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[Art Welter]

Tim Weaver wrote on Sat, 13 February 2010 20:31

So if I have two horns that are both properly designed and both being 60x40 in nominal coverage, but one is physically larger than the other, and they are playing a sine wave at 2k, can I assume that they would be equal in performance? And, if the smaller horn loses pattern control under say 800 hz (becomes unloaded) does this mean the compression driver is essentially radiating into free space? Having lost both pattern control, AND the acoustic coupling of the horn? Will Lassie get Timmy out of the well?

“Proper design” using different designs will result in different performance.

A horn can load the driver, yet not have uniform pattern control.

Measuring phase and amplitude response over the intended bandwidth and coverage  angles can tell if the design is “proper” for your use.

Lassie may summon someone to get Timmy out of the well.

[Ivan Beaver]

Tim Weaver wrote on Sat, 13 February 2010 22:31

So if I have two horns that are both properly designed and both being 60x40 in nominal coverage, but one is physically larger than the other, and they are playing a sine wave at 2k, can I assume that they would be equal in performance? And, if the smaller horn loses pattern control under say 800 hz (becomes unloaded) does this mean the compression driver is essentially radiating into free space? Having lost both pattern control, AND the acoustic coupling of the horn? Will Lassie get Timmy out of the well?

One of the important things to realize is that a horn does not STOP the sound from radiating into a particular area (out of the pattern)-but rather reduces it-as compared to on axis.

For example lets say you have a 1'x1' horn and a 4'x4' horn that for all intents and purposes have the same design and coverage angle.  Of course in reality this is very hard to do-but lets assume so for now.

If you put a 8Khz tone into each of them (well within the freq at which both horns would have "control") the 4'x4' horn would be a bit louder-because it basically has less "leakage" to the area outside the horn coverage pattern.  

This energy is therefore contained within the coverage pattern-making for a higher on axis/off axis ratio.

As others have noted-ther are a lot of other factors that affect horn design that will result in different overall outcomes.

Yet one more reason for large horns.

[Tim Weaver]

Thanks guys,

I'm trying to design new cabinets and going through different Horn and Driver combinations was stirring up these questions that I had no answer to. For instance at Assistance Audio they are bragging about running 1" exit drivers down below 1k. But when I look at the available horn flares, most have a "usable low freq limit" of around 1.5k. Which was quite confusing at first but I guess they are saying that the flare loses all pattern control under 1.5k. I was worried that if I used the wrong horn and crossed something at 1k I would toast my CD.

The other question was the horn size. If you want a certain coverage out of your HF horn you can get that coverage in anything from a horn the size of a coffee cup, all the way up to those old JBL's that were 5 feet long.

Then I read here and there that, there is no such thing as long throw/short throw. There is only SPL and pattern control. Which sorta makes sense, but why then do long throw cabs from the big manufacturers use longer horns? Just for looks? Is it a function of needing a tight pattern down to x-over freq that means a longer horn with a slower flare rate?

Tim "still not the sharpest knife in the elevator" Weaver

[Phillip_Graham]

Tim Weaver wrote on Tue, 16 February 2010 13:35

Thanks guys, I'm trying to design new cabinets and going through different Horn and Driver combinations was stirring up these questions that I had no answer to.

If you are using off the shelf components, horns produced by the manufacturer of the compression driver are less likely to have problems at the throat/driver interface.

Quote:

For instance at Assistance Audio they are bragging about running 1" exit drivers down below 1k. But when I look at the available horn flares, most have a "usable low freq limit" of around 1.5k.

The usable low frequency limit number has very little practical meaning without knowing the horn flare rate and what the manufacturers' primary consideration is in defining the "usuable" low limit.  There are plenty of stout CD that can work on carefully chosen flares below 1kHz

Quote:

The other question was the horn size. If you want a certain coverage out of your HF horn you can get that coverage in anything from a horn the size of a coffee cup, all the way up to those old JBL's that were 5 feet long.

While a crude metric, large horns generally perform better, or at least give more leeway in producing a good performing design.

What do you want the cabinet you are working on to do?  What driver(s) are going to exist below the compression driver(s)?

[Ivan Beaver]

Be VERY careful when doing this!

You cannot just pick a horn and then pick a driver that you like.  They may or may not paly well together.

I remember years ago I took a EV 8Hd horn 120

[Tim Weaver]

I agree about the horn and driver synergy. I am shopping for combinations that are "manufacturer recommended' more or less.

One of the front runners right now is the Selenium D220Ti mounted on a Selenium HL14-25.

This is a 45x45 setup. The paperwork from Selenium show a very good Freq response and reasonable narrowing in the UHF range.



This particular design would be 2 Eminence Deltalite 2510's and the above Horn/driver combo mounted in the middle. The idea is to get small and light with reasonable output and cost. This cabinet would be used at least 2 per side with the idea being that the 4 10's would contribute below x-over and above x-over you would have 1 horn. So it's a 90 degree system with 4 10's and 2 1" horns in 2 cabinets. The cabs would be light and easy to get up high on a pole.


Right now this is just one design I'm kicking around. I don't need super high SPL. The goal I'm looking for is lighter weight, easier transport and setup, and good sound quality for a modest price. This is the cheapest priced option I've got so far.

The subs will likely be 218's, but I'm really only concerned with top boxes right now.

[Art Welter]

That horn/driver combo has less than half the dispersion at 8K as 2K, a big “fail”, unless you are going for a pointillist effect.

Definitely won't array well.

PM me for some suggestions.

[Phillip_Graham]

Tim Weaver wrote on Tue, 16 February 2010 19:25

I agree about the horn and driver synergy. I am shopping for combinations that are "manufacturer recommended' more or less. One of the front runners right now is the Selenium D220Ti mounted on a Selenium HL14-25. This is a 45x45 setup. The paperwork from Selenium show a very good Freq response and reasonable narrowing in the UHF range.

Tim,

This particular horn is a pure exponential.  Not only will it exhibit a cutoff frquequency, it also exhibits extremely substantial narrowing of the coverage angle.

This is nothing like a constant directivity horn.  The axial response looks so good bc the narrowing directivity "squeezes" the sound from the compression driver into an ever narrow range of angles.

This is a poor choice.

[Tim Weaver]

Dang.....



Alright. Coffee breaks over, back on my head!

[Ivan Beaver]

That is why it is important to look at the polars (or a directivity curve etc)-they will give you that information.

Instead of going for 2 cheaper boxes per side-why not 1 good (more expensive) box?

Having a loudspeaker that exhibits smooth coverage across the audience will be a lot better than one that has more highs in one place than another.

If you have FOH "within the pattern"-but not on axis, you might tend to boost the higher freq.  But the people who are on axis are going to complain that it is to bright.

So who is right?  The problem is that the loudspeaker coverage is NOT right.