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Thread: Building an Enclosure Around a D.A.S D-401 2395 Clone

  1. #91
    Senior Member ivica's Avatar
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    Quote Originally Posted by RMC View Post
    Hi Ian,

    Re your sept 8 post # 86 with a tricky question about excursion when doubling cone area. I see nobody replied to you 4 days later... For myself I didn't reply since I had already seen part of the answer, and may be told I cheated.

    However, If you look at my post # 82 dated sept 4 (4 days before yours) you can see I quoted from Dickason's Cookbook, 5th ed., p. 30-1. On those same Dickason pages I read 4-5 days before your question, a partial or incomplete answer to your question appears. So no real contest. Read below for more.

    However again, I'm NOT satisfied with his explanation of driver coupling effect on sensitivity, doesn't seem to make sense, looks like a contradiction or typo made its way in his text. This is why in my sept 4 # 82 post I quoted John Eargle instead for the coupling effect on sensitivity issue, and Dickason on the voltage/impedance issue.

    That speaker experts seem to disagree on science (!) is surprising, but does exist. Look at Bullock's book on p. 62 bottom right column where he says + 6 db for two woofers in parallel, and on p. 66 left column from the middle and on where he repeats that, as opposed to Eargle's clear explanation of + 3db for coupling and another possible + 3 db for power handling I quoted in post # 82 (Handbook of Sound System Design, p. 114, and Loudspeaker Handbook, p. 79). Then have a look at Dickason's, 5th ed., p.30 for a confusing explanation of 3 vs 6 db in 1, 2, and 4 woofer formats ...

    I tend to give more credibility to Eargle since his manuscript was reviewed before publication by W. J. J. Hoge, another well-known Speaker Engineer, who would normally have picked-up a gross error... JBL's own Sound System Design Reference Manual says the same as Eargle (Authors: Augspurger and Eargle).

    Same power input to identical single and double-woofer (in parallel and closely mounted) boxes, gives a 3 db sensitivity advantage to the double-woofer box and cone excursion would be half that of a single woofer box. Dickason stops here, the rest is mine.

    This makes sense because a larger cone area can move more air or "take a bigger "bite" at it" and need not go as far (excursion) to reproduce the same sound. If I remember correctly the good old days, the E-V 30" woofer and the Hartley 21" woofer didn't have nor needed a lot of Xmax considering their huge cone area that moved lots of air more efficiently.

    But since you mention specifically "for the same output spl" then that would imply a half reduction in input power to the double-woofer box (to get - 3 db) for spl to be equal to that of single woofer box. Logically, lower input also means less excursion and distortion, therefore the answer would be "quarter", if its already half the cone travel at + 3 db as mentioned by Dickason for double-woofer compared to single. Regards,

    Richard

    Hi RMC,

    Please read
    http://trace.tennessee.edu/cgi/viewc...t=utk_gradthes

    I think there are a lot of answers. especially section : "Mutual coupling.."
    "....2.3 Mutual Coupling
    The concept of mutual coupling between loudspeakers is familiar to anyone who has mounted two loudspeakers close together. The power output of the two loudspeakers is approximately four times (+6dB) that of a single loudspeaker. Also, if you double the area of the diaphragm of
    a loudspeaker drive-unit, given the same diaphragm velocity, the power output will again increase by +6dB. Reference to equation (2) shows that introducing a second loudspeaker close to a first will approximately double the pressure on each of the diaphragms, thereby doubling the power output of both loudspeakers.
    What is perhaps less obvious however, is how introducing a distant second loudspeaker can double the power output of a loudspeaker. For the 3m separation and 0.15m radius of the pair of loudspeakers in the above examples, the magnitude of the pressure on loudspeaker A due to the operation of loudspeaker B is approximately one twentieth of the pressure on A due to its own velocity. How can an increase in pressure of 5% cause a doubling of power output? The answer lies in the phase of the two pressures. At low frequencies, the pressure on the surface of A due to its own velocity is almost in phase quadrature with the velocity - the radiation impedance is almost totally reactive - whereas that from B arrives almost in-phase with the velocity due to the propagation distance involved. Equation (2) tells us that it is only the in-phase part of the pressure that is responsible for power output. As the distance d is decreased, the magnitude of the pressure due to the second source increases but its phase approaches that of the pressure due to the velocity of the first source - the power increase remaining at +6dB but extending higher in frequency - until the "two close loudspeakers" situation exists. As can be seen from equation (3), the frequency up to which the mutual coupling occurs is determined by the distance between the two sources; as the propagation distance approaches half a wavelength the phase of the pressure from the second source is no longer in phase with the velocity. The distance over which mutual coupling occurs is known as the extent of the hydrodynamic near field of the loudspeakers.
    ...."

