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Thread: Question on the "double scoop" short throw horn.

  1. #1
    Scooter
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    Question on the "double scoop" short throw horn.

    I've helped to build many pairs of JBL short-throw bass horns, a.k.a. "double scoops" (the model number escapes me), following JBL's plans, yet I have never asked about or understood the acoustic principle(s) that are at work which allow the twin 15 inch woofers to act as direct radiators above 150hz and direct the lower frequencies down below out the "scoop". I believe that this model is referred to as a folded horn, but not sure. If someone in-the-know could enlighten me on the basic idea, I'd be grateful.

    Scott

  2. #2
    Registered User paragon's Avatar
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    4520

    "Dual Driver Rear loaded Horn" Model 4520.

    The volume behind the drivers acts as a low pass filter.
    Only frequencies below 150 or 200 Hz going into the hornpath.
    Increase the volume and the frequencies passing the horn cut lower.

    Eckhard

  3. #3
    Dis Member mikebake's Avatar
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  4. #4
    Scooter
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    Thanks guys--especially for the link. I have wondered why JBL stopped using short-throw horns. The 4520 using 2225s was always a favorite at dance venues. We had planned to scale that model up for 2240s, but dismissed it due to size concerns. JBL Pro had told us it would (should) have had a "usable" response to 24hz.

    Scott

  5. #5
    RIP 2010 scott fitlin's Avatar
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    Uh huh!

    Quote Originally Posted by Scooter
    Thanks guys--especially for the link. I have wondered why JBL stopped using short-throw horns. The 4520 using 2225s was always a favorite at dance venues. We had planned to scale that model up for 2240s, but dismissed it due to size concerns. JBL Pro had told us it would (should) have had a "usable" response to 24hz.

    Scott
    This is exactly what we did years ago, upsized the JBL double scoop for 18,s, and althought technically considered a midbass cabinet, it works! Very punchy, clean and good definition, and a nice grumble on the low bottom! We use 2240,s! And we have put different boxes in their place, and I always put the scoops back into service, so now I just leave em in because I realized I like the way they sound! Always did!

    Many cabinet builders still build quite a variety of scoops , they are still popular, sound good, are easy to use and get right, can be used with a wide variety of woofers, reggae bass players love them, and still good in short to medium throw applications where punchy bass is wanted!

    JBL should bring these back!
    scottyj

  6. #6
    Registered User paragon's Avatar
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    4520 and others

    Hi Scott,

    In a Disco (many years ago) i saw a dual driver rear loaded wit 12 inch bass drivers. Was smaller than the original 4520, but sounds very good.
    Are there other double scoops build by JBL than the 4520 ??
    Is the horn with the 18 inch drivers bigger than the 4520 (must be).

    Eckhard

  7. #7
    RIP 2010 scott fitlin's Avatar
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    18in scoops

    The cabinets are copies of JBL scoops uspsized for the 18,s so I would imagine it is a somewhat bigger horn!

    Scoops have been built for every size driver, but JBL only made them for 15,s as far as I know! Other manufacturers made them for wqhatever they wanted to use in them, and then there were custom sound contractors who built them to their own specifications, like Richard Long, he made a double sccop called the Waldorf, they were alot bigger than JBL cabs, he used Gauss or TAD 15,s in them, they had a bigger rear chamber, and just quite bigger than the JBL cabinets of the time! They had a big thumpy low end, they were designed to accentuate the bottom even more than a JBL scoop!

