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

"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

4520 info here

http://www.jblpro.com/pub/obsolete/L...nclosures2.pdf

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

Quote:

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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

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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!

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 :confused:

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!

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 Olson’s 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 Olsen’s 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

Thanks Scotty and Whgeiger.

Eckhard

Quote:

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Originally Posted by Scooter

Thanks guys--especially for the link. I have wondered why JBL stopped using short-throw horns. ......
Scott

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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.

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 :rolleyes: . Yes, there will be locking casters on it.

All I need is time and money:banghead: !

Regards,
Charley

Quote:

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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.

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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!

:)

Quote:

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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!

:)

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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?

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

Quote:

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Originally Posted by Scooter

Scoops belong standing upright; at least that was our concensus in the early 1980s. .....
Scott

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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.

Quote:

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Originally Posted by Scooter

We quickly learned after building our first pair of 4520s how solidly these cabinets need to be built. Cabinet integrity was a concern

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Cabinet integrity is one big reason why the design I came up with will weigh in at over 250 pounds. I don't plan to see them used on the road; they will end up in our basement family room. Besides, hauling a beast like that, even with casters, can be a real roady-killer for most.

Regards,
Charley

Where can i find the Plan for the original 4520 Enclosure?
Who've a Weblink?
Thanks
Dieter

Anyone have this in inches?

http://members.aol.com/xxbase80a/dop....2.15/bau.html

Quote:

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Originally Posted by Scooter

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

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Originally the E-155-8 is what we used in our upsized JBL copies! They were great, the punch, the bass articualtion, and fast transient snap were fantastic! But wasnt the greatest deep bass! The 2240 makes better deeper bottom! If you copy the JBL design the 2242 wont fit, you will have to make the rear chamber deeper, or use spacer rings between the woofer and baffle to facilitate mounting!

As for upright vs on its side, well, according to everything I have ever learned and been told, what happens is that when you have front and rear waves eminating from the cabinet in the same horizontal plane, cancellation arises as when the front and rear waves meet there are phase issues, but when the scoop is upright this avoids that problem as now the front wave is not firing in the same plane as rear, this is what I was always told. My ears tell me they just sound right standing up! Similar to stacking theories!

Scoops are not technically subwoofer cabinets, dont have a long throw, and shouldnt work, but I use them as corner loaded subs, and they DO work! On top of this, they happen to sound great! Clean and audible definition coming directly off the cone, and the extra oomph and grumble from the rear loaded horn! Everybody likes my corner stacks with the double 18in scoops! On an RTA I have usable response down to 30Hz, it actually is flat down to 30, and I can squeeze some response to 25hz, but not alot, but it gets down low pretty well, and while this isnt really 20Hz, most music I play doesnt have any info that low anyway! But it sounds good, its round and punchy. Conversely, I have had dual ported direct radiators in here, with proper power and subwoofer drivers, and found that although they posess deeper extension, the tradeoff for this extension was punch in the bass and upper bass region! They did more way down deep, but not enough between 60Hz to 100Hz! So it wasnt as lively and propulsive sounding! To me this is exactly where science and whats technically correct go out the window, and art takes over! I have also had inverted W bins in the corners, and they offer more upper bass punch, but even less deep bass extension, so back to the scoops with the JBL 2240,s it was, this offers me a decent balance of fairly deep bass extension, great punch, and a nice sounding, round bottom end! Yes, Im partial to a punchy sounding bottom, even if its not technically 100% correct!

It works, and everybody likes them, including me!

That is exactly what I always said/liked about scoops; one word. Punchy. And I agree, whatever the drawbacks were said to be, I always like 'em. :)

The first bass bins I owned were 4530s with 2205a woofers.

They were everything that has been described above.

Nice punchy, round, musical, bass reproduction .

<. Earl K

Ah the memories...I have built hundreds of single and double scoops for all kinds of projects. And while they are no longer in favor ( due to amp / speaker / size issues ) there is NO way to duplicate the punch of bass for dance club installations. I couldn't tell you how many times over the years a BR cabinet was spec'ed, installed and while it sounded OK at sound check, put 300 sabin-suckers on the floor and the bass got lost in the sauce.

Toasted woofer coils, amps burnt from 100% dutycycle ( aren't compressors good for that! ) and overall "where's the bass I paid for" all went away when the 4520's were swapped for the BR boxes.

