# Straight vs Angled Entry Horns



## SSSnake

I know that several of you with the ID horns have modified the horn bodies to support straight entry rather than the angled entry. Could you provide some feedback as to the pros and cons of this modification?


----------



## thehatedguy

AFAIK I am one of the only people with the straight entry ID horns...I only think there were a couple sets made.

Better low level detail is what it gains you.


----------



## SSSnake

Jason,

I thought that I remembered you were running straight entry horns but didn't want to call you out in case I was wrong. Low level detail got it. How about high frequency response? Any more extension?

Charles


----------



## Patrick Bateman

SSSnake said:


> I know that several of you with the ID horns have modified the horn bodies to support straight entry rather than the angled entry. Could you provide some feedback as to the pros and cons of this modification?


The bend in the car audio horns creates a notch in the on and off-axis response. This is due to a reflection which occurs when the radiation from the diaphragm hits that bend, then reflects back down the throat.

So you can see it in frequency response plots, but even worse, it generates high order modes (HOMs) which are basically the obnoxious raspy sound that you hear from most horns.

There's some things that can help:


Remove the bend (duh)
Use a wider radius on the bend. There will still be a notch, but it won't be as deep.
Use a much MUCH smaller compression driver. The frequency of the notch depends on how far the diaphragm is from the kink. Closer is better, because it drives up the frequency of the notch.
Put some polyester fiberfill in the bend. Or better yet, the whole darn horn.

Check out my homster thread on diyaudio. Measurements are in the thread.


----------



## SSSnake

Thanks for the inputs Patrick. The results you referenced were what I expected but I wonder at what frequency the notch appears in the current design. The ID horns that I have are the full bodies with an immediate bend in the throat. I have been toying with putting these back in the current setup but believe that a custom waveguide solution might be more of what I need. I just don't seem to have the time to do the things I want to the car and was looking for a time saver. My real job just keeps gettng in the way of my hobbies.


----------



## Eric Stevens

Patrick Bateman said:


> The bend in the car audio horns creates a notch in the on and off-axis response. This is due to a reflection which occurs when the radiation from the diaphragm hits that bend, then reflects back down the throat.
> 
> So you can see it in frequency response plots, but even worse, it generates high order modes (HOMs) which are basically the obnoxious raspy sound that you hear from most horns.
> 
> There's some things that can help:
> 
> 
> Remove the bend (duh)
> Use a wider radius on the bend. There will still be a notch, but it won't be as deep.
> Use a much MUCH smaller compression driver. The frequency of the notch depends on how far the diaphragm is from the kink. Closer is better, because it drives up the frequency of the notch.
> Put some polyester fiberfill in the bend. Or better yet, the whole darn horn.
> 
> Check out my homster thread on diyaudio. Measurements are in the thread.


Not exactly.

Above a certain frequency yes the reflection causes a notch and high order modes. Below that frequency the wavefront will get reconstructed going in the new direction. Dr Bruce Edgar and I did the math on this and the math supports my statement and predicts the effects of the bend. the notch and response variations are evident in the response of the horn both on and off axis. the most significant effect was in the 15 or 16Khz range and output above the notch also suffered somewhat as well. Dr. Edgar originally worked on this for using folded horns for midbass duties where they have multiple bends. In fact a radius bend or turn causes more modes with a more significant negative effect than a proper 90 degree bend with a 45 degree reflector. The frequency of the notch is controlled by the area of the horn at the bend not the distance from the diaphragm. The sound in the horn is acting like a liquid until the area reaches a certain size relative to the frequency being reproduced, in fact that is what gives a horn such excellent power response (wide bandwidth over a large coverage area).

I have tested 90 degree turns with a radius bend and 45 degree reflector and I can tell you there is a very significant improvement using the the reflector rather than the radius bend. That is why our horns were originally designed with a radius and later modified to have a reflector.

A straight horn is always the best option but not if you have to sacrifice the proper mounting location or even the flare and mouth to accomplish it you are better off with the bend as long as its accomplished correctly.

Eric 
Image Dynamics


----------



## SSSnake

Eric thanks for the insightful post!

You mentioned:


> The frequency of the notch is controlled by the area of the horn at the bend not the distance from the diaphragm.


