is that when one thinks of a "dipole sub" they normally are thinking of a dipolar radiatiing sub "IN" a room, not a dipolar sub that "IS" the room.

Most generally feel that using dipole sub(s) in a room provide a better bass clairity, at the expense of overall SPL's.

My experiments with "multiple subs" just seems to keep inventing questions about the physics.

As a side note, I was also wondering if you could turn an "unused fireplace" into an IB sub, if the chimney was large enough.

[JoshK]

I still don't think that qualifies as a dipole.  I am not an expert in this by any means, but dipole is usually defined by its radiation pattern, two opposing radiations.  In your description, you have to facing radiations, which is why I call it push-pull, but dipole you have opposing radiations.

[John Casler]

I still don't think that qualifies as a dipole.  I am not an expert in this by any means, but dipole is usually defined by its radiation pattern, two opposing radiations.  In your description, you have to facing radiations, which is why I call it push-pull, but dipole you have opposing radiations.

Yeah, I think you are correct.

The only reason I used the term, is because I have seen some dipole subs with two drivers with only the space "inside" the cabinet separating them.

I always wondered what the air movement and physics were on the inside as opposed to the outside, which would be the "dipole radiation" that most of us consider.

Then with my "push/pull" experiments, I was approacing the "inside of the cabinet" dipole effect.

The ultimate progression of that would then be the IB "push/pull" and while I think I have a little idea what that would yeild, I simply wondered if it had ever been done or discussed.

[John Casler]

John,

I'm running stereo dipole subs, positioned half way down each side wall.  They fire front to back, minimizing side waves.  Don't know how this relates to what you've described, but it sure sounds good.   You are welcome to drop by for a listen some time.

Russ

I for sure am looking forward to hearing your gear "someday".

Are your dipole subs "in a box" or "over/unders"?