Vertical vs Round Mouth

[EmilC]

Good morning,guys

 

Can anyone explain why a particular manufacturer would chose one over the other? What are they trying to achieve? What are the sonic differences?

 

I've been told by many to replace my 2380A on my Cornscalas. I think it sounds pretty good but to be honest I haven't heard anything else to compare it to.

 

Thanks

 

b          

[Chris A]

Round-mouth horns (all of them) will have a certain issue with mouth diffraction that a rectangular horn basically will not have:

 

http://www.diyaudio.com/forums/multi-way/256220-axis-null-horn-speakers.html

 

There is no advantage that I see to something round, but there is an advantage to a rectangular (or elliptical) horn profile.  You get a different coverage angle horizontally than vertically.  It's usually much more desirable to have a larger coverage angle horizontally than vertically, especially for home applications with typically low ceilings and nothing on the floor to absorb the floor bounce.

 

Chris

Edited August 14, 2015 by Chris A

[Fjd]

Since both pictures are rectangular mouth horns, rather than "mouth" I think he may be talking about the throat "vertical slot" in the 2380A vs. the smooth transition (e.g., no vertical slot) in the horn (waveguide?) on the left.

Edited August 14, 2015 by Fjd

[Chris A]

I've been told by many to replace my 2380A on my Cornscalas.

 

I'd strongly recommend not using a horn with a slot in it - otherwise called a diffraction slot horn or a "constant coverage" horn.  You'll get a "frying eggs" sound from any horn with a slot in it. 

 

I'd actually recommend a Klipsch K-510 and a 2" compression driver (if you don't already have one) and cross over at 600 Hz or higher.  This would sound the best.

 

You can talk to American Cinema Equipment (Cinequip) for horn-only availability.

 

Chris

Edited August 14, 2015 by Chris A

[EmilC]

Since both pictures are rectangular mouth horns, rather than "mouth" I think he may be talking about the throat "vertical slot" in the 2380A vs. the smooth transition (e.g., no vertical slot) in the horn (waveguide?) on the left.

 

Yes. Sorry for the confusion

[Don Richard]

I'd strongly recommend not using a horn with a slot in it - otherwise called a diffraction slot horn or a "constant coverage" horn. You'll get a "frying eggs" sound from any horn with a slot in it.

 

What source material will show the frying egg sound? I've been using a Peavey CD horn with the recommended Peavey driver and don't hear anything like that.

[Chris A]

Anything with high frequencies above the so-called "cut-on" frequency of the horn...  The classic instrument that exhibits this is a ride cymbal or perhaps a crash cymbal.

 

Chris

[Fjd]

Here are a couple of quotes from a thread that discusses the 2380A.  However, it is not really clear if the observations are in relation to two-way operation or three-way.

 

https://community.klipsch.com/index.php?/topic/95845-anyone-using-jbl-2370-2380-or-2385-midraneg-horns/

 

 

We use the 2380 at work in a variety of configurations and there is no way I would ever consider using them in a home environment. In fact, if it were my choice, we wouldn't be using them at work either.

 

The 2380 certainly has a very decent coverage pattern and can get real loud with the right drivers, but they are shrill as all get out...or more of a congested shrill sound - it's hard to describe. You know there's something wrong when you can walk into other venues and identify the 2380 after hearing just a few seconds of music. Ideally, you just wanna be hearing the music - not the speakers.

 

I actually ran some curves at work to see if there wasn't anything blaringly wrong in the frequency response, but overall they looked well behaved. When I get back home or find an internet connection for my laptop I can post those curves. I recall them being extremely similar to the curves that JBL posts. The only downside is that it's a system response with some JBL2226H drivers in the mix (so I can't verify the LF extension)...I think we're crossing to them at around 800Hz.

 

Actually, here's the PDF for the 2380:
http://www.jblpro.com/pages/pub/components/2380a.pdf

I was just noticing they're rated for 10% distortion at 1W and 10W of input power. [ ]

 

 

Distortion is also the function of the cut-off frequency of the horn, the lower the horn goes, the higher the distortion will be at high frequencies.

 

The 2360 horn has 30% THD with 5W input at 10Khz (for instance)

http://www.jblpro.com/pub/technote/tn_v1n08.pdf

 

The newer OA series 1.5" throat horns and drivers have about 10dB less distortion in the 8Khz region.

http://www.jblpro.com/pub/technote/tn_v1n21.pdf

 

This is due to a higher cut-off frequency, and opening up the slot in the throat.

 

The narrow slot, long tail throat gives rise to a 'quacking' or 'frying bacon' sound at high volumes.

