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Thread: THE JBL 4520 BASS CABINET PAPER TRAIL: AN 8 FT or 13 FT folded horn ?

  1. #16
    Senior Member Horn Fanatic's Avatar
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    Quote Originally Posted by gibber View Post
    Thank you for posting. Were those frequency graphs taken in half space, or free space?

  2. #17
    Senior Member RMC's Avatar
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    Hi Horn Fanatic,
    These two frequency response curves were taken from the document I mentioned at the end of my next post coming in a few minutes. It doesn't say in which environment (half space or free space). Check next post coming in minutes...

    Richard

  3. #18
    Senior Member RMC's Avatar
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    Comments on replies re 4520 horn length

    Hi guys, thanks for your patience.

    I consider we are like "working" in the Lab on this site, searching, digging, exchanging views, sharing info, learning, etc. To me this is a gold mine ! "This is why he is here asking questions." Absolutely true. I never pretended being a horn design expert. I HAVE questioned in other threads: curious ways of stacking randomly in the same tall pile long throw horns (low/high) with short throw horns (low/high freq.) which didn't seem to make sense acoustically (example picture in this thread I avoided commenting); interior skating rink and use of many horns VS challenging acoustics. The comments were fair game. I have often referred to/quoted my sources, and did request HELP here from "horn specialists", "horn guys", "Tech Bible" guys on this site I named (my post March 7, 2017). Now on with our business, trying to stay on track.

    To be clear on my position, in absence of justifications from JBL, I'm willing to accept any 4520 horn length number as long as it's scientifically defendable or logical. I have already indicated: I'm a believer in truthful science, and a few times recently said things seem to be pointing (physically) in the direction of an 8 ft or so horn. But interesting new stuff from HF now changes the approach to this issue...

    EAULIVE: Hands-on practical re-building 4520 experience that's pretty good (huge job, I'm impressed!). Since you've been there/seen that , I understand why you are categorical about (physical) horn length. That's exactly what I'm trying to find out if JBL has a "high-flying" (U-2 type)(written before HF SR-71) way of calculation for this horn's length (see Horn Fanatic's very feasible explanation; horns do appear to be "rocket science" compared to vented boxes, for the "common man"). I never even thought about your point of possible "rough doubling" of the 4530 horn length number they MAY have taken. Though it would seem careless on their part, it could(?) have been a form of Marketing hype Greg Timbers talked about in his recent interview elsewhere on this site, as Engineers say Marketing is Marketing. However, this would not be really worthy of a Company I happen to respect.

    Out of curiosity for myself, why 2225H (recones) on E-140 frames for the 4520 ? Why not E-140 recones ? Or 2225H recones on 2225 frames ? Only thing available/on hand ? Cheapest solution (money, ya that bugger)? For the longer cone travel of 2225 (5mm) VS E-140 (3.56mm)? For the smaller .17 Qts of the E-140 (closer to 2205 Qts of .21) compared to 2225's .28 Qts ? Since there's a lot of other "hybrids" out there (e.g. 2205 reconed with 2225), I have always wondered what happens in these cases to driver T/S parameters, a mix of both ? And how does the driver reacts in the box: acoustically like a 2225H but electrically like a E-140 ? A mix of both ? (I MAY SEND THIS ISSUE TO A NEW THREAD IN THE NEAR FUTURE, SINCE I'M REALLY CURIOUS TO KNOW ANSWERS ABOUT THESE QUESTIONS.)

    HORN FANATIC: Great short primer on this issue. Glad you share with us. The effective (horn) length concept is in fact used in the 1952 or so brochure description of the "JBL Signature No. 34 rear-loaded folded horn corner console enclosure", mentioning an "... effective length of six feet." In the plan, the sound path is shown. In the catalogs outside cabinet dimensions have varied a little (1952: 39 3/4"H, 23 3/4"W, 22 1/2" D, a bit different from the brochure; 1962 C34: 39 3/4" H, 23 3/4" W, 23 3/8" D). Some dimensions are not mentioned in the plan, but from the many available, it appears cabinet size is not too far from the 4530 measurements (less pedestal). Two 15" woofer numbers are given in the brochure for this box: 130A, D130. Every time I try to upload something on this site, it just won't work... So if a few people (not 200 persons hopefully) are interested in having the 1952 or so 2 page brochure for this No. 34 box I'll be glad to forward it to them free, if they provide an e-mail address.

