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Old 12th July 2006, 05:12 AM   #11
Hara is offline Hara  United States
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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).
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Old 12th July 2006, 06:17 PM   #12
ScottG is offline ScottG  United States
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Originally posted by 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.
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.
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Old 12th July 2006, 11:47 PM   #13
Paul W is offline Paul W  United States
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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.
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Old 13th July 2006, 12:24 AM   #14
AJinFLA is offline AJinFLA  United States
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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.

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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.

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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?

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Dipole woofers still excite room modes, though differently
I would say differently, but not as extensively. Correct me if I am wrong.

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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
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Old 13th July 2006, 12:34 AM   #15
AJinFLA is offline AJinFLA  United States
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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
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Old 13th July 2006, 12:49 AM   #16
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Originally posted by AJinFLA


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.
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Old 13th July 2006, 07:09 AM   #17
ScottG is offline ScottG  United States
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Originally posted by Paul W


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.


..my thoughts as well.
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Old 14th July 2006, 12:33 AM   #18
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"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.

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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.
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Old 14th July 2006, 12:55 AM   #19
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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?
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