what's the difference between a wave guide and a horn?

[Daddy Dee]

been doing a bunch of reading on Zilch Advent econowave conversions. noticed waveguide and horn aren't exactly used interchangeably.

are they the same thing or what's the diff? is there a downside to using a horn in an econowave project?

any help appreciated.

[Edgar]

In the most general terms, an acoustical horn is an impedance transformer and an acoustical waveguide controls directivity.

In the early days of little or no amplification, horns were designed to make minute signals as loud as possible, and things like beamwidth and directivity were secondary. Later, as cheap amplification became available, it became worthwhile to trade some sensitivity for pattern control. So horns and waveguides, though very similar in configuration, are designed for different purposes.

[Deang]

Nicely explained. I was going to say that horns are big and difficult to deal with while waveguides are small and relatively simple to deal with. :-)

[Daddy Dee]

thanks gentlemen.

[WMcD]

It seems to me that the term "wave guide" is mostly used in microwave radio frequency work. The waveguide is somewhat a substitute for coaxial cable and really resembles a metal pipe. It is used to get the radio frequency power from the transmitter to an antenna.

http://en.wikipedia.org/wiki/Waveguide

But a popular antenna used in microwave work is a conical horn (if rectangular in cross section).

http://en.wikipedia.org/wiki/Microwave_horn

I suspect that some audio guy adopted the term wave guide because "horn" had a bad implication. But in microwave, a wave guide is not a horn.

As far as audio horns, I always direct attention to D.B. Don Keele's paper titled, "What's So Sacred About Exponential Horns." He has a rule of thumb equation for mouth size and cone angle. I suspect he got it from the microwave guys.

So there are enough analogies between electromagnetic waves and acoustics to adopt one area of design to the other.

WMcD

[DrWho]

been doing a bunch of reading on Zilch Advent
econowave conversions. noticed waveguide and horn aren't exactly used
interchangeably.

are they the same thing or what's the diff? is there a downside to using a horn in an econowave project?

any help appreciated.

I would argue that "waveguide" is
merely a marketing term to avoid the association with the crappy
exponential diffraction slot horns of the past.

Polar response and
impedance matching are two facets of compromising variables in good
horn design - you are (should be) consciously balancing the two
components to achieve the desired result (and doing lots of crazy math
and prototyping to get there).

I personally get a bad taste in my
mouth when I hear people talking about waveguides because some of the
strong proponents of those approaches tend to be extremist and
completely ignore other very real facets to good 'dacoustic' esign. I also
think it works to discredit the great research of the past and I don't
think those acoustic pioneers should be dissed that way - I know it's
not intentional, but it's just my take on it.

Audiophilia run rampant.

Btw, I'm probably overstating it a bit because I do feel (until lately) that polar response hasn't been concentrated on enough.

All that to say, if you're doing an econowave type project, then most any horn will do. What did you have in mind?

[djk]

"I would argue that "waveguide" is
merely a marketing term to avoid the association with the crappy
exponential diffraction slot horns of the past."

+1

[Edgar]

I suspect that some audio guy adopted the term wave guide because "horn" had a bad implication.

Working entirely out of memory here (draw your own conclusions about that), but I believe that the first time I saw a distinction between the two was in something that Earl Geddes wrote. He makes a strong distinction between horns designed for acoustic loading, and waveguides designed to avoid higher-order modes (internal reflections) -- and the geometry associated with that also leads to constant-directivity.

Greg

[Don Richard]

Working entirely out of memory here (draw your own conclusions about that), but I believe that the first time I saw a distinction between the two was in something that Earl Geddes wrote. He makes a strong distinction between horns designed for acoustic loading, and waveguides designed to avoid higher-order modes (internal reflections) -- and the geometry associated with that also leads to constant-directivity.

http://forums.klipsch.com/forums/storage/3/1322842/How%20Horns%20Work%20Revisited%20by%20Dr.%20Earl%20Geddes%20(compressed).pdf

[Edgar]

Thanks, Don. I was actually referring to Geddes' JAES articles, but that paper summarizes the point very well.

Greg

[WMcD]

Whoops, it was myself who posted that article. In it Geddes adopts the term and also says it is misused. So maybe I was correct. Smile.

Somewhat off topic, it is interesting to consder a classic acoustic horn and a microwave design which wasn't used for a few decades.

If you look at the Voigt horn we see his tractrix bass horn aimed at a reflector, the latter is used to dispurse rather than focus the high freq sounds. (And let me add that the bass section is a cone shaped device which the back of the driver loads about one-third down its length. Isn't this a tapped bass horn?)