    The analogy of a horn with a ducted port is very clever for understanding purposes (good for me I'm more of a vented-box guy, with a genuine interest in horns, up to the point where the math get too complicated ). "The effective length being on either end of the duct..." Since "The effective length of the 4520 may extend two to three feet past the horn mouth subject to frequency." then, in theory and subject to your disagreement with JBL's mention of direct radiator above 150HZ, when considering also the other end of the horn (symmetrical or not), I understand it MAY happen that effective length reaches up to 13 feet (subject to calculations). If that is the case, then what would be missing in JBL's more recent documentation is the mention of "effective horn length" or something like "practically acting as a X ft horn..", even though the physical length may be around 8 ft. For my own knowledge, can the rear chamber or any part of it, somehow have to be included/considered in the effective length calculation, or is it unsound thinking ?

    As for driver choice to load the 4520/4530, I agree with you the 2225 and 2226 are not the best choices considering their T/S parameters with regards to the enclosure, but I understand it was roughly the closest things JBL had left in the catalog after they discontinued so many drivers. Based on many JBL documents I've seen, the 2225 appears to have been made in 1982 with the 46 series in mind (e.g. Cabaret series). With regards to the 2220 being the proper driver to load into 4520/4530, I must disagree with you for a few reasons. First, to my knowledge, JBL never recommended the 2220 for these cabinets, but rather the 2205 and K/E-140. Second, my understanding is that the 2205 was designed for use in these boxes and released at the same time in 1971, being presented as a "Heavy Duty" woofer (no wonder why, JBL sure anticipated they'd be beaten like they were). Third, a number of essential T/S parameters of the 2220 are similar to 2205/K/E-140 making the 2220 quite compatible for use in 4520/4530 I agree on that, however, for real life commercial use (clubs, discos, etc.) where it WILL be given the ride of its life, it's another story: it has less power handling, less cone stiffness, less cone excursion, and 5-7 HZ higher Fs(*). Though it was not a JBL specifically recommended driver for these cabinets, a number of people did use the K/E-145 with good sounding results since some of its parameters were not far off (e.g. a little higher Qts than 2205), but more important to all of these guys it had much greater cone travel to use and abuse...

    Best regards,

    Richard

    (*) "The lower resonances and longer excursion capabilities of the 2205, E 140 and E 145 enable these loudspeakers (4550/4560) to provide somewhat better deep bass response compared to the 2220 at the expense of some midrange sensitivity." In the field, this phrase was also applied to the 4520/4530... JBL, Professional Series, Low Frequency Enclosures, May 1980, page 3.

  4. #19
    Senior Member Horn Fanatic's Avatar
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    [QUOTE=RMC;403636]Hi guys, thanks for your patience.

    "For my own knowledge, can the rear chamber or any part of it, somehow have to be included/considered in the effective length calculation, or is it unsound thinking ?"

    That will be a no. The acoustical low-pass filter is a separate element in the horn circuit. The constriction of the filter is the horn throat.

    The analogies are thus;

    The chamber volume represents an acoustical compliance, or in electrical terms, a capacitance. Both measured in Farrad.

    The chamber volume also is comprised of an acoustical resistance.

    The horn throat presents an acoustical mass, or in electrical terms, an inductor. Both measured in Henry.

    The math for either is worked in the same manner. When you resonate a mass with a compliance, or capacitance with an inductance, you have a low-pass filter.

    I have physically test an acoustical low-pass structure many years ago, and it does what it is designed to do. Roll off.

    Good luck, HF

  5. #20
    Senior Member Hoerninger's Avatar
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    effective length?

    Hi guys,
    I have tried to follow, but I'm slow as English is my second language.
    As far as I have understood there is the question about the physical length of a JBL-horn.
    Neither do I have the correct data nor a JBL horn itself. Without these the answer can't be given.