    You can find somebody to build scoops for 12,s if you want that! JBL never made 12in scoops to the best of my knowledge, they made a dbl 15 and a single 15in scoop!
    scottyj

  8. #8
    whgeiger
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    Olson Design, Circa 1936

    S,

    This type of horn enclosure was addressed by Harry F. Olson and others as early as 1936 [1] & [3]. Subsequently, a similar design was presented by James B. Lansing [5]. In Olsonís book, [2], [4] & [6], a recap of the design considerations may be found. Note that a two unit array of single driver scoop horns is acoustically equivalent to a scoop enclosure housing dual drivers.
    Regards,
    WHG

    [1]
    Title: Combination Horn and Direct Radiator Loudspeaker
    Author: Harry F. Olson
    Author: R. A. Hackley
    Publication: IRE-P, Vol. 24, No. 12, p. 1557, 1936
    Abstract: None

    [2]
    Title: Combination Horn and Direct Radiator Loudspeaker
    Author: Harry F. Olson
    Publication: Acoustical Engineering, D. Van Norstrand Co., May-1957, Sec. 6.15, p. 163-167
    Abstract: Both freestanding and room corner variants of back loading bass horns are addressed here.
    [3]
    Title: A Compound Horn Loudspeaker
    Author: Harry F. Olson
    Author: Frank Massa
    Publication: ASA-J, Vol. 8, No. 1, p. 48-52, (Jul-1936)
    Abstract: A new type of loudspeaker is described in which a single mechanism is coupled to two horns: a straight axis high frequency horn and a folded low frequency horn. A theoretical analysis of the combined system is given and experimental data are shown which indicate smooth uniform response from 50 to 9000 cycles, and an efficiency of the order 50 percent over a large portion of this range.

    [4]
    Title: A Compound Horn Loudspeaker
    Author: Harry F. Olson
    Publication: Acoustical Engineering, D. Van Norstrand Co., May-1957, Sec.7.4.C, p. 237-238
    Abstract: Brief description. acoustic model and example presented.

    [5]
    Title: ?
    Author: James B. Lansing
    Publication: SMPE-J, Vol. 46, No. 3, p. 212, 1946
    Abstract: A back loading bass horn enclosure for placement in a room corner is presented. The design is a precursor to the original Hartsfield design.

    [6]
    Title: Acoustical Engineering
    Publication: D. Van Nostrand Co., Inc. (1957)
    Publication: Professional Audio Journals, Inc. (1991)
    URL: http://www.audioxpress.com/bksprods/books/bkpa1.htm
    Author: Harry F. Olson
    Abstract: Comprehensive, but dated, text on the subject of acoustical engineering. Its reprinting at this late date says volumes about the value and significance of Olsenís work. For those involved in this discipline, a copy of this book should be considered a necessary addition to their reference library.

    Legend
    IRE-P - Institute of Radio Engineers, Proceedings
    SMPE-J - Society of Motion Picture Engineers
    ASA-J - Acoustical Society of America, Journal

  9. #9
    Registered User paragon's Avatar
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    4520

    Thanks Scotty and Whgeiger.

    Eckhard

  10. #10
    Dis Member mikebake's Avatar
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    Quote Originally Posted by Scooter
    Thanks guys--especially for the link. I have wondered why JBL stopped using short-throw horns. ......
    Scott
    JBL at the time designated boxes which performed well up to 75-80 feet as short throw, but not only is that a pretty good distance inside, these boxes perform decently outdoors.

    I would speculate that their demise in the product lineup was due to the evolution of more powerful amps, the ability to get comparable output in BR boxes, with the subsequent weight and size reductions, and the bad rap rear-loaded boxes developed for various phase/response problems based on direct vs. rear wave interaction, etc. Back loaded horns are often dissed by some. There is only one design I have heard of that somehow seemed to escape the problems of the back horn, and IIRC it was an old Jensen design.
    Anyway, I like front horn loaded bass, but the size is unwieldy.......

    Having said all that, I still like the old scoops and they don't bother me, but I haven't tried listening to them in a high-fidelity kinda way.

  11. #11
    Charley Rummel
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    The 4520 has been a long time favorite of mine. One of these years I wish to build two of a version I came up with (I've spoken about it in past threads) in which I recalculated the horn path charactoristics and developed a number of different construction features, for lack of better words. Otherwise, this design still looks like the good ole 4520/C55 with a suitable finish (as would be required to meet the Wife Acceptance Factor codes) and will weigh in at around 250 pounds per unit . Yes, there will be locking casters on it.