I thought, apparently incorrectly, that when the soundfield encountered a change in flare rate or fold in the horn a percentage of the energy was reflected to the other end of the horn (beginning of the throat). In this scenario the distance between the bend and the emitter would dictate the frequency of the constructive and destructive interference. I thought, again apparently incorrectly, that treatments such as a "reflector" merely decreased the amplitude of the reflection. I assume the statements above are false because of the "liquid" behaviour of the wavefront.

Either way the discussion seems to be academic only (although I would really love to comprehend this) as the null seems to be high enough to have very little effect in pratical application.

I have searched in vain to find good books on horn design and construction (I did find some AES pubs). Do you have any recommendations?


----------



## SQram

Eric,

With compression drivers getting smaller and smaller these days, has Image Dynamics considered R&D'ing a straight entry horn for future release?


----------



## Patrick Bateman

Eric Stevens said:


> Not exactly.
> 
> Above a certain frequency yes the reflection causes a notch and high order modes. Below that frequency the wavefront will get reconstructed going in the new direction. Dr Bruce Edgar and I did the math on this and the math supports my statement and predicts the effects of the bend. the notch and response variations are evident in the response of the horn both on and off axis. the most significant effect was in the 15 or 16Khz range and output above the notch also suffered somewhat as well. Dr. Edgar originally worked on this for using folded horns for midbass duties where they have multiple bends. In fact a radius bend or turn causes more modes with a more significant negative effect than a proper 90 degree bend with a 45 degree reflector. The frequency of the notch is controlled by the area of the horn at the bend not the distance from the diaphragm. The sound in the horn is acting like a liquid until the area reaches a certain size relative to the frequency being reproduced, in fact that is what gives a horn such excellent power response (wide bandwidth over a large coverage area).
> 
> I have tested 90 degree turns with a radius bend and 45 degree reflector and I can tell you there is a very significant improvement using the the reflector rather than the radius bend. That is why our horns were originally designed with a radius and later modified to have a reflector.
> 
> A straight horn is always the best option but not if you have to sacrifice the proper mounting location or even the flare and mouth to accomplish it you are better off with the bend as long as its accomplished correctly.
> 
> Eric
> Image Dynamics


You can literally measure the notch with a ruler. Like this:










All of what you said is true in theory. The most important part of your post is the idea of sound "acting like a liquid." To put it simply, when the wavelength exceeds the dimensions of the waveguide or horn, it will behave like this.

Things go haywire for a couple of reasons though.

First, *What happens to waves that aren't travelling in a well behaved manner down the center of the horn?*

And second, *What happens to waves whose length are smaller than the dimensions of the horn, waveguide, and compression driver?*

In the first case, you get reflected energy which travels right back to the diaphragm, and this is how you end up with a notch. Besides causing a problem in the response, it makes the horn sound "raspy." These are higher order modes. Anything and everything that you can do to avoid them in your horn is A Good Thing, and it's why I used the Geddes foam in mine.

Also, I should note, that bend in the throat is a MUCH smaller problem than what's going on at the mouth. It's the mouth and the throat where we really have to do our homework, and I would seriously discourage anyone with horns from sweating the bend too much. Treat the mouth, that's where you'll get some real concrete and audible gains.

And the second case applies to nearly an octave, where the dimensions of the sound are smaller than the dimensions of the horn or the waveguide. (13,500hz is an inch long.) Then again, most compression drivers don't have much output above 16khz, so it's not something I lose too much sleep over.


----------



## fredswain

I remember back in the 90's at Audio Designs, Matt would modify the horns in the competition cars to have the 45 degree ramp. He used plain old Bondo for this. Eric had advised him on this back then so it's neat to see that he implemented this in the horns later on. At first it sounded strange to hear that we should be modding these this way but a result is worth more than a thousand expert opinions. Then again, I don't exactly question Dr. Bruce Edgar or Eric Stevens when it comes to horns! I know you can throw textbook theories out there but the fact of the matter was that these cars sounded better with the mod. We could hear it. It made a difference.


----------



## Eric Stevens

Patrick, the horn in your picture is a *very *poor example of a properly done 90 degree turn in a horn. And you can even see the effects of that 90 degree bend very clearly in the impedance curve of the system (driver on horn) and the frequency response. That bend suffers from a reflection back to the driver itself with a resulting notch as well as the problem caused by the area progression of the horn being all wrong. Do not assume that all 90 degree bends will exhibit the same characteristics. 

A horn produces a spherical wavefront not spurious waveforms like a direct radiator. So you don't have to worry about the sound waves traveling neatly down the center of the horn. 