 

If you think about it, the air has to create a vacum on its rear-wave to go above 162dB (at the diaphragm). This creates a 'clap' similar to a lightning bolt when the air rushes back in, this is the audible 'quack' that can be heard. Keep in mind that most of these large drivers are about 117dB/mW on a terminated tube, or 162dB for 32W input. (the Carver PM1.5 was often seen driving the 2445, it can put out in excess of 350W/16R on program material)

 

The air in the throat simply overloads.

 

PS, I've had the Atlas drivers 'quack' with less than 100W on the wrong type horn.

 

If you want something that doesn't 'quack', and has much lower distortion than any other midrange driver I've heard, look into the Community M200 on the SH494 horn.

 

 

[EmilC]

 

Here are a couple of quotes from a thread that discusses the 2380A.  However, it is not really clear if the observations are in relation to two-way operation or three-way.

 

https://community.klipsch.com/index.php?/topic/95845-anyone-using-jbl-2370-2380-or-2385-midraneg-horns/

 

 

We use the 2380 at work in a variety of configurations and there is no way I would ever consider using them in a home environment. In fact, if it were my choice, we wouldn't be using them at work either.

 

The 2380 certainly has a very decent coverage pattern and can get real loud with the right drivers, but they are shrill as all get out...or more of a congested shrill sound - it's hard to describe. You know there's something wrong when you can walk into other venues and identify the 2380 after hearing just a few seconds of music. Ideally, you just wanna be hearing the music - not the speakers.

 

I actually ran some curves at work to see if there wasn't anything blaringly wrong in the frequency response, but overall they looked well behaved. When I get back home or find an internet connection for my laptop I can post those curves. I recall them being extremely similar to the curves that JBL posts. The only downside is that it's a system response with some JBL2226H drivers in the mix (so I can't verify the LF extension)...I think we're crossing to them at around 800Hz.

 

Actually, here's the PDF for the 2380:

http://www.jblpro.com/pages/pub/components/2380a.pdf

I was just noticing they're rated for 10% distortion at 1W and 10W of input power. [ ]

 

 

Distortion is also the function of the cut-off frequency of the horn, the lower the horn goes, the higher the distortion will be at high frequencies.

 

The 2360 horn has 30% THD with 5W input at 10Khz (for instance)

http://www.jblpro.com/pub/technote/tn_v1n08.pdf

 

The newer OA series 1.5" throat horns and drivers have about 10dB less distortion in the 8Khz region.

http://www.jblpro.com/pub/technote/tn_v1n21.pdf

 

This is due to a higher cut-off frequency, and opening up the slot in the throat.

 

The narrow slot, long tail throat gives rise to a 'quacking' or 'frying bacon' sound at high volumes.

 

If you think about it, the air has to create a vacum on its rear-wave to go above 162dB (at the diaphragm). This creates a 'clap' similar to a lightning bolt when the air rushes back in, this is the audible 'quack' that can be heard. Keep in mind that most of these large drivers are about 117dB/mW on a terminated tube, or 162dB for 32W input. (the Carver PM1.5 was often seen driving the 2445, it can put out in excess of 350W/16R on program material)

 

The air in the throat simply overloads.

 

PS, I've had the Atlas drivers 'quack' with less than 100W on the wrong type horn.

 

If you want something that doesn't 'quack', and has much lower distortion than any other midrange driver I've heard, look into the Community M200 on the SH494 horn.

 

 

OMG!

[Fjd]

 

OMG!

 

 

 

I believe that those guys may have better "trained ears" than most given their respective involvement in sound reinforcement/reproduction. 

 

I stuck JBL 2380A horns on top my Cornwall II's for a three-way setup during 2006/2007 timeframe for a near-field listening setup; and like you now, the horns were fine.  Of course, I joined the Klipsch forum in 2009, then decided to immediately jump down the "rabbit hole of no return" by modifying my 1976 Khorns with the wood tractrix 2" throat mid horn offerings on the forum. 

 

My lessons learned, of course, you can find something much better than the slot horn, but at a price.  I like the suggestion of Chris A above of looking into the K510 horn if you have a strong desire to upgrade. In my situation I finally ended up with Jubilees during 2011.

Edited August 14, 2015 by Fjd

[EmilC]

Thanks for the Klipsch k510 suggestion. They look like a drop in replacement for the 2380 in the Crites Cornscala.

 

I did send an email out to American Cinema for availability. Other than that, very little in via Google. Are these horns still being made? Any substitutes?

[Chris A]

Yes, this is frequency-dependent behavior.  The problem with diffraction slot horns is actually that they have an upper frequency limit (the "cut-on" frequency), above which the so called "evanescent modes", or higher order modes (HOMs) exit the horn's mouth, sounding like frying bacon or eggs. 

