Getting Dipole bass out of a monopole subwoofer

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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.
 
(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.
 
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
 
(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.
 
..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.
 
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.
 
(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.
 
Audiobility tests would also be interesting inorder to see how far down in frequency you need to go to where dipole bass and monopole bass become indistinguishable given a set of room parameters in order to determine an ideal cross-over point for dipole/monopole hybrid systems.

But so far from this discussion, DRC remains just an augmenter rather than a cure all (as usual) for bass issues helping both monopoles and dipoles (Just like traditional room correction, a plus for all speaker systems).
 
john k... said:
(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.

LOL..

Its VERY funny that you would mention this reasoning (or lack thereof) - i.e. a "single-minded" pursuit, AND Earl G. in the same paragraph. I've never "met" anyone that displays this character more than Earl G (..by F A R).

At one time SL (on his website) either stated or alluded that he didn't know why he preferred dipole behaviour, despite having a lengthy abstract on radiation and room behaviour. Additionally consider that he sometimes advocates the use of monopole subs, and that he listens to other systems with different radiation properties (actually liking them), has built an omni, etc.. At least in this respect then I'd say he isn't really "single-minded". I will say though that perhaps what he likes is NOT dipole radiation per se (especially over such a broad passband), but rather more the properties that free-air operation provide.

To my way of thinking - reasoning that a dipoles "superior" behavior is due (or just largely due) to its interaction with room behaviour is the equivalant of jamming a square peg into a round hole.
 
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?

I believe this point is too often overlooked, perhaps because it seems difficult to quantify. The big payoff for me comes from reducing the influence the box has on the driver...whether it be reradiation, compression, etc. Drivers sound more like the original signal/insturment without the influence of a box.

If you can do away with the box (not always possible but, I believe, the single largest step) the choice of a specific baffle shape (U, H, flat, etc) become more an implementation detail depending on system goals, room, placement, etc. etc. Depending on the need, I'll continue to build all the OB shapes and, when I don't have a choice, boxes.

Note: My comments have to do with woofers as I don't think dipoles can be particularly effective as SUBwoofers. For subs, think IB...sorta no box.;)
 
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.

Yes, but let's be perfectly clear for the rest of the folks out there John.
Earl G is not just for monopole radiation ala your CRAW in bipole mode. Rather, he is for monopole radiation *with heavy room treatment* (passive correction if you will), by making the room more lossy at low frequencies. Effectively, he is correcting for the spectral imbalance caused by the upward tilting power response at low frequencies, much like a dipole would. Or your CRAW in cardioid mode. I don't recall you using or calling for the mandatory use any such bass absorbtion like Earl does.

I do hear differences, but one format was never best over all.
Agree. But someone can also say the same thing about so called "Fullrange" (dynamic/cone) drivers. I don't see either one of us using such a driver any time soon, do I?
So maybe we do have some tendencies/preferences as to what is "best over all" format wise.

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
"Interpreting" what Peter meant would be rather presumptuous. The rest sounds a lot like the cheap shot you usually profess not to take at SL. He is for sure strongly opinionated. Sound familiar? Who here isn't, including me?

Dipole woofers still excite room modes, though differently

I would say differently, but not as extensively. Correct me if I am wrong.

so why wouldn't they also benefit from the same type of DRC? That's a rhetorical question. Obviously they would.

Sure, why not? I don't recall ever seeing SL say it shouldn't be used. It's one of the luxuries I have by using DSP for the entire system. The possibility of utilizing some form of correction in the bass region is there, but obviously not as extensive as the TACT. Whole lot cheaper though;).

cheers,

AJ
 
I don't think dipoles can be particularly effective as SUBwoofers. For subs, think IB...sorta no box.

You posted as I slowly typed Paul. I think you, SL, JPK and I can all agree that for 20hz pressurization of the room at satisfying levels, monopole radiation is a must. IB is a terrific choice if available. Or 4(+) sub 50hz boxes around the room as I have opted for (2 bipole for a total of 6 drivers).

cheers,

AJ
 
AJinFLA said:


Yes, but let's be perfectly clear for the rest of the folks out there John.
Earl G is not just for monopole radiation ala your CRAW in bipole mode. Rather, he is for monopole radiation *with heavy room treatment* (passive correction if you will), by making the room more lossy at low frequencies.