You are right that the bend is not much to worry about but if it can be eliminated it is better.

Horns are not all created equal, and the horn has a far larger or significant effect on the sound than the compression driver being used. For example take a TAD TD2001 (best 1" compression driver made currently) on a poor horn like the one you picture, versus a mediocre compression driver such as a Radian on a well done properly designed horn. The Mediocre driver on the good horn will sound FAR better than the TAD TD2001 compression driver on a poorly designed horn. 

Eric
Image Dynamics


----------



## Eric Stevens

SQram said:


> Eric,
> 
> With compression drivers getting smaller and smaller these days, has Image Dynamics considered R&D'ing a straight entry horn for future release?


We never stop working to improve things. Nothing to discuss yet though.

Eric


----------



## Patrick Bateman

Eric Stevens said:


> Patrick, the horn in your picture is a *very *poor example of a properly done 90 degree turn in a horn. And you can even see the effects of that 90 degree bend very clearly in the impedance curve of the system (driver on horn) and the frequency response. That bend suffers from a reflection back to the driver itself with a resulting notch as well as the problem caused by the area progression of the horn being all wrong. Do not assume that all 90 degree bends will exhibit the same characteristics.
> 
> A horn produces a spherical wavefront not spurious waveforms like a direct radiator. So you don't have to worry about the sound waves traveling neatly down the center of the horn.
> 
> You are right that the bend is not much to worry about but if it can be eliminated it is better.
> 
> Horns are not all created equal, and the horn has a far larger or significant effect on the sound than the compression driver being used. For example take a TAD TD2001 (best 1" compression driver made currently) on a poor horn like the one you picture, versus a mediocre compression driver such as a Radian on a well done properly designed horn. The Mediocre driver on the good horn will sound FAR better than the TAD TD2001 compression driver on a poorly designed horn.
> 
> Eric
> Image Dynamics


You state that _"A horn produces a spherical wavefront not spurious waveforms like a direct radiator."_ If that was true, then we would be free to do things like bend a wave ninety degrees with no ill effect.

But I do not agree with that statement.

Read this:

http://www.gedlee.com/downloads/Horn Theory reply.pdf

Of particular interest is page 3, where it's noted that "whenever the walls of the horn recede beyond the line where they can be illuminated by the center of the throat (as shown by the straight line) then the equation fails to be reliable.**This also happens to be exactly the same point where the wave‐fronts would have to diffract if they are to remain in contact with the walls."

In a nutshell, we both agree that straight entry is ideal. I'd take it a step further and argue that we can't rely on horn math when our horns are so far removed from an idealized shape. (IE, they have a bend and they're wildly asymmetrical.)

The mods that I make to horns are straightforward and inexpensive and make a measurable improvement to the polar response. If you're curious about it, send me a set, I'll mod 'em, and then you can give them a listen. I have a measurement rig, so I could record the polar response if you're curious.

I think you'd be surprised by how audible an improvement it is when you treat diffraction.


----------



## thehatedguy

Hyugen's wavefront equations shows how a deflector reassmebles the wavefront back to a spherical wave.


----------



## TREETOP




----------



## thehatedguy

It is mathematical. There is a very rigid set of criteria for it to work.

Download Section

Read Dr. Edgar's articles on the Show horn and the Monolith horn. He discusses it there and references are listed.




cajunner said:


> is this mathematical or is it based on trial and error models?
> 
> I'd be real interested to know how closely the deflector's positional angle has to be to "fit" the bend, if this is can be calculated, and whether or not it works when doing 45 degree bends, 30 degree bends, 60 and 90 degree bends?
> 
> My interest is in modifying a radius bend of a USD roto-mount with a deflector, which, whether this is feasible as a simple glue-in to test or hopeless? Would a small error in angle or position of the deflector plate cause the waveform to not "reassemble" or... ?


----------



## fredswain

Patrick: I read your HOMster thread and found it very informative. You definitely found ways to improve the USD horn design. However have you actually performed the same tests on an Image Dynamics horn or are you basing your car audio horn opinion purely on the experiences you had with the USD? Both horns are vastly different from each other not only in looks but also how they sound. I'm not saying either is perfect but just because one horn suffers from a certain problem doesn't mean the other does. There are certain things that each may have in common though. It has been about 13 or 14 years ago now but Matt was running tests on the Image horns and the new mini's at the time and also a set of USD's that I had. The results were very different. Perhaps you should get a pair to test. 