Our boxes incorporated interior pathway improvements to smooth out the response and correct structural weak points and a couple of times were made of 3/4 plain-sliced oak plywood and were trimmed out ( flushed in the walls ) during construction. One DJ liked to mess with people by putting a car dimmer switch ( the old high-current stomp kind ) in series with one that was hidden near the bar. Of course the bottom of that cabinet was waterproofed from the spilled drinks...:)

In reference to a post, we did ( and still do ) make a 4520 variant that uses a single 18 and this is a REAL popular box for the rave crowd.

There was a company in upstate NY ( rochester ) that made a single 12 scoop but it had no advantage over a BR 12 due to the short horn.

sub

This has to be one of the very few threads where everybody posting agrees 100%!


As for size and weight issues, if it goes into a club, where its never going to have to move around, and go from venue to venue, whats the difference? It stays where it plays, and " If it dont weigh enough, it cant play enough " !

Agree,

The 4530 with his old 2205A standing in the corners in my little "listening" room
working down under 50 Hz and sounds very good.
Eckhard

Wow, glad to have found this thread. When I first got my double-scoop cabinets sans drivers, I searched around here but found little discussion about them. Anyway, I got them with the intention of carting them around to gigs. Boy, was I wrong. A guy offered them for free because he wanted to reclaim real estate in his garage after storing them for 25 years. He had inherited them from some old-time JBL guy who had also stored them in his garage for nearly as long. At over 200lbs each EMPTY, I quickly decided not to use them on the road, like when I was unloading them to put in the garage for the first time. I says, "well, these things are never going to move again."

Mine came with some wierdo protruding front baffle to angle the drivers allowing deeper drivers to be installed. I've always wanted to have a bunch of blank front baffles made to facilitate messing around with them. One of the wacky ideas I'd like to try is to have three 10" drivers across the front. The two outside ones would be longish throw with the center one with, perhaps, an accordian surround. Actively cross them over at 150-200Hz, depending on where the mid comes in at, to have each section covering about two octaves. A bi-amped woofer, if you will. Another crazy idea is to have 16 5" drivers per cab in a 5-6-5 array. You may be scatching your head asking, "why?" Well, um, er, you got me on that one. I dunno, I just like fooling around with insane ideas.

Anyway, my double-scoops stand ready and waiting for whenever I get around to pulling zany stunts. Until then, they will have to suffice with being a nice home for some mice underneath them.

Simulation 4520-4530

Interesting thread.

Some people in the Hi End Hi sensitivity driver scene still use rear loaded scoops for drivers like the Coral Beta 10 & 8 driven by low powered SE amps.

The transient performance is amazing.

Ian

Quote:

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Originally Posted by Ian Mackenzie

Interesting thread.

Some people in the Hi End Hi sensitivity driver scene still use rear loaded scoops for drivers like the Coral Beta 10 & 8 driven by low powered SE amps.

The transient performance is amazing.

Ian

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I have seen cabinets like the ones you describe! For the Lowther drivers, too!

Goes back to what I always say, some things work well, and sound right to the ear, in spite of not being textbook correct!

:)

Scoop Builders,

Have scoop designs for the following drivers made by Precision Devices (Old Harmon Company in England):

Super Scoop for PD-1850 (Back Loading Version, 18" Drivers)

Magnum Scoop PD-2150 (Front Loading Version, 21" Drivers)

Drawing files are available in both .gif and .dwg (AutoCAD) formats.

Send me an e-mail for copies.

Regards,

WHG

There are a lot of scoops builded for smaller drivers like Lowther, Fostex, Coral and others.
LF output of these is limited at 70-80 Hz.
Years ago i heared a Lowther Auditorium Audiovector (rear and frontloaded) with a Klipschorn Sub.
Great !!

Eckhard :D

Quote:

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Originally Posted by scott fitlin

Goes back to what I always say, some things work well, and sound right to the ear, in spite of not being textbook correct!:)

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I couldn't agree with you more, Scott! Besides, how often do we really hear live music in a so-called technically correct environment? Furthermore, I built an vacuum tube power amp a few years ago in which I "tweaked" the circuit on a bread board, and ultimately ended up with something which everybody says sounds clean, crisp and powerful (and not just to be polite either!), but has many far from perfect specs when analysed on the bench :D .

Regards,
Charley

Nice to see that so many have the scoop on scoops!