Well, to be complete there is one further aspect that Earl is insistent on for subs - lots of them. The lossy room serves to equalize the power spectrum, but he also says that many subs (I think he uses 5) scattered about the room are also 'needed' to provide more uniform modal excitation.

Taken all together this does seem like a successful approach, but it's available to such a vanishingly small segment of the population that I'm not sure how valuable it is.
 



"Interpreting" what Peter meant would be rather presumptuous. The rest sounds a lot like the cheap shot you usually profess not to take at SL. He is for sure strongly opinionated. Sound familiar? Who here isn't, including me?






I was stating an observation and an interpretation based on a life time of experience of individuals being complimentary to each other at public forms such as the CES might present, even though their ideas may be diametrically opposed, as in corner loaded woofer with DRC vs. dipole woofers. Peter made a statement which supported his position and then added a caveat complimentary to the other position. And I would refrain from interpreting “single minded” with negative connotations. I didn’t say close minded, I said single minded. I think it is more than an accurate statement to say that SL is pretty single minded with regard to observation that dipole bass is the optimal format for room which are acoustically small. Look at his publication of the subject. Look at his web page where, last I looked, he states that he is continuing to try to analyze why dipole bass sounds better. He is looking for a way to quantify his observation/belief. However, I fail to see any negative connotation in that.

But still, being inquisitive I have to pull on the thread. Assume for the moment that dipole woofers are categorically better than monopole woofers in acoustically small rooms. That said we also know, regardless of our preferences, that neither is perfect. So if some DRC system comes along that make a highly flawed monopole woofer sound as good as an only slightly flawed dipole woofer then you have to question what it would do for a dipole. Since we are really dealing with the control of room modes, and/ or eq of room pressurization and since all woofer system excite room modes in some form, then it’s a clear point that DRC will also improve the bass response of a dipole woofer. That is because the woofer format has little to do with it. The DRC is not applied to the woofer, it is applied to the system of the woofer/room. Now, looking back at the statement, “What is required for good bass is monopole woofer with DRC or dipole woofers”, we can quickly append that statement and find the underlying truth, what is really needed for good bass is DRC. That may not be what was intended, but it is ultimately where the statement leads.



Effectively, he is correcting for the spectral imbalance caused by the upward tilting power response at low frequencies, much like a dipole would.



I would have to ask if by low frequency you mean above or below the room fundamental? I've done the math on power response with constant directivity systems and the 4Pi to 2Pi transition due to a ground plane (i.e. a speaker where the woofer sits on the floor and radiates effectively into 2Pi space where as the mids are removed from the GP and radiate into 4Pi space). For a system with flat anechoic response and constant directivity factor the 2pi transition due to the presents of the GP results in a 3dB reduction in radiated power at low frequency. It doesn’t matter if it’s a dipole or omnidirectional source. The lossy room aspect above the fundamental isn’t equalizing power, it’s there to dissipate energy stored in the oscillations associated with room modes. The power radiated into the room remains constant. But the energy stored in the resonant modes is dissapated faster, thus the modes do not achieve the same amplitude.

I agree with you accessment that room treatment is a passve approach to controling room modes where DCR ia an active arrpoach. And I agree that monopole subs (sealed boxes or wall mounted IB subs) are required for reproduction below the room funamental. No amount of DRC or passive treatment is going to get 20 Hz response in a room with 40 Hz fundamental with a dipole woofer. (Don't read that as verbatim. What I mean is that as the frequency drops a dipole becomes less and less capably of producing any output because it can not excite the DC mode.) You might start to get a good breeze though.
 
John K,

Is it really the inability to pressurize the room that makes the dipole response fall off sharply below the room fundamental? My thinking is that below this threshold the baffle size ceases to be of significance and the room itself determines the phase relationship of the front and rear waves. This results in bass roll-off in direct relation to the increase in wavelength instead of the normal 6db/oct dipole roll-off above the room threshold.

Also, can we please include cardoid and hybrid cardoid/dipole response in this discussion?
 
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
Sound like you are doing what I think i'd like to do a sub down low and dipoles from about 50-200 to reach my fullrangers. I don't have DSP or much technical knowledge yet, so I'm just hoping to run them off sub plate amps on each side running. What do you recommend (Karlson or hopefully something that doesn't look quite so much like a butt). As far as drivers I do like the Dayton brand a lot, it sounds like four 8's or four10's would probably do it.

Thanks for any help you can provide
 
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