Before actually testing to verify things, I would be very careful about making assumptions on an Image horn based solely on tests done on a vastly different USD horn. Remember you designed and built several horns on your own that you took the time to work out and yet you ended up being very mad about how good you made the nonperfect USD horn sound by comparison to a much "better" design. What should have happened on paper and what did in the real world didn't seem to agree.


----------



## thehatedguy

I have used the foam in the ID horns. I sent Eric a piece of foam to play around with too. I think he has had some positive improvements with it. I never tried the round overs just because they were too large to fit well in my car.


----------



## fredswain

If you'd just cut your legs off at the knees your space problems would be solved!


----------



## Eric Stevens

thehatedguy said:


> I have used the foam in the ID horns. I sent Eric a piece of foam to play around with too. I think he has had some positive improvements with it. I never tried the round overs just because they were too large to fit well in my car.


The foam smoothed out the sound in the upper midrange but required boosting the top end 8Khz and above.


----------



## Eric Stevens

thehatedguy said:


> I never tried the round overs just because they were too large to fit well in my car.


The round overs the way that Patrick did them to the USD horn would have a negative effect on the area progression causing HOM high order modes that are what the foam is reducing so not suggested. Further to that the pattern control which is one of the benefits of the horn would be sacrificed in a negative way.

If Patricks idea were to function correctly it would be on the lower portion of the mouth and would have to be installed below the mouth not in the mouth. It would be best to use a half round molding piece bonded to the bottom of the mouth. Problem is this might cause the horns to get in the way of your feet. Something to play with. Top side of the horn is in most instances terminated into a flat panel and wont have the diffraction effect patricks round overs are trying to correct.

Eric


----------



## SSSnake

I wondered about that as well... So you are saying that if the edge is flushed with the lip of the horn mouth you will see better results (rather than the center of the pipe lining up with the center of the horn mouth lip)?

Above assumes only bottom "lip" coverage.


----------



## thehatedguy

Yeap.

And I couldn't put a 2" round over (or half of a 2" pipe) on the bottom of my horns and really get my feet under them comfortably.

The Le Cléac'h roundover really needs to be calculated for best results...but being in the car I guess a good guess would work too.


----------



## fredswain

You could get some clay to stuff in the bend to see how it would work before you commit to bondo.


----------



## Patrick Bateman

cajunner said:


> thanks for the pre-requisite reading materiel.
> 
> if I simply pour bondo into the roto-mount's curve, how will I know what angle to tilt it?
> 
> and would this improve a radius design, or do you have to start from scratch?
> 
> Also, does anyone know if Veritas used the radius before going to deflector plate 90 degree turn, or that was a given by that point?
> 
> From what I understood, the Veritas has the greatest capacity, or lowest frequency potential out of all the full body designs, so if there is negative with this design, maybe we could hear about it?
> 
> like, are HOM likely to cause more of a choppy response due to the complex angles, or is it that because the outside flare of the horns adjacent to the mouth are so far from the origin, the HOM aren't reflected back into the mouth and interfering directly?
> 
> Because I can see how a combination of the Veritas and the Image Dynamics designs, might be useful if one wished to get more depth in the midrange out of the high efficiency/great PLD of the horns..


HOMs are basically waves which are not going down the center of the horn. Geddes can explain it better than I can, but u get the idea. The reason that they're so nasty is that early reflections create a type of coloration which sounds intensely irritating. HOMs are the reason that a horn can measure well and sound like ****.

It doesn't take a lot of money or time to investigate this. Buy a QSC waveguide, attach to your compression driver, and listen to it. The thing that's so funny about HOMs is that it's SO OBVIOUS when they're gone. I was doing some measurements on the QSC horns this week, and I could hear a HUGE improvement literally SECONDS after sound was coming out. And this wasn't even MUSIC! This was pink noise, in my garage, and I was fifteen feet away.

The QSC horns are twelve bucks. I've seen guys spend five times that much on an RCA cable, so we're not talking about a big investment here. You can spend eighty bucks at QSC and get a waveguide that's comparable to what Mark Eldridge is using in his Buick Regal, except the QSC waveguide can play MUCH lower than what Mark is using, and the compression driver has 15db more headroom than the dome tweeter that Mark is using. For eighty bucks, that's a steal. Part number is pl-000722-ts. I don't have the part number of the compression driver handy, but it's listed on Brandon's blog. I don't work in car audio or compete, so I'm always trying to take a "open source" approach to this. (I write software for a living.)