    or read here:
    https://books.google.com/books?id=Ts...upling&f=false


    regards
    Ivica
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  2. #92
    Senior Member RMC's Avatar
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    Hi Ian,

    To me, It's not only a question of being correct (which someone can get with a lucky guess), but more important is being able to explain why it is so, as I did.

    Re your statement "The trade off is double the enclosure size." The enclosure size is not really a "trade-off" in my view since for that larger size you get double woofers and more output (these two are not give away to get something else, but rather additions).

    After writing my post # 89 I thought about another way of saying the same thing as I did differently:
    Halving of power to double-woofer box, to match 3 db lower spl from single woofer box, results in another halving of the previously halved excursion for coupled double-woofer box. Since the half of a half is one quarter, therefore the answer is one quarter of the excursion, at same spl, compared to single woofer box... Regards,

    Richard

    P.S. Ivica you keep bringing back the SAME text on and on that I already commented on... this is getting to look like a fixation on your part.

  3. #93
    Senior Member Ian Mackenzie's Avatar
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    This is no a PA website.

    If the member has a Barn or Shed like l have seen in Missouri l get it.

    If he drives Monster trucks l get it

  4. #94
    Senior Member Ian Mackenzie's Avatar
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    Hi lnvica,

    That is a good paper. I enjoyed reading it.

    Newell and Holland also did a study on horns.

    Newell still designs studios and monitors in Europe

    He also has a book(s) published on the subject.

    I think JBLs stated sensitivity on the 4355 confirms the situation on the woofer.

    http://www.audioheritage.org/vbullet...php?10614-4355

    As a practical matter (2) 2235H last longer than a single 2235H from a reliability perspective.

  5. #95
    Senior Member Ian Mackenzie's Avatar
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    My only feedback here is try and avoid quote responses too often.

    It makes it a very long winded read

    Try and paragraph your thoughts, not big blocks as it difficult to read.

    And there is nothing wrong with intellectual curiosity as long as it relevant to the origin of the thread

    If this creates a robust discussion the mark a Mod to move those posts into a new thread.

  6. #96
    Senior Member ivica's Avatar
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    Mutual Coupling..again

    Quote Originally Posted by RMC View Post

    P.S. Ivica you keep bringing back the SAME text on and on that I already commented on... this is getting to look like a fixation on your part.
    Hi Richard,

    If carefully read the pages 17 ... 22 in the suggested link,

    https://books.google.rs/books?id=Tsc...upling&f=false

    from the: "Loudspeaker and Headphone Handbook", edited by John Borwick
    I believe that everything would be clear, why at low frequencies (relative to the sound sources distances) conclusions are different then at the higher frequencies.

    All of my effort here is not only to convince You, but mostly to give some information to the other AH Forum members, who are puzzled by some not technically precise information that can be get from lot of (even respectable) authors 'here-and-there' (some of them mentioned in Your posts).
    Just for Your reminder:
    1.even JBL said that they have to 're-tune' their card for the JBL4343 applied in the bi-amp mode (to be -6dB at the crossover frequency)
    so please read
    http://www.audioheritage.org/vbullet...ull=1#post6248

    2.remember why LR-networks (has -6dB for the lower crossover frequency solution...)

    regards
    ivica

  7. #97
    Senior Member Ian Mackenzie's Avatar
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    Ivicta has a valid point

  8. #98
    Senior Member Ian Mackenzie's Avatar
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    Anyway l have excavated a hole for in the ground loudspeaker measurements.