    All I need is time and money !

    Regards,
    Charley

  12. #12
    RIP 2010 scott fitlin's Avatar
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    Jensen

    Quote Originally Posted by mikebake
    JBL at the time designated boxes which performed well up to 75-80 feet as short throw, but not only is that a pretty good distance inside, these boxes perform decently outdoors.

    I would speculate that their demise in the product lineup was due to the evolution of more powerful amps, the ability to get comparable output in BR boxes, with the subsequent weight and size reductions, and the bad rap rear-loaded boxes developed for various phase/response problems based on direct vs. rear wave interaction, etc. Back loaded horns are often dissed by some. There is only one design I have heard of that somehow seemed to escape the problems of the back horn, and IIRC it was an old Jensen design.
    Anyway, I like front horn loaded bass, but the size is unwieldy.......

    Having said all that, I still like the old scoops and they don't bother me, but I haven't tried listening to them in a high-fidelity kinda way.
    Jensen did have scoop type cabinets, and they had hyperbolic rear horn loading!

    My scoops sound good, they are punchy and dynamic sounding, and make a nice round sounding bottom! My experience with the associated phase discrepancies of front and rear waves meeting and cancelling is they work better standing up woofers on the top, scoop underneath, rather than on their sides, which is how I have seen many a scoop used! I was told that as long as the front and rear waves arent side by side you will avoid cancellation and phase problems! We did try the scoops laying on their sides and we always thought they sound better, quite a bit better, standing upright!

    I am putting medium power into my scoops and they sound super, and they are corner placed to boot, but then, I want the bump this gives!

    Ontop of my scoops are my front loaded 15in horns! Great combination!

    scottyj

  13. #13
    Dis Member mikebake's Avatar
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    Quote Originally Posted by scott fitlin
    We did try the scoops laying on their sides and we always thought they sound better, quite a bit better, standing upright!

    Ontop of my scoops are my front loaded 15in horns! Great combination!

    I have also noticed the difference in scoops on their side vs. woofer on top. What woofer do you use the in the scoops? And which ones in the top front loaded horns? What is the efficiency difference between the two boxes?

  14. #14
    Scooter
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    Smile

    Scoops belong standing upright; at least that was our concensus in the early 1980s. Our woofer of preference was the 2225, which we typically used with bridged Peavey CS800s or CS 1200s. I think that the clipping LEDs were on more than they were off. We pushed our equipment hard, yet averaged about one recone per year. E140s had punch, but lacked that reverberant depth that we also coveted. The 2225s had a combination of both. Our concerns back then were more quantitative than qualitative--it was the "my woofer has a bigger magnet than your woofer" phase of our lives. We quickly learned after building our first pair of 4520s how solidly these cabinets need to be built. Cabinet integrity was a concern when we pondered scaling the 4520 up by 1/5 for the 2240 or the E155. If a 15 inch model weighed 215 pounds, what would an 18 inch weigh? The carcass had to be 1 inch stock. Extra bracing a must. Door frames could present a problem in non-fixed applications. Nobody wanted to do all the arithmetic either. We did not use calculations much back then, or the JBL technical notes. We did things by "feel". Today, if I had the time, money and location, I would build a pair of 18 inch scoops and load them, preferably, with E155s. 2242s might do well also. There are many more options now. There's something to be said for comparative simplicity.

    Forgive the non-technical walk down memory lane. Scoops bring back lots of high SPL memories.

    Scott

  15. #15
    Dis Member mikebake's Avatar
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    Quote Originally Posted by Scooter
    Scoops belong standing upright; at least that was our concensus in the early 1980s. .....
    Scott
    Upright is how I always used them, but I did hear some stacked on their sides, more than once. Not sure what changes, other than the proximity of the woofer to the floor boundary, and perhaps subsequent problems.

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