Obviously, they're huge. That's the big drawback. But keep in mind that u can literally hack off seventy five percent of a waveguide and it's still ONE HUNDRED percent usable. You'll have to move up your crossover point, but that's not a big deal really.

If anyone wants to use the QSC waveguides, your crossover point will be equal to the width of the waveguide. For instance, I am crossing my tweeters at 3500hz, so I'm going to hack my 12" waveguides down to 4" in diameter. (speed of sound / 3500hz.)

If u hack up a waveguide, be sure to terminate it properly. I can start a thread on waveguide termination if anyones interested.

Also, I'm putting my money where my mouth is. I ordered five today


----------



## Eric Stevens

cajunner said:


> but if the sound traveling from the mouth has the tendency to travel along the bottom of the dash and then radiate upwards to the listening position, would having a bottom round-over like that, cause the stage to dip somewhat?
> 
> Nope only if it created a floor bounce effect like in a home system.
> 
> Like, some of the energy that was directed up would be equally loaded on the bottom and you'd end up with a central wavefront that created a polar response below the one created with no bottom lip?
> 
> No it really depends on the acoustic loading of the mouth and I doubt you are going to alter it enough to change the polar response in any significant way.
> 
> 
> And, with all the experimenting about cutting off the larger parts of the horn in the full body designs and still getting a decently controlled dispersion, is all of this as important as the initial flare rates and expansion modes in the first 1/3 of the horn mouth?
> 
> The first part of the horn is an important part but there are a lot of considerations necessary to declare any portion the most important, each part of the horn affects the pattern control over a different range of frequencies and usually with different forces at work.
> 
> .


Eric


----------



## Patrick Bateman

Eric Stevens said:


> The round overs the way that Patrick did them to the USD horn would have a negative effect on the area progression causing HOM high order modes that are what the foam is reducing so not suggested. Further to that the pattern control which is one of the benefits of the horn would be sacrificed in a negative way.
> 
> If Patricks idea were to function correctly it would be on the lower portion of the mouth and would have to be installed below the mouth not in the mouth. It would be best to use a half round molding piece bonded to the bottom of the mouth. Problem is this might cause the horns to get in the way of your feet.


A bigger roundover will work to a lower frequency. A 2" roundover is good to about 1687hz or so. (speed of sound / diameter / 2)

I used a 2" roundover in these graphs, and you can see the difference is most pronounced above those frequencies. It's particularly noticeable on axis - the peaks and dips are moderated by the roundover.
[/quote]


Eric Stevens said:


> Something to play with. Top side of the horn is in most instances terminated into a flat panel and wont have the diffraction effect patricks round overs are trying to correct.
> 
> Eric


I tried it both ways, with the roundover under the horn, and also with a full 360 degree roundover extending *into* the horn. I'd expected the low frequencies would suffer with the roundover extending into the horn, but they didn't, so I left it that way.

The improvement in the polar response wasn't subtle:









It's particular noticeable in the two octaves from 500hz to 2khz.









This is about as close to ideal as you're going to get. This is what I'm running at home. Handbuilt by Dr Geddes himself.









Here's the polar response with the foam AND the roundover. It's interesting that the polar response has improved to such a great extent. I think that this indicates that a significant percentage of the energy is HOMs. Otherwise how do we explain why the efficiency has fallen so dramatically, while the polar response has improved so much?

All of this for about five dollars worth of foam and PVC.


----------



## Patrick Bateman

fredswain said:


> Patrick: I read your HOMster thread and found it very informative. You definitely found ways to improve the USD horn design. However have you actually performed the same tests on an Image Dynamics horn or are you basing your car audio horn opinion purely on the experiences you had with the USD? Both horns are vastly different from each other not only in looks but also how they sound. I'm not saying either is perfect but just because one horn suffers from a certain problem doesn't mean the other does.


You are correct. The better the horn design is, the less of an effect you'll see with the foam. Check this one out:










Here's what the foam does to the $12 QSC horn. It barely does a thing. HOMs are waves which don't travel down the axis of the horn. I think this graph demonstrates that the QSC doesn't have much of a HOM problem to begin with. If it DID, I think you'd see a larger effect on the frequency response - the foam would attenuate it to a greater degree, since some HOMs will travel right back to the diaphragm, then back out the horn mouth.



fredswain said:


> There are certain things that each may have in common though. It has been about 13 or 14 years ago now but Matt was running tests on the Image horns and the new mini's at the time and also a set of USD's that I had. The results were very different. Perhaps you should get a pair to test.


