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[Tim Weaver]

If I have two horns for a 1" exit driver and they are both 60x40, and one has a total mouth size of say, 12 inches by 12 inches and the other has a mouth that is 7 inches by 7 inches, which is better and why?

They both do the same thing, but what is the advantage of the larger horn? Better pattern control? Lower cutoff (this seems obvious but let's assume that both will play down to 1.6k the assumed X-over freq)? Is one an easier load for the driver? Is one more efficient?

I need to clarify some things in my mind here about HF horns.

Thanks all!

-=Tim=-

[Jeff Wheeler]

I have done only a little reading on this topic, but the Wikipedia page was enough to tell me it's pretty complicated!  You may wish to read it, but there appears to be no universal answer to your question; the type of horn, and many dimensions besides just the mouth, are a significant factor.  http://en.wikipedia.org/wiki/Horn_loudspeaker

[Mike Smith]

Flare rate determines the horn's low frequency cutoff. A larger mouth just provides better pattern control down to that frequency.

The smaller horn, if properly designed, will have better high frequency dispersion than the larger horn. This will be at the expense of lower frequency pattern control (directivity).

In a perfect world, your high frequency dispersion at the crossover point would be roughly the same as the low frequency driver's dispersion at the same point.

We don't live or work in that world.

Depending on the specific application, you can jack with the compromises you have to make. Long throw, high output, wide coverage, speech range -- go with the bigger horn. Short throw, moderate output, hi-fi sound quality on-axis -- the little horn is the one to use.

[Ivan Beaver]

Mike Smith wrote on Sat, 13 February 2010 00:15

. The smaller horn, if properly designed, will have better high frequency dispersion than the larger horn.

Just wondering exactly what you mean by that statement.  Are you saying that the smaller horn will be more true to the horns rated pattern than the larger horn?  Or something else.

I guess I am looking for the meaning of "dispersion" in your statement.  I usually think of it as coverage angle.

[Ivan Beaver]

Tim Weaver wrote on Fri, 12 February 2010 20:08

If I have two horns for a 1" exit driver and they are both 60x40, and one has a total mouth size of say, 12 inches by 12 inches and the other has a mouth that is 7 inches by 7 inches, which is better and why? They both do the same thing, but what is the advantage of the larger horn? Better pattern control? Lower cutoff (this seems obvious but let's assume that both will play down to 1.6k the assumed X-over freq)? Is one an easier load for the driver? Is one more efficient? I need to clarify some things in my mind here about HF horns. Thanks all! -=Tim=-

The larger horn is going to have pattern control down lower-but will also be deeper (which might pose a problem).
Just because they will both go down to a particular freq (on axis)-does not mean that they are controlling that freq in the rated coverage pattern.

It takes larger horns to control lower freq.

[Mike Smith]

Ivan Beaver wrote on Sat, 13 February 2010 13:36

Mike Smith wrote on Sat, 13 February 2010 00:15 . The smaller horn, if properly designed, will have better high frequency dispersion than the larger horn. Just wondering exactly what you mean by that statement.  Are you saying that the smaller horn will be more true to the horns rated pattern than the larger horn?  Or something else. I guess I am looking for the meaning of "dispersion" in your statement.  I usually think of it as coverage angle.

It is my understanding that, all other things being equal, the smallest possible radiating area provides the widest possible coverage angle. In what way is "dispersion" different than "coverage angle", aside from "dispersion" being a less precise term?

I am also aware that when referring to horn-loaded devices other factors count as well: flare angle, the horn's throat geometry, etc. I should have used an example like: the same big-mouth horn that will give optimum loading and low frequency pattern control will probably have a hard time delivering wide, non-beaming high frequency coverage. Although with a really brilliant horn design I guess it's possible. Little bitty horns tend to have wider coverage. That's my own non-scientific observation.

Rated patterns are just nominal, like frequency response, power handling, or anything else. They are a snapshot framed between whichever parameters the manufacturer or independent tester imagine.

It's all about trade-offs, isn't it?

