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RE: Is there anything in production similar to a JBL 2220 for horn loading?

Posted by tomservo (M) on December 29, 2023 at 06:24:14

In Reply to: Is there anything in production similar to a JBL 2220 for horn loading? posted by Oldbean2 on December 28, 2023 at 17:16:37:

A cool thing about horns is you can put any driver on any horn and it will make sound. The flip side is there is one combination of horn parameters that gives the highest efficiency / output for a given set of driver parameters and bandwidth.

For a 2220 with a 40Hz to 270Hz efficient bandwidth, the ideal horn paramete5rs looks like this.
throat area 192in sq (.69:1)
Rear volume 2850 in^3
Front volume 654 in^3
Hyperbolic expansion =.24
N=54%

Notice the ideal throat is larger than the driver area (negative compression ratio) and the driver xmax is only 3mm. The compression ratio is a multiplier so far as how much sound vs how much excursion and one of the advantages of horn is that for a given spl, there is less driver motion and so less distortion. Most of a drivers distortion is related to how far it is moving.

The 2220 is more suited to a wider bandwidth, this spec here (all other things being equal) is what increases the ideal compression ratio.
For instance if one asked for a 40Hz to 400Hz bandwidth, the ideal horn looks like;

throat area 80in sq (1.6:1)
Rear volume 2050 in^3
Front volume 169 in^3
Hyperbolic expansion =.4
N=48%

The compression ratio means much less excursion for a given spl compared to the first and so lower distortion at normal levels. Fwiw, compression drivers often have a compression ration greater than 8 to 1.

There is a 12 inch driver in a similar category if interested, look at an 18sound 12nmb1000.

Lastly, all the math i used above is for simple full size horns, normally what can be built is smaller than that so modeling the response of what you can build is the next step.
Thankfully now days one can model horns with programs like hornresp and what i use called Akabak, this ability to model / predict is something only possible in the last 20 years or so of horn design, something the ancients couldn't do.
Big?? No problem modeling works at any scale, here is an example of 1 channel of a large subwoofer modeled this way and used for outdoor movie projections.

Tom

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