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Author Topic: HF horns. Which has the advantage?  (Read 6031 times)

Tim Weaver

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HF horns. Which has the advantage?
« on: February 12, 2010, 08:08:28 pm »

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=-
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Jeff Wheeler

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Re: HF horns. Which has the advantage?
« Reply #1 on: February 12, 2010, 08:56:38 pm »

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
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Mike Smith

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Re: HF horns. Which has the advantage?
« Reply #2 on: February 13, 2010, 12:15:07 am »

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.

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Mike Smith

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Ivan Beaver

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Re: HF horns. Which has the advantage?
« Reply #3 on: February 13, 2010, 01:36:40 pm »

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.
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Ivan Beaver
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Ivan Beaver

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Re: HF horns. Which has the advantage?
« Reply #4 on: February 13, 2010, 01:40:48 pm »

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.
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Mike Smith

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Re: HF horns. Which has the advantage?
« Reply #5 on: February 13, 2010, 02:20:12 pm »

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?


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Mike Smith

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Ivan Beaver

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Re: HF horns. Which has the advantage?
« Reply #6 on: February 13, 2010, 06:49:11 pm »

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? Rolling Eyes   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.
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Tim Weaver

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Re: HF horns. Which has the advantage?
« Reply #7 on: February 13, 2010, 10:31:24 pm »

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?
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Jon Waller

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Re: HF horns. Which has the advantage?
« Reply #8 on: February 15, 2010, 11:16:22 am »

  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.
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Phillip_Graham

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Re: HF horns. Which has the advantage?
« Reply #9 on: February 15, 2010, 01:42:13 pm »

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?
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Art Welter

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Re: HF horns. Which has the advantage?
« Reply #10 on: February 15, 2010, 02:45:16 pm »

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.
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Ivan Beaver

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Re: HF horns. Which has the advantage?
« Reply #11 on: February 15, 2010, 06:46:28 pm »

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.
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Ivan Beaver
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Tim Weaver

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Re: HF horns. Which has the advantage?
« Reply #12 on: February 16, 2010, 01:35:17 pm »

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
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Phillip_Graham

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Re: HF horns. Which has the advantage?
« Reply #13 on: February 16, 2010, 05:19:27 pm »

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)?
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Ivan Beaver

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Re: HF horns. Which has the advantage? CAUTION
« Reply #14 on: February 16, 2010, 05:25:44 pm »

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
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Tim Weaver

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Re: HF horns. Which has the advantage? CAUTION
« Reply #15 on: February 16, 2010, 07:25:15 pm »

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.
index.php/fa/28147/0/


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.
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Art Welter

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Re: HF horns. Which has the advantage? CAUTION
« Reply #16 on: February 16, 2010, 09:02:25 pm »

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.
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Phillip_Graham

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Re: HF horns. Which has the advantage? CAUTION
« Reply #17 on: February 16, 2010, 11:13:13 pm »

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.
index.php/fa/28147/0/


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.
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Tim Weaver

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Re: HF horns. Which has the advantage? CAUTION
« Reply #18 on: February 16, 2010, 11:17:43 pm »

Dang.....



Alright. Coffee breaks over, back on my head!
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Ivan Beaver

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Re: HF horns. Which has the advantage? CAUTION
« Reply #19 on: February 17, 2010, 07:44:59 am »

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.
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Danley Sound Labs

Tim Weaver

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Re: HF horns. Which has the advantage? CAUTION
« Reply #20 on: February 17, 2010, 06:41:15 pm »

I'm going for 2 or more smaller cabs vs one big cab, because I run this rig solo. Even if it's lightweight a large cabinet can be a bear to stack by yourself. I do it on occasion with some srx725's. They aren't that heavy, but can be a pain to stack just because of the size.

Bonus #2 is the ease of elevating a small cab. Stick it on a pole and its up as high as you need it.

OK. I am sending out some emails to try and get more info about BMS stuff now.
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Phillip_Graham

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Re: HF horns. Which has the advantage? CAUTION
« Reply #21 on: February 18, 2010, 12:15:52 am »

Tim Weaver wrote on Wed, 17 February 2010 18:41


OK. I am sending out some emails to try and get more info about BMS stuff now.


BMS, Celestion, B&C, Beyma, 18Sound, and Faital could all be on that list...
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