Getting Dipole bass out of a monopole subwoofer

[Hara]

Monopole subwoofers have more output (and thus lower distorition at similar listening levels) and extension while utilizing less drivers (adding more drivers will further lower distortion) than dipole subwoofers especially when in a ported enclosure such as a BR or TL cabinet.

Dipole's offer a more natural bass raved by many users on this forum, however, somewhere on Linkwitz's website he mentions experiencing dipole bass from a monopole with digitial room correction.

I believe a specific discussion on what factors give dipole sound and the methods to achieve those factors from a monopole would be beneficial to the subwoofer building community.

[richie00boy]

A link would be a good start to kick things off more then...

[john k...]

(JPK) I don't usually chime in on subwoofers but I though I might be able to add something on this topic. I believe if you search SL's site what he said was in regard to what he heard at the 2005 CES. If I recall correctly it was in reference to digital room correction and was simply to the effect that with the particular DRC being used it was the first time he heard bass response form a monopole woofer system that was of similar quality to dipole bass. I don't believe he when much further. I haven't checked back at his site so there might be additional comments I don't recall.

You might consider looking at the following articles at my site. The first one addresses how a dipole woofer anechoic on axis response is affected by listening distance. It shows that a dipole woofer designed for flat on axis response far away will have boosted low frequency response when the listing distance is reduced. A monoploe woofer does not have this characterist.

http://www.musicanddesign.com/Dipole-axis.html

This second article looks at the mechanics of room pressurization and show that dipole woofers can not pressurize a room. Therefore the dipole response falls off below the room fundamental as opposed to being augmented by the pressurization effect as happens with a monopole.

http://www.musicanddesign.com/roomgain.html


This 3rd article looks at finite element simulations of a dipole and monopole woofer in room. The results show how dipole and monopole woofers excite different room modes and also the show how the woofers behave below the room fundamental where room pressurization effects are important.

http://www.musicanddesign.com/roomgain2.html

Aside form the differences in total radiated acoustic power, the results indicate to me that the most significant difference between monopole and dipole woofers is the behavior below the room fundamental. The dipole tends to tune itself to the room fundamental.

[AJinFLA]

My skepticism about the subjective effectiveness of different room correction methods was greatly reduced after hearing the Lyngdorf Audio (formerly TACT) TDA 2200 Digital Amplifier with its room correction module driving a pair of MH-1 Mk II speakers and two W210 Corner Woofers in a small hotel room. The correction algorithm, designed by Jan Abildgaard Pedersen, uses the information from several sound field sample points at random locations in the room and from a sample at the listening position, rather than taking samples only near the listening position or measuring only the acoustic load impedance that the room presents to the woofer cone. Small room acoustics are a multi-dimensional problem (time, frequency, space, psycho-acoustics) where both global and local characteristics affect the perceived sound. I was very impressed by the articulation that the correction produced in the bass region completely removing the boominess that was there otherwise and without artificial spatial effects. Peter Lyngdorf expressed to me his opinion that accurate bass reproduction requires either dipoles or conventional woofers with room correction.

I'll save a couple grand and keep my dipole subs with below 35hz monopole reinforcement LOL.
Maybe when something like the TACT starts selling for $300, I'll reconsider. But since my mains (and John's LOL) remain dipoles, maybe not.

cheers,

AJ

[john k...]

(JPK) High AJ. Thanks for posting the comment from SL's site. I though it was with regard to TACT but I wasn't sure. I am still of the opinion that the major factor is the room pressurization with a monopole woofer. It would be interesting to see the transfer function of the DRC for a typical case.

[ScottG]

..the natural progression is radiation behaviour and room effects, but methinks there is significantly more here to their audible character than that.

I'll add to the radiation thing though..

Specifically the side null available to a "subwoofer" run into lower-to-mid midrange as a dipole seems to have benefical effects with regard to apparent channel seperation.

This isn't something you will get with a monopole and any amount of digital correction.

[AJinFLA]

John,

I would take it a step further and say I would like to see some double blind testing of dipole (or cardioid) vs monopole (even with DRC).
I can claim my ears tell me that dipole, open baffle woofer systems sound superior to monopoles, but I certainly can't prove it.
IIRC, Dr. Geddes tested his Summa vs a pair of Gradients (Cardioid/Dipole hybrid). The results were a statistical tie, again IIRC. I would really have liked to see the test conditions, music selection, etc. (never mind that the Gradient uses a modest SEAS custom coax vs the near state of the art BC units in the Summa).
He is a proponent of heavy (low frequency) room treatment (as opposed to DRC, although I imagine they could be combined), something I simply don't find feasible (and I suspect most others do also).
I'm sure this would still settle very little, since it would be very generalized to the particular driver/cabinet combinations used, etc. A fairly wide scope of systems would probably be necessary for any statistical significance. And even then, Dipole X can always outperform Monopole Y and vice versa, depending on the great many factors (driver linearity, room, modes, etc) involved.
Like just about everything else, there is no one answer.
What I would also like to see is a investigation into how perceptible (if at all) sound (re)radiation through a closed box woofers cone and enclosure is. Is it masked below audibility from primary radiation? Is that really part of the allure of an OB system? Or is it just the power radiation?

Cheers,

AJ

on a side note, the replacements for my Mutants will also be full range dipoles, but will have two built in monopole subs operating upwards of 50hz and two more seperate monopole subwoofers operating in the same range, in the rear of the room. Still no DRC LOL.

[Hara]

AJ posted the section but the original link is
http://www.linkwitzlab.com/design_of_loudspeakers.htm

John K., awesome technical articles. I'm trying to eventually setup some sort of DRC setup to experiment with and get actual room response measurements but I don't have all the equipment necessary yet.

[john k...]

(JPK) I think I would tend to agree with Earl G. After experimenting with the CRAW for over a year I really can't say I would categorically say any one woofer format is best suited for good bass response. I do hear differences, but one format was never best over all. And to be honest, when I read, "Peter Lyngdorf expressed to me his opinion that accurate bass reproduction requires either dipoles or conventional woofers with room correction. ", it sounds more to me like Peter is being polite than anything else. I mean Peter was talking to some one who is, shall we say, as singled minded about audio reproduction as they come. This type of verbage between individuals with differing points of view is pretty comon in most scientific communities.

Dipole woofers still excite room modes, though differently, so why wouldn't they also benefit from the same type of DRC? That's a rhetorical question. Obviously they would.

[vadi]

So does the TDA2200 eliminate room modes by altering the signal (to create standing waves which cancel the modes out). Would this be possible?