    There came up the proposal to make a kind of reverse engineering by using the „lower frequency limit“. There may be differences between the definition of the term and what is claimed in a brochure. The graphes uploaded by Gibber seem to clarify but there is another obstacle. What is the „effective length“? Seen from a physical point of view of it makes sense. But there is no defined mathematical approach:

    Classical horn theorie, Weber 1919, uses plane wave fronts, so there is no clearance about „effective length“.

    In 1927 P.G.A.H. Voigt patented the so called Tractrix horn, He argues that the wave front will be orthogonal to the boundaries and with this not plane. He describes a graphical solution, he does not realize that he uses the tractrix function and he gives up the exponential law. Further more he says in his patent:
    In a horn constructed according to this invention, the taper at any point is as nearly as possible such that the sound is expanding as if the source was at a fixed distance which is at least a quarter wavelength, of the lowest frequency at which full efficiency is required, away.
    With this he falles back to classical horn theorie, as the demand for a quater wave length is derived by using plane wave fronts.
    The tractrix uses no „flare rate“, so it is comprehensible when Dr. Bruce Edgar says that the Tractrix is not suitable for bass horns. BTW. a Tractrix horn has a directivity similar to exponential horns (AES, Lambert and Jensen, 1954).
    The theorie of tractrix horns does not help to define the effective length of a horn.

    The KLANGFILM labs (Germany) invented the spherical Wave Horn (Kugelwellentrichter), patent starting 1940 as I discovered about a year ago. There is obviously a difference between the geometrical length and the physical /effective length. But it should be cleared whether the approach with a constant radius all over the horn for all frequencies is proven by experiments.
    The Kugelwellentrichter may be ended by a plane as the tractrix horn does and it has an improved divergence.

    It is unlikely that JBL knew this patent and that it is applied for their scoops.
    Klangfilm used this patent since about 1952 for their mid/high horns and for bass horns (EURONOR II and EURONOR junior).
    ____________
    Peter
    Last edited by Hoerninger; 03-13-2017 at 06:15 AM. Reason: header

  6. #21
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    [QUOTE=Hoerninger;403647]Hi guys,

    Greetings, Hoerninger -

    "What is the „effective length“? Seen from a physical point of view of it makes sense. But there is no defined mathematical approach:"

    Yes, there is a defined mathematical approach, and it is quite simple. It is spelled out in detail by Leo Beranek in his 1954 book titled, 'Acoustics' in chapter 5 under Radiation Impedance, and pp. 132-133 on Acoustic Elements. The subject was also sighted in Phillip M. Morse's 1936 book titled, 'Vibration and Sound', pp. 235 & 247. The effective length is the volume of air exiting an orifice which has yet to dissipate. In essence, a continuation of the air column outside the tube or horn which is subject to area and frequency.

    And I do believe you're referencing Arthur Gordon Webster's 1919 paper titled, 'Experiments on the Vibration of Air in Conical Horns'. And Lambert's two part paper, 'Acoustical Studies of the Tractrix Horn'.

    The Tractrix curve dates back to a study conducted by Christiaan Huygens in 1692. I am not convinced of Bruce Edgar's opinion that the Tractrix curve is unsuitable for low frequency horns. Technically, Tractrix horns should be round, but I have heard round high frequency Tractrix horns, including his, and IMHO, they sound awful. Edgar is a very smart guy, but I have little faith in his ear. John Tucker and Jeff Markwart designed their full Tractrix system they called the Exemplar Horn many years ago, and it sounded wonderful. The transition between the bass horn and high frequency horn was acoustically seamless. Planer like is my description.

    BTW - It's nice to see someone here who knows their horn design history.