Definitely! I'd love to tweak them, and see if there's a measurable improvement.



fredswain said:


> Before actually testing to verify things, I would be very careful about making assumptions on an Image horn based solely on tests done on a vastly different USD horn. Remember you designed and built several horns on your own that you took the time to work out and yet you ended up being very mad about how good you made the nonperfect USD horn sound by comparison to a much "better" design. What should have happened on paper and what did in the real world didn't seem to agree.


These are great observations! "The Homster" really made me re-evaluate all of the blood sweat and tears I'd invested in building horns. I was flabbergasted that such a dysfunctional horn could be improved so dramatically by five bucks. The whole project was a goof, I never expected it to make such a dramatic improvement.


----------



## Patrick Bateman

cajunner said:


> I have had a poor grasp (still, alas...) of how sound travels down a horn and some of these recent posts make me question that 'mind's eye' portion, where you develop spatial apportioning to invisible wave energy...
> 
> well, let me just try and see what still sticks, or slides down.
> 
> so, my assumption was, as sound travels down a horn, the walls of the horn provide a frictional modulus for the wave energy as the air molecules "rub" the sides, and this causes a slight delay in comparison to the energy in the center of the horn, which is what creates the dome wavefront in a circular horn. The sides decrease the amount of energy available at termination, but the center of the wavefront propagates unimpeded.
> 
> so, if you direct wave energy down a 90 degree bend, there's going to be a resonant reflection that coincides with the 45/45 phase change, and a notch comes about at the terminus. From what I understand, the Fulcrum Acoustics DSP model can adjust electronically for this.
> 
> Now, this whole idea of a more hydraulic explanation of air pressure/force, and the idea that a wave "reassembles", is hard to understand. I can accept that if you have the bend at the diaphragm, you are starting off with the smallest propagation of resonant modes, or HOM, based simply on distance between the sound origin and the reflecting point within the guide. As I understand it, Higher Order Modes, are just waves that don't belong. Some of these waves are energy directed back into the horn and wreaking havoc, some are constructive with the wavefront and create peaks in the listening space, some cancel, etc. but these modes are unmappable to me, I have to go on faith that by changing some characteristic of the horn's physical criteria, you can effect these HOM and with foam, absorb them.


A few comments :

#1 - Waveguides can seem like complicated beasts, but they're surprisingly simple. The waveguide constrains the sound into a cone. At the mouth of the waveguide you need to transition gently, or else it will diffract. Diffraction creates "phantom" copies of the original signal, smeared in time, and located at the point of diffraction. *Have you ever noticed how the sound from a HLCD seems to emanate from the mouth?* That's diffraction. If you eliminate diffraction, the sound seems to emanate from the throat - like a conventional dome tweeter. *A good waveguide sounds like a conventional dome, but with massiver power handling.*

#2 - Hornresp can simulate all this for you. When you can watch an actual animation of the soundwave, all of these pieces make a lot more sense.

#3 - I wrote a "waveguides for dummies" thread. Here:

Audio Psychosis • View topic - Waveguides for Dummies

I hope no one takes offense to it. Half of this stuff made no sense to me five years ago, and when I tried to read the literature it was easy to get lost in formulas.


----------



## Eric Stevens

Patrick Bateman said:


> I used a 2" roundover in these graphs, and you can see the difference is most pronounced above those frequencies. It's particularly noticeable on axis - the peaks and dips are moderated by the roundover.
> 
> I tried it both ways, with the roundover under the horn, and also with a full 360 degree roundover extending *into* the horn. I'd expected the low frequencies would suffer with the roundover extending into the horn, but they didn't, so I left it that way.
> 
> The improvement in the polar response wasn't subtle:


Patrick, 

IMHO you band-aided a poor design. I think most of what you observed/measured/heard was/is due to an improvement to the flare of the USD horn correcting for the very poor acoustical loading and pattern control etc of that design. The reason the round over didnt reduce the low frequency range is due to the poor design of the horn and lack of proper loading at those frequencies. If I sent you a horn and you just listened to the USD versus the ID unmodified with the same driver on both you would be floored at the difference. I am telling you this not because I want to tear down another product, but I think it will shed light on the fact that what you experienced was not necessarily what you think it was. 