    It's the way Jbl does it

    So if you have a big box come and see me!

    It needed an excavator lifted over the house by a large crane.

    Spared no expense.
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  9. #99
    Senior Member RMC's Avatar
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    Hi Ivica,

    Trying to convince me I already replied to that. Giving info to other members is great that's what I do. But stating "... who are puzzled by some not technically precise information that can be get from lot of (even respectable) authors 'here-and-there' (some of them mentioned in Your posts)." is grossly exagerated.

    I've seen here nobody puzzled but you. Authors "here and there"? Jbl, Yamaha, E-V, Augspurger, Bullock, Dickason, Eargle, I don't see them as "here and there" and find that insulting to them and me... If you don't believe in JBL then why are you here in this site? Plus I did outline specific contradictions among experts... So I do think my info is more varied, balanced and complete than yours (i.e. gives a better picture).

    Richard

  10. #100
    Senior Member ivica's Avatar
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    Quote Originally Posted by RMC View Post
    Hi Ivica,

    Trying to convince me I already replied to that. Giving info to other members is great that's what I do. But stating "... who are puzzled by some not technically precise information that can be get from lot of (even respectable) authors 'here-and-there' (some of them mentioned in Your posts)." is grossly exagerated.

    I've seen here nobody puzzled but you. Authors "here and there"? Jbl, Yamaha, Augspurger, Bullock, Dickason, Eargle, I don't see them as "here and there" and find that insulting to them and me... If you don't believe in JBL then why are you here in this site? Plus I did outline specific contradictions among experts... So I do think my info is more balanced than yours.

    Richard
    Hi Richard,

    Not to argue with You, I can understand from your statements that term "speaker mutual coupling" MEANS NOTHING, so I only wonder who on Earth "introduce" such term that from Your point of view is irrelevant.
    As shown in my previous post, even JBL have accepted the evident present of the mentioned "speaker mutual coupling" phenomena,

    http://www.audioheritage.org/vbullet...ull=1#post6248

    so here we are not in the church to talk about anybody personal belief or thrust, here I am talking about real physical law that exist in the sound propagation, but understanding such phenomena can not be explained with easy logic analogy.

    Respecting the great scientist You have mentioned, I have said "...not technically precise information..." , so neglecting special cases where the sound sources are very near each other (relative to the wave length of the frequencies of the reproduced sound).

    regards
    ivica

  11. #101
    Senior Member Ian Mackenzie's Avatar
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    I have no interest in the different point of view here but l would suggest the point of the Holland article is that it gives a more complete understanding by discussing not just a single case of "mutual coupling" but the wider and equally important and less known relationship when using two drivers at increased distances.

    I don't think Invica can be accused of jaw slapping here as he has bought new and fresh information that is not obvious but important in practice.

    But l do think it's important as a poster to demonstrate with some examples even with a graphic how a quoted reference applies and what it means in A) your "own words" and B) so anyone other than yourselves can relate more than a reference to their own situation.

    In terms of clarity it might be easier to use a footnote (1) and place a link or full detail of your reference st the bottom of the post under References

    We do have an annex is the reference section where anyone can go read an article btw.

    Otherwise just quote the link and let someone read it for themselves.

  12. #102
    Senior Member RMC's Avatar
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    Hi Ian,

    Thanks for your summary of the Holland article: "...discussing not just a single case of "mutual coupling" but the wider and equally important and less known relationship when using two drivers at increased distances."

    What would then be the interest of "using two drivers at increased distances" as you say and at the same time wanting the mutual coupling effect? Specially in view of Eargle's statement that I quoted in post # 82:

    "The above equation assumes that the LF units are located as closely together as possible, and this is an important requirement in getting the most out of mutual coupling." (John Eargle, Handbook of Sound System Design, ELAR, 1989, P. 115). The nominal spacing between drivers is considered in the equation he mentions. But at NO time in his books, same for Dickason, JBL and E-V, do they go to the sophistication level mentioned by you."

    Seems to me either you want the effect or not. Could someone show a desire for a "mid-way" or "middle of the road" coupling effect? For sensitivity matching issues maybe? Or for lobing related issues of closely spaced drivers?