 

In a smooth-wall horn the HOMs aren't excited nearly as much.  In a diffraction slot horn, the HOMs really can't get any worse since they are all tripped via the slot.  The trick is to cross over below the cut-on frequency with a diffraction slot horn.  The problem is, those slots are there for spreading out the higher frequencies...oops.  I'm not sure what that cut-on frequency is for the JBL horn mentioned, but my recollection is that somewhere around 2-4 kHz that the HOMs turn on and exit the horn's mouth.  This is a function of the horn profile and also the slot geometry-size.

 

As far as smooth-throat horns, they tend to have water vapor condensation issues in the throat at extremely high SPL, which is why Klipsch designs their horns for faster expansion in the throat - leading to reduced harmonic distortion. 

 

 

Are these horns still being made? Any substitutes?

 

Yes...and probably, but I have no data on other horns of this category. 

 

I remember a 1" throat QSC horn that basically approximates the profile the older-profile 2"-throat K-510 horn (without "mumps"), but that doesn't address your problem.

 

http://www.parts-express.com/qsc-pl-000446gp-replacement-waveguide-horn-for-hpr152i-2-bolt--245-625

 

Chris

Edited August 14, 2015 by Chris A

[Chris A]

I found the formula for the cut-on frequency of a circular cross section horn.  From Fahy, Foundations of Engineering Acoustics, Academic Press, (2001), pg.220:

 

f(c0) = 1.84c/2πa

 

where c = speed of sound in air at the operating temperature, and a = radius of the horn at which you are looking for the cut-on frequency.

 

For a 2" throat horn, this is 3978 Hz, about the effective size of the slot in the horn, or perhaps a bit lower in frequency.

 

Chris

Edited August 31, 2015 by Chris A

[Don Richard]

Anything with high frequencies above the so-called "cut-on" frequency of the horn...  The classic instrument that exhibits this is a ride cymbal or perhaps a crash cymbal.

 

Chris

 

I just put a Styx album on that has good cymbal work, no eggs. Same with Sousa march music. The HF horn I am using has a short diffraction slot, 2.25 in. tall by 5/8in. wide. The vertical expansion slot expands from 5/8 in. to the 2.25in. slot height. Most slot type CD horns I've seen use a taller vertical slot than that, so maybe that's the difference?

[Schu]

no one wants a sqwanky sounding horn...

[Chris A]

Any discontinuity in the throat of the horn increases the generation of HOMs, so the issue must be: "...by how much?".  I don't have a formula for that, unfortunately. 

 

So my rule of thumb is to avoid slots.  The exact horn profile that the OP mentioned exhibited a large amount of frying egg sound when I had it biamped between the Jubs.  It wasn't subtle.  The horn was used full-range with a K-69-A driver and crossed over at 600 Hz, IIRC.  I used REW and a Dx38 to flatten the response.  SSSSS's were killers. 

[Fjd]

It seemed like I saw scores of the used JBL 2380A horn / 2445 compression driver combination for sale cheap back in 2005/2006.  Maybe a lot of upgrades during those years put a lot on the used market.  I think a pair of this horn/driver combination had cost me between $200 and $250 enticing me to try something different. 

 

Given the JBL specs had shown ~ ±3dB from 600 Hz to about 7 KHz with no EQ, I couldn’t resist buying a pair.  I used mine within that bandwidth crossed over at 600 Hz on the low end and either 6 KHz or 4 KHz depending upon the tweeter used.  Based on Chris' calculations, I can see how I benefited keeping it narrow in a three-way set up.

[djk]

"I've been using a Peavey CD horn with the recommended Peavey driver and don't hear anything like that."

 

The 44XT is a nice driver (I own a pair), you can use a Radian, JBL, or True Extant diaphragm with this driver.

 

http://peavey.com/products/index.cfm/item/718/80780/44XT%26trade%3Bw_adapterDriver

 

This CD horn does not 'quack'.

 

http://peavey.com/products/index.cfm/item/718/118293/CH%26trade%3B642QT

 

Nor does this one (I own a pair).

 

http://peavey.com/products/index.cfm/item/718/118133/CH%E2%84%A26-9Horn

Edited August 15, 2015 by djk

[djk]

This film was so bad at an average level of about 85dB on the music scenes that I had to leave the theater, all the trumpets sounded like they were 'quacking'. Carmike Theater with a new JBL system (double 15 JBL 4508 boxes with 2445 on a slot throat horn, 2380 or 2360 depending on the floor size).

 

http://www.imdb.com/title/tt0104802/

 

This Peavey horn 'quacks' really bad, whether with an Atlas PD5 or a Peavey T22 driver. I was crossing at 800hz and using a McIntosh MC2120 on the HF.