Question on the "double scoop" short throw horn.

[Scooter]

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

[paragon]

"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

[mikebake]

4520 info here

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

[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

[scott fitlin]

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!

[paragon]

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

[mikebake]

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.

[scott fitlin]

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!