    Richard

  13. #103
    Senior Member RMC's Avatar
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    Hi Ian and Ivica,

    RE MUTUAL COUPLING ADDITIONAL ISSUE RAISED BY IVICA AND CORRELATED/UNCORRELATED SOUND

    Looking for something else in Dickason's Cookbook, Crossover Networks chapter, I came across something quite interesting in relation to the above-mentioned subject matter. No wonder I didn't see it in the "multiple woofer format" (mutual coupling) section of his book, since he covers it with X-over issues.

    The theory outlined in the Holland article seems to have its objectors, not the least of which appears to be Dickason himself in pretty strong terms that one rarely sees in tech books, in the section dealing with Crossover Network and Power Response. Quoting his whole explanation would be much too long (short quotes with reference are preferred by some, reader can look for himself), so here are the "juicy" parts of his disagreement:

    After talking about conventional wisdom re how power response is derived differently on and off axis, correlated phase for the former and "as if phase were uncorrelated" for the latter, he mentions "Although there is some disagreement as to what importance, if any, should be given to the power response difference...". (...)

    "Although it is not popular to go against the mainstream of thought in any field, this view of power response is simply not correct. The reality is much simpler." (...) "Calculating a crossover's power response as though the signals are uncorrelated is unjustified, in my view." (...).

    "But when two drivers are mounted on the same baffle, radiating from very nearly the same plane and being fed by the same program material, there is no other way to process the two signals as being anything but phase correlated. They are phase correlated on-axis and they are phase correlated in the power domain. No difference exists between the power response of any crossover network and the on-axis response." (...). (Vance Dickason, The Loudspeaker Design Cookbook, 5 th ed., 1995, P. 96-100).

    I understand from Dickason that only some distance between the drivers could justify otherwise. Why would someone do that if it "defeats the purpose"? What would be the interest in doing so in the context of wanting mutual coupling, subject to what mentioned in my post # 102?

    I think the above explains the reason why many (JBL, E-V, Eargle, etc.) don't seem to bother with the precision level outlined by the theory (i.e. too much sophistication for little or nothing in practice, if coupling done correctly). Regards,

    Richard

  14. #104
    Senior Member Ian Mackenzie's Avatar
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    I think the key issue is context - A stereo pair or second loudspeaker 3 metre distance

    Secondly, I don't think its appropriate to be arbitrating or questioning on what you think two scientists are saying or not saying on this site.

    If you have a concern or need clarity on what you "think" just email them first.

    They will get back to you and you can then report on the "truth" a supposed to diatribe debate.

    In the past I alway got prompt replies from the these guys be it Douglas Self, Philip Newell, Nelson Pass, Seigfried Linkwitz, Charles Hanson.

    quote for pdf Mutual coupling Dr Holland:

    "What is perhaps less obvious however, is how introducing a distant second loudspeaker can double the power output of a loudspeaker. For the 3m separation and 0.15m radius of the pair of loudspeakers in the above examples, the magnitude of the pressure on loudspeaker A due to the operation of loudspeaker B is approximately one twentieth of the pressure on A due to its own velocity. How can an increase in pressure of 5% cause a doubling of power output? The answer lies in the phase of the two pressures. At low frequencies, the pressure on the surface of A due to its own velocity is almost in phase quadrature with the velocity - the radiation impedance is almost totally reactive - whereas that from B arrives almost in-phase with the velocity due to the propagation distance involved"

  15. #105
    Senior Member RMC's Avatar
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    Hi Ian,

    "A stereo pair or second loudspeaker 3 metre distance" Is quite a different story and has nothing to do with what is commonly known and used for "mutual coupling" in sound reinforcement for example. That's the only issue raised by me. Other ways of getting "mutual coupling" may exist (e.g. Holland, and described by himself as "perhaps less obvious") however they are far from being widespread, and even talked about in many loudspeaker books...

    Nobody has asked anyone to arbitrate or question what I think scientists say or don't say... That's purely in your mind. Dickason's quote in post # 103 only shows there are other ways of thinking, has Holland's does, but the latter remains unusual and rarely talked about in "mutual coupling" circles...

    Richard

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