There are many tricks to smooth the frequency response of a horn system like creating a rubber mouth, this is a gap between the driver and the throat of the horn, it has a damping effect that reduces the peaks in the response. But this doesn't cure the problem just puts a band-aid on it and still not as good as a properly done horn system. 

A quick look at impedance vs frequency response on the USD tells a story on what is going on. I have done all this in depth and wish I had something to share still but I did this 17 or 18 years ago. If you want to have some fun measure the impedance of the compression driver and then the driver and horn together. Then put the same driver on good horn and measure the system again. You will quickly see there is something going on there and it isnt good.

I can tell you from experience and with a fair degree of certainty that doing the same to our horn with the round over would yield a net negative effect. I agree that reducing diffraction is a good thing with a net positive result but it would need to be below the mouth with our horn. 

The foam in the mouth however does yield a positive result but its not night and day or even dramatic but noticeable. 

Eric


----------



## RogerK

There are at least two people on here running ID horns with roundovers who have experienced very nice improvements. No horn is perfect.


----------



## subwoofery

RogerK said:


> There are at least two people on here running ID horns with roundovers who have experienced very nice improvements. No horn is perfect.


That doesn't mean the install was perfect either  

Kelvin


----------



## Eric Stevens

RogerK said:


> There are at least two people on here running ID horns with roundovers who have experienced very nice improvements. No horn is perfect.


You are correct, ID horns arent perfect. 

Based upon my experience though I doubt that putting tubing into the mouth is going produce a net positive effect. It may have improved one area and detracted from another. I would need to test for positive confirmation. 

Using the roundover outside the mouth to terminate the horn is a different story but it does create installation issues.

Eric


----------



## CraigMBA

Eric Stevens said:


> You are correct, ID horns arent perfect.
> 
> Based upon my experience though I doubt that putting tubing into the mouth is going produce a net positive effect.


Good, because that's not what he's talking about.



> Using the roundover outside the mouth to terminate the horn is a different story but it does create installation issues.
> 
> Eric


Even better, because that's exactly what he's talking about.


----------



## RogerK

To clarify, the roundovers extended into the mouth of the ID horns and resulted in a significant subjective improvement. This is actual practice and not just theory on what effect the roundovers have on ID horns


----------



## SSSnake

RogerK,

The comment was the mod made significant _subjective_ improvement. Subjective evaluations are tough because in these cases the beauty is in the eye of the beholder. What if you prefer output with MORE HOMs? More HOMs will likely cause the output levels to increase. Most studies show that higher output levels = better sound quality to most people (typicallyt un-trained ears). I would love to see some objective measurements coupled with some subjective commentary. From my very limited understanding of how horns and waveguides work extending the roundover into the mouth should cause adverse affects (energy reflected back into the horn contributing to more HOMs - if this energy helps to level the FR and/or increase output levels then it may appear to sound better). Not saying this IS the case in this situation but it certainly COULD be...

Eagerly awaiting more discussion on this subject.


----------



## subwoofery

^ Yup same here... Waiting for some graphs and results. Please RogerK, enlight us

Kelvin


----------



## Patrick Bateman

Eric Stevens said:


> Patrick,
> 
> IMHO you band-aided a poor design. I think most of what you observed/measured/heard was/is due to an improvement to the flare of the USD horn correcting for the very poor acoustical loading and pattern control etc of that design. The reason the round over didnt reduce the low frequency range is due to the poor design of the horn and lack of proper loading at those frequencies. If I sent you a horn and you just listened to the USD versus the ID unmodified with the same driver on both you would be floored at the difference. I am telling you this not because I want to tear down another product, but I think it will shed light on the fact that what you experienced was not necessarily what you think it was.
> 
> There are many tricks to smooth the frequency response of a horn system like creating a rubber mouth, this is a gap between the driver and the throat of the horn, it has a damping effect that reduces the peaks in the response. But this doesn't cure the problem just puts a band-aid on it and still not as good as a properly done horn system.
> 
> A quick look at impedance vs frequency response on the USD tells a story on what is going on. I have done all this in depth and wish I had something to share still but I did this 17 or 18 years ago. If you want to have some fun measure the impedance of the compression driver and then the driver and horn together. Then put the same driver on good horn and measure the system again. You will quickly see there is something going on there and it isnt good.
> 
> I can tell you from experience and with a fair degree of certainty that doing the same to our horn with the round over would yield a net negative effect. I agree that reducing diffraction is a good thing with a net positive result but it would need to be below the mouth with our horn.
> 
> The foam in the mouth however does yield a positive result but its not night and day or even dramatic but noticeable.
> 
> Eric


The foam and the roundover is definitely a band aid, but I'm still curious why it's so effective. I spent some time this morning reviewing the measurements, and I think there's a fairly significant indicator that there's diffraction at the mouth that's getting re-radiated right down the throat.