[WMcD]

Some decades later, we see a microwave antenna where what is probably a conical horn directing the energy to a parabolic reflector which here is used to focus the RF energy. Its kinda spooky that they are similar.

[WMcD]

You have to wonder if anyone creating the microwave horn shouted down it or put an audio driver in place at the narrow end. They would have a nice party system out on the lawn.

Smile.

WMcD

[DrWho]

It turns out that RF Frequencies and Audible Acoustic Waves have very similar wavelengths. The behavior for both is also described by the same wave equation (different coefficients), which is why the RF world and Acoustic world often have very similar solutions when it comes to directivity and impedance matching.

You should see the horns we have in our test chambers at Shure [] One of them looks a lot like the K400 actually.

[seti]

Whoops, it was myself who posted that article. In it Geddes adopts the term and also says it is misused. So maybe I was correct. Smile.

Somewhat off topic, it is interesting to consder a classic acoustic horn and a microwave design which wasn't used for a few decades.

If you look at the Voigt horn we see his tractrix bass horn aimed at a reflector, the latter is used to dispurse rather than focus the high freq sounds. (And let me add that the bass section is a cone shaped device which the back of the driver loads about one-third down its length. Isn't this a tapped bass horn?)

Nice.. Have you heard the Voigt corner horn?

There was a guy selling the reflectors on ebay a while back. I believe plans can be purchased from the voigt museum.

[Daddy Dee]

Gentlemen, thank you for the contributions. This is most helpful.

Dr. Who, The recommended driver from Zilch (in the limited amount of material I've read so far) is the Selenium D220Ti.

I think he originally used that with a JBL (discontinued) waveguide of which the Dayton H6512 is a clone.

Here are the horns I've been considering. Also, at the bottom is a link to a PE offered buyout of the THX Ultra2 horn/driver combo.

Any thoughts/advice from Dr. Who and others are appreciated.

Pyle
PH612

http://www.parts-express.com/pe/showdetl.cfm?partnumber=292-2572

Dayton
Audio H6512

http://www.parts-express.com/pe/pshowdetl.cfm?&Partnumber=270-318&scqty=1

Eminence
H290S

http://www.parts-express.com/pe/showdetl.cfm?partnumber=290-555

Selenium
HC23-25

http://www.parts-express.com/pe/showdetl.cfm?partnumber=264-318

one combo i've wondered about is the PE buyout of the THX Ultra2 for $44.80 which includes the driver too. Some savings over purchasing horn + driver alacarte.

http://www.parts-express.com/pe/showdetl.cfm?partnumber=279-106

[jacksonbart]

about $1200 give or take $1200.

[DrWho]

My preference for 1" throat horns has been the QSC HPR:

http://www.parts-express.com/pe/showdetl.cfm?partnumber=245-625

It has very well behaved directivity and mates well to a 15" woofer with a 1kHz xover. I'm not sure the K33 is going to get you to 1kHz though, but the K48 from the Chorus II will.

The Selenium D220Ti is a good driver. I personally went with the 3x more expensive BMS 4550.

I believe the QSC horn was designed for the Celestion CDX1:
http://www.parts-express.com/pe/showdetl.cfm?partnumber=294-2124

Dunno if that's worth the upgrade for you or not.

[sunnysal]

In the most general terms, an acoustical horn is an impedance transformer and an acoustical waveguide controls directivity.

In the early days of little or no amplification, horns were designed to make minute signals as loud as possible, and things like beamwidth and directivity were secondary. Later, as cheap amplification became available, it became worthwhile to trade some sensitivity for pattern control. So horns and waveguides, though very similar in configuration, are designed for different purposes.

I come form a telecommunications background and this is how we would explain it as well....I expect horns to amplify the input signal (and hopefully provide some directional control) and wave guides to simply transport signal, minimizing signal loss along the way. as someone mentioned perhaps microwave technology is not directly applicable at hi-fi sound frequency levels but there it is...regards, T

[Chris A]

...noticed "waveguide" and "horn" aren't exactly used interchangeably...are they the same thing or what's the diff?

A horn is actually an expanding waveguide.

If you listen to Earl Geddes, an "acoustic waveguide" is a conical horn with a smoothly transitioning throat, i.e., basically the same thing as the Peavey "Quadratic Throat Waveguide". Geddes, however, doesn't believe in the audibility of modulation distortion, and doesn't believe that efficiency is a goal for waveguide design.

Roy has flatly stated that acoustic waveguides and horns are the same thing.

Chris