A few thoughts at large: I have a basic understanding of the principles involved relating to vented boxes, but I am quite ignorant of the physics involved relating to rear-loaded horns. JBL describes their double scoop design as having maximum loading at 42hz--not sure what that means, but it prompted some ponderings about the effects of varying the horn volume, changing sizes and angles of baffles and fillets, changing the length of the curved path, etc. As a curiosity, say we wanted to build a dual 15 inch super scoop, making use of some of the modern 15 inch woofer designs (including subwoofers) that have greater power handling and a much larger x max than the originally recommended 2205 woofer. I would guess that some woofers with large cone mass would cause a deterioration in transient punchiness. But what if we were interested in maximum projection of bass in the 30 to 40 hz region. How could we change the loading to say, 30hz? How would we interpret the T/S parameters so as to make educated guesses at which woofers would work, with or without scoop modifications? Is there software for horns that would help predict frequency responses and cone motion? What if we wanted to use the same woofers that JBL uses in their VLF cabinets (cannot think of the model number)--could it be done? I realize that this sounds like Tim "The Tool Man" Taylor and "more power", but I like to hear some speculations and informed opinions.

Scott

Yes there is. Called "AJ-Horn" by AJ-Systems. Look at page 2 (Sim 4520-4530).
Eckhard

Quote:

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Originally Posted by paragon

Yes there is. Called "AJ-Horn" by AJ-Systems. Look at page 2 (Sim 4520-4530).
Eckhard

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Hello Eckhard,
can you post the complete Plan from this Horn, please?
Have you also the original 4520 Plan?
Thanks Dieter :)

This horn is a little bit longer, has a smaller rear chamber and throat (?) than the original 4520. But this has no effect on lower bass response :banghead: . So it doesnt work better than the original.
Plan is at page 2 of thread.

Eckhard

4520 black, 4520 mod. red

Quote:

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Originally Posted by paragon

This horn is a little bit longer, has a smaller rear chamber and throat (?) than the original 4520. But this has no effect on lower bass response :banghead: . So it doesnt work better than the original.
Plan is at page 2 of thread.

Eckhard

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Thanks,
but on the Plan of page 2 are not all Measurements, special the Horncurve.
Miss some Angel of Boards.
Maybe you or other Members have the complete Plan?
Dieter

Mmmhhh,

Can anybody help ?

Eckhard

Eckhard / Dieter

Well, not exactly the plan you're after - but this should still be useful.

(a)
Here's essentially the plan for a 4530, but "up-sized" for 18" woofers .

The above plan is from SpeakerPlans.com - a British sound outfit .

(b) PA EXPONENTIAL SYSTEMS is another useful horn site from Germany that has some plans .


regards <. Earl K

Thanks Earl !

Eckhard

Thanks Earl! :)

Thanks Earl!

:)

Can anyone comment on the merits of a front loaded bass horn? Cerwin Vega still makes several versions of this desin, where the 18" woofer has a small rear chamber and the driver fires in to a folded horn. These seem to be fairly compact and portable. Do they get low (40Hz, or so) and do they project the low bass any better then direct radiators? Would these be better for large rooms or outdoor use?
Sunn used to make these too. (see pic)

Thanks,

Tom

Quote:

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Originally Posted by Tom Loizeaux

Can anyone comment on the merits of a front loaded bass horn? Cerwin Vega still makes several versions of this desin, where the 18" woofer has a small rear chamber and the driver fires in to a folded horn. These seem to be fairly compact and portable. Do they get low (40Hz, or so) and do they project the low bass any better then direct radiators? Would these be better for large rooms or outdoor use?
Thanks,

Tom

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The Cerwin Vega folded horns get down pretty low, not into the 20,s but definitely 40hz, maybe into the 30,s if you cluster four cabinets together!

Horns project the bass out fairly far, compared to a direct radiator, and have high efficiency! They are good for dance clubs, or any event that wants high impact bottom end, they have that punch and growl.

For a large room, or outdoor use, if you want your bottom to project out a good distance, then, yes horns are still good!

The T-36 offers really high efficiency, power handling, and long throw, and Vega recommends using them in multiples of four to get the LF extension and mutaul coupling!

The new high power model ( 1000 w ) is the EL-36, and vega rates the usable response of all three horn models from 30Hz to 300Hz!


www.cerwinvega.com

i am dating myself here but, then again i'm a dinosaur. going back to the late 70's we used to use the scoop (lot's of them) mainly because choices were limited and they were the suggested mate for the 4560.
for P.A. we complained that there was no throw until someone decided that laying them on their sides in pairs end to end with the woofers alinged together and the scoop ends opposite formed a perfect folded horn with drivers coupled. we would mount 8 singles per side, (4 high sideways) TALK ABOUT PUNCH AND THROW!

There's a double scoop short throw horn with two 15's that are NOT mounted on the same plane. Think it's a 4550 ?? They are mounted on a front panel that's in a "v" shape - so that the 15's are firing off at slightly different angles.

How does that cabinet compare to the one with two 15's mounted on the same plane?



c-ya

Guy