    HF

  7. #22
    Senior Member Hoerninger's Avatar
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    Quote Originally Posted by Horn Fanatic View Post
    ...
    And I do believe you're referencing Arthur Gordon Webster's 1919 paper titled, 'Experiments on the Vibration of Air in Conical Horns'. And Lambert's two part paper, 'Acoustical Studies of the Tractrix Horn'.
    HF, thank you for your response.
    The second paper you are mentioning is o.k. the first one is
    A.G. WEBSTER. 1919, Acoustical impedance, and the theory of horns and of the phonograph, Proc. Natl. Acad. Sci. (U.S.) 5, 275–282.
    reprinted in: Journal of Audio Engineering Society, 1977, 25(1-2), 24–28

    which I got as a copy in my students time.
    Unfortunately I missed to write down a remark similar to the following which I read somewhere:
    websters work was highly appreciated as with his theorie it was finally possible to build good sounding gramophone horns.but he was blamed for the late publication, as he had kept it in a drawer for quite a while.
    As said, I do not know where I have read it.


    the Chapter of Beranek I will read in the afternoon, thank you for the hint.


    I have only little experience with Tractrix horns (mids), only this one:
    http://www.audioheritage.org/vbulletin/showthread.php?11909-Paragon-XXL&p=121157&viewfull=1#post121157

    My next idea is a front loaded horn with Kugelwellen shape, which is comparable short (similar to EURONOR II but with compression chamber).
    ____________
    Peter






  8. #23
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    [QUOTE=Hoerninger;403663]HF, thank you for your response.

    A.G. WEBSTER. 1919, Acoustical impedance, and the theory of horns and of the phonograph,
    Proc. Natl. Acad. Sci. (U.S.) 5,
    275–282.
    reprinted in: Journal of Audio Engineering Society, 1977, 25(1-2), 24–28

    Ha! I do have that paper also. It was paper clipped behind the conical horn paper. I thought the title of the paper you sighted sounded familiar.

    HF

  9. #24
    Senior Member Eaulive's Avatar
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    Quote Originally Posted by RMC View Post
    Out of curiosity for myself, why 2225H (recones) on E-140 frames for the 4520 ? Why not E-140 recones ? Or 2225H recones on 2225 frames ? Only thing available/on hand ? Cheapest solution (money, ya that bugger)? For the longer cone travel of 2225 (5mm) VS E-140 (3.56mm)? For the smaller .17 Qts of the E-140 (closer to 2205 Qts of .21) compared to 2225's .28 Qts ? Since there's a lot of other "hybrids" out there (e.g. 2205 reconed with 2225), I have always wondered what happens in these cases to driver T/S parameters, a mix of both ? And how does the driver reacts in the box: acoustically like a 2225H but electrically like a E-140 ? A mix of both ? (I MAY SEND THIS ISSUE TO A NEW THREAD IN THE NEAR FUTURE, SINCE I'M REALLY CURIOUS TO KNOW ANSWERS ABOUT THESE QUESTIONS.)
    Originally I was planning on loading the cabs with 2225s but since I had a bunch of E140 frames on hand I checked the possibility and tried to predict the behaviour of the E-140/2225 mix.
    Both frames have the same gap width and length, the only difference lies in the magnet strength. The 2225 has a 1.2T motor while the E-140 has a 1.35T motor so I figure after much reading here and elsewhere that the only difference would be in higher frequency response outside the band I was planning to use them (my 4520s are crossed at 150Hz with my midbass horn) so I went with that.
    Besides, I don't like the aluminum dust cap on a speaker system that is intended to be a sound "reproducer", not a sound "producer"

    A friend had original 2225s so we swapped them for fun and did not see a difference for that specific application (4520s crossed at 150Hz)

    As for the other "mixes" a 2225 on a 2205 frame is basically a 2225 because the frame and magnet structures are identical, the big NO-NO is using these cones on a 2220 frame as I saw in the past... Lee will remember the source of my 4520s and the drivers the guy wanted to push on us ;-)
    My avatar: 4520 loaded with 2225H on E140 frames,
    1x B&C 12PE32 on custom front loaded horn, 2x 2426 on 2370.

  10. #25
    Senior Member RMC's Avatar
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    Thanks EAULIVE for your input. Very informative. As you know this issue is now continued in a separate new thread re "Hybrid" reconed drivers... I have transfered your reply in this new thread. Thanks again .

    Richard

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