I'd anticipate that the affect of this re-radiation would be the perception that the sound is coming from the mouth, not the throat, and a lot of "horn honk."

The Image Dynamics horns have a dramatic expansion in the last couple inches which reduce the need for the roundover. Having said that, we both agree it would be effective on the underside. It's pretty easy to test, just duct tape it to the bottom half and listen to see if the sound stage appears to move backwards.

I posted a thorough reply on diyaudio since Geddes isn't a member of this forum. He might reply here:

The HOMster! (or How I Learned How to Fix a Horn) - Page 12 - diyAudio


----------



## Patrick Bateman

Here's some more horn porn to consider.

Over on diyaudio, a member named Elias did some wavelet transformations on horn output. It's a doozy of a thread, and it makes my head hurt. But the pictures seem to demonstrate which horns "honk" less. What we're looking for in the graph is a situation where the energy from the horn decays VERY quickly, and consistently. What you'll notice in the "honky" horns are duplicate images, smeared in time. It's particularly nocticeable on the small Altec.

I'll start with the best, and work my way down. Note that the best horn has a whopper of a roundover.


















Le'Cleach 321, by Musique Concrete, a 320hz horn

























The $12 waveguide from the QSC HPR 152i. Nice performance, at any price. The mold on the left is my own work, which I made a few years before QSC. Curves are virtually identical as you can see.

















Altec 511. Note that it's virtually the same curve as the 811, just bigger. Note that the larger mouth makes a huge improvement at low frequency.

















Altec 811 horn​


----------



## Patrick Bateman

I posted updates to the "homster" thread that I started sixteen months ago. Here they are:

Audio Psychosis • View topic - The Homster pt2! (or How I Learned More About Fixing a Horn)

There should be some "food for thought" here, particularly in regards to various horn geometries.


----------



## veritasz34

I tried the poly fill in the mouth of the horn and didn't like the results,but then again I wasn't using ID horns..


----------



## subwoofery

veritasz34 said:


> I tried the poly fill in the mouth of the horn and didn't like the results,but then again I wasn't using ID horns..


???  What do you mean? The ID horns are the one that don't need foam in the mouth... 
That has been confirmed by Eric Stevens since they are not a straight horn version. 

Kelvin


----------



## Patrick Bateman

veritasz34 said:


> I tried the poly fill in the mouth of the horn and didn't like the results,but then again I wasn't using ID horns..


A couple of thoughts -

Did you use an equalizer to 'bump up' output on the top end of the horn after you modded them?

High order modes sound nasty, but they can add a lot of output, particularly at high frequencies. In a horn that is sub-optimum, the foam will definitely lower efficiency, and it's not linear. (IE, you lose more at the top than in the midrange.)

To EQ it properly you need a microphone and an EQ with a lot of bands, but it's not impossible to do it by ear, particularly since the effect is predicatable. (You lose a lot at the top, not so much in the midrange.)

Also, be sure that you're using polyester fiberfill (same stuff you use for a pillow, they sell it at craft stores and at Wal Mart's craft department), or better yet, reticulated foam. Closed cell foam WON'T work properly. (It's too dense.)

Also, it takes a bit of getting used to, because we're accustomed to the sound of HOMs. I'd argue that HOMs are the main reason that it's hard to listen to horns for a long time, whereas conventional loudspeakers can be listened to for hours on end.


----------



## Patrick Bateman

veritasz34 said:


> I tried the poly fill in the mouth of the horn and didn't like the results,but then again I wasn't using ID horns..


I just re-read this, and realized that your putting foam *in the mouth.*
That won't make much of a difference, because the amplitude is larger at the throat than at the mouth. So the best 'bang for the buck' is by filling the throat, and then treating the mouth with a roundover.

I do both, in fact I fill up the whole damn horn. In the Gedlee speakers the foam extends a good four inches beyond the mouth, right into the room.


----------

