Should dipole woofers be placed close to wall boundaries?

[Amphiprion]

I was reading about different radiation patterns and came across something called a linear quadrupole. Its radiation pattern is like that of a dipole, but with narrower lobes (greater off-axis cancellation). Since this would lead to somewhat lesser excitation of room modes, should people consider this when placing a dipole woofer/subwoofer in-room? I haven't yet modeled what a non-perfect reflection boundary (ie a normal wall) would have on the resultant polar plot, but I'll get around to it at some point, just wanted to toss this out for ideas.

https://web.archive.org/web/20060902033832/http://www.kettering.edu/~drussell/Demos/rad2/mdq.html

[ThomasW]

My hands on experience is that they can be closer to the side walls, but need to be the same distance away from the rear wall as monopole.

[Tommythecat]

Im not sure I understand what the linear quadrupole has to do with placing a dipole speaker near boundries? Could you explain that?

And yes, in the experience I've had there wasn't too much worry about placing the dipole woofers near side walls. Making the optimal distance between the woofers for the best "sweet spot" - if you will - was a higher priority.

[Amphiprion]

Placing a dipole near/against a perfectly reflective boundary (infinitely stiff wall) would make a linear quadrupole if you use the mirror image analysis method.

[Tommythecat]

I'm not well versed in acoustics/waves, but I'd assume you get a linear quadrupole-esqe response if you shoved the dipole against the back wall, not the side wall.

[Amphiprion]

Yes, the dipole would have to be orthoganol to the boundary.

[Tommythecat]

*bing* The bulb over my head is on now. I was thinking only about placing dipole woofers near side boundaries. I got ya now.

Well, let this confuse us all:



I have the impression that achieving the response in room by the use of a boundary would not be possible. We have to consider the reflection caused behind the listener from the front of the dipole source. What Linkwitz advises of course is to use the a=b rule to cancel out the D1/D2 reflections, so that the listener is the same distance from "wall 2" as the speaker is from "wall 1".

So before we take it into account/consider it, we'd need to show that we can achieve that response.

[Amphiprion]

I was thinking more theoretically than actual in-room stuff at this point, but you're right, it does raise an interesting point. I might run some simulations in Matlab if I can ever find the time to write some code and simulate say up to the 3rd or 4th reflection points in a more normal sized (not square) room. Don't anyone hold their breath on that though, I got a lot of stuff going on Too many interesting ideas and not enough time.

[Rudolf]

Mark,
to give you some guideline, here are the equations for the quadrupole. "Punktquelle" is point source. The green marks show the increasing angle dependent complexity of radiation. Red marks show how efficiency increases with frequency (making the quadrupole very inefficient at low frequencies).
All derived from page 124 of www-eep.physik.hu-berlin.de/~lohse/musik/lecture.ppt



Rudolf

[Amphiprion]

Hi Rudolf,

Thanks for the info! Their linear quadrupole is oriented +-+- instead or +--+, but I think I can manage the derivations from the info presented on the graph. I expected efficiency to be lower since the idea behind the quadrupole is to increase off-axis cancellation.

[AJINFLA]

I suspect that we may have one here

Gallery not available

even though it's being identified as a dipole. There would certainly be force cancellation, something that I like to incorporate into designs when possible.
But coupling to room modes with the different near/far field radiation?
Beneficial? Anyone here attend RMAF by chance?

cheers,

AJ

[ThomasW]

Anyone here attend RMAF by chance?

Yes....

[AJINFLA]

Yes....

Gee, thanks Thomas
Did you see/hear these? Might I be guessing correctly?
Don't make me have to call this guy to find out :B .

cheers,

AJ

[ThomasW]

Nope sorry I didn't see/hear those...So I think a phone call is in your future.....

[kingpin]

Yes....

:rofl: :rofl:

[ThomasW]

Digital Signal Processing (DSP) in loudspeakers is such a good idea that I’m surprised so few designers take advantage of the technique’s merits. With DSP, the designer can create any crossover slope he wishes, equalize the system, and time-align the drivers.

The advantages of DSP-based loudspeakers was demonstrated by Emerald Physics, a new company with a most unusual product, the CS1. The four-piece system employs a 1” compression driver tweeter mated to two 8” midrange units in one flat open panel, coupled with another open panel consisting of four 15” woofers in a dipole configuration (two forward firing, two rear firing). A DSP unit from DBX provides the electronic crossover and other processing. Six amplifier channels are required, although the amplifiers can be low power owing to the system’s high sensitivity (100dB 1W/1m).

The demo I heard produced a super-precise spatial presentation, smooth and flat tonal balance, wide dynamics, and terrific bass extension without the lumpiness one often hears in hotel rooms.

The downside is that the CS1 is a “form follows function” design, meaning that it has rather utilitarian cosmetics and finish.

Nonetheless, the CS1 is a fascinating product, and at a list price of $4750, could represent a stunning value. Full production is scheduled to commence in January

....

[Carl V]

hmmmm, for what it's worth I was at RMAF...& heard this design 2-3X.
I'm, interested in Open Baffles & Wave guides.

It's a nice design...but it's also a design which is music genre
limited. For instance on Solo Piano (classical) it did poorly.
It didn't gel as I have heard in the past. It had Great Depth
and damn fine Phantom center image but it also had strong
L- R speaker sounds....in other words 3 sound sources.

Playing solo guitar was fantastic. Playing older Jazz was
pretty nice. But remember many 50's recordings had hard
panned sound. Playing some Pop recording was Ok. Again
think processed....Santana's big recent hits.

If the recording was overly 'wet' it was too much of a good
thing. Chesky stuff like Rebecca Pigeon,

Breaking this down to component parts....Nice deep soundstage.
Nice bass impact. Good Tone & timber. Good midrange dynmaics.
I also nver really heard good soundstage separation in between
the center image & the L-R speaker locations.

But on a whole and for many types of recordings.....it wasn't my
cup of tea. And I am one who wanted it to be my cup of tea.

YMMV....


Oh & Thomas once again thank you for being a generous Host.
I know Saurav & CJ were amazed at hearing the bass line in
Cosmic Hippo could be so well articulated.

[AJINFLA]

So I think a phone call is in your future.....

My suspicions confirmed. It's a Quadrupole. Website with technical data in Jan (according to him) :T .

cheers,

AJ