[Ivan Beaver]

Mike Smith wrote on Sat, 13 February 2010 14:20

Ivan Beaver wrote on Sat, 13 February 2010 13:36 Mike Smith wrote on Sat, 13 February 2010 00:15 . The smaller horn, if properly designed, will have better high frequency dispersion than the larger horn. Just wondering exactly what you mean by that statement.  Are you saying that the smaller horn will be more true to the horns rated pattern than the larger horn?  Or something else. I guess I am looking for the meaning of "dispersion" in your statement.  I usually think of it as coverage angle. It is my understanding that, all other things being equal, the smallest possible radiating area provides the widest possible coverage angle. In what way is "dispersion" different than "coverage angle", aside from "dispersion" being a less precise term? Rated patterns are just nominal, like frequency response, power handling, or anything else. They are a snapshot framed between whichever parameters the manufacturer or independent tester imagine. It's all about trade-offs, isn't it?

But is there such a thing as a wide 60x40 horn?   You are correct about a smaller driver having a wider coverage-but when that angle is contrained by a horn, then the pattern is that of the horn-down to the point at which it loses control-due to size.  All the driver has to do is to "fill the horn" and then the horn dictates the pattern-so it doesn't matter how wide the coverage may be in the "open air".

And a smaller 60x40 horn should not be any wider than a large 60x40 horn-if properly designed.

On a proper designed horn-the coverage pattern should be the same (give or take a bit) from the highest freq down to the point at which the horn no longer has control.

If it doesn't, then it is not a very well designed horn.

Yes there are "numbers" that are associated-but a reputable manufacturer will provide such things as polar plots-directivity graphs-EASE data (or various combinations) and so forth-so the end user can look at and determine how well a particular product suits their needs.

You cannot describe something as complex as pattern coverage with a single number.  Or you can-but it is usually only good for 1 partiuclar freq.

[Tim Weaver]

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?

[Jon Waller]

  Assuming they have approximately equal cutoff frequencies, the one with the larger mouth should have smoother frequency response, especially near the cutoff frequency.  But it could suffer from a poor design and this may not be the case.

[Phillip_Graham]

Tim Weaver wrote on Fri, 12 February 2010 20:08

If I have two horns for a 1" exit driver and they are both 60x40, and one has a total mouth size of say, 12 inches by 12 inches and the other has a mouth that is 7 inches by 7 inches, which is better and why?

Its impossible to say which is better, because mouth size alone is not a sufficient indicator of horn performance.

The flare rate of the horn will determine if the horn has a low frequency cutoff frequency, and if so, how severe it is.  Some flare profile experience this cutoff, and some do not.  Exponential horns do, but conical flares do not, for instance.

The flare rate will also determine the size and nature of the ripples of the acoustic impedance that is loading the driver.  Certain flares have better behavior in this regard than others.

Some horns are designed with the flare rates calculated by assuming a plane wave propagates in the horn, and some are not designed on this assumption.

Some flares will have a secondary flare rate near the mouth to smooth the impedance mismatch when the flare terminates, and some do not.  Some flares will need this, and some will not.

Some horns will match the incident flare rate at the mouth of the compression driver phase plug, and some will not.  A well designed horn that does not match well at the CD/throat junction may have problems.

Quote:

They both do the same thing, but what is the advantage of the larger horn? Better pattern control? Lower cutoff (this seems obvious but let's assume that both will play down to 1.6k the assumed X-over freq)? Is one an easier load for the driver? Is one more efficient?

You need not concern yourself with load for the driver, as that is not an issue for modern drivers.  The acoustic impedance that the driver sees matters most acutely for the smoothness of the horn behavior in the bandpass of frequencies in which it behaves like a horn.

A large and small horn with the same flare rate will behave the same at frquencies well away from the lower cutoff frequency.  The longer horn (ie the one with the larger mouth), will of course have the energy from any reflections as the mouth delayed out over a longer period of time.  The nature and degree of these reflections will depend on how close to the flare rate frequency the horn is being used.  It then depends on the nature of the of the acoustic impedance in this frequency range.  At higher frequencies an axis-symmetric horn of carefully chosen flare rate will generally propagate without mouth reflection issues.

Does this help answer your questions?

Can you dig down and try to pin down a more specific question for us?